WO2014064361A1

WO2014064361A1 - Negative electrode for an electrochemical energy storage cell, corresponding electrochemical cell and battery and use thereof in an electric vehicle

Info

Publication number: WO2014064361A1
Application number: PCT/FR2013/052435
Authority: WO
Inventors: Bruno DELOBEL
Original assignee: Renault S.A.S
Priority date: 2012-10-24
Filing date: 2013-10-11
Publication date: 2014-05-01
Also published as: FR2997228B1; FR2997228A1

Abstract

The invention relates to a negative electrode that can be used in an Li-ion-type electrochemical energy storage cell, said negative electrode being made from a composite material comprising a carbon compound that can receive lithium inserted therein and a pre-determined proportion of Li₃X, wherein X is selected from N, P, As, Sb. The invention also relates to an electrochemical cell provided with such a negative electrode, an L-ion battery comprising at least one such electrochemical cell and the use of said battery in order to supply electric power to the electric motor of an electric vehicle.

Description

NEGATIVE ELECTRODE FOR ELECTROCHEMICAL ENERGY STORAGE CELL, CORRESPONDING ELECTROCHEMICAL CELL AND BATTERY AND USE THEREOF

ELECTRIC VEHICLE

The invention relates to the field of lithium batteries, in particular for use in the field of electric motor vehicles.

In general, the accumulators or batteries are formed of at least one electrochemical cell for storing electrical energy, each cell comprising a positive electrode, a negative electrode and an electrolyte between these electrodes. Several electrochemical cells, for example four to twenty cells, can be grouped into a module and a battery can comprise one or more modules. Thus, a battery, especially for a motor vehicle, can comprise nearly 200 cells and weigh between 150 and 300 kilograms.

There are two main types of lithium batteries. The first is the lithium metal battery, where the negative electrode is composed of lithium metal. The second type is the so-called "lithium-ion" accumulator, where the lithium remains in the ionic state thanks to the use of an insertion compound both at the negative electrode, generally in graphite, and the positive electrode, which may be cobalt dioxide, manganese dioxide or iron phosphate. The so-called lithium polymer batteries are an alternative to lithium-ion batteries, they deliver a little less energy, but are much safer.

Other lithium batteries are of the "lithium-air" and "lithium-sulfur" type.

Unlike other accumulators, lithium-ion batteries are not linked to an electrochemical couple. Any material that can accommodate lithium ions can be the basis of a lithium ion battery. This explains the profusion of existing variants, faced with the consistency observed with other couples. It is therefore difficult to draw general rules about this battery, markets of high volume (mobile electronics) and high energy (automotive, aerospace, etc.) not having the same needs in terms of lifetime, cost or power. Lithium-ion batteries have the main advantages of a high mass energy (two to five times more than the Ni-MH for example) as well as the absence of memory effect. Finally, the self-discharge is relatively small compared to other accumulators. However, the cost remains high and has long confined lithium to small systems.

The composite material constituting a positive lithium-ion battery electrode may comprise transition metals in a form capable of solubilizing in the electrolyte of the battery. Due to this solubilization, migration of a transition metal cation can occur from the positive electrode to the negative electrode, which can cause a loss of battery capacity.

This loss of capacity can be due to two different mechanisms: (A) - lithium extrusion of a graphite-based negative electrode LiCe according to the reaction: M ^{+ n} + nLiCe-> M + nLi ⁺ + nCe (1 )

(B) - pollution of the solid passivation layer by transition metal cations. This solid lithium-based passivation layer, called the solid electrolyte interphase (SEI) layer, is formed on the surface of the negative electrode. This SEI layer, electrically insulating but still providing sufficient ionic conductivity, prevents decomposition of the electrolyte after the second charge of a battery and also protects the negative electrode. It is generally accepted that the presence of this layer plays a key role in battery performance by ensuring the viability of lithium-ion technology. This pollution of the SEI layer is known and generates an increase in lithium consumption and thus an acceleration of the loss of capacity of the battery.

Although not negligible, the degradation due to lithium extrusion is generally much lower than the degradation due to pollution of the SEI layer.

Document US2007 / 020241 1A1 proposes a solution for limiting the capacity loss due to the migration of transition metal cations in a Li-ion battery whose cathode comprises a material containing manganese. This solution consists in covering the anode with an inorganic material based on titanium, such as T1O2 and T1S2, having a certain affinity with manganese. Due to this affinity, the manganese deposits on the inorganic material rather than on the anode, so that the anode is preserved. This affinity of the inorganic material however, has been described for manganese only and not for other transition metals.

There is therefore a need to reduce the loss of capacity of the batteries due to the migration of transition metal cations to an anode comprising carbon, in particular an anode which can be degraded by the presence of transition metal cations in the process. 'electrolyte.

For this purpose, the subject of the invention relates to a negative electrode of an electrochemical cell for storing electrical energy, said negative electrode being made of a composite material comprising a carbon compound capable of receiving lithium in insertion and a predetermined proportion. of L13X, with X selected from N, P, As, Sb.

The Applicant has discovered that this compound L13X acts as a transition metal trap, which makes it possible to limit a loss of capacity due to migration of cations of a transition metal and inducing lithium extrusion and / or pollution of the metal. the SEI at the negative electrode.

The transition metal can be any element from periods 4 to 7 and groups 3 to 12 of the periodic table of classification (IUPAC), except for lanthanides and actinides. In particular, the transition metal may be any element usually used in the constitution of positive electrodes, such as cobalt, nickel, iron or manganese. Trapping is likely to occur for different cations present simultaneously in the electrolyte of an electrochemical cell.

Without being bound by theory, the trapping of the transition metals could occur by substitution of lithium ions of the L13X compound with the cations of the transition metal present in the electrolyte (or transition metals present in the electrolyte).

For example, the mechanism could be the following for an anode based on LiCo graphite, in the presence of manganese cations:

Li ₃ X + Mn + ² + LiC ₆ Li ₃ MnX + Ce + Li ⁺ (2)

Mn + ² + Li ₃ Mn + LiC ₆ + Ce + Li ₂ Mn ₂ X + Li ⁺ (3)

Mn ² + Li ₂ Mn ₂ X + LiC ₆ ^ Ce + X + Li LiMn ₃ ⁺ (4)

Mn + ² + LiMn ₃ X + LiCl ₆ Ce + Mn ₄ X + Li ⁺ (5)

Or, the mechanism could be the following for an anode based on LiCo graphite, in the presence of iron cations:

Fe ⁺³ + Li ₃ X + LiC ₆ C ₆ + Li ₂ FeX + ₂ Li ⁺ (6) Fe ⁺³ + Li ₂ FeX + LiCe ^ C ₆ + LiFe ₂ X + 2Li ⁺ (7)

Fe ⁺³ + LiFe ₂ X + LiCe ^ C ₆ + Fe ₃ X + 2Li ⁺ (8)

Similar mechanisms can be envisaged for all transition metals, namely the elements of periods 4 to 7 and groups 3 to 12 of the periodic table of classification (IUPAC), except for lanthanides and actinides.

A combination of these reactions is not excluded when different cations are simultaneously present in the electrolyte of an electrochemical cell.

The amount of L13X of the composite material can be determined according to the estimated amount of transition metal cation likely to be present in the electrolyte over the lifetime of an electrochemical cell for a given application. It has been measured that the amount of transition metal cation can reach at most 1000 ppm for Li-ion batteries used in the field of motor vehicles. The amount of L13X of the composite material may be from 2 to 500 times greater than the estimated amount L13X calculated.

It must be understood that the composite material in question is a "raw" composition before any use, which does not result from an electrochemical reaction with lithium.

Very advantageously, the amount of L13X is in the range from 0.01% to 15% by weight of LiaX relative to the total mass of the composite material, for example from 0.1% to 10% by weight of L13X. relative to the total mass of the composite material, in particular from 1% to 8% by weight of LiaX relative to the total mass of the composite material.

The negative electrode is conventionally a conductive insertion electrode, advantageously based on conductive carbon.

The carbon compound capable of receiving lithium by insertion of the composite material may be chosen from graphite (natural or synthetic), coke, anthracite, graphitic carbon derived from petroleum pitch (for example MCMB: meso carbon micro bead "or mesocarbon microbead), carbon fibers, carbon whiskers, crosslinked vitreous carbons, pyrolytic carbons, fullerenes, carbon nanotubes, or any other form of amorphous or crystalline carbon. Mixtures of several kinds of these carbons may also be employed. The proportion of carbon compound capable of receiving lithium in insertion is, for example, in the range from 70% to 98% relative to the total weight of the composite material.

The composite material may also comprise a binder, for example of the vinylidene fluoride (PVDF) polymer type, the copolymers thereof, for example with hexafluoropropylene, such as polyvinylidene-hexafluoropropylene fluoride (PVDF). HFP), and mixtures thereof.

The proportion of binder is for example in the range of values ranging from 1% to 10% relative to the total weight of the composite material.

The composite material may also comprise conductive carbon, for example at contents of 1% to 15% by weight relative to the total weight of the electrode. This conductive carbon is for example carbon black (for example Ketjen Black or SUPER P® carbon black), MCMB, graphite, hard carbon ("hard carbon" in English), or soft carbon (" soft carbon ").

The negative electrode can thus comprise:

carbon, preferably at levels of 70% to 98% by weight relative to the total weight of the electrode, for example graphite, a binder, preferably at levels of 1% to 10% by weight relative to total weight of the electrode

L13X, preferably at levels as specified above.

The sum of the respective proportions of L13X, carbon, and binder is 100%.

The negative electrode may also comprise conductive carbon, preferably at levels of 1% to 15% by weight relative to the total weight of the electrode, the sum of the respective proportions of L13X, carbon, conductive carbon and binder being 100%.

Such negative electrodes can be prepared by mixing the above components used in the composition of the composite material, for example in the form of a powder, in the presence of a solvent for solubilizing the binder.

Conventionally, the powder mixture is dispersed in the binder, for example consisting of polyvinylidene fluoride (PVDF), dissolved in an organic solvent, such as N-vinylpyrrolidone. The mass ratio of the Solvent on the total mass of the components of the composite material varies in the range of 0.05 to 0.8. The whole is a slurry, or paste, this suspension or paste or ink which therefore comprises in particular the carbon, L13X and the polymeric binder, is then applied to an electrode collector constituted by a metal sheet, such as a sheet of copper or thin aluminum. The suspension is then dried to remove the solvent, typically at temperatures between 100 ° C and 170 ° C, for 1 h-48 h.

Alternatively, it is conceivable to deposit a layer of L13X on the surface of a previously manufactured negative electrode by any suitable method. For example, the negative electrode can be immersed in a solution containing L13X, then the evaporated solution and the dried electrode, for example at temperatures between 100 ° C and 170 ° C, for 1h-48h.

The invention also relates to an electrochemical cell comprising a negative electrode according to the invention made of a composite material comprising a carbon compound capable of receiving lithium in insertion and a predetermined quantity of L13X, with X chosen from N, P, As, Sb.

The negative electrode according to the invention is that described above.

The electrochemical cell further comprises conventionally a positive electrode and an aprotic electrolyte so that this cell can perform its function.

The positive electrode of an electrochemical cell is conventionally made of a composite material comprising at least one lithiated component.

The lithiated component is not limited and may be any material used or usable in the field including Li-ion batteries.

This lithiated component may be a lithium component selected from LiMO ₂ , L1M2O4, Li ₂ MSiO ₄ and LiMPO ₄ (M = transition metal). Advantageously, it may be a lithiated metal oxide component and in particular an oxide component of a lithiated transition metal.

Particularly preferably, the lithiated component is selected from the group consisting of L 1 COO 2, LiNiX _x Co _x - _z Al _z O 2 (with 0 <x <1.0 <z <0.2), Li _{1+ a} (NibMn _c Coci) i-aO2 with (b + c + d = 1.0 <a <0.2), Lii _{+ e} Mn ₂ -eO ₄ with 0 <e <0.2, LiMn ₂ - _f NifO ₄ with 0 < f <0.5, LiMPO ₄ with M = Fe, Mn, Co, Ni, L1COO2, LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiFePO ₄ , LiFePO ₄ / C, LiNi _x Al _x O ₂ , Li [ Ni _x Co ₍ i_xx) Mn] 0 ₂ . Among these materials, LiNiO2 has the best potential for L1COO2. Indeed, LiMn2O ₄ despite its low cost and low toxicity, has a significant loss of capacity cycling. The orthorhombic or lamellar LiMnO2 phases prepared by exchange turn into spinels during the cycles. The LiFePO ₄ component, whose limitations in cycling resulting from slow lithium intercalation and deintercalation kinetics, can be compensated by the use of nanocomposite materials such as LiFePO ₄ / C, characterized by a large exchange surface with the nanoparticles. current collectors.

The proportion of lithiated component in the composite material constituting said positive electrode is advantageously between 80% and 98% by weight relative to the total weight of the composite material. A proportion selected from this range confers the best conductivity properties of the species in the electrochemical cell, which would be explained by an intimate structure of the composite material optimal in terms of texture and porosity.

Advantageously, the composite material of the positive electrode further comprises a conductive component, preferably conductive carbon, in proportions preferably of between 1 and 15% by weight relative to the total weight of the composite material.

The composite material may also comprise a binder, which may be the same as that described above, in proportions preferably of between 1 and 10% by weight relative to the total weight of the composite material.

The sum of the respective proportions of lithium compound, conductive carbon, and binding of the positive electrode is 100%.

The aprotic electrolyte advantageously comprises a lithium salt, such as LiPF ₆ LiClO ₄ , LiBF ₄ , LiTFSI and LiFSI, in mixtures of organic carbonates, preferably alkyl carbonates, such as ethylene carbonate, propylene, dimethyl, ethylmethyl, diethyl and mixtures thereof, or tetrahydrofuran. Such an aprotic electrolyte is necessary to avoid degrading very reactive electrodes. The concentration of lithium salt is preferably in the range of 0.7 M to 1.2 M.

The positive and negative electrodes can be separated by a separator, for example a polymer such as polypropylene, soaked with aprotic electrolyte. Advantageously, the electrochemical cell is a Li-ion battery or accumulator or is part of a Li-ion battery or accumulator.

Such Li-ion batteries are widely known and their mode of operation, and many developments and improvements are the subject of publications and marketing. Those skilled in the art will refer to encyclopaedias and other reference works, the invention being in no way limited to the arrangement of the battery, to the sizes and shapes of the positive and negative electrodes, to the electrolytes, to the various devices necessary for the operation of said Li-ion battery or for its manufacture, such as current or voltage supply devices, provided that they achieve the intended purpose.

The invention finally relates to the use of a Li-ion battery or accumulator according to the invention for supplying an electric motor of a motor vehicle.

The invention is described in more detail by the following examples with reference to FIG. 1, which illustrates a graph representing the capacity degradation due to the presence of transition metal cations, with a conventional negative electrode (example 1) and a negative electrode containing according to the invention L13N.

Example 1 (comparative)

A positive electrode of 10 Ah of capacity containing LiNii / 3MnI / 3CeI / 302, conductive carbon, the binder PVDF-HFP is prepared according to the proportions:

76.92 g LiNii / 3MnI / 3CeI / 302, considering that the specific capacity of this material is 0.130 Ah. g ¹ .

3.27 g of carbon conductive carbon SUPER P®

2.45 g of PVDF-HFP,

- 50 g of NMP (N-methyl-2-pyrrolidone) in order to have a mass ratio of the solvent / (mass of the three powders + solvent mass) equal to 0.38.

The powders of these three components are mixed in the presence of NMP solvent to create an ink. The ink is then spread on a current collector and dried at 150 ° C for 24 hours.

A negative electrode of 10 Ah of capacity containing graphite, conductive carbon, a PVDF-HFP binder is prepared according to the proportions: - 26.88g of graphite (90%), the graphite having a specific capacity of 0.372 Ah. g ¹

- 1, 15g carbon conductive carbon (4%) SUPER P®

0.896 g of PVDF-HFP (3%)

- 50g of NMP

The positive and negative electrodes are then assembled and separated by a polypropylene separator impregnated with an electrolyte composed of 1M LiPF 6 dissolved in a mixture of ethylene carbonate / dimethyl carbonate (1: 1 by mass).

The solid line curve of FIG. 1 represents the impact of the presence of transition metal cations on the usable capacity of the positive electrode compared to the negative electrode.

Thus for a Li-ion cell of 10 Ah, there is a loss of capacity of nearly 35% after 140 days of use. It will be noted that such a loss of capacitance can not be due solely to the lithium extrusion of the negative electrode according to the mechanism (A) described above. Indeed, the extrusion reaction (1) would generate a loss of 0.05Ah for a cell of 10Ah, a loss of 0.5%. The solid curve shows that the loss of capacity is much greater, confirming that the main degradation is due to pollution of the SEI according to the mechanism (B).

Example 2

A positive electrode of 10 Ah of capacity containing LiNii _/ 3MnI _/ 3CeI _/ 302, conductive carbon is prepared, the PVDF-HFP binder identical to that prepared in Example 1.

A negative electrode of 10 Ah of capacity containing graphite, conductive carbon, a binder PVDF-HFP and L13N is prepared according to the proportions:

- 26.88g of graphite, the graphite having a specific capacity of 0.372 Ah.g ¹

- 1, 15g of conductive carbon

- 0.896g of PVDF-HFP

- 0.896g of Li ₃ N - 50g of NMP

The respective mass proportions (excluding the solvent) are: 90%; 4%; 3% and 3% (Li ₃ N).

The powders of these four components are mixed in the presence of NMP solvent to create an ink. The ink is then spread on a current collector and dried at 150 ° C for 24 hours.

The positive and negative electrodes are then assembled and separated by a polypropylene separator impregnated with an electrolyte composed of 1M LiPF6 dissolved in a mixture of ethylene carbonate / dimethyl carbonate (1: 1 by mass).

Assuming that it will be necessary to trap 1000 ppm of manganese ions (9, 1 10 ^{~ 4} moles of Mn ^{+ 2} ) present in the electrolyte during the life of the electrochemical cell, and assuming that one mole of L13N makes it possible to capture 4 moles of Mn ²⁺ ion (according to the reactions (1) to (4) described above), it is then necessary to take 7.9 mg of L13N to capture these 100Oppm, which would represent only 0.027% in mass of L13N with respect to the total mass of the electrode.

The amount of L13N added in the present example is much greater than the minimum amount calculated on the basis of reactions (1) to (4).

The dotted line curve of FIG. 1 represents the degradation of the usable capacitance of the positive electrode compared to the negative electrode when L13N is added to the negative electrode. Note that the degradation of the capacity is of the order of 15% only after 140 days of use, a gain of capacity of nearly 25% compared to a negative electrode devoid of L13N (Example 1).

Claims

1. Negative electrode of an electrochemical cell for storing electrical energy, said negative electrode being made of a composite material comprising a carbon compound capable of receiving lithium in insertion and a predetermined proportion of L13X, with X chosen from N, P, As, Sb.

The negative electrode according to claim 1, wherein the amount of L13X is in the range of 0.01% to 15% by weight of LiaX based on the total mass of the composite material.

A negative electrode according to claim 1 or 2, wherein the amount of L13X is in the range of 0.1% to 10% by weight of LiaX based on the total mass of the composite material.

4. Negative electrode according to one of claims 1 to 3, wherein the carbon compound capable of receiving lithium insertion of the composite material may be selected from graphite (natural or synthetic), coke, anthracite, carbon graphite from petroleum pitch, carbon fibers, carbon whiskers, cross-linked vitreous carbons, pyrolytic carbons, fullerenes, carbon nanotubes, any other form of amorphous or crystalline carbon, or a mixture of several kinds of these carbons.

5. Negative electrode according to one of claims 1 to 4, wherein the proportion of carbon compound capable of receiving lithium insertion is for example in the range of values ranging from 70% to 98% relative to the total weight of composite material.

6. Electrochemical cell comprising a negative electrode according to one of the preceding claims.

7. The electrochemical cell of claim 6, wherein the positive electrode is a composite material comprising at least one lithiated component.

Lithium-ion battery comprising at least one electrochemical cell according to claim 6 or 7.

9. Use of a lithium-ion battery according to claim 8 for supplying an electric motor of a motor vehicle.