Electrolyte containing organic nitrile additive and application

Abstract

The invention discloses an electrolyte containing an organic nitrile additive and application, and belongs to the field of lithium batteries. In particular to an organic nitrile electrolyte suitable for a high-voltage system, the electrolyte contains an organic nitrile substance, the molecular structure general formula of the nitrile substance is R-XC-CN, X is the number of hydrogen connected with carbon adjacent to a carbon-nitrogen triple bond, the number of the hydrogen is smaller than or equal to 1 (namely 0 or 1), and R-XC is a chain-shaped or annular organic group. By using the electrolyte containing the nitrile substance additive, the cycling stability of the electrolyte under high voltage can be obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium batteries and relates to electrolytes containing organic nitrile additives and their applications, particularly to an organic nitrile electrolyte solvent suitable for high-voltage systems. Background Technology

[0002] Rechargeable batteries (secondary batteries) are now ubiquitous in modern life. Lithium-ion batteries, due to their high conversion efficiency, long lifespan, and flexible size adjustment capabilities, are widely used in various fields such as mobile phones, drones, and electric vehicles. Energy density and power density are two crucial performance parameters that directly determine a battery's application range. High energy density means longer battery life with limited mass, while power density determines whether a battery can provide a large amount of electrical energy output in a short time. Therefore, improving the energy density and power density of lithium-ion batteries has always been a goal pursued by industry professionals and researchers.

[0003] Increasing the operating voltage of the cathode material is an effective method, as it can not only improve the specific capacity of the cathode material but also enhance the overall power level of the battery. However, at high voltages (typically referring to a full-cell voltage ≥ 4.4V), conventional organic electrolyte components undergo decomposition reactions, such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Batteries using these solvents exhibit poor cycle performance at high voltages, limiting the practical application of high-voltage systems.

[0004] Under normal conditions, nitrile preferentially undergoes chemisorption on the cathode surface at high voltages compared to other solvents, forming an oxidation-resistant organic complex that prevents side reactions between other solvents and the electrode. Simultaneously, similar to the carbonate functional groups in alkyl carbonate solvents, the electron-rich CN-terminal group of nitrile acts as a highly nucleophilic site for coordinating cations, capable of complexing cobalt ions released from the cathode due to high potential, thus preventing cobalt ions from interfering with the anode material. Therefore, nitrile substances, as additives, can effectively improve the cycle stability of batteries at high voltages. However, the anodic and cathode stability of electrolytes are often contradictory. Although nitrile has strong antioxidant capabilities, its compatibility with lithium metal is extremely poor. In electrolytes, it undergoes severe side reactions with strongly reducing lithium metal or lithium-intercalated graphite (LiC6), limiting its application in electrolytes. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a class of organic nitrile additives with a special structure. Electrolytes containing this additive can achieve stable operation at high voltages, thereby improving the cycle stability of lithium-ion batteries at high voltages.

[0006] This invention aims to provide a nitrile electrolyte additive that does not undergo side reactions with a highly reducing negative electrode and can effectively suppress electrolyte oxidative decomposition and cathode transition metal dissolution. Electrolytes containing this additive can effectively improve the cycle performance of lithium-ion batteries at high voltages.

[0007] To achieve the above objectives, the technical solution adopted by the present invention includes:

[0008] In a first aspect, the present invention provides an electrolyte containing organic nitrile additives, wherein the electrolyte contains organic nitrile substances.

[0009] The general molecular formula of the organic nitriles is R-XC-CN, where X is the number of hydrogen atoms attached to the carbon atom adjacent to the carbon-nitrogen triple bond, and the number of hydrogen atoms is 0 or 1, and R-XC is a chain-like or cyclic organic group.

[0010] Furthermore, the carbon adjacent to the carbon-nitrogen triple bond is carbon in a ring structure, and the ring structure is a ring structure within six members (i.e., a 3, 4, 5 or 6-membered ring).

[0011] The ring structure has one or more of nitrogen atoms or carbon-carbon unsaturated bonds.

[0012] This invention effectively suppresses side reactions between nitrile substances and the battery negative electrode by controlling the number of carbon-hydrogen bonds in the carbon atoms adjacent to the carbon-nitrogen triple bond. Simultaneously, the carbon atoms adjacent to the carbon-nitrogen triple bond in the additive have a cyclic structure with nitrogen atoms or unsaturated carbon-carbon bonds. These structural features effectively suppress side reactions between nitrile additives and the strongly reducing negative electrode, improving their compatibility and allowing them to function as high-voltage electrolyte additives.

[0013] Furthermore, the organic nitrile substances include one or more of the following: trimethylacetonitrile, N-cyano-N'-methylacetamidine, trichloroacetonitrile, dichloroacetonitrile, 2-bromopropionitrile, dibromoacetonitrile, 2-chloro-6-trifluoromethylnicotinonitrile, 2-chloro-6-methyl-3-pyridinecarboxynitrile, 2-chloro-3-cyanopyridine, and 3-cyano-6-trifluoromethylpyridine.

[0014] Preferably, in the organic nitriles, the carbon adjacent to the carbon-nitrogen triple bond is carbon in a ring structure, the ring structure is a ring structure within a six-membered ring, and the ring has at least one or two of nitrogen atoms or carbon-carbon unsaturated bonds.

[0015] The organic nitrile is one or more of 2-chloro-6-trifluoromethyl nicotinonitrile, 2-chloro-6-methyl-3-pyridinecarboxylonitrile, 2-chloro-3-cyanopyridine, and 3-cyano-6-trifluoromethylpyridine.

[0016] The organic nitrile substance accounts for 0.1%-10% of the electrolyte by weight, preferably 0.5%-3%.

[0017] Furthermore, the electrolyte is a non-aqueous high-voltage lithium-ion battery electrolyte, and the electrolyte also includes a non-aqueous organic solvent and an electrolyte lithium salt;

[0018] The non-aqueous organic solvent includes one or more of carbonate solvents or carboxylic acid ester solvents; the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the carboxylic acid ester solvent includes one or more of methyl acetate, ethyl acetate, methyl butyrate, ethyl butyrate, and methyl propionate.

[0019] The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, and lithium bis(fluorosulfonyl)imide, preferably lithium hexafluorophosphate;

[0020] The concentration of the lithium salt in the electrolyte is 0.2 mol / L-3 mol / L, preferably 0.8 mol / L-1.5 mol / L.

[0021] Furthermore, the electrolyte also contains additives, which are one or more of the following: ethylene sulfate, 1,3-propanesulfonate lactone, lithium difluorophosphate, vinylene carbonate (VC), ethylene ethylene carbonate, and fluoroethylene carbonate (FEC). The weight percentage of the additives in the electrolyte is 0.1%-10%, preferably 0.5%-5%.

[0022] Secondly, the present invention provides a lithium-ion battery comprising the electrolyte described above.

[0023] Thirdly, the present invention provides an application of the electrolyte in a lithium-ion battery.

[0024] Furthermore, the operating voltage of the lithium-ion battery is ≥4.4V, preferably 4.4V-5V.

[0025] Beneficial Effects: This invention selects a special type of nitrile substance as an electrolyte additive. The nitrile solvent has the general molecular formula R-XC-CN, where X is the number of hydrogen atoms attached to the carbon atom adjacent to the carbon-nitrogen triple bond, and the number of hydrogen atoms is 0 or 1. R-XC represents a chain-like or cyclic organic group. The carbon atom adjacent to the carbon-nitrogen triple bond is a carbon atom in a cyclic structure, and the cyclic structure is a cyclic structure within six members (i.e., a 3, 4, 5, or 6-membered ring).

[0026] The cyclic structure contains one or more nitrogen atoms or carbon-carbon unsaturated bonds. Nitrile additives with the above structure can effectively inhibit redox reactions between nitrile additives and the strongly reducing negative electrode. Simultaneously, introducing nitrile additives with specific structures into the electrolyte enhances the electrolyte's antioxidant properties and improves the battery's cycle stability at high voltages, thereby increasing the overall energy density of the battery. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] This invention protects an electrolyte containing organic nitrile additives, wherein the nitrile additives have the general molecular formula R-XC-CN, and the number of hydrogen atoms in the elements adjacent to the carbon, nitrogen, and carbon triads is ≤1. The electrolyte should also contain one or more of carboxylic acid ester solvents or carbonate solvents. It should also contain one or more lithium salts, and furthermore, one or more electrolyte additives. The above electrolyte can be used in battery systems with a battery voltage ≥4.4V to improve the cycle stability of the battery at high voltages.

[0029] The following are specific examples.

[0030] Example 1

[0031] This embodiment uses a 5Ah lithium-ion battery to test the electrolyte performance. The 5Ah lithium-ion battery is a pouch battery. The positive electrode active material is lithium cobalt oxide (LCO), the binder is polyvinylidene fluoride (PVDF), and the conductive agent is conductive carbon black (SP). The positive electrode formulation is 95% LCO + 2% PVDF + 3% SP (by weight). The positive electrode is prepared into a positive electrode sheet through stirring, rolling, and die-cutting processes. The dimensions of the positive electrode sheet are width * length = 74mm * 106mm, the thickness of the prepared electrode sheet is 51μm, and the areal density is 7.2mg / cm³. 2 The main material of the battery negative electrode is graphite, the binders are styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC), and the conductive agent is conductive carbon black (SP). The negative electrode formulation is 95% graphite + 1% CMC + 2% SBR + 2% SP (by weight). The negative electrode is prepared into a positive electrode sheet through stirring, rolling, and die-cutting processes. The prepared electrode sheet has a thickness of 97 μm and an areal density of 4.68 mg / cm³. 2The negative electrode sheet measures 776mm x 108mm (width x length). The battery has 27 positive electrode layers and 28 negative electrode layers. The battery separator is a 12μm PE separator with a width of 89mm. The positive and negative electrodes are alternately stacked through the separator and placed within the space enclosed by the battery casing, which is made of aluminum-plastic film.

[0032] The above-mentioned batteries were assembled into three groups, namely A, B, and C. The variable was the electrolyte, which consisted of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) solvents, with EC accounting for 30% and EMC accounting for 70% by weight. The lithium salt was 1 mol / L lithium hexafluorophosphate, and the additives included vinylene carbonate (VC) and fluoroethylene carbonate (FEC), with VC and FEC each accounting for 2% of the total electrolyte weight. Group A contained no nitrile additives, Group B contained 0.2% dichloroacetonitrile additive by weight, and Group C contained 1% 2-chloro-6-trifluoromethylnicotinonitrile additive by weight. The effects of different electrolyte components on battery cycle performance were tested. The battery cycle performance was tested with a charge / discharge voltage range of 4.6V, a charge / discharge current of 5A, and a test temperature of 25±2℃. The number of cycles to 80% capacity retention was compared under different electrolyte systems. The test results are shown in Table 1.

[0033] Table 1

[0034] Group C contains the additive 2-chloro-6-trifluoromethylnicotinonitrile. In the chemical structure of 2-chloro-6-trifluoromethylnicotinonitrile, the carbon adjacent to the carbon-nitrogen triple bond is a cyclic carbon with one active hydrogen atom, and this cyclic structure contains a nitrogen atom. Therefore, 2-chloro-6-trifluoromethylnicotinonitrile exhibits excellent compatibility with the negative electrode. Simultaneously, as an electrolyte additive, 2-chloro-6-trifluoromethylnicotinonitrile enhances the electrolyte's antioxidant properties and improves the battery's cycle stability at high voltages. Group B contains the additive dichloroacetonitrile. In dichloroacetonitrile, the number of active hydrogen atoms on the carbon adjacent to the carbon-nitrogen triple bond is one. This structure of dichloroacetonitrile effectively reduces its reactivity with the highly reducing negative electrode. Furthermore, by utilizing dichloroacetonitrile to improve the electrolyte's high-voltage characteristics, the cycle performance of Group B batteries is superior to that of Group A. Compared to group C, in dichloroacetonitrile, the carbon atoms adjacent to the carbon-nitrogen triple bond are in a chain structure, while in 2-chloro-6-trifluoromethylnicotinonitrile, the carbon atoms adjacent to the carbon-nitrogen triple bond are in a ring structure containing nitrogen atoms. Therefore, 2-chloro-6-trifluoromethylnicotinonitrile is more compatible with highly active negative electrodes than dichloroacetonitrile. Consequently, the cycle performance of group C batteries is superior to that of group B.

[0035] Example 2

[0036] This embodiment uses a 5Ah lithium-ion battery to test the electrolyte performance for comparison. The 5Ah lithium-ion battery is a pouch battery, and the positive electrode active material is lithium cobalt oxide (LCO). The positive electrode formulation is 95% LCO + 2% PVDF + 3% SP (by weight). The positive electrode is prepared into a positive electrode sheet through stirring, rolling, and die-cutting processes. The positive electrode sheet has a size of 74mm * 106mm, a thickness of 51μm, and an areal density of 7.2mg / cm³. 2 The main material of the battery negative electrode is graphite, with a formula of 95% graphite + 1% CMC + 2% SBR + 2% SP (by weight). The negative electrode is prepared into a positive electrode sheet through stirring, rolling, and die-cutting processes. The prepared electrode sheet has a thickness of 97 μm and an areal density of 4.68 mg / cm³. 2 The negative electrode sheet measures 76mm x 108mm. The battery has 27 positive electrode layers and 28 negative electrode layers. The battery separator is a 12μm PE separator with a width of 89mm. The positive and negative electrodes are alternately stacked through the separator and placed within the space enclosed by the battery casing, which is made of aluminum-plastic film.

[0037] The batteries were divided into six groups: A, B, C, D, E, and F. The variables were the type and amount of nitrile additives. The electrolyte solvents were EC and EMC, with EC accounting for 30% and EMC accounting for 70% by weight. The lithium salt was 1 mol / L lithium hexafluorophosphate. Additives included VC and FEC, each accounting for 2% of the total electrolyte weight. Group A contained no nitrile additives; Group B contained 0.1% (by weight) of 2-chloro-6-trifluoromethylnicotinonitrile; Group C contained 0.5% (by weight); Group D contained 3% (by weight); Group E contained 5% (by weight); and Group F contained 10% (by weight). The effects of different electrolyte components on battery cycle performance were tested. The cycle performance of the batteries at 4.6V was tested, and the number of cycles to 80% discharge capacity retention was compared under different electrolyte systems. The test results are shown in Table 2.

[0038] Table 2

[0039]

[0040] Comparing the cycle performance of six groups (A, B, C, D, E, and F), it can be seen that groups B, C, D, E, and F show a significant improvement in cycle performance compared to group A, proving that 2-chloro-6-trifluoromethylnicotinonitrile, as an electrolyte additive, can effectively improve the battery cycle performance of the electrolyte under high voltage. Groups C and D show the greatest improvement, while the improvement in battery cycle performance decreases with increasing additive dosage in groups D, E, and F. This is mainly because as the additive dosage increases, the solid electrolyte film formed at the positive and negative electrodes becomes thicker, resulting in a significant increase in battery internal resistance and a decline in battery cycle performance. Table 2 shows that the optimal battery cycle performance of the electrolyte under high voltage is achieved when the dosage of the nitrile additive added in this application is 0.5%-3%.

[0041] Example 3

[0042] This embodiment uses a 5Ah lithium-ion battery to test the electrolyte performance for comparison. The 5Ah lithium-ion battery is a pouch battery, and the positive electrode active material is lithium cobalt oxide (LCO). The positive electrode formulation is 95% LCO + 2% PVDF + 3% SP (by weight). The positive electrode is prepared into a positive electrode sheet through stirring, rolling, and die-cutting processes. The positive electrode sheet has a size of 74mm * 106mm, a thickness of 51μm, and an areal density of 7.2mg / cm³. 2 The main material of the battery negative electrode is graphite, with a formula of 95% graphite + 1% CMC + 2% SBR + 2% SP (by weight). The negative electrode is prepared into a positive electrode sheet through stirring, rolling, and die-cutting processes. The prepared electrode sheet has a thickness of 97 μm and an areal density of 4.68 mg / cm³. 2 The negative electrode sheet measures 76mm x 108mm. The battery has 27 positive electrode layers and 28 negative electrode layers. The battery separator is a 12μm PE separator with a width of 89mm. The positive and negative electrodes are alternately stacked through the separator and placed within the space enclosed by the battery casing, which is made of aluminum-plastic film.

[0043] The batteries were divided into five groups: A, B, C, D, and E. The variable was the type of nitrile additive. The electrolyte solvents were EC and EMC, with EC accounting for 30% and EMC accounting for 70% by weight. The lithium salt was 1 mol / L lithium hexafluorophosphate. The additives included VC and FEC, each accounting for 2% of the total electrolyte weight. Group A contained no nitrile additives; Group B contained 0.5% dichloroacetonitrile; Group C contained 0.5% 2-chloro-6-trifluoromethylnicotinonitrile; Group D contained 0.1% acetonitrile; and Group E contained 0.5% adiponitrile. The effects of different electrolyte components on battery cycle performance were tested. The cycle performance of the batteries at 4.6V was tested, and the number of cycles to 80% capacity retention was compared under different electrolyte systems. The test results are shown in Table 3.

[0044] Table 3

[0045]

[0046]

[0047] Comparing the cycle performance of groups A, B, C, D, and E, it can be seen that groups B and C show significant improvements over group A. This indicates that dichloroacetonitrile and 2-chloro-6-trifluoromethylnicotinonitrile, as electrolyte additives, effectively improve the battery cycle performance under high voltage. This is mainly because dichloroacetonitrile and 2-chloro-6-trifluoromethylnicotinonitrile have excellent compatibility with the negative electrode, and the carbon-nitrogen triple bond structure in dichloroacetonitrile and 2-chloro-6-trifluoromethylnicotinonitrile can effectively improve the high-voltage stability of the battery. The cycle performance of groups D and E decreased after the addition of nitrile additives, mainly because acetonitrile and adiponitrile are incompatible with the highly reducing negative electrode. These substances undergo side reactions with the LiC6 negative electrode, leading to side reactions during battery cycling, resulting in worse cycle performance than group A.

[0048] Example 4

[0049] This embodiment uses a 5Ah lithium-ion battery to test the electrolyte performance for comparison. The 5Ah lithium-ion battery is a pouch battery, and the positive electrode active material is lithium cobalt oxide (LCO). The positive electrode formulation is 95% LCO + 2% PVDF + 3% SP (by weight). The positive electrode is prepared into a positive electrode sheet through stirring, rolling, and die-cutting processes. The positive electrode sheet has a size of 74mm * 106mm, a thickness of 51μm, and an areal density of 7.2mg / cm³. 2 The main material of the battery negative electrode is graphite, with a formula of 95% graphite + 1% CMC + 2% SBR + 2% SP (by weight). The negative electrode is prepared into a positive electrode sheet through stirring, rolling, and die-cutting processes. The prepared electrode sheet has a thickness of 97 μm and an areal density of 4.68 mg / cm³. 2 The negative electrode sheet measures 76mm x 108mm. The battery has 27 positive electrode layers and 28 negative electrode layers. The battery separator is a 12μm PE separator with a width of 89mm. The positive and negative electrodes are alternately stacked through the separator and placed within the space enclosed by the battery casing, which is made of aluminum-plastic film.

[0050] The batteries described above are divided into five groups: A, B, C, D, and E. The variable is the type of nitrile additive. The electrolyte solvents are EC and EMC, with EC accounting for 30% of the solvent by weight and EMC accounting for 70% of the solvent by weight. The lithium salt is 1 mol / L lithium hexafluorophosphate. The additives include VC and FEC, with VC and FEC each accounting for 2% of the total weight of the electrolyte. Group A contains 0.5% by weight of trimethylacetonitrile additive; Group B contains 0.5% by weight of N-cyano-N'-methylacetamidine additive; Group C contains 0.5% by weight of trichloroacetonitrile additive; Group D contains 0.5% by weight of 2-bromopropionitrile additive; Group E contains 0.5% by weight of dibromoacetonitrile additive; Group F contains 0.5% by weight of 2-chloro-6-methyl-3-pyridinecarboxynitrile; Group G contains 0.5% by weight of 2-chloro-3-cyanopyridine; Group H contains 0.5% by weight of 3-cyano-6-trifluoromethylpyridine; and Group I contains no nitrile additives. The effect of different electrolyte compositions on battery cycle performance was tested. The cycle performance of the batteries at 4.6V was tested, and the number of cycles to 80% capacity retention was compared under different electrolyte systems. The test results are shown in Table 4.

[0051] Table 4

[0052]

[0053] By comparing the number of cycles to 80% capacity retention for each group, Group I, which does not contain nitrile additives, has the worst cycling performance. Groups F, G, and H contain nitrile additives, and the structure of the nitrile substances they contain conforms to the carbon-nitrogen triple bond, with adjacent carbon atoms in a ring structure containing nitrogen atoms and unsaturated bonds. Therefore, Groups F, G, and H have the best cycling performance.

[0054] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. An electrolyte containing organic nitrile additives, characterized in that: The electrolyte contains organic nitrile substances. The general molecular formula of the organic nitriles is R-XC-CN, where X is the number of hydrogen atoms attached to the carbon atom adjacent to the carbon-nitrogen triple bond, and the number of hydrogen atoms is 0 or 1, and R-XC is a chain-like or cyclic organic group.

2. The electrolyte according to claim 1, characterized in that: The carbon adjacent to the carbon-nitrogen triple bond is carbon in a ring structure, and the ring structure is a ring structure within a six-membered ring. The ring structure has one or more of nitrogen atoms or carbon-carbon unsaturated bonds.

3. The electrolyte according to claim 1 or 2, characterized in that: The organic nitrile substances include one or more of the following: trimethylacetonitrile, N-cyano-N'-methylacetamidine, trichloroacetonitrile, dichloroacetonitrile, 2-bromopropionitrile, dibromoacetonitrile, 2-chloro-6-trifluoromethylnicotinonitrile, 2-chloro-6-methyl-3-pyridinecarboxynitrile, 2-chloro-3-cyanopyridine, and 3-cyano-6-trifluoromethylpyridine.

4. The electrolyte according to claim 1 or 2, characterized in that: The organic nitrile is one or more of 2-chloro-6-trifluoromethyl nicotinonitrile, 2-chloro-6-methyl-3-pyridinecarboxylonitrile, 2-chloro-3-cyanopyridine, and 3-cyano-6-trifluoromethylpyridine.

5. The electrolyte according to any one of claims 1-4, characterized in that: The organic nitrile substance accounts for 0.1%-10% of the electrolyte by weight, preferably 0.5%-3%.

6. The electrolyte according to any one of claims 1-5, characterized in that: The electrolyte is a non-aqueous high-voltage lithium-ion battery electrolyte, and the electrolyte also includes a non-aqueous organic solvent and an electrolyte lithium salt; The non-aqueous organic solvent includes one or more of carbonate solvents or carboxylic acid ester solvents; the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the carboxylic acid ester solvent includes one or more of methyl acetate, ethyl acetate, methyl butyrate, ethyl butyrate, and methyl propionate. The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, and lithium bis(fluorosulfonyl)imide, preferably lithium hexafluorophosphate; The concentration of the lithium salt in the electrolyte is 0.2 mol / L-3 mol / L, preferably 0.8 mol / L-1.5 mol / L.

7. The electrolyte according to claim 6, characterized in that: The electrolyte also contains additives, which are one or more of the following: ethylene sulfate, 1,3-propanesulfonate lactone, lithium difluorophosphate, vinylene carbonate, ethylene ethylene carbonate, and fluoroethylene carbonate. The weight percentage of the additives in the electrolyte is 0.1%-10%, preferably 0.5%-5%.

8. A lithium-ion battery, characterized in that: It comprises the electrolyte according to any one of claims 1-7.

9. The application of the electrolyte according to any one of claims 1-7 in a lithium-ion battery.

10. The application according to claim 9, characterized in that: The lithium-ion battery has an operating voltage of ≥4.4V, preferably 4.4V-5V.

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