DESCRIPTION
TITLE OF INVENTION: NEGATIVE ELECTRODE ACTIVE MATERIAL
TECHNICAL FIELD
[000 11
The present invention relates to an electrode active material, and more
particularly to a negative electrode active material.
BACKGROUNDART
[0002]
Recently, small electronic appliances such as home video cameras, note PCs,
and smart phones have become widespread, and attaining higher capacity and longer
service life of batteries has become a technical problem.
[0003]
Given that hybrid vehicles, plug-in hybrid vehicles, and electric vehicles will
be further spread, size reduction of batteries is also a technical problem.
[0004]
At present, graphite-based negative electrode active materials are utilized for
lithium ion batteries. However, graphite-based negative electrode active materials
have technical problem as described above.
[0005]
Accordingly, alloy-based negative electrode active materials have gained
attention, which have higher capacity than those of the graphite-based negative
electrode active materials. As an alloy-based negative electrode active material,
silicon (Si)-based negative electrode active materials and tin (Sn)-based negative
electrode active materials are known. To realize a lithium ion battery having a
smaller size and a longer life, various studies have been conducted on the above
described alloy-based negative electrode active materials.
[OOOC;]
However, an alloy-based negative electrode active material repeatedly
undergoes large expansion and contraction in volume at the time of
chargingldischarging. For that reason, the capacity of the alloy-based negative
electrode active material is prone to deteriorate. For example, a volume
expansiodcontraction rate of graphite associated with charging is about 12%. In
contrast, the volume expansion/contraction rate of Si single substance or Sn single
substance associated with charging is about 400%. For this reason, if a negative
electrode plate of Sn single substance is repeatedly subjected to charging and
discharging, significant expansion and contraction occur, thereby causing cracking in
negative electrode compound which is applied on the current collector of the
negative electrode plate. Conseq~lentfyt,h e capacity of the negative electrode plate
sharply decreases. This is chiefly caused by the fact that some of the active
substances are freed due to volume expansiodcontraction and thereby the negative
electrode plate loses electron conductivity.
j00071
US2008/0233479A (Patent Literature 1) proposes a method for solving the
above described problem of an alloy-based negative electrode active material. To
be specific, the negative electrode material of Patent Literature 1 includes a Ti-Ni
superelastic alloy, and Si particles formed in the superelastic alloy. Patent
Literature 1 describes that a large expansiodcontraction change of Si particle whlch
occur following occlusion and release of lithium ions can be suppressed by a
superelastic alloy.
[0008]
However, it is questionable that the technique disclosed in Patent Literature 1
sufficiently improves the charge-discharge cycle characteristics of the secondary
battery. Most of all, it may be highly difficult to actually produce the negative
electrode active material proposed by Patent Literature 1.
CITATION LIST
PATENT LITERATURE
[OOO9]
Patent Literature 1 : US2008/0233479A
SUMMARY OF INVENTION
[OO 101
It is an objective of the present invention to provide a negative electrode
active material which is utilized for nonaqueous electrol~ese condary batteries
represented by a lithium ion secondary battery and can improve the capacity per
voluixe and charge-discharge cycle characteristics thereof.
l0011]
The negative electrode active material according to the present embodiment
contains an alloy phase. The alloy phase undergoes thermoelastic diff~~sionless
transformation when releasing or occluding metal ions.
BRIEF DESCRIPTION OF DRAWINGS
j0012l
[FIG. 11 FIG. 1 is a diagram illustrating an X-ray diffraction profile of Cu-15.5 at%
Sn alloy among Examples, and a simulation result by Rietveld method.
/FIG. 21 FIG. 2 is a perspective view of DOi structure.
[FIG. 31 FIG. 3 is a diagram illustrating an X-ray diffraction profile of Cu-15.5 at%
Sn alloy before and after charginddischarging, and a simulation result by Rietveld
method.
[FIG. 4A] FIG. 4A is a schematic diagram of DO? structure of the matrix phase of
the alloy phase of the present embodiment.
[FIG. 4B] FIG. 4B is a schematic diagram of 2H structure of yl' phase which is a
kind of martensite phase.
[FIG. 4C1 FIG. 4C is a schematic diagram of a crystal plane to explain thermoelastic
diffusionless transformation from DOs structure to 2H structure.
[FIG. 4D1 FIG. 4D is a schematic diagram of another crystal plane different from
that of FIG. 4C.
[FIG. 4E] FIG. 4E is a schematic diagram of another crystal plane different from
those of FIGS. 4C and 4D.
[FIG. 51 FIG. 5 is a diagram illustrating a charge-discharge cycle characteristics of
Cu-15.5 at% alloy among Examples.
[FIG. 61 FIG. 6 is a diagram illustrating an X-ray diffraction profile of Cu-25.0 at%
Sn alloy, and a simulation result by Rietveld method.
[FIG. 71 FIG. 7 is a diagram illustrating an X-ray diffraction profile of Cu- 18.5 at%
Sn alloy, and a simulation result by Rietveld method.
[FIG. 81 FIG. 8 is a diagram illustrating an X-ray diffraction profile of Cu-5.0 at%
Zn-25.0 at% Sn alloy, and a simulatio~rle sult by Rietveld method.
[FIG. 91 FIG. 9 is a diagram illustrating an X-ray diffraction profile of Cu-10.0 at%
Zn-25.0 at% Sn alloy, and a simulation result by Rietveld method.
[FIG. 101 FIG. 10 is a diagram illustrating an X-ray diffraction profile of Cu-20.5
at% Sn alloy, and a simulation result by Rietveld method.
DESCRIPTION OF EMBODIMENTS
[00 131
Hereinafter, with reference to the drawings, embodiments of the present
invention will be described in detail. Like parts or corresponding parts in the
drawings are given a like reference symbol and description thereof will not be
repeated.
[00 141
The negative electrode active material according to the present embodiment
contains an alloy phase. The alloy phase undergoes thermoelastic diffusionless
transformation when releasing or occluding metal ions.
100 151
A "negative electrode active material" referred herein is preferably a negative
electrode active material for nonaqueous electrolyte secondary batteries. A
"thermoelastic diffusionless transformation" referred herein is so-called
thermoelastic martensitic transformation. A "metal ion" refers to, for example, a
lithium ion, magnesium ion, sodium ion, and the like. A preferable metal ion is
lithium ion.
[OO 161
This negative electrode active material may contain other phases different
from the above described alloy phases. The other phases include, for example, a
silicon (Si) phase, a tin (Sn) phase, other alloy phases (alloy phases which do not
undergo thermoelastic diffusionless transformation) excepting the above described
alloy phases, and the like.
LOO 171
Preferably, the above described alloy phases are main componerlts (main
phases) of the negati\re electrode active material. "Main component" refers to a
component which occ~lpiesn ot less than 50% by volume. The alloy phase may
contain impurities to the extent that the spirit of the present invention is unimpaired.
However, the impurities are contained preferably as little as possible.
100 181
A negative electrode formed of a negative electrode active material of the
present embodiment has a higher volumetric discharge capacity (discharge capacity
per volume) than that of a negative electrode made of graphite, when used in a
nonaqueous electrolyte secondary battery. Further, a nonaqtteous electrolyte
secondary battery using a negative electrode containing a negative electrode active
material of the present embodiment has a higher capacity retention ratio than one
using a conventional alloy-based negative electrode. Therefore, the negative
electrode active material has a potential to sufficiently improve the cliarge-discharge
cycle characteristics of the nonaqueous electrolyte secondary battery.
100191
A possible reason why the capacity retention ratio is high is that strain due to
expansion/contraction that occurs at the time of charging/discharging is relaxed by
thermoelastic diffusionless transformation.
/0020]
The alloy phase may be of any one of the following types 1 to 4.
(002 1 )
The alloy phase of type 1 undergoes thermoelastic difft~sionless
transformation when occluding metal ions, and ttndergoes reverse transformatiorr
when releasing metal ions. In this case, the alloy phase is a matrix phase in a
normal state.
(0022)
The alloy phase of type 2 undergoes reverse transformation when occluding
metal ions, and undergoes thermoelastic diff~~sionletsrsa nsformation kvben releasing
metal ions. In this case, the alloy phase is a martensite phase in a normal state,
[0023 1
The alloy phase of type 3 undergoes supplemental deformation (slip
deformation or twin deformation) when occluding metal ions, and returns to the
original martensite phase when releasing metal ions. In this case, the alloy phase is
a martensite phase in a normal state.
[0024]
The alloy phase of type 4 transforms from a martensite phase to another
martensite phase when occluding metal ions, and returns to the original martensite
phase when releasing metal ions. In this case, the alloy phase is a martensite phase
in a normal state.
100251
In the case of the alloy phase of type 1, preferably, the crystal structure of the
alloy phase after thermoelastic diffusionless transformation is either of 21-1, 3R, SR,
9R, 18R, M2H, M3R, M6R, M9R, and M18R in the Ramsdell notation, and the
crystal stmcture of the alloy phase after reverse transformation is DO3 in the
Str~tkturberichtn otation. More preferably, the crystal structure of the alloy phase
after thermoelastic diffusionless transformation is the above described 2H, and the
crystal stmcture of the alloy phase after reverse transformation is the above described
DO?.
100261
In the case of the alloy phase of type 1, preferably, the negative electrode
active material contains Cu and Sn, and also contains the above described 2H
structure after thermoelastic diffusionless transformation, and the above described
DO3 structure after reverse transformation.
100271
The above described negative electrode active material may contain one or
more selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, B,
and C, and Sn, with balance being Cu and impurities.
[0028]
The above described negative electrode active material may contain one or
more selected from the group consisting of 6 phase of F-Cell structure, E phase of 2H
structure, q' phase of monoclinic crystal, and a phase having DO3 structure, each
including site deficiency.
[0029]
All of these 6 phase, E phase, q' phase, and phase having DO3 structure, each
including site deficiency form a storage site and a diffusion site of metal ions (Li ions,
etc.) in the negative electrode active material. Thereby, the volumetric discharge
capacity and the cycle characteristics of the negative electrode active material are
further improved.
j00301
In the above described negative electrode active material, a volume expansion
ratio or volu~nec ontraction ratio of a unit cell of the above described alloy phase
before and after the phase transformation is preferably not more than 20%, and more
preferably not more than 10%. The volume expansion ratio of unit cell is defined
by the following Formula (I), and the volume contraction ratio of unit cell is defined
by the following Formula (2).
(Volume expansion ratio of unit cell) = [(volume of unit cell when metal ions
are occluded) - (volume of unit cell when metal ions are released)ll(volume of unit
cell when metal ions are released) x 100 ...( 1)
(Volume contraction ratio of unit cell) = [(volume of unit cell when metal
ions are occluded) - (volume of unit cell when metal ions are released) l/(volume of
unit cell when metal ions are occluded) x 100 . . .(2)
The volume of unit cell at the time of releasing, which corresponds to a
crystal lattice range of unit cell at the time of occluding, is substituted into "volume
of unit cell when metal ions are released" in Formulas (1) and (2).
[003 11
The above described negative electrode active material can be used as active
material for making up an electrode, particularly electrode of a nonaqueous
electrolyte secondary battery. An example of the nonaqueous electrolyte secondary
battery is a Lithium ion secondary battery.
[0032]
Hereinafter, negative electrode active materials according to the present
embodiment will be described in detail.
100331

A negative electrode active material relating to the present embodiment of the
invention contains an alloy phase. The alloy phase undergoes thermoelastic
diffusionless transformation when releasing metal ions represented by Li ions. or
occluding the metal ions, as described above. The therrnoetastic diffusionless
transformation is also called as thermoelastic martensitic transformation.
Hereinafter, in the present description, the thermoelastic rnartensitic transformation is
simply referred to as "M transformation" and the martensite phase as "M phase".
An alloy phase that undergoes M transformation when occluding or releasing metal
ions is also referred to as a "specific alloy phase".
100341
The specific alloy phase is dominantly made up of at least one of M phase and
a matrix phase. The specific alloy phase repeats occlusion/release of metal ions at
the time of chargingldischarging. Then, the specific alloy phase undergoes M
transformation, reverse transformation, supplemental deformation, etc. in response to
occlusion and release of metal ions. These transformation behaviors mitigate strain
which is caused by expansion and contraction of the alloy phase when occluding and
releasing metal ions.
[0035]
The specific alloy phase may be of any one of the above described types 1 to
4. Preferably, the specific alloy phase is of type 1. That is, the specific alloy
phase preferably undergoes M transformation when occluding metal ions, and
undergoes reverse transformation when releasing metal ions.
100361
The crystal structure of the specific alloy phase is not specifically limited. If
the alloy phase is of type 1, and the crystal structure of the specific alloy phase (that
is, a matrix phase) after reverse transformation is PI phase (DO3 structure), the
crystal structure of the specific alloy phase (that is, M phase) after M transformation
is, for example, Pi' phase (M18R1 structure of monoclinic crystal or 1 8R1s tmct~rreo f
orthorhombic crystal), yl' phase (M2H structure of monoclinic crystal or 2H structure
of orthorhombic crystal), PI " phase (M 18R2 structure of monoclinic crystal or 1 8R2
structure of orthorhombic crystal), al' phase (M6R structure of monoclinic crystal or
6R structure of orthorhombic crystal), and the like.
[0037]
If the crystal structure of the matrix phase of the specific alloy phase is P2
phase (B2 structure), the crystal structure of M phase of the specific alloy phase is,
for example, P2' phase (M9R structure of rnonoclinic crystal or 9R st~~~ctouf re
orthorhombic crystal), z'p hase (M2H structure of monocli~iicc rystal or 2I-1 structure
of orthorhombic crystal), and a*' phase (M3R structure of monoclinic crystal or 3R
structure of orthorhombic crystal).
[0038]
If the matrix phase of the alloy phase has a face-centered cubic lattice, the
crystal stn~ctureo f M phase of the alloy phase has, for example, a face-centered
tetragonal lattice, and a body-centered tetragonal lattice.
100391
Such symbols as the above described 2H, 3R, 6R, 9R, 18R, M2H, M3R, M6R,
M9R, and M18R are used as the method of denoting crystal structures of a layered
construction according to Ramsdell's classification. The symbols I3 and R mean
that respective symmetries in the direction perpendicular to the lamination plane are
hexagonal symmetry and rhombohedra1 symmetry. If there is no M appended at the
beginning, it means that the crystal structure is an orthorhombic crystal. If there is
M appended at the beginning, it means that the crystal structure is a monoclinic
crystal. Even if same classification symbols are used, there are cases in which
distinction is made by the difference in the order of the layers. For example, since
PI' phase and 0," phase, which are two kinds of M phase, have a different layered
construction, there are cases in which they are distinguished by being denoted as
18Rt and 18Rz, or M18R1 and M18R2 etc., respectively.
[0040]
In General, M transformation and reverse transformation in normal shape
memory effects and pseudoelastic effects often involve volume contraction or
volume expansion. When a negative electrode active material relating to the
present embodiment electrochemically releases or occludes metal ions (for example,
Lithium ions), it is considered that the crystal structure often changes in consistent
with the phenomena of volume contraction or volume expansion in the direction of
respective transformation.
1004 1 ]
I-lowever, the negative electrode active material according to the present
embodiment will not be paticularly limited by such restriction. m e n M
transformation or reverse transformation occurs following occlusion and release of
metal ions in the specific alloy phase, there may be generated other crystal structures
than the crystal structure that appears at the time of ordinary shape memory effects
and pseudoelastic effects.
10042)
When the specific alloy phase is of type 3, the specific alloy phase undergoes
slip deformation or twin deformation following occlusion or release of metal ions.
In slip deformation, since dislocation is introduced as the lattice defect, reversible
defomation is difficult. Therefore, when the specific alloy phase is of type 3, it is
preferable that twin deformation dominantly occurs.
100431
[Chemical Composition Of Negative electrode active materialj
The chemical composition of a negative electrode active material containing
the above described specific alloy phase will not be particularly limited provided that
the crystal str~tcturea t the time of M transformation and reverse transformation
contains the above described crystal structures.
100441
When the specific alloy phase is of type 1, the chemical composition of the
negative electrode active material containing the specific alloy phase contains, for
example, Cu (copper) and Sii (tin).
to0451
m e nt he specific alloy phase is of type 1, preferably, the crystal struct~lreo f
the specific alloy phase after reverse transformation caused by discharge of rrietal
ions is DO-, structure, and the crystal stnicture of the specific alloy phase after M
transformation caused by occlusion of metal ions is 2H stn~cture.
[004Sl
Preferably, the chemical composition of negative electrode active material
contains Sn, with the balance being Fe and impurities. More preferably, the
negative electrode active material contains 10 to 20 at% or 21 to 27 at% of Sn, with
the balance being Cu and impurities, wherein the negative electrode active material
contains 2H structure after M transformation, and DO3 structure after reverse
transformation. A more preferable Sn content in the negative electrode active
material is 13 to 16 at%, 18.5 to 20 at%, or 21 to 27 at%.
[0047]
The chemical composition of negative electrode active material may contain
one or more selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al,
Si, B, and C, and Sn, with the balance being Cu and impurities.
[0048]
Preferably, the chemical composition of the negative electrode active material
in this case contains: Sn: 10 to 35 at%, and one or more selected from the group
consisting of Ti: 9.0 at% or less, V: 49.0 at% or less, Cr: 49.0 at% or less, Mn: 9. 0
at% or less, Fe: 49.0 at% or less, Co: 49.0 at% or less, Ni: 9.0 at% or less, Zn: 29.0
at% or less, Al: 49.0 at% or less, Si: 49.0 at% or less, B: 5.0 at% or Less, and C: 5.0
at% or less, with the balance being Cu and impurities. The above described Ti, V,
Cr, Mn, Fe, Co. Ni, Zn, Al, Si, B and C are optional elements.
100491
A preferable upper limit of Ti content is 9.0 at% as described above. The
upper limit of Ti content is more preferably 6.0 at%, and ft~rthepr referably 5.0 at%.
A lower limit of Ti content is preferably 0.1 at%, more preferably 0.5 at%, and
further preferably at 1.0 at%.
[OOSO]
A preferable upper limit of V content is 49.0 at% as described above. The
upper limit of V content is more preferably 30.0 at%, further preferably 15.0 at%,
and furthermore preferably 10.0 at%. A lower limit of V content is preferably 0.1
at%, more preferably 0.5 at%, and further preferably at 1.0 at%.
COO5 11
A preferable upper limit of Cr content is 49.0 at% as described above. The
upper limit of Cr content is more preferably 30.0 at%, further preferably 15.0 at%,
and furthermore preferably 10.0 at%. A lower limit of Cr content is preferably 0.1
at%, more preferably 0.5 at%, and further preferably at 1 .O at%.
lo0521
A preferable upper limit of Mn content is 9.0 at% as described above. The
upper limit of Mn content is more preferably 6.0 at%, and further preferably 5.0 at%.
A lower limit of Mn content is preferably 0.1 at%, more preferably 0.5 at%, and
further preferably at 1 .O at%.
100531
A preferable upper limit of Fe content is 49.0 at% as described above. The
upper limit of Fe content is more preferably 30.0 at%, further preferably 15.0 at%,
and ft~rthermorep referably 10.0 at%. A lower limit of Fe content is preferably 0.1
at%, more preferably 0.5 at%, and further preferably at 1.0 at%.
[0054]
A preferable upper limit of Co content is 49.0 at% as described above. The
upper limit of Co content is more preferably 30.0 at%, further preferably 15.0 at%,
and furthermore preferably 10.0 at%. A lower limit of Co content is preferably 0.1
at%, more preferably 0.5 at%, and further preferably at 1.0 at%.
[0055]
A preferable upper limit of Ni content is 9.0 at% as described above. The
upper limit of Ni content is more preferably 5.0 at%, and further preferably 2.0 at%.
A lower limit of Ni content is preferably 0.1 at%, more preferably 0.5 at%, and
further preferably at 1.0 at%.
lo0561
A preferable upper limit of Zn content is 29.0 at% as described above. The
upper limit of Zn content is more preferably 27.0 at%, and further preferably 25.0
at%. A lower limit of Zn content is preferably 0.1 at%, more preferably 0.5 at%,
and further preferably at 1.0 at%.
[0057]
A preferable upper limit of A1 content is 49.0 at% as described above. The
upper limit of A1 content is more preferably 30.0 at%, further preferably 15.0 at%,
and furthermore preferably 10.0 at%. A lower limit of A1 content is preferably
0.1 %, more preferably 0.5 at%, and further preferably at 1.0 at%.
[0058]
A preferable upper limit of Si content is 49.0 at% as described above. The
upper limit of Si content is more preferably 30.0 at%, further preferably 15.0 at%,
and furlhermore preferably 10.0 at%. A lower limit of Si content is preferably 0. I
at%, more preferably 0.5 at%, and further preferably at 1.0 at%.
LO0591
A preferable upper limit of B content is 5.0 at%. The lower limit of B
content is preferably 0.01 at%, more preferably 0.1 at%, further preferably 0.5 at%,
and furthermore preferably 1.0 at%.
(00601
A preferable upper limit of C content is 5.0 at%. The lower limit of C
content is preferably 0.01 at%, more preferably 0.1 at%, fttrther preferably 0.5 at%,
and f~trthermorep referably 1.0 at%.
1006 11
Preferably, the negative electrode active material contains one or more
selected from the group consisting of 6 phase of F-Cell stnlcture containing site
deficiency, r phase of 2H structtire containing site deficiency, q' phase of monoclinic
crystal containing site deficiency, and a phase having DO3 structure containing site
deficiency. Hereinafter, these 6 phase, E phase, q' phase, and phase having DO3
structure, each containing site deficiency is also referred to as "site deficient phase".
Here, "site deficiency" means a state of a crystal structure in which occupancy factor
is less than 1 in a specific atomic site.
E00621
These site deficient phases include a plurality of site deficiencies in the crystal
structure. These site deficiencies function as a storage site or a diffusion site of
metal ions (such as Li ions). Therefore. if a negative electrode active material
contains an alloy phase which becomes 2H structure after M transfomation and
becomes DO3 structure after reverse transfomation, and at least one phase among
the above described site deficient phases, the volumetric discharge capacity and the
cycle characteristics of the negative electrode active material are further improved.
200631
The chemical composition of a negative electrode active material may further
contain a Group 2 element and/or rare earth metal (REM) for the purpose of
increasing discharge capacity. The Group 2 elements include, for example,
magnesium (Mg) calcium (Ca) and the like. REMs include, for example,
lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd) and the like.
100641
If a negative electrode active material contains a Group 2 element and/or
REM, the negative electrode active material becomes brittle. Therefore, in the
production process of the electrode, a bulk material or an ingot made of the negative
electrode active material is easy to be pulverized, making it easy to produce an
electrode.
LO0651
The negative electrode active material may be made up of the above described
specific alloy phase, or may contain the above described specific alloy phase and
another active material phase which is metal ion-active. Another active material
phase includes, for example, a tin (Sn) phase, a silicon (Si) phase, an aluminum (Al)
phase, a Co-Sn alloy phase, a Cu6Sn5 compound phase (q' phase or q phase) and the
like.
COO661
[Volume Expansion Ratio And Volume Contraction Ratio Of Specific Alloy Phase]
When the above described specific alloy phase undergoes M transformation
or reverse transformation following occlusion and release of metal ions, preferable
volume expansionlcontraction ratio of unit cell of the specific alloy phase is not more
than 20%. In this case, it is possible to sufficiently relax the strain due to a volume
change which occurs following occlusion and release of metal ions. The volume
expansiodcontraction ratio of unit cell of the specific alloy phase is more preferably
not more than lo%, and further preferably not more than 5%.
[0067]
The volume expansionlcontraction ratio of the specific alloy phase can be
measured by an in-situ X-ray diffraction during charging/discharging. To be
specific, an electrode plate of negative electrode active material, a separator, a
counter electrode lithium, and electrolytic solution are placed and sealed in a
dedicated charge/discharge cell including a window made of beryllium which
transmits X-ray, within a glove box in pure argon gas atmosphere in which moisture
is controlled such that due point is not more than -80°C. Then, this
charge/discharge cell is mounted onto the X-ray diffraction apparatus. After
mounting, an X-ray diffraction profile of the specific alloy phase is obtained in each
of an initially charged state and an initially discharged state in the course of charging
and discharging. From this X-ray diffraction profile, a lattice constant of the
specific alloy phase is found. From the lattice constant, it is possible to calculate
the volume change ratio in consideration of crystal lattice conespondence of the
specific alloy phase.
[0068]
When the shape of X-ray diffraction profile changes due to full width at half
maximurn etc. in the charge-discharge cycling process, analysis is performed after
repeating charging and discharging 5 to 20 times as needed. Then, an average value
of volume change ratio is found from a plurality of X-ray diffraction profiles having
high reliability.
100691
[Analysis Method Of Crystal Structure Of Alloy Phase Contained By Negative
electrode active material]
(I) The crystal stmcture of the phase (including an alloy phace) contained in
the negative electrode active material can be analyzed by Rietveld method based on
the X-ray diffraction profile obtained by using an X-ray diffraction apparatus. To
be specific, the crystal structure is analyzed by the following method.
COO70 j
For a negative electrode active material before use for a negative electrode, Xray
diffraction measurement is performed on the negative electrode active material to
obtain meast~redd ata of X-ray diffraction profile. Based on the obtained X-ray
diffraction profile (measured data), the configuration of phases in the negative
electrode active lnaterial is analyzed by Rietveld method. For the analysis by
Rietveld neth hod, either of "RIETAN2000" (program name) or "RIETAN-FP"
(program name) which are general-purpose analysis software is used.
1007 11
(2) The crystal structure of a
negative electrode active material in a negative electrode before charging in a battery
is determined by the same method as that in (1). To be specific, the battery, which
is in an uncharged state, is disassembled within the glove box in argon atmosphere,
and the negative electrode is taken out from the battery. The negative electrode
taken out is enclosed with Myler foil. Thereafter, the perimeter of the Myler foil is
sealed by a thermocompression bonding machine. Then, the negative electrode
sealed by the Myler foil is taken out of the glove box.
lo0721
Next, a measurement sample is fabricated by bonding the negative electrode
to a reflection-free sample plate (a plate of a silicon single crystal which is cut out
such that a specific crystal plane is in parallel with the measurement plane) with hair
spray. The measurement sample is mounted onto the X-ray diffraction apparatus
and X-ray diffraction measurement of the measurement sample is performed to
obtain an X-ray diffraction profile. Based on the obtained X-ray diffraction profile,
the crystal structure of the negative electrode active material in the negative electrode
is determined by the Rietveld method.
[0073]
(3) Crystal structures of the negative electrode active material in the negative
electrode after charging one to multiple times and after discharging one to multiple
times are determined by the same method as that in (2).
[0074]
To be specific, the battery is fully charged in a charging/discharging test
apparatus. The fully charged battery is disassembled in the glove box, and a
measurement sample is fabricated by a method similar to that of (2). The
meas~iremenst ample is mounted onto the X-ray diffraction apparatus and X-ray
diffraction measurement is performed.
100751
Moreover, the battery is f ~ ~ ldliysc harged, and the fully discharged battery is
disassembled in the glove box and a measurement sample is fabricated by a method
similar to that of (2) to perform X-ray diffraction measurement.
100761

The method for producing a negative electrode active material containing the
above described specific alloy phase, and a negative electrode and a battery utilizing
the negative electrode active material will be described.
[0077]
Molten metal of a negative electrode active material containing the specific
alloy phase is produced. For example, molten metal having the above described
chemical composition is produced. The molten metal is produced by melting
starting material by an ordinary melting method such as arc melting or resistance
beating melting. Next, an ingot (bulk alloy) is produced by an ingot casting method
by using the molten metal. By the above described processes, a negative electrode
active material is produced.
[0078]
Preferably, the negative electrode active material is produced by subjecting
the molten metal to rapid solidification. This method is called a rapid solidification
method. Examples of the rapid solidification method include a strip casting method,
a melt-spinning method for producing ribbons, a gas atomization method, a melt
spinning method for producing fibers, a water atomization method, an oil
atomizatio~ml ethod, and the like.
100791
Wlen processing the negative electrode active material into powder, the bulk
alloy (ingot) obtained by melting is (I) cut, (2) coarsely crushed by a hammer mill
etc,, or (3) finely p~ilverized mechanically by a ball mill, an attsitor, a disc mill, a jet
mill, a pin mill, and the llke to adjust it into a necessary particle size. When the
bulk alloy has ductility and ordinary pulverization is difficult, the bulk alloy may be
subjected to cutting and pulverization by a grinder disc, which is cmbedded with
diamond abrasive particles, and the like. When M phase due to stress induction is
formed in these pulverization processes, the formation ratio thereof is adjusted as
needed by appropriately combining the alloy design, heat treatment, and
pulverization conditions thereof. When powder generated by an atomization
method can be used as melted or as heat treated, there may be cases where no
pulverization process is particularly needed. Moreover, when melted material is
obtained by a strip casting method and crushing thereof is difficult due to its ductility,
the melted material is adjusted to have a predetermined size by being subjected to
mechanical cutting such as shearing. Moreover, in such a case, the melted material
may be heat treated in a necessary stage, to adjust; the ratio between M phase and a
matrix phase, and the like.
[OOSO]
When a negative electrode active material is heat treated to adjust the
constitution ratio of the specific alloy phase, etc., the negative electrode active
material may be rapidly cooled as needed after being retained at a predetermined
temperature for a predetermined time period in inert atmosphere. In this occasion,
the cooling rate may be adjusted by selecting a quenching medium such as water, salt
water, and oil according to the size of the negative electrode active material, and
setting the quenching medium to a predetermined temperature.
[OOS l]

A negative electrode using a negative electrode active material relating to an
embodiment of the present invention can be produced by a method well known to
those skilled in the art.
[OOSZ]
For example, a binder such as polyvinylidene fluoride (PVDF), polymethyl
methacrylate (PMMA), polytetrafluoroethylene (PTFE), and styrene-butadiene
rubber (SBR) is admixed to powder of a negative electrode active material of an
embodiment of the present invention, and further carbon material powder such as
natural graphite, artificial graphite, and acetylene black is admixed thereto to impart
sufficient conductivity to the negative electrode. After being dissolved by adding a
solvent such as N-methylpyrrolidone (NMP), dimethylformamide (DMF) and water,
the binder is stirred well using a homogenizer and glass beads if necessary, and
formed into a slurry. This slurry is applied on an active substance support member
such as a rolled copper foil and an electrodeposited copper foil and is dried.
Thereafter, the dried product is subjected to pressing. Through the above described
processes, a negative electrode plate is produced.
[0083]
The amount of the binder to be admixed is preferably about 5 to 10 mass%
from the viewpoint of the mechanical strength and battery characteristics of the
negative electrode. The support menber is not limited to a copper foil. The
support member may be, for example, a foil of other metals such as stainless steel
and nickel, a net-like sheet punching plate, a mesh braided with a metal element wire
and the like.
[0084]
The particle size of the powder of negative electrode active material affects
the thickness and density of electrode, that is, the capacity of electrode. The
thickness of electrode is preferably as thin as possible. This is because a smaller
thickness of electrode can increase the total surface area of the negative electrode
active material included in a battery. Therefore, an average particle size of the
powder of negative electrode active material is preferably not more than 100 pm.
As the average particle size of the powder of negative electrode active material
decreases, the reaction area of the powder increases, thereby resulting in excellent
rate characteristics. However, when the average particle size of the powder of
negative electrode active material is too small, the properties and condition of the
surface of the powder change due to oxidation etc. so that it becomes difficult for
lithium ions to enter into the powder. In such a case, the rate characteristics and the
efficiency of charging/discharging may decline over time. Therefore, the average
particle size of the powder of negative electrode active material is preferably 0.1 to
100 pm, and more preferably 1 to 50 bm.
[0085]

A nonaqueous electrolyte secondary battery according to the present
embodiment includes a negative electrode, a positive electrode, a separator, and an
electrolytic solution or electrolyte as described above. The shape of the battery may
be a cylindrical type, a square shape as well as a coin type and a sheet type. The
battery of the present embodiment may be a battery utilizing a solid electrolyte such
as a polymer battery and the like.
(00861
The positive electrode of the battery of the present embodiment preferably
contains a transition metal compound containing a metal ion as the active material.
More preferably, the positive electrode contains a lithium (Li)-containing transition
metal compound as the active material. An example of the Li-containing transition
metal compound is LiM1-xM'x02, or LiM2yM104. Where, in the chemical formulae,
0 5 x, y 5 1, and M and M' are respectively at least one kind of barium (Ba), cobalt
(Go), nickel (Ni), manganese (Mn), chromium (Gr), titanium (Ti), vanadium (V),
iron (Fe), zinc (Zn), aluminum (AI), indium (In), tin (Sn), scandium (Sc) and yttrium
(-0.
[OO87]
However, the battery of the present embodiment may use other positive
electrode materials such as transition metal chalcogenides; vanadium oxide and
lithium (Li) compound thereof; niobium oxide and lithium compound thereof;
conjugated polymers using organic conductive substance; Shepureru phase
compound; activated carbon; activated carbon fiber; and the like.
[OOSS]
The electrolytic solution of the battery of the present embodiment is generally
a nonaqueous electrolytic solution in which lithium salt as the supporting electrolyte
is dissolved into an organic solvent. Examples of lithium salt include LiC104,
LiBF4, LiPF6, LiAsF6, LiB(C6Mj), LiCF3S03, L iCH3S03,L i(CF3S02)2NL, iC4F9S03,
Li(CF2S02)2L, iCl, LiBr, and Lil. These may be used singly or in combination.
The organic solvent is preferably carbonic ester, such as propylene carbonate,
ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl
carbonate. However, other various kinds of organic solvents including carboxylate
ester and ether are usable. These organic solvents rnay be used singly or in
combinatio~~.
[OO89 ]
The separator is placed between the positive electrode and the negative
electrode. The separator serves as an insulator. Further, the separator greatly
contrib~rtest o the retention of electrolyte. The battery of the present embodiment
may inclitde a well known separator. The separator is made of, for example,
polypropylene or polyethylene, which is polyolefin-based material, or mixed fabric
of the two, or a porous body such as a glass filter.
[OOSO
Hereinafter, the negative electrode active material. the negative electrode, and
the battery of the present embodiment described above wiii be described in more
detail by using Examples. It is noted that the negative electrode active material, the
negative electrode, and the battery of the present embodiment will not be limited to
Examples shown below.
[Example I]
COO9 1 J
Powdered negative electrode active materials, negative electrodes, and coin
batteries of Inventive Examples 1 to 13 of the present invention and Comparative
Example 1 were produced by the following method. Then, changes in the crystal
structure of each negative electrode active material caused by chargingldischarging
were confirmed. Further, discharge capacity (discharge capacity per volume) and
cycle characteristics of each battery were investigated.
10092 1
[Inventive Example 1 Of The Present Invention]
[Production Of Negative electrode active material]
Molten metal was produced such that the chemical composition of powdered
negative electrode active material is Cu-15.5 at% Sn, that is, the chemical
composition of negative electrode active material contains 15.5 at% of Sn, with the
balance being CLI and impurities. To be specific, a mixture of 22.34 g of copper and
7.66 g of tin was subjected to high-frequency induction melting to produce molten
metal. The molten metal was cast to produce an ingot having a diameter of about
25 mm and a height of about 7 mm.
[0093 1
The ingot was longit~tdinallyc ut into halves. The cut pieces of the ingot
were vacuum sealed into a silica tube, and were heat treated at 720°C for 24 hours.
Next, the silica tube was broken in water with ice of O°C, thereby causing the water
with ice to enter inside the silica tube, and the ingot was rapidly cooled directly with
the water u~ithic e.
LO0941
The strrface of the ingot after rapid cooling was ground to remove a nearsurface
portion thereof. A diamond file of grit size #270 was used to pulverize the
ingot after grinding into a powder form such that the particle size was not more than
45 pm. This pulverized product (powder) was used as the negative electrode active
material. The chemical composition of the negative electrode active material was
Cu-15.5 at% Sn. That is, the chemical composition of the negative electrode active
material contained 15.5 at% of Sn, with the balance being Cu and impurities.
10095)
[Production Of Negative Electrode]
The above powdered negative electrode active material, acetylene black (AB)
as a conductive assistant, styrene-butadiene rubber (SBR) as a binder (2-fold
dilution), and carboxymethylcellulose (CMC) as a thickening agent were mixed in a
mass ratio of 75: 15: 10:s (blending quantity was Ig: 0.2g: 0.134g: 0.067g). Then, a
kneading machine was used to produce a negative electrode compound slurry by
adding distilled water to the mixture such that slurry density was 27.2%. Since the
styrene-butadiene rubber was used by being diluted 2-fold with water, 0.134 g of
styrene-butadiene rubber was blended when weighing.
100961
The produced negative electrode compound slurry was applied on a copper
foil by using an applicator (150 pm). The copper foil applied with the slurry was
dried at 100°C for 20 minutes. The copper foil after drying had a coating film made
up of the negative electrode active material on the surface. The copper foil having
the coating film was subjected to punching to produce a disc-shaped copper foil
having a diameter of 13 mm. The copper foil after punching was pressed at a press
pressure of 500 kgf/crn2 to produce a plate-shaped negative electrode material.
10097 1
[Production of Battery]
The produced negative electrode material, EC-DMC-EMC-VC-KC as the
electrolytic solution, a polyolefin separator ($171nm) as the separator, and a metal Li
plate ($19 x 1 mmt) as the positive electrode material were prepared. Thus
prepared negative electrode material, the electrolytic sol~~tiotnh,e separator, and the
positive electrode material were used to produce a coin battery of 2016 type.
Assembly of the coin battery was performed within a glove box in argon atmosphere.
[0098]
[Determination Of Crystal Structure]
The crystal structures of the powdered negative electrode active material
before use for the negative electrode, the negative electrode active material in the
negative electrode before initial charging, and the negative electrode active material
in the negative electrode after one to multiple times of charging and discharging were
determined by the following method. X-ray diffraction measurements were carried
out for the target negative electrode active materials to obtain measured data. Then,
based on the obtained measured data, crystal stn~cturesin cluded in the target
negative electrode active materials were determined by Rietveld method. More
specifically, the crystal structures were determined by the following method.
[0099]
(1) Crystal structure analysis of powdered negative electrode active material
before use in negative electrode
X-ray diffraction measurements were carried out for the powder (not more
than 45 pm) of the negative electrode active materials before use in the negative
electrode to obtain measured data of X-ray diffraction profile.
[OlOOl
To be specific, RINTIOOO (product of Rigaki~C o., Ltd) (rotor target
rnaxim~~ornu tput 18KW; 60kV-300mA, or Tube target maximum output 3kW;
50kV-60mA) was used to obtain X-ray diffraction profiles of the powder of the
negative electrode active materials.
[0 10 11
Based on the obtained X-ray diffraction profiles (measured data), crystal
structures of alloy phases in the negative electrode active material were analyzed by
Rietveld method.
[O 1021
Analysis revealed that yl' phase (2H structure) which is a kind of M phase,
and phase (DO3 structure) which is the matrix phase thereof were mixed in the
negative electrode active material of Inventive Example 1. The matrix phase had a
crystal structure in which a part of Sn site in the DO3 structure is replaced by Cu.
The analysis procedure will be described in detail below.
LO 1031
FIG. I is a diagram illustrating an X-ray diffraction profile of Inventive
Example 1 ((d) in the figure), and a simulation result by Rietveld method ((a) and (b)
in the figure). Literature data of powder of Cu-15.5 at% Sn is shown as a reference
((c) in the figure). The literature data is that disclosed in S.Miura, Y.Morita,
N.Nakanishi, "Shape Memory Effects in Alloys," Plenum Press, N.Y. (1975) 389.
[O1041
The binary system diagram of Cu-Sn is known, and Cu- 15.5 at% Sn alloy is
in @ phase at 720°C based on the binary system diagram. It is known that when the
p phase is rapidly cooled, the crystal structure becomes DO? ordered structrtre.
[OlOS]
The DO3 ordered structure is an ordered structure as shown in FIG. 2. In the
crystal structure of Cu-15.5 at% Sn, in FIG. 2, Cu is present at atomic sites shown by
black circle, and 38 at% of Cu and 62 at% of Sn are present at atomic sites shown by
white circle. It is knowt~th at such a crystal structure falls into No. 225 (Fm-3m) of
International Table (Volume-A) in the classification of space group representation.
The lattice constant and atomic coordinates of this space group number are as shown
in Table 1
[Table I]
TABLE 1
Filings:
--
Parent phase (PI Phase), Crystal Structure: DO?, Composition: Cu-15.5 at% Sn
Space Group Number (International Table A): No.225 (Fm-3m)
Lattice Constant: a = 6.05 A
[0107j
Accordingly, with the structure model of this space group number being as the
initial stntcture model of Rietveld analysis, a calculated value of diffraction profile
(hereinafter, referred to as a calculated profile) of PI phase (DO3 structure) of this
chemical composition was found by Rietveld method. Rietan-FP (program name)
was used for Rietveld analysis.
[OlOS]
Further, it was anticipated that when an ingot was ground with a diamond file,
M phase of yl' was formed in the outer layer of the ingot by deformation-induced M
transformation, and was mixed into the powder. Therefore, a calcurlnted profile of
the crystal structure of yl' phase of this chemical composition was found as well.
[0109]
The crystal structure of yl'was 2H structure in the notation of Ramsdell
symbol. and the space group was No, 25 (Pmm2) of International Table (Volume-A),
or No. 59-2 (Pmmn) of International Table (Volume-A). The lattice constant and
atomic coordinates of No. 25 (Pmm2) are shown in Table 2, and the lattice constant
and atomic coordinates of No. 59-2 (Pmrnn) are shown in Table 3.
[Ol lo]
[Table 21
TABLE 2
Filings:
M Phase (yll Phase), Crystal Structure: 2M, Composition: Cu-15.5 at% Sn
Space Group Number (International Table A): No.25 (Pmm2)
Lattice Constants: a = 5.498 A, b = 4.379 A, c = 4.615 A
Site Name Atomic
Species
[Table 3 ]
TABLE 3
Filings:
MultiplicitylWyckoff Atomic Coordinates
Symbol
I JSb1p aPchea Gser o(yulp' P Nhuamseb),e Cr (rIynsttearln Sattriuocntaulr Te:a b2lHe, A C)o: mNpoo.5s9it-i2o n(:P Cmu-m15~.5) at% Sn I
Lattice Constants: a = 4.379 A, b = 5.498 A, c = 4.615 A
Atomic
Site Name
Species
M~lltiplicity/Wyckoff
Symbol
No matter which space group number is selected, there is no effect on the
analysis by Rietveld method. Then, a calculated profile was found by using
RETAN-f;P supposing that the crystal structure of the space group number of the
above describe Table 2 be the initial structure model of Rietveld analysis.
[0113]
In FIG. 1, (a) shows a calculated profile of DO3 structure, and (b) shows a
calculated profile of 2W structure. Referring to FIG. 1, diffraction peaks of a
measured X-ray diffraction profile ((d) in the figure) corresponded with those of the
calculated profile of (a). Further, there were seen portions of the X-ray profile of
(d), which corresponded with peaks of the calculated profile of (b). Therefore, it
was confirmed that the powdered negative electrode active material of Inventive
Example 1 contained DO3 structure, and also contained 2H structure due to
deformation-induced M transformation by a file.
[0114]
It is noted that in the X-ray diffraction profile of (d), diffraction peaks that
appeared in a range of diffraction angle 20 of 37 to 48' approximately corresponded
with the angle range of diffraction peaks that appeared in the measured value of the
X-ray diffraction profile of the powder of Cu-15.5 at% Sn ((c) in FIG. 1) described in
the literature reported by Miura et al. However, in the powder of the present
Example, full width at half maximum of diffraction peaks were broadened as a result
of that strain was introduced into powder particles during grinding by a diamond file.
[OllSj
(2) Crystal Structure Analysis Of Negative electrode active tnaterial In
Negative Electrode
The crystal structure of a negative electrode active material in a negative
electrode before charging was also determined by the same nlethod as that in (I). A
measured X-ray diffraction profile was lneasured by the following method.
101 161
The above described coin battery, which was before being charged, was
disassembled within the glove box in argon atmosphere, and a plate-shaped negative
electrode was taken out from the coin battery. The negative electrode taken out was
enclosed in Myler foil (manufactured by DuPont). Thereafter, the perimeter of the
Myler foil was sealed by a thermocompression bonding machine. Then, the
negative electrode sealed by the Myler foil was taken out of the glove box.
101 171
Next, a measurement sample was fabricated by bonding the negative electrode
to a reflection-free sample plate manufacttired by Rigaku Co., Ltd. (a plate of a
silicon single crystal which was cut out such that a specific crystal plane was in
parallel with the meastrrement plane) with a hair spray.
[0118]
The measurement sample was mounted onto the X-ray diffraction apparatus
described below in (4), and the X-ray diffraction measurement of the measurement
sample was performed under measurement conditions described below in (4).
101 191
(3) Analysis Of Crystal Structure Of Negative electrode active material In
Negative Electrode After Charging And After Discharging
The crystal structure of the negative electrode active material in the negative
electrode after one to multiple times of charging and after one to multiple times of
discharging was also determined by the same method as that in (1). Measured Xray
diffraction profiles were measured by the following method.
[01201
The above described coin battery was fully charged in a charging/discharging
test apparatus. The f~111yc harged coin battery was disassembled in the glove box,
and a measuremerrt sample was fabricated by the same method as that in (2). The
measurement sample was mounted onto the X-ray diffraction apparatus described
below in (4), and X-ray diffraction measurement of the measurement sample was
performed under measurement conditions described below in (4).
[0121]
Moreover, the above described coin battery was fully discharged. The fully
discharged coin battery was disassembled in the glove box, and a measurement
sample was fabricated by the same method as in (3). The measurement sample was
mounted onto the X-ray diffraction apparatus described below in (4), and X-ray
diffraction measurement of the measurement sample was performed at measurement
conditions described below in (4).
(0 1221
For a negative electrode which had been subjected to charging and
discharging repeatedly in a coin battery, X-ray diffraction measurement was
performed by the same mehod.
LO1231
(4) X-Ray Diffraction Apparatus And Measurement Conditions
- Apparatus: RlNTlOOO (product name) manufactured by Rigaku Co., Ltd.
- X-ray tube: Cu-Ka ray
- Filter: Ni (cutting off Cu-KP ray)
- X-ray output: 40 kV, 30 mA
- Optical system: Bragg-Brenrano geometry
- Divergence slit: 1 degree
- Scattering slit: 1 degree
- Receiving slit: 0.3 mm
- Monochrome receiving slit: 0.8 mrn
- Goniometer: RlNTf 000 vertical goniometer
- X-ray - sample distance: 185.0 rnm
34
- Sample - receiving slit distance: 185.0 mrn
- X-ray - divergence slit distance: 100.0 rnm
- Solar slit - receiving slit distance: 54.0 mm
- Monochrometer: bent graphite monochrometer
- Detector: scintillation counter (SC50 type)
- Scan range: 10 to 120 degree(2 0 )
- Scan step: 0.02 degree e(2 0 )
- Scan mode: time is fixed at each measurement STEP angle
- Measurement time: 2 sec/STEP
10 1241
(5) Analysis results of X-ray diffraction measurement data
X-ray diffraction data obtained in (I), (2), and (3) are shown in FIG. 3. In
FIG. 3, (d) is an X-ray diffraction profile of powder of a negative electrode active
material, which was found in (I). In the figure, (e) is an X-ray diffraction profile of
the negative electrode active material in the negative electrode before initial
charging; (f) is an X-ray diffraction profile of the negative electrode active material
after first charging; and (g) is an X-ray diffraction profile after first discharging. In
the figure, (h) is an X-ray diffraction profile of the negative electrode active material
after 12th charging; and (i) is an X-ray diffraction profile after 12th discharging. In
FIG. 3, (a) is a calculated profile of DO3 structure in the chemical composition of the
present Example as with (a) in Fig. I, and (b) in FIG. 3 is a calculated profile of 2H
structure in the chemical composition of the present Example as with (b) in FIG. 1.
[0125]
(5-1)
Referring to FIG. 3, the X-ray diffraction profile of (e) was the same as the Xray
diffraction profile of (d). This confirmation confirmed that there was no
significant chemical reaction progressed between the negative electrode active
material and the electrolytic solution.
[0 126)
(5-2)
X-ray diffraction profiles of the "negative electrode active material after
charging" (FIG. 3 (f), (h)) and X-ray diffraction profiles of the "negative electrode
active material after discharging" (FIG. 3 (g), (i)) are respectively compared with
each other. The results revealed that diffraction lines reversibly changed repeatedly
at a position where the diffraction angle 20 was near 38 to 39' (position caused by M
phase (yi' phase))(hereinafter, referred to as an essential diffraction line position).
That is. structural change was suggested.
[O 1271
(5-3)
Accordingly, the crystal structures of the "negative electrode active material
after charging" and the "negative electrode active materials after discharging" were
determined by using Rietveld method.
[0128]
For example, explaining based on the way of taking the crystal axes shown in
Table 3, in the negative electrode active material, the crystal plane A shown in FIG.
4D and the crystal plane B shown in FIG. 4C are alternately layered in the DO3
structure of the matrix phase shown in FIGS. 2 and 4A. When a phase
transformation occurs between the DO3 structure and yl' phase which is a kind of M
phase, as shown in FIGS. 4A and 4B, the crystal plane B regularly undergoes
shuffling due to shear stress, thereby being displaced to the position of crystal plane
B'. In this case, phase transformation (M transformation) occurs without diff~~sion
of the host lattice. In the 2H structure after M transformation, the crystal plane A
shown in FIG. 4D and the crystal plane B' shown in FIG. 3E are alternately layered.
I01291
Then, it is judged whether the crystal structure of the negative electrode active
material in the negative electrode of the present Example involves M tsai~sfos~nation
or not accompanied thereby (that is, involves diffusion of host lattice at the time of
charging/discharging) by comparing the measured data of the X-ray diffraction
profiles of the negative electrode active material after charging and after discharging,
calculated profile ((a) in FIG. 3) of PI phase (DOs structure), and calculated profile
((b) in FIG. 3) of yl' phase (2W structure).
[0 1301
Referring to FIG. 3, in the X-ray diffraction profile, the intensity of diffraction
line near 38 to 39' increased as a result of initial charging, and decreased as a result
of consecutive discharging. It can be judged that this diffraction line resulted from
the formation of M phase (yl') by M transformation, as will be next described, from
calci~latedp rofiles ((a) and (b) in FIG. 3) of RIETAN-m).
101311
To be specific, as shown in (b), an intensity peak occitrred at 38 to 39' of an
X-ray diffraction profile, in 2I-I structure. On the other hand, in DO3 structure ((a)
in the figure), no intensity peak occurred at 38 to 39'. In contrast, in the X-ray
diffraction profiles after charging ((0an d (h) in FIG. 3), an intensity peak occurred
at 38 to 39'. On the other hand, in the X-ray diffraction profiles after discharging
((g) and (i) in FIG. 31, no intensity peak occurred at 38 to 39O. Further, the intensity
peak at 38 to 39' did not appear in the X-ray profiles of other crystal structures
(sirnillation result) besides 2M.
10132j
From the above, the negative electrode of the present Exalnple contained an
alloy phase which u~lderwenMt transformation to become M phase (2W structure) as
a result of charging, and became a matrix phase (DO3 strx~cturea) s a result of
discharging. That is, the negative electrode of the present Example contained an
alloy phase which underwent M transformation when occluding lithium ions which
are metal ions, and underwent reverse transformation when releasing lithium ions.
101331
This was also proved from the fact that the most intense line (see FIG. 3 (a))
of the matrix phase (PI) appeared sharply after discharging of 12th cycle. In the
negative electrode of the present Example, M transformation at the time of charging,
and reverse transformation at the time of discharging were repeated.
10 1341
In FIG. 3, the full width at half maximum of a diffraction line decreased along
with charge-discharge cycles. From this, it is considered that occlusion and release
of lithium ions relaxed strain of the negative electrode active material.
[0135]
[Charge-Discharge Performance Evaluation Of Coin Battery]
Next, discharge capacity and cycle characteristics of the battery of Inventive
Example 1 were evaluated.
101361
Constant current doping (corresponding to the insertion of lithium ions into
electrode, and the charging of lithium ion secondary battery) was performed to a coin
battery at a current value of 0.1 rnA (a current value of 0.075 m~lcm') or a current
value of 1 .O MA (a current value of 0.75 rnA/cm" until the potential difference
against the counter electrode becomes 0.005 V. Thereafter, doping capacity was
measured by continuing doping against the counter electrode at a constant voltage
until the current value became 7.5 ,u~/cm' while retaining 0.005 V.
[0137]
Next, de-doping capacity was measured by performing de-doping (which
corresponds to desorption of lithium ions from the electrode, and discharge of the
Lithium ion secondary battery) at a current value of 0.1 mA (a current value of 0.075
m~/cm" or a current value of 1.0 rnA (a current value of 0.75 rnAlcm2) until the
potential difference becomes 1.2 V.
[0 13 81
The doping capacity and de-doping capacity correspond to charge capacity
and discharge capacity when the electrode is used as the negative electrode of the
lithium ion secondary battery. Therefore, the measured dope capacity was defined
as the charge capacity, and a measured de-doping capacity was defined as the
discharge capacity.
LO1391
Charging and discharging were repeated, The doping capacity and the dedoping
capacity were measure for each charging and discharging. Measured results
were used to obtain charge-discharge cycle characteristics shown in FIG. 5.
[O 1401
Referring to FIG. 5, the initial charge capacity of the coin battery of Inventive
Example 1 was 2634 rnAh/cd, and the discharge capacity was 1569 &crn3.
The initial discharge capacity of a coin battery of Inventive Exa~nple1 is about twice
the theoretical capacity of graphite. Further, the discharge capacity after 40 cycles
was 1304 m ~ / c ma~nd, the capacity retention ratio was as high as 83%.
[0141]
From FIG. 5, the coin battery of Inventive Example 1 had stable chargedischarge
cycle characteristics.
101421
[Inventive Examples 2 to 131
In Inventive Examples 2 to 13, a negative electrode active material, a negative
electrode, and a coin battery were produced by the following method.
101431
(I) Production Of Negative electrode active material
A mixture of multiple starting materials (elesnents) was subjected to high
frequency melting in a silica nozzle or a nozzle made of boron nitride in argori gas
atmosphere such that the final chemical composition of each negative electrode
active material became the chemical composition described in the "chemical
composition" column in Table 4, thereby producing molten metal. The molten
metal was sprayed onto a rotating copper roll to produce a rapidly solidified foil strip.
The thickness of the foil strip was 20 to 40 pm. This foil strip was pulverized with
a Raikai mixer (automatic mortar) into alloy powder of not more than 45 pm. This
alloy powder was used as the negative electrode active material. The final chemical
composition of the negative electrode active material of each Inventive Example was
as described in the "chemical composition" col~tnnin Table 4.
[O 1441
[Table 4)
TABLE 4
I / Discharge Capacity 1 I - . 1 - I
Classification Composition
I Time I Cycling /
Inventive Example / 6A / ~i~-l.0at%~e-15.5atc/o/ ~n 15.55 / 1563 1 25 1 I01 / 0.1 /
Inventive Example
Inventive Example
Inventive Example
Inventive Example
4 1 Cu- I .Oat%Cr-15.5at%Sn 1375
5 Cu- 1 .Oat%Mn- 15.5at%Sn 1463
155 1
1604
20
25
113
if0
0.1
0.1
Inventive Example I 12B / Cu-14.5at%Sn-1 .Oat%Al 1 1 103 / 1276 / 92 / 1 16 1 1.0 /
[0 1451
Referring to Table 4, for example, the chemical composition of the powdered
negative electrode active material of Inventive Example 2 was Cu-1.0 at% Ti-15.5
at% Sn. That is, the chemical composition of Inventive Example 2 contained 15.5
at% of Sn and 1.0% of Ti, with the balance being Cu and impurities. Similarly, the
chemical composition of Inventive Example 3 contained 15.5 at% of Sn and 1.0% of
V, with the balance being Cu and impurities.
101461
(2) Prodtiction Of Negative Electrode And Coin Battery
Negative electrodes and coin batteries were produced by the same production
method as that in hventive Example 1 by using the produced negative electrode
active material of each Inventive Example.
10 1471
(3) Determination Of Crystal Structure And Evaluation Of Cycle
Characteristics
[Determination Of Crystal Structure]
The crystal structure of the powdered negative electrode active material
before use for the negative electrode of each of Inventive Examples 2 to 13 was
determined by the same method as that in Inventive Example 1. Further, the crystal
structure of the negative electrode active material in the negative electrode of each
Inventive Example before initial charging was determined by the same method as
that of Inventive Example 1. Further, the crystal structures of the negative electrode
active material in the negative electrode of each Inventive Example after one to
multiple times of charging and after one to multiple times of discharging were
determined by the same method as that in Inventive Example 1, thereby confirming
Inventive Example 13 Cu-14.5at%Sn- 1 .Oat%Si 1270 1324 14 104 0.1 1
Comparative Example 1 Natural Graphite 83 1 810 20 97 0.1
how the crystal structure of the negative electrode active material was changed by
chargingfdischarging.
[0148]
As a result of determination, in all of Inventive Examples, all of the crystal
structures of negative electrode active material in the negative electrode after one to
multiple times of discharging included DOs structure. Further, all of the crystal
structures of negative electrode active material after one to multiple times of
charging included 2H structure. To be specific, after one to multiple times of
charging, an intensity peak was confirmed in a range of 38 to 39O of diffraction angle
20 (hereinafter, referred to a specific diffractio~al ngle range) in the X-ray diffraction
profile. Moreover, after discharging, no peak was confirmed in the specific
diffraction angle range. Therefore, this confirmed that the negative electrode active
materials of Inventive Examples 2 to 13 had a crystal structure that underwent M
transformation when occluding lithium ions, and undenvent reverse transformation
when releasing lithium ions.
101491
[Cycle Characteristics]
Discharge capacity of a coin battery of each Inventive Example was found by
the same method as that in Inventive Example 1, and cycle characteristics was
evaluated. As a result, any of the initial discharge capacities of the coin batteries in
Inventive Examples 2 to 13 was higher than the discharge capacity of Comparative
Example 1 (negative electrode active material made of graphite) to be described
below. Further, any of discharge capacities after cycles listed in Table 4 was as
high as 922 rnAh/cm3 or more, meaning that excellent cycle characteristics was
obtained compared with conventional alloy-based negative electrode materials (refer
to Table 4). In Table 4, there were Inventive Examples in which the capacity
retention rate was more than 100%. This may be because, in these negative
electrode active materials, as the charge-discharge cycle was repeated, Li ions were
diffused into the inside of the negative electrode active material, and the proportion
thereof that contributed chargingldischarging increased.
[O 1501
It is noted that the chemical compositions of negative electrode active
materials of Inventive Examples 6A and 6B were identical to each other, and also the
chemical compositions of the negative electrode active materials of Inventive
Examples 12A and 12B were identical to each other. In Inventive Examples 6A
and 12A, the current value at the time of chargingldischarging was set to 0.1 mA,
and in Inventive Examples 6B and 12B, the current value at the time of
charging/discharging was set to 1.0 mA. In the description below, Inventive
Examples 6A and 6B are referred to together simply as "Inventive Example 6", and
Inventive Examples 12A and 12B are referred to together simply as "Inventive
Example 12".
[015l]
[Comparative Example 11
Natural graphite was used as the negative electrode active material. By
using natural graphite powder as the negative electrode active material, a negative
electrode and a coin battery were produced by the same production method as that in
Inventive Example 1. Then, a discharge capacity was found in the same way as in
Inventive Example 1.
loisal
[Test Results]
As described above, the negative electrode active materials of Inventive
Examples 1 to 13 all included, after charging, 2H stnlcture which was formed from
DO3 stn~ctureth rough M transformation, and included, after discharging, DO3
str~rcturew hich was formed from the 2H structure through reverse transformation.
101531
Further, all of the initial discharge capacities of Inventive Examples 1 to 13
were higher than that of the graphite negative electrode of Comparative Example 1.
[O 1 541
Further, the initial discharge capacities (when the current value was 0.1 mA)
of Inventive Examples 6 and 12 were equal to, or not less than that of Inventive
Example 1. This may be because one more kind of element was blended in the
negative electrode active materials of Inventive Examples 6 and 12 compared with in
the powder of the negative electrode active material of Inventive Example 1.
Compared with in the negative electrode active material of Inventive Example 1,
disarrangement of lattice occuned and so-called lattice defects increased in the
negative electrode active materials of Inventive Examples 6 and 12. This ensured
more diffusion paths and storage sites of lithium ions. As a result, it is considered
that the initial capacity and the charge-discharge rate characteristics of the coin
batteries of Inventive Examples 6 and 12 were improved. Improvement of the
charge-discharge rate characteristics was confirmed by that Inventive Examples 6B
and 12B showed excellent discharge capacities.
[Example 21
[0155]
Negative electrode active materials, negative electrodes, and coin batteries of
Inventive Examples 14 to 53 were produced by the same method as that in Example
1. Further, negative electrode active materials, negative electrodes, and coin
batteries of Comparative Examples 2 to 4 were produced. Then, the crystal
structure of each Inventive Example and Comparative Example was determined, and
discharge capacities ( m h ~ / c mo~f )th e initial time and after multiple times of
charging-discharging were obtained. The results are shown in Table 5.
[O i561
[Table 51
TABLE 5
/ Discharge Capacity I
(mANcmS) Number
Composition
Initial I After of Cycles
Classification
I Time / Cvcling 1
Comparative Example 1 2
Inventive Example 1 14
Inventive Examule 1 15
Inventive Example
1 Inventive Example / 20
Inventive Examule ! 21
I Inventive Example 1 22
I - 7 iI 1 LO
Cu- 1 oat'; %I]-??at'; SII I 711 1 1 70
/ 111ventive Example 1 25
1 Inventive Exampie 1 28
I lnventive Example / 3 1
1 fnventive Example 1 34
1 Inventke Example
lnventive Example
l~iventiveE xamule
Inventive Example
inventive Example
Inventive Examnle 10
/ lnventive Example / 11
Inventive Example 1 42
Inventive Examole / 43
1 lnventive Example 1 44
Inventive Example 1 45
Inventive Examale / 16
Cu-Sat%Fe-25atr/rSn 1 2506 1 1506 / 20
Cu- lOat%Fe-25at%Sn I 2522 / 1745 1 20
/ Inventive Example / 17
Inventive Example 5 1
Inventive Example 5 2
Inventive Example 53
/ Comparative Exarnnle / 3
/ Comparati\\.r Example 1 6
Comparative Example 1 7 1 Cu- lOat%Mn-25atCioSn / 157 1 0.1 /
Comparative Example 1 8 I Cu-50at%Zn-25atcicSn I 706 1 455 1 20 / 64 / 0.1
Comwarative Examole / 9 / Cn-50at%A1-25at%Sn 1 666 1 419 1 20 / 0.1
Com~arativeE xample 1 10 I Cu-50at%Si-25atBSn 1 1395 1 175 / 20 1 13 1 0.1 1
Comparative Example / 1 I / Cu- 1 Oat%Ti-25at%Sn 1 240 / 296 / 20 / 124 / 0.1
Comparative Example 1 12 I Cu-5at%Cr-25at%Sn 1 230 1 421 1 20 1 183 1 0. I
Comparative Example 1 13 I Cu-50at%Fe-25at%Sn / 3141 168 1 20 1 53 / 0.1
Comparative Example 1 14 Cu-SOatBCo- 15at%Sn 423 300 20 7 1 0.1
Comparative Example 1 I5 Cu-50at%V-25at%Sn 343 215 20 63 0.1
Initial Time: the value of the cycle ar which capacity started to be stabilized, among 1st to 4th cycles is adopted.
[O157]
Referring to Table 5, each of Inventive Examples and Comparative Examples
will be described.
[01 581
[Inventive Example 141
A mixture in which Cu and Sn were mixed was prepared. As with Inventive
Examples 2 to 13, the prepared mixture was subjected to high-frequency induction
melting in a silica nozzle or a nozzle made of boron nitride in argon atmosphere,
thereby producing molten metal. The molten metal was sprayed onto a rotating
copper roll, thereby producing a rapidly solidified foil strip. The thickness of the
foil strip was 20 to 40 pm. This foil strip was pulverized with a Raikai mixer
(automatic mortar) into alloy powder of not more than 45 pm. This alloy powder
was used as the negative electrode active material.
The final chemical composition of the negative electrode active material of
Inventive Example 14 was Cu-25 at% Sn. That is, the chernical composition of
Inventive Example 14 contained 25 at% of Sn, with the balance being Cu and
impurities.
By using the produced negative electrode active material of the present
Inventive Example, a negative electrode and a coin battery were produced by the
same method as that of Inventive Example 2.
[0161]
[Determination Of Crystal Structure]
The crystal structure of the powdered negative electrode active material
before use in the negative electrode of Inventive Example 14 was determined by the
same method as that of Inventive Example 1. Moreover, the crystal structure of the
negative electrode active material in the negative electrode of each Inventive
Example before initial charging was determined by the same method as that of
Inventive Example 1. Further, the crystal structures of the negative electrode active
material in the negative electrode of each Inventive Example after initial charging,
after initial discharging, after multiple times of charging, after m~rltipleti mes of
discharging were determined by the same method as that of Inventive Example I,
thereby confirming how the crystal structure of the negative electrode active
materials was changed by charging/discharging.
[0162]
Hereinafter, the method of determining crystal structures of a powdered
negative electrode active material before use in a negative electrode, a negative
electrode active material in a negative electrode before charging, a negative electrode
active material after one to multiple times of charging and discharging will be
described in detail.
/0163]
(I) Analysis Of Crystal Structure Of Powdered Negative electrode active
material
Analysis of the crystal structure of powder (not more than 45 pm) of negative
electrode active material was performed by X-ray diffraction measurement. To be
specific, SrnartLab manuhctured by Ligaku Go., Ltd. (maximum output of rotor
target 9 KW; 45 KV - 200 mA) was used to acquire an X-ray diffraction profile of
the powder of negative electrode active material. Then, as with Inventive Example
1, the configuration of phases of the negative electrode active substance alloy was
analyzed by Rietveld method (using RIETAN2000 and RIETAN-FP).
101641
FIG. 6 is a diagram illustrating a measured X-ray diffraction profile and a
profile fitting result (calculated profile) by Rietveld method. Referring to FIG. 6,
the powdered negative electrode active material of Inventive Example 14 contained E
phase having the same structure as that of yl' phase (2H structure) which is a kind of
M phase.
[0 1651
That is, in the present Inventive Example, the crystal structure of martensite
phase after rapid cooling was 2H structure. That crystal stmcture was the same as
2H structure shown in FIG. 4B. The result of Rietveld analysis revealed that the
lattice constants of 2H structure of Inventive Example 14 were as follows: a = 4.339
A, b = 5.524 A, and c = 4,758 A, in the manner of taking crystal axes of the space
group shown in Table 3.
[O 1661
(2) Crystal Structure Analysis Of Negative Electrode Active Substance Alloy
Before Charging
A measurement sample was fabricated by the same method as that of
Inventive Example 1. Then, the measurement sample was mounted to the X-ray
diffraction apparatus described below in (4), and X-ray diffraction measurement of
the measurement samples was performed under the measurement conditions
described below in (4).
101671
(3) IvleasurementlAnalysis Method Of Crystal Structure Of Negative
Electrode Active Substance Alloy After Charging And After Discharging
Measurement samples were fabricated by the same method as that in (2)
described above with the above described coin batteries being fully charged or fully
discharged in a charge-discharge test apparatus. Then, the measurcmcnt sample
was mounted to the X-ray diffraction apparatus described below in (41, and X-ray
diffraction measurement of measured sample was performed under the measurement
conditions described below in (4).
101681
(4) X-Ray Diffraction Apparatus And Measurement Conditions
- Apparatus: SrnartLab manufactured by Rigaku Co., Ltd.
- X-ray tube: Cu-Ka ray
- X-ray output: 40 kV, 200 mA
- Incident monochrometer: Johannson type crystal (which filters out Cu-Ka2
ray and CLI-KP ray)
- Optical system: Bragg-Brentano geornetry
- Incident parallel slit: 5.0 degrees
- Incident slit: 1/2 degrees
- Length limiting slit: 10.0 mrn
- Receiving slit 1: 8.0 mm
- Receiving slit 2: 13.0 rnm
- Receiving parallel slit: 5.0 degrees
- Goniometer: SmartLab goniometer
- X-ray source - mirror distance: 90.0 mm
- X-ray source - selection slit distance: 114.0 mrn
- X-ray source - sample distance: 300.0 rnm
- Sample - receiving slit 1 distance: 187.0 rnm
- Sample - receiving slit 2 distance: 300.0 rnrn
- Receiving slit 1 - receiving slit 2 distance: 113.0 mrn
- Sample - detector distance: 33 1.0 mm
- Detector: D!Tex Ultra
- Scan range: 10 to 120 degrees
- Scan step: 0.02 degrees
- Scan mode: Continuous scan
- Scanning speed: 2 degrees/min
[O 1691
[Analysis Of X-Ray Diffraction Measurement Data]
By using measured values of X-ray diffraction profiles obtained in (2) and (a),
fitting was performed by Rietveld analysis, and crystal structures were determined by
the same method as that of Inventive Example 1. Then, how the crystal structL~reo f
negative electrode active material was changed by charging!discharging was
confirmed.
[01701
As a res~rlto f determination, the crystal structure of the negative electrode
active material before charging was the same 2H structure as in FIG. 6. However,
as charging and discharging were repeated, the negative electrode active material
after charging included 2H structure, and the negative electrode active material after
discharging included DO3 structure.
[0171]
To be Specific, after one to multiple times of charging, an intensity peak was
confirmed in a range of 38 to 39' of diffraction angle 20 (specific diffraction angle
range). and after discharging, no intensity peak was confirmed in the specific
diffraction angle range. Thus, this confirmed that the negative electrode active
material of Inventive Example 14 had a crystal structure that underwent M
transformation when occluding lithiutn ions, and underwent reverse transformation
when releasing lithium ions.
[O 1721
[Charge-Discharge Performance Evaluation Of Coin Battery]
Discharge capacity of the coin battery of each Inventive Example was found
by the same method as that of Inventive Example 1, and cycle characteristics was
evaluated. Where, as shown in Table 5, the current value at the time of
chargingldischarging was 0.1 rnA in Inventive Example 14.
101731
Referring to Table 5, the initial discharge capacity of the coin battery was
2459 rnANcm3, and was higher than that of the negative electrode active material
made of graphite. Further, the discharge capacity was 1934 cm" after 20
cycles of charging and discharging, and the capacity retention ratio was as high as
79%, exhibiting excellent cycle characteristics.
[0174]
[Inventive Example 151
Inventive Example 15 had the same negative electrode active material,
negative electrode, and battery as those of Inventive Example 14. In Inventive
Example 15, the current value at the time of charging/discharging when measuring
discharge capacity was 1.0 mA as shown in Table 5.
101751
As a result of the measurement, the initial discharge capacity was 1540
rn~h/cm', and was higher than in the case of graphite. Further, the discharge
capacity after 80 cycles of charging and discharging was 1461 rnAhicm3, and the
capacity retention rate was as high as 95%. Therefore, the battery of Inventive
Example 15 had excellent charge-discharge rate characteristics.
[0176]
[Inventive Examples 16 and 171
A negative electrode active material of each Inventive Example was produced
by the same production method as that of Inventive Example 2. The chemical
compositions of the produced negative electrodc active materials were as shown in
Table 5. The produced negative electrode active materials were used to produce
negative electrodes and coin batteries by the same method as that of Inventive
Example 2.
[0177]
The crystal structure of the powdered negative electrode active material
before use in the negative electrode of each Inventive Example described above was
determined by the same method as that of Inventive Example 14. Further, crystal
struct~~roefs the negative electrode active material in the negative electrode of each
Inventive Example after one to multiple times of charging, and after one to multiple
times of discharging were determined by the same method as that of Inventive
Example 14, thereby confirming how the crystal struct~lreo f the negative electrode
active material was changed by charging/discharging.
[O 1781
As a result of determination, in all of Inventive Examples, all of the crystal
structures of negative electrode active material in the negative electrode after one to
multiple times of discharging ilicluded DO? stsucture. Further, all of the crystal
structures of negative electrode active material after one to multiple times of
charging included 2H structure. Therefore, this confirmed that the negative
electrode active materials of Inventive Examples 16 to 17 had a crystal structure that
~mderwentM transformation when occluding lithium ions, and underwent reverse
transformation when releasing lithium ions.
101791
Further, the discharge capacity of the coin battery of each Inventive Example
was found by the same method as that of Inventive Example 14, thereby evalriating
the cycle characteristics thereof. Where, the current value at the time of charging
and discharging was as shown in Table 5.
[0 1801
Referring to Table 5, the initial discharge capacity of the coin battery was
higher than that of a negative electrode active material made of graphite. Further,
the capacity retention ratio after passage of the number of cycles shown in Table 5
was as high as not less than 5096, exhibiting excellent cycle characteristics.
[0181]
[Inventive Example 181
A negative electrode active material whose chemical composition was Cu-
18.5 at% Sn was produced by the same method as that of Inventive Example 2.
Further, a negative electrode and a coin battery were produced by the same method
as that of Inventive Example 2.
[0182]
Measurement and analysis of the powder (not more than 45pm) of the
negative electrode active material were performed by the same method as that of
Inventive Example 14.
101831
As a result, the negative electrode active substance alloy was identified to be
6 phase having F-cell structtire and a phase having DOi structure which is a kind of
matrix phase. FIG.7 is a diagram illustrating measured data of an X-ray diffraction
profile of Inventive Example 18, and a profile fitting result (calculated profiles) by
Rietveld method. Rietan-2000 was used for Rietveld analysis.
[O 1841
The quantitative analysis by Rietveld method shown in FIG. 7 resulted in that
the negative electrode active material of Inventive Example 18 comained 80 mass%
of 6 phase of F-cell structure, and 20 mass% of matrix phase of DO3 structure. That
is, the crystal structure of the negative electrode active material of Inventive Example
18 contained DO3 structure.
[O 1851
The fact that the diffraction profile of the matrix phase was broadened
indicated that strain had been introduced into the negative electrode active material.
[O 1861
Further, the crystal structures of the negative electrode active material in the
negative electrode of Inventive Example 18 after one to multiple times of charging,
and after one to multiple times of discharging were determined by the same method
as that of Inventive Example 1 to confirm how the crystal structure of the negative
electrode active material was changed by chargingldischarging.
[O 1871
The result of determination revealed that all of the crystal stsuctures of the
negative electrode active material in the negative electrode after one to multiple
times of discharging included DO3 structure. Further, all of the crystal structures of
the negative electrode active material after one to multiple times of charging
included 2I-I structure. Thus, this confirmed that the negative electrode active
material of Inventive Example 18 had a crystal structure that underwent M
transformation when occluding lithium ions, and underwent reverse transformation
when releasing lithium ions.
LO1881
[Charge-Discharge Performance Evaluation Of Coin Battery]
Discharge capacity and capacity retention ratio were measured as with
Inventive Example 14. As a result, as shown in Table 5, the initial discharge
capacity of Inventive Example 18 was 769 m/"ih/cm", and was equal to that of the
negative electrode active material made of graphite. However, the discharge
capacity after 20 cycles of charging and discharging was 1199 rnAh/cm3, and the
capacity retention ratio after 20 cycles increased to 156% (see Table 5).
[0 1891
Since the matrix phase having DO3 structure functioned as a negative
electrode active substance in Inventive Example 18, an initial discharge capacity of
an equal level to that of graphite was achieved. Further, it was considered that 6
phase of F-cell stnicture functioned as a diffusion phase of lithium ions.
[01901
Table 6 shows results of Rietveld analysis of Inventive Example 18.
[0191]
[Table 61
TABLE 6
Space Group Number (International Table A): No.216 (I;-43m)
As shown in Table 6, many of site occupancy factors in the long-period
ordered stn~cturew ere smaller than in normal F-Cell stmcture shown in Comparative
Example 2 described below, indicating that many site deficiencies occurred.
Therefore, it is considered that 6 phase of F-Cell structure functioned as a diffusion
site of lithium ions.
(01931
A chief cause why the capacity increased during cycling may be that the
proportion of capacity which was born by the active material phase increased along
with the number of cycles.
(01941
[Inventive Examples 19 to 221
A negative electrode active material of each Inventive Example was produced
by the same production method as that of Inventive Example 2. The chemical
compositions of the prod~lcedn egative electrode active materials were as shown in
Table 5. The produced negative electrode active materials were used to produce
negative electrodes and coin batteries by the same method as that of Inventive
Example 2.
101951
The crystal stmcture of the powdered negative electrode active material
before use in the negative electrode of each Inventive Example described above was
determined by the same method as that of Inventive Example 14. Further, crystal
structures of the negative electrode active material in the negative electrode of each
Inventive Example after initial charging, after initial discharging, after multiple times
of charging, and after multiple times of discharging were determined by the same
method as that of Inventive Example 14, thereby confirming how the crystal
structure of the negative electrode active material was changed by
chargingldischarging.
10 1961
The determination resulted in that in all of Inventive Examples, the crystal
structure of negative electrode active material in the negative electrode after one to
multiple times of discharging included DO3 structure. Further, all of the crystal
structures of the negative electrode active material after one to multiple times of
charging included 2W structure. Thus, this confirmed that the negative electrode
active material of Inventive Examples 19 to 22 had a crystal stnlcture that underwent
M transformation when occluding lithium ions and underwent reverse transformation
when releasing lithium ions.
10 1971
Further, discharge capacity of the coin battery of each Inventive Example was
fo~~bnyd t he same method as that of Inventive Example 14, thereby evaluating the
cycle characteristics thereof. It is noted that the current value at the time of
charging and discharging was as shown in Table 5.
(01981
Referring to Table 5, the initial discharge capacity of the coin battery was
higher than that of a negative electrode active material made of graphite. Further,
the capacity retention ratio after passage of the number of cycles shown in Table 5
was as high as not less than 50%, exhibiting excellent cycle characteristics.
[O 1991
[Inventive Example 231
A negative electrode active material whose chemical composition was Cu-5.0
at% Zn-25 at% Sn was produced by the same method as that of Inventive Example 2.
Further, a negative electrode and a coin battery were produced by the same method
as that of Inventive Example 2.
[0200]
Measurement and analysis of crystal structure of the powder (not more than
45 prn) of the negative electrode active material were performed by the same method
as that of Inventive Example 14.
[020 1 ]
The result revealed that in the structure of the negative electrode active
material, E phase of 2H structure and q' phase of monoclinic structure were identified.
FIG. 8 is a diagram illustrating measured data of an X-ray diffraction profile of
Inventive Example 23, and profile fitting results (calculated profiles) by Rietveld
method. Rietan-2000 was used for Rietveld analysis.
[0202 J
As a result of quantitative analysis by Rietveld method shown in FIG. 8, the
structure of the present Inventive Example included 97 mass% of E phase of 2f-I
structure and 3 mass% of 17j' phase of monoclinic structure. Further, regarding E
phase of 2f-I stmcture, the result of Rietveld analysis revealed that under a
preposition that the site of Cu be replaced by Zn, atomic deficiencies occurred in
some part of atomic sites of Cu and Sn. In FIG. 8, the reason why intensities of
diffraction lines near 32.3" and near 37.5" had increased was pres~rmablyd ue to
these site deficiencies. As a result of Rietveld analysis, due to such site deficiencies,
the site occupancy factor was 53% at 4e site of Cu and Zn, and the site occupancy
factor was 52% at 2b site of Sn (see Table 7).
[0203]
[Table 71
TABLE 7
As a reference, a result of Rietveld analysis of q' phase is shown in Table 8.
102051
[Table 81
TABLE 8
q' Phase (CU~SII~M) onoclinic structure Composition: cu-44.6 at% Sn
Space Group Number (International Table A): No. 15 (C2/c)
Lattice Constants: a = 11.1016 A, b = 7.25028 A, c = 9.90445 A,
0 = 98.8" (After Refinement)
Multiplicity
Wyck.
Atomic Coorc Occupancy
factor
Further, crystal structures of the negative electrode active material in the
negative electrode of Inventive Example 23 after one to rnultiple times of charging
and discharging were determined by the same method as that of Inventive Example
14, thereby confirming how the crystal structure of the negative electrode active
material was changed by chargingidischarging.
[0207]
The result of the determination revealed that the crystal structure was
dominantly 2H structure before initial charging as shown in FIG. 8. However, the
crystal structure changed in the course of charging and discharging, and a diffraction
line of DO3 structure was recognized in the X-ray diffraction profile after
discharging. Thus, this confirmed that the negative electrode active material of
Inventive Example 23 had a crystal structure that underwent M transfornation when
occluding lithium ions, and underwent reverse transformation when releasing lithium
ions.
[0208]
The discharge capacity of the coin battery was measured by the same method
as that of Inventive Exarnple 14. The result revealed that referring to Table 5, the
discharge capacity was 2152 rnA7n/cm3 initially and 1986 &cm%fter 20 cycles of
charging and discharging, and the capacity retention ratio was 92%.
102091
In the present Inventive Example, it is considered that a small amount of q'
phase, in addition to E phase of 2H structure, functioned as negative electrode active
substance, thereby achieving discharge capacity. It is also considered that a site
deficiency of the E phase also functioned as a storage site and a diffusion site of
lithium ions.
[0210]
[Inventive Example 241
Powder of the negative electrode active material having the chemical
composition shown in Table 5 was produced by the same method as that of Inventive
Example 2. Further, a negative electrode and a coin battery were produced by the
same method as that of Inventive Example 2.
(021 l]
Measurement and analysis of crystal structure of the powder (not more than
45 prn) of the negative electrode active material were performed by the same method
as that of inventive Example 14. The result revealed that in the negative electrode
active material, a phase having DO3 structure which is a kind of matrix phase, q'
phase of monoclinic structure, 6 phase having F-cell structure, and Sn phase were
mixedly present.
[0212]
FIG. 9 is a diagram illustrating X-ray diffraction profiles thereof (measured
data. and calculated profiles of the phase having DO3 stnrcture, q' phase. 6 phase,
and Sn phase) along with a profile fitting result by Rietveld method. Rietan-2000
was used for Rietveld analysis.
102131
The result of quantitative analysis by Rietveld method shown in FIG. 9
revealed that the negative electrode active material of inventive Example 23
contained 3 1.5 mass% of a phase having DO? structure, 21.5 mass% of q' phase of
rnonoclinic structure, 46.0 mass% of 6 phase having F-cell structure, and 1.0 mass%
of Sn phase.
(02 141
Table 9 shows a result of Rietveld analysis of the phase having DO? structure,
Table 10 shows that of Q' phase, and Table I I shows that of 6 phase having F-Cell
structure.
(0215l
[Table 91
TABLE 9
Space Group Number (International Table A): No.225 (Fm-3m)
Structure Model Reference (Fe3AI;D07): 1lyushin.J. Solid State Chem. 17,1976,385
[Table 101
TABLE 10
[Table 1 I]
TABLE 11
Referring to Tables 9 to 11, it was revealed that under a preposition that the
site of Cu be replaced by Zn, atomic deficiency occurred in some part of atomic sites
of CLI and Sn, respectively in the phase having DO3 structure, q' phase, and 6 phase
having F-cell stritcture.
Further, the crystal structures of the negative electrode active material in the
negative electrode of Inventive Example 24 before initial charging, after initial
charging, after initial discharging, after multiple times of charging, and after multiple
times of discharging were determined by the same method as that of Inventive
Example 14, thereby confirming how the crystal stnlcture of the negative electrode
active material was changed by charging/discharging.
[0220]
The result of the determination revealed that the negative electrode active
material before initial charging included DO3 structure as shown in FIG. 9. Further,
it changed in the course of charging and discharging, and a diffraction line of DO3
structure was recognized again in the X-ray diffraction profile after discharging.
Thus, this confirmed that the negative electrode active material of Inventive Example
23 had a crystal structure that underwent M transformation when occluding lithium
ions, and ~lnderwentr everse transformation when releasing lithium ions.
[0221]
The discharge capacity of the battery was measured as with Inventive
Exarnple 14. The result revealed that, as shown in Table 5, the discharge capacity
of the coin battery was 241 1 m ~ ~ c imnit"ial ly and 2013 mnh/cm3 after 20 cycles of
charging and discharging, and the capacity retention ratio was 84%.
p222 1
In the present Inventive Example, it is considered that a phase having DO?
strrrcture, q' phase, and Sn phase f~~iictioneads negative electrode active substance,
thereby achieving discharge capacity. Moreover, it is considered that site
deficiencies of the phase having DOi structure, q' phase, and 6 phase having F-Cell
structure also functioned as a storage site and a diffusion site of lithium ions.
102231
[Inventive Examples 25 and 261
Powders of the negative electrode active materials having the chemical
compositions shown in Table 5 were produced by the same method as that of
Inventive Example 2. Further, negative electrodes and coin batteries were produced
by the same method as that of Inventive Example 2.
[0224f
Measurement and analysis of crystal structures of the negative electrode
active materials were performed by the same method as that of Inventive Example 14.
The result thereof revealed that the powdcrs and uncharged negative electrode active
materials of Inventive Examples 25 and 26 included a phase having DOs structure, q'
phase of monoclinic structure, 6 phase having F-cell structure, and Sn phase, as with
Inventive Example 24. Further, as with Inventive Example 24, the crystal structures
of Inventive Examples 25 and 26 changed in the course of charging/discharging, and
a diffraction line of 2H structure was recognized at the time of charging, and a
diffraction line of DO3 structure was recognized again in an X-ray diffraction profile
after discharging. Thus, this confirmed that the negative electrode active materials
of Inventive Examples 25 and 26 had a crystal structure that underwent M
transformation when occluding lithium ions, and ~mderwenrte verse transformation
when releasing lithium ions.
/02251
The initial discharge capacities of the coin batteries of Inventive Examples 25
and 26 were high, and the capacity retention ratios thereof were high as well (see
Table 5).
102261
In Inventive Examples 25 and 26, a phase of DO? structure, q' phase, and Sn
phase functioned as negative electrode active substance, thereby achieving discharge
capacity, as with Inventive Example 24. It Is considered that the reason why the
discharge capacities of these Inventive Examples increased more than that of
Inventive Example 24 was because the proportion of Sn phase was high. It is also
considered that the reason why, nevertheless, the capacity retention ratio was
satisfactory as well was because the phase having DO3 strtlcture which is a peripheral
phase induced martensitic transformation and reverse transformation in the course sf
charging and discharging thereby mitigating internal stress and thus preventing
disintegration of active substance.
102271
[Inventive Example 271
Inventive Example 27 was made up of the same negative electrode active
material, negative electrode, and battery as those of Inventive Example 26. In
Inventive Example 27, the current value at the time of chargingldischarging when
measuring discharge capacity was 1.0 mA as shown in Table 5.
(02281
The discharge capacity was 1971 cm3 initially and 1698 cm3 after
80 cycles of charging and discharging, and the capacity retention ratio was 86% (see
Table 4). Inventive Example 27 had excellent charge-dischasge rate characteristics.
102291
j Inventive Example 281
Powder of the negative electrode active material having the chemical
composition shown in Table 5 was produced by the same method as that of Inventive
Example 2. Further, a negative electrode and a coin battery were produced by the
same method as that of Inventive Example 2. The chemical composition of the
negative electrode active material was Cu-25.0 at% Zn-25 at% Sn.
102301
Crystal struct~~wrea s determined by the same method as that of Inventive
Example 14. As with Inventive Example 24, the result thereof revealed that the
negative electrode active material of the present Inventive Example contained a
phase having DO? structure, q' phase having a nionoclinic structrrre, 6 phase having
F-cell structure, and Sn phase.
1023 11
Further, results of X-ray diffraction and Rietveld analysis confirmed that the
negative electrode active material of Inventive Example 28 had a crystal structure
that underwent M transformation when occluding lithium ions, and underwent
reverse transformation when releasing lithium ions.
(02321
The discharge capacity of the coin battery was 2972 mAh/cm3 initially and
2700 m~hicma'f ter 20 cycles of charging and discharging, and the capacity
retention ratio was 9 1 % (see Table 5).
1023 3 1
It is considered that in the present Inventive Example, as with Inventive
Example 24, a phase having DO1 structure, q' phase, and Sn phase f~~nctioneasd
negative electrode active substance, thereby achieving discharge capacity. It is
considered that the reason why the discharge capacity of the present Inventive
Example increased more than that of Inventive Example 24 was because the
proportion of Sn phase was high. It is also considered that the reason why,
nevertheless, the capacity retention ratio was satisfactory as well was because the
phase having DO? structure in the periphery of Sn phase induced martensitic
transformation and reverse transformation in the course of charging and discharging
thereby mitigating internal stress and thus preventing disintegration of active
substance.
LO2341
Inventive Example 291
The same coin battery as that of Inventive Example 28 was used to measure
discharge capacity with the current value at the time of chargingldischarging being
set to 1.0 mA. The discharge capacity was 2307 m ~ ~ cinmitia'l ly and 1925
d h i c m ' after KO cycles of charging and discharging, and the capacity retention ratio
was 83% (see Table 5).
[0235]
[Inventive Example 301
Powder of negative electrode active material was produced by the same
method as that of Inventive Example 2. Further, a negative electrode and a coin
battery were produced by the same method as that of Inventive Exarnple 2. The
chemical composition of the negative electrode active material was Cu-2.0 at% Al-
25 at% Sn as shown in Table 5. Determination of crystal structure and evaluation
of discharge capacity were performed by the same method as that of Inventive
Example 14.
102361
Results of X-ray diffraction and Rietveld analysis revealed that the structure
of the negative electrode active material of Inventive Example 30 had E phase of 2W
stnlcture in which a small amount of q' phase was included. Further, the results
confirmed that the structure after discharging included DO? structure, and the
structure after charging included 2H stnlcture in the course of charging and
discharging.
10237)
The discharge capacity of the present Inventive Example was 2287 rnAh/cm3
initially and 1777 m4h/cm3 after 20 cycles of charging and discharging, and the
capacity retention ratio was 78% (see Table 5). It is considered that in the present
Inventive Example, E phase of 2H structure and q' phase functioned as active
material phases.
102381
[Ellventive Example 3 1 J
Powder of negative electrode active material was produced by the same
method as that of Inventive Example 2. Further, a negative electrode and a coin
battery were prod~icedb y the same method as that of Inventive Example 2. The
chemical composition of the negative electrode active material was Cu-10.0 at% Al-
25 at% Sn as shown in Table 5. Determination of crystal structure and evaluation
of discharge capacity were performed by the same method as that of lnventivc
Example 14.
102391
Resuits of X-ray diffraction and Rietveld analysis revealed that the structure
of the negative electrode active material of Inventive Example 3 1 had a matrix phase
of DO3 structure in which q' phase was included. Further, the results confirmed
that the strtlcture after discharging included DO3 stmcture, and the stmcture after
charging included 2H structure in the course of charging and discharging.
[0240]
The discharge capacity of the present Inventive Example was 25 12 d h l c m '
initially and 2255 cm' after 20 cycles of charging and discharging, and the
capacity retention ratio was 81% (see Table 5). It is considered that in the present
Inventive Example, the matrix phase of DO? structure and q' phase filnctioned as
active material phases.
[024 1 1
[ Inventive Example 321
The same coin battery as that of Inventive Example 28 was used to measure
discharge capacity with the current value at the time of charging/discharging being
set to 1.0 mA. The discharge capacity was 1826 mhhlcm7 initially and 1187
m411/cm3 after 80 cycles of charging and discharging, and the capacity retention ratio
was 8 1 % (see Table 5).
10242 1
[Inventive Example 33 1
Polvder of ilegative electrode active material was produced by the same
rnethod as that of Inventive Example 3. Further, a negative electrode and a coin
battery were produced by the same method as that of Inventive Example 2. The
chemical composition of the negative electrode active material was Cu-2.0 at% Al-
23 at% Sn as shown in Table 5. Determination of crystal structure and evaluation
of discharge capacity were performed by the same method as that of Inventive
Example 14.
102431
Results of X-ray diffraction and Rietveld analysis revealed that in the
structure of the negative electrode active material of Inventive Example 33 before
initial charging, E phase of 2H structure was singly present. Further, the results
confirmed that the structure after discharging included DO3 structure, and the
structure after charging incl~~de2df- I structure in the course of charging and
discharging.
102431
The dischasge capacity of the present Inventive Example was 2448 mn~~.h/crn~
initially and 1892 rnAh/cm3 after 20 cycles of charging and discharging, and the
capacity retention ratio was 78% (see Table 5). In the present Inventive Example, E
phase functioned as an active material phase as with Inventive Example 14.
10245 1
[Inventive Example 341
Powder of negative electrode active material was produced by the same
method as that of Inventive Example 2. Further, a negative electrode and a coin
battery were produced by the same method as that of Inventive Example 2. The
chemical composition of the negative electrode active material was Cu-5.0 at% Si-25
at70 Sn as shown in Table 5. Determination of crystal structure and evaluation of
discharge capacity were performed by the same method as that of Inventive Example
14,
LO246 1
Results of X-ray diffraction and Rietveld analysis revealed that in the
structure of the negative electrode active material of Inventive Example 34 before
initial charging, a matrix phase of DO3 structure was present substantially in a single
phase. Further, the results confirmed that the structure after discharging included
DO3 stmcture, and the structure after charging included 2H structure in the course of
charging and discharging.
102471
The discharge capacity of the present Inventive Example was 2809 cm3
initially and 2382 rnAhicrn3 after 20 cycles of charging and discharging, and the
capacity retention ratio was 85% (see Table 5). In the present Inventive Example,
the matrix phase of DO3 structure functioned as an active rnaterial phase.
LO2481
[Inventive Example 351
Powder of negative electrode active rnaterial was produced by the same
method as that of Inventive Example 2. Further, a negative electrode and a coin
battery were produced by the same method as that of Inventive Example 2. The
chemical composition of the negative electrode active material was Cu-10.0 at% Si-
25 at% Sn as shown in Table 5. Determination of crystal structure and evaluation
of discharge capacity were performed by the same method as that of Inventive
Example 14.
102493
Results of X-ray diffraction and Rietveld analysis revealed that the structure
of the negative electrode active material of Inventive Example 35 before initial
charging had a matrix phase of DO3 stmcture in which q' phase and a minute amount
of Sn single phase were present. Further, the results confirmed that the strr~cture
after discharging included DO3 stmcture, and the stntcture after charging included
2H strtlcture in the course of charging and discharging.
[0250]
The discharge capacity of the present Inventive Example was 3073 mAh/cd
initially and 2509 m~hlcm' after 20 cycles of charging and discharging, and the
capacity retention ratio was 82% (see Table 5).
102.5 11
In the present Inventive Example, the matrix phase of DO3 structure, q' phase,
and a minute amount of Sn single phase functioned as active material phases.
102521
The result of Rietveld analysis revealed that in the crystal structure of q' phase,
as in Table 10, many site occupancy factors were smaller than those in the crystal
structure of normal q' phase, thus indicating that many site deficiencies occurred.
Therefore, it is considered that q' phase functioned as a diffusion site of lithium ions.
[0253]
[Inventive Example 361
The same coin battery as that of Inventive Example 35 was used to measure
discharge capacity with the current value at the time of chargi~igldischargingb eing
set to 1.0 mA. The discharge capacity was 2414 rnAh/cd initially and 2023
mAh/cm3 after 80 cycles of charging and discharging, and the capacity retention ratio
was 84% (see Table 5).
[0254]
[Inventive Example 371
Powder of the negative electrode active material was produced by the same
method as that of Inventive Example 2. Further, a negative electrode and a coin
battery were produced by the same method as that of Inventive Example 2. The
chemical composition of the negative electrode active material was Gu-2.0 at% Si-23
at% Sn as shown in Table 5. Determination of crystal stnicture and evaluation of
discharge capacity were performed by the same method as that of Inventive Example
14.
[0255]
Results of X-ray diffraction and Rietveld alialysis revealed that in the
structure of the negative electrode active material of Inventive Example 37 before
initial charging, E phase having 2H structure was substantially singly present.
Further, the results confirmed tha~th e structure after discharging included DO3
structure, and the structure after charging included 2H structure in the course of
charging and discharging.
202561
The discharge capacity of the present Inventive Example was 2520 cm3
initially and 1720 cm' after 20 cycles of charging and discharging, and the
capacity retention ratiowas 68% (see Table 5). In the present Inventive Example, r
phase f~~nctioneads an active material phase.
LO2571
I Inventive Examples 38 to 531
Negative electrode active materials of each Inventive Example were prod~lced
by the same production method as that of Inventive Example 2. The chemical
compositions of the produced negative electrode active materials were as shown in
Table 5. By using the produced negative electrode active materials, negative
electrodes and coin batteries were produced by the same method as that of I~iventive
Example 2.
[02581
Crystal struct~treso f the negative electrode active material of each Inventive
Example after multiple times of charging and discharging were determined by the
same method (X-ray diffraction and Rietveld analysis) as that of Inventive Example
14, thereby confirming how the crystal structure of the negative electrode active
material was changed by charging/discharging.
to2591
The result of the determination revealed that in all of the Inventive Examples,
all of the crystal structures of the negative electrode active material in the negative
electrode after multiple times of discharging included DO3 structure. Further, all of
the crystal structures of the negative electrode active materials after multiple times of
charging included 2H structure. Thus, this confirmed that the negative electrode
active material of each Inventive Example had a crystal structure that underwent ful
transformation when occluding lithium ions, and underwent reverse transformation
when releasing lithium ions.
102601
Further, discharge capacity of the coin battery of each Inventive Example was
found by the same method as that of Inventive Example 14. The current value at
the time of charging/discklarging was as shown in Table 5. Refewing to Table 5, the
initial discharge capacity (which was measured at a current value of 0.1 mA) of the
coin battery was higher than that of a negative electrode active material made of
graphite. Further, the capacity retention ratio after passage of the number of cycles
shown in Table 5 was as high as not less than 50%, exhibiting excellent cycle
characteristics.
1026 1 ]
A main cause of the increase in the capacity during cycling in Inventive
Exarnple 49 is considered that the proportion of electric capacity which was born by
the active material phase increased along with the number of cycles as with Inventive
Example 18.
[0262 1
[Comparative Example 21
A powdered negative electrode active material was produced by the same
method as that of Inventive Example 1. !%'here, heat treatment was conducted at a
temperature of 550°C. As shown in Table 5, the chemical composition of the
produced negative electrode active material was Cu-20.5 at% Sn. A negative
electrode and a coin battery were produced by the same rnethod as that of Inventive
Example 1.
LO2631
The crystal stmcture of the negative electrode active substance before initial
charging was analyzed by the same method (X-ray analysis and Rietveld analysis) as
that of Inventive Example 14.
102641
FIG. 10 is a diagram illustrating measured values of X-ray diffraction profile
and a profile fitting result by Rietveld method. Rietan-FP was used for Rietvefd
analysis.
10265 1
The chemical composition of the present Comparative Example was known as
6 phase on an eq~~ilibriudmia gram, and the crystal structure thereof was F-cell
ordered stmcture shown in Table 12. This crystal structure corresponds to No. 216
(F-43m) of International Table (Volume-A) in terms of the classification of space
groups. The lattice constants and atomic coordinates thereof are as shown in Table
13.
102661
[Table 121
TABLE 12
LO2671
The result of Rietveld analysis revealed that the crystal structure of the
negative electrode active substance was F-cell ordered stn~cture. Further, the
negative electrode active substance after charging did not include 2H structure, and
the negative electrode active substance after discharging did not include DO?
stn~ctuire.
102681
The discharge capacity of the coin battery of Comparative Example 2 was
fo~ound by the same method as that of Inventive Example 14. The cunent value at
the time of chargingldiscbarging was as shown in Table 5. The discharge capacity
was 11 8 mAh/crn3 initially and 55 mA;i7/cm3 after 20 cycles of charging and
discharging (see Table 5)- As shown by the present Comparative Example, almost
no chargeldischarge capacity as a battery was achieved by 6 phase whose crystal
structure was F-cell structure.
102693
[Comparative Example 31
A powdered negative electrode active material was produced by the same
method as that of Inventive Example 2. As shown in Table 5, the chemical
composition of the produced negative electrode active material was Ni-50 at% Ti.
A negative electrode and a coin battery were produced by the same method as that of
Inventive Example 2.
[02701
The crystal structure of the negative electrode active substance before initial
charging was analyzed by the same method (X-ray analysis and Rietveld analysis) as
that of Inventive Example 14. The result thereof revealed that the structure of the
negative electrode active srkbstance incl~ldedn either a phase of DO3 stn~cturen or a
phase of 2H structure. Further, the discharge capacity was measured in the same
way as in Inventive Example 14. The result revealed that initial discharge capacity
hardly showed up (see Table 5). Therefore, it is considered that Ti-Ni alloy was not
lithium-active.
1027 11
j Comparative Example 41
A powdered negative electrode active material was produced by the same
method as that of Inventive Example 2. As shown in Table 5. the chemical
composition of the produced negative electrode active material was Ni-52.0 at% Ti-5
at% Si. A negative electrode and a coin battery were produced by the same method
as that of Inventive Example 2.
102721
The crystal structure of the negative electrode active substance before initial
charging was analyzed by the same method (X-ray analysis and Rietveld analysis) as
that of Inventive Example 14. The result revealed that thc structure of the negative
electrode active substance included neither a phase of DO3 structure nor a phase of
2H structure. Further, the discharge capacity was measured in the same way as in
Inventive Example 14. The result revealed that initial discharge capacity hardly
showed up (see Table 5). Therefore, it may be because in the present Comparative
Example, Silicon which can be active substance was unable to exist as a simple
substance, and compo~mdso f Si, Ti, and Ni were formed.
10273 1
[Coxnparative Example 51
A powdered negative electrode active material was produced by the same
method as that of Inventive Example 2. As shown in Table 5, the chemical
composition of the produced negative electrode active material was Ni-25.0 at% Ti-
50 at% Si. A negative electrode and a coin battery were produced by the same
method as that of Inventive Example 2.
102741
The crystal structure of the negative electrode active substance before initial
charging was analyzed by the same method (X-ray analysis and Rietveld analysis) as
that of Inventive Example 14. The result revealed that the structure of the negative
electrode active substance included neither a phase of DO3 structure nor a phase of
2E-I structure. Further, the discharge capacity was measured in the same way as in
Inventive Example 14. The result revealed that initial discharge capacity was
merely about half of that in the case of graphite (see Table 5). Therefore, it was
considered in the present Comparative Example, Silicon which can be active material
was unable to be sufficiently present, because compounds of Si, Ti, and Ni were
formed.
102751
[Comparative Example 61
A powdered negative electrode active material was produced by the same
method as that of Inventive Example 2. As shown in Table 5, the chemical
composition of the produced negative electrode active material was Cu-5 at% Ni-25
at% Sn. A negative electrode and a coin battery were produced by the same method
as that of Inventive Example 2.
LO2761
The crystal structure of the negative electrode active material before initial
charging was analyzed by the same method (X-ray analysis and Rietveld analysis) as
that of Inventive Example 14. The result revealed that the structure of the negative
electrode active material included neither a phase of DO3 stnicture nor a phase of 2H
stnlcture. Further, the discharge capacity was measured in the same way as in
Inventive Example 14. The result revealed that sufficient discharge capacity was
not achieved in the present Comparative Example.
102771
[Comparative Example 71
A powdered negative electrode active material was produced by the same
method as that of Inventive Example 2. As shown in Table 5, the chemical
composition of the produced negative electrode active material was Cu-10 at% Ni-25
at% Sn. A negative electrode and a coin battery were produced by the same method
as that of Inventive Example 2.
LO2781
The crystal structure of the negative electrode active substance before initial
charging was analyzed by the same method (X-ray analysis and Rietveld analysis) as
that of Inventive Exanlple 13. The result thereof revealed that the strrrcture of the
negative electrode active material incl~rdedn either a phase of DO3 \tr~icturen or a
phase of 2H structure. Further, the discharge capacity was measured in the same
way as in Inventive Example 14. The result revealed that sufficient discharge
capacity was not achieved in the present Comparative Example.
[0279]
[Comparative Example 81
A powdered negative electrode active material was produced by the same
method as that of Inventive Example 2. As shown in Table 5, the chemical
composition of the produced negative electrode active material was CLI-50 at% Ni-25
at% Sn. A negative electrode and a coin battery were produced by the same method
as that of Inventive Example 2.
/0280]
The crystal structure of the negative electrode active material before initial
charging wJas ar~alyzedb y the same method (X-ray analysis and Rietveld analysis) as
that of Inventive Example 14. The res~~relvt ealed that the stmctlire of the negative
electrode active material included neither a phase of DO3 structure nor a phase of 2H
structure. Further, the discharge capacity was measured in the same way as in
Inventive Example 14. The result revealed that sufficient discharge capacity was
not achieved in the present Comparative Example.
LO2811
1 Comparative Example 91
A powdered negative electrode active material was prodticed by the same
method as that of Inventive Example 2. As shown in Table 5, the chemical
cotnposition of the produced negative electrode active material was CLI-50 at% AI-25
at% Sri. A negative electrode and a coin battery were produced by the same method
as that of Inventive Example 2.
[0282]
The crystal structure of the negative electrode active material before initial
charging was analyzed by the same method (X-ray analysis and Rietveld analysis) as
that of Inventive Example 14. The result revealed that the structure of the negative
electrode active material included neither a phase of Do3 structure nor a phase of 2W
stnlcture. Further, the discharge capacity was measured in the same way as in
Inventive Example 14. The result revealed that sufficient discharge capacity was
not achieved in the present Comparative Exaniple.
[0283]
[Comparative Example 101
A powdered negative electrode active material was produced by the same
metbod as that of Inventive Example 2. As shown in Table 5, the chemical
composition of the produced negative electrode active material was Cu-50 at% Si-25
at% Sn. A negative electrode and a coin battery were produced by the same method
as that of Inventive Example 2.
10284 J
The crystal structure of the negative electrode active material before initial
charging was analyzed by the same method (X-ray analysis and Rietveld analysis) as
that of Inventive Example 14. The result revealed that the stnicture of the negative
electrode active material included neither a phase of DO3 structure nor a phase of 2H
stnrcture. Further, the discharge capacity was measured in the same way as in
Inventive Example 14. The result revealed that although the initial discharge
capacity was high, the cycle characteristics (capacity retention ratio) were low.
102851
[Comparative Examples 11 to 151
Powdered negative electrode active materials were produced by the same
lnethod as that of Inventive Example 2. The chemical compositions of the
produced negative electrode active materials of each Comparative Example were as
shown in Table 5. Negative electrodes and coin batteries were produced by the
same method as that of Inventive Example 2.
102861
The crystal structure of each negative electrode active material before initial
charging was analyzed by the same method (X-ray analysis and Rietveld analysis) as
that of Inventive Example 14. The result revealed that the structure of each
negative electrode active material included neither a phase of DO3 structure nor a
phase of 2H structure. Further, the discharge capacity was measured in the same
way as in Inventive Example 14. The result revealed that sufficient discharge
capacity was not achieved in all of each Comparative Example.
102871
So far, embodiments of the present invention have been described. However,
the above described embodiments are merely examples to carry out the present
invention. Therefore, the present invention will not be limited to the above
described embodiments, and can be carried out by appropriately modifying the above
described embodiments within a range not departing from the spirit thereof.
We claim:
1. A negative electrode active material, comprising an alloy phase that
undergoes thennoelastic diffusionless transformation either when releasing metal
ions, or when occluding the metal ions.
2. The negative electrode active material according to claim 1, wherein
the alloy phase undergoes the thermoelastic diffusionless transformation when
occluding the metal ions, and undergoes reverse transformation when releasing the
metal ions.
3. The negative electrode active material according to claim 2, wherein
the alloy phase after the thermoelastic diffrtsionless transformation contains a
crystal structure urhich is 2H in Ramsdell notation, and
the alloy phase after the reverse transformation contains a crystal structure
which is DO3 in Stnrkturbericht notation.
4. The negative electrode active material according to claim 2 or 3, wherein
the negative electrode active material contains Cu and Sn.
5. The negative electrode active material according to claim 4, wherein
the negative electrode active material contains 10 to 20 at% or 21 to 27 at% of
Sn, with the balance being Cu and impurities.
6. The negative electrode active material according to claim 4, wherein
the negative electrode active material contains, in place of a part of Cu, one or
more selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, B,
and 6.
The negative electrode active material according to claim 6, wherein
the negative electrode active material contains:
Sn: 10 to 35at%, and
one or more selected from the group consisting of Ti: 9.0 at% or less, V: 49.0
at% or less, Cr: 49.0 at% or less, Mn: 9.0 at% or less, Fe: 49.0 at% or less, Co: 49.0
at% or less, Ni: 9.0 at% or less, Zn: 29.0 at% or less, Al: 49.0 at% or less, Si: 49.0
at% or less, B: 5.0 at% or less, and C: 5.0 at% or less,
with the balance being Cu and impurities.
The negative electrode active material according to any one of claims 3 8. to 7,
wherein
the negative electrode active material further contains one or more selected
from the group consisting of 6 phase of F-Cell structure, E phase, q' phase, and a
phase having DOs structure, each including site deficiency.
9. A negative electrode, comprising the negative electrode active material
according to any one of claims 1 to 8.
10. A battery, comprising the negative electrode according to claim 9.