Electrolyte and lithium-ion battery

Abstract

The present invention belongs to the field of lithium-ion battery technology and specifically relates to an electrolyte comprising a first additive, a second additive, and vinyl sulfate; the first additive is a triazole additive; and the second additive is a phosphate additive containing an unsaturated group. The electrolyte employs the triazole additive, the phosphate additive containing an unsaturated group, and the vinyl sulfate, which synergistically enhance the high- and low-temperature cycling and storage performance of lithium-ion batteries and improve electrode film formation. The present invention also discloses a lithium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to an electrolyte and a lithium ion battery. Background Art

[0002] CN 114094166 A discloses a non-aqueous electrolyte for lithium-ion batteries and a lithium-ion battery. The sulfonate of 1,2,4-triazole is capable of being reduced before the electrolyte, thereby forming a film that inhibits further decomposition of the electrolyte. The sulfonate used includes 1-[2-(2,4-difluorophenyl)-2,3-epoxypropane]-1H-1,2,4-triazole methanesulfonate and combinations thereof with other sulfonates.

[0003] Application TW201309657A protects an electrode additive comprising an amine compound (A). The amine compound (A) is a 1,2,4-triazole having one to five amino groups, and is selected from at least one of 3-amino-1,2,4-triazole, 3,5-diamino-1,2,4-triazole, 3-amino-5-methyl-1,2,4-triazole, 3-amino-5-ethyl-1,2,4-triazole, 3-amino-5-propyl-1,2,4-triazole, and 3-amino-5-butyl-1,2,4-triazole. The amine compound (A), which has an amino group and an oxidation potential of 3.8V to 4.2V relative to metallic lithium, captures hydrofluoric acid and other acids generated by the reaction of trace amounts of water within the battery with lithium-containing electrolytes such as LiPF6 through a neutralization reaction. This suppresses the dissolution of transition metal ions from lithium transition metal polyoxides, improving charge-discharge cycle performance and high-temperature storage properties. By using an electrode containing the electrode additive of the present invention, the high-temperature charge-discharge cycle performance and high-temperature storage characteristics of a lithium-ion battery or lithium-ion capacitor can be improved.

[0004] It can be seen that the functions of 1,2,4-triazole derivatives vary depending on their connecting groups. They can cooperate with sulfonic acid groups to form films, and when combined with amino groups, they can improve high-temperature performance.

[0005] The main purpose of this case is to improve the high-temperature and low-temperature cycle and storage performance of the electrolyte of lithium-ion batteries and improve the film formation effect. Summary of the Invention

[0006] The present invention aims to provide an electrolyte solution, which uses triazole additives, phosphate additives containing unsaturated groups, and vinyl sulfate. The vinyl sulfate can reduce the charge migration impedance of the interface film between the electrode and the electrolyte at low temperatures, thereby improving the low-temperature performance of the battery; the phosphate additives containing unsaturated groups can effectively suppress the initial impedance of the battery, the impedance increase after high-temperature storage and the impedance at low temperatures, thereby improving the high- and low-temperature performance of the battery; the triazole additives have weak alkalinity and can reduce the HF content at high voltage, thereby improving the high-temperature storage and high-voltage performance of the battery. The synergistic effect of the triazole additives can improve the high- and low-temperature cycling and storage performance of the lithium-ion battery and improve the electrode film-forming effect.

[0007] At the same time, the invention also discloses a lithium ion battery.

[0008] The technical solution of the present invention is:

[0009] An electrolyte comprising a first additive, a second additive, and vinyl sulfate;

[0010] The first additive is a triazole additive; the second additive is a phosphate additive containing an unsaturated group.

[0011] In the above electrolyte, the triazole additive is specifically represented by the following general formula 1:

[0012]

[0013] R is alkyl, fluoroalkyl, H, cycloalkyl, heterocycloalkyl, vinyl or ethynyl.

[0014] The alkyl group is preferably an alkyl group having 1 to 6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, etc.; preferably methyl, ethyl, n-propyl, isopropyl;

[0015] The fluoroalkyl group is preferably fluoromethyl, 1-fluoroethyl, 2-fluoroethyl, 1-fluoropropyl, 2-fluoropropyl;

[0016] The cycloalkyl group is preferably a saturated or unsaturated five-membered ring or six-membered ring; the unsaturated six-membered ring may be a benzene ring;

[0017] The heterocycloalkyl group may be a saturated five-membered or six-membered heterocycle, wherein the heterocycle is a nitrogen heterocycle, a sulfur heterocycle, an oxygen heterocycle, etc.;

[0018] In the above electrolyte, the second additive is tripropylene phosphate or tripropynyl phosphate.

[0019] In the above electrolyte, the ratio of the first additive, the second additive and vinyl sulfate is 1-10:1-10:10.

[0020] Preferably, the ratio of the first additive, the second additive, and vinyl sulfate is 1-8:1-8:10;

[0021] Preferably, the ratio of the first additive, the second additive, and vinyl sulfate is 2-8:2-8:10;

[0022] Preferably, the ratio of the first additive, the second additive, and vinyl sulfate is 3-7:3-7:10;

[0023] Preferably, the ratio of the first additive, the second additive, and vinyl sulfate is 4-6:4-6:10;

[0024] In the above electrolyte, the total amount of the first additive, the second additive, and the vinyl sulfate is equivalent to 0.1-10 wt % of the total amount of the electrolyte, more preferably 0.5-5 wt %; more preferably 1-4 wt %, wt % is hereinafter referred to as %;

[0025] The total amount of the first additive, the second additive, and the vinyl sulfate is equivalent to 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, or 9% of the total amount of the electrolyte;

[0026] In the above-mentioned electrolyte, the lithium salt in the electrolyte is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorophosphate, lithium difluorooxalatophosphate, lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalatophosphate), and lithium bis(fluorosulfonyl)imide, and the concentration of the lithium salt is 0.5-2 M. Generally, the concentration of the more commonly used lithium salt is 1-1.5 M; however, higher or lower lithium salt concentrations are also acceptable.

[0027] In this embodiment, the lithium salt is preferably lithium hexafluorophosphate or lithium bis(fluorosulfonyl)imide;

[0028] More preferably, two lithium salts are compounded to achieve a combination of the advantages of different lithium salts, such as selecting at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorophosphate, lithium difluorooxalatephosphate, lithium tetrafluorooxalatephosphate, and lithium difluorobis(oxalatophosphate) as the main lithium salt, and selecting lithium bis(fluorosulfonyl)imide as the secondary lithium salt; the amount of the main lithium salt is greater than that of the secondary lithium salt.

[0029] The concentration of lithium salt can be selected as: 0.5M, 1M, 1.5M or 2M;

[0030] As the nonaqueous solvent used in the nonaqueous electrolytic solution of the present invention, can preferably enumerate one or more than two kinds that are selected from cyclic carbonate, chain ester, lactone, ether and acid amides.From the viewpoint that improves electrochemical characteristic collaboratively in a wide temperature range, preferably contain chain ester, more preferably contain chain carbonate, further preferably contain cyclic carbonate and chain carbonate these two.

[0031] More preferably, the non-aqueous organic solvent in the electrolyte is a cyclic organic solvent and / or a chain organic solvent;

[0032] In addition, the electrolyte of the present invention may further contain any one or more combinations of the following auxiliary additives. The amount of the auxiliary additives is not recommended to exceed 5%; preferably 0.1-2%;

[0033] Auxiliary additives include: nitrile additives, aromatic additives, isocyanate additives, other triple bond additives, S=O group additives, cyclic acetal additives, other P-containing additives, cyclic anhydride additives, cyclic phosphazene additives, and fluorine-containing additives; such as:

[0034] One or more nitriles selected from the group consisting of acetonitrile, propionitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile and sebaconitrile; aromatic compounds with branched alkyl groups such as cyclohexylbenzene, fluorocyclohexylbenzene compounds (1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), tert-butylbenzene, tert-amylbenzene, 1-fluoro-4-tert-butylbenzene, biphenyl, terphenyl (ortho, meta, para), diphenyl ether, fluorobenzene, difluorobenzene (ortho, meta, para), anisole, 2,4-difluoroanisole, partial hydrogenations of terphenyl (1,2-dicyclohexylbenzene, 2-phenylbicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl) and other aromatic compounds; one or more isocyanate compounds selected from methyl isocyanate, ethyl isocyanate, butyl isocyanate, phenyl isocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 1,4-phenylene diisocyanate, 2-isocyanatoethyl acrylate, and 2-isocyanatoethyl methacrylate; 2-propynyl methyl carbonate, 2-propynyl acetate, 2-propynyl formate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, 2-propynyl 2-(methanesulfonyloxy)propionate, di(2-propynyl) oxalate, 2 One or more triple bond-containing compounds selected from the group consisting of methyl 2-propynyl oxalate, ethyl 2-propynyl oxalate, di(2-propynyl glutarate), 2-butyne-1,4-diyl dimethanesulfonate, 2-butyne-1,4-diyl dicarboxylate, and 2,4-hexadiyn-1,6-diyl dimethanesulfonate; sultones selected from the group consisting of 1,3-propane sultone, 1,3-butane sultone, 2,4-butane sultone, 1,4-butane sultone, 1,3-propylene sultone, 2,2-dioxy-1,2-oxathiolan-4-yl acetate, 5,5-dimethyl-1,2-oxathiolan-4-one 2,2-dioxide, ethylene sulfite, hexadecene One or more S═O group-containing compounds selected from cyclic sulfites such as hydrobenzo[1,3,2]dioxathiolane-2-oxide (also known as 1,2-cyclohexanediol cyclic sulfite), 5-vinyl-hexahydro-1,3,2-benzodioxathiol-2-oxide, sulfonates such as butane-2,3-diyl dimethanesulfonate, butane-1,4-diyl dimethanesulfonate, and methylene methane disulfonate, and vinyl sulfone compounds such as divinyl sulfone, 1,2-bis(vinylsulfonyl)ethane, and bis(2-vinylsulfonylethyl)ether; and cyclic acetal compounds selected from 1,3-dioxolane, 1,3-dioxane, and 1,3,5-trioxane;Selected from trimethyl phosphate, tributyl phosphate, trioctyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate, bis(2,2,2-trifluoroethyl) ethyl phosphate, bis(2,2,2-trifluoroethyl) 2,2-difluoroethyl phosphate, bis(2,2,2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl phosphate, bis(2,2-difluoroethyl) 2,2,2-trifluoroethyl phosphate, bis(2,2,3,3-tetrafluoropropyl) 2,2,2-trifluoroethyl phosphate 2-(dimethylphosphoryl)acetate, 2-(dimethylphosphoryl)ethyl acetate, 2-(dimethylphosphoryl)ethyl acetate, 2-(diethylphosphoryl)acetate, 2-(diethylphosphoryl)ethyl acetate, 2-(diethylphosphoryl)acetate, 2-(diethylphosphoryl)ethyl acetate, 2-(diethylphosphoryl)acetate, 2-(diethylphosphoryl)ethyl acetate, 2-(diethylphosphoryl)acetate, 2-(diethylphosphoryl)acetate, 2-(diethylphosphoryl)acetate, 2-(diethylphosphoryl)acetate, 2-(diethylphosphoryl)acetate, 2-(dimethyl ...ethylphosphoryl)acetate, 2-(dimethylphosphoryl)acetate, 2-(dimethylphosphoryl)acetate, 2-(diethylphosphoryl)acetate, 2-(diethylphosphoryl)acetate Phosphorus-containing compounds selected from the group consisting of 2-(dimethylphosphoryl)acetic acid 2-propynyl ester, 2-(diethylphosphoryl)acetic acid 2-propynyl ester, 2-(dimethoxyphosphoryl)acetic acid methyl ester, 2-(dimethoxyphosphoryl)ethyl acetate, 2-(diethoxyphosphoryl)acetic acid methyl ester, 2-(diethoxyphosphoryl)ethyl acetate, 2-(dimethoxyphosphoryl)acetic acid 2-propynyl ester, 2-(diethoxyphosphoryl)acetic acid 2-propynyl ester, methyl pyrophosphate, and ethyl pyrophosphate; acetic anhydride, propionic acid anhydride, or cyclic anhydrides such as succinic anhydride, maleic anhydride, 2-allylsuccinic anhydride, glutaric anhydride, itaconic anhydride, 3-sulfo-propionic anhydride; cyclic phosphazene compounds such as methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, or ethoxyheptafluorocyclotetraphosphazene; fluorinated compounds such as ethyl methyl fluorocarbonate, dimethyl fluorocarbonate, diethyl fluorocarbonate, ethyl fluoropropionate, propyl fluoropropionate, methyl fluoropropionate, ethyl fluoroacetate, methyl fluoroacetate, or propyl fluoroacetate;

[0035] The cyclic organic solvent is one or more combinations of PC, EC and BC;

[0036] The chain organic solvent is one or more combinations of DMC, DEC, EMC, MPC, MF, EF, MA, and EA.

[0037] More preferably, the ratio of the cyclic organic solvent to the chain organic solvent is 1-5:1-5; more preferably, the ratio of the cyclic organic solvent to the chain organic solvent is 1-2:1-2; more preferably, the ratio is 1:1;

[0038] At the same time, the present invention also discloses a lithium ion battery, which uses the electrolyte as described above.

[0039] In the above-mentioned lithium-ion battery, the positive electrode of the lithium-ion battery is selected from lithium transition metal oxides, wherein the lithium transition metal oxides are LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, Li 1+a Mn 1-x MxO2、LiCo 1-x M x O2、LiFe 1-x M x PO4, Li2Mn 1-x O4, wherein M is one or more selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, and F, 0≤a<0.2, 0≤x<1; and the negative electrode is selected from at least one of graphite, silicon-carbon composite material, and lithium titanate.

[0040] In the present invention, the lithium-ion battery is well known to include a separator and a negative electrode;

[0041] The negative electrode active material in the negative electrode includes at least one of a carbonaceous material, a silicon-carbon material, an alloy material, and a lithium-containing metal composite oxide material, but is not limited thereto. The negative electrode active material can be selected from various conventionally known materials that can be used as negative electrode active materials for electrochemical devices and can electrochemically intercalate and deintercalate active ions.

[0042] The method for preparing the negative electrode sheet is a method for preparing the negative electrode sheet that can be used for electrochemical devices that is well known in the art; the negative electrode active material layer also contains a binder and a solvent. The negative electrode active material is added with a binder and a solvent and a thickener, a conductive agent, a filler, etc. are added as needed to form a negative electrode slurry, and then the negative electrode slurry is coated on the negative electrode current collector, dried, and pressed to prepare a negative electrode sheet. The negative electrode slurry forms a negative electrode active material layer after drying and cold pressing. Similarly, a solvent is usually added in the preparation of the negative electrode slurry. The solvent is removed during the drying process. The binder is a binder that is well known in the art and can be used as a negative electrode active material layer, such as but not limited to styrene-butadiene rubber. The solvent is a solvent that is well known in the art and can be used as a negative electrode active material layer, such as but not limited to water. The thickener is a thickener that is well known in the art and can be used as a negative electrode active material layer, such as but not limited to carboxymethyl cellulose. In some embodiments, when the negative electrode active material contains an alloy material, the negative electrode active material layer can be formed by evaporation, sputtering, plating, etc.

[0043] The separator is any separator known in the art that can be used in electrochemical devices and is stable to the electrolyte used, such as, but not limited to, resin, glass fiber, and inorganic substances.

[0044] For example, the separator comprises at least one of polyolefin, aromatic polyamide, polytetrafluoroethylene, and polyethersulfone. Preferably, the polyolefin comprises at least one of polyethylene and polypropylene. Preferably, the polyolefin comprises polypropylene. Preferably, the separator is formed by laminating multiple layers of material, for example, a three-layer separator comprising polypropylene, polyethylene, and polypropylene in that order.

[0045] The beneficial effects of the present invention are as follows:

[0046] The electrolyte of the present invention adopts triazole additives, phosphate additives containing unsaturated groups, and vinyl sulfate;

[0047] Among them, vinyl sulfate can reduce the charge transfer impedance of the interface film between the electrode and the electrolyte at low temperatures, thereby improving the low-temperature performance of the battery;

[0048] Phosphate additives containing unsaturated groups can effectively suppress the initial impedance of the battery, the impedance after high-temperature storage, and the increase in impedance at low temperatures, thereby improving the high and low temperature performance of the battery;

[0049] Triazole additives are weakly alkaline and can reduce the HF content at high voltage, thereby improving the high-temperature storage and high-voltage performance of the battery;

[0050] The synergy of these factors can improve the high-temperature and low-temperature cycling and storage performance of lithium-ion batteries and improve the electrode film formation effect. DETAILED DESCRIPTION

[0051] Example 1

[0052] 1. Preparation of electrolyte: EC and DEC were used as solvents, mixed in a volume ratio of 1:1, and lithium salt LiPF6 was added to adjust the concentration of lithium salt in the system to 1.0M; additives: 1,2,4-triazole, tripropylene phosphate, and vinyl sulfate were added; their respective amounts were equivalent to 0.2%, 0.2%, and 0.6% of the total weight of the electrolyte.

[0053] 2. Preparation of positive electrode sheet: positive electrode material (LiNi 0.5 Mn 1.5 O4), conductive agent SuperP, adhesive PVDF and carbon nanotubes (CNT) are mixed evenly in a mass ratio of 95:2.3:2:0.7 to form a lithium ion battery positive electrode slurry with a certain viscosity, which is coated on both sides of the aluminum foil used for the current collector. The coating amount is 35g / m 2 , dried at 85℃ and then cold pressed; then trimmed, cut into pieces, and slit, and after slitting, dried at 85℃ under vacuum conditions for 4 hours, and the tabs were welded to make lithium-ion battery positive plates that meet the requirements.

[0054] 3. Preparation of negative electrode sheet: Graphite, conductive agent SuperP, thickener CMC, and adhesive SBR (styrene-butadiene rubber emulsion) are mixed in a mass ratio of 95:1.5:1.0:2.5 to make a slurry, mix them evenly, apply the mixed slurry on both sides of the copper foil, dry and roll to obtain the negative electrode sheet, and make a lithium-ion battery negative electrode sheet that meets the requirements.

[0055] 4. Preparation of lithium-ion batteries: The positive electrode sheet, negative electrode sheet and separator prepared according to the above process are laminated to form a lithium-ion battery with a thickness of 4.7mm, a width of 55mm and a length of 60mm. The battery is vacuum-baked at 75°C for 10 hours and the above electrolyte is injected. After standing for 24 hours, the battery is charged to 4.8V with a constant current and constant voltage of 0.1C (100mA), and then discharged to 3.0V with a constant current of 0.1C (180mA); then charged to 4.8V with a constant voltage of 0.5C (500mA), and then discharged to 3.0V with a constant current of 0.5C (500mA). Repeat the charge and discharge twice, and finally charge the battery to 4.8V with 1C (1000mA) to complete the battery production.

[0056] Example 2

[0057] The method is substantially the same as Example 1, except that 1,2,4-triazole, tripropylene phosphate, and vinyl sulfate account for 0.4%, 0.4%, and 1.2% of the total weight of the electrolyte, respectively.

[0058] Example 3

[0059] The method is substantially the same as Example 1, except that 1,2,4-triazole, tripropylene phosphate, and vinyl sulfate account for 0.8%, 0.8%, and 2.4% of the total weight of the electrolyte, respectively.

[0060] Example 4

[0061] The method is substantially the same as Example 1, except that 1,2,4-triazole, tripropylene phosphate, and vinyl sulfate account for 0.1%, 0.1%, and 0.8% of the total weight of the electrolyte, respectively.

[0062] Example 5

[0063] The method is substantially the same as Example 2, except that 1,2,4-triazole, tripropylene phosphate, and vinyl sulfate account for 0.2%, 0.2%, and 1.6% of the total weight of the electrolyte, respectively.

[0064] Example 6

[0065] The method is substantially the same as Example 2, except that 1,2,4-triazole, tripropylene phosphate, and vinyl sulfate account for 0.3%, 0.3%, and 1.4% of the total weight of the electrolyte, respectively.

[0066] Example 7

[0067] The method is substantially the same as Example 2, except that 1,2,4-triazole, tripropylene phosphate, and vinyl sulfate account for 0.5%, 0.5%, and 1% of the total weight of the electrolyte, respectively.

[0068] Example 8

[0069] The method is substantially the same as Example 2, except that 1,2,4-triazole, tripropylene phosphate, and vinyl sulfate account for 0.6%, 0.6%, and 0.8% of the total weight of the electrolyte, respectively.

[0070] Example 9

[0071] The method is substantially the same as Example 2, except that 1,2,4-triazole, tripropylene phosphate, and vinyl sulfate account for 0.8%, 0.8%, and 0.4% of the total weight of the electrolyte, respectively.

[0072] Example 10

[0073] The process is substantially the same as that of Example 2, except that the first additive is 1,2,4-1-methyl-triazole.

[0074] Example 11

[0075] The process is substantially the same as that of Example 2, except that the first additive is 1,2,4-1-fluoro-triazole.

[0076] Example 12

[0077] The process is substantially the same as that of Example 2, except that the second additive is tripropynyl phosphate.

[0078] Comparative Example 1

[0079] It is basically the same as Example 2, except that it does not contain any additives.

[0080] Comparative Example 2

[0081] The method is substantially the same as Example 2, except that the first additive is not included, and tripropylene phosphate and vinyl sulfate account for 0.6% and 1.4% of the total weight of the electrolyte, respectively.

[0082] Comparative Example 3

[0083] The method is substantially the same as Example 2, except that the second additive is not included, and 1,2,4-triazole and vinyl sulfate account for 0.6% and 1.4% of the total weight of the electrolyte, respectively.

[0084] Comparative Example 4

[0085] The method is substantially the same as Example 2, except that vinyl sulfate is not contained, and 1,2,4-triazole and tripropylene phosphate account for 1% and 1% of the total weight of the electrolyte, respectively.

[0086] Comparative Example 5

[0087] The process is substantially the same as Example 2, except that the additive contains only 2% of 1,2,4-triazole.

[0088] Comparative Example 6

[0089] The method is substantially the same as Example 2, except that the additive only contains 2% tripropylene phosphate.

[0090] Comparative Example 7

[0091] It is substantially the same as Example 2, except that the additive contains only 2% vinyl sulfate.

[0092] Performance Testing

[0093] Test Item 1: High Temperature Performance Test

[0094] The high temperature cycle performance and high temperature storage performance tests were performed on the lithium ion batteries in Examples 1 to 12 and Comparative Examples 1 to 7. The test methods are as follows:

[0095] High-temperature cycling performance: At 45°C, charge the lithium-ion battery at a constant current of 1C to a voltage of 4.8V, then charge at a constant voltage of 4.8V to a current of 0.05C, and then discharge at a constant current of 1C to 3V. Record the discharge capacity of the first cycle. Perform 200 charge and discharge cycles, and record the discharge capacity of the 200th cycle.

[0096] Capacity retention rate = (200th discharge capacity / 1st discharge capacity) × 100%

[0097] High temperature storage performance: At room temperature, the lithium-ion battery is charged at a constant current of 1C to a voltage of 4.8V, charged at a constant voltage of 4.8V to a current of 0.05C, and then discharged at 1C to 3V, and recorded as the discharge capacity before storage; the lithium-ion battery is charged at a constant current of 1C to a voltage of 4.8V, charged at a constant voltage of 4.8V to a current of 0.05C, and then stored in a 60°C oven for 14 days. After being taken out and cooled to room temperature, it is first discharged at 1C to 3V, and the discharge capacity after storage is recorded; the discharged lithium-ion battery is then charged at a constant current of 1C to a voltage of 4.8V, charged at a constant voltage of 4.8V to a current of 0.05C, and then discharged at 1C to 3V. The above steps are repeated for 10 weeks, and the discharge capacity in the 10th week is the recovery capacity after storage.

[0098] High temperature storage capacity retention rate = (discharge capacity after storage / discharge capacity before storage) × 100%

[0099] High temperature storage capacity recovery rate = (recovery capacity after storage / discharge capacity before storage) × 100%

[0100] Test Item 2: Low temperature performance test

[0101] The lithium ion batteries in Examples 1 to 12 and Comparative Examples 1 to 7 were tested for low-temperature discharge performance using the following test method:

[0102] At room temperature, charge the lithium-ion battery at a constant current of 1C to a voltage of 4.8V, then charge it at a constant voltage of 4.8V to a current of 0.05C, recording this as the room temperature discharge capacity. Then, place the battery in a -20°C low-temperature cabinet for >4 hours. Once the battery temperature drops to -20°C, discharge it at 0.5C to 3V, recording this as the -20°C 0.5C discharge capacity.

[0103] -20℃ discharge capacity retention rate = (-20℃ 0.5C discharge capacity / room temperature discharge capacity) × 100%

[0104] The test results are shown in Table 1 below:

[0105] Table 1 Lithium-ion battery test results

[0106]

[0107]

[0108] Result Analysis

[0109] 1. Comparative Examples 1-4 show that any combination of two can synergistically improve high-temperature performance, but for low-temperature performance, the performance of 1,2,4-triazole is hindered by the other two and does not show excellent results.

[0110] 2. According to the comparison of Comparative Examples 1, 5-7, it can be seen that the electrochemical performance trends of the battery using 1,2,4-triazole, tripropylene phosphate, and vinyl sulfate are similar. These three have certain contributions to the high and low temperature performance, among which 1,2,4-triazole is the most excellent.

[0111] 3. By comparing Example 2 with Comparative Examples 1-3, it can be seen that the high-temperature storage, cycling, and low-temperature storage cycling performances are significantly improved. This indicates that the reduction of initial impedance, the suppression of impedance increase during the cycle, and the suppression of HF continuously decomposed from the electrolyte are one of the fundamental reasons for achieving the above-mentioned purpose.

[0112] 4. By comparing Example 2 with Examples 10-12, it can be found that when the first additive is 1,2,4-1-fluoro-triazole and the second additive is tripropylene phosphate, the performance of the entire system is optimal.

[0113] 5. By comparing Examples 1-3, it can be found that when 1,2,4-triazole, tripropylene phosphate, and vinyl sulfate account for 2% of the total weight of the electrolyte, the performance of the entire system is optimal.

[0114] 6. By comparing Examples 1, 4 with 2, 5, 6, 7, 8, and 9, it was found that the performance of the entire system was optimal when the ratio of 1,2,4-triazole, tripropylene phosphate, and vinyl sulfate was 1:1:3.

[0115] The above embodiments are preferred implementations of the present invention, but the implementations of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte contains a first additive, a second additive, and vinyl sulfate; The first additive is a triazole additive; the second additive is a phosphate additive containing an unsaturated group, and the triazole additive is specifically represented by the following general formula 1: Formula 1; R is alkyl, fluoroalkyl, H, cycloalkyl, heterocycloalkyl, vinyl or ethynyl; The ratio of the first additive, the second additive and vinyl sulfate is 1-10:1-10:

10.

2. The electrolyte according to claim 1, characterized in that The second additive is tripropylene phosphate or tripropynyl phosphate.

3. The electrolyte according to claim 1, characterized in that The total amount of the first additive, the second additive and the vinyl sulfate is equivalent to 0.1-10 wt % of the total amount of the electrolyte.

4. The electrolyte according to claim 1, characterized in that The lithium salt in the electrolyte is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorophosphate, lithium difluorooxalatophosphate, lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalatophosphate) and lithium bis(fluorosulfonyl)imide, and the concentration of the lithium salt is 0.5-2M.

5. The electrolyte according to claim 1, characterized in that The non-aqueous organic solvent in the electrolyte is a cyclic organic solvent and / or a chain organic solvent; The cyclic organic solvent is one or more combinations of propylene carbonate, ethylene carbonate and butylene carbonate; The chain organic solvent is one or more combinations of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, ethyl formate, methyl acetate, and ethyl acetate.

6. A lithium-ion battery, characterized in that: The electrolyte used is as described in any one of claims 1-5.

7. The lithium-ion battery according to claim 6, characterized in that The positive electrode of the lithium ion battery is selected from lithium transition metal oxides, wherein the lithium transition metal oxides are LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, Li 1+a Mn 1-x MxO2、LiCo 1-x M x O2、LiFe 1-x M x PO4, Li2Mn 1-x O4, wherein M is one or more selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, and F, 0≤a<0.2, 0≤x<1; and the negative electrode is selected from at least one of graphite, silicon-carbon composite material, and lithium titanate.

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