An electrolyte and a battery

Abstract

This invention relates to the field of battery technology, specifically to an electrolyte and a battery comprising the electrolyte. The electrolyte includes a first additive having the structure shown in formula (Ⅰ), wherein R1 and R2 are each independently selected from H, C1-C20 alkyl, C1-C20 olefin, C1-C20 alkyne, and C6-C26 aryl, and at least one of R1 and R2 is selected from a C1-C20 olefin or a C1-C20 alkyne. The electrolyte of this invention exhibits high stability, is not easily decomposed, has a low oxidation rate on the positive electrode surface, and contains a low amount of free HF. Batteries obtained using the electrolyte of this invention can withstand high voltage, have low self-discharge, and possess higher cycle stability and safety performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to an electrolyte and a battery comprising the electrolyte. Background Technology

[0002] A lithium-ion battery is a rechargeable battery that primarily functions by the movement of lithium ions between the positive and negative electrodes. During charging and discharging, Li... + Intercalation and deintercalation back and forth between the two electrodes: During charging, Li + Lithium-ion batteries deintercalate from the positive electrode and intercalate into the negative electrode via the electrolyte, placing the negative electrode in a lithium-rich state; the process is reversed during discharge. Due to their advantages such as high energy density and long cycle life, lithium-ion batteries are widely used in various electronic products and, in recent years, have also been extensively used in electric vehicles, power tools, and energy storage devices.

[0003] With the improvement of people's living standards and their aspirations for a better life, higher demands are being placed on battery energy density. To improve battery energy density, further increasing the voltage of the positive electrode material in lithium-ion batteries is a common approach. However, as the limiting voltage of the positive electrode material continues to increase, its specific capacity gradually increases, leading to severe deterioration of the battery's high-temperature performance and an inability to guarantee long cycle life. Especially at high voltages (>4.5V), during long-term charge-discharge cycles, the volume of the positive electrode material expands, causing severe cracks. Electrolyte enters the interior of the positive electrode material, damaging its structure. Simultaneously, the release of active oxygen further accelerates the oxidative decomposition of the electrolyte. Furthermore, the protective film on the negative electrode surface is continuously damaged, ultimately resulting in severe capacity decay. Currently, oxide coatings are generally used to modify the surface of the positive electrode material, or different morphologies and structures of the positive electrode material are prepared. However, these processes are complex, costly, and offer poor protection.

[0004] Therefore, it is very important to invent a battery that can withstand high voltage, has more stable cycle performance, and is safer. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned problems in the prior art and to provide an electrolyte and a battery comprising the electrolyte. The electrolyte of this invention has high stability, is not easily decomposed, has a low oxidation rate on the positive electrode surface, and contains a small amount of free HF. The battery obtained using the electrolyte of this invention can withstand high voltage, has a low self-discharge rate, and exhibits higher cycle stability and safety performance.

[0006] The inventors of this invention have discovered that by reducing the oxidation rate of the electrolyte on the positive electrode surface and reducing the amount of free HF in the electrolyte, the self-discharge level of the battery can be reduced, and the battery's high-voltage tolerance, cycle stability, and safety performance can be improved.

[0007] Through further in-depth research, the inventors of this invention discovered that, in order to reduce the oxidation rate of the electrolyte on the positive electrode surface and decrease the amount of free HF in the electrolyte, a specific substance can be added to the electrolyte. This substance reacts with the free HF in the electrolyte and forms a protective film on the positive electrode surface, thereby improving the stability of the electrolyte. The inventors of this invention, through extensive and in-depth research, identified a specific compound that can react with the free HF in the electrolyte and form a protective film on the positive electrode surface.

[0008] To achieve the above objectives, a first aspect of the present invention provides an electrolyte comprising a first additive having the structure shown in formula (I).

[0009]

[0010] R1 and R2 are each independently selected from H, C1-C20 alkyl, C1-C20 olefin, C1-C20 alkyne, and C6-C26 aryl, and at least one of R1 and R2 is selected from C1-C20 olefin or C1-C20 alkyne.

[0011] The second aspect of this invention provides a battery in which the electrolyte is the electrolyte described in the first aspect of this invention.

[0012] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0013] (1) The electrolyte of the present invention contains a small amount of free HF;

[0014] (2) The electrolyte of the present invention has a low oxidation rate on the positive electrode surface under a high voltage of 4.5V+ system;

[0015] (3) The electrolyte of the present invention is not easily decomposed;

[0016] (4) The electrolyte of the present invention has high stability;

[0017] (5) The battery of the present invention has a low self-discharge rate;

[0018] (6) The battery of the present invention has high cycle stability;

[0019] (7) The battery of the present invention has high safety performance;

[0020] (8) The battery of the present invention can withstand voltages of 4.5V or higher.

[0021] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0022] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0023] A first aspect of the present invention provides an electrolyte comprising a first additive having the structure shown in formula (I).

[0024]

[0025] R1 and R2 are each independently selected from H, C1-C20 alkyl, C1-C20 olefin, C1-C20 alkyne, and C6-C26 aryl, and at least one of R1 and R2 is selected from C1-C20 olefin or C1-C20 alkyne.

[0026] The substituents in the first additive contain unsaturated bonds, which can undergo polymerization on the positive electrode surface to form a protective film, thereby reducing the oxidation rate of the electrolyte on the positive electrode surface. Furthermore, the anionic group BF4 in the first additive... - Compared to PF6 in existing electrolytes - Anionic groups are more stable and less prone to decomposition. Therefore, introducing the first additive into the electrolyte improves the stability of the electrolyte.

[0027] By adding the first additive with the aforementioned specific structure to the electrolyte, the electrolyte can achieve higher stability than in the prior art. To further improve the effect, one or more of the technical features can be further optimized.

[0028] R1 and R2 can be the same or different, and each can be independently selected from H, C1-C20 alkyl, C1-C20 olefin, C1-C20 alkyne, or C6-C26 aryl.

[0029] In one example, R1 and R2 can each be independently selected from C1-C10 alkyl, C1-C10 olefin, C1-C10 alkynyl, and C6-C12 aryl.

[0030] R1 and R2 may each contain at least one olefinic group or an alkyneic group selected from C1-C20.

[0031] In one example, at least one of R1 and R2 is selected from an olefinic group or an alkyne group selected from C1-C10.

[0032] In one example, R1 is selected from C1-C10 olefinic groups and C1-C10 alkyneic groups.

[0033] In one example, R2 is selected from C1-C10 olefinic groups and C1-C10 alkyneic groups.

[0034] In a preferred embodiment, R1 and R2 may each be independently selected from C1-C10 olefinic groups and C1-C10 alkyneic groups.

[0035] According to one specific embodiment, R1 and R2 can each be independently selected from C1-C10 alkyl, C1-C10 olefin, C1-C10 alkyne, and C6-C12 aryl, and at least one of R1 and R2 is selected from C1-C10 olefin or C1-C10 alkyne.

[0036] The C1-C20 alkyl group is selected, for example, from methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, cyclopentyl, 2,2-dimethylpropyl, 1-ethylpropyl, 1-methylbutyl, 2-methylbutyl, n-hexyl, isohexyl, 2-hexyl, 3-hexyl, cyclohexyl, 2-methylpentyl, 3-methylpentyl 1,1,2-Trimethylpropyl, 3,3-Dimethylbutyl, n-Heptyl, 2-Heptyl, 3-Heptyl, 2-Methylhexyl, 3-Methylhexyl, 4-Methylhexyl, Isoheptyl, Cycloheptyl, n-Octyl, Cyclooctyl, Nonyl, Decyl, Undecyl, Dodecyl, Tridecyl, Tetradecyl, Pentadecyl, Hexadecyl, Heptadecanyl, Octadecanyl, Nonadecanyl, Eicosanyl.

[0037] The C1-C20 olefinic group is selected, for example, from vinyl, propenyl, 2-propenyl, n-butenyl, isobutenyl, sec-butenyl, tert-butenyl, cyclobutenyl, n-pentenyl, isopentenyl, tert-pentenyl, neopentenyl, cyclopentenyl, 2,2-dimethylpropenyl, 1-ethylpropenyl, 1-methylbutenyl, 2-methylbutenyl, n-hexenyl, isohexenyl, 2-hexenyl, 3-hexenyl, 2-methylpentenyl, 3-methylpentenyl 1,1,2-Trimethylpropenyl, 3,3-Dimethylbutenyl, n-Heptenyl, 2-Heptenyl, 3-Heptenyl, 2-Methylhexenyl, 3-Methylhexenyl, 4-Methylhexenyl, Isoheptenyl, Cycloheptenyl, n-Octenyl, Cyclooctenyl, Nonenyl, Decenyl, Undecenyl, Dodecenyl, Tridedecenyl, Tetradecenyl, Pentadecenyl, Hexadecenyl, Heptadecenyl, Octadecenyl, Nonadecenyl, Eicoseneyl.

[0038] The C1-C20 alkyne group is selected, for example, from ethynyl, propynyl, 2-propynyl, n-ynylenyl, isobutynyl, sec-butynyl, tert-butynyl, cyclobutynyl, n-pentynyl, isopentenynyl, tert-pentynyl, neopentynyl, cyclopentynyl, 2,2-dimethylpropynyl, 1-ethylpropynyl, 1-methylbutynyl, 2-methylbutynyl, n-hexynyl, isohexynyl, 2-hexynyl, 3-hexynyl, 2-methylpentynyl, 3-methylpentynyl 1,1,2-Trimethylpropynyl, 3,3-Dimethylbutynyl, n-Heptynyl, 2-Heptynyl, 3-Heptynyl, 2-Methylhexynyl, 3-Methylhexynyl, 4-Methylhexynyl, Isoheptynyl, Cycloheptynyl, n-Octyynyl, Cyclooctyynyl, Nonynyl, Decynyl, Undecynyl, Dodecaynyl, Tridecaynyl, Tetradecynyl, Pentadecynyl, Hexadecynyl, Heptadecynyl, Octadecaynyl, Nonadecaynyl, Eicosynyl.

[0039] The aryl group of C6-C26 is selected, for example, from benzyl, p-tolyl, o-tolyl, m-tolyl, p-ethylphenyl, m-ethylphenyl, o-ethylphenyl, 3,5-dimethylphenyl, 2,6-dimethylphenyl, 3,5-diethylphenyl, 2,6-diethylphenyl, 3,5-diisopropylphenyl, 2,6-diisopropylphenyl, 3,5-di-n-propylphenyl, 2,6-di-n-propylphenyl, 3,5-di-n-butylphenyl, 2,6-di-n-butylphenyl, 3,5-diisopropylphenyl, 3,5-di-n-propylphenyl, 2,6-di-n-propylphenyl, 3,5-di-n-butylphenyl, 2,6-di-n-butylphenyl.

[0040] In one instance, the first additive is an ionic compound containing tetrafluoroborate.

[0041] According to one specific embodiment, the first additive is selected from one or more of the following structures:

[0042]

[0043] The first additive can be obtained commercially or prepared using conventional preparation processes.

[0044] According to one specific embodiment, based on the total weight of the electrolyte, the content of the first additive is 0.1-5 wt% (e.g., 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.3 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.3 wt%, 3.5 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.8 wt%, 5 wt%).

[0045] In one example, the content of the first additive is 0.1 to 2 wt% based on the total weight of the electrolyte.

[0046] In one example, the electrolyte further includes dinitrile compounds and polynitrile compounds.

[0047] In one example, the polynitrile compound is selected from one or more of trinitrile and tetranitrile compounds.

[0048] The inventors of this invention have discovered that adding a polynitrile compound to the electrolyte, where the polynitrile compound and the first additive polymerize to form a network structure that works together on the surface of the positive electrode, further reduces side reactions in the electrolyte and the positive electrode, thereby improving the stability of the electrolyte.

[0049] In one example, the content of the dinitrile compound is 1 to 5 wt% (e.g., 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%) based on the total weight of the electrolyte.

[0050] In one example, the content of the polynitrile compound is 0.1-8 wt% (e.g., 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%) based on the total weight of the electrolyte.

[0051] In one example, the content of the polynitrile compound is 0.5 to 3 wt% based on the total weight of the electrolyte.

[0052] In one example, the electrolyte includes both the first additive and the polynitrile compound.

[0053] In one example, the electrolyte simultaneously includes the first additive and the polynitrile compound, which includes at least the tetranitrile compound.

[0054] In one example, the electrolyte simultaneously includes the first additive, the dinitrile compound, and the trinitrile compound.

[0055] In one example, the electrolyte simultaneously includes the first additive, the dinitrile compound, and the tetranitrile compound.

[0056] In one example, the electrolyte simultaneously includes the first additive, the dinitrile compound, the trinitrile compound, and the tetranitrile compound.

[0057] In one example, the weight ratio of the first additive to the polynitrile compound is (0.1-5):1 (e.g., 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1).

[0058] In one example, the weight ratio of the first additive to the polynitrile compound is (0.5-3):1.

[0059] The dinitrile compound, for example, has the structure shown in formula (II). R3 can be selected from substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted C2-C10 unsaturated hydrocarbon groups, substituted or unsubstituted C4-C10 heterocyclic alkyl groups, substituted or unsubstituted C1-C10 alkoxy groups, phenyl groups, substituted or unsubstituted C6-C10 phenylalkyl groups, substituted or unsubstituted C4-C10 heteroaryl groups, substituted or unsubstituted C4-C10 carbonyl groups containing heteroatoms, and substituted or unsubstituted C2-C10 ether groups.

[0060] The trinitrile compound, for example, has the structure shown in formula (Ⅲ). R4 can be selected from substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted C2-C10 unsaturated hydrocarbon groups, substituted or unsubstituted C4-C10 heterocyclic alkyl groups, substituted or unsubstituted C1-C10 alkoxy groups, phenyl groups, substituted or unsubstituted C6-C10 phenylalkyl groups, substituted or unsubstituted C4-C10 heteroaryl groups, substituted or unsubstituted C4-C10 carbonyl groups containing heteroatoms, and substituted or unsubstituted C2-C10 ether groups.

[0061] The tetranitrile compound, for example, has the structure shown in formula (Ⅳ). R5 can be selected from substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted C2-C10 unsaturated hydrocarbon groups, substituted or unsubstituted C4-C10 heterocyclic alkyl groups, substituted or unsubstituted C1-C10 alkoxy groups, phenyl groups, substituted or unsubstituted C6-C10 phenylalkyl groups, substituted or unsubstituted C4-C10 heteroaryl groups, substituted or unsubstituted C4-C10 carbonyl groups containing heteroatoms, and substituted or unsubstituted C2-C10 ether groups.

[0062] Taking the dinitrile compound as an example, the dinitrile compound has the structure shown in formula (II). It can be seen that nitrile groups (-CN) are attached to both sides of R3. Therefore, any alkyl, unsaturated hydrocarbon, heterocyclic alkyl, alkoxy, phenyl, benzoalkyl, heteroaryl, carbonyl, or ether group containing heteroatoms selected for R3 can satisfy the structure of formula (II). For example, if R3 is methyl, then the structure of methyl is -CH2-. Similarly, R4 and R5 can also satisfy the structures of formulas (III) and (IV), respectively.

[0063] In one instance, the substituent may be selected from one or more of F and C4-C10 alkyl groups containing heteroatoms.

[0064] In this invention, the meaning of "substituted or unsubstituted" is, for example, "substituted or unsubstituted C1-C10 alkyl group", indicating that the H on the alkyl group can be substituted or can be left unsubstituted. When the alkyl group is substituted by F, one H in the alkyl group can be substituted by F, multiple H can be substituted by F, or all H can be substituted by F.

[0065] In one example, the dinitrile compound is selected from one or more of butadionitrile, glutaronitrile, adiponitrile (ADN), sebaconitrile, nonadionitrile, dicyanobenzene, terephthalonitrile, pyridine-3,4-dianitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorobutadionitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiamethylene malononitrile, trans-butenedionitrile, ethylene glycol bis(propionitrile) ether, and 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile.

[0066] In one example, the trinitrile compound is selected from one or more of 1,3,6-hexanetrionitrile, 1,3,5-cyclohexanetrionitrile, 1,3,5-phenyltricyanide, 1,2,3-propanetrionitrile, and glyceroltrionitrile.

[0067] In one example, the tetranitrile compound is selected from one or more of 1,1,3,3-propanetetracarbonitrile, 1,2,2,3-tetracyanopropane, 1,2,4,5-tetracyanobenzene, 2,3,5,6-pyrazinetetracarbonitrile, 3-methyl-3-propyl-cyclopropane-1,1,2,2-tetracarbonitrile, 7,7,8,8-tetracyano-p-benzodiquinone dimethylane, and tetracyanoethylene.

[0068] In one instance, the electrolyte further includes a second additive.

[0069] In one example, the second additive is selected from one or more of 1,3-propanesulfonate lactone (PS), vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, vinyl sulfite, methanedisulfonate, and vinyl sulfate.

[0070] According to one specific embodiment, the weight content of the second additive is 5-12% based on the total weight of the electrolyte.

[0071] In one instance, the electrolyte is a non-aqueous electrolyte.

[0072] According to one specific embodiment, the electrolyte further includes lithium salt and organic solvent.

[0073] In one example, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide, lithium difluorobis(oxalate)phosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(trifluoromethanesulfonyl)imide, lithium di(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, or lithium di(trifluoromethanesulfonyl)imide.

[0074] According to one specific embodiment, the lithium salt content is 10-20% by weight, based on the total weight of the electrolyte.

[0075] In one example, the organic solvent is a carbonate and / or a carboxylic acid ester.

[0076] In one example, the carbonate is selected from one or more of the following solvents, either F-substituted or unsubstituted: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0077] In one example, the carboxylic ester is selected from one or more of the following fluorinated or unsubstituted solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl butyrate, and ethyl n-butyrate.

[0078] According to one specific embodiment, the organic solvent has a weight content of 60-80% based on the total weight of the electrolyte.

[0079] The second aspect of this invention provides a battery in which the electrolyte is the electrolyte described in the first aspect of this invention.

[0080] The materials and preparation methods for the battery, excluding the electrolyte, can be carried out in accordance with the practices in this field, and all can achieve the effects of low-temperature impedance, good cycle stability, and high safety performance.

[0081] The battery is preferably a lithium-ion battery.

[0082] The battery has a charge / discharge range of 3.0-4.53V.

[0083] According to one specific embodiment, the battery further includes a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material, and a separator.

[0084] The positive electrode sheet can be a conventional positive electrode sheet in the art. For example, the positive electrode sheet includes a positive current collector and a positive active material layer coated on one or both surfaces of the positive current collector. The positive active material layer includes a positive active material, a conductive agent, and a binder.

[0085] In one example, the positive electrode active material is selected from one or more of transition metal lithium oxides, lithium iron phosphate, and lithium manganese oxide.

[0086] In one example, the positive electrode active material is a transition metal lithium oxide, and the chemical formula of the transition metal lithium oxide is Li. 1+x Ni y Co z M (1-y-z) O2, where -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; where M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0087] In one example, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material is 80-99.8 wt%, the content of the conductive agent is 0.1-10 wt%, and the content of the binder is 0.1-10 wt%.

[0088] Preferably, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material is 90-99.6 wt%, the content of the conductive agent is 0.2-5 wt%, and the content of the binder is 0.2-5 wt%.

[0089] The negative electrode sheet can be a conventional negative electrode sheet in the art. For example, the negative electrode sheet includes a negative current collector and a negative active material layer coated on one or both surfaces of the negative current collector. The negative active material layer includes a negative active material, a conductive agent, and a binder.

[0090] In one example, the negative electrode active material is selected from one or more of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.

[0091] In one example, the conductive agent is selected from one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0092] In one example, the adhesive is selected from one or more of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0093] In one example, based on the total weight of the negative electrode active material layer, the content of the negative electrode active material is 80-99.8 wt%, the content of the conductive agent is 0.1-10 wt%, and the content of the binder is 0.1-10 wt%.

[0094] Preferably, based on the total weight of the negative electrode active material layer, the content of the negative electrode active material is 90-99.6 wt%, the content of the conductive agent is 0.2-5 wt%, and the content of the binder is 0.2-5 wt%.

[0095] Because the battery of the present invention contains the electrolyte described herein, the battery can withstand higher voltage, reduce self-discharge, improve cycle stability, and enhance safety performance.

[0096] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0097] The following examples illustrate the electrolyte of the present invention.

[0098] Example 1

[0099] (1) Preparation of ingredients

[0100] First additive: 1.5 parts by weight of having the structure shown in (Ⅰ-4);

[0101] Polynitrile compound: 1.5 parts by weight of 1,1,3,3-propanetetracarboxynitrile;

[0102] Dinitrile compound: ADN 3 parts by weight;

[0103] Organic solvents: EC 7 parts by weight, PC 7 parts by weight, DEC 14 parts by weight, PP 40 parts by weight, FEC 8 parts by weight;

[0104] Lithium salt: 13 parts by weight of lithium hexafluorophosphate (LiPF6);

[0105] Second additive: 5 parts by weight of PS.

[0106] (2) Electrolyte preparation

[0107] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), EC / PC / DEC / PP are mixed evenly. Then, fully dried lithium salt is quickly added to the mixture. After dissolving, FEC is added, followed by the first additive, 1,1,3,3-propanetetracarbonyl nitrile, ADN, and PS. The mixture is then thoroughly mixed to obtain the desired electrolyte.

[0108] Example 2 group

[0109] This set of examples is used to illustrate the effects of changing the weight ratio of the first additive to the tetranitrile compound.

[0110] The embodiments in this group are based on Embodiment 1, except that the weight ratio of the first additive to the tetranitrile compound is changed, as detailed in Table 1.

[0111] Example 3

[0112] This embodiment is based on Example 1, except that the choice of polynitrile compound is changed, as detailed in Table 1.

[0113] Example 4

[0114] This embodiment is based on Example 1, except that no polynitrile compound is added. See Table 1 for details.

[0115] Example 5 group

[0116] This example illustrates the effects of changing the first additive.

[0117] This set of embodiments is based on Embodiment 1, except that the selection of the first additive is changed, as detailed in Table 1.

[0118] Table 1

[0119]

[0120]

[0121] Comparative Example 1

[0122] The procedure was carried out according to Example 1, except that no first additive and polynitrile compound were added to the electrolyte.

[0123] Comparative Example 2

[0124] (1) Preparation of ingredients

[0125] 3 parts by weight of 1,3,6-hexanetrionitrile;

[0126] Lithium hexafluorophosphate (LiPF6) 13 parts by weight, EC 7 parts by weight, PC 7 parts by weight, DEC 14 parts by weight, PP 40 parts by weight, FEC 8 parts by weight, ADN 3 parts by weight, PS 5 parts by weight.

[0127] (2) The preparation method of the electrolyte is the same as in Example 1.

[0128] Comparative Example 3

[0129] (1) Preparation of ingredients

[0130] 1-Hexyl-3-methylimidazolium tetrafluoroborate (with) 1.5 parts by weight of (the structure shown) and 1.5 parts by weight of 1,1,3,3-propanetetracarbonyl nitrile;

[0131] Lithium hexafluorophosphate (LiPF6) 13 parts by weight, EC 7 parts by weight, PC 7 parts by weight, DEC 14 parts by weight, PP 40 parts by weight, FEC 8 parts by weight, ADN 3 parts by weight, PS 5 parts by weight.

[0132] (2) The preparation method of the electrolyte is the same as in Example 1.

[0133] Comparative Example 4

[0134] The experiment was conducted in accordance with Comparative Example 3, except that 1-hexyl-3-methylimidazolium tetrafluoroborate was adjusted to the same weight parts. Compounds with the structure shown.

[0135] Comparative Example 5

[0136] The experiment was conducted in accordance with Comparative Example 3, except that 1-hexyl-3-methylimidazolium tetrafluoroborate was adjusted to the same weight parts. Compounds with the structure shown.

[0137] Preparation Example

[0138] Batteries were prepared using the electrolytes obtained in the examples and comparative examples, respectively, in the following manner:

[0139] (1) Preparation of positive electrode

[0140] Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), super P (SP), and carbon nanotubes (CNT) were mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it formed a uniform and fluid positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of an aluminum foil. The coated aluminum foil was dried and then rolled and slit to obtain the desired positive electrode sheet.

[0141] (2) Preparation of negative electrode sheet

[0142] The negative electrode active materials, artificial graphite, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs), were mixed in a mass ratio of 94.5:2.5:1.5:1:0.5. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a negative electrode active slurry. The negative electrode active slurry was uniformly coated on both surfaces of a copper foil. The coated copper foil was dried at room temperature and then transferred to an 80°C oven for 10 hours. After cold pressing and slitting, the negative electrode sheet was obtained.

[0143] (3) Electrolyte

[0144] The electrolytes obtained in the above-described embodiments and comparative examples were used respectively.

[0145] (4) Preparation of lithium-ion batteries

[0146] After stacking the positive electrode sheet from step (1), the negative electrode sheet from step (2), and the separator in the order of positive electrode sheet, separator and negative electrode sheet, the cells are then wound to obtain the battery cell. The battery cell is placed in the outer packaging aluminum foil, and the electrolyte from step (3) is injected into the outer packaging. After vacuum sealing, standing, formation, shaping and sorting, a lithium-ion battery is obtained.

[0147] Test case

[0148] The batteries obtained in the examples and comparative examples were subjected to the following tests:

[0149] (1) Cyclic performance test at 45℃

[0150] The battery was charged and discharged at 45°C for 300 / 500 / 800 cycles at a rate of 1C within the charge and discharge cutoff voltage range. The discharge capacity of the first cycle was measured as x1 mAh, and the discharge capacity of the Nth cycle was measured as y1 mAh. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R1 = y1 / x1.

[0151] (2) Safety performance test

[0152] 1. Charge the battery cell at 0.5C to the upper limit cutoff voltage and maintain the voltage at 0.05C; 2. At an ambient temperature of 25℃±5℃, place the fully charged sample in a thermal shock test chamber, then raise the temperature to 140℃±2℃ at a rate of 15℃±2℃ / min and maintain this temperature for 42 minutes. After the test, observe whether the battery catches fire or explodes. If it does not catch fire or explode, the safety performance is indicated as "safe"; if it only catches fire, it is indicated as "fire"; if it only explodes, it is indicated as "explosion"; if it catches fire and explodes, the safety performance is indicated as "fire and explosion".

[0153] The results are recorded in Table 2.

[0154] Table 2

[0155]

[0156]

[0157] As can be seen from Table 2, and through the comparative examples and embodiments, the safety performance of the battery prepared with the electrolyte in the embodiments is significantly improved, and the cycle capacity retention rate is significantly enhanced. This indicates that the introduction of the first additive of the present invention reduces the oxidation rate of the electrolyte on the positive electrode surface and reduces the amount of free HF in the electrolyte, thereby improving the safety and cycle stability of the battery.

[0158] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A battery, characterized in that, The battery includes a positive electrode sheet containing a positive electrode active material and an electrolyte, wherein the positive electrode active material is lithium cobalt oxide; The electrolyte includes a first additive having the structure shown in formula (I). （Ⅰ）， R1 and R2 are each independently selected from C1-C20 olefinic groups, C1-C20 alkyneic groups, and C6-C26 aryl groups, and at least one of R1 and R2 is selected from C1-C20 olefinic groups and C1-C20 alkyneic groups. The electrolyte further includes a dinitrile compound and a polynitrile compound, wherein the polynitrile compound is selected from one or more of a trinitrile compound and a tetranitrile compound, and the polynitrile compound includes at least a tetranitrile compound. The weight ratio of the first additive to the polynitrile compound is (0.1-5):

1. Based on the total weight of the electrolyte, the content of the first additive is 0.1-5 wt%, the content of the polynitrile compound is 0.1-8 wt%, and the content of the dinitrile compound is 1-5 wt%.

2. The battery according to claim 1, wherein, R1 and R2 are each independently selected from C1-C10 olefinic groups, C1-C10 alkyneic groups, and C6-C12 aryl groups, and at least one of R1 and R2 is selected from C1-C10 olefinic groups and C1-C10 alkyneic groups.

3. The battery according to claim 1, wherein, R1 and R2 are each independently selected from C1-C10 olefinic groups and C1-C10 alkyneic groups.

4. The battery according to claim 1, wherein, The first additive is selected from one or more of the following structures: （Ⅰ-2）、 （Ⅰ-4）、 （Ⅰ-9）、 （Ⅰ-10）、 （Ⅰ-11）。 5. The battery according to claim 1, wherein, The polynitrile compounds are trinitrile compounds and tetranitrile compounds, and the dinitrile compounds have the structure shown in formula (II). (II) The trinitrile compound has the structure shown in formula (III). (III) The tetranitrile compound has the structure shown in formula (IV). (Ⅳ); R3, R4, and R5 are each independently selected from substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted C2-C10 unsaturated hydrocarbon groups, substituted or unsubstituted C4-C10 heterocyclic alkyl groups, substituted or unsubstituted C1-C10 alkoxy groups, phenyl groups, substituted or unsubstituted C6-C10 phenylalkyl groups, substituted or unsubstituted C4-C10 heteroaryl groups, substituted or unsubstituted C4-C10 carbonyl groups containing heteroatoms, and substituted or unsubstituted C2-C10 ether groups; the substituents are selected from one or more of F and C4-C10 alkyl groups containing heteroatoms.

6. The battery according to claim 5, wherein, The dinitrile compound is selected from one or more of the following: succinic anionyl nitrile, glutaronitrile, adiponitrile, sebaconitrile, anonadionitrile, dicyanophenylene, terephthalonitrile, pyridine-3,4-dianitronitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorosuccinic anionyl nitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiamethylene malononitrile, trans-butenedionitrile, ethylene glycol bis(propionitrile) ether, and 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile; and / or, The trinitrile compound is selected from one or more of 1,3,6-hexanetrionitrile, 1,3,5-cyclohexanetrionitrile, 1,3,5-phenyltricyanide, 1,2,3-propanetrionitrile, and glyceryltrionitrile; and / or, The tetranitrile compound is selected from one or more of 1,1,3,3-propanetetracarbonitrile, 1,2,2,3-tetracyanopropane, 1,2,4,5-tetracyanobenzene, 2,3,5,6-pyrazinetetracarbonitrile, 3-methyl-3-propyl-cyclopropane-1,1,2,2-tetracarbonitrile, 7,7,8,8-tetracyano-p-benzodiquinone dimethyl ether, and tetracyanoethylene.

7. The battery according to claim 1, wherein, The weight ratio of the first additive to the polynitrile compound is (0.5-3):1.

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