An electrolyte and a battery including the electrolyte

Abstract

The present invention provides an electrolyte and a battery comprising the electrolyte. The electrolyte and the battery comprising the electrolyte can coordinate with transition metals through cyano functional groups to reduce the oxidation of the electrolyte by transition metals. At the same time, due to the presence of enamine functional groups, a functional protective film with the function of inhibiting acid corrosion can be formed on the surfaces of the positive and negative electrodes. The synergistic protection of the dual functional groups can significantly reduce side reactions of the electrolyte, reduce the rupture of the CEI film of the battery and the loss of positive electrode active materials under high-temperature conditions, and at the same time reduce the rupture of the SEI film of the negative electrode and the loss of negative electrode active materials, thereby improving the stability of the battery and significantly improving the high-temperature and high-pressure performance of the battery.

Description

Technical Field

[0001] The present invention relates to an electrolyte and a battery including the electrolyte, belonging to the technical field of batteries. Background Art

[0002] Lithium-ion batteries have a long cycle life and a relatively high energy density, and are widely used in various electronic products, electric vehicles, and energy storage devices. With the progress of technology, batteries need to pursue higher energy density, and thus the voltage of the positive electrode of lithium-ion batteries is getting higher and higher.

[0003] Currently, the voltage of commercially available lithium-ion batteries is as high as 4.45V - 4.48V. When the voltage is further increased to above 4.5V, traditional carbonate-based electrolytes are increasingly difficult to withstand such high voltages, especially under high-temperature conditions. In order to improve the performance of lithium-ion batteries under high-temperature and high-voltage conditions, it is necessary to develop more new high-voltage additives, so as to better achieve the cycle stability and high-temperature performance of high-voltage batteries and realize the commercialization of high-energy density batteries.

[0004] Under high-temperature and high-voltage conditions, there are also problems of oxidation of the electrolyte by high-valent transition metals and corrosion of the positive and negative electrode protective films and active materials by HF generated from the decomposition of the electrolyte, resulting in accelerated consumption of the electrolyte, increased film-forming impedance, and rapid attenuation of the battery capacity. Traditional nitrile additives can coordinate with transition metals to reduce the oxidation of the electrolyte, but they cannot inhibit the corrosion of the protective film and active materials by HF. Summary of the Invention

[0005] In order to solve the problems of oxidation of the electrolyte by high-valent transition metals in existing batteries and corrosion of the positive and negative electrode protective films and positive and negative electrode active materials by HF generated from the decomposition of the electrolyte, the object of the present invention is to provide an electrolyte and a battery including the electrolyte. The electrolyte and the battery including the electrolyte can coordinate with transition metals to reduce the oxidation of the electrolyte by transition metals, and at the same time can form a functional protective film with the function of inhibiting acid corrosion on the surfaces of the positive and negative electrodes, thereby significantly reducing side reactions of the electrolyte, reducing the rupture of the battery CEI film and the loss of positive electrode active materials under high-temperature conditions, and at the same time reducing the rupture of the battery SEI film and the loss of negative electrode active materials, so as to improve the stability of the battery and significantly improve the high-temperature and high-voltage performance of the battery.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] An electrolyte, the electrolyte includes an organic solvent, an electrolyte salt, and a functional additive, wherein the functional additive includes additive A, and additive A is selected from enamine compounds containing a cyano group.

[0008] For the electrolyte according to the present invention, the cyano-containing enamine compound refers to a compound containing a cyano group (-CN) and an enamine group (-N-C=C-).

[0009] For the electrolyte according to the present invention, the cyano-containing enamine compound is selected from at least one of the compounds represented by formula (1):

[0010]

[0011] In formula (1), R1, R2, and R3 are the same or different and are independently selected from H, -NR5R6, -CN, unsubstituted or optionally substituted by one, two, or more R a substituted C 1-10 alkyl, and at least one of the groups R1, R2, and R3 is selected from -CN; each R a is the same or different and is independently selected from halogen, C 1-10 alkyl, -C(=O)-C 1-10 alkyl, -C(=O)-O-C(=O)-C 1-10 alkyl, C 6-14 aryl, 5-14 membered heteroaryl; R5 and R6 are the same or different and are independently selected from H or C 1-10 alkyl;

[0012] R4 and R5 are the same or different and are independently selected from H, unsubstituted or optionally substituted by one, two, or more R b substituted C 1-10 alkyl; each R b is the same or different and is independently selected from halogen, C 1-10 alkyl, -C(=O)-C 1-10 alkyl, -C(=O)-O-C(=O)-C 1-10 alkyl, C 6-14 aryl, 5-14 membered heteroaryl;

[0013] R3 and R4 may also be connected to form a cyclic structure.

[0014] For the electrolyte according to the present invention, in formula (1), R1, R2, and R3 are the same or different and are independently selected from H, -NR5R6, -CN, unsubstituted or optionally substituted by one, two, or more R a substituted C 1-6 alkyl, and at least one of the groups R1, R2, and R3 is selected from -CN; each R a is the same or different and is independently selected from halogen, C 1-6 alkyl; R5 and R6 are the same or different and are independently selected from H or C 1-6 alkyl;

[0015] R4 and R5 are the same or different and are each independently selected from H, unsubstituted or optionally substituted by one, two or more Rs b substituted C 1-6 alkyl; each R b is the same or different and is each independently selected from halogen, C 1-6 alkyl;

[0016] R3 and R4 may also be joined to form a cyclic structure.

[0017] In the electrolyte according to the present invention, in formula (1), R1, R2, and R3 are the same or different and are each independently selected from H, -NR5R6, -CN, C 1-6 alkyl, and at least one of the groups R1, R2, and R3 is selected from -CN; R5 and R6 are the same or different and are each independently selected from H or C 1-6 alkyl;

[0018] R4 and R5 are the same or different and are each independently selected from H, C 1-6 alkyl;

[0019] R3 and R4 may also be joined to form a cyclic structure.

[0020] In the electrolyte according to the present invention, in formula (1), R1, R2, and R3 are the same or different and are each independently selected from H, -NR5R6, -CN, C 1-3 alkyl, and at least one of the groups R1, R2, and R3 is selected from -CN; R5 and R6 are the same or different and are each independently selected from H or C 1-3 alkyl;

[0021] R4 and R5 are the same or different and are each independently selected from H, C 1-3 alkyl;

[0022] R3 and R4 may also be joined to form a cyclic structure.

[0023] In the electrolyte according to the present invention, the enamine compound containing a cyano group is selected from at least one of the compounds represented by the following formulas (2) to (9):

[0024]

[0025]

[0026] In the electrolyte according to the present invention, the additive A can be prepared by a method known in the art or obtained by commercial means.

[0027] For the electrolyte according to the present invention, the addition amount of the additive A is 0.1-5.0 wt% of the total mass of the electrolyte, such as 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% or 5 wt%.

[0028] For the electrolyte according to the present invention, the functional additive further includes additive B, and the additive B is selected from fluorinated ethylene carbonate.

[0029] For the electrolyte according to the present invention, the addition amount of the additive B is 2-30 wt% of the total mass of the electrolyte, such as 2 wt%, 5 wt%, 10 wt%, 12 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt% or 30 wt%.

[0030] For the electrolyte according to the present invention, the electrolyte salt is selected from lithium salts.

[0031] For the electrolyte according to the present invention, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(trifluoromethylsulfonyl)imide, lithium difluorobis(oxalato)phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methyl or lithium bis(trifluoromethylsulfonyl)imide.

[0032] For the electrolyte according to the present invention, the addition amount of the electrolyte salt is 11-18 wt% of the total mass of the electrolyte, such as 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%.

[0033] For the electrolyte according to the present invention, the organic solvent is selected from carbonate esters and / or carboxylic acid esters. The carbonate esters are selected from one or more of the following fluorinated or unsubstituted solvents: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate; the carboxylic acid esters are 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, n-ethyl butyrate.

[0034] For the electrolyte according to the present invention, the functional additive further includes additive C, and additive C is selected from at least one of the following compounds: 1,3-propane sultone, 1,3-propene sultone, succinonitrile, adiponitrile, glycerol trinitrile, 1,3,6-hexane trinitrile, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluoro bis(oxalate) phosphate.

[0035] For the electrolyte according to the present invention, the addition amount of additive C is 0-10 wt% of the total mass of the electrolyte, for example, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%.

[0036] For the electrolyte according to the present invention, the electrolyte is used for high-voltage batteries. Exemplarily, it is used for high-voltage lithium cobalt oxide batteries, high-voltage ternary batteries or high-voltage lithium-rich manganese-based batteries.

[0037] Preferably, the electrolyte is used for high-voltage lithium cobalt oxide batteries.

[0038] The present invention also provides a battery, and the battery includes the above-mentioned electrolyte.

[0039] For the battery according to the present invention, the battery is a lithium-ion battery.

[0040] For the battery according to the present invention, 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.

[0041] For the battery according to the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one or both surfaces of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder.

[0042] For the battery according to the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent and a binder.

[0043] For the battery according to the present invention, the mass percentage content of each component in the positive electrode active material layer is: 80-99.8 wt% of positive electrode active material, 0.1-10 wt% of conductive agent, and 0.1-10 wt% of binder.

[0044] Preferably, the mass percentage content of each component in the positive electrode active material layer is: 90-99.6 wt% of positive electrode active material, 0.2-5 wt% of conductive agent, and 0.2-5 wt% of binder.

[0045] For the battery according to the present invention, the mass percentage content of each component in the negative electrode active material layer is: 80-99.8 wt% of negative electrode active material, 0.1-10 wt% of conductive agent, and 0.1-10 wt% of binder.

[0046] Preferably, the mass percentage content of each component in the negative electrode active material layer is: 90-99.6 wt% of negative electrode active material, 0.2-5 wt% of conductive agent, and 0.2-5 wt% of binder.

[0047] For the battery according to the present invention, the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.

[0048] For the battery according to the present invention, the binder is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0049] For the battery according to the present invention, the negative electrode active material includes a carbon-based negative electrode material.

[0050] For the battery according to the present invention, the carbon-based negative electrode material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.

[0051] For the battery according to the present invention, the negative electrode active material may further include a silicon-based negative electrode material.

[0052] For the battery according to the present invention, the silicon-based negative electrode material is selected from at least one of nano-silicon, silicon oxide negative electrode material (SiOx(0<x<2)), and silicon-carbon negative electrode material.

[0053] For the battery according to the present invention, in the negative electrode active material, the mass ratio of the carbon-based negative electrode material to the silicon-based negative electrode material is 10:0 to 1:19, for example, 1:19, 1:18, 1:17, 1:16, 1:15, 1:14, 1:13, 1:12, 1:11, 1:10, 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, or 10:0.

[0054] The battery according to the present invention, wherein the positive electrode active material is selected from one or more of transition metal lithium oxides, lithium iron phosphate, and lithium-rich manganese-based materials; the chemical formula of the transition metal lithium oxide is Li 1+x Ni y Co z M (1-y-z) O2, wherein, -0.1 ≤ x ≤ 1; 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and 0 ≤ y + z ≤ 1; wherein, M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0055] For the battery according to the present invention, the charging cut-off voltage of the battery is 4.5 V or more.

[0056] Term Definitions and Explanations

[0057] Herein, "more than one" means three or more.

[0058] The term "halogen" refers to F, Cl, Br, and I. In other words, F, Cl, Br, and I can be described as "halogen" in this specification.

[0059] The term "C 1-10 alkyl" should be understood to preferably represent a straight-chain or branched-chain saturated monovalent hydrocarbon group having 1 to 10 carbon atoms. Specifically, "C 1-10 alkyl" should be understood to preferably represent a straight-chain or branched-chain saturated monovalent hydrocarbon group having 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 carbon atoms. The alkyl group is, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, 2-methylbutyl, 1-methylbutyl, 1-ethylpropyl, 1,2-dimethylpropyl, neopentyl, 1,1-dimethylpropyl, 4-methylpentyl, 3-methylpentyl, 2-methylpentyl, 1-methylpentyl, 2-ethylbutyl, 1-ethylbutyl, 3,3-dimethylbutyl, 2,2-dimethylbutyl, 1,1-dimethylbutyl, 2,3-dimethylbutyl, 1,3-dimethylbutyl, or 1,2-dimethylbutyl, etc. or their isomers. In particular, the group has 1, 2, 3, 4, 5, 6 carbon atoms ("C 1-6 alkyl"), such as methyl, ethyl, propyl, butyl, isopropyl, isobutyl, sec-butyl, tert-butyl, and more particularly, the group has 1, 2, or 3 carbon atoms ("C 1-3 alkyl"), such as methyl, ethyl, n-propyl, or isopropyl.

[0060] The term "C 6-14 aryl" should be understood to preferably represent a monovalent aromatic or partially aromatic monocyclic, bicyclic, or tricyclic hydrocarbon ring having 6 to 14 carbon atoms. The term "C6-14 "Aryl" should preferably be understood to represent a monocyclic, bicyclic or tricyclic hydrocarbon ring which is monovalent, aromatic or partially aromatic and has 6, 7, 8, 9, 10, 11, 12, 13 or 14 carbon atoms ("C 6-14 aryl"), in particular a ring having 6 carbon atoms ("C6 aryl"), such as phenyl; or biphenyl, or a ring having 9 carbon atoms ("C9 aryl"), such as indanyl or indenyl, or a ring having 10 carbon atoms ("C 10 aryl"), such as tetrahydronaphthyl, dihydronaphthyl or naphthyl, or a ring having 13 carbon atoms ("C 13 aryl"), such as fluorenyl, or a ring having 14 carbon atoms ("C 14 aryl"), such as anthryl.

[0061] The term "5- to 14-membered heteroaryl" should be understood to include such monovalent monocyclic, bicyclic or tricyclic aromatic ring systems: which have 5 to 14 ring atoms and contain 1 to 4 heteroatoms independently selected from N, O and S. The term "5- to 14-membered heteroaryl" should be understood to include such monovalent monocyclic, bicyclic or tricyclic aromatic ring systems: which have 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 ring atoms, in particular 5 or 6 or 9 or 10 carbon atoms, and which contain 1 to 5, preferably 1 to 3 heteroatoms independently selected from N, O and S and, additionally in each case, may be benzo-fused. In particular, heteroaryl is selected from thienyl, furyl, pyrrolyl, oxazolyl, thiazolyl, imidazolyl, pyrazolyl, isoxazolyl, isothiazolyl, oxadiazolyl, triazolyl, thiadiazolyl, thieno-4H-pyrazolyl, etc. and their benzo derivatives, such as benzofuryl, benzothienyl, benzoxazolyl, benzoisoxazolyl, benzimidazolyl, benzotriazolyl, indazolyl, indolyl, isoindolyl, etc.; or pyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, etc., and their benzo derivatives, such as quinolinyl, quinazolinyl, isoquinolinyl, etc.; or azocinyl, indolizinyl, purinyl, etc. and their benzo derivatives; or cinnolinyl, phthalazinyl, quinazolinyl, quinoxalinyl, naphthyridinyl, pteridinyl, carbazolyl, acridinyl, phenazinyl, phenothiazinyl, phenoxazinyl, etc.

[0062] Advantages of the present invention:

[0063] The present invention provides an electrolyte and a battery including the electrolyte. The electrolyte and the battery including the electrolyte can coordinate with transition metals through cyano functional groups to reduce the oxidation of the electrolyte by transition metals. At the same time, due to the presence of enamine functional groups, a functional protective film with the function of inhibiting acid corrosion can be formed on the surfaces of the positive and negative electrodes. The synergistic protection of the dual functional groups can significantly reduce the side reactions of the electrolyte, reduce the rupture of the CEI film of the battery and the loss of the positive electrode active material under high-temperature conditions, and at the same time reduce the rupture of the SEI film of the battery and the loss of the negative electrode active material, thereby improving the stability of the battery and significantly improving the high-temperature and high-pressure performance of the battery. Detailed Embodiments

[0064] The following will further elaborate on the present invention in detail with reference to specific embodiments. It should be understood that the following embodiments are only for illustrative and explanatory purposes of the present invention and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0065] Unless otherwise specified, the experimental methods used in the following embodiments are all conventional methods; the reagents, materials, etc. used in the following embodiments can all be obtained from commercial channels unless otherwise specified.

[0066] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0067] It can be understood that the battery of the present invention includes a negative electrode sheet, an electrolyte, a positive electrode sheet, a separator, and an outer package. The positive electrode sheet, the separator, and the negative electrode sheet are stacked to obtain an electrode core, or after the positive electrode sheet, the separator, and the negative electrode sheet are stacked, they are wound to obtain an electrode core. The electrode core is placed in the outer package, and the electrolyte is injected into the outer package to obtain the battery of the present invention.

[0068] Examples 1-9 and Comparative Example 1

[0069] The batteries of Examples 1-9 and Comparative Example 1 were prepared through the following steps:

[0070] 1) Preparation of the positive electrode sheet

[0071] Mix the cathode active material lithium cobalt oxide (LiCoO₂), polyvinylidene fluoride (PVDF), SP (super P), and carbon nanotubes (CNT) in a mass ratio of 96:2:1.5:0.5, add N-methylpyrrolidone (NMP), and stir under a vacuum mixer until the mixed system becomes a homogeneous and flowable cathode active paste; uniformly coat the cathode active paste on both surfaces of the aluminum foil; dry the coated aluminum foil, and then obtain the required cathode sheet through rolling and slitting.

[0072] 2) Preparation of the anode sheet

[0073] Mix the anode active material artificial graphite, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) in a mass ratio of 96:1.5:1.5:0.95:0.05, add deionized water, and obtain the anode active paste under a vacuum mixer; uniformly coat the anode active paste on both surfaces of the copper foil; air-dry the coated copper foil at room temperature, then transfer it to an 80 °C oven and dry for 10 h, and then obtain the anode sheet through cold pressing and slitting.

[0074] 3) Preparation of the electrolyte

[0075] In a glove box filled with argon (H₂O < 0.1 ppm, O₂ < 0.1 ppm), mix EC / PC / DEC / PP evenly in a mass ratio of 10 / 20 / 40 / 30, then quickly add 1 mol / L of fully dried lithium hexafluorophosphate (LiPF₆), add vinylene carbonate based on 8 wt% of the total mass of the electrolyte after dissolution, 2 wt% of 1,3-propane sultone, 2 wt% of 1,3,6-hexanetricarbonitrile, and the additives described in Table 1, stir evenly, and obtain the required electrolyte after passing the moisture and free acid tests.

[0076] 4) Preparation of the battery

[0077] Stack the cathode sheet from step 1), the anode sheet from step 2), and the separator in the order of cathode sheet, separator, and anode sheet, and then wind them to obtain the battery core; place the battery core in the outer packaging aluminum foil, inject the electrolyte from step 3) into the outer packaging, and obtain the battery through processes such as vacuum packaging, standing, formation, shaping, and sorting. The charge and discharge range of the battery of the present invention is 3.0 - 4.5 V.

[0078] Perform high-temperature storage performance tests at 60 °C and 85 °C, and 45 °C cycle performance tests on the batteries obtained in the examples and comparative examples respectively. The test results are shown in Table 2.

[0079] 1) 60 °C storage performance test

[0080] Charge the battery in Table 1 at a rate of 1C to the cut-off voltage at 25°C, with a cut-off current of 0.025C, let it stand for 5 min, and measure the thickness of the lithium-ion battery (this is the thickness before storage). The fully charged cell / battery is left open-circuited at (60 ± 2)°C for 35 days. After 35 days of storage, it is left open-circuited at room temperature for 2 h, and the cold thickness after storage is measured. Calculate the thickness expansion rate of the lithium-ion battery:

[0081] Thickness expansion rate = [(thickness after storage - thickness before storage) / thickness before storage] × 100%

[0082] 2) 85°C storage performance test

[0083] Charge the battery in Table 1 at a rate of 1C to the cut-off voltage at 25°C, with a cut-off current of 0.025C, let it stand for 5 min, and measure the thickness of the lithium-ion battery (this is the thickness before storage). The fully charged cell / battery is left open-circuited at (85 ± 2)°C for 10 h. After 10 h of storage, it is left open-circuited at room temperature for 2 h, and the cold thickness after storage is measured. Calculate the thickness expansion rate of the lithium-ion battery:

[0084] Thickness expansion rate = [(thickness after storage - thickness before storage) / thickness before storage] × 100%

[0085] 3) 45°C cycle performance test

[0086] Charge and discharge the battery in Table 1 at a rate of 1C within the charge and discharge cut-off voltage range at 45°C. Measure the discharge capacity in the first week as x2 mAh, and the discharge capacity in the Nth cycle as y2 mAh; divide the capacity in the Nth week by the capacity in the first week to obtain the cycle capacity retention rate R2 = y2 / x2 in the Nth week. When the cycle capacity retention rate R2 drops below 80%, record the cycle number at this time.

[0087] Composition of electrolyte additives in the batteries of Examples and Comparative Examples in Table 1

[0088]

[0089] Performance test results of the batteries of Examples and Comparative Examples in Table 2

[0090]

[0091]

[0092] As can be seen from Table 2, the thickness expansion rates of Comparative Example 1 without the additive A that can coordinate with transition metals and is resistant to HF for CEI film and SEI film at 60 °C and 85 °C storage are significantly greater than those with additive A. Moreover, the higher the content of additive A, the lower the thickness expansion rate. However, when the addition amount is greater than 4%, the further increase in the additive content has less and less impact on the thickness expansion rate.

[0093] As can be seen from Table 2, the number of 45 °C cycles of Comparative Example 1 without additive A is significantly less than that of Examples 1-7 with an appropriate amount of additive A that can form an acid-suppressing CEI film and SEI film, which proves that additive A has a significant improvement effect on the high-voltage high-temperature cycling performance.

[0094] From Comparative Examples 1-4 and Example 2, it can be seen that adding ordinary nitrile additives or enamine additives alone can also slightly improve high-temperature storage and high-temperature cycling. There is no obvious synergistic effect when adding nitrile additives and enamine additives simultaneously. However, adding additive A that includes both an enamine group (-N-C=C-) and a cyano group (-CN) has a relatively more significant improvement effect on high-temperature storage and high-temperature cycling, which proves that having two functional groups in the molecule has a synergistic effect. Since the cyano group (-CN) and the enamine group (-N-C=C-) are on the same molecule, there is no problem of sequential film formation for the relatively separate two molecular structures, and they will be more evenly distributed on the SEI film and CEI film, enabling them to better play a synergistic function, thus achieving a more significant improvement effect on high-temperature storage and high-temperature cycling performance.

[0095] Furthermore, from Examples 1-4, it can be seen that as the addition amount of additive A increases, the improvement of its high-temperature cycling performance first becomes stronger and then weaker. Thus, it can be shown that adding an appropriate amount of additive A is beneficial to the improvement of the battery cycling performance. When adding an excessive amount, the side effects such as the increase in impedance caused by additive A begin to become more significant.

[0096] From Examples 5-6, it can be seen that the compounds shown in Formula (2) and Formula (7) both have the same effect of improving high-temperature storage and high-temperature cycling performance. The improvement effect of the compound shown in Formula (7) is slightly weaker than that of the compound shown in Formula (2), which may be because the nitrile functional group of the compound shown in Formula (7) per unit molecular formula is relatively less than that of compound (2).

[0097] From Example 7, it can be seen that the compounds shown in Formula (2) and Formula (7) can be used in combination to improve the high-temperature storage and high-temperature cycling performance of the battery.

[0098] It can be seen from Example 8 and Example 9 that adding an excessive amount of additive A no longer improves the high-temperature cycling performance of the battery. On the contrary, it will deteriorate the cycling performance of the battery. This is because the formed CEI film and SEI film have poor conductivity and too large impedance, which is not conducive to the cycling of the battery.

[0099] In summary, the electrolyte added with additive A in this application can coordinate with transition metals through cyano functional groups to reduce the oxidation of the electrolyte by transition metals. At the same time, the presence of enamine functional groups can form a functional protective film with the function of inhibiting acid corrosion on the positive and negative electrodes. The synergistic protection of the dual functional groups can significantly reduce the side reactions of the electrolyte, reduce the rupture of the battery CEI film and the loss of positive active materials under high-temperature conditions, and at the same time reduce the rupture of the battery SEI film and the loss of negative active materials, thereby improving the stability of the battery and significantly improving the high-temperature and high-pressure performance of the battery.

[0100] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte includes an organic solvent, an electrolyte salt, and a functional additive. Among them, the functional additive includes additive A, and additive A is selected from enamine compounds containing a cyano group; The enamine compound containing a cyano group is selected from at least one of the compounds represented by formula (1): In formula (1), R1, R2, and R3 are the same or different and are each independently selected from H, -NR5R6, -CN, unsubstituted or optionally substituted by one, two, or more R a substituted C 1-10 alkyl, and at least one group of R1, R2, and R3 is selected from -CN; each R a is the same or different and is each independently selected from halogen, C 1-10 alkyl, -C(=O)-C 1-10 alkyl, -C(=O)-O-C(=O)-C 1-10 alkyl, C 6-14 aryl, 5- to 14-membered heteroaryl; R5 and R6 are the same or different and are each independently selected from H or C 1-10 alkyl; R4 and R5 are the same or different and are each independently selected from H, unsubstituted or optionally substituted by one, two or more R b substituted C 1-10 alkyl; each R b is the same or different and is independently selected from halogen, C 1-10 alkyl, -C(=O)-C 1-10 alkyl, -C(=O)-O-C(=O)-C 1-10 alkyl, C 6-14 aryl, 5-14-membered heteroaryl; R3 and R4 may also be connected to form a cyclic structure.

2. The electrolyte according to claim 1, characterized in that, In formula (1), R1, R2, and R3 are the same or different and are each independently selected from H, -NR5R6, -CN, unsubstituted or optionally substituted by one, two, or more R a substituted C 1-6 alkyl, and at least one of the groups R1, R2, and R3 is selected from -CN; each R a is the same or different and is each independently selected from halogen, C 1-6 alkyl; R5 and R6 are the same or different and are each independently selected from H or C 1-6 alkyl; R4 and R5 are the same or different and are each independently selected from H, unsubstituted or optionally substituted by one, two or more R b substituted C 1-6 alkyl; each R b is the same or different and is each independently selected from halogen, C 1-6 alkyl; R3 and R4 may also be connected to form a cyclic structure.

3. The electrolyte according to claim 2, characterized in that, In formula (1), R1, R2, and R3 are the same or different and are each independently selected from H, -NR5R6, -CN, C 1-6 alkyl, and at least one of the groups R1, R2, and R3 is selected from -CN; R5 and R6 are the same or different and are each independently selected from H or C 1-6 alkyl; R4 and R5 are the same or different and are each independently selected from H, C 1-6 alkyl; R3 and R4 may also be connected to form a cyclic structure.

4. The electrolyte according to claim 3, characterized in that, The enamine compound containing a cyano group is selected from at least one of the compounds represented by the following formula (2) to formula (9):

5. The electrolyte according to any one of claims 1-4, characterized in that, The addition amount of additive A is 0.1-5.0 wt% of the total mass of the electrolyte.

6. The electrolyte according to any one of claims 1-4, characterized in that, The functional additive further includes additive B, and additive B is selected from fluoroethylene carbonate; The addition amount of additive B is 2-30 wt% of the total mass of the electrolyte.

7. The electrolyte according to any one of claims 1-4, characterized in that, The functional additive further includes additive C, and additive C is selected from at least one of the following compounds: 1,3-propane sultone, 1,3-propene sultone, succinonitrile, adiponitrile, glycerol trinitrile, 1,3,6-hexane trinitrile, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluoro bis(oxalate) phosphate; The addition amount of additive C is 0-10 wt% of the total mass of the electrolyte.

8. The electrolyte according to claim 6, characterized in that, The functional additive further includes additive C, and additive C is selected from at least one of the following compounds: 1,3-propane sultone, 1,3-propene sultone, succinonitrile, adiponitrile, glycerol trinitrile, 1,3,6-hexane trinitrile, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluoro bis(oxalate) phosphate; The addition amount of additive C is 0-10 wt% of the total mass of the electrolyte.

9. A battery, characterized in that, The battery includes the electrolyte according to any one of claims 1-8.

10. The battery according to claim 9, characterized in that, The charging cut-off voltage of the battery is 4.5 V or more.

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