Lithium ion battery electrolyte based on silicon spiro compound, preparation method of lithium ion battery electrolyte and ternary lithium ion battery

Abstract

The invention discloses a lithium ion battery electrolyte based on a silicon spiro compound, a preparation method of the lithium ion battery electrolyte and a ternary lithium ion battery. The lithium ion battery electrolyte comprises an organic solvent system, a lithium salt system and an additive system, the organic solvent system comprises at least one cyclic carbonate and at least one chain carbonate; the additive system comprises a silicon spiro compound and has the following structural formula. Wherein the X group and the Y group are respectively and independently selected from any one of an oxygen atom, a carbonyl group, a sulfinyl group, a sulfuryl group, a substituted or unsubstituted C1-C6 alkylene group, a substituted or unsubstituted C2-C10 alkenyl group, a substituted or unsubstituted C2-C10 alkynyl group, a substituted or unsubstituted C2-C10 cyano group and an aryl group; according to the invention, a stable battery-electrolyte interface can be generated on an electrode interface, the phase change of an NCM811 positive electrode ternary material can be particularly and obviously inhibited, and the cycle performance and the service life of the ternary lithium ion battery (especially the NCM811 ternary lithium ion battery) can be obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to a lithium-ion battery electrolyte based on silicon-based spirocyclic compounds and its preparation method, as well as a ternary lithium-ion battery. Background Technology

[0002] In lithium-ion battery systems, nickel-cobalt-manganese ternary materials (LiNi) x Co y Mn 1-x-y O2 (NCM) combines the advantages of lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide. Among them, NCM811 has high nickel content, high energy density, low cost, and low toxicity, and is widely used in portable electronic devices and electric vehicles.

[0003] However, ternary lithium materials (especially NCM811) face challenges such as cation mixing, poor thermal stability, and unstable surface structure. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a lithium-ion battery electrolyte based on silicon-based spirocyclic compounds and its preparation method, as well as a ternary lithium-ion battery, which is beneficial to the generation of a stable battery-electrolyte interface at the electrode interface, can particularly significantly suppress the phase transition of NCM811 cathode ternary material, and can significantly enhance the cycle performance and battery life of ternary lithium-ion batteries (especially NCM811 ternary lithium-ion batteries).

[0005] The technical solution adopted in this invention is as follows: A lithium-ion battery electrolyte based on a silicon-based spirocyclic compound includes an organic solvent system, a lithium salt system, and an additive system; the organic solvent system includes at least one cyclic carbonate and at least one chain carbonate; the additive system includes a silicon-based spirocyclic compound, wherein the silicon-based spirocyclic compound has the following structural formula: Wherein, the X group and the Y group are independently selected from oxygen atom, carbonyl group, thionyl group, thionyl group, substituted or unsubstituted C1-C6 alkylene group, substituted or unsubstituted C2-C6 alkylene group, respectively. 10 alkenyl, substituted or unsubstituted C2-C 10 Alkyne, substituted or unsubstituted C2-C 10 Contains either a cyano group or an aryl group.

[0006] Preferably, the silicon-based spirocyclic compound accounts for 0.5-5% of the electrolyte in the lithium-ion battery by mass; more preferably, it accounts for 1-4%.

[0007] Preferably, the cyclic carbonate accounts for 15-35% of the mass fraction of the electrolyte in the lithium-ion battery; the chain carbonate accounts for 55-75% of the mass fraction of the electrolyte in the lithium-ion battery.

[0008] Preferably, the cyclic carbonate is ethylene carbonate (EC) and / or propylene carbonate (PC); the chain carbonate is ethyl methyl carbonate (EMC) and / or dimethyl carbonate (DMC) and / or diethyl carbonate (DEC).

[0009] Preferably, the lithium salt system includes any one or a mixture of several of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalatoborate) (LiBOB), and lithium tetrafluoroborate (LiBF4).

[0010] Preferably, the concentration of the lithium salt system in the lithium-ion battery electrolyte is 0.8-1 mol·L⁻¹. -1 .

[0011] Preferably, the additive system further includes the combined use of at least two of the following: lithium difluorooxalate borate (LiODFB), ethylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), propanesulfonate lactone (PS), lithium difluorophosphate (LiPO2F2), and methylene disulfonate (MMDS), which together account for 0.5-5% of the mass fraction of the lithium-ion battery electrolyte.

[0012] Preferably, a method for preparing a lithium-ion battery electrolyte based on a silicon-based spirocyclic compound as described above involves mixing raw materials of an organic solvent system to obtain an organic solvent mixture, freezing the organic solvent mixture for 1-3 hours, adding the lithium salt system to the organic solvent mixture for mixing, and finally adding an additive system for mixing to obtain the electrolyte for the lithium-ion battery.

[0013] Preferably, a ternary lithium-ion battery uses a lithium-ion battery electrolyte based on a silicon-based spirocyclic compound as described above; its positive electrode active material includes a nickel-cobalt-manganese ternary material LiNi as the ternary positive electrode material. x Co y Mn 1-x-y O2, NCM.

[0014] Preferably, the nickel-cobalt-manganese ternary material is NCM811.

[0015] The silicon-based spirocyclic compound provided in this application has a unique cyclic structure and features low toxicity, no pollution, excellent thermal stability, and low viscosity. When used as an additive in ternary lithium-ion battery electrolytes, it helps to form a stable battery-electrolyte interface at the electrode interface, and can significantly suppress the phase transition of NCM811 cathode ternary materials, thereby significantly enhancing the cycle performance and battery life of ternary lithium-ion batteries (especially NCM811 ternary lithium-ion batteries). Detailed Implementation

[0016] This embodiment proposes a silicon-based spirocyclic compound with the following structural formula: The X and Y groups are independently selected from oxygen, carbonyl, thionyl, thionyl, substituted or unsubstituted C1-C6 alkylene, substituted or unsubstituted C2-C6 alkylene, respectively. 10 alkenyl, substituted or unsubstituted C2-C 10 Alkyne, substituted or unsubstituted C2-C 10 Contains either a cyano group or an aryl group.

[0017] Preferably, in this embodiment, the silicon-based spirocyclic compound comprises the following structure: , , Any one or a mixture of several of them.

[0018] Preferably, this embodiment proposes a method for preparing silicon-based spirocyclic compounds according to the above description, using silicon tetrahalide as a raw material, reacting it with a nucleophile in an organic solvent environment to obtain a reaction product; after post-treatment of the reaction product, a silicon-based spirocyclic compound is obtained; preferably, in this embodiment, the nucleophile is dispersed in an organic solvent, the temperature is controlled at 0-30℃ (more preferably 0-20℃, even more preferably 0-10℃), silicon tetrahalide is slowly added dropwise, and after the addition is completed, the reaction is continued at the temperature for 5-8 hours, so that the silicon-based spirocyclic compound achieves complete cyclization.

[0019] Preferably, in this embodiment, silicon tetrahalide is any one or a mixture of silicon tetrachloride, silicon tetrabromide, and silicon tetrafluoride; preferably, in this embodiment, nucleophile is any one or a mixture of methyl disulfonic acid, 2-fluoromethyl disulfonic acid, and 2,2-difluoromethyl disulfonic acid.

[0020] Preferably, in this embodiment, the organic solvent includes any one or a mixture of several of the following: ether organic solvents, carbonate organic solvents, carboxylic acid ester organic solvents, chlorinated hydrocarbons, alkanes, and nitrile organic solvents.

[0021] Preferably, in this embodiment, the molar ratio of the nucleophile to silicon tetrahalide is 2-4:1, more preferably 2-2.5:1; and / or the amount of organic solvent added is 5-15 times the weight of the nucleophile, more preferably 8-10 times.

[0022] Preferably, the post-treatment includes cooling (preferably cooling the reaction product to -10 to 0°C), filtration, washing with fresh organic solvent to remove byproducts, and drying (preferably vacuum drying).

[0023] Preferably, this embodiment proposes an application of the silicon-based spirocyclic compound described above, in which the silicon-based spirocyclic compound is added to the electrolyte of a battery.

[0024] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0025] Based on the above-described implementation schemes, this application further proposes the following specific embodiments: First, it should be noted that the reagent raw materials used in the following specific embodiments and comparative examples of the present invention are sourced from the following: Unless otherwise specified, all raw materials are ordinary commercially available products.

[0026] The test methods used in the specific embodiments and comparative examples of this invention are as follows: Nuclear magnetic resonance (NMR) analysis was performed using a Bruker AVANCE II 400 MHz spectrometer. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0027] Example 1: A certain amount of methanedisulfonic acid (as a nucleophile) was dispersed in acetonitrile (as an organic solvent), and silicon tetrachloride was slowly added dropwise while maintaining the temperature at 0°C. After the addition was completed, the reaction was continued at this temperature for 6 hours to achieve complete ring closure of the silicon-based spirocyclic compound. The molar ratio of methanedisulfonic acid to silicon tetrachloride was 2.1:1, and the weight ratio of acetonitrile to methanedisulfonic acid was 10:1. After the reaction was completed, the reaction product was cooled to -5°C and washed multiple times with fresh acetonitrile and dichloromethane during filtration to remove byproducts. The filter cake was then vacuum dried at 30°C to obtain a silicon-based spirocyclic compound with the following structural formula: ; The silicon-based spirocyclic compounds synthesized above were characterized by NMR (1H, 13C): 1H NMR: δ 6.32 (4H, s); 13C NMR: δ 45.5 (2C, s).

[0028] Example 2: A certain amount of 2-fluoromethyldisulfonic acid (as a nucleophile) was dispersed in acetonitrile (as an organic solvent), and silicon tetrachloride was slowly added dropwise while maintaining the temperature at 0°C. After the addition was completed, the reaction was continued at this temperature for 7 hours to achieve complete cyclization of the silicon-based spirocyclic compound. The molar ratio of 2-fluoromethyldisulfonic acid to silicon tetrachloride was 2.0:1, and the weight ratio of acetonitrile to 2-fluoromethyldisulfonic acid was 10:1. After the reaction was completed, the reaction product was cooled to -5°C and washed multiple times with fresh acetonitrile and dichloromethane during filtration to remove byproducts. The filter cake was then vacuum dried at 30°C to obtain a silicon-based spirocyclic compound with the following structural formula: ; The silicon-based spirocyclic compounds synthesized above were characterized by NMR (1H, 13C): 1 ¹H NMR: δ 7.89 (2H, s); 13 C NMR: δ 73.2 (2C, s).

[0029] Example 3: A certain amount of 2,2-difluoromethyldisulfonic acid (as a nucleophile) was dispersed in acetonitrile (as an organic solvent), and silicon tetrachloride was slowly added dropwise while maintaining the temperature at 20°C. After the addition was completed, the reaction was continued at this temperature for 5 hours to achieve complete cyclization of the silicon-based spirocyclic compound. The molar ratio of 2,2-difluoromethyldisulfonic acid to silicon tetrachloride was 2.0:1, and the weight ratio of acetonitrile to 2,2-difluoromethyldisulfonic acid was 10:1. After the reaction was completed, the reaction product was cooled to -10°C. During filtration, the product was washed multiple times with fresh acetonitrile and dichloromethane to remove byproducts. The filter cake was then vacuum dried at 30°C to obtain a silicon-based spirocyclic compound with the following structural formula: ; The silicon-based spirocyclic compounds synthesized above were characterized by NMR (13C): 13 C NMR: δ 150.5 (2C,s), no H signal.

[0030] Example 4: The remaining technical solutions of Example 4 are the same as those of Example 1, except that in Example 4, the temperature is controlled at 5°C and the heat preservation reaction time is 9 hours.

[0031] Example 5: The remaining technical solutions of Example 5 are the same as those of Example 1, except that in Example 5, the temperature is controlled at 10°C and the heat preservation reaction time is 4 hours.

[0032] Comparative Example 1: The rest of the technical solutions of Comparative Example 1 are the same as those of Example 1, except that in Comparative Example 1, the temperature is controlled at 25°C and the heat preservation reaction time is 10 hours.

[0033] Comparative Example 2: The rest of the technical solutions of Comparative Example 2 are the same as those of Example 1, except that in Comparative Example 2, the temperature is controlled at 30°C and the heat preservation reaction time is 10 hours.

[0034] Comparative Example 3: Using the spirocyclic organosilicon compound 1 provided in Example 1 of patent CN106220667B: .

[0035] The purity and yield of the products from Examples 1-5 and Comparative Examples 1-2 are shown in Table 1 below:

[0036] As can be seen from Table 1 above, the reaction conditions proposed in the embodiments of this application are mild, and the product purity and yield are high.

[0037] To further verify the application effects achieved in Embodiments 1-3 of this application, the following comparative application experiments were conducted on the products provided in Embodiments 1-3 and Comparative Example 3 respectively: The pouch cells corresponding to Examples 1-3 and Comparative Example 3 were fabricated according to the following steps: Electrolyte preparation: Prepared in a glove box under N2 atmosphere; the water content of the organic solvent system is <10 ppm; the electrolyte includes: The organic solvent system with a mass fraction of 84.5% is specifically composed of diethyl carbonate (DEC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) in a mass ratio of 1:1:1 (wt%). The lithium salt system uses 1.0 mol·L⁻¹ -1 Lithium hexafluorophosphate (LiPF6); The products provided in Examples 1-3 and Comparative Example 3 were selected respectively, and the product accounted for 2% of the electrolyte by mass. The rest are other additives, specifically composed of ethylene carbonate (VC): fluoroethylene carbonate (FEC): propanesulfonate lactone (PS): methylene dimethyl sulfonate (MMDS) = 2:1:1:1 (wt%). After the raw materials of the organic solvent system are mixed evenly in a fixed ratio, the mixture is frozen and cooled for 1.5-2 hours to obtain an organic solvent mixture. The lithium salt system is added and mixed evenly. Finally, the products provided in Examples 1-3 and Comparative Example 3, as well as other additives, are added and mixed evenly for later use.

[0038] Preparation of the battery positive electrode: Using methylpyrrolidone (NMP) as a solvent, 2% (w / w) of polyvinylidene fluoride (PVDF) was uniformly dispersed to obtain a mixture. Then, 2% (w / w) of carbon nanotubes (CNTs) were added and uniformly mixed. Next, 96% (w / w) of the positive electrode active material (lithium cobalt oxide, LiCoO2) was added and mixed uniformly. The mixture was then uniformly coated onto aluminum foil using a coating machine. After drying, rolling, and cutting, the positive electrode sheet was formed with an areal density ranging from 350-450 g / cm³. 2 (Double-sided); Preparation of the battery negative electrode: Using deionized water as a solvent, 1% by mass of carboxymethyl cellulose (CMC) is uniformly dispersed to obtain a mixture. Then, 2% by mass of conductive carbon black (SP) and 96% by mass of negative electrode active material (specifically, vapor-deposited silicon carbon, material type SH-SO2) are added and uniformly mixed. Finally, 1% by mass of styrene-butadiene rubber (SBR) is added and uniformly mixed. After uniform mixing, the mixture is evenly coated onto copper foil using a coating machine. After drying, rolling, and cutting, the negative electrode sheet is formed with an areal density ranging from 200-350 g / cm³. 2 (Double-sided); To further demonstrate the effectiveness of the implementation, this application also includes the following comparative examples 4, 5, and 6: Comparative Example 4: The soft-pack battery solution prepared in Comparative Example 4 is the same as that in Example 1, except that the product in Example 1 is replaced with the additive methyl methyl disulfonate (MMDS) in Comparative Example 4.

[0039] Comparative Example 5: The soft-pack battery solution prepared in Comparative Example 5 is the same as that in Example 1, except that the product in Example 1 is replaced with the additive propanesulfonate lactone (PS) in Comparative Example 5.

[0040] Comparative Example 6: The soft-pack battery solution prepared in Comparative Example 6 is the same as that in Example 1, except that the product in Example 1 is replaced with the additive lithium difluorophosphate LiPO2F2.

[0041] Therefore, we obtained pouch cells assembled from electrolytes provided in Examples 1-3 and Comparative Examples 3-6 as specific additives, with each pouch cell using 25g of electrolyte. Then, we conducted the following performance comparison tests on each pouch cell: Four groups of each soft-pack battery corresponding to Examples 1-3 and Comparative Examples 3-6 were prepared. Each group was subjected to a 500-cycle test at 25°C and 45°C, and a 35-day storage test at -20°C and 55°C, respectively. The charge and discharge conditions used in each cycle test were: a charge / discharge rate of 1C / 1C and a voltage range of 3.0V-4.5V. The measured capacity retention rates of the lithium-ion batteries are shown in Table 2 below:

[0042] To further enhance the effectiveness of the silicon-based spirocyclic compounds provided in the above embodiments of this application in lithium-ion batteries, this embodiment also proposes a lithium-ion battery electrolyte based on silicon-based spirocyclic compounds, including an organic solvent system, a lithium salt system, and an additive system; the organic solvent system includes at least one cyclic carbonate and at least one chain carbonate; the additive system includes a silicon-based spirocyclic compound, wherein the silicon-based spirocyclic compound is the silicon-based spirocyclic compound provided in the above embodiments of this application.

[0043] Preferably, in this embodiment, the silicon-based spirocyclic compound accounts for 0.5-5% of the electrolyte mass fraction of the lithium-ion battery; more preferably, it is 1-4%.

[0044] Preferably, in this embodiment, the cyclic carbonate accounts for 15-35% of the mass fraction of the electrolyte in the lithium-ion battery; the chain carbonate accounts for 55-75% of the mass fraction of the electrolyte in the lithium-ion battery; preferably, in this embodiment, the cyclic carbonate is ethylene carbonate EC and / or propylene carbonate PC; the chain carbonate is ethyl methyl carbonate EMC and / or dimethyl carbonate DMC and / or diethyl carbonate DEC.

[0045] Preferably, in this embodiment, the lithium salt system includes any one or a mixture of several of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), and lithium tetrafluoroborate (LiBF4); preferably, in this embodiment, the concentration of the lithium salt system in the lithium-ion battery electrolyte is 0.8-1 mol·L⁻¹. -1 .

[0046] Preferably, in this embodiment, the additive system further includes the combined use of at least two of the following: lithium difluorooxalate borate (LiODFB), ethylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), propanesulfonate lactone (PS), lithium difluorophosphate (LiPO2F2), and methylene disulfonate (MMDS), which account for 0.5-5% of the mass fraction of the lithium-ion battery electrolyte.

[0047] Preferably, this embodiment proposes a method for preparing a lithium-ion battery electrolyte based on silicon-based spirocyclic compounds as described above. The method involves mixing the raw materials of an organic solvent system to obtain an organic solvent mixture, freezing the organic solvent mixture for 1-3 hours, adding a lithium salt system to the organic solvent mixture for mixing, and finally adding an additive system for mixing to obtain the lithium-ion battery electrolyte.

[0048] Preferably, this embodiment also proposes a ternary lithium-ion battery, employing a lithium-ion battery electrolyte based on a silicon-based spirocyclic compound as described above; its positive electrode active material includes a nickel-cobalt-manganese ternary material (LiNi) as the ternary positive electrode material. x Co y Mn 1-x-y O2, NCM); More preferably, in this embodiment, the nickel-cobalt-manganese ternary material is NCM811, which means that the ratio between N (representing nickel), C (representing cobalt), and M (representing manganese) is 8:1:1.

[0049] To further verify the effectiveness of the electrolyte for ternary lithium-ion batteries proposed in the above embodiments of this application, this application further provides the following embodiments and comparative examples: Example 6: An electrolyte for a ternary lithium-ion battery, comprising: The organic solvent system with a mass fraction of 84.5% is specifically composed of ethylene carbonate EC: ethyl methyl carbonate EMC: dimethyl carbonate DMC = 3:3:4 (wt%). The lithium salt system uses 1.0 mol·L⁻¹ -1 Lithium hexafluorophosphate (LiPF6); Example 1 provides a product with a mass fraction of 2%; The remainder consists of other additives, specifically composed of ethylene carbonate (VC): fluoroethylene carbonate (FEC): propanesulfonate lactone (PS): methylene dimethyl sulfonate (MMDS) = 2:1:1:1 (wt%). The electrolyte is prepared in a glove box under N2 atmosphere, ensuring that the water content of the solvent system is <10ppm. During preparation, the raw materials of the organic solvent system are first mixed evenly in a fixed ratio, and then the mixture is cooled to a freezing temperature of 1.5-2 hours to obtain an organic solvent mixture. The lithium salt system is then added and mixed evenly. Finally, the product provided in Example 1 and other additives are added and mixed evenly before use.

[0050] Example 7: The remaining technical solutions of Example 7 are the same as those of Example 6, except that in Example 7, the product provided in Example 2 is used instead of the product provided in Example 1.

[0051] Example 8: The remaining technical solutions of Example 8 are the same as those of Example 6, except that in Example 8, the product provided in Example 3 is used instead of the product provided in Example 1.

[0052] Comparative Example 7: The remaining technical solutions of Comparative Example 7 are the same as those of Example 6, except that in Comparative Example 7, the product provided by Comparative Example 3 is used instead of the product provided by Example 1.

[0053] Comparative Example 8: The remaining technical solutions of Comparative Example 8 are the same as those of Example 6, except that in Comparative Example 8, the organic solvent system is specifically composed of ethylene carbonate EC: propylene carbonate PC = 1:1 (wt%).

[0054] Then, the pouch cells corresponding to Examples 6-8 and Comparative Examples 7-8 were fabricated according to the following steps: Preparation of the battery positive electrode: Using methylpyrrolidone (NMP) as a solvent, 2% (w / w) of polyvinylidene fluoride (PVDF) was uniformly dispersed to obtain a mixture. Then, 2% (w / w) of carbon nanotubes (CNTs) were added and uniformly mixed. Next, 96% (w / w) of the positive electrode active material (using a ternary system NCM811) was added and mixed evenly. The mixture was then uniformly coated onto aluminum foil using a coating machine. After drying, rolling, and cutting, the positive electrode sheet was formed with an areal density ranging from 350-450 g / cm³. 2 (Double-sided); Preparation of the battery negative electrode: Using deionized water as a solvent, 1% by mass of carboxymethyl cellulose (CMC) is uniformly dispersed to obtain a mixture. Then, 2% by mass of conductive carbon black (SP) and 96% by mass of negative electrode active material (specifically graphite) are added and uniformly mixed. Finally, 1% by mass of styrene-butadiene rubber (SBR) is added and uniformly mixed. After uniform mixing, the mixture is evenly coated onto copper foil using a coating machine. After drying, rolling, and cutting, the negative electrode sheet is formed with an areal density ranging from 200-350 g / cm³. 2 (Double-sided); Therefore, we obtained: NCM811|| graphite pouch batteries assembled from electrolytes provided by Examples 6-8 and Comparative Examples 7-8 respectively as specific additives, with each pouch battery using 25g of electrolyte. To further demonstrate the application effect of the embodiments of this application in a specific ternary system of NCM811, this application also provides the following embodiment 9: Example 9: The remaining technical solutions of Example 9 are the same as those of Example 6, except that in the soft-pack battery of Example 9, the positive electrode active material is a ternary system NCM622, and the corresponding NCM622||graphite soft-pack battery is assembled.

[0055] Then, the following performance comparison tests were conducted on each pouch battery: Four groups of each soft-pack battery corresponding to Examples 6-9 and Comparative Examples 7-8 were prepared. Each group was subjected to a 500-cycle test at 25°C and 45°C, and a 35-day storage test at -20°C and 55°C, respectively. The charge and discharge conditions used in each cycle test were: a charge / discharge rate of 1C / 1C. The voltage range of the NCM811|| graphite soft-pack battery was 2.75V-4.2V, and the voltage range of the NCM622|| graphite soft-pack battery was 2.75V-4.4V. The measured capacity retention rates of lithium-ion batteries are shown in Table 3 below:

[0056] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0057] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A lithium-ion battery electrolyte based on a silicon-based spirocyclic compound, comprising an organic solvent system, a lithium salt system, and an additive system; characterized in that, The organic solvent system comprises at least one cyclic carbonate and at least one chain carbonate; the additive system comprises a silicon-based spirocyclic compound, wherein the silicon-based spirocyclic compound has the following structural formula: Wherein, the X group and the Y group are independently selected from oxygen atom, carbonyl group, thionyl group, thionyl group, substituted or unsubstituted C1-C6 alkylene group, substituted or unsubstituted C2-C6 alkylene group, respectively. 10 alkenyl, substituted or unsubstituted C2-C 10 Alkyne, substituted or unsubstituted C2-C 10 Contains either a cyano group or an aryl group.

2. The lithium-ion battery electrolyte based on silicon-based spirocyclic compounds according to claim 1, characterized in that, The silicon-based spirocyclic compound accounts for 0.5-5% of the electrolyte in the lithium-ion battery; more preferably 1-4%.

3. The lithium-ion battery electrolyte based on silicon-based spirocyclic compounds according to claim 1, characterized in that, The cyclic carbonate accounts for 15-35% of the mass fraction of the electrolyte in the lithium-ion battery; the chain carbonate accounts for 55-75% of the mass fraction of the electrolyte in the lithium-ion battery.

4. The lithium-ion battery electrolyte based on silicon-based spirocyclic compounds according to claim 1, characterized in that, The cyclic carbonates are made of ethylene carbonate (EC) and / or propylene carbonate (PC); the chain carbonates are made of ethyl methyl carbonate (EMC) and / or dimethyl carbonate (DMC) and / or diethyl carbonate (DEC).

5. The lithium-ion battery electrolyte based on silicon-based spirocyclic compounds according to claim 1, characterized in that, The lithium salt system includes any one or a mixture of several of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), and lithium tetrafluoroborate (LiBF4).

6. The lithium-ion battery electrolyte based on silicon-based spirocyclic compounds according to claim 5, characterized in that... The characteristic is that the concentration of the lithium salt system in the lithium-ion battery electrolyte is 0.8-1 mol·L⁻¹. -1 .

7. The lithium-ion battery electrolyte based on silicon-based spirocyclic compounds according to claim 1, characterized in that, The additive system also includes the combined use of at least two of the following: lithium difluorooxalate borate (LiODFB), ethylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), propanesulfonate lactone (PS), lithium difluorophosphate (LiPO2F2), and methylene disulfonate (MMDS), which account for 0.5-5% of the mass fraction of the lithium-ion battery electrolyte.

8. A method for preparing a lithium-ion battery electrolyte based on a silicon-based spirocyclic compound according to any one of claims 1-7, characterized in that, The raw materials of the organic solvent system are mixed to obtain an organic solvent mixture. After freezing the organic solvent mixture for 1-3 hours, the lithium salt system is added to the organic solvent mixture for mixing. Finally, the additive system is added and mixed to obtain the electrolyte of the lithium-ion battery.

9. A ternary lithium-ion battery, characterized in that, The lithium-ion battery electrolyte based on a silicon-based spirocyclic compound, as described in any one of claims 1-7, is used; its positive electrode active material includes a nickel-cobalt-manganese ternary material (LiNi) as a ternary positive electrode material. x Co y Mn 1-x-y O2, NCM).

10. The ternary lithium-ion battery according to claim 9, characterized in that, The nickel-cobalt-manganese ternary material is NCM811.

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