High-voltage electrolyte and preparation method and application thereof

Abstract

The invention relates to a high-voltage electrolyte as well as a preparation method and application thereof. The high-voltage electrolyte comprises an electrolyte, a non-aqueous organic solvent and an additive, the additives comprise an organic compound additive, a lithium salt additive and a film-forming additive; the structural formula of the organic compound additive is shown in the specification, wherein R1 and R2 are alkyl or oxygen-containing alkyl with the carbon atom number of 1-12; the non-aqueous organic solvent comprises a cyclic solvent, a chain ester solvent and a fluorine-containing solvent; when the high-voltage electrolyte is applied to the lithium ion battery, the cycle performance, the rate capability and the safety performance of the lithium ion battery under a high-voltage condition can be remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and in particular to a high-voltage electrolyte, its preparation method, and its application. Background Technology

[0002] Currently, the application of high-performance power batteries hinges on improving their specific energy and safety. Specific energy is equal to the product of the electrode material's specific capacity and its operating voltage. Two main ways to increase the energy density of lithium-ion batteries are: first, increasing the specific capacity of the electrode material; and second, increasing its plateau voltage.

[0003] Currently, the capacity of transition metal oxide cathodes is approaching its limit due to electrolyte stability constraints. To further improve the energy density of lithium-ion batteries (LIBs), the most promising strategies are to increase the cutoff voltage of mainstream cathodes or explore novel high-capacity and high-voltage cathode materials, as well as to replace graphite anodes with Si / Si-C or lithium metal. However, commercial ethylene carbonate (EC)-based electrolytes exhibit relatively low cathode stability and cannot withstand higher voltages. The bottleneck limiting the electrochemical performance of lithium-ion batteries has shifted to novel electrolytes suitable for next-generation cathodes, Si / Si-C, or lithium metal anodes, as the oxidation resistance of the electrolyte and the in-situ formed cathode-electrolyte interface (CEI) layer and solid electrolyte interface (SEI) layer on the anode strictly control the electrochemical performance of these high-voltage lithium-ion batteries.

[0004] Conventional carbonate electrolyte systems primarily operate at 4.2V. However, for high-energy-density cathode materials, electrolytes capable of withstanding even higher voltages are required. The upper limit of the charging voltage for ordinary electrolytes is less than 4.3V. This is mainly because when the battery charging voltage exceeds 4.3V, deterioration begins rapidly. The electrolyte starts to decompose, generating gases such as H2, alkanes, and alkenes, causing increased internal pressure or bulging, reducing its electrical performance, and leading to premature battery failure. Furthermore, the oxidation capacity of lithium-ion battery cathode materials with charging voltage limits exceeding 4.3V also increases with increasing charging voltage, accelerating the decomposition of carbonate electrolytes. Existing industrial electrolytes are insufficient to meet the requirements of cathode materials operating at 4.3V-5.0V charge-discharge platforms.

[0005] However, high cutoff voltage conditions lead to cathode structural degradation and rapid capacity decay. This is because increasing the cutoff voltage accelerates the dissolution of the oxide cathode material and interfacial side reactions between the electrolyte, even causing cracks due to phase transitions. When the charging voltage exceeds 4.3V, with the increase of Li... + Excessive extraction from the crystal leads to the collapse of the layer structure and oxygen evolution, as well as the dissolution of transition metals from the surface of the cathode material, resulting in severe surface structure degradation, irreversible phase transition, and rapid capacity degradation.

[0006] Existing lithium batteries experience increased polarization and deteriorated discharge performance at low temperatures. The main issue with lithium-ion batteries at low temperatures is diffusion, a reversible process that does not significantly damage the original battery composition and structure. + The diffusion rate in the electrolyte and in the electrode surface film, and Li + Both the charge transfer rate of electrons (e) at the electrode / electrolyte interface and the rate of charge transfer decrease significantly with decreasing temperature. Therefore, in the low-temperature electrochemical impedance spectroscopy of lithium-ion batteries, the resistance of the electrolyte (R0) and the resistance of the positive and negative electrode surface films (R...)... i ) and charge transfer impedance (R ct All of them increased significantly. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing a high-voltage electrolyte, its preparation method, and its application.

[0008] The high-voltage electrolyte provided in this invention combines organic compound additives with negative electrode film-forming additives with special molecular structures. On the one hand, since the LUMO energy of the negative electrode film-forming additives is much lower than that of the electrolyte solvent, the negative electrode film-forming additives decompose preferentially in the electrolyte compared to the solvent, thereby effectively suppressing the gas generation problem caused by electrolyte decomposition. On the other hand, the solid electrolyte interphase (SEI) film formed on the negative electrode surface by the decomposition products of the negative electrode film-forming additives is thin and has high mechanical strength, which can reduce the impedance of the negative electrode interphase film and ensure cycle stability. Furthermore, lithium salt additives can effectively suppress the precipitation of metal ions at the positive electrode under high voltage or high temperature conditions during battery charging and discharging, resulting in a denser and more stable SEI film on the negative electrode, effectively inhibiting the reduction of metal ions at the negative electrode. The positive electrode interface also has a low charge transfer impedance and good low-temperature performance. At the same time, the high-voltage electrolyte provided by this invention adds partially or fully fluorinated organic solvents. The introduction of fluorine reduces the HOMO and LUMO energies of the molecules, inducing a higher oxidation potential and stronger antioxidant capacity. It can also reduce the viscosity of the electrolyte, which is beneficial to the wetting of the electrolyte and the utilization of battery capacity. At the same time, it improves the flame retardancy of the electrolyte. When used in combination with commonly used high dielectric constant carbonate and sulfone solvents as well as low viscosity carbonate and carboxylic acid ester solvents, it significantly improves the cycle performance and rate performance of lithium-ion batteries under high voltage conditions.

[0009] To achieve the above objectives, in a first aspect, embodiments of the present invention provide a high-voltage electrolyte, the high-voltage electrolyte comprising: an electrolyte, a non-aqueous organic solvent, and additives;

[0010] The additives include: organic compound additives, lithium salt additives, and film-forming additives;

[0011] The structural formula of the organic compound additive is:

[0012] R1 and R2 are hydrocarbon groups or oxygen-containing hydrocarbon groups with 1 to 12 carbon atoms;

[0013] The non-aqueous organic solvents include: cyclic solvents, chain ester solvents, and fluorinated solvents.

[0014] Preferably, the electrolyte is a lithium electrolyte salt, including one or more of the following: lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium perchlorate, lithium (fluorosulfonyl)trifluoromethanesulfonylimide, lithium tetrachloroaluminate, and lithium hexafluoroarsenate; the concentration of the electrolyte in the high-voltage electrolyte is 0.8 mol / L to 2 mol / L; and the lithium electrolyte salt is different from the lithium salt additive.

[0015] Preferably, the cyclic solvent comprises one or more of the following: ethylene carbonate, propylene carbonate, vinylene carbonate, ethylene ethylene carbonate, γ-butyrolactone, sulfolane, and 3-methylsulfolane; the cyclic solvent accounts for 24% to 27% of the total solvent mass of the high-voltage electrolyte;

[0016] The chain-like ester solvent includes one or more of the following: dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and methyl butyrate; the chain-like ester solvent accounts for 56% to 63% of the total solvent mass of the high-voltage electrolyte.

[0017] The fluorinated solvent includes one or more of the following: fluoroethylene carbonate, fluoromethyl ethyl carbonate, 2-fluorotetrahydrofuran, 3-fluorotetrahydrofuran, 3-trifluoromethyltetrahydrofuran, 2-trifluoromethyltetrahydrofuran, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether; the fluorinated solvent accounts for 10% to 20% of the total solvent mass of the high-voltage electrolyte.

[0018] Preferably, the organic compound additive accounts for 0.5% to 5% of the total mass of the high-voltage electrolyte;

[0019] The lithium salt additive includes one or more of lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), lithium difluorooxalateborate, and lithium tetrafluoroborate, and the mass of the lithium salt additive accounts for 0.1% to 3% of the total mass of the high-voltage electrolyte.

[0020] The film-forming additive includes one or more of the following: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, 1,3-propane sulpholactone, 1,3-propene sulpholactone, vinyl sulfate, vinyl sulfite, propylene sulfite, and 4-methyl vinyl sulfite; the mass of the film-forming additive accounts for 0.1% to 3% of the total mass of the high-voltage electrolyte.

[0021] Secondly, embodiments of the present invention provide a method for preparing the high-voltage electrolyte described in the first aspect above, the preparation method comprising:

[0022] The preparation of an organic compound additive includes: mixing raw materials 2,5-difluoroterephthalic acid and sulfoxide with catalyst N,N-dimethylformamide, and reacting at a certain temperature to generate 2,5-difluoroterephthaloyl chloride; reacting the 2,5-difluoroterephthaloyl chloride with a nitrogen-containing compound under dehydration conditions to obtain an organic compound additive containing a cyano group; the structural formula of the organic compound additive is:

[0023] R1 and R2 are hydrocarbon groups or oxygen-containing hydrocarbon groups with 1 to 12 carbon atoms;

[0024] The preparation of the precursor electrolyte includes: mixing a cyclic solvent, a chain ester solvent, and a fluorinated solvent in an argon-filled glove box to obtain a non-aqueous organic solvent, allowing it to stand in a low-temperature environment, then adding an electrolyte to the non-aqueous organic solvent, stirring until the electrolyte dissolves, and obtaining the precursor electrolyte.

[0025] Preparation of high-voltage electrolyte: In an argon-filled glove box, the organic compound additive, lithium salt additive, and film-forming additive are added to the precursor electrolyte and stirred evenly to obtain the high-voltage electrolyte.

[0026] Preferably, the mass ratio of 2,5-difluoroterephthalic acid to sulfoxide is 1:1.4 to 1:2.5; the mass of N,N-dimethylformamide is 0.5% to 2% of the mass of 2,5-difluoroterephthalic acid; and the reaction temperature is 60°C to 80°C.

[0027] The method of reacting the 2,5-difluoroterephthaloyl chloride with a nitrogen-containing compound under dehydration conditions to obtain an organic compound additive containing a cyano group specifically includes: dissolving a certain mass of 2,5-difluoroterephthaloyl chloride in an organic solvent under constant temperature conditions of 25℃~80℃, then adding the nitrogen-containing compound, stirring for 30min~60min, continuing to raise the temperature to 120℃~140℃, adding zinc oxide catalyst, and reacting for 4h~6h to obtain the organic compound additive containing a cyano group.

[0028] The organic solvent comprises xylene and / or chlorobenzene, and 3-5 L of organic solvent is used per 1 kg of 2,5-difluoroterephthaloyl chloride; the mass ratio of 2,5-difluoroterephthaloyl chloride to the nitrogen-containing compound is 1-1.45; the nitrogen-containing compound comprises ammonia and / or urea; the mass of zinc oxide is 0.1%-0.5% of the mass of 2,5-difluoroterephthaloyl chloride.

[0029] Preferably, the water and oxygen content in the glove box is less than or equal to 0.1 PPM;

[0030] The cyclic solvent includes one or more of the following: ethylene carbonate, propylene carbonate, vinylene carbonate, ethylene ethylene carbonate, γ-butyrolactone, sulfolane, and 3-methylsulfolane; the cyclic solvent accounts for 24% to 27% of the total solvent mass of the high-voltage electrolyte;

[0031] The chain-like ester solvent includes one or more of the following: dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and methyl butyrate; the chain-like ester solvent accounts for 56% to 63% of the total solvent mass of the high-voltage electrolyte.

[0032] The fluorinated solvent includes one or more of the following: fluoroethylene carbonate, fluoromethyl ethyl carbonate, 2-fluorotetrahydrofuran, 3-fluorotetrahydrofuran, 3-trifluoromethyltetrahydrofuran, 2-trifluoromethyltetrahydrofuran, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether; the fluorinated solvent accounts for 10% to 20% of the total solvent mass of the high-voltage electrolyte.

[0033] The temperature of the low-temperature environment is -20℃ to 0℃; the standing time is 2 hours to 8 hours;

[0034] The electrolyte is a lithium salt, including one or more of the following: lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium difluorophosphate, lithium difluorooxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium perchlorate, lithium (fluorosulfonyl)trifluoromethanesulfonylimide, lithium tetrachloroaluminate, and lithium hexafluoroarsenate; the concentration of the electrolyte in the high-voltage electrolyte is 0.8 mol / L to 2 mol / L.

[0035] Preferably, the organic compound additive accounts for 0.5% to 5% of the total mass of the high-voltage electrolyte;

[0036] The lithium salt additive includes one or more of lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate borate), lithium difluorooxalate borate, and lithium tetrafluoroborate. The lithium salt additive accounts for 0.1% to 3% of the total mass of the high-voltage electrolyte. The lithium salt additive is of a different type than the lithium salt in the electrolyte.

[0037] The film-forming additive includes one or more of the following: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, 1,3-propane sulpholactone, 1,3-propene sulpholactone, vinyl sulfate, vinyl sulfite, propylene sulfite, and 4-methyl vinyl sulfite; the mass of the film-forming additive accounts for 0.1% to 3% of the total mass of the high-voltage electrolyte.

[0038] Thirdly, embodiments of the present invention provide a lithium-ion battery, the lithium-ion battery comprising: the high-voltage electrolyte described in the first aspect above, as well as a positive electrode, a negative electrode, and a separator.

[0039] Preferably, the positive electrode active material of the positive electrode sheet includes: LiNi x Co y Mn z L (1-x-y-z) O2, Li a MPO4, LiCo b L (1-b) One or more of O2, wherein L is at least one element selected from Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, and Fe, M is at least one element selected from Fe, Mn, and Co, and 0≤x≤1, 0≤y≤1, 0≤z≤1, 0<x+y+z≤1, 0.5≤a≤1, and 0<b≤1;

[0040] The negative electrode active material of the negative electrode sheet includes one or more of the following: artificial graphite, natural graphite, silicon, silicon oxide, silicon-based alloy, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, and lithium titanate.

[0041] The diaphragm comprises one or more of the following: polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyurethane, polyester, aramid, and natural fibers.

[0042] The high-voltage electrolyte, its preparation method, and its application provided in this invention have the following beneficial effects:

[0043] (1) The present invention provides a method for preparing a high-voltage electrolyte by adding an organic compound additive with a special structure, a lithium salt additive, and a negative electrode film-forming additive to a precursor electrolyte to form a high-voltage electrolyte. The three additives work synergistically, giving the high-voltage electrolyte provided by the present invention the advantages of high electrochemical performance and high safety.

[0044] (2) The high-voltage electrolyte provided in this embodiment of the invention utilizes an organic compound additive that possesses excellent dehydration, deacidification, and high-voltage performance due to the presence of two cyano functional groups. This organic compound additive interacts with the cathode material; the high electronegativity of the cyano group (C≡N) in the organic compound additive makes the molecule as a whole exhibit strong polarity, allowing it to preferentially adsorb onto the surface of the cathode material, occupying the metal active sites of the cathode material and forming a physical barrier. Furthermore, the nitrogen atom in the cyano group contains a lone pair of electrons, which can interact with transition metals (such as Ni) on the surface of the cathode material. 3+ Co 3+ It can coordinate with trace amounts of HF in the electrolyte to inhibit the dissolution of transition metals. In addition, C≡N can form a hydrogen bond network with trace amounts of HF in the electrolyte through polar interaction, thereby adsorbing acidic impurities on the molecular surface. It can also adsorb water molecules through hydrogen bonding to achieve the effect of removing water and acid, thereby improving the high voltage resistance of the electrolyte.

[0045] (3) The high-voltage electrolyte provided in this embodiment of the invention uses organic compound additives with special molecular structures in combination with negative electrode film-forming additives. On the one hand, since the LUMO energy of the negative electrode film-forming additives is much lower than that of the electrolyte solvent, the negative electrode film-forming additives decompose preferentially in the electrolyte compared with the solvent, thereby effectively suppressing the gas generation problem caused by electrolyte decomposition. On the other hand, the solid electrolyte interphase (SEI) film generated on the negative electrode surface by the decomposition products of the negative electrode film-forming additives is thin and has high mechanical strength, which can reduce the impedance of the negative electrode interphase film and ensure cycle stability.

[0046] (4) The high-voltage electrolyte provided in this embodiment of the invention, with lithium salt additives, can effectively suppress the precipitation of metal ions at the positive electrode under high voltage or high temperature conditions during battery charging and discharging. The resulting negative electrode SE I film is denser and more stable, effectively suppressing the reduction of metal ions at the negative electrode. The positive electrode interface also has a low charge transfer impedance and good low-temperature performance.

[0047] (5) In addition, the high-voltage electrolyte provided in this embodiment of the invention is supplemented with partially or fully fluorinated organic solvents. The introduction of fluorine reduces the HOMO and LUMO energies of the molecules, induces a higher oxidation potential, has stronger antioxidant capacity, and can reduce the viscosity of the electrolyte, which is beneficial to the wetting of the electrolyte and the utilization of battery capacity. At the same time, it improves the flame retardancy of the electrolyte. When used in combination with commonly used high dielectric constant cyclic solvents (such as carbonate cyclic solvents and sulfone cyclic solvents) and low viscosity chain ester solvents (such as carbonate chain ester solvents and carboxylic acid ester chain ester solvents), the cycle performance and rate performance of lithium-ion batteries under high voltage conditions are significantly improved.

[0048] (6) Applying the high-voltage electrolyte provided in the embodiments of the present invention to lithium-ion batteries can significantly improve the safety, cycle performance and rate performance of lithium-ion batteries. Attached Figure Description

[0049] Figure 1 A flowchart illustrating the preparation method of high-voltage electrolyte provided in an embodiment of the present invention. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0051] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0052] This invention provides a high-voltage electrolyte, comprising: an electrolyte, a non-aqueous organic solvent, and additives.

[0053] The electrolyte is a lithium electrolyte salt, including one or more of the following: lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium perchlorate, lithium (fluorosulfonyl)trifluoromethanesulfonylimide, lithium tetrachloroaluminate, and lithium hexafluoroarsenate; the concentration of the electrolyte in the high-voltage electrolyte is 0.8 mol / L to 2 mol / L, and can be any value within this range, such as: 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0054] Non-aqueous organic solvents include: cyclic solvents, chain ester solvents, and fluorinated solvents.

[0055] Specifically, the cyclic solvent includes one or more of the following: ethylene carbonate, propylene carbonate, vinylene carbonate, ethylene ethylene carbonate, γ-butyrolactone, sulfolane, and 3-methylsulfolane; the cyclic solvent accounts for 24% to 27% of the total mass of the solvent in the high-voltage electrolyte, and can be any value within this range, such as 24%, 25%, 26%, 27%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] The chain ester solvent includes one or more of the following: dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and methyl butyrate; the chain ester solvent accounts for 56% to 63% of the total mass of the solvent in the high-voltage electrolyte, and can be any value within this range, such as 56%, 57%, 58%, 59%, 62%, 61%, 62%, 63%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0057] Fluorinated solvents include one or more of the following: fluoroethylene carbonate, fluoromethyl ethyl carbonate, 2-fluorotetrahydrofuran, 3-fluorotetrahydrofuran, 3-trifluoromethyltetrahydrofuran, 2-trifluoromethyltetrahydrofuran, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether; the fluorinated solvent accounts for 10% to 20% of the total mass of the solvent in the high-voltage electrolyte, and can be any value within this range, such as 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0058] Additives include: organic compound additives, lithium salt additives, and film-forming additives.

[0059] Specifically, the structural formula of the organic compound additive is as follows:

[0060] R1 and R2 are hydrocarbon groups or oxygen-containing hydrocarbon groups with 1 to 12 carbon atoms; the mass of the organic compound additive accounts for 0.5% to 5% of the total mass of the high-voltage electrolyte, and can be any value within this range, such as: 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0061] The organic compound additive provided by this invention exhibits excellent dehydration, deacidification, and high-pressure performance due to the presence of two cyano functional groups. This organic compound additive interacts with the cathode material; the high electronegativity of the cyano group (C≡N) in the additive makes the entire molecule highly polar, allowing it to preferentially adsorb onto the surface of the cathode material, occupying the metal active sites and forming a physical barrier. Furthermore, the nitrogen atom in the cyano group contains a lone pair of electrons, which can interact with transition metals (such as Ni) on the surface of the cathode material. 3+ Co 3+ It can coordinate with trace amounts of HF in the electrolyte to inhibit the dissolution of transition metals. In addition, C≡N can form a hydrogen bond network with trace amounts of HF in the electrolyte through polar interaction, thereby adsorbing acidic impurities on the molecular surface. It can also adsorb water molecules through hydrogen bonding to achieve the effect of removing water and acid, thereby improving the high voltage resistance of the electrolyte.

[0062] The lithium salt additives include one or more of the following: lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate-borate), lithium difluorooxalate-borate, and lithium tetrafluoroborate. The lithium salt additives account for 0.1% to 3% of the total mass of the high-voltage electrolyte, and can be any value within this range, such as 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, etc., but are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0063] In this invention, the lithium salt additive and the electrolyte lithium salt are not the same type. The electrolyte lithium salt (such as lithium hexafluorophosphate) is the main component, providing the basic ionic conductivity; the lithium salt additive (such as lithium difluorophosphate) is used for film formation at the positive electrode interface to solve the oxidation problem under high voltage, with strong functional targeting and low dosage. The difference in type between the two is necessary to achieve synergistic effects, thereby meeting the requirements for high voltage resistance.

[0064] Film-forming additives include one or more of the following: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, 1,3-propane sulpholactone, 1,3-propene sulpholactone, vinyl sulfate, vinyl sulfite, propylene sulfite, and 4-methyl vinyl sulfite; the mass of the film-forming additives accounts for 0.1% to 3% of the total mass of the high-voltage electrolyte, and can be any value within this range, such as 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable. This film-forming additive is a negative electrode film-forming additive. Since the LUMO energy of the negative electrode film-forming additive is much lower than that of the electrolyte solvent, the negative electrode film-forming additive decomposes preferentially in the electrolyte compared with the solvent, thereby effectively suppressing the gas generation problem caused by electrolyte decomposition. Furthermore, the solid electrolyte interphase (SEI) film formed on the negative electrode surface by the decomposition products of the negative electrode film-forming additive is thin and has high mechanical strength, which can reduce the impedance of the negative electrode interphase film and ensure cycle stability.

[0065] This invention provides a method for preparing the above-mentioned high-voltage electrolyte, such as... Figure 1 As shown, the specific steps include:

[0066] Step 110, preparing an organic compound additive, includes: mixing raw materials 2,5-difluoroterephthalic acid, sulfonium chloride and catalyst N,N-dimethylformamide, and reacting them at a certain temperature to generate 2,5-difluoroterephthaloyl chloride; reacting 2,5-difluoroterephthaloyl chloride with a nitrogen-containing compound under dehydration conditions to obtain an organic compound additive containing cyano groups.

[0067] Specifically, the mass ratio of 2,5-difluoroterephthalic acid to thionyl chloride is 1:1.4 to 1:2.5; the mass of N,N-dimethylformamide is 0.5% to 2% of the mass of 2,5-difluoroterephthalic acid; and the reaction temperature is 60℃ to 80℃.

[0068] 2,5-Difluoroterephthaloyl chloride is reacted with a nitrogen-containing compound under dehydration conditions to obtain an organic compound additive containing a cyano group. Specifically, the reaction involves dissolving a certain mass of 2,5-difluoroterephthaloyl chloride in an organic solvent at a constant temperature of 25℃ to 80℃, then adding the nitrogen-containing compound, stirring for 30 to 60 minutes, further heating to 120℃ to 140℃, adding zinc oxide as a catalyst, and reacting for 4 to 6 hours to obtain the organic compound additive containing a cyano group. The organic solvent includes xylene and / or chlorobenzene, and 3 to 5 L of organic solvent is used per 1 kg of 2,5-difluoroterephthaloyl chloride. The mass ratio of 2,5-difluoroterephthaloyl chloride to the nitrogen-containing compound is 1 to 1.45; the nitrogen-containing compound includes ammonia and / or urea; and the mass of zinc oxide is 0.1% to 0.5% of the mass of 2,5-difluoroterephthaloyl chloride.

[0069] The structural formula of the organic compound additive is:

[0070] R1 and R2 are hydrocarbon groups or oxygen-containing hydrocarbon groups with 1 to 12 carbon atoms.

[0071] Step 120, preparing the precursor electrolyte, includes: mixing a cyclic solvent, a chain ester solvent and a fluorinated solvent in an argon-filled glove box to obtain a non-aqueous organic solvent, allowing it to stand in a low-temperature environment, then adding an electrolyte to the non-aqueous organic solvent, stirring evenly to dissolve the electrolyte, and obtaining the precursor electrolyte.

[0072] Specifically, the water and oxygen content inside the glove box is less than or equal to 0.1 PPM;

[0073] Cyclic solvents include one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), γ-butyrolactone, sulfolane, and 3-methylsulfolane; cyclic solvents account for 24% to 27% of the total solvent mass of the high-voltage electrolyte;

[0074] The chain ester solvent includes one or more of the following: dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and methyl butyrate; the chain ester solvent accounts for 56% to 63% of the total mass of the solvent in the high-voltage electrolyte.

[0075] Fluorinated solvents include one or more of the following: fluoroethylene carbonate, fluoromethyl ethyl carbonate, 2-fluorotetrahydrofuran, 3-fluorotetrahydrofuran, 3-trifluoromethyltetrahydrofuran, 2-trifluoromethyltetrahydrofuran, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether; the fluorinated solvents account for 10% to 20% of the total solvent mass of the high-voltage electrolyte;

[0076] The low-temperature environment is -20℃ to 0℃; the standing time is 2 hours to 8 hours. Step 130, preparation of high-voltage electrolyte: In a glove box filled with argon gas, organic compound additives, lithium salt additives and film-forming additives are added to the precursor electrolyte and stirred evenly to obtain the high-voltage electrolyte;

[0077] The electrolyte is a lithium electrolyte salt, including one or more of the following: lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium perchlorate, lithium (fluorosulfonyl)trifluoromethanesulfonylimide, lithium tetrachloroaluminate, and lithium hexafluoroarsenate; the concentration of the electrolyte in the high-voltage electrolyte is 0.8 mol / L to 2 mol / L.

[0078] The organic compound additives account for 0.5% to 5% of the total mass of the high-voltage electrolyte;

[0079] The lithium salt additives include one or more of the following: lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), lithium difluorooxalateborate, and lithium tetrafluoroborate. The lithium salt additives account for 0.1% to 3% of the total mass of the high-voltage electrolyte. The lithium salts used in the lithium salt additives are different from those used in the electrolyte lithium salt.

[0080] The film-forming additives include one or more of the following: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, 1,3-propane sulpholactone, 1,3-propene sulpholactone, vinyl sulfate, vinyl sulfite, propylene sulfite, and 4-methyl vinyl sulfite; the mass of the film-forming additives accounts for 0.1% to 3% of the total mass of the high-voltage electrolyte.

[0081] In this invention, the high-voltage electrolyte employs three solvents: a cyclic solvent, a chain ester solvent, and a fluorinated solvent. The cyclic solvent is characterized by high polarity and high dielectric constant, providing excellent ion dissociation capability. The chain ester solvent is characterized by low viscosity, low melting point, and good fluidity, used to reduce electrolyte viscosity and improve low-temperature performance. The fluorinated solvent is characterized by high oxidation stability, low flammability, and enhanced electrochemical performance, which is beneficial for improving the safety of lithium batteries, such as inhibiting dendrite growth and effectively improving the wide temperature range performance of lithium batteries.

[0082] The high-voltage electrolyte prepared by the preparation method provided in this embodiment of the invention can be used in lithium-ion batteries, which also include a positive electrode, a negative electrode, and a separator.

[0083] The positive electrode active material of the positive electrode sheet includes, but is not limited to: LiNi x Co y Mn z L (1-x-y-z) O2, Li a MPO4, LiCo b L (1-b) One or more of O2, wherein L is at least one element selected from Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, and Fe, M is at least one element selected from Fe, Mn, and Co, and 0≤x≤1, 0≤y≤1, 0≤z≤1, 0<x+y+z≤1, 0.5≤a≤1, and 0<b≤1.

[0084] The negative electrode active material of the negative electrode sheet includes, but is not limited to, one or more of the following: artificial graphite, natural graphite, silicon, silicon oxide, silicon-based alloy, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, and lithium titanate.

[0085] The separator includes, but is not limited to, one or more of the following: polyethylene separator, polypropylene separator, polyvinylidene fluoride separator, polytetrafluoroethylene separator, polyacrylonitrile separator, polyimide separator, polyurethane separator, polyester separator, aramid separator, natural fiber separator, and composite separator.

[0086] To better understand the technical solution provided by the present invention, the preparation process and characteristics of the high-voltage electrolyte of the present invention are illustrated below with several specific examples.

[0087] Example 1

[0088] This embodiment provides a preparation process for a high-voltage electrolyte, as detailed below.

[0089] (1) Preparation of organic compound additives, specifically including: mixing 1 kg of 2,5-difluoroterephthalic acid, 1.4 kg of thionyl chloride and 10 g of N,N-dimethylformamide catalyst, and reacting at 80°C to generate 2,5-difluoroterephthaloyl chloride; dissolving 1 kg of 2,5-difluoroterephthaloyl chloride in 3 L of toluene under constant temperature of 80°C, then adding 1 kg of ammonia water, stirring for 40 min, continuing to heat to 120°C, adding 3 g of zinc oxide catalyst, and reacting for 5 hours to obtain an organic compound additive containing cyano groups, with the following structural formula:

[0090]

[0091] The mass ratio of 2,5-difluoroterephthalic acid to thionyl chloride is 1:1.4, and the mass of N,N-dimethylformamide is 1% of the mass of 2,5-difluoroterephthalic acid.

[0092] (2) Preparation of precursor electrolyte, specifically including: mixing ethylene carbonate, ethyl methyl carbonate and methyl fluorocarbonate in a mass ratio of 27:60:13 in a glove box filled with argon gas and containing both water and oxygen content ≤0.1PPM to obtain a non-aqueous organic solvent; letting the non-aqueous organic solvent stand in a low temperature environment of -10℃ for 4 hours; then adding the electrolyte lithium hexafluorophosphate to the non-aqueous organic solvent and stirring evenly to dissolve the electrolyte to obtain a precursor electrolyte with a lithium hexafluorophosphate molar concentration of 1mol / L.

[0093] (3) Preparation of high-voltage electrolyte, specifically including: in a glove box filled with argon gas and with both water and oxygen content ≤0.1PPM, adding the organic compound additive, lithium salt additive lithium difluorophosphate and film-forming additive vinylene carbonate prepared in step (1) to the precursor electrolyte prepared in step (2), stirring evenly to obtain high-voltage electrolyte; wherein, the organic compound additive, lithium difluorophosphate and vinylene carbonate account for 0.5%, 0.5% and 1.5% of the mass of the high-voltage electrolyte, respectively.

[0094] The high-voltage electrolyte prepared in this embodiment was used to assemble a lithium-ion battery (5Ah soft-pack cell), and the lithium-ion battery was tested. The specific process is as follows, and the test data is detailed in Table 2.

[0095] The upper limit voltage of the single-crystal ternary cathode material LiNi is 4.45V. 0.4 Co 0.3 Mn 0.2 02 (NCM432), conductive carbon black, multi-walled carbon nanotube slurry, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 95.5:2:0.5:2. The mixture was then coated onto a 12μm double-sided smooth aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet with a compaction density of 3.35 g / cm³. 3 .

[0096] The negative electrode active material, artificial graphite, conductive carbon black, multi-walled carbon nanotube slurry, dispersant, carboxymethyl cellulose (CMC), and binder, styrene-butadiene rubber latex (SBR), were mixed at a mass ratio of 95.5:1:0.5.

[0097] After thoroughly mixing the 1.2:1.8 ratio in deionized water, the mixture is coated onto a 6µm double-sided bright copper foil, dried, and cold-pressed to obtain a negative electrode sheet with a compaction density of 1.5 g / cm³. 3 .

[0098] The separator is a 16μm double-layer ceramic-coated microporous polyethylene membrane. The electrolyte used is the high-voltage electrolyte prepared in this embodiment, with an injection coefficient of 3.0g / Ah. The high-voltage electrolyte, positive electrode, negative electrode and separator are prepared according to conventional methods to form the 5Ah soft-pack battery cell to be tested.

[0099] The manufactured 5Ah soft-pack battery underwent performance testing. The test indicators and methods are as follows:

[0100] (1) Room temperature cycling performance is demonstrated by testing the capacity retention rate after N cycles at 0.5C at room temperature. The specific method is as follows: at 25℃, the formed battery is charged to 4.45V with a constant current and constant voltage of 0.5C, and the cutoff current is 0.05C. Then, it is discharged to 3.0V with a constant current of 0.5C, and the charge / discharge rest time is 10min. After such charge / discharge cycles, the capacity retention rate after the 500th cycle is calculated to evaluate its room temperature cycling performance.

[0101] The formula for calculating the capacity retention rate after 500 cycles at room temperature is as follows:

[0102] Capacity retention rate after 500 cycles (%) = (Discharge capacity after 500 cycles / Discharge capacity after 1st cycle) × 100%.

[0103] (2) DC internal resistance test: After formation, the battery is charged to 4.45V with a constant current and constant voltage of 0.5C and the cutoff current is 0.05C. Then it is discharged to 3.0V with a constant current of 0.5C and the initial discharge capacity of the battery is measured. Then it is charged to 50% capacity with 0.5C, left to stand for 1 hour and discharged with a current of 3C for 10s. The value of DC impedance DCIR is calculated.

[0104] The calculation formula is as follows:

[0105] (50% SOC) DCIR = (Discharge start voltage - Termination voltage) / 3C corresponding current × 100%.

[0106] (3) Low-temperature discharge performance: At 25℃, the formed battery was charged to 4.45V with a constant current and constant voltage of 0.5C and the cutoff current was 0.05C. Then, it was discharged to 3.0V with a constant current of 0.5C, and the discharge capacity of the battery at room temperature was measured. The above charging steps were repeated, and the battery was placed in a constant temperature chamber at -20℃ for 8 hours and discharged to 3.0V with a current of 0.5C to obtain the discharge capacity ratio at low temperature.

[0107] The calculation formula is as follows:

[0108] Discharge capacity percentage at -20℃ (%) = (Discharge capacity at -20℃ / Discharge capacity at room temperature) × 100%

[0109] (4) Rate discharge performance: At 25°C, the formed battery was charged to 4.45V using a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C. Then, it was discharged to 3.0V using a constant current of 0.5C, and the discharge capacity of the battery at 0.5C was measured. Subsequently, the same method was used to discharge to 3.0V at discharge rates of 1C / 3C / 5C, respectively, to obtain the discharge capacity ratio at 1C / 3C / 5C rates.

[0110] The calculation formula is as follows:

[0111] Discharge rate percentage (%) = (Discharge capacity at 1C / 3C / 5C rates / Discharge capacity at 0.5C) × 100%.

[0112] Example 2

[0113] This embodiment provides a preparation process for a high-voltage electrolyte, as detailed below.

[0114] (1) Preparation of organic compound additives, specifically including: mixing 1 kg of 2,5-difluoroterephthalic acid, 1.8 kg of thionyl chloride, and 5 g of N,N-dimethylformamide catalyst, and reacting at 80°C to generate 2,5-difluoroterephthaloyl chloride; dissolving 1 kg of 2,5-difluoroterephthaloyl chloride in 4 L of chlorobenzene under constant temperature of 80°C, then adding 1.1 kg of urea, stirring for 60 min, continuing to raise the temperature to 130°C, adding 5 g of zinc oxide catalyst, and reacting for 4 hours to obtain an organic compound additive containing cyano groups, with the following structural formula:

[0115]

[0116] The mass ratio of 2,5-difluoroterephthalic acid to thionyl chloride is 1:1.8, and the mass of N,N-dimethylformamide is 0.5% of the mass of 2,5-difluoroterephthalic acid.

[0117] (2) The process of preparing the precursor electrolyte is the same as in Example 1.

[0118] (3) The process of preparing the high-voltage electrolyte is the same as in Example 1.

[0119] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0120] Example 3

[0121] This embodiment provides a preparation process for a high-voltage electrolyte, as detailed below.

[0122] (1) Preparation of organic compound additives, specifically including: mixing 1 kg of 2,5-difluoroterephthalic acid, 2 kg of sulfoxide, and 8 g of N,N-dimethylformamide catalyst, and reacting at 80°C to generate 2,5-difluoroterephthaloyl chloride; dissolving 1 kg of 2,5-difluoroterephthaloyl chloride in 3 L of toluene under constant temperature of 80°C, then adding 1 kg of ammonia water, stirring for 40 min, continuing to heat to 120°C, adding 2 g of zinc oxide catalyst, and reacting for 6 hours to obtain an organic compound additive containing cyano groups, with the following structural formula:

[0123]

[0124] The mass ratio of 2,5-difluoroterephthalic acid to thionyl chloride is 1:2, and the mass of N,N-dimethylformamide is 0.8% of the mass of 2,5-difluoroterephthalic acid.

[0125] (2) The process of preparing the precursor electrolyte is the same as in Example 1.

[0126] (3) The process of preparing the high-voltage electrolyte is the same as in Example 1.

[0127] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0128] Example 4

[0129] This embodiment provides a preparation process for a high-voltage electrolyte, as detailed below.

[0130] (1) Preparation of organic compound additives, specifically including: mixing 1 kg of 2,5-difluoroterephthalic acid, 2.2 kg of sulfoxide, and 15 g of N,N-dimethylformamide catalyst, and reacting at 80°C to generate 2,5-difluoroterephthaloyl chloride; dissolving 1 kg of 2,5-difluoroterephthaloyl chloride in 5 L of toluene under constant temperature of 80°C, then adding 1 kg of urea, stirring for 40 min, continuing to heat to 140°C, adding 3 g of zinc oxide catalyst, and reacting for 5 hours to obtain an organic compound additive containing cyano groups, with the following structural formula:

[0131]

[0132] The mass ratio of 2,5-difluoroterephthalic acid to thionyl chloride is 1:2.2, and the mass of N,N-dimethylformamide is 1.5% of the mass of 2,5-difluoroterephthalic acid.

[0133] (2) The process of preparing the precursor electrolyte is the same as in Example 1.

[0134] (3) The process of preparing the high-voltage electrolyte is the same as in Example 1.

[0135] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0136] Example 5

[0137] This embodiment provides a preparation process for a high-voltage electrolyte, as detailed below.

[0138] (1) Preparation of organic compound additives, specifically including: mixing 0.5 kg of 2,5-difluoroterephthalic acid, 1.15 kg of thionyl chloride, and 7.5 g of N,N-dimethylformamide catalyst, and reacting at 80 °C to generate 2,5-difluoroterephthaloyl chloride; dissolving 1 kg of 2,5-difluoroterephthaloyl chloride in 3 L of toluene under constant temperature of 80 °C, then adding 1 kg of ammonia water, stirring for 40 min, continuing to heat to 120 °C, adding 3 g of zinc oxide catalyst, and reacting for 5 hours to obtain an organic compound additive containing cyano groups, with the following structural formula:

[0139]

[0140] The mass ratio of 2,5-difluoroterephthalic acid to thionyl chloride is 1:2.3, and the mass of N,N-dimethylformamide is 1.5% of the mass of 2,5-difluoroterephthalic acid.

[0141] (2) The process of preparing the precursor electrolyte is the same as in Example 1.

[0142] (3) The process of preparing the high-voltage electrolyte is the same as in Example 1, except that the organic compound additives, lithium difluorophosphate and vinylene carbonate account for 1%, 0.5% and 1.5% of the mass of the high-voltage electrolyte, respectively.

[0143] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0144] Example 6

[0145] This embodiment provides a preparation process for a high-voltage electrolyte, as detailed below.

[0146] (1) Preparation of organic compound additives, specifically including: mixing 0.5 kg of 2,5-difluoroterephthalic acid, 1.25 kg of thionyl chloride, and 10 g of N,N-dimethylformamide catalyst, and reacting at 80 °C to generate 2,5-difluoroterephthaloyl chloride; dissolving 1 kg of 2,5-difluoroterephthaloyl chloride in 3 L of toluene under constant temperature of 80 °C, then adding 1 kg of ammonia water, stirring for 40 min, continuing to heat to 120 °C, adding 3 g of zinc oxide catalyst, and reacting for 5 hours to obtain an organic compound additive containing cyano groups, with the following structural formula:

[0147]

[0148] The mass ratio of 2,5-difluoroterephthalic acid to thionyl chloride is 1:2.5, and the mass of N,N-dimethylformamide is 2% of the mass of 2,5-difluoroterephthalic acid.

[0149] (2) The process of preparing the precursor electrolyte is the same as in Example 1.

[0150] (3) The process of preparing the high-voltage electrolyte is the same as in Example 1, except that the organic compound additives, lithium difluorophosphate and vinylene carbonate account for 1%, 0.5% and 1.5% of the mass of the high-voltage electrolyte, respectively.

[0151] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0152] Example 7

[0153] This embodiment provides a preparation process for a high-voltage electrolyte, as detailed below.

[0154] (1) Preparation of organic compound additives, specifically including: mixing 1.5 kg of 2,5-difluoroterephthalic acid, 2.4 kg of sulfoxide, and 10.5 g of N,N-dimethylformamide catalyst, and reacting at 80°C to generate 2,5-difluoroterephthaloyl chloride; dissolving 1 kg of 2,5-difluoroterephthaloyl chloride in 3 L of toluene under constant temperature of 80°C, then adding 1 kg of ammonia water, stirring for 40 min, continuing to heat to 120°C, adding 3 g of zinc oxide catalyst, and reacting for 5 hours to obtain an organic compound additive containing cyano groups, with the following structural formula:

[0155]

[0156] The mass ratio of 2,5-difluoroterephthalic acid to thionyl chloride is 1:1.6, and the mass of N,N-dimethylformamide is 0.7% of the mass of 2,5-difluoroterephthalic acid.

[0157] (2) The process of preparing the precursor electrolyte is the same as in Example 1.

[0158] (3) The process of preparing the high-voltage electrolyte is the same as in Example 1, except that the organic compound additives, lithium difluorophosphate and vinylene carbonate account for 1%, 0.5% and 1.5% of the mass of the high-voltage electrolyte, respectively.

[0159] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0160] Example 8

[0161] This embodiment provides a preparation process for a high-voltage electrolyte, as detailed below.

[0162] (1) Preparation of organic compound additives, specifically including: mixing 1.5 kg of 2,5-difluoroterephthalic acid, 2.85 kg of sulfoxide, and 12 g of N,N-dimethylformamide catalyst, and reacting at 80°C to generate 2,5-difluoroterephthaloyl chloride; dissolving 1 kg of 2,5-difluoroterephthaloyl chloride in 3 L of toluene under constant temperature of 80°C, then adding 1 kg of ammonia water, stirring for 40 min, continuing to heat to 120°C, adding 3 g of zinc oxide catalyst, and reacting for 5 hours to obtain an organic compound additive containing cyano groups, with the following structural formula:

[0163]

[0164] The mass ratio of 2,5-difluoroterephthalic acid to thionyl chloride is 1:1.9, and the mass of N,N-dimethylformamide is 0.8% of the mass of 2,5-difluoroterephthalic acid.

[0165] (2) The process of preparing the precursor electrolyte is the same as in Example 1.

[0166] (3) The process of preparing the high-voltage electrolyte is the same as in Example 1, except that the organic compound additives, lithium difluorophosphate and vinylene carbonate account for 1%, 0.5% and 1.5% of the mass of the high-voltage electrolyte, respectively.

[0167] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0168] Example 9

[0169] This embodiment provides a preparation process for a high-voltage electrolyte, as detailed below.

[0170] (1) Preparation of organic compound additives, specifically including: mixing 2 kg of 2,5-difluoroterephthalic acid, 2.9 kg of sulfoxide, and 11 g of N,N-dimethylformamide catalyst, and reacting at 80°C to generate 2,5-difluoroterephthaloyl chloride; dissolving 1 kg of 2,5-difluoroterephthaloyl chloride in 3 L of toluene under constant temperature of 80°C, then adding 1 kg of ammonia water, stirring for 40 min, continuing to heat to 120°C, adding 3 g of zinc oxide catalyst, and reacting for 5 hours to obtain an organic compound additive containing cyano groups, with the following structural formula:

[0171]

[0172] The mass ratio of 2,5-difluoroterephthalic acid to thionyl chloride is 1:1.45, and the mass of N,N-dimethylformamide is 0.55% of the mass of 2,5-difluoroterephthalic acid.

[0173] (2) The process of preparing the precursor electrolyte is the same as in Example 1.

[0174] (3) The process of preparing the high-voltage electrolyte is the same as in Example 1, except that the organic compound additives, lithium difluorophosphate and vinylene carbonate account for 1.5%, 0.5% and 1.5% of the mass of the high-voltage electrolyte, respectively.

[0175] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0176] Example 10

[0177] This embodiment provides a preparation process for a high-voltage electrolyte, as detailed below.

[0178] (1) Preparation of organic compound additives, specifically including: mixing 2 kg of 2,5-difluoroterephthalic acid, 4.5 kg of thionyl chloride, and 24 g of N,N-dimethylformamide catalyst, and reacting at 80°C to generate 2,5-difluoroterephthaloyl chloride; dissolving 1 kg of 2,5-difluoroterephthaloyl chloride in 3 L of toluene under constant temperature of 80°C, then adding 1 kg of ammonia water, stirring for 40 min, continuing to heat to 120°C, adding 3 g of zinc oxide catalyst, and reacting for 5 hours to obtain an organic compound additive containing cyano groups, with the following structural formula:

[0179]

[0180] The mass ratio of 2,5-difluoroterephthalic acid to thionyl chloride is 1:2.25, and the mass of N,N-dimethylformamide is 1.2% of the mass of 2,5-difluoroterephthalic acid.

[0181] (2) The process of preparing the precursor electrolyte is the same as in Example 1.

[0182] (3) The process of preparing the high-voltage electrolyte is the same as in Example 1, except that the organic compound additives, lithium difluorophosphate and vinylene carbonate account for 1.5%, 0.5% and 1.5% of the mass of the high-voltage electrolyte, respectively.

[0183] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0184] Example 11

[0185] This embodiment provides a high-voltage electrolyte preparation process. The preparation steps (1) and (2) are the same as those in Example 1. The difference from Example 1 is that the proportions of the three additives are different. In step (3), the organic compound additive, lithium salt additive lithium difluorophosphate and film-forming additive vinylene carbonate account for 2%, 1% and 2% of the mass percentage of the high-voltage electrolyte, respectively.

[0186] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0187] Example 12

[0188] This embodiment provides a high-voltage electrolyte preparation process. The preparation steps (1) and (2) are the same as those in Example 2. The difference from Example 2 is that the types of lithium salt additives are different and the proportions of the three additives are different. In step (3), the organic compound additive, lithium salt additive lithium difluorosulfonylimide, and film-forming additive vinylene carbonate account for 2%, 1%, and 2% of the mass percentage of the high-voltage electrolyte, respectively.

[0189] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0190] Example 13

[0191] This embodiment provides a high-voltage electrolyte preparation process. The preparation steps (1) and (2) are the same as those in Example 3. The difference from Example 3 is that the types of lithium salt additives and film-forming additives are different, and the proportions of the three additives are different. In step (3), the organic compound additives, lithium bis(trifluoromethanesulfonyl)imide and ethylene ethylene carbonate account for 3%, 1% and 2% of the mass of the high-voltage electrolyte, respectively.

[0192] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0193] Example 14

[0194] This embodiment provides a high-voltage electrolyte preparation process. The preparation steps (1) and (2) are the same as those in Example 4. The difference from Example 4 is that the types of lithium salt additives and film-forming additives are different, and the proportions of the three additives are different. In step (3), the mass percentages of organic compound additives, lithium bis(oxalato)borate and fluoroethylene carbonate in the high-voltage electrolyte are 3%, 1% and 2%, respectively.

[0195] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0196] Example 15

[0197] This embodiment provides a high-voltage electrolyte preparation process. The preparation steps (1) and (2) are the same as those in Example 5. The difference from Example 5 is that the types of lithium salt additives and film-forming additives are different, and the proportions of the three additives are different. In step (3), the organic compound additives, lithium difluorooxalate borate and 1,3-propane sulfonyl lactone account for 4%, 1% and 2% of the mass of the high-voltage electrolyte, respectively.

[0198] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0199] Example 16

[0200] This embodiment provides a high-voltage electrolyte preparation process. The preparation steps (1) and (2) are the same as those in Example 6. The difference from Example 6 is that the types of lithium salt additives and film-forming additives are different, and the proportions of the three additives are different. In step (3), the organic compound additives, lithium difluorooxalate borate and 1,3-propenesulfonate lactone account for 4%, 1% and 2% of the mass of the high-voltage electrolyte, respectively.

[0201] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0202] Example 17

[0203] This embodiment provides a high-voltage electrolyte preparation process. The preparation steps (1) and (2) are the same as those in Example 7. The difference from Example 7 is that the types of lithium salt additives and film-forming additives are different, and the proportions of the three additives are different. In step (3), the organic compound additives, lithium difluorooxalate borate and ethylene sulfate account for 4%, 1% and 2% of the mass of the high-voltage electrolyte, respectively.

[0204] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0205] Example 18

[0206] This embodiment provides a high-voltage electrolyte preparation process. The preparation steps (1) and (2) are the same as those in Example 8. The difference from Example 8 is that the types of lithium salt additives and film-forming additives are different, and the proportions of the three additives are different. In step (3), the organic compound additives, lithium tetrafluoroborate and ethylene sulfite account for 5%, 1% and 2% of the mass of the high-voltage electrolyte, respectively.

[0207] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0208] Example 19

[0209] This embodiment provides a high-voltage electrolyte preparation process. The preparation steps (1) and (2) are the same as those in Example 9. The difference from Example 9 is that the types of lithium salt additives and film-forming additives are different, and the proportions of the three additives are different. In step (3), the organic compound additives, lithium tetrafluoroborate and propylene sulfite account for 5%, 1% and 2% of the mass of the high-voltage electrolyte, respectively.

[0210] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0211] Example 20

[0212] This embodiment provides a high-voltage electrolyte preparation process. The preparation steps (1) and (2) are the same as those in Example 10. The difference from Example 10 is that the types of lithium salt additives and film-forming additives are different, and the proportions of the three additives are different. In step (3), the organic compound additives, lithium tetrafluoroborate and 4-methyl ethylene sulfite account for 5%, 1% and 2% of the mass of the high-voltage electrolyte, respectively.

[0213] The high-voltage electrolyte prepared in this embodiment was used to assemble lithium-ion batteries, and the lithium-ion batteries were tested. The assembly and testing processes were the same as in Example 1. Detailed test data are shown in Table 2.

[0214] To better illustrate the effects of the embodiments of the present invention, a comparative example is provided to be made with the embodiments described above.

[0215] Comparative Example 1

[0216] This comparative example uses the precursor electrolyte prepared in step (2) of Example 1 to assemble a lithium-ion battery, and the lithium-ion battery is tested. The assembly and testing process is the same as in Example 1. The test data are detailed in Table 2.

[0217] Comparative Example 2

[0218] This comparative example provides an electrolyte that differs from Example 1 in that step (3) only adds lithium salt additive lithium difluorophosphate to the precursor electrolyte prepared in step (2) of Example 1, without using organic compound additives and film-forming additives, wherein the mass of lithium difluorophosphate is 1% of the total mass of the electrolyte.

[0219] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0220] Comparative Example 3

[0221] This comparative example provides an electrolyte that differs from Example 1 in that step (3) only adds the film-forming additive vinylene carbonate to the precursor electrolyte prepared in step (2) of Example 1, without using organic compound additives and lithium salt additives. The mass of vinylene carbonate is 1.5% of the total mass of the electrolyte.

[0222] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0223] Comparative Example 4

[0224] This comparative example provides an electrolyte that differs from Example 1 in that step (3) adds lithium salt additive lithium difluorophosphate and film-forming additive vinylene carbonate to the precursor electrolyte prepared in step (2) of Example 1, without using organic compound additives. The mass percentages of lithium difluorophosphate and vinylene carbonate in the electrolyte are 1% and 1.5%, respectively.

[0225] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0226] Comparative Example 5

[0227] This comparative example provides an electrolyte that is compared with Example 1. The difference is that in step (3), an organic compound additive and a lithium salt additive, lithium difluorophosphate, are added to the precursor electrolyte prepared in step (2) of Example 1, and the film-forming additive, vinylene carbonate, is not used. The organic compound additive and lithium difluorophosphate account for 1% and 0.5% of the electrolyte by mass, respectively.

[0228] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0229] Comparative Example 6

[0230] This comparative example provides an electrolyte that is compared with Example 2. The difference is that in step (3), the organic compound additive and film-forming additive vinylene carbonate of Example 2 are added to the precursor electrolyte prepared in step (2) of Example 2, and lithium difluorophosphate is not used. The organic compound additive and vinylene carbonate account for 1% and 1.5% of the mass of the electrolyte, respectively.

[0231] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0232] Comparative Example 7

[0233] This comparative example provides an electrolyte that is compared with Example 3. The difference is that in step (3), the organic compound additive and lithium salt additive lithium bis(oxalato)borate of Example 3 are added to the precursor electrolyte prepared in step (2) of Example 3, and the film-forming additive vinylene carbonate is not used. The organic compound additive and lithium bis(oxalato)borate account for 1% and 1% of the mass percentage of the electrolyte, respectively.

[0234] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0235] Comparative Example 8

[0236] This comparative example provides an electrolyte that is compared with that of Example 4. The difference is that in step (3), the organic compound additive and film-forming additive vinylene carbonate of Example 4 are added to the precursor electrolyte prepared in step (2) of Example 4, and the lithium salt additive lithium bis(oxalato)borate is not used. The organic compound additive and vinylene carbonate account for 2% and 1.5% of the mass of the electrolyte, respectively.

[0237] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0238] Comparative Example 9

[0239] This comparative example provides an electrolyte that is compared with Example 5. The difference is that in step (3), the organic compound additive and lithium salt additive lithium difluorooxalate borate of Example 5 are added to the precursor electrolyte prepared in step (2) of Example 5, and the film-forming additive vinylene carbonate is not used. The organic compound additive and lithium difluorooxalate borate account for 2% and 1.5% of the electrolyte by mass, respectively.

[0240] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0241] Comparative Example 10

[0242] This comparative example provides an electrolyte that is compared with that of Example 6. The difference is that in step (3), the organic compound additive and film-forming additive vinylene carbonate of Example 6 are added to the precursor electrolyte prepared in step (2) of Example 6, and the lithium salt additive lithium difluorooxalate borate is not used. The organic compound additive and vinylene carbonate account for 2% and 2% of the mass of the electrolyte, respectively.

[0243] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0244] Comparative Example 11

[0245] This comparative example provides an electrolyte that is compared with that of Example 7. The difference is that in step (3), the organic compound additive and lithium salt additive lithium difluorosulfonylimide of Example 7 are added to the precursor electrolyte prepared in step (2) of Example 7, and the film-forming additive vinylene carbonate is not used. The organic compound additive and lithium difluorosulfonylimide account for 3% and 1.5% of the electrolyte by mass, respectively.

[0246] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0247] Comparative Example 12

[0248] This comparative example provides an electrolyte that is compared with that of Example 8. The difference is that in step (3), the organic compound additive and film-forming additive vinylene carbonate of Example 8 are added to the precursor electrolyte prepared in step (2) of Example 8, and the lithium salt additive lithium bisfluorosulfonylimide is not used. The organic compound additive and vinylene carbonate account for 3% and 2% of the mass of the electrolyte, respectively.

[0249] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0250] Comparative Example 13

[0251] This comparative example provides an electrolyte that is compared with that of Example 9. The difference is that in step (3), the organic compound additive and lithium salt additive lithium difluorosulfonylimide of Example 9 are added to the precursor electrolyte prepared in step (2) of Example 9, and the film-forming additive vinylene carbonate is not used. The organic compound additive and lithium difluorosulfonylimide account for 4% and 1.5% of the electrolyte by mass, respectively.

[0252] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0253] Comparative Example 14

[0254] This comparative example provides an electrolyte that is compared with that of Example 10. The difference is that in step (3), the organic compound additive and film-forming additive vinylene carbonate of Example 10 are added to the precursor electrolyte prepared in step (2) of Example 10, and the lithium salt additive lithium difluorosulfonylimide is not used. The organic compound additive and vinylene carbonate account for 4% and 2% of the mass of the electrolyte, respectively.

[0255] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0256] Comparative Example 15

[0257] This comparative example provides an electrolyte that is compared with that of Example 10. The difference is that in step (3), the organic compound additive and lithium salt additive lithium bis(trifluoromethanesulfonyl)imide of Example 10 are added to the precursor electrolyte prepared in step (2) of Example 10, and the film-forming additive vinylene carbonate is not used. The organic compound additive and lithium bis(trifluoromethanesulfonyl)imide account for 5% and 1% of the mass percentage of the electrolyte, respectively.

[0258] Lithium-ion batteries were assembled using the electrolyte from this comparative example, and the lithium-ion batteries were tested. The assembly and testing procedures were the same as in Example 1. Detailed test data are shown in Table 2.

[0259] Table 1 summarizes the mass percentage of the three additives in the electrolyte in Examples 1-20 and Comparative Examples 1-15:

[0260]

[0261]

[0262] Tables 1 and 2 summarize the test data of the lithium-ion batteries assembled in Examples 1-20 and Comparative Examples 1-15:

[0263]

[0264]

[0265] Table 2

[0266] As can be seen from the test data in Table 2, compared with Comparative Examples 1-15 which did not fully incorporate the three mixed additives (organic compound additive, lithium difluorophosphate additive, and film-forming additive vinylene carbonate), the battery with the mixed additive of the present invention showed significantly improved performance in room temperature cycling, -20℃ low temperature, and rate discharge when charged to the upper limit voltage of 4.45V. The DC internal resistance was also significantly reduced at 50% SOC. This indicates that the high-voltage electrolyte provided in the embodiments of the present invention can significantly improve the safety, cycle performance, and rate performance of lithium-ion batteries.

[0267] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-voltage electrolyte, characterized in that, The high-voltage electrolyte comprises: electrolyte, non-aqueous organic solvent, and additives; The additives include: organic compound additives, lithium salt additives, and film-forming additives; The structural formula of the organic compound additive is: R1 and R2 are hydrocarbon groups or oxygen-containing hydrocarbon groups with 1 to 12 carbon atoms; The non-aqueous organic solvents include: cyclic solvents, chain ester solvents, and fluorinated solvents.

2. The high-voltage electrolyte according to claim 1, characterized in that, The electrolyte is a lithium electrolyte salt, including one or more of the following: lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium perchlorate, lithium (fluorosulfonyl)trifluoromethanesulfonylimide, lithium tetrachloroaluminate, and lithium hexafluoroarsenate; the concentration of the electrolyte in the high-voltage electrolyte is 0.8 mol / L to 2 mol / L; the lithium electrolyte salt is different from the lithium salt additive.

3. The high-voltage electrolyte according to claim 1, characterized in that, The cyclic solvent includes one or more of the following: ethylene carbonate, propylene carbonate, vinylene carbonate, ethylene ethylene carbonate, γ-butyrolactone, sulfolane, and 3-methylsulfolane; the cyclic solvent accounts for 24% to 27% of the total solvent mass of the high-voltage electrolyte; The chain-like ester solvent includes one or more of the following: dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and methyl butyrate; the chain-like ester solvent accounts for 56% to 63% of the total solvent mass of the high-voltage electrolyte. The fluorinated solvent includes one or more of the following: fluoroethylene carbonate, fluoromethyl ethyl carbonate, 2-fluorotetrahydrofuran, 3-fluorotetrahydrofuran, 3-trifluoromethyltetrahydrofuran, 2-trifluoromethyltetrahydrofuran, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether; the fluorinated solvent accounts for 10% to 20% of the total solvent mass of the high-voltage electrolyte.

4. The high-voltage electrolyte according to claim 1, characterized in that, The organic compound additive accounts for 0.5% to 5% of the total mass of the high-voltage electrolyte; The lithium salt additive includes one or more of lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), lithium difluorooxalateborate, and lithium tetrafluoroborate, and the mass of the lithium salt additive accounts for 0.1% to 3% of the total mass of the high-voltage electrolyte. The film-forming additive includes one or more of the following: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, 1,3-propane sulpholactone, 1,3-propene sulpholactone, vinyl sulfate, vinyl sulfite, propylene sulfite, and 4-methyl vinyl sulfite; the mass of the film-forming additive accounts for 0.1% to 3% of the total mass of the high-voltage electrolyte.

5. A method for preparing the high-voltage electrolyte according to any one of claims 1-4, characterized in that, The preparation method includes: The preparation of an organic compound additive includes: mixing raw materials 2,5-difluoroterephthalic acid and sulfoxide with catalyst N,N-dimethylformamide, and reacting at a certain temperature to generate 2,5-difluoroterephthaloyl chloride; reacting the 2,5-difluoroterephthaloyl chloride with a nitrogen-containing compound under dehydration conditions to obtain an organic compound additive containing a cyano group; the structural formula of the organic compound additive is: R1 and R2 are hydrocarbon groups or oxygen-containing hydrocarbon groups with 1 to 12 carbon atoms; The preparation of the precursor electrolyte includes: mixing a cyclic solvent, a chain ester solvent, and a fluorinated solvent in an argon-filled glove box to obtain a non-aqueous organic solvent, allowing it to stand in a low-temperature environment, then adding an electrolyte to the non-aqueous organic solvent, stirring until the electrolyte dissolves, and obtaining the precursor electrolyte. Preparation of high-voltage electrolyte: In an argon-filled glove box, the organic compound additive, lithium salt additive, and film-forming additive are added to the precursor electrolyte and stirred evenly to obtain the high-voltage electrolyte.

6. The preparation method according to claim 5, characterized in that, The mass ratio of 2,5-difluoroterephthalic acid to sulfoxide is 1:1.4 to 1:2.5; the mass of N,N-dimethylformamide is 0.5% to 2% of the mass of 2,5-difluoroterephthalic acid; the reaction temperature is 60°C to 80°C. The method of reacting the 2,5-difluoroterephthaloyl chloride with a nitrogen-containing compound under dehydration conditions to obtain an organic compound additive containing a cyano group specifically includes: dissolving a certain mass of 2,5-difluoroterephthaloyl chloride in an organic solvent under constant temperature conditions of 25℃~80℃, then adding the nitrogen-containing compound, stirring for 30min~60min, continuing to raise the temperature to 120℃~140℃, adding zinc oxide catalyst, and reacting for 4h~6h to obtain the organic compound additive containing a cyano group. The organic solvent comprises xylene and / or chlorobenzene, and 3-5 L of organic solvent is used per 1 kg of 2,5-difluoroterephthaloyl chloride; the mass ratio of 2,5-difluoroterephthaloyl chloride to the nitrogen-containing compound is 1-1.45; the nitrogen-containing compound comprises ammonia and / or urea; the mass of zinc oxide is 0.1%-0.5% of the mass of 2,5-difluoroterephthaloyl chloride.

7. The preparation method according to claim 5, characterized in that, The water and oxygen content in the glove box is less than or equal to 0.1 PPM; The cyclic solvent includes one or more of the following: ethylene carbonate, propylene carbonate, vinylene carbonate, ethylene ethylene carbonate, γ-butyrolactone, sulfolane, and 3-methylsulfolane; the cyclic solvent accounts for 24% to 27% of the total solvent mass of the high-voltage electrolyte; The chain-like ester solvent includes one or more of the following: dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and methyl butyrate; the chain-like ester solvent accounts for 56% to 63% of the total solvent mass of the high-voltage electrolyte. The fluorinated solvent includes one or more of the following: fluoroethylene carbonate, fluoromethyl ethyl carbonate, 2-fluorotetrahydrofuran, 3-fluorotetrahydrofuran, 3-trifluoromethyltetrahydrofuran, 2-trifluoromethyltetrahydrofuran, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether; the fluorinated solvent accounts for 10% to 20% of the total solvent mass of the high-voltage electrolyte. The temperature of the low-temperature environment is -20℃ to 0℃; the standing time is 2 hours to 8 hours; The electrolyte is a lithium salt, including one or more of the following: lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium difluorophosphate, lithium difluorooxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium perchlorate, lithium (fluorosulfonyl)trifluoromethanesulfonylimide, lithium tetrachloroaluminate, and lithium hexafluoroarsenate; the concentration of the electrolyte in the high-voltage electrolyte is 0.8 mol / L to 2 mol / L.

8. The preparation method according to claim 5, characterized in that, The organic compound additive accounts for 0.5% to 5% of the total mass of the high-voltage electrolyte; The lithium salt additive includes one or more of lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate borate), lithium difluorooxalate borate, and lithium tetrafluoroborate. The lithium salt additive accounts for 0.1% to 3% of the total mass of the high-voltage electrolyte. The lithium salt additive is of a different type than the lithium salt in the electrolyte. The film-forming additive includes one or more of the following: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, 1,3-propane sulpholactone, 1,3-propene sulpholactone, vinyl sulfate, vinyl sulfite, propylene sulfite, and 4-methyl vinyl sulfite; the mass of the film-forming additive accounts for 0.1% to 3% of the total mass of the high-voltage electrolyte.

9. A lithium-ion battery, characterized in that, The lithium-ion battery comprises: the high-voltage electrolyte as described in any one of claims 1-4, as well as a positive electrode, a negative electrode, and a separator.

10. The lithium-ion battery according to claim 9, characterized in that, The positive electrode active material of the positive electrode sheet includes: LiNi x Co y Mn z L (1-x-y-z) O2, Li a MPO4, LiCo b L (1-b) One or more of O2, wherein L is at least one element selected from Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, and Fe, M is at least one element selected from Fe, Mn, and Co, and 0≤x≤1, 0≤y≤1, 0≤z≤1, 0<x+y+z≤1, 0.5≤a≤1, and 0<b≤1; The negative electrode active material of the negative electrode sheet includes one or more of the following: artificial graphite, natural graphite, silicon, silicon oxide, silicon-based alloy, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, and lithium titanate. The diaphragm includes one or more of the following: polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyurethane, polyester, aramid, natural fiber, and composite diaphragm.

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