阅读说明：本技术 用于锂离子电化学电池的电解质组合物 (Electrolyte composition for lithium-ion electrochemical cells ) 是由 朱利安·德莫 马莱内·奥斯瓦尔德 于 2020-03-02 设计创作，主要内容包括：一种用于锂离子电化学电池的电解质组合物,其包含：-至少一种四氟化或六氟化锂盐,-双(氟磺酰基)酰亚胺锂LiFSI盐,-碳酸亚乙烯酯,-硫酸亚乙酯,-二氟磷酸锂,-选自环状或线性碳酸酯、环状或线性酯、环状或线性醚及其混合物的至少一种有机溶剂,在添加至溶剂之前,硫酸亚乙酯的质量与碳酸亚乙烯酯的质量之比严格小于1,双(氟磺酰基)酰亚胺锂的质量百分比占由所述至少一种四氟化或六氟化锂盐、所述双(氟磺酰基)酰亚胺锂盐和所述至少一种有机溶剂组成的组的质量的小于1％。在锂离子电化学电池中使用该组合物增加了电池的寿命,尤其是在低温和高温循环条件下。(An electrolyte composition for a lithium-ion electrochemical cell, comprising: -at least one lithium salt of tetrafluoride or hexafluoride, -lithium bis (fluorosulfonyl) imide LiFSI salt, -vinylene carbonate, -ethylene sulfate, -lithium difluorophosphate, -at least one organic solvent selected from cyclic or linear carbonates, cyclic or linear esters, cyclic or linear ethers and mixtures thereof, the ratio of the mass of ethylene sulfate to the mass of vinylene carbonate being strictly less than 1 before addition to the solvent, the mass percentage of lithium bis (fluorosulfonyl) imide representing less than 1% of the mass of the group consisting of said at least one lithium salt of tetrafluoride or hexafluoro, said lithium salt of bis (fluorosulfonyl) imide and said at least one organic solvent. The use of the composition in a lithium-ion electrochemical cell increases the life of the cell, especially under low and high temperature cycling conditions.)

1. An electrolyte composition comprising:

-at least one lithium tetrafluoride or hexafluoro salt,

-lithium bis (fluorosulfonyl) imide LiFSI salt,

-a vinylene carbonate (C-CO),

-an ethylene sulphate,

-a lithium difluorophosphate,

-at least one organic solvent selected from the group consisting of cyclic or linear carbonates, cyclic or linear esters, cyclic or linear ethers and mixtures thereof,

the ratio of the mass of ethylene sulfate to the mass of vinylene carbonate before addition to the solvent is strictly less than 1,

the mass percentage of lithium bis (fluorosulfonyl) imide is less than 1% of the mass of the group consisting of the at least one lithium tetrafluoride or hexafluoroide salt, the lithium bis (fluorosulfonyl) imide salt, and the at least one organic solvent.

2. The electrolyte composition of claim 1, wherein the lithium tetrafluoride or hexafluoro salt is selected from lithium hexafluorophosphate, LiPF₆Lithium hexafluoroarsenate LiAsF₆Lithium hexafluoroantimonate LiSbF₆And lithium tetrafluoroborate LiBF₄。

3. The electrolyte composition of claim 1 or 2, wherein lithium ions from the lithium bis (fluorosulfonyl) imide salt comprise at least 30 mole% of the total amount of lithium ions present in the electrolyte composition.

4. The electrolyte composition of one of claims 1 to 3, wherein lithium ions from the lithium tetrafluoride or hexafluoroide salt constitute up to 70 mol% of the total amount of lithium ions present in the electrolyte composition.

5. The electrolyte composition according to one of the preceding claims, wherein the mass percentage of vinylene carbonate represents between 0.1% and 5%, preferably between 0.5% and 2%, of the mass of the group consisting of the at least one lithium tetrafluoride or hexafluoroide salt, the lithium bis (fluorosulfonyl) imide salt and the at least one organic solvent.

6. The electrolyte composition according to one of the preceding claims, wherein the mass percentage of ethylene sulfate is comprised between 0.1% and 5%, preferably between 0.5% and 1% of the mass of the group consisting of the at least one lithium tetrafluoride or hexafluoroide salt, the lithium bis (fluorosulfonyl) imide salt LiFSI and the at least one organic solvent.

7. The electrolyte composition according to one of the preceding claims, wherein the mass percentage of lithium difluorophosphate represents from 0.1% to less than 1%, preferably from 0.5% to less than 1%, of the mass of the group consisting of the at least one lithium tetrafluoride or hexafluoroide salt, the lithium bis (fluorosulfonyl) imide salt and the at least one organic solvent.

8. The electrolyte composition according to one of the preceding claims, wherein the ratio of the mass of ethylene sulfate to the mass of vinylene carbonate is less than or equal to 0.5.

9. The electrolyte composition according to one of the preceding claims, wherein the ratio of the mass of lithium difluorophosphate to the sum of the masses of vinylene carbonate plus ethylene sulfate is strictly less than 0.2.

10. The electrolyte composition according to claims 8 and 9, wherein the ratio of the mass of ethylene sulfate to the mass of vinylene carbonate is less than or equal to 0.5, the ratio of the mass of lithium difluorophosphate to the sum of the masses of vinylene carbonate plus ethylene sulfate being strictly less than 0.2.

11. The electrolyte composition according to one of the preceding claims, not comprising sultone (sultone).

12. A lithium-ion electrochemical cell comprising:

-at least one negative electrode;

-at least one positive electrode;

-the electrolyte composition according to one of the preceding claims.

13. The electrochemical cell according to claim 12, wherein the negative electrode comprises a carbon-based, preferably graphite, active material.

14. The electrochemical cell of claim 12 or 13, wherein the positive electrode active material comprises one or more of compounds i) through v):

-formula Li_xMn_1-y-zM'_yM”_zPO₄Wherein M 'and M' are different from each other and are selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, wherein x is more than or equal to 0.8 and less than or equal to 1.2; y is more than or equal to 0 and less than or equal to 0.6; z is more than or equal to 0 and less than or equal to 0.2;

-formula Li_xM_2-x-y-z-wM'_yM”_zM”'_wO₂Compound ii) of (a), wherein M, M ', M "and M'" are selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, with the proviso that M or M 'or M "or M'" are selected from Mn, Co, Ni or Fe; m, M ', M ", and M'" are different from each other; wherein x is more than or equal to 0.8 and less than or equal to 1.4; y is more than or equal to 0 and less than or equal to 0.5; z is more than or equal to 0 and less than or equal to 0.5; w is 0-0.2 and x + y + z + w<2.2；

-formula Li_xMn_2-y-zM'_yM”_zO₄Compound iii) of (a), wherein M 'and M' are selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo;

m 'and M' are different from each other, and 1. ltoreq. x.ltoreq.1.4; y is more than or equal to 0 and less than or equal to 0.6; z is more than or equal to 0 and less than or equal to 0.2;

-formula Li_xFe_1-yM_yPO₄Compound iv) of (a), wherein M is selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; and x is more than or equal to 0.8 and less than or equal to 1.2; y is more than or equal to 0 and less than or equal to 0.6;

-formula xLi₂MnO₃；(1-x)LiMO₂The compound of (v) wherein M is selected from the group consisting of Ni, Co and Mn and x.ltoreq.1.

15. The electrochemical cell of claim 14, wherein the positive electrode active material comprises a compound i) wherein x ═ 1; m' represents at least one element selected from the group consisting of Fe, Ni, Co, Mg and Zn; 0< y <0.5 and z ═ 0.

16. The electrochemical cell of claim 14, wherein the positive electrode active material comprises compound ii) and

m is Ni;

m' is Mn;

m' is Co and

m' "is selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb and Mo;

wherein x is more than or equal to 0.8 and less than or equal to 1.4; y is more than 0 and less than or equal to 0.5; z is more than 0 and less than or equal to 0.5; w is more than or equal to 0 and less than or equal to 0.2, and x + y + z + w is less than 2.2.

17. The electrochemical cell of claim 14, wherein the positive electrode active material comprises compound ii), and M is Ni; m' is Co; m' is Al; x is more than or equal to 1 and less than or equal to 1.15; y > 0; z > 0; w is 0.

18. Use of an electrochemical cell according to one of claims 12 to 17 for storage, charging or discharging at a temperature of at least 80 ℃.

19. Use of an electrochemical cell according to one of claims 12 to 17 for storage, charging or discharging at a temperature lower than or equal to-20 ℃.

Technical Field

The technical field of the invention is that of electrolyte compositions for lithium-ion rechargeable electrochemical cells.

Background

Lithium ion type rechargeable electrochemical cells are known in the art. They are promising sources of electrical energy due to their high mass and volumetric energy density. They include at least one positive electrode (which may be a lithiated transition metal oxide) and at least one negative electrode (which may be graphite-based). However, such batteries have a limited service life when used at temperatures of at least 80 ℃. Their components degrade rapidly, resulting in short-circuiting of the battery or an increase in internal resistance. For example, the capacity loss of such a battery may reach 20% of its initial capacity after cycling at 85 ℃ for about 100 charges/discharges. In addition, these batteries have also been found to have a limited useful life when used at temperatures below-10 ℃.

The object was therefore to make available new lithium-ion type electrochemical cells with improved service life when cycled at temperatures of at least 80 ℃, preferably at least 85 ℃ or at temperatures below-10 ℃. This object is considered to be achieved when these cells are capable of operating under cycling conditions by performing at least 200 cycles, in which the depth of discharge is 100% and the loss of capacity is not more than 20% of their initial capacity.

Document CN 106099171 describes that its electrolyte comprises lithium hexafluorophosphate LiPF₆Lithium bis (fluorosulfonyl) imide LiFSI, ethylene sulfate ESA, vinylene carbonate VC, and lithium difluorophosphate LiPO₂F₂A lithium-ion electrochemical cell of (1). In the examples in this document, the ratio between the amount of ethylene sulfate and the amount of vinylene carbonate is at least 1. This high ratio results in rapid dissolution of the passivation layer of the negative electrode. Reconstituting a new passivation layer to replace the dissolved passivation layer has the effect of consuming lithium ions from the electrolyte and thus resulting in a reduction in the amount of lithium ions in the electrolyte. This results in a degradation of the battery performance during cycling, especially at high temperatures.

Document CN 108539267 describes an electrolyte for lithium-ion electrochemical cells. The examples in this document describe the inclusion of LiPF₆LiFSI, ESA, VC andLiPO₂F₂the electrolyte of (1). In examples 1 to 4, the ESA/VC mass ratio was greater than or equal to 1. As described in the above-mentioned documents, this high ratio causes rapid dissolution of the passivation layer of the negative electrode, which results in a decrease in the amount of lithium ions in the electrolyte, which ultimately leads to a decrease in the cycle performance of the battery. Furthermore, example 5 describes a composition comprising 1% LiPO₂F₂The electrolyte composition of (1). At such concentrations, the solubility limit of the compound is approached. When approaching the solubility limit, LiPO₂F₂The presence of crystals limits the quality of the cells filled with electrolyte. After filling, LiPO₂F₂May not be uniformly distributed within the electrochemical cell. This may result in degradation of battery performance.

Document CN 108054431 describes electrolyte compositions for lithium ion batteries suitable for use at low and high temperatures. Example 3 describes a composition of 5% m LiFSI, 5% m LiPF ₆1% m LiPO₂F₂An electrolyte composition consisting of 0.5% mvc and 0.5% mESA. In this example, the mass ratio ESA/VC equals 1. As in the two previously mentioned documents, this high ratio leads to a degradation of the performance of the battery during cycling.

Document CN 107706455 describes electrolyte compositions for lithium ion batteries that can be operated at high and low temperatures. The composition comprises LiPF₆、LiFSI、LiPO₂F₂VC and ESA. In examples 1 to 3, 6, 7, 9 to 11 and comparative examples 1 to 3, 6, the mass% of ESA was 0.5%, and the mass% of VC was 0.3%, resulting in an ESA/VC ratio of 1.67. As described above, a high ESA/VC ratio results in a decrease in the performance of the battery during cycling.

New electrochemical cells capable of cycling through a wide temperature range (i.e., capable of operating at temperatures as low as about-20 ℃ and up to 80 ℃ or higher) are being sought.

Disclosure of Invention

Accordingly, the present invention relates to an electrolyte composition comprising:

-at least one lithium tetrafluoride or hexafluoro salt,

-lithium bis (fluorosulfonyl) imide LiFSI salt,

vinylene carbonate

-an ethylene sulphate,

-a lithium difluorophosphate,

-at least one organic solvent selected from the group consisting of cyclic or linear carbonates, cyclic or linear esters, cyclic or linear ethers and mixtures thereof,

the ratio of the mass of ethylene sulfate to the mass of vinylene carbonate before addition to the solvent is strictly less than 2.

The electrolyte may be used in a lithium ion type electrochemical cell. It allows the device to operate at high temperatures (e.g., at least 80 ℃). It also allows the device to operate at low temperatures (e.g., about-20 ℃).

According to one embodiment, the lithium tetrafluoride or hexafluoro salt is selected from lithium hexafluorophosphate LiPF₆Lithium hexafluoroarsenate LiAsF₆Lithium hexafluoroantimonate LiSbF₆And lithium tetrafluoroborate LiBF₄。

According to one embodiment, the lithium ions from the lithium bis (fluorosulfonyl) imide salt constitute at least 30 mole% of the total amount of lithium ions present in the electrolyte composition.

According to one embodiment, lithium ions from a lithium tetrafluoride or hexafluoro salt constitute up to 70 mol% of the total amount of lithium ions present in the electrolyte composition.

According to one embodiment, the mass percentage of vinylene carbonate is comprised between 0.1% and 5%, preferably between 0.5% and 2%, of the mass of the group consisting of said at least one lithium tetrafluoride or hexafluoride salt, lithium bis (fluorosulfonyl) imide salt and said at least one organic solvent.

According to one embodiment, the mass percentage of ethylene sulfate is comprised between 0.1% and 5%, preferably between 0.5% and 1%, of the mass of the group consisting of the at least one lithium tetrafluoride or hexafluoride salt, lithium bis (fluorosulfonyl) imide salt LiFSI salt and the at least one organic solvent.

According to one embodiment, the mass percentage of lithium difluorophosphate is comprised between 0.1% and 2%, preferably between 0.5% and 1%, of the mass of the group consisting of the at least one lithium tetrafluoride or hexafluoride salt, lithium bis (fluorosulfonyl) imide salt and at least one organic solvent.

According to one embodiment, the ratio of the mass of ethylene sulfate to the mass of vinylene carbonate is less than or equal to 1, preferably less than or equal to 0.5.

According to one embodiment, the ratio of the mass of lithium difluorophosphate to the sum of the masses of vinylene carbonate and ethylene sulfate is strictly less than 0.2.

According to one embodiment, the composition does not comprise a sultone-lactone.

The invention also relates to a lithium-ion electrochemical cell comprising:

-at least one negative electrode;

-at least one positive electrode;

-an electrolyte composition as described above.

According to one embodiment, the negative electrode comprises an active material based on carbon, preferably graphite.

According to one embodiment, the positive electrode active material comprises one or more of compounds i) to v):

-formula Li_xMn_1-y-zM'_yM”_zPO₄The compound i) of (a), wherein M 'and M' are different from each other and are selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, wherein 0.8. ltoreq. x.ltoreq.1.2; y is more than or equal to 0 and less than or equal to 0.6; z is more than or equal to 0 and less than or equal to 0.2;

-formula Li_xM_2-x-y-z-wM'_yM”_zM”'_wO₂Compound ii) of (a), wherein M, M ', M "and M'" are selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, with the proviso that M or M 'or M "or M'" are selected from Mn, Co, Ni or Fe; m, M ', M ", and M'" are different from each other; wherein x is more than or equal to 0.8 and less than or equal to 1.4; y is more than or equal to 0 and less than or equal to 0.5; z is more than or equal to 0 and less than or equal to 0.5; w is 0-0.2 and x + y + z + w<2.2；

-formula Li_xMn_2-y-zM'_yM”_zO₄The compound of (iii), wherein M 'and M' are selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, B,Nb and Mo; m 'and M' are different from each other, and 1. ltoreq. x.ltoreq.1.4; y is more than or equal to 0 and less than or equal to 0.6; z is more than or equal to 0 and less than or equal to 0.2;

-formula Li_xFe_1-yM_yPO₄Compound iv) of (a), wherein M is selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; and x is more than or equal to 0.8 and less than or equal to 1.2; y is more than or equal to 0 and less than or equal to 0.6;

-formula xLi₂MnO₃；(1-x)LiMO₂The compound of (v) wherein M is selected from the group consisting of Ni, Co and Mn and x.ltoreq.1.

According to one embodiment, the positive electrode active material comprises a compound i), wherein x ═ 1; m' represents at least one element selected from the group consisting of Fe, Ni, Co, Mg and Zn; 0< y <0.5 and z ═ 0.

According to one embodiment, the positive electrode active material comprises compound ii), and

m is Ni;

m' is Mn;

m' is Co and

m' "is selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb and Mo;

wherein x is more than or equal to 0.8 and less than or equal to 1.4; y is more than 0 and less than or equal to 0.5; z is more than 0 and less than or equal to 0.5; w is more than or equal to 0 and less than or equal to 0.2, and x + y + z + w is less than 2.2.

According to one embodiment, the positive electrode active material comprises compound ii) and M is Ni; m' is Co; m' is Al; x is more than or equal to 1 and less than or equal to 1.15; y > 0; z > 0; w is 0.

The invention also relates to the use of an electrochemical cell as described above for storage, charging or discharging at a temperature of at least 80 ℃.

The invention also relates to the use of an electrochemical cell as described above for storage, charging or discharging at a temperature lower than or equal to-20 ℃.

Drawings

Fig. 1 shows the change in capacity of cells A, B and C during cycling at 85 ℃.

Fig. 2 shows the capacity change during cycling of batteries A, B and C at temperatures of 25 ℃, 0 ℃, -20 ℃, and 25 ℃.

FIG. 3 shows the storage of the electrolyte at a temperature of 85 ℃ for two weeksThen, as containing 1 mol. L^-1Change in the percentage of transesterification of Ethyl Methyl Carbonate (EMC) as a function of the percentage of lithium difluorophosphate in the EMC, 2 mass% vinylene carbonate and lithium difluorophosphate electrolyte.

Fig. 4 shows the capacity change of cells F, G and H during cycling at 25 ℃ and 60 ℃.

Fig. 5 shows the change in capacity of batteries F, I and J during cycling at 25 ℃ and 60 ℃.

Fig. 6 shows at the top the gas chromatogram of electrolyte composition G at the end of the cycle at 60 ℃ for a cell comprising electrolyte composition G. The bottom spectrum is the spectrum of electrolyte composition H at the end of the cycle at 60 ℃ for the cell containing electrolyte composition H.

Fig. 7 shows at the top the gas chromatogram of electrolyte composition I at the end of the cycle at 60 ℃ for a cell comprising electrolyte composition I. The bottom spectrum is the spectrum of electrolyte composition J at the end of the cycle at 60 ℃ for the cell containing electrolyte composition J.

Fig. 8 shows the change in capacity of battery K, L, M, N and O during cycling at 85 ℃.

Fig. 9 shows the change in capacity of battery P, Q, R, S and T during cycling at 85 ℃.

Fig. 10 shows the capacity change of the battery K, L, M, N and O during cycling at temperatures of 20 ℃, 0 ℃, -20 ℃, 25 ℃ and 85 ℃.

Fig. 11 shows the capacity change of the battery P, Q, R, S and T during cycling at temperatures of 20 ℃, 0 ℃, -20 ℃, 25 ℃ and 85 ℃.

Fig. 12 shows the capacity change during cycling of batteries a to E at 85 ℃.

Fig. 13 shows the capacity changes of the batteries a to E during cycling at temperatures of 25 ℃, 0 ℃, -20 ℃, and 25 ℃.

Detailed Description

Various components of the electrolyte composition according to the invention and of an electrochemical cell comprising the electrolyte composition according to the invention are described below.

Electrolyte composition:

the electrolyte composition comprises at least one organic solvent in which the following compounds are dissolved:

-at least one lithium tetrafluoride or hexafluoro salt,

lithium bis (fluorosulfonyl) imide salt (LiFSI) of formula:

[ chemical formula 1]

-Vinylene Carbonate (VC) of formula:

[ chemical formula 2]

-Ethylene Sulfate (ESA) of formula:

[ chemical formula 3]

Lithium difluorophosphate of formula (LiPO2F2)

[ chemical formula 4]

Lithium difluorophosphate LiPO₂F₂Dissociation is very weak in organic media and its presence contributes negligibly to the increase in the amount of lithium ions in the electrolyte. Which will be considered hereinafter as an additive rather than a salt of the electrolyte. The at least one organic solvent is selected from cyclic or linear carbonates, cyclic or linear esters, cyclic or linear ethers or mixtures thereof.

Examples of cyclic carbonates are Ethylene Carbonate (EC), Propylene Carbonate (PC) and Butylene Carbonate (BC). Ethylene Carbonate (EC), Propylene Carbonate (PC) and mixtures thereof are particularly preferred. The electrolyte composition may be free of cyclic carbonates other than EC and PC.

Examples of linear carbonates are dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC) and methylpropyl carbonate (MPC). Dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) and mixtures thereof are particularly preferred. The electrolyte composition may be free of linear carbonates other than DMC and EMC.

The cyclic or linear carbonates and cyclic or linear esters may be substituted with one or more halogen atoms, such as fluorine.

Examples of linear esters are ethyl acetate, methyl acetate, propyl acetate, ethyl butyrate, methyl butyrate, propyl butyrate, ethyl propionate, methyl propionate and propyl propionate.

Examples of cyclic esters are gamma-butyrolactone and gamma-valerolactone.

Examples of linear ethers are dimethoxyethane and propylethyl ether.

An example of a cyclic ether is tetrahydrofuran.

According to one embodiment, the electrolyte composition comprises one or more cyclic carbonates, one or more cyclic ethers and one or more linear ethers.

According to one embodiment, the electrolyte composition comprises one or more cyclic carbonates, one or more linear carbonates and at least one linear ester.

According to one embodiment, the electrolyte composition comprises one or more cyclic carbonates, one or more linear carbonates and no linear esters. Preferably, the electrolyte composition does not comprise any solvent compounds other than cyclic or linear carbonates. When the solvent compound is a mixture of cyclic and linear carbonates, the cyclic carbonate may constitute up to 50 volume percent of the volume of the carbonate and the linear carbonate may constitute at least 50 volume percent of the volume of the carbonate. Preferably, the cyclic carbonate constitutes from 10 to 40 volume percent of the volume of the carbonate, and the linear carbonate constitutes from 90 to 60 volume percent of the carbonate. Preferred mixtures of organic solvents are mixtures of EC, PC, EMC and DMC. The EC may comprise from 5% to 15% by volume of the organic solvent mixture. The PC may be 15% to 25% by volume of the organic solvent mixture. EMC may occupy 20 to 30 vol% of the volume of the organic solvent mixture. The DMC may comprise 40% to 50% by volume of the organic solvent mixture.

The nature of the lithium tetrafluoride or hexafluoro salt is not particularly limited. Mention may be made of lithium hexafluorophosphate LiPF₆Lithium hexafluoroarsenate LiAsF₆Lithium hexafluoroantimonate LiSbF₆And lithium tetrafluoroborate LiBF₄. Preferably, lithium hexafluorophosphate LiPF will be chosen₆. Other lithium salts than lithium tetrafluoride or hexafluoro salt and lithium bis (fluorosulfonyl) imide LiFSI salt may also be present in the at least one organic solvent. Preferably, the electrolyte composition does not comprise any lithium salt other than the lithium tetrafluoride or hexafluoro salt and the lithium bis (fluorosulfonyl) imide LiFSI salt. For example, the electrolyte composition does not have lithium bis (trifluorosulfonyl) imide salt LiTFSI that exhibits both lower ionic conductivity and lower ability to passivate the interface compared to LiFSI. Still preferably, the only lithium salt in the electrolyte composition is LiPF₆And LiFSI.

The total lithium ion concentration in the electrolyte composition is typically 0.1mol · L^-1To 3 mol. L^-1Preferably 0.5 mol. L^-1To 1.5 mol. L^-1More preferably about 1 mol. L^-1。

Lithium ions from lithium tetrafluoride or hexafluoroide salts typically account for up to 70% of the total amount of lithium ions present in the electrolyte composition. They may also represent 1% to 70% of the total amount of lithium ions present in the electrolyte composition. They may also represent 10% to 70% of the total amount of lithium ions present in the electrolyte composition.

The lithium ions from the lithium bis (fluorosulfonyl) imide salt typically constitute at least 30% of the total amount of lithium ions present in the electrolyte composition. They may also represent 30% to 99% of the total amount of lithium ions present in the electrolyte composition. They may also represent 30% to 90% of the total amount of lithium ions present in the electrolyte composition.

Vinylene carbonate, ethylene sulfate, and lithium difluorophosphate serve as additives to help stabilize the passivation layer (SEI for the solid electrolyte interface) formed on the negative electrode surface of the electrochemical cell during the first charge/discharge cycle of the cell. Additives other than vinylene carbonate, ethylene sulfate, and lithium difluorophosphate may also be added to the mixture.

In a preferred embodiment, the electrolyte composition does not comprise any additives other than vinylene carbonate, ethylene sulfate and lithium difluorophosphate. The amount of additive introduced into the mixture is measured in mass relative to the mass of the group consisting of lithium tetrafluoride or hexafluoroide salt, lithium bis (fluorosulfonyl) imide LiFSI salt and the at least one organic solvent. The mass of the two other additives is neglected with respect to the mass of the group consisting of lithium tetrafluoride or hexafluoroide salt, lithium bis (fluorosulfonyl) imide salt LiFSI salt and the at least one organic solvent.

According to one embodiment, the mass percentage of vinylene carbonate is 0.1 to 5 mass%, preferably 0.5 to 3 mass%, more preferably 1 to 2 mass% of the mass of the group consisting of lithium tetrafluoride or hexafluoroide, lithium bis (fluorosulfonyl) imide, and the at least one organic solvent.

According to one embodiment, the mass percentage of ethylene sulfate is 0.1 to 5 mass%, preferably 0.5 to 2 mass%, more preferably 1 to 2 mass% of the mass of the group consisting of the lithium tetrafluoride or hexafluoroide salt, the lithium bis (fluorosulfonyl) imide salt, and the at least one organic solvent.

According to one embodiment, the mass percentage of lithium difluorophosphate is comprised between 0.1 and 2%, preferably between 0.5% and 1.5%, more preferably between 0.5% and 1% of the mass of the group consisting of lithium tetrafluoride or hexafluoroide salt, lithium bis (fluorosulfonyl) imide salt and said at least one organic solvent. Preferably, the mass percentage of lithium difluorophosphate is 0.1% to less than 1%, or 0.1% to 0.9% or 0.1% to 0.8% of the mass of the group consisting of lithium tetrafluoride or hexafluoroide salt, lithium bis (fluorosulfonyl) imide salt and the at least one organic solvent.

The ethylene sulfate may account for 20 to 30 mass% of the total mass of the ethylene sulfate, vinylene carbonate, and lithium difluorophosphate.

The vinylene carbonate may account for 40 to 60 mass% of the total mass of the ethylene sulfate, vinylene carbonate, and lithium difluorophosphate.

Lithium difluorophosphate may account for 10 to 40 mass% of the group consisting of ethylene sulfate, vinylene carbonate, and lithium difluorophosphate.

The ratio of the mass of ethylene sulfate to the mass of vinylene carbonate is strictly less than 2. Preferably, it is less than or equal to 1. More preferably, it is less than or equal to 0.5. A ratio greater than or equal to 2 results in the passivation layer dissolving too quickly on the negative electrode and results in a degradation of the cell performance during cycling.

The ratio of the mass of lithium difluorophosphate to the sum of the masses of vinylene carbonate and ethylene sulfate may be strictly less than 0.2. Too high a ratio may result in the passivation layer on the negative electrode being too soluble, resulting in a degradation of the battery performance during cycling.

In particular, the electrolyte composition does not comprise sultone (sultone). The presence of sultone has a disadvantage over ethylene sulfate in that the passivation layer (SEI) on the negative electrode surface is less conductive in cold applications than when ethylene sulfate is present. Furthermore, for thermal applications, the passivation layer on the surface of the negative electrode is stronger in the presence of ethylene sulfate and less soluble in the electrolyte than in the presence of sultone.

There are several procedures for preparing electrolyte compositions. According to a preferred procedure, the at least one lithium tetrafluoride or hexafluoro salt, lithium bis (fluorosulfonyl) imide salt, vinylene carbonate, ethylene sulfate and lithium difluorophosphate may be obtained. These compounds are solids. The mass of each additive is weighed with respect to the mass of the group consisting of lithium tetrafluoride or hexafluoride salt, lithium bis (fluorosulfonyl) imide salt LiFSI salt and said at least one organic solvent. The mass of the other two additives was ignored. Preparing the at least one organic solvent. It may be a mixture of several organic solvents. The solvents were mixed in the desired volume ratio. An additive, at least one lithium tetrafluoride or hexafluoro salt, and a lithium bis (fluorosulfonyl) imide salt are added to at least one organic solvent. Vinylene carbonate is then added to at least one organic solvent containing additives. In this procedure, vinylene carbonate is finally introduced into the electrolyte to minimize the risk of reactions between vinylene carbonate and other additives or salts. However, vinylene carbonate may be introduced simultaneously with other additives.

Negative electrode active material:

the active material of the negative electrode (anode) of the electrochemical cell is preferably a carbonaceous material which may be selected from the group consisting of graphite, coke, carbon black and vitreous carbon.

In another preferred embodiment, the active material of the negative electrode comprises a silicon-based compound.

Positive electrode active material:

the positive electrode active material of the positive electrode (cathode) of the electrochemical cell is not particularly limited. It may be selected from:

-formula Li_xMn_1-y-zM'_yM”_zPO₄(LMP) wherein M 'and M' are different from each other and are selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, wherein 0.8. ltoreq. x.ltoreq.1.2; y is more than or equal to 0 and less than or equal to 0.6; z is more than or equal to 0 and less than or equal to 0.2;

-formula Li_xM_2-x-y-z-wM'_yM”_zM”'_wO₂(LMO2) wherein M, M ', M "and M'" are selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, W and Mo, with the proviso that M or M 'or M "or M'" is selected from Mn, Co, Ni or Fe; m, M ', M ", and M'" are different from each other; wherein x is more than or equal to 0.8 and less than or equal to 1.4; y is more than or equal to 0 and less than or equal to 0.5; z is more than or equal to 0 and less than or equal to 0.5; w is more than or equal to 0 and less than or equal to 0.2, and x + y + z + w<2.2；

-formula Li_xMn_2-y-zM'_yM”_zO₄(LMO) compound iii) wherein M 'and M' are selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; m 'and M' are different from each other, and x is 1. ltoreq. x.ltoreq.1.4; y is more than or equal to 0 and less than or equal to 0.6; z is more than or equal to 0 and less than or equal to 0.2;

-formula Li_xFe_1-yM_yPO₄Compound iv) of (2), wherein M is selected fromB. Mg, Al, Si, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; and x is more than or equal to 0.8 and less than or equal to 1.2; y is more than or equal to 0 and less than or equal to 0.6;

-formula xLi₂MnO₃；(1-x)LiMO₂The compound v) of (1), wherein M is selected from the group consisting of Ni, Co and Mn and x.ltoreq.1,

or mixtures of compounds i) to v).

An example of a compound i) is LiMn_1-yFe_yPO₄. A preferred example is LiMnPO₄。

The compound ii) may have the formula Li_xM_2-x-y-z-wM'_yM”_zM”'_wO₂Wherein x is more than or equal to 1 and less than or equal to 1.15; m represents Ni; m' represents Mn; m 'represents Co and M' is selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo or a mixture thereof; 2-x-y-z-w>0；y>0；z>0；w≥0。

The compound ii) may have the formula LiNi_1/3Mn_1/3Co_1/3O₂。

The compounds ii) may also have the formula Li_xM_2-x-y-z-wM'_yM”_zM”'_wO₂Wherein x is more than or equal to 1 and less than or equal to 1.15; m represents Ni; m' represents Co; m 'represents Al and M' is selected from B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo or a mixture thereof; 2-x-y-z-w>0；y>0；z>0; w is more than or equal to 0. Preferably, x ═ 1; 2-x-y-z is more than or equal to 0.6 and less than or equal to 0.85; y is more than or equal to 0.10 and less than or equal to 0.25; z is 0.05-0.15 and w is 0.

The compound ii) may also be selected from LiNiO₂、LiCoO₂、LiMnO₂Ni, Co and Mn, which may be selected from Mg, Mn (LiMnO)₂Except for Al), B, Ti, V, Si, Cr, Fe, Cu, Zn, Zr.

An example of a compound iii) is LiMn₂O₄。

An example of compound iv) is LiFePO₄。

An example of a compound v) is Li₂MnO₃。

The positive electrode active material may be at least partially covered with a carbon layer.

Binders for positive and negative electrodes:

the positive and negative active materials of a lithium-ion electrochemical cell are typically mixed with one or more binders, the function of which is to bind the active material particles together and to bind them to the current collector on which they are deposited.

The binder may be selected from the group consisting of carboxymethylcellulose (CMC), styrene-butadiene copolymer (SBR), Polytetrafluoroethylene (PTFE), Polyamideimide (PAI), Polyimide (PI), styrene-butadiene rubber (SBR), polyvinyl alcohol, polyvinylidene fluoride (PVDF), and mixtures thereof. These binders may be used in the positive electrode and/or the negative electrode in general.

Current collector for positive and/or negative electrode:

the current collectors for the positive and negative electrodes are in the form of solid or perforated metal foils. The foil may be made of different materials. Mention may be made of copper or copper alloys, aluminum or aluminum alloys, nickel or nickel alloys, steel and stainless steel.

The current collector of the positive electrode is typically a foil made of aluminum or an alloy mainly containing aluminum. The current collector of the negative electrode is typically a foil made of copper or an alloy mainly containing copper. The thickness of the positive electrode foil may be different from the thickness of the negative electrode foil. The foil of the positive or negative electrode is typically 6 μm to 30 μm thick.

According to a preferred embodiment, the aluminum current collector of the positive electrode is covered with a conductive coating, such as carbon black, graphite.

Manufacturing of negative electrode:

the negative active material is mixed with one or more of the above binders and optionally a good conductive compound (e.g., carbon black). The result is an ink deposited on one or both sides of the current collector. The ink coated current collector was laminated to adjust its thickness. Thereby obtaining a negative electrode.

The composition of the ink deposited on the negative electrode may be as follows:

-75% to 96% of a negative active material, preferably 80% to 85%;

-2% to 15% of binder, preferably 5%;

-2% to 10% of a conductive compound, preferably 7.5%.

Fabrication of positive electrode:

the same procedure was used as for the negative electrode, but starting with the positive active material.

The composition of the ink deposited on the positive electrode may be as follows:

-75% to 96% of a negative active material, preferably 80% to 90%;

-2% to 15% binder, preferably 10%;

2% to 10% carbon, preferably 10%.

A spacer:

the material of the spacer may be selected from the following materials: polyolefins such as polypropylene, polyethylene, polyesters, polymer-bonded fiberglass, polyimides, polyamides, polyaramides, polyamideimides, and cellulose. The polyester may be selected from the group consisting of polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Advantageously, the polyester or polypropylene or polyethylene comprises or is coated with a material selected from the group consisting of metal oxides, carbides, nitrides, borides, silicides and sulfides. The material may be SiO₂Or Al₂O₃。

Preparation of electrochemical assemblies:

an electrochemical assembly is formed by interposing a separator between at least one positive electrode and at least one negative electrode. The electrochemical assembly is inserted into the cell container. The battery container may be in the form of a parallelepiped or a cylinder. In the latter case, the electrochemical assembly is coiled to form a cylindrical electrode assembly.

Filling of the container:

the container provided with the electrochemical assembly is filled with the electrolyte composition as described above.

The battery according to the invention generally comprises a combination of the following elements:

a) at least one positive electrode whose active material is a lithium oxide of a transition metal comprising nickel, manganese and cobalt;

b) at least one negative electrode whose active material is graphite;

c) the electrolyte composition as described above;

d) a polypropylene spacer.

Applicants have found that the combination of two lithium salts (i.e., lithium tetrafluoride or hexafluoroide salt and lithium bis (fluorosulfonyl) imide LiFSI salt) with three additives (i.e., vinylene carbonate, ethylene sulfate, and lithium difluorophosphate) has the following advantages:

reducing the impedance of the electrochemical cell.

Electrochemical cells can operate over a wide temperature range (i.e. -temperatures of-10 ℃ or even-20 ℃ up to 80 ℃ or even 100 ℃).

The risk of electrolyte decomposition is reduced.

-reducing the heat generated by the battery during cycling.

Electrochemical cells can be cycled with significant changes in ambient temperature.

Electrochemical cells lose capacity more slowly when used under cycling conditions. Thus, the present invention can extend the useful life of a battery operating under cycling conditions (whether low temperature cycling or high temperature cycling).

Reduced gas formation in the case of cells with graphite-based anodes.

The viscosity of the electrolyte composition is reduced, thereby increasing the filling speed of the container and is of interest when the invention is implemented on an industrial scale.