SPECIFIC ELECTROCHEMICAL CELL FOR ACCUMULATOR OPERATING ACCORDING TO THE PRINCIPLE OF FORMING AN ALLOY WITH THE ACTIVE MATERIAL OF THE NEGATIVE ELECTRODE COMPRISING A SPECIFIC PAIR OF ELECTRODES

Abstract

An electrochemical cell for an accumulator operating according to the principle of forming an alloy with the active material of the negative electrode during the charge process comprising: a negative electrode comprising, as active material, a material alloyable with an element M, M being a metal element; a positive electrode comprising, as active material, a conversion material; an electrolyte comprising at least one salt of M disposed between the negative electrode and the positive electrode.

Claims

1. An electrochemical cell for accumulator operating according to the principle of forming an alloy with the active material of the negative electrode during the charge process comprising: a negative electrode comprising, as active material, an active material comprising a material alloyable with an element M, M being an alkali element or an alkaline earth element ; a positive electrode comprising, as active material, an active material comprising a conversion material; an electrolyte comprising at least one salt of M disposed between the negative electrode and the positive electrode.

2. The electrochemical cell according to claim 1, wherein the element M is an alkaline element selected from: lithium, the alloyable material comprising, in this case, lead with oxidation degree 0, tin with oxidation degree 0, silicon with oxidation degree 0, germanium with oxidation degree 0, antimony with oxidation degree 0, phosphorus with oxidation degree 0 or combinations thereof; sodium, the alloyable material comprising, in this case, lead with oxidation degree 0, tin with oxidation degree 0, silicon with oxidation degree 0, germanium with oxidation degree 0, antimony with oxidation degree 0, phosphorus with oxidation degree 0 or combinations thereof; potassium, the alloyable material comprising, in this case, lead with oxidation degree 0, tin with oxidation degree 0, silicon with oxidation degree 0, germanium with oxidation degree 0, antimony with oxidation degree 0, phosphorus with oxidation degree 0 or combinations thereof.

3. The electrochemical cell according to claim 1, wherein the element M is lithium and the alloyable material comprises silicon with oxidation degree 0.

4. The electrochemical cell according to claim 1, wherein the active material of the negative electrode further comprises at least one active element capable of intercalating the element M during the charge process.

5. The electrochemical cell according to claim 4, wherein the active element is graphite.

6. The electrochemical cell according to claim 1, wherein the negative electrode further comprises: a polymer binder; and/or one or more electrically conductive adjuvants.

7. The electrochemical cell according to claim 1, wherein the conversion material comprises a fluoride of at least one transition metal element, a phosphide of at least one transition metal element, a sulphide of at least one transition metal element, an oxide of at least one transition metal element and/or mixtures thereof.

8. The electrochemical cell according to claim 1, wherein the conversion material is a fluoride of at least one transition metal element.

9. The electrochemical cell according to claim 1, wherein the conversion material is an iron and copper fluoride.

10. The electrochemical cell according to claim 1, wherein the positive electrode further comprises: a polymer binder; and/or one or more electrically conductive adjuvants.

11. The electrochemical cell according to claim 1, wherein the electrolyte is a liquid electrolyte comprising one or more organic solvents and at least one salt of M.

12. The electrochemical cell according to claim 11, wherein the organic solvent(s) are carbonate solvents.

13. The electrochemical cell according to claim 11, wherein the salt(s) of M are selected from the salts of the following formulas: MI, M(PF.sub.6).sub.n, M(BF.sub.4)n, M(ClO.sub.4).sub.n, M(bis(oxalato)borate).sub.n, MCF.sub.3SO.sub.3, M[N(FSO.sub.2).sub.2].sub.n, M[N(CF.sub.3SO.sub.2).sub.2].sub.n, M[N(C.sub.2F.sub.5SO.sub.2).sub.2].sub.n, M[N(CF.sub.3SO.sub.2)(R.sub.FSO.sub.2)].sub.n, wherein R.sub.F is group C.sub.2F.sub.5, C.sub.4F.sub.9 or CF.sub.3OCF.sub.2CF.sub.3, M(AsF.sub.6).sub.n, M[C(CF.sub.3SO.sub.2).sub.3].sub.n, M.sub.2S.sub.n, M(C.sub.6F.sub.3N.sub.4), C.sub.6F.sub.3N.sub.4 corresponding to 4,5-dicyano-2-(trifluoromethyl) imidazole, M being an alkali element or an alkaline earth element and n corresponds to the degree of valence of the element M.

14. The electrochemical cell according to claim 11, wherein the electrolyte includes one or more additives selected from vinylidene carbonate, fluoroethylene carbonate and mixtures thereof.

15. The electrochemical cell according to claim 1, which is a cell comprising: a negative electrode comprising, as active material, a graphite-silicon composite; a positive electrode comprising, as active material, an iron and copper fluoride; an electrolyte comprising a mixture of carbonate solvents, a lithium salt and, as additives, vinylidene carbonate and trifluoroethylene carbonate.

16. A lithium accumulator comprising one or more electrochemical cells as defined in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] FIG. 1 is a graph illustrating the evolution of the discharge capacity C (in mAh/g) as a function of the number of cycles N for batteries exemplified in Example 1 below.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

EXAMPLE 1

[0065] This example illustrates the preparation of a cell according to the invention in the form of a button battery comprising:

[0066] as negative electrode, a negative electrode comprising, as active material, a silicon-graphite composite; and

[0067] as a positive electrode, an electrode comprising, as active material, an iron and copper fluoride corresponding to the formula Cu.sub.0.5Fe.sub.0.5F.sub.2; and

[0068] an electrolyte placed between said positive electrode and the negative electrode, the composition of which will be explained below.

[0069] First, the active material of the positive electrode with the formula Cu.sub.0.5Fe.sub.0.5F.sub.2 is prepared by ball milling. For this purpose, an equivalent number of moles of the two precursors CuF.sub.2 and FeF.sub.2 (obtained from the supplier Aldrich) were placed in a 50 mL stainless steel grinding bowl containing 15 balls of different diameters. The grinding bowl, filled under argon in a glove box, is closed by a flange and placed on a RETCH PM100 planetary mill. After a grinding time of 12 hours at 300 revolutions/min, the grinding bowl is unloaded in a glove box under argon and the material in powder form is characterised by X-ray diffraction under kapton, in order to preserve its structure.

[0070] The powder thus obtained is thoroughly mixed up in an amount of 80%, in a glove box and under argon, with 10% Super P carbon, 10% polyvinylidene fluoride (PVDF) in N-methyl-2-pyrrolidone (NMP), the resulting mixture being coated on an aluminium strip with a doctor blade set to a wet thickness of 100 m. After drying under vacuum at 80 C., the electrode is then obtained by cutting a disc with a diameter of 14 mm followed by compression, still under argon.

[0071] Secondly, the negative electrode is prepared, in a dry room, by mixing the active material, which is a silicon-graphite (60/40) composite, with carboxymethylcellulose (CMC), a styrene-butadiene (SBR) latex and carbon fibres VGCF, said active material being present in an amount of 88% by mass of the mixture, carboxymethylcellulose being present in an amount of 2% by mass of the mixture, the latex being present in an amount of 4% by mass of the mixture and the fibres being present in an amount of 6% by mass of the mixture. The mixture is then deposited on a copper strip. The electrode is then obtained by cutting a disc with a diameter of 16 mm.

[0072] The negative electrode thus obtained is subjected to a prelithiation (in other words, so that it is in the charged state) by mounting it in a button battery facing a metallic lithium electrode, the two electrodes being separated by a Celgard 2500 type separator impregnated with an electrolyte comprising a mixture of carbonate solvents (ethylene carbonate/diethyl carbonate) (1:1 by volume), vinylidene carbonate in an amount of 2% by mass relative to the total mass of the electrolyte, trifluoroethylene carbonate in an amount of 10% by mass relative to the total mass of the electrolyte and a lithium salt LiPF.sub.6 (1M).

[0073] After prelithiation, the button battery is removed in a glove box then the negative electrode is recovered and rinsed with dimethyl carbonate and then dried under argon. The negative electrode is then mounted in a button battery facing the positive electrode comprising, as active material, Cu.sub.0.5Fe.sub.0.5F.sub.2, this positive electrode having an equivalent capacity, so as to balance the button battery. In this battery, the two electrodes are separated by a Celgard 2500 type separator impregnated with an electrolyte comprising a mixture of carbonate solvents (ethylene carbonate/diethyl carbonate) (1:1 by volume), vinylidene carbonate in an amount of 2% by mass relative to the total mass of the electrolyte, trifluoroethylene carbonate in an amount of 10% by mass relative to the total mass of the electrolyte and a lithium salt LiPF.sub.6 (1M).

[0074] In parallel, a similar button battery is produced except that the negative electrode including, as active material, a silicon-graphite composite, is replaced by a negative electrode made of metallic lithium.

[0075] The two button batteries are subjected to electrical tests at C/50 between 4.25 V and 1 V and the evolution of the discharge capacity C (in mAh/g) is determined as a function of the number of cycles N, the results being reported on the single figure (called [FIG. 1]) attached in the annex (curve a) for the battery in accordance with the invention and curve b) for the battery not in accordance with the invention).

[0076] It appears that the button battery in accordance with the invention has a higher discharge capacity than the button battery not in accordance with the invention, for example, a discharge capacity of about 240 mAh/g for the second cycle for the button battery in accordance with the invention against 150 mAh/g for the button battery not in accordance with the invention.