A non-aqueous electrolyte and a battery

Abstract

To overcome the problem of insufficient high-temperature cycle and high-temperature storage performance of existing batteries, the present invention provides a non-aqueous electrolyte, which includes a solvent, an electrolyte salt, and a first additive. The first additive is selected from at least one of the compounds represented by Structural Formula 1: A-D-B-E-C Structural Formula 1 wherein A, B, and C are each independently selected from groups containing a cyclic carbonate group, a cyclic sulfate group, a cyclic sulfite group, a cyclic sulfonate group, a cyclic sulfone group, a cyclic sulfoxide group, a cyclic carboxylate group, or a cyclic anhydride group; D and E are each independently selected from a single bond, or a group containing an alkylene group, an ether bond, a sulfur-oxygen double bond, or a carbon-oxygen double bond; the methanol content in the non-aqueous electrolyte is 200 ppm or less. At the same time, the present invention also discloses a battery including the above non-aqueous electrolyte. The non-aqueous electrolyte provided by the present invention can effectively improve the high-temperature performance of the battery while ensuring the stability of its performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a non-aqueous electrolyte and a battery. Background Art

[0002] Lithium-ion batteries are widely used in life and production due to their excellent performance. In recent years, with the development of consumer electronic products and new energy vehicles, people have put forward higher requirements for the performance of lithium-ion batteries, especially the cycle performance and storage performance under high-temperature conditions need to be further improved. In lithium-ion batteries, the non-aqueous electrolyte is an important factor affecting the battery performance, and the additives in the non-aqueous electrolyte are particularly important for the performance of the battery at high temperatures. During the first charging process of the lithium-ion battery, a passivation film will be formed on the surfaces of the positive and negative electrodes in contact with the electrolyte, which not only prevents the further decomposition of the electrolyte but also plays a role in transporting lithium ions. Therefore, the passivation film determines the quality of the lithium-ion battery performance. However, although the existing additives can improve the cycle and storage performance of the battery to a certain extent, they have different disadvantages. For example, the common negative electrode film-forming additive VC has the disadvantage of large film-forming impedance, and the common positive electrode protection additive DTD faces the cost problem of low-temperature storage and transportation.

[0003] On the other hand, the substances in the electrolyte will also interact with each other, thereby having different effects on the battery performance. For example, the same additive can improve the battery performance in one electrolyte system, but it cannot play a role when used in other electrolyte systems. Therefore, how to reduce the influence of variable factors in the electrolyte to provide an electrolyte that can stably improve the high-temperature cycle and high-temperature storage performance of the battery still needs to be further developed. Summary of the Invention

[0004] Aiming at the problem of insufficient high-temperature cycle and high-temperature storage performance of existing batteries, the present invention provides a non-aqueous electrolyte and a battery.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0006] On the one hand, the present invention provides a non-aqueous electrolyte, including a solvent, an electrolyte salt, and a first additive, and the first additive is selected from at least one of the compounds shown in Structural Formula 1:

[0007] A-D-B-E-C

[0008] Structural Formula 1

[0009] Wherein, A, B, and C are each independently selected from groups containing a cyclic carbonate group, a cyclic sulfate group, a cyclic sulfite group, a cyclic sulfonate group, a cyclic sulfone group, a cyclic sulfoxide group, a cyclic carboxylate group, or a cyclic anhydride group;

[0010] D and E are each independently selected from a single bond, or a group containing an alkylene group, an ether bond, a sulfoxide double bond or a carbonyl double bond;

[0011] The methanol content in the non-aqueous electrolyte is 200 ppm or less.

[0012] Optionally, the number of cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylate groups and cyclic anhydride groups contained in A, B, and C independently of each other is 1 to 5, and the total number of cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylate groups and cyclic anhydride groups of A, B, and C is less than or equal to 10.

[0013] Optionally, A and C are each independently selected from the groups shown in Structural Formula 2:

[0014]

[0015] wherein, n is an integer selected from 0 to 4, and R1 is selected from hydrogen, halogen, a C1-C5 hydrocarbon group or a halogenated hydrocarbon group; R2, R3, R4, R5, R6, and R7 are each independently selected from a C1-C3 alkylene group, a C1-C3 alkoxy group, an oxygen atom, At least one of R2, R3, and R4 is selected from and at least one of R2, R3, and R4 is selected from an oxygen atom, and at least one of R5, R6, and R7 is selected from and at least one of R5, R6, and R7 is selected from an oxygen atom.

[0016] Optionally, B is selected from the group shown in Structural Formula 3:

[0017]

[0018] wherein, m is an integer selected from 1 to 4, and R8, R9, R 10 are each independently selected from a C1-C3 alkylene group, a C1-C3 alkoxy group, an oxygen atom, R8, R9, R 10 At least one of them is selected from and at least one of R8, R9, and R 10 is selected from an oxygen atom.

[0019] Optionally, D and E are each independently selected from the groups shown in Structural Formula 4:

[0020]

[0021] Among them, z is selected from integers from 0 to 4, and R 11 and R 13 each independently selected from a single bond or a C1-C5 alkylene group, and R 12 is selected from a single bond,

[0022] Optionally, D and E are each independently selected from a single bond or a C1-C5 alkylene group, and A, B, and C are each independently selected from a substituted or unsubstituted cyclic carbonate group, cyclic sulfate group, cyclic sulfite group, cyclic sulfonate group, cyclic sulfone group, cyclic sulfoxide group, cyclic carboxylate group, or cyclic anhydride group.

[0023] Optionally, when A, B, or C is substituted, the substituent is selected from a halogen, a hydrocarbon group, or a halogenated hydrocarbon group. More preferably, when A, B, or C is substituted, the substituent is selected from a halogen, an alkyl group, or a halogenated alkyl group.

[0024] Optionally, A and C are the same as each other, A and B are the same or different from each other, and D and E are the same as each other.

[0025] Optionally, the first additive is selected from one or more of the following compounds:

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

[0033] Optionally, based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the first additive is 0.01-5.0%.

[0034] Optionally, the non-aqueous electrolyte further includes a second additive, and the second additive is selected from at least one of the compounds shown in Structural Formula 5 and the compounds shown in Structural Formula 6. Based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the second additive is 0.01-4%:

[0035]

[0036] Among them, R 17 is selected from a C2-C5 fluoroalkylene group or an unsaturated alkylene group, and R18 , R 19 , R 20 , R 21 , R 22 , R 23 Each independently selected from a hydrogen atom, a halogen atom, or a C1-C5 saturated hydrocarbon group, unsaturated hydrocarbon group, or halogenated hydrocarbon group.

[0037] Optionally, the compound represented by Structural Formula 5 is selected from one or more of the following compounds:

[0038]

[0039] The compound represented by Structural Formula 6 is selected from one or more of the following compounds:

[0040]

[0041]

[0042] Optionally, the non-aqueous electrolyte further comprises a third additive selected from one or more of LiPO2F2, LiODFB, LiDFOP, LiBOB, LiBF4, LiFSI, and LiTFSI; based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the third additive is 0.01-4%.

[0043] On the other hand, the present invention provides a battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte as described above.

[0044] According to the non-aqueous electrolyte provided by the present invention, the inventors unexpectedly found that by adding the compound represented by Structural Formula 1 as the first additive to the electrolyte, in some battery systems, the high-temperature cycle and high-temperature storage performance of the battery can be significantly improved, and at the same time, the generation of gas during the battery cycle can be reduced; while in some other battery systems, it is difficult to achieve a good improvement effect; through experimental reverse deduction, it was found that in the battery systems with insignificant performance improvement, the electrolytes used contained a certain detectable amount of methanol impurities, while in the battery systems with significant performance improvement, the electrolytes used contained relatively less methanol impurities. Therefore, through further experimental verification of setting the alcohol content, the improvement amplitude of the first additive on the battery performance is related to the methanol content in the electrolyte. When the methanol content in the electrolyte is controlled to be less than or equal to 200 ppm, the first additive can significantly improve the high-temperature storage and high-temperature cycle performance of the lithium-ion battery. Detailed Embodiments

[0045] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0046] An embodiment of the present invention provides a non-aqueous electrolyte, which includes a solvent, an electrolyte salt and a first additive, and the first additive is selected from at least one of the compounds shown in Structural Formula 1:

[0047] A-D-B-E-C

[0048] Structural Formula 1

[0049] Wherein, A, B, and C are each independently selected from groups containing a cyclic carbonate group, a cyclic sulfate group, a cyclic sulfite group, a cyclic sulfonate group, a cyclic sulfone group, a cyclic sulfoxide group, a cyclic carboxylate group or a cyclic anhydride group;

[0050] D and E are each independently selected from a single bond, or a group containing an alkylene group, an ether bond, a sulfur-oxygen double bond or a carbon-oxygen double bond;

[0051] The methanol content in the non-aqueous electrolyte is 200 ppm or less.

[0052] The inventors unexpectedly found through experiments that adding a compound shown in Structural Formula 1 as a first additive to the electrolyte can significantly improve the high-temperature cycle and high-temperature storage performance of the battery in some battery systems, and at the same time can reduce the generation of gas during the battery cycle; while in some other battery systems, it is difficult to play a better improvement role; through experimental reverse deduction, it was found that in the battery systems with insignificant performance improvement, the electrolytes used all contained a certain detectable amount of methanol impurities, while in the battery systems with obvious performance improvement, the electrolytes used contained relatively less methanol impurities. Therefore, through further experimental verification of setting the alcohol content, the improvement amplitude of the first additive on the battery performance is related to the methanol content in the electrolyte. When the methanol content in the electrolyte is controlled to be lower than or equal to 200 ppm, the first additive can significantly improve the high-temperature storage and high-temperature cycle performance of the lithium-ion battery.

[0053] Regarding the relationship between the first additive and methanol in the electrolyte, it is speculated that the first additive itself can participate in the film formation on the surfaces of the positive and negative electrodes, but the quality of the formed film is sensitive to methanol. When the methanol content is low, the first additive forms a relatively stable film, which can avoid the rupture and reconstruction of the film under high-temperature conditions. When the methanol content is greater than 200 ppm, methanol will undergo a transesterification reaction with the first additive. On the one hand, this leads to ring-opening reactions and reduces the effective content of the first additive. On the other hand, it is speculated that the by-products generated by the reaction will react with the solvent or lithium salt in the electrolyte, consuming the electrolyte, and at the same time, the generated by-products may also damage the film structures on the positive and negative electrodes.

[0054] In some embodiments, the number of cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylate groups or cyclic anhydride groups independently contained in each of A, B, and C is 1 to 5, and the total number of cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylate groups or cyclic anhydride groups of A, B, and C is less than or equal to 10.

[0055] In some embodiments, A and C are each independently selected from the groups shown in Structural Formula 2:

[0056]

[0057] Among them, n is an integer selected from 0 to 4, and R1 is selected from hydrogen, halogen, a C1-C5 hydrocarbon group or a halogenated hydrocarbon group; R2, R3, R4, R5, R6, and R7 are each independently selected from a C1-C3 alkylene group, a C1-C3 alkoxy group, an oxygen atom, At least one of R2, R3, and R4 is selected from and at least one of R2, R3, and R4 is selected from an oxygen atom, and at least one of R5, R6, and R7 is selected from and at least one of R5, R6, and R7 is selected from an oxygen atom.

[0058] In a preferred embodiment, the combined groups of -R3-R2-R4- and -R7-R5-R6- are each independently selected from

[0059] In some embodiments, B is selected from the group shown in Structural Formula 3:

[0060]

[0061] Among them, m is an integer selected from 1 to 4, and R8, R9, R 10Each independently selected from C1-C3 alkylene groups, C1-C3 alkoxy groups, oxygen atoms, R8, R9, R 10 at least one of which is selected from and at least one of R8, R9, R 10 is selected from an oxygen atom.

[0062] In a preferred embodiment, the combined group of -R9-R8-R 10 is independently selected from

[0063] In some embodiments, D and E are each independently selected from the groups shown in Structural Formula 4:

[0064]

[0065] wherein z is an integer selected from 0 to 4, R 11 and R 13 are each independently selected from a single bond or a C1-C5 alkylene group, and R 12 is selected from a single bond,

[0066] In some embodiments, A and C are the same as each other, A and B are the same or different from each other, and D and E are the same as each other.

[0067] When A and C are the same as each other, and D and E are the same as each other, the compound shown in Structural Formula 1 has a symmetric structure. Compared with the asymmetric structure, the compound shown in the symmetric Structural Formula 1 is easier to synthesize, the product yield is higher, and it is beneficial to reduce the production cost.

[0068] In some embodiments, D and E are each independently selected from a single bond or a C1-C5 alkylene group, and A, B, and C are each independently selected from a substituted or unsubstituted cyclic carbonate group, cyclic sulfate group, cyclic sulfite group, cyclic sulfonate group, cyclic sulfone group, cyclic sulfoxide group, cyclic carboxylate group, or cyclic anhydride group.

[0069] As an example, the first additive can be selected from one or more of the following compounds:

[0070]

[0071]

[0072]

[0073]

[0074] In some embodiments, D and E are each independently selected from the groups represented by Structural Formula 4:

[0075]

[0076] wherein z is selected from integers from 1 to 4, R 11 and R 13 are each independently selected from a single bond or a C1-C5 alkylene group, and R 12 is selected from

[0077] A, B, and C are each independently selected from a substituted or unsubstituted cyclic carbonate group, cyclic sulfate group, cyclic sulfite group, cyclic sulfonate group, cyclic sulfone group, cyclic sulfoxide group, cyclic carboxylate group, or cyclic anhydride group. Preferably, when A, B, or C is substituted, the substituent is selected from a halogen, a hydrocarbon group, or a halogenated hydrocarbon group. More preferably, when A, B, or C is substituted, the substituent is selected from a halogen, an alkyl group, or a halogenated alkyl group.

[0078] As an example, the first additive may be selected from one or more of the following compounds:

[0079]

[0080]

[0081]

[0082] In some embodiments, the first additive may also be selected from one or more of the following compounds:

[0083]

[0084]

[0085] It should be noted that the above are some of the compounds claimed in the present invention, but are not limited thereto, and should not be construed as a limitation of the present invention.

[0086] Those skilled in the art can know the preparation methods of the above compounds according to the common general knowledge in the field of chemical synthesis when knowing the structural formula of the compound of Structural Formula 1. For example:

[0087] Compound 1-1 can be prepared by the following method:

[0088] Sorbitol, dimethyl carbonate, methanol, the alkaline substance catalyst potassium hydroxide, and organic solvents such as DMF are placed in a reaction vessel and reacted under heating conditions for several hours. Then, a certain amount of oxalic acid is added to adjust the pH to neutral. After filtration and recrystallization, intermediate product 1 can be obtained. Next, intermediate product 1, carbonate, thionyl chloride, etc. are subjected to an esterification reaction under high-temperature conditions to obtain intermediate product 2, and then intermediate product 2 is oxidized using an oxidant such as sodium periodate to obtain compound 1-1.

[0089] Compound 1-2 can be prepared by the following method:

[0090] Diacetone-D-mannitol, dimethyl carbonate, methanol, potassium carbonate, dioxane, etc. are reacted under heating and stirring for several hours. Then, a certain amount of oxalic acid is added to adjust the pH of the solution to neutral. After filtration and concentration, intermediate product 3 is obtained; an appropriate amount of pure water, carbonate, acid, etc. are added to intermediate product 3 for a hydrolysis reaction to obtain intermediate product 4; then intermediate product 4, thionyl chloride, and carbonate solvent are prepared under heating conditions to obtain intermediate product 5; finally, intermediate product 5 is oxidized using an oxidant such as sodium periodate to obtain compound 1-2.

[0091] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the first additive is 0.01 - 5.0%.

[0092] When the addition amount of the first additive is too small, it cannot play a film-forming protection role, and the improvement effect on battery performance is not obvious; when the addition amount of the first additive is too large, not only will the film be too thick resulting in too large impedance, but also the viscosity of the electrolyte will be significantly increased, affecting the performance of the battery. Therefore, adding an appropriate amount of the first additive can improve the high-temperature performance of the battery.

[0093] In some embodiments, the methanol content in the non-aqueous electrolyte is 200 ppm or less.

[0094] Specifically, the methanol content in the non-aqueous electrolyte can be 0 ppm, 0.1 ppm, 1 ppm, 5 ppm, 10 ppm, 20 ppm, 50 ppm, 100 ppm, 150 ppm, 200 ppm.

[0095] It should be noted that the methanol present in the non-aqueous electrolyte deteriorates the film formation of the first additive. Therefore, within a certain range, the smaller the methanol content in the non-aqueous electrolyte, the better. When the methanol content in the non-aqueous electrolyte is 200 ppm or less, a battery with better high-temperature cycle and high-temperature storage performance can be obtained, and further reducing the methanol content has no obvious effect on the film formation of the first additive.

[0096] In some embodiments, the non-aqueous electrolyte further includes a second additive, and the second additive is selected from the compounds shown in Structural Formula 5 and / or the compounds shown in Structural Formula 6. Based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the second additive is 0.01-4%:

[0097]

[0098] Among them, R 17 is selected from fluoroalkylene or unsaturated alkylene groups having 2 to 5 carbon atoms, and R 18 , R 19 , R 20 , R 21 , R 22 , R 23 are each independently selected from a hydrogen atom, a halogen atom, or a saturated hydrocarbon group, an unsaturated hydrocarbon group, or a halogenated hydrocarbon group having 1 to 5 carbon atoms.

[0099] Among them, the second additive can cooperate with the first additive to form a more stable SEI film on the negative electrode surface, inhibit gas generation, and thus further improve the high-temperature storage performance.

[0100] In some embodiments, the compound shown in Structural Formula 5 is selected from one or more of the following compounds:

[0101]

[0102]

[0103] In some embodiments, the compound shown in Structural Formula 6 is selected from one or more of the following compounds:

[0104]

[0105] In a preferred embodiment, based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the second additive is 0.01-4%.

[0106] In some embodiments, the total addition amount of the first additive and the second additive is 0.04-8%.

[0107] When the total amount of the first additive and the second additive is less than 0.04%, it is not sufficient to form a complete passivation film on the positive and negative electrodes, resulting in the decomposition of the electrolyte solvent. The decomposition products are unstable, leading to a rapid decay of the battery capacity retention rate under high-temperature storage, and at the same time, serious gas generation causes the battery to expand; when the total amount of the first additive and the second additive is greater than 8%, it will cause an increase in the thickness of the passivation film formed on the positive and negative electrodes, which is not conducive to reducing the battery impedance.

[0108] In a preferred embodiment, the total addition amount of the first additive and the second additive is 1-4%.

[0109] In some embodiments, the non-aqueous electrolyte further includes a third additive selected from one or more of LiPO2F2, LiODFB, LiDFOP, LiBOB, LiBF4, LiFSI, and LiTFSI; based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the third additive is 0.01-4%.

[0110] The third additive is also a film-forming additive that participates in the formation of the passivation film on the surfaces of the positive and negative electrodes. This passivation film can also isolate the direct contact between the electrolyte and the material, reduce the occurrence of interfacial side reactions, and thus inhibit gas generation and impedance growth. However, when the third additive is added alone to form the passivation film on the positive and negative electrodes, it contains more LiF and it is difficult to inhibit the growth of LiF, resulting in a decrease in the lithium-ion conductivity of the passivation film and a reduction in the lithium-ion transmission rate. During the charge and discharge process of the battery, the polarization increases, causing the battery capacity to decay during high-temperature storage and cycling, and the impedance to increase. By adding the first additive and the third additive together, the two can participate in film formation simultaneously, jointly construct the film components on the surfaces of the positive and negative electrodes, increase the dissolution of the inorganic components (such as LiF / Li2CO3, etc.) in the film components, inhibit the generation and growth of the inorganic components, and greatly improve the component ratio of the organic layer and the inorganic layer of the passivation film. It can not only improve the lithium-ion conduction rate of the passivation film, but also protect the structures of the positive and negative electrodes, improve the stability of the battery materials, better isolate the contact between the battery materials and the electrolyte, thereby reducing battery polarization, inhibiting the growth of the high-temperature cycle impedance of the battery, and improving the high-temperature cycle performance of the battery.

[0111] In some embodiments, the solvent includes one or more of ether solvents, nitrile solvents, carbonate solvents, and carboxylate solvents.

[0112] In some embodiments, the ether solvents include cyclic ethers or chain ethers. Specifically, the cyclic ethers can be, but are not limited to, one or more of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF); specifically, the chain ethers can be, but are not limited to, one or more of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), and tetraethylene glycol dimethyl ether (TEGDME). The nitrile solvents can be, but are not limited to, one or more of acetonitrile, glutarodinitrile, and malononitrile. The carbonate solvents include cyclic carbonates or chain carbonates. Specifically, the cyclic carbonates can be, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); specifically, the chain carbonates can be, but are not limited to, one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The carboxylate solvents can be, but are not limited to, one or more of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0113] In some embodiments, the electrolyte salts include one or more of lithium salts, sodium salts, potassium salts, magnesium salts, zinc salts, and aluminum salts. In a preferred embodiment, the electrolyte salts are selected from lithium salts.

[0114] In a more preferred embodiment, the electrolyte salts include at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0115] In some embodiments, in the non-aqueous electrolyte, the concentration of the electrolyte salt is 0.1 mol / L - 8 mol / L. In a preferred embodiment, in the non-aqueous electrolyte, the concentration of the electrolyte salt is 0.5 mol / L - 4 mol / L. Specifically, the concentration of the electrolyte salt can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, or 4 mol / L.

[0116] Another embodiment of the present invention provides a battery, including a positive electrode, a negative electrode, and the non-aqueous electrolyte as described above.

[0117] Since the battery adopts the non-aqueous electrolyte as described above, a passivation film with excellent performance can be formed on the positive electrode and the negative electrode, thereby effectively improving the high-temperature storage performance and high-temperature cycling performance of the battery and enhancing the battery power characteristics.

[0118] In some embodiments, the battery is a secondary battery, which can be a lithium secondary battery, a potassium secondary battery, a sodium secondary battery, a magnesium secondary battery, a zinc secondary battery, an aluminum secondary battery, etc.

[0119] In a preferred embodiment, the battery is a lithium metal battery, a lithium ion battery or a lithium sulfur battery.

[0120] In some embodiments, the positive electrode includes a positive electrode active material. The type of the positive electrode active material is not particularly limited as long as it is a positive electrode active material capable of reversibly inserting / extracting metal ions (such as lithium ions, sodium ions, potassium ions, magnesium ions, zinc ions, aluminum ions, etc.). Preferably, the positive electrode active material is selected from at least one of nickel cobalt manganese ternary materials, LiFePO4, LiCoO2, sulfur and its composites.

[0121] In some embodiments, the negative electrode includes a negative electrode active material, and the negative electrode active material includes one or more of a carbon-based negative electrode, a tin-based negative electrode, a lithium negative electrode, a sodium negative electrode, a potassium negative electrode, a magnesium negative electrode, a zinc negative electrode and an aluminum negative electrode. Among them, the carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; the tin-based negative electrode may include tin, tin carbon, tin oxygen, tin metal compounds; the lithium negative electrode may include metallic lithium or a lithium alloy. The lithium alloy may specifically be at least one of a lithium-silicon alloy, a lithium-sodium alloy, a lithium-potassium alloy, a lithium-aluminum alloy, a lithium-tin alloy and a lithium-indium alloy.

[0122] In some embodiments, the battery further includes a separator, and the separator is located between the positive electrode and the negative electrode.

[0123] The separator can be an existing conventional separator, which can be a polymer separator, a non-woven fabric, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP and three-layer PP / PE / PP separators.

[0124] The present invention is further described below through examples.

[0125] I. Preparation of Examples 1-59 and Comparative Examples 1-16

[0126] 1) Preparation of electrolyte

[0127] Ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed according to a mass ratio of EC:DEC:EMC = 1:1:1, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and then each additive is added according to Table 1-5. The dosage of the additive is calculated as a percentage of the total mass of the electrolyte. The methanol content in the electrolyte is measured as shown in Table 1-5.

[0128] 2) Preparation of positive electrode plate

[0129] Mix the cathode active material LiNi 0.5 Co 0.2 Mn 0.3 O₂, conductive carbon black Super - P and binder polyvinylidene fluoride (PVDF) in a mass ratio of 93:4:3, and then disperse them in N - methyl - 2 - pyrrolidone (NMP) to obtain the cathode slurry. Coating the slurry evenly on both sides of the aluminum foil, through drying, calendaring and vacuum drying, and welding the aluminum lead - out wire with an ultrasonic welder to obtain the cathode plate, and the thickness of the plate is 120 - 150 μm.

[0130] 3) Preparation of the anode plate

[0131] Mix the anode active material graphite, conductive carbon black Super - P, binder styrene - butadiene rubber (SBR) and carboxymethyl cellulose (CMC) in a mass ratio of 94:1:2.5:2.5, and then disperse them in deionized water to obtain the anode slurry. Coating the slurry on both sides of the copper foil, through drying, calendaring and vacuum drying, and welding the nickel lead - out wire with an ultrasonic welder to obtain the anode plate, and the thickness of the plate is 120 - 150 μm.

[0132] 4) Preparation of the battery cell

[0133] Place a three - layer separator with a thickness of 20 μm between the cathode plate and the anode plate, then wind the sandwich structure composed of the cathode plate, the anode plate and the separator, and then flatten the wound body and put it into an aluminum foil packaging bag, and bake it in vacuum at 75 °C for 48 h to obtain the battery cell to be injected with electrolyte.

[0134] 5) Injection of electrolyte and formation of the battery cell

[0135] In a glove box with water and oxygen contents below 20 ppm and 50 ppm respectively, inject the above - prepared electrolyte into the battery cell, and after vacuum packaging, let it stand at 45 °C for 24 h.

[0136] Then carry out the conventional formation of the first charge according to the following steps: constant - current charge at 0.05C for 180 min, constant - current charge at 0.1C for 180 min, constant - current charge at 0.2C for 120 min, after aging at 45 °C for 48 h, carry out secondary vacuum sealing, and then further charge at a constant current of 0.2C to 4.2V and discharge at a constant current of 0.2C to 3.0V.

[0137] II. Performance testing

[0138] 1. Carry out the following performance tests on the lithium - ion batteries prepared in Examples 1 - 48 and Comparative Examples 1 - 9:

[0139] High - temperature cycle performance test

[0140] The prepared lithium-ion battery was placed in an oven at a constant temperature of 45 °C and charged at a constant current of 1C to 4.4V (LiNi 0.5 Co 0.2 Mn 0.3 O2 / AG), then charged at a constant current and constant voltage until the current dropped to 0.05C, and then discharged at a constant current of 1C to 3.0V. This cycle was repeated, and the discharge capacity of the first cycle and the last cycle were recorded.

[0141] The capacity retention rate of the high-temperature cycle was calculated according to the following formula:

[0142] Capacity retention rate = Discharge capacity of the last cycle / Discharge capacity of the first cycle × 100%.

[0143] High-temperature storage performance test

[0144] The formed lithium-ion battery was charged at a constant current of 1C to 4.4V (LiNi 0.5 Co 0.2 Mn 0.3 O2 / AG) at room temperature, then charged at a constant current and constant voltage until the current dropped to 0.05C, and then discharged at a constant current of 1C to 3.0V. The initial discharge capacity and the initial battery volume were measured. Then, after being fully charged and stored in an environment of 60 °C for 30 days, it was discharged to 3V at 1C, and the retained capacity, recovered capacity and the battery volume after storage were measured. The calculation formulas are as follows:

[0145] Battery capacity retention rate (%) = Retained capacity / Initial capacity × 100%;

[0146] Battery capacity recovery rate (%) = Recovered capacity / Initial capacity × 100%;

[0147] Volume expansion rate (%) = (Battery volume after storage - Initial battery volume) / Initial battery volume × 100%.

[0148] For the following data tests, the batteries used had the same conditions except for the differences listed in each table.

[0149] 1.1. The test results obtained from Examples 1 to 12 and Comparative Examples 1 to 4 were filled in Table 1.

[0150] Table 1

[0151]

[0152]

[0153] As can be seen from the test results in Table 1, when the methanol content in the electrolyte is less than or equal to 200 ppm, using the compound shown in Structural Formula 1 as the first additive can improve the high-temperature storage performance and high-temperature cycling performance of the battery within a relatively large addition range. Moreover, as the content of the first additive increases, the high-temperature storage performance and high-temperature cycling performance of the battery first increase and then decrease. In particular, when the content of the first additive is 1%, the battery has the best comprehensive performance.

[0154] When the methanol content in the electrolyte is higher than 200 ppm, even if the optimal proportion of the first additive is added, the battery performance does not improve, indicating that there is an adverse side reaction between methanol and the first additive, which in turn affects the improvement of battery performance.

[0155] 1.2. The test results obtained from Examples 12 to 18 and Comparative Examples 2 and 6 are filled in Table 2.

[0156] Table 2

[0157]

[0158] As can be seen from the test results in Table 2, compared with other alcohols such as ethanol and ethylene glycol, methanol has the most obvious deterioration effect on the first additive, indicating that the reaction between methanol and the first additive has a certain specificity.

[0159] 1.3. The test results obtained from Examples 19 to 36 and Comparative Example 1 are filled in Table 3.

[0160] Table 3

[0161]

[0162]

[0163] As can be seen from the test results in Table 3, under the condition that the methanol content is less than 200 ppm, by adding different compounds shown in Structural Formula 1 to the electrolyte, the high-temperature storage performance and high-temperature cycling performance of the battery are improved to varying degrees.

[0164] 1.4. The test results obtained from Examples 37 to 48 and Comparative Examples 1, 7 to 9 are filled in Table 4.

[0165] Table 4

[0166]

[0167]

[0168] As can be seen from the test results in Table 4, compared with the single addition of the first additive or the second additive, the simultaneous addition of the first additive and the second additive in the non-aqueous electrolyte can effectively improve the capacity retention rate of the lithium-ion battery during high-temperature storage. More significantly, the gas generation of the lithium-ion battery is better inhibited, and the stability of the volume form of the lithium-ion battery can be maintained under high-temperature conditions, avoiding the swelling and bulging of the lithium-ion battery. At the same time, as can be seen from Table 4, when the addition amount of the first additive is 0.5-2% and the addition amount of the second additive is 0.5-2%, the two have the best cooperation effect in improving the high-temperature storage performance of the battery.

[0169] 2. The following performance tests were carried out on the lithium-ion batteries prepared in Examples 49-59 and Comparative Examples 10-16:

[0170] High-temperature cycling performance test

[0171] The prepared lithium-ion battery was placed in an oven at a constant temperature of 45 °C and charged at a constant current of 1C to 4.4V (LiNi 0.5 Co 0.2 Mn 0.3 O2 / AG), then charged at a constant current and constant voltage until the current dropped to 0.05C, and then discharged at a constant current of 1C to 3.0V. Such cycles were carried out, and the impedance of the first time and the impedance of the last time were recorded.

[0172] The impedance growth rate of the high-temperature cycle was calculated according to the following formula:

[0173] Impedance growth rate = (impedance of the last time - impedance of the first time) / impedance of the first time × 100%.

[0174] After 1000 high-temperature cycles, the battery was disassembled to obtain the negative electrode, and the proportion of the inorganic components in the passivation film was analyzed. The proportion test of the inorganic and organic components of the passivation film was carried out by XPS test and analysis of the electrode sheet: after using DMC to wash off the residual electrolyte on the surface of the electrode sheet, it was transferred to a PHI versaprobe III instrument using a vacuum transfer chamber for surface composition testing, and the multipak software was used for peak fitting after the test.

[0175] The test results obtained in Examples 49-59 and Comparative Examples 10-16 were filled into Table 5.

[0176] Table 5

[0177]

[0178] As can be seen from the test results in Table 5, compared with the single addition of the first additive or the third additive, the simultaneous addition of the first additive and the third additive in the non-aqueous electrolyte can effectively inhibit the impedance growth of the lithium-ion battery in a high-temperature environment. At the same time, it can be seen that when the third additive is added alone, the content of inorganic components in the formed passivation film is relatively high, while after adding the first additive, the proportion of inorganic components in the passivation film can be effectively reduced, thereby inhibiting the increase in impedance.

[0179] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A non-aqueous electrolyte, characterized in that, It includes a solvent, an electrolyte salt, and a first additive, and the first additive is selected from one or more of the following compounds: The methanol content in the non-aqueous electrolyte is less than or equal to 200 ppm; The non-aqueous electrolyte further includes a second additive, and the second additive is selected from the compounds shown in Structural Formula 5, Structural Formula 5 wherein, R 17 is selected from fluoroalkylene or unsaturated alkylene having 2 to 5 carbon atoms; Based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the first additive is 0.5% - 2.0%, and the addition amount of the second additive is 0.5% - 2.0%.

2. The non-aqueous electrolyte according to claim 1, characterized in that, The compounds shown in Structural Formula 5 are selected from one or more of the following compounds:

3. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous electrolyte further includes a third additive, and the third additive is selected from one or more of LiPO2F2, LiODFB, LiDFOP, LiBOB, LiBF4, LiFSI, and LiTFSI; based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the third additive is 0.01 - 4%.

4. A battery, characterized in that, It includes a positive electrode, a negative electrode, and the non-aqueous electrolyte according to any one of claims 1 to 3.

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