A lithium-ion battery

Abstract

To overcome the problems of gas expansion and impedance increase that occur in existing lithium-ion batteries during cycling, this invention provides a lithium-ion battery, including a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode includes a negative electrode active material containing a silicon-based material, wherein the silicon element in the silicon-based material accounts for 2% to 50% of the mass percentage of the negative electrode active material. The non-aqueous electrolyte includes an additive, which includes at least one compound as shown in structural formula 1: A-D-B-E-C structural formula 1, wherein A, B, and C are each independently selected from groups containing cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfoxide groups, cyclic carboxylic acid ester groups, or cyclic anhydride groups; D and E are each independently selected from single bonds, or groups containing hydrocarbon groups, ether bonds, sulfur-oxygen double bonds, or carbon-oxygen double bonds; the amount of the compound shown in structural formula 1 added is 0.01% to 5.0%. This invention can effectively solve problems such as gas expansion and impedance growth during lithium-ion battery cycling, and has excellent cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of battery material technology, specifically relating to a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in 3C digital devices and new energy vehicles due to their advantages such as high energy density, long cycle life, low self-discharge rate, and environmental friendliness. One approach to improving the energy density of lithium-ion batteries is to use high-energy-density anode active materials. Silicon-based anode materials, with their high theoretical specific capacity (4200 mAh / g), far exceeding that of graphite anodes (372 mAh / g), have become an important direction for improving the energy density of lithium-ion batteries. However, silicon-based anodes exhibit a large volume effect (≥300%) during cycling, causing the solid electrolyte interface film on the silicon-based anode surface to continuously rupture and regenerate during battery cycling. This leads to electrolyte consumption, loss of active lithium, and increased interfacial impedance, thus deteriorating cycle performance. Simultaneously, during the charging and discharging process of lithium-ion batteries, side reactions generate a large amount of reducing gas, causing the battery to swell, drastically worsening cycle performance. Furthermore, when the gas accumulates to a certain level inside the battery, it may cause an explosion, posing a safety hazard.

[0003] Therefore, it is necessary to provide a lithium-ion battery that uses graphite and silicon-based composite materials as the negative electrode and employs a non-aqueous electrolyte that can effectively improve the gas expansion and impedance growth of the lithium-ion battery during cycling, thereby improving the battery's cycle performance. Summary of the Invention

[0004] The technical problem solved by this invention is to address the problems of gas expansion and impedance increase that occur in existing lithium-ion batteries during cycling, thereby providing a lithium-ion battery with excellent cycle performance.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode comprises a negative electrode active material, which contains a silicon-based material, wherein the silicon element in the silicon-based material accounts for 2% to 50% of the mass percentage of the negative electrode active material.

[0007] The non-aqueous electrolyte comprises a solvent, an electrolyte salt, and an additive, wherein the additive comprises at least one of the compounds shown in structural formula 1:

[0008] ADBEC

[0009] Structural Formula 1

[0010] Among them, A, B, and C are each independently selected from groups containing cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylic acid ester groups, or cyclic anhydride groups.

[0011] D and E are each independently selected from single bonds, or groups containing alkylene groups, ether bonds, sulfur-oxygen double bonds, or carbon-oxygen double bonds;

[0012] Based on the total mass of the non-aqueous electrolyte being 100%, the amount of the compound shown in structural formula 1 added is 0.01~5.0%.

[0013] Optionally, A, B, and C may each contain 1 to 5 cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylic acid ester groups, and cyclic anhydride groups, and the total number of cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfonate groups, cyclic carboxylic acid ester groups, and cyclic anhydride groups in A, B, and C may be less than or equal to 10.

[0014] Optionally, A and C may be independently selected from the groups shown in structural formula 2:

[0015]

[0016] Structural Formula 2

[0017] Where n is selected from an integer from 0 to 4, R1 is selected from hydrogen, halogen, C1 to C5 hydrocarbon group or haloalkyl group; R2, R3, R4, R5, R6, and R7 are each independently selected from C1 to C3 alkylene group, C1 to C3 alkoxy group, oxygen atom, etc. , or At least one of R2, R3, and R4 is selected from , or Furthermore, at least one of R2, R3, and R4 is selected from oxygen atoms, and at least one of R5, R6, and R7 is selected from... , or Furthermore, at least one of R5, R6, and R7 is selected from oxygen atoms.

[0018] Optionally, B is selected from the group shown in structural formula 3:

[0019]

[0020] Structural Formula 3

[0021] Where m is selected from integers 1 to 4, R8, R9, R 10Each is independently selected from C1-C3 alkylene groups, C1-C3 alkoxy groups, oxygen atoms, , or R8, R9, R 10 At least one of them is selected from , or And R8, R9, R 10 At least one of them is selected from oxygen atoms.

[0022] Optionally, D and E may be independently selected from the groups shown in structural formula 4:

[0023]

[0024] Structural Formula 4

[0025] Where z is selected from integers between 0 and 4, and R 11 and R 13 Each is independently selected from a single bond or a C1-C5 hydrocarbon group, R 12 Selected from single bonds, , , , , , , , , or .

[0026] Optionally, D and E are each independently selected from single bonds or C1~C5 alkylene groups, and A, B, and C are each independently selected from substituted or unsubstituted cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylic acid ester groups, or cyclic anhydride groups.

[0027] Optionally, when A, B, or C is substituted, the substituent is selected from halogen, hydrocarbon, or haloalkyl. More preferably, when A, B, or C is substituted, the substituent is selected from halogen, alkyl, or haloalkyl.

[0028] Optional: A and C are the same; A and B are the same or different; D and E are the same.

[0029] Optionally, the compound shown in structural formula 1 is selected from one or more of the following compounds:

[0030]

[0031]

[0032]

[0033] Optionally, with the mass percentage of silicon in the negative electrode active material as T%, and the mass percentage of the compound shown in structural formula 1 in the non-aqueous electrolyte as W%, the above substances satisfy the following:

[0034] 2≤T≤10, and 0.01≤W≤3; or 10<T≤50, and 0.05≤W≤5.

[0035] Optionally, the silicon-based material is selected from at least one of silicon materials, silicon oxides, silicon-carbon composites, and silicon alloys.

[0036] The lithium-ion battery provided by this invention uses silicon-based materials as the negative electrode material, which can produce a high-energy-density lithium-ion battery. Based on the silicon-based negative electrode material, by adding the compound shown in Structural Formula 1 to the electrolyte, not only can the energy density be improved, but also the problems of battery cycle gas expansion and increased impedance can be significantly improved, reducing the generation of gas during battery cycle and maintaining a significant increase in cycle capacity. The inventors found through a large number of experiments that the battery cycle performance does not improve linearly with the increase of the content of the compound shown in Structural Formula 1. The improvement of battery performance by the compound shown in Structural Formula 1 is related to the mass ratio of silicon element in the negative electrode active material. When the mass ratio of silicon element in the negative electrode active material is 2% to 50% and the amount of compound shown in Structural Formula 1 added is 0.01% to 5.0%, the battery cycle performance is significantly improved. Detailed Implementation

[0037] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode comprises a negative electrode active material, which contains a silicon-based material, wherein the silicon element in the silicon-based material accounts for 2% to 50% of the mass percentage of the negative electrode active material.

[0039] The non-aqueous electrolyte comprises a solvent, an electrolyte salt, and an additive, wherein the additive comprises at least one of the compounds shown in structural formula 1:

[0040] ADBEC

[0041] Structural Formula 1

[0042] Among them, A, B, and C are each independently selected from groups containing cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylic acid ester groups, or cyclic anhydride groups.

[0043] D and E are each independently selected from single bonds, or groups containing alkylene groups, ether bonds, sulfur-oxygen double bonds, or carbon-oxygen double bonds;

[0044] Based on the total mass of the non-aqueous electrolyte being 100%, the amount of the compound shown in structural formula 1 added is 0.01~5.0%.

[0045] According to the lithium-ion battery provided by the present invention, based on silicon-based anode materials, by adding the compound shown in structural formula 1 to a non-aqueous electrolyte, not only can a high-energy-density lithium-ion battery be prepared, but it can also significantly improve problems such as battery cycle gas expansion and increased impedance, reduce gas generation during battery cycling, and maintain a significant increase in cycle capacity. However, it is difficult to achieve a good improvement effect in other battery systems. Through a large number of experiments, the inventors found that the battery cycle performance does not improve linearly with the increase of the content of the compound shown in structural formula 1. The improvement of battery performance by the compound shown in structural formula 1 is related to the mass ratio of silicon element in the anode active material. When the mass ratio of silicon element in the anode active material is 2% to 50% and the amount of compound shown in structural formula 1 added is 0.01% to 5.0%, the battery performance is significantly improved.

[0046] Regarding the relationship between the compound shown in Structural Formula 1 and silicon in the negative electrode active material, when the silicon content is between 2% and 50%, the compound shown in Structural Formula 1 is applied to silicon-based negative electrode batteries. During battery formation, the additive undergoes reduction and decomposition on the surface of the silicon-based negative electrode to form an interface film. The organic components in the interface film complex with silicon in a certain proportion, effectively suppressing the volume effect of the silicon-containing negative electrode during charge and discharge, improving cycle gas expansion, and maintaining a significant increase in cycle capacity. When the silicon content is greater than 50%, adding the compound shown in Structural Formula 1 does not effectively improve the cycle. The speculated reasons are as follows: due to the excessively high silicon content, adding a small amount of this additive cannot form a complete complex and dense interface film during the formation process, resulting in insufficient protection for the silicon-based material, and the high-temperature cycle performance of the battery is basically not improved; while adding a large amount of this additive will lead to excessively thick local interface films at the negative electrode interface, severely increasing the battery impedance and causing uneven lithium insertion / extraction, which also fails to effectively improve the cycle performance.

[0047] In some embodiments, A, B, and C each independently contain 1 to 5 cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfone groups, cyclic sulfoxide groups, cyclic carboxylic acid ester groups, or cyclic anhydride groups, and the total number of cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfonate groups, cyclic carboxylic acid ester groups, or cyclic anhydride groups in A, B, and C is less than or equal to 10.

[0048] In some embodiments, A and C are each independently selected from the groups shown in structural formula 2:

[0049]

[0050] Structural Formula 2

[0051] Where n is selected from an integer from 0 to 4, R1 is selected from hydrogen, halogen, C1 to C5 hydrocarbon group or haloalkyl group; R2, R3, R4, R5, R6, and R7 are each independently selected from C1 to C3 alkylene group, C1 to C3 alkoxy group, oxygen atom, etc. , or At least one of R2, R3, and R4 is selected from , or Furthermore, at least one of R2, R3, and R4 is selected from oxygen atoms, and at least one of R5, R6, and R7 is selected from... , or Furthermore, at least one of R5, R6, and R7 is selected from oxygen atoms.

[0052] In a preferred embodiment, the -R3-R2-R4- combination group and the -R7-R5-R6- combination group are each independently selected from... , , , , , or .

[0053] In some embodiments, B is selected from the group shown in structural formula 3:

[0054]

[0055] Structural Formula 3

[0056] Where m is selected from integers 1 to 4, R8, R9, R 10 Each is independently selected from C1-C3 alkylene groups, C1-C3 alkoxy groups, oxygen atoms, , or R8, R9, R 10 At least one of them is selected from , or And R8, R9, R 10 At least one of them is selected from oxygen atoms.

[0057] In a preferred embodiment, -R9-R8-R 10 - The combined groups are each independently selected from , , , , , or .

[0058] In some embodiments, D and E are each independently selected from the groups shown in structural formula 4:

[0059]

[0060] Structural Formula 4

[0061] Where z is selected from integers between 0 and 4, and R 11 and R 13 Each is independently selected from a single bond or a C1-C5 hydrocarbon group, R 12 Selected from single bonds, , , , , , , , , or .

[0062] In some embodiments, A and C are the same as each other, A and B are the same as or different from each other, and D and E are the same as each other.

[0063] In some embodiments, D and E are each independently selected from single bonds or C1-C5 alkylene groups, and A, B, and C are each independently selected from substituted or unsubstituted cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfoxide groups, cyclic carboxylic acid ester groups, or cyclic anhydride groups. When A, B, or C is substituted, the substituent is selected from halogens, alkyl groups, or haloalkyl groups.

[0064] As an example, the compound shown in structural formula 1 may be selected from one or more of the following compounds:

[0065]

[0066]

[0067]

[0068]

[0069] In some embodiments, D and E are each independently selected from the groups shown in structural formula 4:

[0070]

[0071] Structural Formula 4

[0072] Where z is selected from integers from 1 to 4, and R 11 and R 13 Each is independently selected from a single bond or a C1-C5 hydrocarbon group, R 12 Selected from , , , , , , , , or ;

[0073] A, B, and C are each independently selected from substituted or unsubstituted cyclic carbonate groups, cyclic sulfate groups, cyclic sulfite groups, cyclic sulfonate groups, cyclic sulfoxide groups, cyclic carboxylic acid ester groups, or cyclic anhydride groups; preferably, when A, B, or C is substituted, the substituent is selected from halogen, hydrocarbon, or haloalkyl groups; more preferably, when A, B, or C is substituted, the substituent is selected from halogen, alkyl, or haloalkyl groups.

[0074] As an example, the compound shown in structural formula 1 may be selected from one or more of the following compounds:

[0075]

[0076] In some embodiments, the compound represented by structural formula 1 may also be selected from one or more of the following compounds:

[0077]

[0078]

[0079] It should be noted that the above are some of the compounds claimed by this invention, but are not limited thereto and should not be construed as limiting the invention.

[0080] Those skilled in the art, knowing the structural formula of the compound shown in structural formula 1, can understand the preparation method of the above compound based on common knowledge in the field of chemical synthesis. For example:

[0081] Compound 1-1 can be prepared by the following methods:

[0082] Sorbitol, dimethyl carbonate, methanol, potassium hydroxide catalyst, and organic solvents such as DMF were placed in a reaction vessel and reacted under heating conditions for several hours. Then, a certain amount of oxalic acid was added to adjust the pH to neutral. After filtration and recrystallization, intermediate product 1 was obtained. Then, intermediate product 1, carbonate, thionyl chloride, etc. were subjected to esterification reaction under high temperature conditions to obtain intermediate product 2. Then, intermediate product 2 was oxidized with oxidizing agents such as sodium periodate to obtain compound 1-1.

[0083] Compounds 1-2 can be prepared by the following methods:

[0084] Diacetone-D-mannitol, dimethyl carbonate, methanol, potassium carbonate, and dioxane were reacted under heating and stirring for several hours. A certain amount of oxalic acid was added to adjust the pH of the solution to neutral. After filtration and concentration, intermediate 3 was obtained. A suitable amount of pure water, carbonate, and acid were added to intermediate 3 for hydrolysis to obtain intermediate 4. Then, intermediate 4, thionyl chloride, and carbonate solvent were heated to prepare intermediate 5. Finally, intermediate 5 was oxidized using an oxidizing agent such as sodium periodate to obtain compounds 1-2.

[0085] In some embodiments, the amount of the compound shown in structural formula 1 added is 0.01~5.0% based on the total mass of the non-aqueous electrolyte as 100%. Specifically, the amount of the compound shown in structural formula 1 added can be 0.01%, 0.02%, 0.05%, 0.1%, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, or 5.0%.

[0086] When the amount of the compound shown in Structural Formula 1 is too small, it cannot provide film protection and the improvement effect on battery performance is not obvious. When the amount of the compound shown in Structural Formula 1 is too large, the interfacial film formed at the negative electrode interface is too thick, which is not conducive to lithium ion shuttle and the cycle performance is deteriorated. Therefore, only by adding an appropriate amount of the compound shown in Structural Formula 1 can the cycle performance of the battery be improved.

[0087] In some embodiments, the additive further includes at least one of unsaturated cyclic carbonate compounds, fluorinated cyclic carbonate compounds, sulfonyl lactone compounds, lithium difluorophosphate, vinyl sulfate (DTD), and lithium bis(fluorosulfonyl)imide (LiFSI);

[0088] In some embodiments, the unsaturated cyclic carbonate compound includes at least one of vinylene carbonate (VC) and ethylene ethylene carbonate (VEC); the fluorinated cyclic carbonate compound includes fluoroethylene carbonate (FEC); and the sulfonyl lactone compound is selected from at least one of 1,3-propanesulfonyl lactone (PS), 1,4-butanesulfonyl lactone (BS), and 1,3-propenesulfonyl lactone (PST).

[0089] In some embodiments, based on the total mass of the non-aqueous electrolyte of the lithium-ion battery (100%), the content of unsaturated cyclic carbonate compounds is 0.1-5%; the content of fluorinated cyclic carbonate compounds is 0.1-30%; the mass percentage of sulfonyl lactone compounds is 0.1-5%; the mass percentage of lithium difluorophosphate is 0.1-2%; the mass percentage of vinyl sulfate (DTD) is 0.1-5%; and the mass percentage of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.1-5%.

[0090] In some embodiments, the solvent includes one or more of ether solvents, nitrile solvents, carbonate solvents, and carboxylic acid ester solvents.

[0091] In some embodiments, the ether solvent includes cyclic ethers or chain ethers. Specifically, the cyclic ether may be, but is not limited to, one or more of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF); the chain ether may be, but is not limited to, one or more of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), and diethylene glycol dimethyl ether (TEGDME). The nitrile solvent may be, but is not limited to, one or more of acetonitrile, glutaronitrile, and malononitrile. Carbonate solvents include cyclic carbonates or chain carbonates. Cyclic carbonates may specifically include, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); chain carbonates may specifically include, but are not limited to, one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). Carboxylic acid ester solvents may specifically include, 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.

[0092] In some embodiments, the electrolyte salt includes one or more of lithium salts, sodium salts, potassium salts, magnesium salts, zinc salts, and aluminum salts.

[0093] In a preferred embodiment, the electrolyte salt is selected from lithium salts. In a more preferred embodiment, the lithium salt includes one or more of LiPF6, LiBF4, LiBOB, LiDFOB, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, and LiN(SO2F)2.

[0094] In some embodiments, the concentration of the electrolyte salt in the non-aqueous electrolyte is 0.1 mol / L to 8 mol / L. In a preferred embodiment, the concentration of the electrolyte salt in the non-aqueous electrolyte is 0.5 mol / L to 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.

[0095] In some embodiments, the positive electrode includes a positive electrode active material capable of reversibly inserting / deintercalating metal ions (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, nickel-cobalt-aluminum ternary materials, LiFePO4, LiCoO2, LiMnO2, LiNiMnO2 and their composites.

[0096] In some embodiments, with the mass percentage of silicon in the negative electrode active material being T%, and the mass percentage of the compound shown in structural formula 1 in the non-aqueous electrolyte being W%, the above substances satisfy the following:

[0097] When 2≤T≤10, it is preferred that 0.01≤W≤3; or when 10<T≤50, it is preferred that 0.05≤W≤5.

[0098] Through research and verification by the inventors, it has been found that when the mass percentage of silicon in the negative electrode active material is between 2% and 10%, adding an appropriate amount of electrolyte containing 0.01% to 3% of the compound described in Structural Formula 1 can effectively improve the high-temperature cycle performance of the battery. However, when the addition amount is 3% to 5%, the cycle performance decreases due to the increased impedance caused by the interfacial film formed by the compound shown in Structural Formula 1. When the mass percentage of silicon in the negative electrode material increases to between 10% and 50%, the optimal content of the compound shown in Structural Formula 1 required to form a complete interfacial film increases. Therefore, a compound content of 0.05% to 5% can effectively improve the cycle performance of the battery.

[0099] In some embodiments, the silicon-based material is selected from at least one of silicon materials, silicon oxides, silicon-carbon composites, and silicon alloys.

[0100] In some embodiments, the battery further includes a separator located between the positive electrode and the negative electrode.

[0101] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an organic-inorganic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0102] In some embodiments, the mass percentage of silicon in the negative electrode active material is 2% to 50%. Specifically, the mass percentage of silicon in the negative electrode active material can be 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%.

[0103] When the silicon content is between 2% and 50%, the compound shown in Structural Formula 1 is applied to silicon-based anode batteries. During battery formation, the compound shown in Structural Formula 1 undergoes reduction and decomposition on the surface of the silicon-based anode to form an interface film. The organic components in the interface film complex with silicon in a certain proportion, effectively suppressing the volume effect of the silicon-containing anode during charge and discharge, improving cycle gas expansion, and maintaining a significant increase in cycle capacity. When the silicon content is greater than 50%, adding the compound shown in Structural Formula 1 does not effectively improve the cycle performance. The speculated reasons are as follows: due to the excessively high silicon content, adding a small amount of the compound shown in Structural Formula 1 cannot form a complete complex and dense interface film during the formation process, resulting in insufficient protection for the silicon-based material, and the high-temperature cycle performance of the battery is basically not improved; while adding a large amount of the compound shown in Structural Formula 1 will lead to excessively thick local interface films at the anode interface, severely increasing the battery impedance and causing uneven lithium insertion / extraction, which also fails to effectively improve the cycle performance.

[0104] The present invention will be further illustrated by the following examples.

[0105] I. Examples 1-62 and Comparative Examples 1-17

[0106] 1) Preparation of electrolyte

[0107] Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC = 1:1:1. Lithium hexafluorophosphate (LiPF6) was then added to a molar concentration of 1 mol / L. Additives were then added according to the tables below. The amount of additives was calculated as a percentage of the total mass of the electrolyte.

[0108] 2) Preparation of the positive electrode plate

[0109] The positive electrode active material LiNi was mixed at a mass ratio of 93:4:3. 0.5 Co 0.2 Mn 0.3 O2, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) are mixed and dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry is uniformly coated on both sides of an aluminum foil, dried, calendered, and vacuum dried, and then aluminum leads are welded on using an ultrasonic welder to obtain a positive electrode plate with a thickness of 120-150 μm.

[0110] 3) Preparation of negative electrode plate

[0111] The negative electrode active material SiO-C (graphite:silicon = 9:1), conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1:2.5:2.5, and then dispersed in deionized water to obtain the negative electrode slurry. The slurry was coated on both sides of a copper foil, dried, rolled, and vacuum dried, and then nickel leads were welded on using an ultrasonic welder to obtain the negative electrode plate. The thickness of the electrode plate was 120-150 μm.

[0112] 4) Cell fabrication

[0113] A three-layer separator with a thickness of 20 μm is placed between the positive and negative plates. Then, the sandwich structure composed of the positive plate, negative plate and separator is wound up, and the wound body is flattened and placed in an aluminum foil packaging bag. It is then vacuum baked at 75°C for 48 hours to obtain the cell to be injected with electrolyte.

[0114] 5) Electrolyte injection and formation of battery cells

[0115] In a glove box with water and oxygen contents of less than 20 ppm and 50 ppm respectively, the electrolyte prepared above was injected into the battery cell, vacuum sealed, and left at 45°C for 24 hours.

[0116] Then, perform the first charging routine formation as follows: 0.05C constant current charging for 180 min, 0.1C constant current charging for 180 min, 0.2C constant current charging for 120 min, age at 45℃ for 48 h, then vacuum seal a second time, and then further charge at 0.2C constant current to 4.4V, and discharge at 0.2C constant current to 2.75V.

[0117] Performance testing

[0118] 1. The lithium-ion batteries prepared in Examples 1-62 and Comparative Examples 1-17 were subjected to the following performance tests: High-temperature cycling performance test

[0119] 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 / SiO-C), then charge at constant current and constant voltage until the current drops to 0.05C, then discharge at constant current of 1C to 2.75V, and repeat this cycle. Record the discharge capacity and impedance of the first cycle and the discharge capacity and impedance of the last cycle, and measure the initial battery volume and the volume after 800 cycles.

[0120] The capacity retention, impedance growth rate, and gas expansion rate during high-temperature cycling are calculated using the following formula:

[0121] Capacity retention rate = Discharge capacity of the last cycle / Capacity of the first cycle × 100%;

[0122] Impedance growth rate = (Impedance of the last loop - Impedance of the first loop) / Impedance of the first loop × 100%;

[0123] Inflation rate = (Battery volume after cycle - Initial battery volume) / Initial battery volume × 100%.

[0124] 1.1 The test results obtained from Examples 1-23 and Comparative Examples 1-12 are filled in Table 1.

[0125] Table 1

[0126]

[0127]

[0128] The test results in Table 1 show that when the silicon content in the negative electrode active material is between 2% and 50% by mass, and the compound shown in Formula 1 is used as an additive at a concentration of 0.01% to 5.0%, the battery capacity retention rate is significantly improved compared to when the compound shown in Formula 1 is not added, while the impedance growth rate and gas expansion rate are significantly reduced. This indicates that adding the compound shown in Formula 1 to the non-aqueous electrolyte can significantly improve the battery's cycle performance over a wide range. Comparative Examples 1-4 show that when the silicon content in the negative electrode active material is between 2% and 50% by mass, the battery capacity without the compound shown in Formula 1 experiences a significant drop, a "plummeting" effect. This "plummeting" refers to the nonlinear capacity decay process of lithium-ion batteries during cycling, characterized by a rapid decrease in battery capacity within a short period. Comparative Examples 5-12 show that when the silicon content in the negative electrode active material is greater than 50% by mass, even adding 0.01% to 5.0% of the compound shown in Formula 1 does not improve the battery's cycle performance.

[0129] Meanwhile, based on the data from Examples 1-23, it was found that although the content of the compound shown in Structural Formula 1 was increasing, the improvement in battery cycle performance was not linear. This indicates that the improvement in battery performance is related not only to the content of the compound shown in Structural Formula 1, but also to the mass percentage of silicon in the negative electrode active material. Only when the contents of both are coordinated within a certain range can they have a significant effect on improving the battery performance.

[0130] 1.2 The test results obtained from Examples 24-35 and Comparative Example 1 are filled in Table 2.

[0131] Table 2

[0132]

[0133] As can be seen from the test results in Table 2, the silicon mass percentage (T%) in the negative electrode active materials of Examples 24-29 is in the range of 2-10%, and the content of the compound shown in Structural Formula 1 is in the range of 0.01-3%. Although the silicon mass percentage (T%) in the negative electrode active materials of Examples 30-35 is also in the range of 2-10%, the content of the compound shown in Structural Formula 1 is greater than 3%. The test results show that the minimum capacity retention rate of Examples 24-29 can reach 73.1%, while the maximum capacity retention rate of Examples 30-35 is only 75.1%, and the minimum capacity retention rate is only 63.6%. At the same time, the impedance growth rate and gas expansion rate of Examples 24-29 are generally lower than those of Examples 30-35. When the mass percentage of silicon in the negative electrode active material is between 2% and 10%, adding an appropriate amount of electrolyte containing 0.01% to 3% of the compound shown in Structural Formula 1 can effectively improve the high-temperature cycle performance of the battery. However, when the addition amount is 3% to 5%, the cycle performance decreases due to the increased impedance caused by the interfacial film formed by the compound shown in Structural Formula 1. This indicates that when the mass percentage (T%) of silicon in the negative electrode active material is 2% to 10%, and the content of the compound shown in Structural Formula 1 is 0.01% to 3%, it has a significant effect on improving the battery cycle performance.

[0134] 1.3 The test results obtained from Examples 11, 12, 36-44 and Comparative Example 13 are filled in Table 3.

[0135] Table 3

[0136]

[0137] As can be seen from the test results in Table 3, the silicon mass percentage (T%) in the negative electrode active materials of Examples 11, 12, and 36-39 is all in the range of 10-50%, and the content of the compound shown in Structural Formula 1 is all 0.05-5%. Although the silicon mass percentage (T%) in the negative electrode active materials of Examples 40-44 is also in the range of 10-50%, the content of the compound shown in Structural Formula 1 is less than 0.05%. The test results show that the capacity retention rate of Examples 11, 12, and 36-39 after 800 cycles at 45°C is all above 70%, while the capacity retention rate of Examples 40-44 after 800 cycles at 45°C is below 70%. At the same time, the impedance growth rate and gas expansion rate of Examples 11, 12, and 36-39 are also about 20 percentage points lower than those of Examples 40-44. When the mass percentage of silicon in the anode material increases to between 10% and 50%, the optimal content of the compound shown in Structural Formula 1 required to form a complete interface film increases. Therefore, a compound content of 0.05% to 5% can effectively improve the cycle performance of the battery. This indicates that when the mass percentage of silicon in the anode active material is 10% < T ≤ 50%, a content of the compound shown in Structural Formula 1 of 0.05% to 5% significantly improves the battery's impedance, gas expansion, and cycle performance.

[0138] 1.4 The test results obtained from Examples 11, 45-58 and Comparative Examples 1-4 are entered into Table 4.

[0139] Table 4

[0140]

[0141] As can be seen from the test results in Table 4, under the condition that the mass percentage of silicon in the negative electrode active material is 2-50%, the cycle performance of the battery is improved to varying degrees when different compounds shown in structural formula 1 are added to the electrolyte.

[0142] 1.5 The test results obtained from Examples 59-62 and Comparative Examples 14-17 are entered into Table 5.

[0143] Table 5

[0144]

[0145] As can be seen from the data in Table 5, in Examples 59-62, the compound shown in Structural Formula 1 was used in combination with conventional additives for lithium batteries, while in Comparative Examples 14-17, no compound shown in Structural Formula 1 was added. Test results show that the capacity retention rate of Examples 59-62 after 800 cycles at 45°C was significantly higher than that of Comparative Examples 14-17, while the impedance growth rate and gas expansion rate were lower. This indicates that the combination of the compound shown in Structural Formula 1 with conventional additives for lithium batteries can further improve the high-temperature cycling performance of the battery.

[0146] In summary, this invention, by adding the compound shown in Structural Formula 1 to a non-aqueous electrolyte, can significantly improve problems such as battery cycle swelling and increased impedance, reduce gas generation during battery cycling, and maintain a significant increase in cycle capacity. Furthermore, through extensive experiments, the inventors discovered that battery performance does not improve linearly with increasing content of the compound shown in Structural Formula 1. The performance improvement of the compound shown in Structural Formula 1 is related to the mass ratio of silicon in the negative electrode active material. When the mass ratio of silicon in the negative electrode active material is 2% to 50%, the compound shown in Structural Formula 1 can effectively improve the battery's cycle performance. Further research revealed that when the mass percentage of silicon in the negative electrode active material is 2% to 10%, and the content of the compound shown in Structural Formula 1 is 0.01% to 3%, it has a significant effect on improving battery cycle performance. Similarly, when the mass percentage of silicon in the negative electrode active material is 10% < T ≤ 50%, and the content of the compound shown in Structural Formula 1 is 0.05% to 5%, it significantly improves battery swelling, impedance, and cycle performance.

[0147] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, characterized in that, The negative electrode includes a negative electrode active material, which contains a silicon-based material, wherein the silicon element in the silicon-based material accounts for 2% to 50% of the mass percentage of the negative electrode active material. The non-aqueous electrolyte comprises a solvent, an electrolyte salt, and an additive. The solvent comprises one or more of ether solvents, nitrile solvents, carbonate solvents, and carboxylic acid ester solvents. The additive comprises at least one of the compounds shown in structural formula 1, wherein the compound shown in structural formula 1 is selected from one or more of compounds 1-1 to 1-4. Based on the total mass of the non-aqueous electrolyte being 100%, the amount of the compound shown in structural formula 1 added is 0.01~5.0%.

2. The lithium-ion battery according to claim 1, characterized in that, The additives also include at least one of the following: unsaturated cyclic carbonate compounds, fluorinated cyclic carbonate compounds, sulfonyl lactone compounds, lithium difluorophosphate, vinyl sulfate, and lithium difluorosulfonylimide.

3. The lithium-ion battery according to claim 2, characterized in that, The unsaturated cyclic carbonate compounds include at least one of vinylene carbonate and ethylene ethylene carbonate. The fluorocyclic carbonate compounds include fluoroethylene carbonate; The sulfonyl lactone compound is selected from at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone.

4. The lithium-ion battery according to claim 2, characterized in that, Based on the total mass of the non-aqueous electrolyte of the lithium-ion battery (100%), the content of unsaturated cyclic carbonate compounds is 0.1-5%; and / or Based on the total mass of the non-aqueous electrolyte of the lithium-ion battery (100%), the content of the fluorinated cyclic carbonate compound is 0.1-30%; and / or Based on the total mass of the non-aqueous electrolyte of the lithium-ion battery as 100%, the mass percentage of the sulfonyl lactone compound is 0.1-5%.

5. The lithium-ion battery according to claim 2, characterized in that, Based on the total mass of the non-aqueous electrolyte of the lithium-ion battery being 100%, the mass percentage of lithium difluorophosphate is 0.1-2%; and / or Based on the total mass of the non-aqueous electrolyte of the lithium-ion battery as 100%, the mass percentage of ethylene sulfate is 0.1-5%; and / or Based on the total mass of the non-aqueous electrolyte of the lithium-ion battery being 100%, the mass percentage of lithium bisfluorosulfonylimide is 0.1-5%.

6. The lithium-ion battery according to claim 1, characterized in that, The ether solvents include cyclic ethers or chain ethers, wherein the cyclic ethers include one or more of 1,3-dioxolane, 1,4-dioxolane, crown ethers, tetrahydrofuran, 2-methyltetrahydrofuran, and 2-trifluoromethyltetrahydrofuran; The chain ether includes one or more of dimethoxymethane, 1,2-dimethoxyethane, and diethylene glycol dimethyl ether; The nitrile solvents include one or more of acetonitrile, glutaronitrile, and malononitrile; The carbonate solvent includes cyclic carbonates or chain carbonates, wherein the cyclic carbonates include one or more of ethylene carbonate, propylene carbonate, γ-butyrolactone, and butylene carbonate; and the chain carbonates include one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate. The carboxylic acid ester solvents include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate.

7. The lithium-ion battery according to claim 1, characterized in that, The electrolyte salt includes lithium salts, and the lithium salts include one or more of LiPF6, LiBF4, LiBOB, LiDFOB, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, and LiN(SO2F)2; In the non-aqueous electrolyte, the concentration of the electrolyte salt is 0.1 mol / L to 8 mol / L.

8. The lithium-ion battery according to claim 1, characterized in that, The positive electrode includes a positive electrode active material, which is selected from at least one of nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, LiFePO4, LiCoO2, LiMnO2, LiNiMnO2 and their composites.

9. The lithium-ion battery according to any one of claims 1-8, characterized in that, With the mass percentage of silicon in the negative electrode active material being T%, and the mass percentage of the compound shown in structural formula 1 in the non-aqueous electrolyte being W%, the above substances satisfy the following: 2≤T≤10, and 0.01≤W≤3; Or 10 < T ≤ 50, and 0.05 ≤ W ≤ 5.

10. The lithium-ion battery according to claim 1, characterized in that, The silicon-based material is selected from at least one of silicon oxides, silicon-carbon composites, and silicon alloys.

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