A NEGATIVE ACTIVE MATERIAL FOR A LITHIUM BATTERY
AND METHOD OF MANUFACTURING THEREOF
This invention relates to a negative active material for a lithium battery and method
of manufacturing thereof. More particularly, the present invention relates to active material
for the negative electrode of secondary rechargeable batteries, wherein the active material is
based on lithium titanium iron ramsdellite oxide with on or two of the following elements :
Ti3+, Co2+, Co3+, Ni2+, Ni3+, Cu2+, Mg2+, Al3+, In3+, Sn4+, Sb5+, Sb5+.
Performances, high energy and high specific power have been improved respecting security
and environment with a reasonable cost.
Anode materials for rechargeable lithium batteries are generally selected from
carbon group. In these batteries, numerous efforts have been made to find alternative
electrochemical active anode materials to replace graphite. Notably, lithium titanium
oxides have been proposed, due to an average voltage around 1.5V vs. Li, such as the
spinel phase Li4Ti5O12 as related in Journal of Electrochemical Society 141 (1994)
L147, or the ramsdellite phase Li2Ti3O7 as reported in Material Research Bulletin 32
(1997) 993. The spinel structure inserts lithium in a two-phase process due to the
spinel to rocksalt phase transition presenting a 1.55V vs. Li plateau, whilst the
ramsdellite inserts lithium topotactically in a solid solution with a flat S-shape charge-
discharge curve corresponding to a one-phase process at a voltage range of 1-2V vs.
Li.
Lithium titanate oxide (Li2Ti3O7) is regarded as promising negative electrode
material because of the low cost of the production, and non-toxicity of titanium, as
reported in Solid State Ionics 83 (1996) 323 and in Journal of the Electrochemical
Society 146 (1999) 4328. The reversible capacities, as reported in Solid State Ionics 82
(1996) 323, J. Electrochemical Society 146 (1999) 4348, J. Power Sources 81 (1999)
85, are between 100 and 140Ah/kg but always for low current densities. In addition,
these papers show that the reversible capacity, the polarisation observed upon lithium
insertion and the required high temperature for the firing process strongly limit the
application field of this compound.
As shown recently in Electrochemistry 69 (2001) 526, a lower temperature for
the synthesis and a better cyclability at low current density can be achieved using a
ceramic route, by substitution of a small amount of Ti4+ by Fe3+ in Li2Ti3O7 However,

the first discharge curve shows a plateau due to the transformation Fe3+/Fe2+ which
limits the reversible capacity, and the other performances are not improved compared
with Li2Ti3O7.
The objective of the invention is to provide for a negative electrode active
material for lithium batteries mat has an increased capacity at high current density, in
the range 1-2V, and has a high capacity retention after cycling compared to the prior
art Li-Ti-(Fe)-0 compounds, and can be prepared with a fast, low temperature and
low-cost process.
The negative electrode active material for lithium battery according to the
invention is represented by a general formula Li2+vTi3-wFexMyM'zO7-, where M and M'
have been chosen in order to improve the electrochemical performances, including
both the electronic and the ionic conductivities. M and M' are metal ions having an
ionic radius between 0.5 and 0.8 A and forming an octahedral structure with oxygen;
and 0, y+z>0 and x+y+z≤0.7. Preferably x≤0.2, y≤0.2 and z≤0.1.
Due to their ionic radii and their electronic configurations the following distinct ions
are considered for M andM1: Ti3+, Co2+, Co3+, Ni2+, Ni3+, Cu2+, Mg2+, Al3+, In3+, Sn4+,
Sb3+, Sb5+. Preferably, y>0 and M=Ni2+ and/or z>0 and M'=Co2+or Cu2+. In another
embodiment y>0 and M=Ni2+ and/or z>0 and M'=A13+, In3+, Sn4+ or Sb3+.
The invention also describes a method of manufacturing a negative electrode
active material as specified above, comprising the steps of griding and mixing a
lithium compound, a titanium compound, an iron compound, and a M and M'
compound by planetary ball milling, followed by a sintering process. In this method,
each metallic compound can be selected from a metal oxide or an inorganic or organic
solid precursor of said metal oxide.
The following oxides are considered: lithium oxide (Li2O), titanium oxide (anatase
TiO2), iron oxide (Fe2O3), and one or two metal oxides (MM') selected from
Ti2O3, CoO, Co2O3, NiO, Ni2O3, CuO, MgO, Al2O3, In2O3, SnO2, Sb2O3, Sb2O5.
Preferably the temperature of the sintering process is between 150°C and 1000°C.

In a further embodiment of the invention a secondary rechargeable battery is
claimed, having an anode material as described above. The cathode material can be a
high voltage positive material such as LiCoO2, LiMn2O4 or a lithium intercalated
compound.
Brief Description of the Accompanying Drawings
Features of the invention are disclosed in the following detailed description and
accompanying figures:
Fig. 1 shows X-ray diffraction patterns (Cu Kα - Intensity a.u. against angle θ) of
Li1.86Ti2.85Fe0.15O6.85(a), Li1.86Ti2.85Fe0.03Ni0.12O6.795 (b),
Li1.93Ti2.85Fe0.03Ni0.09Sn0.03O6.86 (c) and Li1.86Ti2.86Fe0.025Ni0.1Al0.025O6.825 (d)
prepared by the ceramic process.
Fig. 2 shows the charge and discharge profiles (potential in V against capacity in
Ah/kg) in the range 1-2.2V of Li1.86Ti2.85Fe0.15O6.85 (a),
Li1.86Ti2.85Fe0.03Ni0.12O6.795 (b), Li1.93Ti2.85Fe0.03Ni0.09Sn0.03O6.86 (c) and
Li1.86Ti2.86Fe0.025Ni0.1Al0.025O6.825 (d).
Fig. 3 shows the first discharge curve (potential in V against capacity in Ah/kg) of
prior art compound Li1.86Ti2.85Fe0.15O6.85 in the range 1-2.5V. The points A
and B denote the host material and the lithiated compound at the end of the
first discharge, respectively, which are considered for the analysis of the iron
oxidation state by 57Fe Mössbauer spectroscopy in Fig. 4.
Fig. 4 shows 57Fe Mossbauer spectra of prior art compound (relative transmission
against velocity in mm/s) Li1.86Ti2.85Fe0.15O6.85 (a) and the lithiated compound
at the end of the first discharge (b) which correspond to the points A and B of
the electrochemical curve given in Fig. 3, respectively.

Fig. 5 shows variations of discharge capacity with the cycle number (capacity in
Ah/kg against cycle number N) of Li1.86Ti2.85Fe0.15O6.85 (circles •),
Li1.86Ti2.85Fe0..03Ni0.12O6.795 (squares ■), Li1.93Ti2.85Fe0.03Ni0.09Sn0.03O6.86
(triangles ) and Li1.86Ti2.86Fe0.025Ni0.1Al0.025O6.825 (diamonds ♦) at C/10 (a)
and 1.5C (b) rates. The capacity curve of Li2Ti307 at C/10 is also shown for
comparison (open circles O).
Electrochemical properties of the ramsdellite Li2Ti307 used as negative
electrode in Li-ion batteries are based on a one-phase insertion mechanism of lithium
ions, without modifications of the host compound. Such a mechanism requires a good
stability of the host network, vacant sites for the inserted lithium, and the existence of
electrochemical active cations, in this case Ti4+. The structure of Li2Ti307 can be
described from TiO6 edge and face sharing octahedra and channels, which are partially
occupied by the lithium atoms of the host material (2 Li for 7 O). These channels can
be easily filled by electrochemically inserted lithium ions. The crystallographic sites of
titanium are not fully occupied and vacancies (0.5 vacancy for 7 0) can be occupied by
the lithium of the host material. This description can be summarised by the developed
formula of Li2Ti307:
(Li2-.xVa1.5+x)channel(Ti3LixVa0.5-x)networkO7
where Vα denotes the vacancies. Substitution of Ti4+ by Fe3+ is known to decrease the
synthesis temperature of the ramsdellite phase within the system Li2O-TiO2-Fe2O3. In
addition to iron atoms the invention describes the addition of one or two other
elements in order to improve the electrochemical performances. The following
improvements are obtained:
- increase of the specific capacity by increasing the number of possible sites for the
inserted lithium or by making easier the accessibility of the existing vacant sites;
- increase of the efficiency and the cycling through a better stability of the host
network and by improving the reversibility of the lithium insertion mechanism
(increase of the ionic conductivity);
- increase of the charge/discharge rate by increasing ionic and electronic
conductivities in order to increase the specific power.

Co-doping is proposed in order to modify these different properties simultaneously
by considering different elements and different oxidation states. The ions Ti3+, Co2+,
Co3+, Ni2+, Ni3+, Cu2+, Mg2+, Al3+, In3+, Sn4+, Sb3+, Sb5+ have been considered because
they have ionic radii between 0.5A and 0.8A, which is similar to those of Li+ (0.6Å)
and Ti4+(0.7Å). Thus, they can easily replace Ti4+ or Li+, In addition, they easily form
octahedra with oxygen atoms. Two types of substitution are possible:
1) Ti substitution
Transition metals such as Co2+, Ni2+, Cu2+ can be associated with iron in order to avoid
the plateau in the electrochemical potential curves at about 2.1V due to the Fe3+/Fe2+
reduction. The decrease of the cationic average charge (from +4) with Ti3+, Co2+/3+,
Fe2+/3+, Ni2+/3+ and Cu2+ increases the number of oxygen vacancies and the ionic
conductivity.
The p-type elements Al3+, In3+, Sn4+ and Sb3+ increase the covalency of the metal-
oxygen bonds modifying the volume of both the occupied and vacant sites and the
effective charges of the oxygen anions. The Sb5+ ions increase the cationic average
charge and therefore the number of vacant cationic sites.
2) Li substitution
The occupation of the lithium sites of the channels by Mg2+, Ni2+, which have higher
oxidation states than Ii+, tends to decrease the number of lithium ions in the channels
of the host material.
Li2+vTi3-wFexMyM'zO7- compounds according to the invention can be prepared
using a ceramic process. Various amounts of lithium, titanium, iron and metals M
and/or M' are selected using lithium oxide (Li2O), titanium oxide (anatase TiO2), iron
oxide (Fe2O3), and M/M' oxides (Ti2O3, CoO, Co2O3, NiO, Ni2O3, CuO, MgO, A12O3,
In2O3, SnO2, Sb2O3, Sb2O5) as starting materials, which are finely ground and mixed
by planetary ball milling, using for example a Fritsch Pulverisette 7 (15min., speed 8),
and a milling ball weight which is 10 times the product weight. Inorganic or organic
solid precursors of oxides can also be used instead of oxides. The firing or sintering
process involves for example a five step temperature profile including a linear increase
of temperature from room temperature to 150°C at 5°C/min., a plateau at 150°C during
1 hour, a linear increase of temperature from 150°C to 650°C at 2°C/min., a linear
increase of temperature from 650°C to 980°C at 7°C/min. and a subsequent firing

plateau at 980°C for 2 hours. As a higher temperature is required in the last step
(1080°C) for non-doped Li2Ti3O7, the effect of iron or co-doping is clearly to reduce
this temperature, which is interesting in an industrial process.
The preparation process according to the invention is illustrated in the
following examples. Example 1 concerns Li1.86Ti2.85Fe0.03Ni0.12O6.795 which is obtained
from the general formula Ii2+vTi3-wFexMyM'zO7- by considering v=-0.14, w=0.15,
x=0.03, y=0.12, z=0. The material was synthesised using the ceramic process
described above: a mixture of Li2CO3 (448mg), TiO2 (1.487g), Fe2O3 (15.6mg), NiO
(58.5mg) was finely ground by planetary ball milling in the Fritsch Pulverisette 7 and
mixed. The firing process involved the 5 step temperature profile described above.
Example 2 concerns Li1.93Ti2.85Fe0.03Ni0.09Sn0.03O6.86 which is obtained from the
general formula Li2+vTi3-wFexMyM'2O7- by considering v=-0.07, w=0.15, x=0.03,
y=0.09, z=0.03. A mixture of Li2CO3 (465mg), TiO2 (1.487g), Fe2O3 (15.6mg), NiO
(43.7mg), SnO2 (29.5mg) was finely ground by planetary ball milling and mixed. The
firing process described above was used.
Example 3 concerns Li1.86Ti2.86Fe0.025Ni0.1Al0.025O6.825 which is obtained from
the general formula Li2+vTi3-wFexMyM'zO7- by considering v=-0.14, w=0.14, x=0.025,
y=0.1, z=0.025. A mixture of Li2CO3 (447mg), TiO2 (1.487g), Fe2O3 (13mg), NiO
(48.6mg), Al2O3(8.3mg) was finely ground and mixed, followed by the firing process
described before.
X-ray diffraction analysis of the obtained Li2+vTi3-wFexMyM'zO7- shows a
ramsdellite-related structure. This is shown in Fig. 1 for Ii1.86Ti2.85Fe0.15O6.85 with
lattice constants a=0.5014(3)nm, b=0.9556(4)nm, c=0.294(2)nm(la), for
Li1.86Ti2.85Fe0.03Ni0.12O6.795 with lattice constants a=0.501(2)nm, b=0.9572(6)nm,
c=0.295(7)nm (1b) for Li1.93Ti2.85Fe0.03Ni0.09Sn0.03O6.86 with lattice constants
a=0.502(2)nm, b=0.9572(6)nm, c=0.295(7)nm (1c) and for
Li1.86Ti2.86Fe0.025Ni0.1Al0.025O6.825 with lattice constants a=0.502(3)nm, b=0.9569(4)nm,
c=0.295(6)nm (1d). Substitution of Li and Ti by M/M' elements does not modify the

crystal structure which is always of the ramsdellite type, and only weakly affects the
lattice constants.
In order to study the electrochemical properties of Li2+vTi3-wFexMyM'zO7-,
powders according to the invention, carbon black as an electron conducting and
stabilising material, and PVDF as a binder were pressed onto pellets. A two-electrode
cell was made from that mixture as cathode and a lithium foil as anode. A mixture
solution of ethylene carbonate and diethyl carbonate (1:1) including 1M of LiPF6 was
used as electrolyte.
Fig. 2 shows the charge-discharge characteristics of prior art
Li1.86Ti2.85Fe0.15O6.85 (2a) Li1.86Ti2.85Fe0.03Ni0.12O6.795 of Example 1 (2b),
Li1.93Ti2.85Fe0.03Ni0.09Sn0.03O6.86 of Example 2 (2c) and
Li1.86Ti2.86Fe0.025Ni0.1Al0.025O6.825 of Example 3 (2d). The charge-discharge tests were
carried out under galvanostatic mode at a current rate of C/10 (C corresponds to 1
mole Li exchanged, per mole active material, per hour) in the potential range 1-2.2V.
The observed plateau at about 2.1V for prior art Li1.86Ti2.85Fe0.15O6.85 (see
Figs.2a, 3) is due to the reduction reaction of Fe3+ into Fe2+ as shown by comparison
between Mössbauer spectra for the host material (Fig. 4a) and the lithiated material at
the end of the first discharge (Fig. 4b). To avoid the Fe3+/Fe2+ reduction during lithium
insertion, which reduces the capacity of the material, according to the invention
additional oxides of M and/or M' are included during the synthesis of the host material.
Addition of M and /or M' changes Fe3+ into Fe2+ in the host material and eliminates the
plateau at 2.1V as can be observed in Figs.2b and 2c.
The charge-discharge curves of the three co-doped compounds shown in Fig. 2
present a total capacity of about 160Ah/kg in the range 1-2V. There is a small
irreversible capacity of less than about 25Ah/kg at the first discharge and the reversible
capacity of is of about 140Ah/kg (Figs 2b, 2c, 2d) which is higher than that obtained
for the iron doped material: 120 Ah/kg (Fig. 2a).
Variations of discharge capacity with the cycle number of Li1.86Ti2.85Fe0.15O6.85,
Li1.86Ti2.85Fe0.3Ni0.12O6.795,Li1.93Ti2.85Fe0.03Ni0.09Sn0.03O6.86,
Li1.86Ti2.86Fe0.025Ni0.1Al0.025O6.825 are shown at C/10 (Fig. 5a) and 1.5C (Fig. 5b) rates.
Both Li1.93Ti2.85Fe0.03Ni0.09Sn0.03O6.86 and Li1.86Ti2.86Fe0.025Ni0.1Al0.025O6.825 show good
cycling capabilities and reversible capacities of about 140Ah/kg and 90 Ah/kg at C/10

and 1.5C rates, respectively. Similar results are obtained for Li1.86Ti2.85Fe0.03Ni0.12O6.795
at C/10 but not at 1.5C whereas capacities of the iron compound are lower at both C/10
(120Ah/kg) and 1.5C (75Ah/kg). It is interesting to note that undoped Li2Ti3O7
exhibits poor cycling capabilities as shown in Fig. 5a for comparison. For the co-doped
compounds the retention of capacity is better than 90% after 30 cycles.
As a conclusion, the main advantages of co-doping according to the invention
are the decrease of the synthesis temperature, the good reversible capacity at both low
and high current densities and the good cycling capabilities.

WE CLAIM :
1. A negative active material for a lithium battery, having a general formula
Li2+vTi3-wFexMyM'zO7-a, wherein M and M' are metal ions having an ionic radius
between 0.5 and 0.8A and forming an octahedral structure with oxygen; and a is
related to the formal oxidation numbers n and n' of M and M' by the relation 2
=-v+4w-3x-ny-n'z and -0.5≤v≤0.5, 0≤w≤0.2, x>0, y+z>0 and x+y+z≤0.7.
2. The active material as claimed in claim 1, wherein M and M' are selected
from the list consisting of Ti3+, Co2+, Co3+, Ni2+, Ni3+, Cu2+, Mg2+, Al3+, ln3+,
Sn4+, Sb3+, Sb5+.
3. The active material as claimed in claim 2, wherein y>0 and M is Ni2+.
4. The active material as claimed in claims 2 or 3, wherein z>0 and M' is
Co2+or Cu2+.
5. The active material as claimed in claims 2 or 3, wherein z>0 and M' is
selected from the list consisting of Al3+, ln3+, Sn4+or Sb3+.
6. The active material as claimed in any of the previous claims, wherein
x≤0.2, y≤0.2 and z≤0.1.
7. A method of manufacturing a negative electrode active material according
to any one of the claims 1 to 6, comprising the steps of grinding and mixing a
lithium compound, a titanium compound, an iron compound, and a M and M'
compound by ball milling, followed by a sintering process.

8. The method as claimed in claim 7, wherein each metallic compound is
selected from a metal oxide or an inorganic or organic solid precursor of said
metal oxide.
9. The method as claimed in claims 7 or 8, wherein the temperature of the
sintering process is between 150°C and 1000°C.
10. A secondary rechargeable battery having an anode material as claimed in
any one of claims 1 to 6.

An active metrarial for high-voltage negative electrodes (>IV vs Li) of secondary rechargeable lithium batteries is disclosed. Chemical composition is represented by the general formula Li2+v Ti3-w FexMyM’2O7-a+ where M and M are metal ions having an ionic radius between 0.5 and 0.8 A and forming an octahedral structure with oxygen, like Ti3+, Co2+, Co3+ , Ni2+, Ni3+, Cu2+, Mg2+, A 13+, In3+, Sn4+, Sb3,Sb5+, a is related to the formal oxidation numbers n and n’ of M and by the relatio9n 2 a=v+4w, 3x-ny’ z and the ranges of values are –0.5£
V£0.5, 0£w £0.2, x>0, y+z>0 and x+y+z £0.7. The strueture is related to that of remsdellite for all the compositions, The negative active material is prepared by ceramics process wherein lithium oxide, titanium oxide, iron oxide, M and/or M oxide are used as starting material for synthesis, Inorganic or organic solid precursors of the oxides can also be used instead. After reacant dispersion the mixture is field. The resulting electrochemically active material provides low working voltage and capacity with excellent cyeling capabilities at both low and high current densities.