Electrolytes containing high concentrations of LiFSI

Abstract

The present invention relates to an electrolyte composition comprising -5% to 70% by weight of a lithium bis(fluorosulfonyl)imide salt and -20% to 85% by weight of at least one organic solvent. The present invention also relates to electrochemical cells and batteries using such an electrolyte composition.

Description

[Technical Field]

[0001] The present invention relates to an electrolyte composition comprising a lithium bis(fluorosulfonyl)imide salt. The present invention also relates to an electrochemical cell comprising the composition, and a battery comprising the electrochemical cell. [Background technology]

[0002] Lithium (Li) batteries, such as lithium-ion (Li) batteries, are commonly used in electric vehicles, as well as mobile and portable devices.

[0003] A lithium-ion battery comprises at least a negative electrode (anode), a positive electrode (cathode), an electrolyte, and preferably a separator. The electrolyte generally consists of a lithium salt dissolved in a solvent (usually a mixture of organic solvents) to have a good trade-off between the viscosity and dielectric constant of the electrolyte.

[0004] The lithium-ion battery market is seeing a demand for the development of higher-power batteries. This is achieved by increasing the nominal voltage of lithium-ion batteries. Lithium-ion batteries using high-voltage swords (typically >4.5V), such as LMNO, present significant challenges in improving the energy density of the battery. The key is finding an electrolyte that is stable even at high voltages, compatible with aluminum current collectors, and guarantees battery life. Furthermore, a high-purity electrolyte is required to achieve the target voltage.

[0005] In the field of lithium-ion batteries, the most widely used salt currently is LiPF6. However, this salt exhibits many drawbacks, including limited thermal stability, susceptibility to hydrolysis, and consequently, reduced battery safety.

[0006] To improve battery performance, new lithium sulfonylimide salts, particularly LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) and LiFSI (lithium bis(fluorosulfonyl)imide), have been developed. These salts exhibit little to no biodegradation and are more stable to hydrolysis than LiPF6. However, LiTFSI has the disadvantage of being corrosive to aluminum current collectors.

[0007] The passivation layer formed during the battery's first charge / discharge cycle is essential for battery life. This passivation layer includes, in particular, the aluminum passivation, which is generally used as the current collector at the cathode, and the solid electrolyte interface (SEI), an inorganic polymer layer formed at the anode / electrolyte and cathode / electrolyte interfaces. The stability of these interfaces is a major challenge in improving battery life.

[0008] International Publication No. 2018 / 150131 relates to a lithium bis(fluorosulfonyl)imide salt, characterized in that, after dissolving in water to form an aqueous solution, the aqueous solution has a pH between 4 and 8, particularly at a temperature of 25°C, and to its use in Li-ion batteries.

[0009] A paper by C. Luo et al., Electrochimica Acta 419 of 2022 (p.140353), studies the corrosion of LiFSI on aluminum and stainless steel. The proposed solution is to use a high-concentration electrolyte solution in the presence of a fluorinated diluent (LHCE).

[0010] A paper by B. Aktekin et al., Applied Energy Material 2022, 5, 1 (pp. 585-595), describes an electrolyte containing high concentrations of LiFSI (2-6M) in ethylene carbonate.

[0011] Japanese Patent Publication No. 2019-220450 claims an electrolyte that suppresses aluminum corrosion in lithium-ion batteries. This solution is a solution in which the concentration of a lithium salt containing LiFSI in an oxygen-containing solvent (typically methyl 3-methoxypropionate and triethylene glycol dimethyl ether) exceeds 2 moles / kg.

[0012] Chinese Patent Application Publication No. 104300176 claims an electrolyte containing LiPF6 and LiFSI in the presence of a corrosion inhibitor such as LiBOB.

[0013] There is a real need for an electrolyte that can be used, especially at high cutoff voltages exceeding 4.5V, without adversely affecting the lifespan and electronic performance of lithium-ion batteries. There is also a real need for a higher-performance electrolyte that does not corrode aluminum even at temperatures exceeding 40°C over long periods of time. [Overview of the Initiative]

[0014] The present invention, firstly, - 5% to 70% by weight of lithium bis(fluorosulfonyl)imide salt - 20% to 85% by weight of at least one organic solvent and This relates to an electrolyte composition containing the following:

[0015] According to a preferred embodiment, the organic solvent is selected from ethers; carbonate esters or organic carbonates; cyclic carbonates; carboxylic acid esters; lactones; phosphate esters; nitriles; amides; lactams; nitro compounds; sulfones; sulfoxides; ionic liquids containing an FSI (bis(fluorosulfonyl)imide) anion with ammonium, imidazolium, pyrrolidinium, piperidinium, phosphonium, sulfonium, or oxonium-type cations; fluorinated solvents; and mixtures thereof, preferably selected from sulfones, sulfoxides, nitriles, ionic liquids, fluorinated ethers, and fluorinated carbonates; and mixtures thereof.

[0016] The solvent is preferably sulfolane.

[0017] According to another preferred embodiment, the electrolyte composition comprises 10% to 60% by weight, preferably 15% to 50% by weight, and more preferably 20% to 40% by weight of LiFSI, based on the total weight of the electrolyte composition.

[0018] In preferred embodiments, the electrolyte composition contains 30% to 85% by weight, preferably 40% to 85% by weight, more preferably 50% to 80% by weight, and even more preferably 60% to 75% by weight, of the total weight of the electrolyte composition, a solvent.

[0019] In a preferred embodiment, the electrolyte composition further comprises an aluminum salt dissolved such that the weight concentration of aluminum with respect to the weight of the electrolyte composition is between 0.5 and 10,000 ppm by weight, preferably between 0.5 and 9000 ppm by weight, preferably between 0.5 and 8000 ppm by weight, preferably between 0.5 and 7000 ppm by weight, preferably between 0.5 and 6000 ppm by weight, preferably between 0.5 and 5000 ppm by weight, preferably between 0.5 and 4000 ppm by weight, preferably between 0.5 and 3000 ppm by weight, preferably between 0.5 and 2000 ppm by weight, preferably between 0.5 and 1000 ppm by weight, preferably between 0.5 and 900 ppm by weight, preferably between 0.5 and 800 ppm by weight, preferably between 0.5 and 700 ppm by weight, preferably between 0.5 and 600 ppm by weight, preferably between 0.5 and 500 ppm by weight, preferably between 0.5 and 400 ppm by weight, preferably between 0.5 and 300 ppm by weight, preferably between 0.5 and 200 ppm by weight, preferably between 0.5 and 100 ppm by weight, preferably between 0.5 and 90 ppm by weight, preferably between 0.5 and 80 ppm by weight, preferably between 0.5 and 70 ppm by weight, preferably between 0.5 and 60 ppm by weight, preferably between 0.5 and 50 ppm by weight, preferably between 0.5 and 40 ppm by weight, preferably between 0.5 and 30 ppm by weight, preferably between 0.5 and 20 ppm by weight, preferably between 0.5 and 10 ppm by weight.

[0020] According to a preferred embodiment, the electrolyte composition shows a positive current difference between the forward sweep and the reverse sweep over a range of 4.2 to 5 volts in the first cycle in cyclic voltammetry.

[0021] According to a preferred embodiment, the electrolyte composition has a pH of 3.5 or higher when measured at a temperature of 25°C after being diluted to a mass ratio of 1:1 with distilled water at pH 6.5.

[0022] According to another aspect, the present invention relates to an electrochemical cell comprising a negative electrode, a positive electrode, and the electrolyte composition defined above, preferably the negative electrode is made of graphite and the positive electrode is a LNMO electrode.

[0023] According to a preferred embodiment, the electrochemical cell comprises an aluminum current collector electrode support, preferably combined with the positive electrode.

[0024] According to another aspect, the present invention relates to a battery comprising at least one electrochemical cell defined above.

[0025] In a preferred embodiment, the battery has a cut-off voltage of 4.5 V or more.

[0026] According to another aspect, the present invention relates to the use of the electrolyte composition defined above in a Li-ion battery, preferably a Li-ion battery for portable electronic devices such as mobile phones or portable computers, a Li-ion battery for electric vehicles, or a Li-ion battery for storing renewable energy such as solar power energy or wind energy.

[0027] In a preferred embodiment, the Li-ion battery has a cut-off voltage of 4.5 V or more.

[0028] According to another aspect, the present invention relates to the use of the electrolyte composition defined above for extending the life of a Li-ion battery and / or improving the electronic performance of a Li-ion battery, preferably having a cut-off voltage of 4.5 V or more.

[0029] The present invention makes it possible to satisfy the above-mentioned needs. More specifically, the present invention provides a novel electrolyte for lithium-ion batteries that preferably offers improved performance, particularly in terms of SEI quality, Coulomb efficiency, and / or lifespan, and can be used without adversely affecting the lifespan and electronic performance of the lithium-ion battery, for example, in LMNO cathodes and especially in graphite / LMNO cells, at high cutoff voltages above 4.5V. The electrolyte of the present invention advantageously prevents aluminum corrosion and forms SEI at voltages up to 5V and on graphite anodes.

[0030] High concentrations of lithium salts in the electrolyte solvent are particularly advantageous for high-voltage applications (typically above 4.5V). This high concentration prevents transition metals from dissolving into the electrolyte, thus extending battery life.

[0031] This is achieved by the electrolyte composition according to the present invention. More specifically, the fact that the electrolyte composition according to the present invention has a lithium bis(fluorosulfonyl)imide salt content of 5% by weight or more suppresses oxidation of the electrolyte solvent and therefore improves the stability and lifespan of the battery, especially at potentials above 4.5V. [Brief explanation of the drawing]

[0032] [Figure 1] Graphs of voltammetry curves obtained for electrolytes 1 and 2 according to the example. Arrows indicate the sweep direction. [Figure 2] A graph showing the capacity retention rate and Coulomb efficiency of three LNMO / graphite button batteries using electrolytes 1 and 2 according to the example. [Figure 3] A photograph showing the aluminum surface after 200 cycles of voltammetry testing at 60°C using electrolytes 1(b) and 2(a) according to the example. [Modes for carrying out the invention]

[0033] The present invention will be described in more detail and in a non-limiting manner in the following description.

[0034] In the context of this invention, unless otherwise specified, the term "cutoff voltage" means the upper voltage limit of a battery that is considered fully charged. The cutoff voltage is typically selected to obtain the battery's maximum capacity.

[0035] electrolyte composition The present invention relates to an electrolyte composition comprising lithium bis(fluorosulfonyl)imide salt (LiFSI). In the context of the present invention, the terms "lithium bis(fluorosulfonyl)imide salt," "lithium bis(fluorosulfonyl)imide," "LiFSI," and "LiN(FSO2)2" are used synonymously.

[0036] The electrolyte composition has a lithium bis(fluorosulfonyl)imide salt content of 5% to 70% by weight, relative to the total weight of the electrolyte composition. The LiFSI content in the electrolyte can be determined by NMR. This content can be 10% to 60% by weight, preferably 15% to 50% by weight, and more preferably 20% to 40% by weight, relative to the total weight of the electrolyte composition.

[0037] The electrolyte composition according to the present invention is preferably non-aqueous or essentially non-aqueous. In the context of the present invention, the term "essentially non-aqueous" means that the water content in the electrolyte composition is 50 ppm or less, preferably 20 ppm or less.

[0038] The electrolyte composition has an organic solvent content of 20% to 85% by weight relative to the total weight of the electrolyte composition.

[0039] The organic solvent can be selected from ethers; carbonate esters or organic carbonates; cyclic carbonates; carboxylic acid esters; lactones; phosphate esters; nitriles; amides; lactams; nitro compounds; sulfones; sulfoxides; ionic liquids containing ammonium, imidazolium, pyrrolidinium, piperidinium, phosphonium, sulfonium, or oxonium-type cations along with FSI (bis(fluorosulfonyl)imide) anions; and fluorinated solvents.

[0040] The ethers can be selected from, in particular, ethylene glycol dimethyl ether (1,2-dimethoxyethane), ethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, 1,4-dioxane, and 1,3-dioxolane.

[0041] Carbonate esters or organic carbonates can be selected from dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), diphenyl carbonate, and phenylmethyl carbonate.

[0042] Cyclic carbonates can be selected from ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, vinylene carbonate (VC), and vinylethylene carbonate (VEC).

[0043] Carboxylic acid esters can be selected from methyl formate, methyl acetate, methyl propionate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate, vinyl acetate, divinyl adipate, methyl benzoate, and ethyl benzoate.

[0044] Lactones can be selected from γ-butyrolactone, γ-valerolactone, and δ-valerolactone.

[0045] The phosphate esters can be selected from trimethyl phosphate, dimethylethyl phosphate, diethylmethyl phosphate, and triethyl phosphate.

[0046] Nitriles can be selected from acetonitrile, propionitrile, methoxypropionitrile, glutalonitrile, adiponitrile, sebaconitrile, 2-methylglutalonitrile, valeronitrile, butyronitrile, isobutyronitrile, benzonitrile, and tolunitrile.

[0047] The amides can be selected from N-methylformamide, N-ethylformamide, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0048] Lactams can be selected from N-methylpyrrolidone, N-butylpyrrolidone, and N-vinylpyrrolidone.

[0049] Nitro compounds can include, for example, nitromethane.

[0050] The sulfones can be selected from dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, 2,4-dimethyl sulfolane, and sulfolene.

[0051] The sulfoxides can be selected from dimethyl sulfoxide, methyl ethyl sulfoxide, and diethyl sulfoxide.

[0052] The ionic liquids can be selected from EMIM-FSI (1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide), BMIM-FSI (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), PYR14-FSI (1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide), PYR13-FSI (1-propyl-3-methylpyrrolidinium bis(fluorosulfonyl)imide), PIP14-FSI (1-butyl-1-methylpiperidinium bis(fluorosulfonyl)imide), PIP13-FSI (1-methyl-1-propylpiperidinium bis(fluorosulfonyl)imide), P1444-FSI (methyl(tri-n-butyl)phosphonium bis(fluorosulfonyl)imide), and P1222-FSI (methyl(tri-n-ethyl)phosphonium bis(fluorosulfonyl)imide).

[0053] The fluorinating solvent can be selected from fluorinated ethers, fluorinated esters, fluorinated orthoformates, fluorinated carbonates, fluorinated phosphates, fluorinated phosphates, or fluorinated sulfates. Non-exclusive examples include 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, hexafluoroisopropyl methyl ether, 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether, and 1,1,2,3,3,3-hexafluoro Propylmethyl ether, 1,1,2,3,3,3-Hexafluoropropyl ethyl ether, 1,1,1,3,3,3-Hexafluoro-2-(2,2,2-trifluoroethoxy)propane, Bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-Tetrafluoroethyl 2,2,2-Trifluoroethyl ether, Methoxynonanafluorobutane, Ethoxynonanafluorobutane, 1,2-(1,1,2,2-Tetrafluoroethoxy)ethane, 2,2,3,3-Tetrafluoro- 1,4-Dimethoxybutane, 2-(2-ethoxyethyl)-1,1,1-trifluoroethane, 2-(2-(2,2-difluoroethoxy)ethoxy)-1,1-difluoroethane, 2-(2-(2,2-difluoroethoxy)ethoxy)-1,1,1-trifluoroethane, 1,1,1-trifluoro-2-(2-(2-trifluoroethoxy)ethoxy)ethane, 2,2-Difluoroethyl acetate, 2,2,2-Trifluoroethyl acetate, 2,2-Difluoropropionate ethyl acetate, 3,3-Difluoro Propyl ruoloacetate, 3,3-difluoropropyl propionate, 4,4-difluorobutanoate ethyl, difluoroethyl formate, trifluoroethyl formate, 2,2,2-trifluoroethyl orthoformate, 4-fluoro-1,3-dioxolan-2-one (F1EC), 4,5-difluoro-1,3-dioxolan-2-one (F2EC), ethyl 1-fluoroethyl carbonate (F1DEC), 1-fluoroethyl 2,2,2-trifluoroethyl carbonate (F4DEC), bis(2,2,Examples include 2-trifluoroethyl) carbonate (BFEC), 2,2,2-trifluoroethyl methyl carbonate (F3EMC), trifluoropropylene carbonate, monofluorodimethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, 2,2-difluoroethyl methyl carbonate, trifluoroethyl ethyl carbonate, methylhexafluoroisopropyl carbonate, ethylhexafluoroisopropyl carbonate, bis(trifluoroethyl) carbonate, propyltrifluoroethyl carbonate, fluorotoluene, and 1,4-dimethoxytetrafluorotoluene.

[0054] Solvents may be used individually or in combination.

[0055] Sulfones, sulfoxides, nitriles, ionic liquids, fluorinated ethers, and fluorinated carbonates are preferred. Among ionic liquids, pyrrolidiniums, piperidiniums, and phosphoniums are particularly preferred.

[0056] Sulfones, particularly sulfolanes, are more preferred.

[0057] The content of the organic solvent in the electrolyte composition according to the present invention is preferably between 30% and 85% by weight, more preferably between 40% and 85% by weight, more preferably between 50% and 80% by weight, and even more preferably between 60% and 75% by weight, based on the total weight of the electrolyte composition.

[0058] The electrolyte composition according to the present invention may optionally contain one or more additives. The additives can be selected from lithium salts other than LiFSI, silicon-containing organic compounds, boron-containing organic compounds, anhydrides, and aluminum-containing compounds.

[0059] Additional lithium salts other than LiFSI can be selected from LiPF6 (lithium hexafluorophosphate), LiTDI (lithium 2-trifluoromethyl-4,5-dicyanoimidazolate), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiB(C2O4)2), lithium difluoro(oxalato)borate (LiF2B(C2O4)2), lithium tetrafluoride (LiBF4), lithium nitrate (LiNO3), lithium perchlorate (LiClO4), lithium fluoride (LiF), and lithium fluorosulfate (FSO3Li).

[0060] The silicon-containing organic compounds can be selected from diphenylsilanediol, dimethoxyphenylsilane, tetrakis(trimethylsilyl)silane, trimethylsilyl acetate, trimethylsilyl trifluoroacetate, trimethylsilyl trifluoromethanesulfonate, bistrimethylsilyl sulfate, and tert-butyldimethylsilyl trifluoromethanesulfonate.

[0061] The phosphorus-containing organic compounds can be selected from tris(trimethylsilyl) phosphate, tris(hexafluoroisopropyl) phosphate, ethyl polyphosphate, bis(2,2,2-trifluoroethyl) phosphonate, trimethyl phosphate, and tris(trimethylsilyl) phosphate (TMSPi).

[0062] The sulfur-containing organic compounds can be selected from, in particular, propanesultone (PS), propane-1-ene-1,3-sultone (PES), methylenemethanedisulfonate (MMDS), ethylene sulfite, 1,4-butanesultone, and methyl methanesulfonate.

[0063] The boron-containing organic compounds can be selected from, in particular, trimethyl borate, triethyl borate, triisopropyl borate; tributyl borate, tris-2,2,2-trifluoroethyl borate, tris-trimethylsilyl borate, tris(pentafluorophenyl)borane, trimethoxyboroxine, triisopropylboroxine, and triphenylboroxine.

[0064] The anhydride can be selected from maleic anhydride, succinic anhydride, glutaric anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic acid anhydride, cyclopentanetetracarboxylic acid dianhydride, and phenylsuccinic anhydride.

[0065] The aluminum-containing compound (preferably in salt form) can be selected from aluminum tris-bis(fluorosulfonyl)imide (Al(FSI)3=Al[(N(SO2F)2]3), aluminum tris-bis(trifluoromethanesulfonyl)imide (Al(TFSI)3=Al[(N(SO2CF3)2]3), alkylaluminum compounds such as aluminum acetate, aluminum acetylacetonate, aluminum carbonate, aluminum nitrate, aluminum chlorate, and triethylaluminum, and aluminum alkoxides such as aluminum triethylate, with Al(FSI)3 being preferred.

[0066] The additive content in the electrolyte composition may be 0% to 10% by weight, preferably 0% to 5% by weight, relative to the total weight of the electrolyte composition.

[0067] Preferably, the electrolyte composition of the present invention has a weight concentration of aluminum in the electrolyte composition between 0.5 and 10,000 ppm, preferably between 0.5 and 9,000 ppm, preferably between 0.5 and 8,000 ppm, preferably between 0.5 and 7,000 ppm, preferably between 0.5 and 6,000 ppm, preferably between 0.5 and 5,000 ppm, preferably between 0.5 and 4,000 ppm, preferably between 0.5 and 3,000 ppm, preferably between 0.5 and 2,000 ppm, preferably between 0.5 and 1,000 ppm, preferably between 0.5 and 900 ppm, preferably between 0.5 and 800 ppm, preferably between 0.5 and 700 ppm. The solution contains an aluminum salt dissolved to a concentration of 0.5 to 600 ppm, preferably between 0.5 and 500 ppm, preferably between 0.5 and 400 ppm, preferably between 0.5 and 300 ppm, preferably between 0.5 and 200 ppm, preferably between 0.5 and 100 ppm, preferably between 0.5 and 90 ppm, preferably between 0.5 and 80 ppm, preferably between 0.5 and 70 ppm, preferably between 0.5 and 60 ppm, preferably between 0.5 and 50 ppm, preferably between 0.5 and 40 ppm, preferably between 0.5 and 30 ppm, preferably between 0.5 and 20 ppm, and preferably between 0.5 and 10 ppm.

[0068] The aluminum content in the electrolyte composition can be determined by any method known to those skilled in the art, particularly by ICP-MS (inductively coupled plasma mass spectrometry), ICP-AES (inductively coupled plasma atomic emission spectrometry), or X-ray fluorescence spectrometry, with ICP-MS being preferred.

[0069] In certain embodiments, the electrolyte composition according to the present invention exhibits a positive current difference between the forward sweep and the return sweep over a range of 4.2 to 5 V in cyclic voltammetry. Cyclic voltammetry is performed in a cell of three polypropylene Swagelok electrodes including an aluminum working electrode, optionally a lithium metal reference electrode, a lithium metal counter electrode, and the electrolyte composition. Cyclic voltammetry is performed under the following conditions: - Li + Sweep from 3 to 5 V vs. Li - Sweep rate of 1 mV / second - Temperature of 60 °C.

[0070] The positive current difference between the forward sweep and the return sweep over the range of 4.2 to 5 V means that at any potential value Ei selected between 4.2 V and 5 V, the forward sweep current I A (E i ) is greater than the return sweep current I R (E i ), that is, I A (E i ) - I R (E i ) > 0.

[0071] Advantageously, electrolyte compositions exhibiting such characteristics of the voltammetry curve make it possible to avoid corrosion of aluminum and, in particular, to improve the lifetime and the Coulombic efficiency of high-voltage cells.

[0072] In preferred embodiments of the present invention and in certain embodiments that can be combined with other embodiments, the electrolyte composition according to the present invention has a pH of 3.5 or higher when diluted in a mass ratio of 1:1 with distilled water at pH 6.5 and measured at a temperature of 25°C. The pH may be 4 or higher, preferably 4 to 8. The pH may be 3.5 to 4; or 4 to 4.5; or 4.5 to 5; or 5 to 5.5; or 5.5 to 6; or 6 to 6.5; or 6.5 to 7; or 7 to 7.5; or 7.5 to 8; or 8 to 8.5; or 8.5 to 9; or 9 to 9.5; or 9.5 to 10; or 10 to 10.5; or 10.5 to 11; or 11 to 11.5; or 11.5 to 12; or 12 to 12.5; or 12.5 to 13; or 13 to 13.5; or 13.5; or 13.5 to 14.

[0073] pH can be measured by any method known to those skilled in the art. For example, pH can be measured using a glass electrode whose potential can be varied as a function of hydrogen ion concentration according to the Nernst equation. This potential can be measured as a relative value to a reference electrode using a high-impedance potentiometer, commonly known as a pH meter. An example of a usable pH meter is the Radiometer pHM210 model. The pH meter can be pre-calibrated using three types of buffer solutions (e.g., pH = 4.0, 7.0, and 10.0). The aqueous solution can be stirred during pH measurement. It is preferable to measure the pH within one hour of dilution with distilled water.

[0074] The fact that the aqueous solution (prepared by dissolving lithium bis(fluorosulfonyl)imide salt in distilled water) has a pH of 3.5 or higher advantageously allows for the maintenance of stability of high-salt-concentration electrolytes even at high voltages (above 4.5V).

[0075] The electrolyte composition can be prepared by mixing a LiFSI salt, one or more organic solvents, and one or more additives optionally. Preferably, a desired amount of lithium salt is dissolved in one or more organic solvents, and then the optionally selected additives are added.

[0076] Preparation of lithium bis(fluorosulfonyl)imide salts LiFSI can be obtained by any method known to those skilled in the art, in particular by the process described in International Publication No. 2018 / 104674.

[0077] The present invention relates to either an electrolyte initially filled into a battery, or an electrolyte formed in situ during the operation of a battery.

[0078] Electrochemical cells and batteries The present invention also relates to the use of the electrolyte composition in lithium-ion batteries having a high-voltage (4.5V or higher) cathode, particularly in portable electronic devices such as mobile phones or portable computers, or electric vehicles, or in lithium-ion batteries for storing renewable energy such as solar power or wind power.

[0079] The present invention relates to the use of an electrolyte composition according to the present invention for extending the lifespan of a lithium-ion battery and / or improving the electronic performance (Coulomb efficiency) of a lithium-ion battery. More specifically, the present invention relates to the use of an electrolyte composition according to the present invention for forming a stable SEI on graphite in order to improve the Coulomb efficiency and lifespan of a lithium-ion battery.

[0080] The term "improved lithium-ion battery life" is understood to mean an increase in the number of cycles that can maintain at least 80% of the battery's initial capacity.

[0081] The term "improvement in the electronic performance (Coulomb efficiency) of lithium-ion batteries" is understood to mean an improvement in capacity, particularly at high charging or discharging currents after storage at low temperatures and / or high temperatures.

[0082] The term "stable SEI on graphite" is understood to mean achieving a lithium-free capacity that is stable over 5 cycles, i.e., without ±5% variation, and equivalent to at least 90% of the theoretical capacity of the active material. The lithium-free capacity is achieved during the discharge of a Li / graphite half-cell in charge-discharge cycles at a constant current of C / 10 between 0.01 and 1 V. This capacity can be achieved by any method known to those skilled in the art, for example, by a CR2016 button cell assembly comprising a stainless steel spring, a 1 mm diameter stainless steel shim, a 14 mm diameter lithium metal pellet, a 16 mm diameter fiberglass separator impregnated with 100 μL of electrolyte, and a 12 mm diameter graphite pellet.

[0083] The present invention also relates to an electrochemical cell comprising the electrolyte composition described above. The electrochemical cell also includes a negative electrode (or anode) and a positive electrode (or cathode). Preferably, the positive electrode (or cathode) operates at a high voltage (4.5V or higher).

[0084] An electrochemical cell may also include a separator impregnated with an electrolyte.

[0085] The term "negative electrode" refers to the electrode that functions as the anode when the cell is conducting current (i.e., during the discharge process) and as the cathode when the cell is charging.

[0086] The negative electrode typically comprises an electrochemically active material, optionally a conductive material, and optionally a binder.

[0087] "Positive electrode" refers to the electrode that functions as the cathode when the cell is conducting current (i.e., during the discharge process) and as the anode when the cell is charging.

[0088] The positive electrode typically comprises an electrochemically active material, optionally a conductive material, and optionally a binder.

[0089] The term "electrochemically active material" is understood to mean a material into which ions can be reversibly inserted.

[0090] The term "electronically conductive material" is understood to mean a material that can conduct electrons.

[0091] The negative electrode of an electrochemical cell is made of electrochemically active materials, such as graphite, lithium, lithium alloys, and Li4Ti5O. 12 This may include lithium titanate or titanium oxide (TiO2), silicon or lithium-silicon alloys, tin oxide, lithium intermetallic compounds, or mixtures thereof.

[0092] When the negative electrode contains lithium, the lithium can be in the form of a metallic lithium film or a lithium-containing alloy. Among the usable lithium-based alloys, examples that can be cited include lithium-aluminum alloys, lithium-silica alloys, lithium-tin alloys, Li-Zn, Li3Bi, Li3Cd, and Li3SB. An example of a negative electrode is a bright lithium film prepared by winding a lithium strip between rollers.

[0093] Preferably, the negative electrode is made of graphite.

[0094] The positive electrode contains a lithium oxide-type electrochemically active material having the following properties: - A layered structure represented by the formula LiMO2 (wherein M is a metal, particularly nickel, cobalt, manganese, aluminum, magnesium, titanium, chromium, or a combination thereof); - The spinel structure represented by the formula LiM2O4 (wherein M is a metal such as manganese, or a combination of manganese with nickel, cobalt, copper, iron, or chromium, in particular, LiNi 0.5-x Mn 1.5+x O4 (x is between 0 and 0.5), for example, LiNi 1 / 2 Mn 3 / 2 It is O4 (LNMO); - The spinel structure represented by the formula LiMO4 (where M is a combination of manganese, cobalt, iron, chromium, and nickel); - The olivine structure represented by the formula LiMPO4 (wherein M is a metal such as nickel, cobalt, or manganese, or a combination of iron, nickel, manganese, and cobalt); - Li 1+x M 1-x Formula of type O2 (wherein M is a metal such as nickel, cobalt, manganese, aluminum, magnesium, titanium, or chromium, or a combination of these metals); - LiMVO4 type structure (where M is a metal such as nickel); - Formula of type Li2MPO4F (where M is a metal such as cobalt); or - Formula for Li3M2(PO4)3 type (wherein M is a metal such as nickel, cobalt, manganese, iron, vanadium, or a combination of these metals).

[0095] These types of positive electrodes are described in particular in the reference Li, Wangda, Song, Bohang, & Manthiram, Arumugam, High-voltage positive electrode materials for lithium-ion batteries, Chemical Society Reviews, 2017, 46(10).

[0096] The positive electrode is preferably LNMO.

[0097] Alternatively or additionally, the positive electrode may contain sulfur, Li2S, O2, and / or LiO2 as electrochemically active materials.

[0098] The material of each electrode may include, in addition to an electrochemically active material, a conductive material, such as a carbon source (e.g., carbon black, Ketjen® carbon, Shawinigan carbon, graphite, graphene, carbon nanotubes, carbon fibers (e.g., vapor-grown carbon fibers VGCF), non-powdered carbon obtained by carbonization of organic precursors, or a mixture of two or more of these). Other additives, such as lithium salts, or ceramic or glass-type inorganic particles, or other suitable active materials (e.g., sulfur), may be present in the cathode material.

[0099] The material of each electrode may also include a binder. Non-limiting examples of binders include linear, branched, and / or crosslinked polyether polymer binders (e.g., polymers based on poly(ethylene oxide) (PEO) or poly(propylene oxide) (PPO), or mixtures thereof (or EO / PO copolymers), optionally containing crosslinkable units), water-soluble binders (e.g., SBR (styrene / butadiene rubber), NBR (acrylonitrile / butadiene rubber), HNBR (hydrogenated NBR), CHR (epichlorohydrin rubber), ACM (acrylic acid rubber), etc.), or fluoropolymer type binders (e.g., PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), etc.), and combinations thereof. Certain binders, such as water-soluble ones, may also include additives such as CMC (carboxymethylcellulose).

[0100] The metal supports of electrodes that function as current collectors are generally made of aluminum for the cathode and copper for the anode. The metal supports can be surface-treated and may have conductive primers. Conductive primers can include carbonaceous materials, metallic materials, and polymer materials, as described in the review by H. Jeong et al., Chemical Engineering Journal 446, 2022, 136860. The supports can also be woven or nonwoven fabrics made of carbon fiber.

[0101] The separator needs to exhibit thinness, sufficient mechanical strength and heat resistance, good electrochemical resistance to applied voltage, and optimal affinity to electrolytes simultaneously, and more generally, it needs to achieve excellent ionic conductivity. The separator may consist of a porous membrane (substrate). Examples of porous substrates useful as separators in the present invention include, but are not limited to, polyolefins, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, poly(phenylene oxide), poly(phenylene sulfide), polyethylene naphthalene, or mixtures thereof. Non-limiting examples of polyolefin separators include ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, or multilayer structures of the above polymers.

[0102] Alternatively, the separator may be made of glass fiber. Nonwoven fabrics made from natural or synthetic materials can also be used as the substrate for the separator. Porous substrates generally have a thickness of 1 to 50 μm and are typically films or cast nonwovens obtained by extrusion and stretching (wet or dry processes). The porous substrate preferably has a porosity between 5% and 95%. The average pore size (diameter) is preferably between 0.001 and 50 μm, more preferably between 0.01 and 10 μm.

[0103] The separator may include a coating. This coating can optionally be disposed on one or both sides of the porous support. In this case, the coating is used to coat at least one surface of the separator support in the form of a single layer or multiple layers. The coating can be a fluoropolymer alone or a mixture with an acrylic polymer. The fluoropolymer preferably contains monomer units derived from vinylidene fluoride. The separator coating can include inorganic particles that serve to form micropores (gaps between inorganic particles) within the coating. The addition of inorganic particles can also contribute to improving heat resistance or wettability. According to one embodiment, the inorganic particles are selected from the group consisting of: BaTiO3, Pb(Zr,Ti)O3, Pb1-x LaxZryO3 (0 < x < 1, 0 < y < 1), PbMg3Nb2 / 3)3, PbTiO3, hafnia (HfO(HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, Y2O3, boehmite (y-AlO(OH)), Al2O3, TiO2, SiC, ZrO2, borosilicate, BaSO4, nanoclay, or a mixture thereof.

[0104] The present invention also relates to a battery including at least one, preferably two or more, of the above-described electrochemical cells. The electrochemical cells can be assembled in series and / or in parallel within the battery.

[0105] Preferably, the battery according to the present invention has a cut-off voltage of 4.3 V or higher, more preferably 4.5 V or higher.

Examples

[0106] The following examples illustrate the present invention without limiting it.

[0107] Example 1 Electrolyte 1 is prepared by dissolving 2.9 g of LiFSI in 7.8 g of sulfolane.

[0108] The voltammetry curve of this electrolyte is obtained by filling a Swagelok-type polypropylene cell equipped with an aluminum working electrode and a lithium metal counter electrode with electrolyte 1.

[0109] The cyclic voltammetry conditions are as follows: • Sweeping Li+ / Li from 3 to 5V · Sweep speed 1mV / s · Temperature 60℃.

[0110] The voltammetry curve is shown in Figure 1.

[0111] Example 2 (Comparative Example) Electrolyte 2 is prepared by dissolving 0.76 g of LiPF6, 0.1 g of LiFSI, and 0.06 g of LiBOB in 1.98 g of ethyl carbonate (EC), 3.54 g of ethylmethyl carbonate (EMC), and 0.11 g of fluoroethylene carbonate (FEC).

[0112] The voltammetry curve of this electrolyte is obtained by filling a Swagelok-type polypropylene cell equipped with an aluminum working electrode and a lithium metal counter electrode with electrolyte 2.

[0113] The cyclic voltammetry conditions are as follows: • Sweeping Li+ / Li from 3 to 5V · Sweep speed 1mV / s · Temperature 60℃.

[0114] The voltammetry curve is shown in Figure 1.

[0115] Figure 1 shows that, unlike electrolyte 2, electrolyte 1 according to the present invention has a forward sweep current that is greater than the return sweep current over a potential range of 4.2 to 5 V.

[0116] Figure 3 shows that electrolyte 1 according to the present invention does not corrode aluminum (b), unlike electrolyte 2 (a), which shows corrosion traces on aluminum.

[0117] Example 3: Study of battery life using electrolyte 1 and electrolyte 2 To evaluate the effect of the electrolyte on battery life, a button cell was prepared. The button cell consists of a CR2032 case made of 316L stainless steel. The inside of the button cell consists of a lower case surrounded by a polypropylene seal, a 316L stainless steel spring, a 1 mm thick 316L stainless steel shim, a 14 mm diameter disc-shaped graphite anode, a Whatman fiberglass separator impregnated with 100 μL of electrolyte 1 or 2, a 12 mm disc-shaped LNMO cathode, and an aluminum strip that completely covers the upper case.

[0118] The LNMO cathode is prepared using a Thinky mixer by dispersing 93 wt% active material (LNMO TBM129, Haldor Topsoe), 4 wt% carbon black (C65, Imerys), and 3 wt% PVDF binder (Kynar® HSV1810, Arkema) in the solvent NMP (N-methylpyrrolidone) to obtain a solid content of 60%. The resulting ink is coated onto an aluminum collector at a speed of 0.2 m / min using a doctor blade with a height of 270 μm, and then dried in an oven at 90°C for 12 hours.

[0119] The surface area weight of the active material on the cathode is 13.5 mg / cm². 2 The electrodes are calendered to achieve a porosity of 30%.

[0120] The graphite anode is manufactured by NEI (part number BE-150E).

[0121] The surface area weight of the active material on the anode is 6.2 mg / cm². 2 That is the case.

[0122] The electrodes and separators are vacuum-dried at 60°C for 12 hours before battery assembly, and cell assembly is performed under dry room conditions with a dew point of -40°C.

[0123] The LNMO / graphite button cell will be tested with a VMP3 potentiostat (manufactured by Biologic). The test program consists of 400 cycles of formation cycles: two formation cycles at C / 10 (10-hour charge or discharge cycles) followed by CCCV charging (applying a constant current until the potential reaches 4.85V, then applying a constant potential phase until the current falls below C / 10), followed by CC (constant current) discharge (between 3.5V and 4.85V), followed by CCCV charging at C / 5 (5-hour charge or discharge cycles) and CC discharge down to 1C (between 3.5V and 4.85V).

[0124] Figure 2 shows the changes in volume and Coulomb efficiency for three cells containing electrolyte 1 and three cells containing electrolyte 2.

[0125] Using electrolyte 1 improves battery life and Coulomb efficiency compared to electrolyte 2, which is particularly related to the absence of corrosion in the aluminum collector.

Claims

1. An electrolyte composition, - 5% to 70% by weight of lithium bis(fluorosulfonyl)imide salt, - 20% to 85% by weight of at least one organic solvent and An electrolyte composition containing the following:

2. The electrolyte composition according to claim 1, wherein the organic solvent is selected from ethers; carbonate esters or organic carbonates; cyclic carbonates; carboxylic acid esters; lactones; phosphate esters; nitriles; amides; lactams; nitro compounds; sulfones; sulfoxides; ionic liquids containing an FSI (bis(fluorosulfonyl)imide) anion together with ammonium, imidazolium, pyrrolidinium, piperidinium, phosphonium, sulfonium, or oxonium-type cations; fluorinated solvents; and mixtures thereof, preferably selected from sulfones, sulfoxides, nitriles, ionic liquids, fluorinated ethers, and fluorinated carbonates; and mixtures thereof.

3. The electrolyte composition according to claim 1 or 2, wherein the solvent is sulfolane.

4. The electrolyte composition according to any one of claims 1 to 3, comprising 10% to 60% by weight, preferably 15% to 50% by weight, and more preferably 20% to 40% by weight of LiFSI, based on the total weight of the electrolyte composition.

5. The electrolyte composition according to any one of claims 1 to 4, comprising 30% to 85% by weight, preferably 40% to 85% by weight, more preferably 50% to 80% by weight, and even more preferably 60% to 75% by weight, of the total weight of the electrolyte composition, in the amount of solvent.

6. The weight concentration of aluminum relative to the weight of the electrolyte composition is preferably between 0.5 and 10,000 ppm by weight, preferably between 0.5 and 9,000 ppm by weight, preferably between 0.5 and 8,000 ppm by weight, preferably between 0.5 and 7,000 ppm by weight, preferably between 0.5 and 6,000 ppm by weight, preferably between 0.5 and 5,000 ppm by weight, preferably between 0.5 and 4,000 ppm by weight, preferably between 0.5 and 3,000 ppm by weight, preferably between 0.5 and 2,000 ppm by weight, preferably between 0.5 and 1,000 ppm by weight, preferably between 0.5 and 900 ppm by weight, preferably between 0.5 and 800 ppm by weight, preferably between 0.5 and 700 ppm by weight, preferably between 0.5 and 600 ppm by weight. The electrolyte composition according to any one of claims 1 to 5, further comprising an aluminum salt dissolved in such a concentration between 0.5 and 500 ppm by weight, preferably between 0.5 and 400 ppm by weight, preferably between 0.5 and 300 ppm by weight, preferably between 0.5 and 200 ppm by weight, preferably between 0.5 and 100 ppm by weight, preferably between 0.5 and 90 ppm by weight, preferably between 0.5 and 80 ppm by weight, preferably between 0.5 and 70 ppm by weight, preferably between 0.5 and 60 ppm by weight, preferably between 0.5 and 50 ppm by weight, preferably between 0.5 and 40 ppm by weight, preferably between 0.5 and 30 ppm by weight, preferably between 0.5 and 20 ppm by weight, preferably between 0.5 and 10 ppm by weight.

7. The electrolyte composition according to any one of claims 1 to 6, wherein in cyclic voltammetry, it exhibits a positive current difference between the forward sweep and the return sweep in the range of 4.2 to 5 volts in the first cycle.

8. The electrolyte composition according to any one of claims 1 to 7, characterized in that, after being diluted in a mass ratio of 1:1 with distilled water with a pH of 6.5, it has a pH of 3.5 or higher when measured at a temperature of 25°C.

9. An electrochemical cell comprising a negative electrode, a positive electrode, and an electrolyte composition according to any one of claims 1 to 8, wherein the negative electrode is made of graphite and the positive electrode is an LNMO electrode.

10. The electrochemical cell according to claim 9, preferably comprising an aluminum current collector electrode support combined with a positive electrode.

11. A battery comprising at least one electrochemical cell as described in claim 9 or 10.

12. The battery according to claim 11, having a cutoff voltage of 4.5V or higher.

13. Use of the electrolyte composition according to any one of claims 1 to 8 in a lithium-ion battery, preferably a lithium-ion battery for a portable electronic device such as a mobile phone or portable computer, a lithium-ion battery for an electric vehicle, or a lithium-ion battery for storing renewable energy such as solar energy or wind energy.

14. The use of a Li-ion battery having a cutoff voltage of 4.5V or higher, as described in claim 13.

15. Use of an electrolyte composition according to any one of claims 1 to 8, preferably having a cutoff voltage of 4.5V or higher, for extending the lifespan of a Li-ion battery and / or improving the electronic performance of a Li-ion battery.

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