DESCRIPTION
Title of Invention:
NEGATIVE ELECTRODE FOR LITHIUM SECONDARY BATTERY AND METI-IOD FOR
5 MANUFACTURING THE SAME
Technical Field
[OOOl]
The present invention rclates to a negative electrode used in a lithium secondary battery,
10 and a method for manufacturing the same.
Background Art
[0002]
As negative electrodes for lithium secondary batteries, various ones have been proposed so
15 far.
[0003]
For example, Patent Literature 1 discloses a secondary battery comprising an active
material layer on a current collector and comprising an active material and a modified
organometallic complex in the active material layer. In the technique in Patent Literature 1,
20 after applying a binder resin cotuprising an organometallic complex, heat treatment is perfotmed
to eliminate the organic substance of the organometallic complex to form a modified
organometallic complex in an active material layer.
[0004]
Patent Literature 2 discloses a method for forming the negative electrode of a lithium ion
25 battery which includes the steps of depositing a slurry of an electrode composition comprising
electrochemically active particles, metallic conductive diluting particles not electrochemically
active, and nonmetallic conductive diluting particles on a current collector, and performing heat
treatment. As examples of the metallic conductive diluent pat-ticles, copper, iron, nickel, and
titanium are disclosed.
30 [0005]
Patent Literature 3 discloses a lithium secondary battery in which an adhesive layer is
provided between a negative electrode active material layer and a negative electrode current
collector, and in which the binding agent included in the negative electrode active material layer
and the adhesive layer comprises a modified fluorine-containing polymer conlpound.
[0006]
Patent Literature 4 discloses a method for fo~lninga negative electrode for a lithium
secondary battery in which a conductive intermediate layer comprising conductive particles is
placed between a mixture layer comprising active material particles and a current collector. In
5 the method in Patent Literature 4, the negative electrode is formed by first depositing the
conductive intermediate layer and the mixture layer on the current collector and then performing
heat treatment. As examples of the conductive particles, conductive metal particles and
conductive carbon particles are disclosed. As exanlples of the conductive nletal particles,
copper, nickel, iron, and titanium are disclosed.
10
Citation List
Patent Literature
[0007]
Patent Literature 1 : JP20 11-0658 12A
15 Patent Literature 2: JP2009-538513A
Patent Literature 3: JP2004-200011A
Patent Literature 4: JP2004-288520A
Summaly of Invention
2 0 Technical Problem
[OOOS]
Here, an advantage of providing an adhesive layer or a conductive intermediate layer
between an active material layer and a current collector as shown in Patent Literatures 3 and 4 is
that the cycle characteristics and rate characteristics of the battery are improved. However, in
25 Patent Literatures 3 and 4, the adhesive layer or the conductive intermediate layer is formed
using a slurry comprising particles, and in this case, the dispersibility and uniformity of the
particles in the slurry may be problems. For example, particles settle during preparation of the
slur~ya, nd dispersibility of the slutry may decrease. In addition, complicatedness, problems,
and the like in handling the particles themselves or the slu~ryco mprising the particles also occur.
30 Further, when the average particle diameter of the particles is 1 pm or less, the specific surface
area of the particles increases, and therefore, the surfaces of the palticles are easily oxidized.
As a result, conductivity may decrease.
Solution to Problem
[0009]
The exen~plarye mbodiment of the present invention is
a negative electrode for a litl~iums econda~yb atte~yc o~nprisinga current collector
comprising a metal, and an active material layer comprising an active material and a binding
5 agent, wherein,
the negative electrode has a conductive intermediate layer comprising conductive metal
pa~ticlesc omprising the same element as the metal, and a polyimide or polyan~ideimideb, etween
the current collector and the active material layer, and
a content of the conductive metal particles in the conductive intermediate layer is 23% by
10 volume or more and 70% by volun~eo r less.
[OO lo]
In addition, the exempla~ye mbodiment of the present invention is
a method for manufacturing a negative electrode for a lithium secondary battery
comprising a current collector comprising a metal, an active material layer comprising an active
15 material and a binding agent, and a conductive intermediate layer comprising conductive metal
particles between the current collector and the active material layer, comprising steps of:
(1) placing a polyamic acid on the current collector;
(2) causing the metal to move from the current collector into the polyamic acid by
generating migration phenomenon; and
20 (3) heating and curing the polyamic acid,
in this order, wherein
the metal that has moved into the polya~nica cid forms the conductive metal particles.
Advantageous Effects of Invention
25 [OOll]
The exelnplary embodiment of the present invention can provide a negative electrode for a
lithium secondary battery which has excellent discharge characteristics.
[0012]
In addition, the exempla~ye mbodiment of the present invention can provide a method for
30 manufacturing a negative electrode for a lithium secondary battery in which conductive metal
particles can be more uniformly and easily formed in the conductive intermediate layer.
Brief Description of Drawings
[Figure I ] Figure 1 is a schematic diagram sliowing an example of the configuration of a
negative electrode according to the exemplary embodiment of the present invention.
[Figure 21 Figure 2 is a schematic cross-sectional view showing the st~~~ctouf rthee electrode
device of a laminate type secondary battery.
5 [Figure 31 Figure 3 is a diagram showing the results of Examples, Comparative Examples, and
Reference Exanlples.
Description of Embodiments
[0014]
10 "Exemplary Embodiment 1"
The present inventors have studied diligently and discovered that a metal included in a
current collector can be moved into a polyamic acid utilizing migration phenomenon, arriving at
the present invention.
[OOlS]
15 As described above, a manufacturing method in the exemplary embodiment of the present
invention is
a method for manufacturing a negative electrode for a lithium secondary battely
comprising a current collector comprising a metal, an active material layer comprising an active
material and a binding agent, and a conductive intermediate layer comprising conductive metal
2 0 particles between the current collector and the active material layer, comprising the steps of:
(1) placing a polyamic acid on the culxent collector;
(2) causing the metal to move from the current collector into the polyamic acid by
generating migration phenomenon; and
(3) heating and curing the polyamic acid,
25 in this order, wherein
the metal that has moved into the polyamic acid forms the conductive metal particles.
[00 161
In the manufacturing method in the exemplary embodiment of the present invention, first,
a polyamic acid is placed on a current collector. The metal used for the current collector
30 dissolves in a polyamic acid having a carboxyl group that is an acidic group. The metal
included in the current collector is not particularly limited. Examples thereof include copper,
nickel, gold, or silver. The metal is preferably copper, nickel, or silver, more preferably copper
or nickel, and further preferably copper. Therefore, the current collector preferably comprises
at least one selected fro111 copper, nickel, and silver. It is known that various metals used for
current collectors are corroded by a polyamic acid having a carboxyl group (for example, Patent
Literatures JP2009-019132A and JP2005-010360A). In other words, it is known that a metal
used for a culrent collector dissolves in a polyaniic acid. The metal may dissolve in a polyaniic
acid and, as a result, form a complex.
5 [0017]
Next, migration phenon~enonc auses the above metal to move from the current collector
into the polyamic acid. Migration phenomenon herein means a phenomenon in which a metal
in a solid phase beconies an ion and moves to another phase. "generating migration
phenomenon" includes meaning "promoting niigration".
10 [OOlSj
Next, the polyatnic acid is cured to fo~ma polyimide or polyamideimide.
100 191
According to the above steps, a conductive intermediate layer in which conductive metal
particles are included in a polyimide or a polyaniideimide can be formed.
15 [0020]
In this manner, in the exe~npla~emy bodiment of the present invention, the tnetal included
in the current collector can be moved into the polyamic acid by utilizing migration phenomenon.
The metal that has moved into the polyamic acid is then deposited to form conductive metal
particles. It is considered that in the exemplary embodiment of the present inventioti, by
20 promoting the movement and diffusion of the metal included in the current collector into the
polyamic acid by migration phenomenon, the conductive metal particles can be formed in the
conductive intermediate layer. Therefore, in the exe~nplarye mbodiment of the present
invention, it is not necessary to handle particles, and the complicatedness and problem of
handling particles or a slurry comprising particles are eliminated. In addition, by forming the
2 5 conductive metal particles utilizing migration phenomenon, the conductive metal particles can be
more uniformly formed in the conductive intermediate layer, and the rate characteristics of the
battery can be improved. Further, in the exemplary embodiment of the present invention, the
conductive metal particles are formed in the conductive intermediate layer without contact with a
gas phase, and therefore, the oxidation of the surfaces of the conductive metal particles can be
3 0 suppressed.
[0021j
The migration phenomenon is preferably caused by coating the current collector with a
polyamic acid and then performing heat treatment under a condition in which the temperature is
lower than the imidization temperature of the polyamic acid. By performing heat treatment
under a condition in which the tenlperature is lower than the imidization temperature, that is, at a
temperature at which the polya~nica cid is not cured, the dissolution of the metal included in the
current collcctor into the polyamic acid is promoted. The temperature of the heat treatment is
not patticularly limited as long as migration phenomenon occurs. The temperature of the heat
5 treatment is, for example, 80°C or more, preferably 90°C or more, and more preferably 100°C or
more. Further, the temperature of the heat treatment is preferably in the range of 80 to 150°C.
roo221
It is considered that the metal that has moved into the polyamic acid by migration
phenomenon is also deposited under heating conditions. T11e metal lnay be fi~rtl~deerp osited by
10 heat dissipation after the heat treatment.
[0023]
The duration of the heat treatment is preferably 8 hours or more though depending on
conditions, sucll as heating temperature.
[0024]
15 By adding an organic acid to the polyamic acid in the above heat treatment, ~nigration
phenomenon can be further promoted. Examples of the organic acid include phthalic acid,
oxalic acid, or maleic acid. By adding the organic acid to the polyamic acid, the metal included
in the current collector dissolves easily in the polyamic acid.
[0025]
20 The content of the conductive metal particles obtained in the exemplary embodiment of
the present invention is not particularly limited and is preferably 23% by volun~eo r more and
70% by volume or less in the conductive intermediate layer. When the content of the
conductive metal particles is in this range, a negative electrode that has excellent discl~arge
characteristics under large current can be obtained, as described later. The content of the
2 5 conductive metal particles is nlore preferably 26% by volunle or Inore and 50% by volume or
less in the conductive intermediate layer. The content of the conductive metal particles can be
controlled by the conditions of migration phenomenon and can be controlled, for example, by
heat-temperature and heat-time. The higher the heating temperature, and tlle longer the heating
time, the higher is the content.
30 [0026]
The average particle diameter (Dso, volume basis) of the conductive metal particles
obtained in the exemplary embodiment of the present invention is, for example, SO nnl or less,
preferably 1 nm or more and 30 nm or less, and more preferably 5 mn or more and 25 nnl or less.
By depositing conductive metal particles utilizing ~nigrationp heno~nenona s in the exemplary
embodiment of the present invention, fine particles having a small average particle diameter can
be more uniformly formed in the conductive intermediate layer.
[0027]
The metal included in the current collector is preferably a metal that does not form an
5 alloy with Li as described above. Examples of such a metal include copper, nickel, gold, or
silver. In the present specification, "not forming an alloy with Li" refers to "not forming an
alloy in the environment of a secondary battery", and refers to, for example, "not forming an
alloy with Li in the potential range of 0 to 4.5 V ( ~ i / ~ i + ) "T.h e temperature at this time is, for
example, -20 to 60°C.
10 [0028]
Whether or not a metal can be dissolved in the polyamic acid can be determined, for
example, by confirming the coordinate bond between the carboxylic acid group of the polyalnic
acid and the metal by spectroscopic analysis, such as visible and ultraviolet absorption, infrared
absorption, and Raman.
15 [0029]
The negative electrode can be fabricated, for example, by foiming the above conductive
intermediate layer on a current collector and then forming an active material layer comprising an
active material and a binding agent.
[0030]
20 Alternatively, the negative electrode can also be fabricated by placing a polyamic acid on a
current collector and generating migration phenomenon, and then placing an active material
layer slurry on the polyamic acid and perfotlning heating and curing. By using a polyamic acid
as the precursor of the binding agent at this time, crosslinks are formed between the binding
agent and the active material layer, and the binding force can be improved. From the viewpoint
2 5 of more effectively forming crosslinks, the polyamic acid used for the conductive intermediate
layer and the polyamic acid used for the binding agent of the active material layer are preferably
the same.
[003 11
Examples of the method for fonning the active material layer include a doctor blade
30 method, a die coater method, a CVD method, and a sputtering method.
100321
"Exemplary Embodiment 2"
As described above, in the manufacturing tnethod in the exemplary embodiment of the
present invention, the conductive metal particles can be uniformly formed in the conductive
intermediate layer. I11 addition, even if the content of the conductive metal particles in the
conductive interrrlediate layer is high content, fine particles can be more uoifortnly formed
without causing problems i11 the handling of pa~ticless, uch as aggregation. The present
inventors have manufactured negative electrodes for lithium secondaly batteries comprising a
5 conductive intermediate layer between a current collector and an active material layer, using the
manufacturing method in the exemplaly embodiment of the present invention, and discovered
that when the content of the conductive metal particles in the conductive internlediate layer is
23% by volume or more and 70% by volume or less, a negative electrode that has excellent
discharge characteristics under large current can be obtained.
10 [0033]
In other words, a negative electrode for a lithium secondary battery in the exemplary
embodiment of the present invention is
a negative electrode for a lithium secondaly battery comprising a current collector
comprising a metal, and an active material layer comprising an active material and a binding
15 agent, wherein,
the negative electrode comprises a conductive inte~lnediatela yer comprising: conductive
metal particles comprising the same element as the metal, and a polyimide or polyainideimide,
between the current collector and the active material layer, and
the content of the conductive metal particles in the conductive intermediate layer is 23%
20 by volunle or more and 70% by volume or less.
[0034]
The components of the negative electrode for a lithium secondary battery in the exenlplary
embodiment of the present invention will be described in detail below.
[0035]
2 5 (Negative Electrode)
The negative electrode for a lithium secondary battery in the exemplary embodiment of the
present invention comprises a current collector and an active material layer aud comprises a
conductive inte~mediatela yer between the current collector and the active material layer as
shown in Figure 1. It is preferred that the current collector and the conductive intermediate
30 layer be in direct contact with each other, and that the active material layer and the conductive
intermediate layer be in direct contact with each other.
[0036]

The conductive intermediate layer has a configuration in which conductive metal particles
comprising the same element as the metal included in the current collector are included in a
polyimide or polyaniideimide.
[0037]
The content of the conductive metal particles in the conductive intermediate layer is 23%
5 by volume or more and 70% by volume or less. The content of tlie conductive metal particles
in the conductive intermediate layer is preferably 26% by volume or more and 50% by volume
or less, more preferably 26.6% by volume or more and 38.7% by volun~eo r less.
[0038]
The average particle diameter (D5o, volume basis) of the conductive metal particles is
10 preferably 50 tun or Less, preferably larger than 0 and 50 nm or less, more preferably 1 mn or
more and 30 nrn or less, and further preferably 5 nm or more and 25 nm or less.
[0039]
For example, when tlie metal forming the conductive metal pasticles is copper, the weight
ratio corresponding to a content of 23% by volume or more and 50% by volunle or less is about
15 67% by weight or more and 87% by weight or less.
[0040]
The conductive intermediate layer is preferably formed using the manufacturing method in
the exemplary embodiment of the present invention from tlie viewpoint of tlie uniformity of the
fine particles. For example, the conductive intermediate layer can be formed as follows. First,
2 0 a current collector comprising copper (for example, copper foil) is coated with a polyamic acid
having a carboxyl group and then heated under a condition (for example, 80 to 150°C) lower
than a temperature at which the polyamic acid is imidized for 8 to 24 hours to move the copper
from the current collector into the polyamic acid. Then, the coated current collector is heated,
for example, at 300 to 350°C to imidize the polyamic acid. This is considered to be that the
25 copper dissolves in the polyamic acid having a carboxyl group, and that heating induces the
diffusion of copper ions into the layer, and thus the migration of tlie copper occurs. The content
of the conductive metal particles in the conductive intermediate layer can be controlled, for
example, by varying heat-temperature and heat-time. The higher the heating teniperatare is, the
higher the content is. Also, the longer the heating time is, the higher the content is.
30 [0041]
The content (% by volume) of the conductive metal particles in the conductive
intelnlediate layer can be obtained, for example, fsom the true density of the conductive metal
and the polyitnide and the content (% by weight) of the conductive metal particles in the
conductive intermediate layer. The content (% by weight) of the conductive metal particles in
the conductive intermediate layer also can be measured, for example, by dynamic secondary ion
mass spectron~etry( D-SIMS). The average particle diameter (Dm, volume basis) of the
conductive metal particles in the conductive intermediate layer can be obtained, for example, by
subjecting an image obtained by an electron microscope to analysis processing. Examples of
5 the image analysis processing apparatus include LUZEX AP (trade name) manufactured by
NIRECO CORPORATION.
[0042]
The conductive metal particles preferably comprise at least one selected from copper,
nickel, gold, and silver.
10 [0043]
The temperature at which the polyanlic acid is imidized is not particularly limited and is,
for example, more than 150°C, preferably 200°C or more, and more preferably 25OoC or more.
In addition, the temperature is preferably 400°C or less, more preferably 350°C or less.
[0044]
15 The thickness of the conductive intermediate layer is not particularly limited and is, for
exatnple, 0.1 to 10 pm, preferably 0.5 to 5 pm.
[0045]

The metal included in the current collector is preferably a metal that does not form an
20 alloy with Li as described above. Examples of the current collector include copper, nickel, gold,
and silver, and alloys thereof. The current collector preferably comprises copper, nickel, or
silver, and more preferably comprises copper or nickel. Examples of the shape of the current
collector include foil, a flat plate shape, and a mesh shape.
[0046]
25 As the cunent collector, foil or mesh comprising copper as the main component is
preferably used. For example, the ratio of copper in the current collector is preferably 97 to
100% by mass from the viewpoint of conductivity and heat resistance.
[0047]

30 The active material layer (negative electrode active material layer) comprises an active
material (negative electrode active material) and a binding agent (negative electrode binding
agent).
[0048]
The active material is not particularly limited as long as lithium ions can be intercalated
during charge and desorbed during discharge. For exanlple, known ones can be used.
[0049]
Specific examples of the active material include carbon materials, such as graphite, coke,
and hard carbon, lithium alloys, such as lithium-aluminum alloys, lithium-lead alloys, and
5 lithiurn-tin alloys, lithium metal, Si, and metal oxides having lower potential than lithium
manganese composite oxides, such as SnO2, SnO, TiOl, Nb203, and SiO.
[0050]
The active material preferably conxprises at least one selected from Si and Sn. Examples
of such an active material include Si, Sn, or oxides of Si or Sn. These oxides may be crystalline
10 or amorphous, and it is preferred that all or part of the oxides have an amorphous st~ucture. It is
thought that in an oxide having an amorphous structure, there are a relatively small number of
factors caused by nonuniformity, such as grain boundaries and defects. The fact that all or part
of an oxide has an amolphous structure can be confirnxed by X-ray diffraction measurement
(general XRD measurement). Specifically, when all or part of an oxide has an amorphous
15 structure, a broad peak specific to the oxide is observed.
[005 11
Examples of the active material conxprising Si include silicon-containing particles shown
below. Examples of the silicon-containing particles include silicon and silicon compounds.
Examples of the silicon compounds include silicon oxides, silicates, or co~npoundso f transition
20 metals and silicon, such as nickel silicide and cobalt silicide. Silicon compounds play the role
of relieving the expansion and shrinkage of the negative electrode active material itself with
respect to repeated charge and discharge and are preferably used from the viewpoint of charge
and discharge cycle characteristics. Further, silicon compounds also play the role of ensuring
conduction between silicons depending on the types of the silicon compounds, and f?om such a
25 viewpoint, silicon oxides are preferably used as the silicon compounds.
[0052]
The silicon oxide is not particularly limited and is represented, for example, by SiO, (0 < x
< 2). The silicon oxide may comprise Li, and the silicon oxide comprising Li is represented,
for example, by SiLiyO, (y > 0, and 2 > z > 0). The silicon oxide also may comprise a slight
30 amount of a metal element(s) andlor a no~mletale lement(s). The range of x is preferably 0.5 5
x l 1.5. When x is 0.5 or more, the amount of the silicon phase (or Si particles) is prevented
from being excessive, and volume change is easily suppressed. When x is 1.5 or less, the
amount of the silicon phase (Si particles) increases, and the charge and discharge capacity is
easily increased. The silicon oxide preferably has a configuration in which a silicon phase (Si
pat-ticlcs) is present in a silicon oxide phase. By cot~tprisinga silicon phase, the charge and
discharge capacity increases. When a silicon oxide phase is present around a silicon phase,
volume change is suppressed. The content of the Si particles in the silicon oxide is preferably
35 to 65%. The silicon oxide can contain, for example, one or two or more elements selected
5 from among nitrogen, boron, and sulfur, for example, in an amount of 0.1 to 5% by mass. By
containing a slight amount of a metal elcment(s) andlor a nonmetal element(s), the electrical
conductivity of the silicon oxide can be improved. The silicon oxide may be crystalline or
amorphous.
[0053]
10 The content of the active material in the active material layer is preferably 40% by mass or
more and 99% by mass or less, more preferably 50% by mass or more and 95% by mass or less,
and further preferably 65% by mass or more and 90% by mass or less, from the viewpoint of
energy density improvement.
[0054]
15 The active material layer may comprise a conductivity-providing agent from the viewpoint
of improving conductivity. As the conductivity-providing agent, there is no particular
limitation, and, for example, known ones can be used. Examples of the conductivity-providing
agent include carbon materials. Examples of the carbon materials include graphite, amo~phous
carbon, diamond-like carbon, carbon black, ketjen black, acetylene black, vapor-grown carbon
20 fibers, fullerenes, carbon nanotubes, and composites thereof. One of these conductivityproviding
agents may be used alone, or two or more of these conductivity-providing agents may
be used together. Graphite having high crystallinity has high electrical conductivity and has
excellent adhesiveness to a cuwent collector comprising a metal, such as copper, and excellent
voltage flatness. On the other hand, in atnorphous carbon having low crystallinity, the volume
2 5 expansion is relatively small, and therefore, the effect of reducing the volume expansion of the
entire negative electrode is large, and deterioration caused by nonuniformity, such as grain
boundaries and defects, does not occur easily.
[0055]
The content of the conductivity-providing agent in the active material layer is preferably
30 1% by mass or more and 25% by mass or less, more preferably 2% by mass or more and 20% by
mass or less, and further preferably 5% by mass or more and 15% by mass or less. When the
content is 1% by mass or more, sufficient conductivity can be kept. By setting the content to
25% by mass or less, the proportion of the mass of the active material can be increased, and
therefore, the capacity per mass can be increased.
[OOSC]
The binding agent is not particularly limited, and, for example, polyvinylidene fluorides,
vinylidene fluoride-hexafluoropropylene copolynlers, vinylidene fluoride-tetrafluoroethylene
copolymers, styrene-butadiene copolymerized rubbers, polytetrafluoroethylene, polypropylene,
5 polyethylene, polyirnides, and polyanlideimides can be used. The amount of the negative
electrode binding agent used is preferably 7 to 20 parts by mass based on 100 parts by mass of
the negative electrode active material from the viewpoint of "suficient binding force" and
"higher energy" in a trade-off relationship.
[0057]
10 The binding agent is preferably a polyimide or a polyamideimide from the viewpoint of
binding properties to the conductive intermediate layer. As the precursor of the binding agent,
a polyamic acid is preferably used, and the same polyamic acid as the polyamic acid used for the
conductive intermediate layer is more preferably used.
[OOSS]
15 The negative electrode can be fabricated, for example, by forming the above conductive
intermediate layer on a current collector and then forming an active material layer comprising an
active material and a binding agent.
[0059]
Alternatively, the negative electrode can also be fabricated by placing a polyamic acid on a
20 current collector and generating migration phenomenon, and then placing an active material
layer slurry on the polyamic acid and performing heating and curing. By using a polyanlic acid
as the precursor of the binding agent at this time, crosslinks are formed between the binding
agent and the active material layer, and the binding force can be improved. From the viewpoint
of more effectively forming crosslinks, the polyamic acid used for the conductive intermediate
25 layer and the polyamic acid used for the binding agent of the active material layer are preferably
the same.
[0060]
"Exemplary Embodiment 3"
The configuration of a batte~yw ill be described below.
30 [0061]
(Positive Electrode)
In the exemplary embodiment of the present invention, the positive electrode active
material is not particularly limited as long as lithium ions can be intercarated during charge and
desorbed during discharge. For example, known ones can be used. The positive electrode
active material is preferably a lithium transition metal oxide. The lithium transition metal oxide
is not particularly limited. Examples thereof include lithium manganate having a layered
structure or lithium manganate having a spinel structnre, such as LiMnO2 or LiXMn2O4 (0 < x <
2); LiCo02, LiNi02, or lithium transition metal oxides in which parts of the transition metals of
5 these are replaced by other metals; lithium transition metal oxides in which particular transition
metals do not exceed half, such as LiNil~3Coli3Mnl~3l0it2h;i um transition metal oxides having an
olivine st~uctures,u ch as LiFePO4; and these lithium transition metal oxides in which Li is more
excessive than in stoicliiometric compositions. Particularly, LiaNiPCoyA1602 (1 < cr. 5 1.2, p +
y + 6 = 1, p 2 0.7, and y 5 0.2) or LiaNiPCoyMn602 (1 5 cr. 5 1.2, p + y + 6 = 1, 2 0.6, and y 5
10 0.2) is preferred. One of these materials can be used alone, or two or more of these materials
can be used in combination.
[0062]
The positive electrode according to the exemplary embodiment of the present invention
can also comprise a positive electrode conductivity-providing agent and a positive electrode
15 binding agent in addition to the positive electrode active material.
[0063]
As the positive electrode cotiductivity-providing agent, powders of metal substances, such
as aluminum, and conductive oxides, and the like can be used in addition to the carbon materials
that are used for the above negative electrode conductivity-providing agents.
20 [0064]
The positive electrode binding agent is not particularly limited, and, for example,
polyvinylidene fluorides, vinylidene fluoride-hexafluoropropylene copolymers, vinylidene
fluoride-tetrafluoroethylene copolymers, styrene-butadiene copolymerized lubbers,
polytetrafluoroethylene, polypropylene, polyethylene, polyimides, and polyamideimides can be
25 used. Among these, polyvinylidene fluoride (PVdF) is preferred from the viewpoint of
versatility and low cost.
[0065]
The content of the positive electrode binding agent in the positive electrode active material
layer is preferably 1% by mass or more and 25% by mass or less, more preferably 2% by mass or
30 more and 20% by mass or less, and filrther preferably 5% by mass or more and 15% by mass or
less. By setting the content to 1% by mass or more, the occurrence of electrode peeling can be
prevented. By setting the content to 25% by Illass or less, the proportion of the mass of the
positive electrode active material can be increased, atid therefore, the capacity per mass can be
increased.
[0066]
As the positive electrode cul~enct ollector, nickel, copper, silver, atid aluminum, and alloys
tl~ereofa re preferred because of electrochemical stability. Examples of its shape inclt~def oil, a
flat plate shape, and a mesh shape. Particularly, copper foil and alutninum foil are prefened.
5 [0067]
A conductive auxiliary material may be added to the positive electrode active material
layer comprising the positive electrode active material for the purpose of decreasing impedance.
Examples of the conductive auxilialy material include carbonaceous fine patticles, such as
graphite, carbon black, and acetylene black.
10 [0068]
The positive electrode can be fabricated, for example, by mixing a lithium manganese
colllposite oxide, a conductivity-providing agent, and a positive electrode binding agent to
prepare a positive electrode slul~ya,n d forming the positive electrode slurry on a positive
electrode current collector.
15 LO0691
(Electmlyte)
As the electrolyte, for example, liquid-state electrolytes (electrolytic solutions) can be used.
[0070]
The electrolytic solution used in the exemplary embodiment of the present invention is not
20 palticularly limited and comprises, for example, an electrolyte salt and a nonaqueous electrolytic
solvent.
[0071]
The nonaqueous electrolytic solvent is not particularly limited. Examples thereof can
include cyclic carbonates, such as propylene carbonate, ethylene carbonate, butylene carbonate,
25 and vinylene carbonate; chain carbonates, such as dimethyl carbonate, diethyl carbonate, etl~yl
methyl carbonate, and dipropyl carbonate; and lactones, such as y-butyrolactone, from the
viewpoint of being stable at metal lithium potential. One nonaqueous electrolytic solution can
be used alone, or two or more nonaqueous electrolytic solutions can be used in combination.
[0072]
30 The electrolyte salt is not particularly limited. Examples thereof include lithium salts,
such as LiPF6, LiAsF6, LiAIC14, LiC104, LiBF4, LiSbF6, LiCF3S03, LiCF3CO2, Li(CFjS02)2, and
LiN(CF3SOz)z. One electrolyte salt can be used alone, or two or more electrolyte salts can be
used in combination.
[0073]
As the electrolytic solution, ionic liquids can also be used. Exatnples of the ionic liquids
include quaternary an~n~onium-imisdael ts.
[0074]
Further, solid-state electrolytes rather than liquid-state electrolytes may be used.
5 Examples of the solid-state electrolytes include gel electrolytes obtained by impregnating
polymers, such as polyacrylonitrile and polyacrylates, with the above electrolytic solutions, and
solid electrolytes, such as LiPON and LizS-LiP,O, (x = 1 to 2 and y = 2 to 4).
[0075]
(Separator)
10 The separator is not particularly limited, and, for example, known separators can be
adopted. As the separator, for example, porous films and nonwoven fabrics of polypropylene,
polyethylene, and the like can be used. Films of polyimides and araniids, films of cellulose,
and the like can also be used.
[0076]
15 (Package)
As the package, those that are stable in the electrolytic solution and have sufficient water
vapor barrier properties can be used without particular limitation. As the package, for example,
cans of metals, such as iron and aluminum alloys, laminate films can be used. The laminate
films are preferably laminate films in which aluminum or silica is vapor-deposited from the
2 0 viewpoint of water vapor barrier properties.
[0077]
(Configuration of Battery)
The configuration of a secondary battery according to the exemplary embodiment of the
present invention is not particularly limited and can be, for example, a configuration in which an
25 electrode device in which a positive electrode and a negative electrode are disposed opposed to
each other and an electrolytic solution are included in a package. The shape of the secondary
battery is not particularly limited. Examples thereof include a cylindrical type, a flat wound
prismatic type, a laminated prismatic type, a coin type, a flat wound laminate type, or a laminate
type.
30 [0078]
A laminate type secondary battery will be described below as an example. Figure 2 is a
schematic cross-sectional view showing the structure of the electrode device of a laminated type
secondary battery using a laminate film for a package. This electrode device is formed in such
a manner that a plurality of positive electrodes c and a plurality of negative electrodes a are
alternately stacked with separators b sandwiched therebetween. The positive electrode current
collectors e of the positive electrodes care welded and electrically connected to each other at the
ends not covered with the positive electrode active material, and further, a positive electrode
terminal f is welded to the welded part. The negative electrode current collectors d of the
5 negative electrodes a are welded and electrically connected to each other at the ends not covered
with the negative electrode active material, and further, a negative electrode terminal g is welded
to the welded part.
[0079]
"Examples"
10 Specific Examples according to the exemplary embodiment of the present invention will
be described below, but the exemplary embodiment of the present invention is not limited to
these Exanlples.
[OOSO]
[Example I]
15 (Fabrication of Negative Electrode)
n-Metllylpyrrolidone (NMP) and a polya~nic acid (trade name: "U-VARNISH A," Ube
Industries, Ltd.) were mixed, and 10 p1n thick copper foil was coated with the mixture by a
doctor blade, and then, the coated copper foil was heated at 1 10°C for 7 minutes to d ~tyhe NMP.
Then, the coated copper foil was heated at 120°C for 8 hours under a nitrogen atmosphere using
20 an electric furnace to move the copper to the polyamic acid. Then, the electric furnace was
heated at 350°C for 30 minutes under a nitrogen atmosphere to cure the polyamic acid to form a
conductive intermediate layer.
[0081]
The thickness of the obtained conductive intermediate layer was about 1 pm.
25 [0082]
The content (% by weight) of the conductive metal particles (copper particles) in the
conductive intermediate layer was measured using D-SIMS (apparatus used: PHI ADEPT-1010
manufactured by ULVAC-PHI, Incorporated.). The content of the copper paiticles in the
conductive intermediate layer was 66.3% by weight.
30 [0083]
The content (% by volume) of the conductive metal particles (copper particles) in the
conductive intermediate layer was calculated from the true density and % by weight of copper
and U-VARNISH A after being cured.
[0084]
The average particle diameter (Dso, volume basis) of the co~lductivem etal particles
(copper particles) in the conductive intermediate layer was obtained by analyzing a crosssectional
image obtained by an electron microscope. For the analysis, LUZEX AP
mant~facturedb y NIRECO CORPORATION was used. The measurement parameters were
5 adjusted by previously measuring a standard sample (3020A (20 nm +2 nm)) from Thernlo
Fisher Scientific K.K.
[OOS5]
SiO (trade name: "SI005PB," Kojundo Chemical Laboratory Co., Ltd.), carbon black
(trade name: "#3030B," ma~lufacturedb y Mitsubishi Chelllical Corporation), and a polya~nic
10 acid (trade name: "U-VARNISH A," manufactured by Ube Industries, Ltd.) were measured at a
mass ratio of 805: 15. The SiO was adjusted using a sieve so that the average particle diameter
D50w as 25 pm. These and n-methylpyrrolidone (NMP) were mixed usiug a hotnogenizer to
form a slut~y. The mass ratio of the NMP to the solids was 57:43. The conductive
intermediate layer was coated with the slurry using a doctor blade. Then, the coated material
15 was heated at 120°C for 7 minutes to d ~tyhe NMP. Then, the coated material was heated at
350°C for 30 ininutes under a nitrogen atmosphere using an electric furnace to fabricate a
negative electrode.
[0086]
(Fabrication of Positive Electrode)
20 Lithium cobaltate (manufactured by Nichia Corporation), carbon black (trade name:
"#3030B," manufactured by Mitsubishi Chemical Corporation), and polyvinylidene fluoride
(trade name: "#2400," manufactured by KUREHA CORPORATION) were measured at a mass
ratio of 95:2:3. These and NMP were mixed to form a slurry. The mass ratio of the NMP to
the solids was 52:48. 15 pm thick aluminum foil was coated with the slully using a doctor
25 blade. The aluminum foil coated with the slurry was heated at 120°C for 5 minutes to dly the
NMP to fabricate a positive electrode.
[0087]
(Assembly of Secondary Battery)
An aluminum terminal and a nickel terminal were welded to the fabricated positive
30 electrode and negative electrode, respectively. These were superimposed on each other via a
separator to fabricate an electrode device. The mass of the positive electrode and the negative
electrode was adjusted so that the amount of lithium with which SiO, the negative electrode
active material, was doped was any value during a fully charged state. A nickel tennilla1 was
welded to a reference electrode obtained by bonding copper foil to lithium metal, and the
reference electrode was superiniposed on the negative electrode via a separator. The electrode
device and the reference electrodc were packaged with a la~iii~iaftielm , and an electrolytic
solutiorl was injected inside the laminate film. Then, while the pressure inside the laminate film
was reduced, the laminate filni was heat-sealed and sealed. Tl~usa, flat plate type secondary
5 battery before initial charge was fabricated. For the separator, a polypropylene film was used.
For the laminate film, a polypropyle~lef ilm on which aluminum was vapor-deposited was used.
For the electrolytic solution, a solution comprising 1.0 niol/l of LiPF6 as an electrolyte and a
mixed solvent of ethylene carbonate and diethy1 carbonate (7:3 (volume ratio)) as a nonaqueous
electrolytic solvent was used.
10 [OOSS]
(Charge and Discharge Cycle Test of Secondary Battery)
A charge and discharge cycle test was performed on the fabricated secondaly battery in the
battery voltage range of 2.5 to 4.2 V. The charge was performed by a CCCV method, and after
4.2 V was reached, the voltage was kept constant for 1 hour. The discharge was performed by a
15 CC niethod (constant current 0.2 C). Here, 0.2 C cu~~emneta ns a current at which when a
battery in a hlly charged state is subjected to co~istauct unent discharge, complete discharge of
the battery takes 5 hours.
[0089]
(Discharge Rate Test of Secondary Battery after Cycles)
2 0 After 100 cycles of the above-described charge and discharge cycle test was performed, a
discharge rate test was performed. In the discharge rate test, the battery, in a fully charged state,
was discharged at a constant cunent of 0.2 C or 3 C, tlie discharge capacity was measured, and
the ratio of the discharge capacity (3 C10.2 C) was calculated. Here, 3 C current means the
current at which, when a battery in a fully charged state is subjected to constant current discharge,
25 complete discharge of tlie battery takes 20 minutes.
[0090]
[Example 21
A battery was fabricated and evaluated as in Example 1 except that the heating time at
120°C during tlie fabrication of the conductive intermediate layer was changed to 12 hours.
30 [0091]
[Example 31
A battery was fabricated and evaluated as in Example 1 except that the heating time at
120°C during the fabrication of tlie conductive intermediate layer was changed to 16 hours.
[Example 41
A battery was fabricated and evaluated as in Exa~llplc 1 except that the heating time at
120°C during the fabricatiou of the conductive intermediate layer was changed to 24 hours.
[0092]
[Reference Example 11
5 A battery was fabricated and evaluated as in Example 1 except that the heating time at
120°C during the fabrication of the conductive intennediate layer was changed to 1 hour.
[0093]
[Reference Exaniple 21
A battery was fabricated and evaluated as in Example 1 except that the hcating time at
10 120°C during the fabrication of the conductive intermediate layer was changed to 3 hours.
[0094]
[Reference Example 31
A battery was fabricated and evaluated as in Example 1 except that the heating time at
120°C during the fabrication of the conductive intermediate layer was changed to 5 llours.
15 [0095]
[Comparative Example 11
A battery was fabricated and evaluated as in Example 1 except that the conductive
intermediate layer was not fabricated, and the active material layer was formed directly on the
copper foil.
20 [0096]
[Comparative Example 21
A battery was fabricated and evaluated as in Example 1 except that a negative electrode
fabricated as follows was used.
[0097]
2 5 n-Methylpyrrolidone (NMP), a polya~nic acid (trade name: "U-VARNISH A," Ube
Industries, Ltd.), and copper particles (Dsa: 300 nnl) were mixed, and 10 pm thick copper foil
was coated with the mixture by a doctor blade, and then, the coated copper foil was heated at
I 10°C for 7 minutes to dly the NMP. Then, an electric fi~rnacew ax heated at 350°C for 30
minutes under a nitrogen atmosphere to cure the polyamic acid to form a polyimide layer
30 comprising copper particles.
[0098]
SiO (trade name: "SIOOSPB," Kojundo Chemical Laboratory Co., Ltd.), carbon black
(trade name: "#3030B," manufactured by Mitsubishi Chemical Corporation), and a polyamic
acid (trade name: "U-VARNISH A," manufactured by Ube Industries, Ltd.) were measured at a
mass ratio of 80:5:15. The SiO was adjusted using a sieve so that the average particle dianleter
Dso was 25 11111. These and n-methylpyrrolidone (NMP) were mixed using a homogenizer to
form a slurry. The nlass ratio of the NMP to the solids was 57:43. The above polyimide layer
comprising copper particles was coated with the slurry using a doctor blade. Then, the coated
5 material was heated at 120°C for 7 minutes to dry the NMP. Then, the coated material was
heated at 350°C for 30 minutes under a nitrogen atmosphere using an electric furnace to fabricate
a negative electrode.
100991
The evaluation results are shown in Table 1 and Figure 3.
10 [OlOO]
[Table 11
Comparative
Example 1
Comparative
Example 2
Reference
Example 1
Reference
Example 2
Reference
Example 4
Negative
electrode
active material
SiO
SiO
SiO
SiO
SiO
SiO
Heating time Average particle
diameter of conductive
Content of conductive metal
particles in conductive
intermediate layer
(Oh by volume)
-
13.5
16.1
Content of conductive metal
particles in conductive
intermediate layer
(%by weight)
3CIO.2C
(after 100
cycles)
-.-
SiO 12 10 26.6 69.8 0.73
SiO 16 12 32.2 75.2 0.74
SiO 24 20 38.7 80.1 0.74
[OlOl]
As shown in Table 1, in Examples 1 to 4 in which the content of the copper particles in the
conductive intermediate layer was 23% by volume or more, the discharge capacity ratio (3 C10.2
C) was high. The reason for this is presumed to be that when the content of the conductive
5 particles in the conductive inte~rnediatela yer was 23% by volume or more, conductive paths of
the conductive metal particles were formed in the conductive intermediate layer, and the
conductivity increased.
[O 1021
In addition, the negative electrode for a lithium secondary battery in the exemplary
10 embodiment of the present invention can also be grasped as follows.
[0 1031
(Supplementary Note 1)
A negative electrode for a lithium secondary battery comprising a current collector
comprising a metal, and an active material layer conlprising an active material and a binding
15 agent wherein,
the negative electrode has a conductive inte~rnediatela yer comprising: conductive metal
particles comprising the same element as the metal, and a polyiniide or a polyamideimide,
between the current collector and the active material layer, and
an average particle diameter of the conductive metal particles is 50 nm or less.
20 [0104]
(Supplementary Note 2)
The negative electrode for a lithium secondary battery according to supplementary note 1,
wherein a content of the conductive metal particles in the conductive intermediate layer is 23%
by volume or more and 70% by volume or less.
25 [0105]
(Supplementary Note 3)
The negative electrode for a lithium secondary battery according to supplementary note 1
or 2, wherein the content of the conductive metal particles in the conductive intermediate layer is
26% by volume or more and 50% by volume or less.
30 [0106]
(Supplementary Note 4)
The negative electrode for a lithium secondary battery according to any of supplementary
notes 1 to 3, wherein the metal is a metal soluble in a polyamic acid that is a precursor of the
polyimide or the polyamideimide.
[0107]
(Supplementary Note 5)
The negative electrode for a lithium secondary battery according to any of supplementary
notes 1 to 4, wherein the metal is a metal not forming an alloy with Li in a potential range of 0 to
5 4.5 v ( ~ i / ~ i + ) .
[0108]
(Supplen~entaryN ote 6)
The negative electrode for a lithium secondary battery according to ally of supplementary
notes 1 to 5, wherein the collductive metal particles are formed by movement of the metal
10 included in the current collector to a polyamic acid that is a precursor of the polyimide or the
polyimideamide by migration phenomenon.
[0109]
(Supplementary Note 7)
The negative electrode for a lithium secondary battery according to suppleme~ltaryn ote 6,
15 wherein the migration phenomenon is caused by placing the polyamic acid on the current
collector and then performing heat treatment under a condition in which the temperature is lower
than the imidization temperature of the polyarnic acid.
[OllO]
(Supplementary Note 8)
2 0 The negative electrode for a lithium secondary battery according to any of supplementary
notes 1 to 7, wherein the metal is at least one selected from copper, nickel, and silver.
[Olll]
(Supplementary Note 9)
The negative electrode for a lithium secondary battery according to any of supplementary
25 notes 1 to 8, wherein the active material co~nprisesa t least one selected from Si and Sa.
[0112]
(Supplen~entaryN ote 10)
The negative electrode for a lithium secondary battery according to any of supplementary
notes 1 to 9, wherein the binding agent is a polyimide or a polyamideimide.
30 [0113]
(Supplementary Note 11)
A lithium secondary battery comprising the negative electrode for a lithitlm secondary
battery according to any of supplementary notes 1 to 10.
[0114]
This application clainls priority of Japanese Patent Application No. 2012-28147 filed
Febluary 13,2012, the entire disclosure of which is incolporated herein.
[0115]
The invention of this application has been described with reference to the exemplary
5 embodiments and the Examples, but the inveution of this application is not limited to the above
exemplaly embodiments and Examples. Various changes that can be understood by those
skilled in the art can be made in the configuration and details of the invention of this application
within the scope of the invention of this application.
10 Reference Signs List
[0116]
1 current collector
2 conductive intermediate layer
3 conductive metal particles
15 4 active material layer
CLAIMS
[Claim 11
A negative electrode for a lithium secondary batte~y,c omprising: a current collector
comprising a metal, and an active material layer conlprising an active material and a binding
5 agent, wherein
the negative electrode has a conductive intermediate layer comprising conductive metal
particles comprising the same element as the metal, and a polyiniide or a polyamideimide,
between the current collector and the active material layer, and
a content of the conductive metal particles in the conductive inte~nlediatela yer is 23% by
10 volume or more and 70% by volume or less.
[Claim 21
The negative electrode for a lithium secondary battery according to claim 1, wherein tlie
content of tlie conductive metal particles in the conductive intermediate layer is 26% by volume
15 or more and 50% by volume or less.
[Claim 31
The negative electrode for a lithium secondary battery according to claim 1 or 2, wherein
an average particle diameter of the conductive metal particles is 50 nm or less.
2 0
[Claim 41
The negative electrode for a lithium secondary battery according to any of claims 1 to 3,
wherein the metal dissolves in a polyamic acid that is a precursor of the polyimide or the
polyamideimide.
25
[Claim 51
The negative electrode for a lithium secondary battery according to any of claims 1 to 4,
wherein the metal does not form an alloy with Li in a potential range of 0 to 4.5 V ( ~ i / ~ i + ) .
30 [Claim 61
The negative electrode for a lithium secondary battery according to any of claims 1 to 5,
wherein the conductive metal particles are formed by movement of tlie metal included in the
current collector to a polyamic acid that is a precursor of the polyimide or the polyaniideimide
by migration phenomenon.
[Claim 71
The negative electrode for a litliiun~s econdary battery according to claim 6, wherein the
migration phenomenon is caused by placing the polya~nica cid on the current collector and then
5 perfornling heat treatment under a condition in which the temperature is lower than the
imidization temperature of the polyamic acid.
[Claim 81
The negative electrode for a lithium secondary battery according to any of claims 1 to 7,
10 wherein the metal is at least one selected from copper, nickel, and silver.
[Claim 91
The negative electrode for a lithium secondary battery according to any of claims 1 to 8,
wherein the active material comprises at least one selected from Si and Sn.
15
[Claim 101
The negative electrode for a lithium secondary battery according to any of claims 1 to 9,
wherein the binding agent is a polyi~nideo r a polyamideimide.
20 [Claim 1 l]
A lithium secondary battery comprising tile negative electrode for a lithium secondary
battery according to any of claims 1 to 10.
[Claim 121
25 A method for manufacturing a negative electrode for a lithium secondary batte~y
comprising a current collector comprising a metal, an active material layer comprising an active
material and a binding agent, and a conductive inte~mediatela yer comprising conductive metal
particles between the current collector and the active material layer, comprising steps of:
(1) placing a polyamic acid on the current collector;
30 (2) causing the metal to move from the cussent collector into the polyamic acid by
generating migration phenomenon; and
(3) heating and curing the polyamic acid,
in this order, wherein
the metal that has moved into the polyamic acid folms the conductive metal particles.
[Claim 131
The method for manufacturing a negativc electrode for a lithiu~isl econdary battery
according to claim 12, wherein the migration phenomenon is caused by performing heat
5 treatment under a condition in which the temperature is lower than the imidization temperature
of the polyamic acid.
[Claim 141
The method for manufacturing a negative electrode for a lithium secondary battery
10 according to claim 13, wherein a temperature of the heat treatment is in a range of 80 to 150°C.
[Claim 151
The method for manufacturing a negative electrode for a lithiu~ns econdary battery
according to any of claims 12 to 14, wherein the polyamic acid comprises an organic acid.
15
[Claim 161
The method for manufacturing a negative electrode for a lithium secondary battery
according to claim 15, wherein the organic acid is plithalic acid, oxalic acid, or maleic acid.
20 [Claim 171
The method for manufacturing a negative electrode for a lithium secondary batte~y
according to any of claims 12 to 16, wl~ereina content of the conductive metal particles is 23%
by volume or more and 70% by volunle or less in tlie conductive intermediate layer.
25 [Claim 181
The method for manufacturing a negative electrode for a lithium secondary battery
according to any of claims 12 to 17, wherein the content of the conductive metal particles is 26%
by volume or more and 50% by volun~eo r less in tlie conductive intermediate layer.
30 [Claim 191
The method for ~iianufacturinga negative electrode for a lithium secondary battery
according to any of claims 12 to 18, wherein an average particle diameter of the conductive
metal particles is 50 mn or less.
[Claim 201
The method for manufacturing a negative electrode for a lithium secondary battery
according to any of claims 12 to 19, wherein the metal dissolves in the polyamic acid.
5 [Claim 211 . %
The method for manufacturing a negative electrode for a lithium secondary battery
according to any of claims 12 to 20, wherein the metal does not folm an alloy with Li in a
potential range of 0 to 4.5 V (Li/Li+).
10 [Claim 221
The method for manufacturing a negative electrode for a lithium secondary battery
according to any of claims 12 to 21, wherein the metal is at least one selected fro111 copper,
nickel, and silver.
15 [Claim 231
The method for manufacturing a negative electrode for a lithium secondary battery
according to any of claims 12 to 22, wherein the active material comprises at least one selected
from Si and Sn.
20 [Claim 241 ..
The method for manufacturing a negative electrode for a lithium secondary battery
according to any of claims 12 to 23, wherein the binding agent is a polyimide or a
polyamideimide.
Dated this 17.07.2014
WNJNA MEHTA-DUTT)
OF REMFRY & SAGAR
ATTORNEY FOR THE APPLICANT[S]