Negative electrode material for Li-ion batteries
The present invention relates to lithium cells, accumulators or batteries, and more
particularly an active material for the negative electrode of rechargeable batteries.

Batteries of Li-ion type are designed for new applications (portable electronics,
cableless tools, hybrid vehicles) which require still more power and energy in order to
respond to requirements. They should be stable over their life span while cycling and
over long periods of time. Finally, they should respond to society's requirements
associated with safety and protection of the environment.
Graphite is commonly used as the negative electrode for Li-ion batteries. It is
considered however that lithium titanate oxide (ramsdellite, Li2Ti3O7) is a promising
material, by virtue of its electrochemical performance associated with its low
production cost and its non-toxicity. Such a negative electrode material functions at a
higher voltage than that of carbon (> IV), ensuring in this way better functioning
security. Moreover it is less subject to polarization, that is to say the potential
difference between charge and discharge, than graphite and thus lends itself to a use
requiring high power. The capacity of this material is however relatively low,
reaching approximately 130 Ah/kg on a low regime (C/15) and 100 Ah/kg on a high
regime (1 C) but has the advantage of having excellent reversibility during rapid
regime cycling.
The capacity and current density of this Li2Ti3O7 have been first of all improved by
substituting part of the Ti4+ by Fe3+. Then, and according to the teaching of EP-1 623
473, the reversible capacity at a low regime may now reach 140 Ah/kg, by virtue of a
supplementary substitution by one or more of the following elements: Ti3+, Co2+, Co3+,
Ni2+, Ni3+, Cu2+, Mg2+, Al3+, In3+, Sn4+, Sb3+, Sb5+. These substitutions also make it
possible to reduce the synthesis temperature, which reduces production costs.

The present invention proposes above all to improve a substituted ramsdellite, so as to
obtain improved specific capacity, while preserving the other properties of the existing
poly-substituted product.

The present invention relates more precisely to a negative electrode material that
responds to the aforementioned requirements.
The invention relates to an active material for a lithium battery electrode, comprising a
phase having a general formula in which M and M' are
metal ions of groups of 2 to 15 having an ionic radius between 0.5 and 0.8 A in an
octahedral oxygen environment, v, w, x, y, z and a being associated by the
relationships:
2 α = -v +4w-3x-ny-n'z, guaranteeing electroneutrality, with n and n' the respective
formal degrees of oxidation of M and M'; -0.5 ≤ v ≤ +0.5; y + z>0;x + y + z = w; and
0 < w ≤ 0.3; characterized in that at least part of the lithium is substituted by carbon
according to the relationship 0 < c ≤ (2+v)/4.
The M and M' ions may be selected from the list composed of Ti3+, Co2+, Co3+, Ni2+,
Ni3+ Cu2+, Mg2+, Al3+, In3+, Sn4+, Sb3+, et Sb5+. M is preferably Ni2+ and M' Al3+.
The best results are obtained with x ≤ 0.1; y ≤ 0.2; and z ≤ 0.1. Moreover, it is useful to
choose x : y : z ratios within a range 1 : 3.9 to 4.1 : 0.90 to 1.10. It is more
recommended to comply with c ≥ 0.1, preferably c ≥ 0.2.
Another object of the invention relates to a method for synthesizing the active material
defined above, and comprises the steps of:
- reactive mixing and grinding of precursor compounds containing the elements Li, Ti,
Fe, C, O, M and M';
- synthesis of the ceramic phase by heating the mixture in an inert atmosphere at a
temperature of 950 to 1050°C;
- rapid cooling of the ceramic phase.
It is self-evident that a person skilled in the art will be able to define the suitable
quantities of the various reactants, so that the synthesized product corresponds to the
general formula of the desired phase, as defined above.

During this process it is useful for cooling of the ceramic phase to be carried out at at
least 100°C/min, from the synthesis temperature up to no more than 400°C.
The invention also relates to the use of the active material defined above for the
manufacture of lithium cells, accumulators or batteries.
The invention finally relates to lithium cells, accumulators or batteries containing the
active material defined above.
The material of the invention has mass and volume capacities that may reach 190
Ah/kg, or 602 Ah/m3, that is to say greater than those of the prior art, while preserving
the prevously acquired advantages, notably:
- a small loss of capacity at the first cycle, of 2 to 10 Ah/kg;
- excellent cyclability;
- low polarization of 30 to 70 mV in C/15 regime.
The ramsdellite structure consists of a network comprising Ti and Li ions in an
octahedral oxygen environment and channels partly occupied by Li atoms in a
tetrahedral environment. This arrangement leaves a large number of vacant tetrahedral
sites in the channels and the Li/voids distribution may vary according to the synthesis
conditions. Substitution metals occupy the octahedral sites of the network.
It is demonstrated here that carbon may be partially or totally substituted for lithium to
lead to the formation of a modified ramsdellite, low in lithium. A certain number of
25insertion sites represented by the conventional notation correspond with
the general formula Li2+v-4cCcTi3-wFexMyM'zO7-α. This modification favors the
occupation of these sites, and on account of this improves the capacity of the original
material. It is not however excluded for the synthesized material to be a composite, in
particular for high values of the parameter c. The synthesized material therefore
comprises a carbonaceous ramsdellite phase low in Li, and as the case may be also a
non-carbonaceous ramsdellite enriched with Li.
It should be noted that it is tetrahedral lithium that is substituted by carbon,

constituting a CO32- group while being placed in the plane of 3 oxygens, the number of
voids then being dependent on the values of v, x, y, z and c in the general formula
above. For limiting values of substitutions of Li by C, the phase is emptied of
structural lithium. It should be noted that any excess carbon will be deposited
preferably at the grain boundaries and could improve the conductivity of the material.
The first step of the method according to the invention comprises a reactive mixture of
compounds.
Solid precursors in the form of a fine powder are selected and mixed. This mixture
preferably comprises the oxides of Ti and Fe, as well as those of the metals M and M',
Other precursors are equally suitable, it being possible for these to be organic and/or
inorganic compounds capable of forming Me-O-Me bonds (where Me is a metal) by
condensation or hydrolysis/condensation. Reference may be made, as an example, of
oxides, carbonates, acetates, hydroxides, chlorides (e.g. AlCl3), nitrates, Me-
oxoalkoxides, this not being exhaustive and a person skilled in the art will know how
to complete this. As regards lithium, this may be provided by another precursor, such
as an oxide, hydroxide or chloride. Li2CO3 is however preferred.
The mixture will also include carbon or precursors of carbon that will be the most
simple carbohydrate-containing phases, such as saccharides or derivatives of
saccharides, for example glucose, fructose, sucrose, ascorbic acid, and polysaccharides
corresponding to the condensation of saccharides, such as starch, cellulose and
glycogen.

The proportion of each of the metals in the mixture of precursors corresponds to the
stoichiometric proportion of the material in question, leading to the formation of the
composite. The proportion of carbon will be calculated taking account of losses of CO
and CO2 by oxidation. This proportion it may be increased if an excess of carbon is
desired at the grain boundaries.
The second step of the method according to the invention comprises heat treatment.

According to the invention, heat treatment is carried out in a controlled atmosphere
(e.g. N2, Ar). It is carried out at a temperature that may lie between 980°C and
1050°C, preferably between lh 30 and 2h in order to obtain good crystallinity,
connected with a limited particle size. The temperature rise to reach the reaction
plateau may be carried out in a single rapid step since it makes it possible to minimize
secondary reactions and die formation of undesirable titanates.
The last step consists of rapidly cooling the material.
The manufacturing process in its entirety is rapid and has reduced operating costs.
Description of the figures
Figure 1: Scanning electron photomicrographs of the material Li2Ti3O7 substituted
with Fe, Ni, Al without carbon (a) and with various carbon contents from 0.14 (b),
0.27 (c) and 0.68 (d) mole per mole of synthesized material.
Figure 2: Comparison of infrared spectroscopy bands between various materials
substituted with Fe, Ni, Al synthesized without carbon (a) with various carbon
contents, from 0.14 (b), 0.27 (c) and 0.68 (d) mole per mole of material synthesized.

Figure 3: Charge/discharge galvanostatic curves in C/15 regime of the material
Li2Ti3O7 substituted with Fe, Ni, Al without carbon (a) and with 0.27 (b) mole of
carbon per mole of synthesized material.
Figure 4: Specific capacities, in Ah/kg of active material as a function of the quantity
of carbon, in mole per mole of synthesized material, with C/15 and 1C regimes.
Comparative example 1
Example 1 concerns a ramsdellite Li2Ti3O7 substituted by three elements Fe, Ni, Al,
without carbon according to the general formula Li2+v-4cCcTi3-wFexNiyAlzO7-α, where c =
0; v = -0.14; w = 0.15; x = 0.025; y = 0.1; and z = 0.025. Reactive grinding of the
compounds Li2CO3 (0.7235 g), anatase TiO2 with a nanometric size (1.2028 g), Fe2O3
(0.02 lg), NiO (0.0393g) and finally A12O3 (0.0134g) was carried out in a Pulverisette ®

7 (duration 15 min; speed 8) with agate balls and a ratio of the weight of balls/weight
of product equal to 10. Heat treatment was carried out in a boat under Ar in a single
step. A ramp of 7°C/min was applied up to the synthesis temperature of 980°C, this
temperature being maintained for 1h 30. Cooling was carried out rapidly in argon so
as to set the high temperature structure.
Examples 2 to 4
Examples 2 to 4 concern a ramsdellite Li2Ti3O7 substituted by three elements, Fe, Ni,
Al, and by carbon, according to the general formula Li2 +v-4cCcTi3.wFexNiyAlzO7-α, where
v = -0.14; w = 0.15; x = 0.025; y = 0.1 and z = 0.025 and 0.1 ≤ c ≤ 0.465. Sucrose was
added as a carbon precursor, representing 5, 10 and 15 weight % based on the total
weight weighed before synthesis. Refer to table 1 for the various carbon levels.
Reactive grinding of the compounds Li2CO3, anatase TiO2 of nanometric size, Fe2O3,
NiO, A12O3 in stoichiometric quantities, was carried out in a Pulverisette® 7 (duration
min; speed 8) with agate balls and a ratio of the weight of balls/weight of product
equal to 10. Heat treatment was carried out as in example 1.

Figure 1 shows scanning electron photomicrographs of various synthesized examples.
The base material without carbon according to example 1 shows (a) aggregates 10-20
µm in diameter with a porous texture. By substituting the ramsdellite phase with
various carbon levels according to examples 2 to 4, a change in morphology and
texture was observed (b-d) creating an agglomerate of particles and filaments. With
0.68 mole of carbon, according to example 4, the remainder of carbon (d) appears at

the grain boundaries resulting in an excess of this element during synthesis. It should
be noted in point of fact that the maximum carbon that can be inserted in the
ramsdellite structure for v = -0.14 is 0.465 mole/mole, that is a value for the parameter
c of 0.465.

The IR spectra of figure 2 show (b-d), for products prepared according to examples 2
to 4, the presence of vibration bands between 1430 and 1500 cm-1 characteristic of the
group CO32-. This confirms substitution of carbon in the ramsdellite structure. The
product prepared according to example 4 also shows (d) vibration bands towards 1650
cm-1. These correspond to conjugated C-C bands that belong to surface carbon.
Electrochemical tests were carried out in a half cell with two electrodes of which the
negative was a metallic lithium washer. The positive comprised a mixture of 85% by
weight of active material, 5% by weight of carbon black, and 10% by weight of PTFE
binder. The electrolyte used was LiPF6 (1 M) in ethylene carbonate, dimethyl
carbonate and propylene carbonate (1:3:1). Cycling was carried out in galvanostatic
mode at 25°C between 1 and 2.5 V vs Li/Li + at C/15 and 1 C regimes.
Figure 3 (a) shows charge and discharge curves (vs. Li) of the material without carbon,
prepared according to example 1. Figure 3 (b) corresponds to the material with
carbon, according to example 3. These measurements were carried out in galvanostatic
mode at a regime of C/15 between 1 and 2.5 V vs Li/Li+. The capacity observed for the
material without carbon was 130 Ah/kg. In figure 3 (b), the curve shows a shoulder
between 1.4 and 2.4 V. By virtue of the carbon, the values of the reversible capacities
were improved, reaching here 180 Ah/kg with a low irreversible capacity of 8 Ah/kg, and
a low polarization of 67 mV.
In figure 4, the values of specific capacities for the products prepared according to
examples 1 and 4 are shown as a function of the quantity of carbon measured in the
ramsdellite phase. With the two regimes, C/15 and C, the specific capacities increased
with the presence of carbon. The capacity was no longer improved beyond the saturation
point (c = 0.465, beyond which excess carbon was found on the surface of the material.

Claims
1. An active material for a lithium battery electrode, comprising a phase having a
general formula Li2 +v-4cCcTi3-wFexMyM'zO7-α, in which M and M' are metal ions of
groups of 2 to 15 having an ionic radius between 0.5 and 0.8 Å in an octahedral
oxygen environment, v, w, x, y, z and a being associated by the relationships:
2 a = -v +4w-3x-ny-n'z, with n and n' the respective formal degrees of oxidation of
M and M';
-0.5≤v≤+0.5;
y + z>0;
x + y + z = w; and 0 < w ≤ 0.3;
characterized in that at least part of the lithium is substituted by carbon according to
the relationship 0 < c ≤ (2+v)/4.
2. The active material as claimed in claim 1, characterized in that M and M' are
selected from the list composed of: Ti3+, C+o2+, Co3+, Ni2+, Ni3+ Cu2+, Mg2+, Al3+, In3+,
Sn4+, Sb3+ and Sb5+.
3. The active material as claimed in claim 1 or 2, characterized in that M is Ni2+
and M' is Al3+.
4. The active material as claimed in any one of claims 1 to 3, characterized in that
x≤0.1;
y ≤ 0.2; and
z≤0.1.
5. The active material; as claimed in any one of claims 1 to 4, characterized in
that the ratios x : y : z lie within a range of 1 : 3.9 to 4.1 : 0.90 to 1.10.
6. The active material as claimed in any one of claims 1 to 5, characterized in that
c ≥ 0.1, and preferably c ≥ 0.2.
7. The active material as claimed in any one of claims 1 to 6, characterized by the

presence of a phase substantially consisting of carbon.
8. A method for synthesizing the synthetic material as claimed in any one of
claims 1 to 7, comprising the steps of:
- reactive mixing and grinding of precursor compounds containing the elements Li, Ti,
Fe, C, O, M and M';
- synthesis of the ceramic phase by heating the mixture in an inert atmosphere at a
temperature of 950 to 1050°C;
- rapid cooling of the ceramic phase.

9. The method for synthesizing active materials as claimed in claim 8,
characterized in that cooling of the ceramic phase to be carried out at at least
100°C/min, from the synthesis temperature up to no more than 400°C.
10. Use for the manufacture of a lithium cell, accumulator or battery, from the
active material as claimed in any one of claims 1 to 7.
11. A lithium cell, accumulator or battery containing an active material as claimed
in any one of claims 1 to 7.

The present invention relates to lithium cells, accumulators and batteries, and more
particularly an active material for the negative electrode of rechargeable batteries.
It concerns more particularly a material comprising a phase having a general formula
Li2 +v-4cCcTi3-wFexMyM'zO7-α, in which M and M' are metal ions of groups of 2 to 15
having an ionic radius between 0.5 and 0.8 Å in an octahedral oxygen environment, v,
w, x, y, z and a being associated by the relationships:
2 α = -v +4w-3x-ny-n'z, with n and n' the respective formal degrees of oxidation of M
and M'; -0.5 ≤ v ≤ +0.5; y + z>0;x + y + z = w; and 0 < w ≤ 0.3; characterized in that
at least part of the lithium is substituted by carbon according to the relationship 0 < c ≤
(2+v)/4.
The material has improved mass and volume capacities that may reach 190 Ah/kg,
while preserving the previously acquired advantages, notably:
- a small loss of capacity at the first cycle, of 2 to 10 Ah/kg;
- excellent cyclability;
- low polarization of 30 to 70 mV in C/15 régime.