Electrolyte of ternary lithium ion battery, preparation method of electrolyte and ternary lithium ion battery

Abstract

The invention discloses an electrolyte of a ternary lithium ion battery, a preparation method of the electrolyte and the ternary lithium ion battery. The ternary lithium ion battery comprises an organic solvent system, a lithium salt system and an additive system, the organic solvent system is composed of at least one cyclic carbonate and at least one chain carbonate; the additive system comprises a cyclic compound, and the cyclic compound has the following structural formula; wherein X is any one of P, B and P = O; y is a C1-C6 carbon chain group containing an alkylene group, a carbonyl group, a sulfinyl group, a sulfonyl group or a fluoroalkylene group; the flame-retardant and anti-overcharge fabric has flame-retardant and anti-overcharge And moreover, by regulating and controlling the composition of the SEI film, the growth of lithium dendrites can be inhibited, the dissolution of transition metal can be reduced, the stability of the ternary lithium ion positive electrode material is improved, and the cycle life of the ternary lithium ion battery is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to an electrolyte for a ternary lithium-ion battery and its preparation method, and a ternary lithium-ion battery. Background Technology

[0002] Internal short circuits in ternary lithium-ion batteries can lead to overheating or thermal runaway. The flammable carbonate / ether electrolytes commonly used in these batteries can act as fuel, and the released oxygen and high temperatures provide conditions for combustion and explosion.

[0003] Therefore, it is essential to improve the flame retardant and overcharge protection properties of ternary lithium-ion batteries. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an electrolyte for a ternary lithium-ion battery and a method for preparing the same, as well as a ternary lithium-ion battery that has both flame-retardant and overcharge protection functions; moreover, by adjusting the composition of the SEI film, lithium dendrite growth can be suppressed and transition metal dissolution can be reduced, thereby improving the stability of the ternary lithium-ion cathode material and extending the cycle life of the ternary lithium-ion battery.

[0005] The technical solution adopted in this invention is as follows: An electrolyte for a ternary lithium-ion battery includes 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 lithium salt system comprises any one or a mixture of several of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium perchlorate (LiClO4), lithium trifluoromethanesulfonate (LiOTf), and lithium tetrafluoroborate (LiBF4); the additive system comprises a cyclic compound, wherein the cyclic compound has the following structural formula: Where X is any one of P, B, or P=O; Y is a C1-C6 carbon chain containing an alkylene group, carbonyl group, sulfinyl group, sulfonyl group, or fluoroalkylene group.

[0006] Preferably, the organic solvent system accounts for 60%-90% of the mass fraction of the electrolyte in the ternary lithium-ion battery, and more preferably 65.5%-87.9%.

[0007] Preferably, the cyclic carbonate accounts for 15%-35% of the mass fraction of the electrolyte in the ternary lithium-ion battery; the chain carbonate accounts for 45-75% of the mass fraction of the electrolyte in the ternary lithium-ion battery.

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

[0009] Preferably, the concentration of the lithium salt system in the electrolyte of the ternary lithium-ion battery is 0.5-2 mol·L⁻¹. -1 ; and / or the cyclic compound accounts for 0.08%-3% of the mass fraction of the electrolyte in the ternary lithium-ion battery, preferably 0.1%-2%.

[0010] Preferably, the cyclic compound comprises the following structure: , , , , Any one or a mixture of several of them.

[0011] Preferably, the additive system accounts for 0.2%-6% of the mass fraction of the electrolyte in the ternary lithium-ion battery; the additive system further includes the combined use of at least two of the following: ethylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and propanesulfonate lactone (PS).

[0012] Preferably, a method for preparing the electrolyte of a ternary lithium-ion battery as described above 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 the lithium salt system to the organic solvent mixture for mixing, and finally adding an additive system for mixing to obtain the electrolyte of the ternary lithium-ion battery.

[0013] Preferably, a ternary lithium-ion battery uses the electrolyte of a ternary lithium-ion battery as described above; its positive electrode active material includes lithium nickel cobalt manganese oxide (Li(NiCoMn)O2) and / or lithium nickel cobalt aluminum oxide as ternary positive electrode materials.

[0014] Preferably, the negative electrode active material of the ternary lithium-ion battery includes graphite.

[0015] This application specifically proposes the use of specific cyclic phosphorus-based and boron-based bridged ring compounds as additives for specific ternary lithium-ion battery electrolyte systems. These compounds not only act as scavengers of free radicals (such as hydrogen radicals and hydroxyl radicals), which are crucial for initiating combustion chain reactions, but also form a stable electrode / electrolyte interface phase, possessing both flame-retardant and overcharge-prevention functions. Furthermore, by regulating the composition of the SEI film, the cyclic phosphorus-based and boron-based bridged ring compounds can inhibit lithium dendrite growth and reduce transition metal dissolution, thereby improving the stability of ternary lithium-ion cathode materials and extending the cycle life of ternary lithium-ion batteries.

[0016] Furthermore, the preferred preparation method for specific cyclic phosphorus-based and boron-based bridged ring compounds provided in this application has simple steps and improves synthesis efficiency; the reaction conditions are mild and do not require harsh high temperature, high pressure or strong acid and alkali environments, which reduces equipment requirements and production costs, while also reducing energy consumption and environmental pollution. After separation, purification and other post-processing steps, the reaction products can obtain target products with high purity and high yield. Detailed Implementation

[0017] This embodiment proposes a cyclic compound with the following structural formula: Where X is any one of P, B, or P=O; Y is a C1-C6 carbon chain group containing an alkylene group, carbonyl group, sulfinyl group, sulfonyl group, or fluoroalkylene group. Preferably, in this embodiment, when X is P, the cyclic compound is endowed with abundant phosphorus chemical activity and can participate in a variety of nucleophilic and electrophilic reactions; when X is B, the electron-deficient characteristics of boron atoms give the cyclic compound unique Lewis acidity, exhibiting special properties in catalytic reactions and material modification; when X is P=O, the strong polarity of the phosphorus-oxygen double bond will significantly affect the physicochemical properties of the cyclic compound, such as solubility and reaction selectivity. Preferably, in this embodiment, when Y is an alkylene group, it can be a straight-chain structure such as methylene (-CH2-) or ethylene (-CH2-CH2-), or a branched structure such as (CH3)2C=CH-. This structural diversity provides the possibility of controlling the steric hindrance, flexibility, and electron cloud distribution of the compound. When Y is a carbonyl group (>C=O), it enhances the polarity of the compound and affects its interaction with other molecules. When Y is a sulfinyl group (>S=O) or a sulfonyl group (-SO2-), its unique sulfur-oxygen bond structure endows the compound with special redox properties and chemical stability. Preferably, in this embodiment, fluoroalkylene refers to the alkylene group described above in this embodiment where at least one hydrogen atom is replaced by a fluorine atom, or all hydrogen atoms may be replaced by fluorine atoms. The substitution position and number of fluorine atoms are arbitrary. The fluoroalkylene group can be straight-chain or branched. The introduction of fluorine atoms greatly alters the physicochemical properties of the compound, such as increasing the compound's hydrophobicity, improving its thermal stability and chemical stability.

[0018] Preferably, in this embodiment, the cyclic compound comprises the following structure: , , , , , , , , Any one or a mixture of several of them.

[0019] Preferably, this embodiment proposes a method for preparing the cyclic compound as described above, wherein a phosphorus source or boron source as the initial raw material reacts with its corresponding ligand in an organic solvent environment, and the cyclic compound is obtained after post-treatment of the reaction product. Preferably, in this embodiment, the phosphorus source includes any one or a mixture of several of phosphoric acid, phosphorous acid, pyrophosphoric acid and its metal salts, pyrophosphoryl chloride, pyrophosphorous acid and its metal salts, and pyrophosphoryl chloride. It should be noted that different phosphorus sources have different reactivity and chemical properties. For example, phosphoric acid can participate in nucleophilic substitution reactions under mild conditions to introduce phosphorus atoms; while pyrophosphoryl chloride has high reactivity and is suitable for constructing complex phosphorus-based structures. Preferably, in this embodiment, the boron source includes any one or a mixture of boric acid, boric anhydride, and pyroboric acid; it should be particularly noted that boric acid is a commonly used boron source, which is inexpensive and readily available, and can introduce boron atoms through multiple reaction pathways in the reaction; boric anhydride has relatively high reactivity, which can accelerate the reaction process and is suitable for synthetic routes with high reaction efficiency requirements. Preferably, in this embodiment, the ligand includes any one or a mixture of several of saturated haloalkanes, acyl halides, alcohols, aldehydes, and ketones. It is particularly important to note that the ligand plays a crucial role in the reaction, as it can regulate the electron cloud density and steric hindrance of the metal ion, thus affecting the selectivity and reactivity of the reaction. For example, saturated haloalkane ligands can guide the reaction in a specific direction through the electronic effects and steric hindrance of halogen atoms; alcohol ligands can form stable coordinate bonds with metal ions, promoting the formation of reaction intermediates. Preferably, in this embodiment, the organic solvent is any one or a mixture of several of the following: ether-based organic solvents, carbonate-based organic solvents, carboxylic acid ester-based organic solvents, chlorinated hydrocarbons, and alkanes. More specifically, ether-based organic solvents may include, for example, diethyl ether or tetrahydrofuran; carbonate-based organic solvents may include, for example, dimethyl carbonate or ethylene carbonate; carboxylic acid ester-based organic solvents may include, for example, ethyl acetate or ethyl benzoate; chlorinated hydrocarbons may include, for example, chloroform or dichloromethane; and alkanes may include, for example, n-hexane or n-heptane. Different organic solvents have different polarities, boiling points, and solubilities, which affect the solubility of the reactants, the reaction rate, and the selectivity. Those skilled in the art can select appropriate organic solvents based on the chosen phosphorus source, boron source, and ligands during actual implementation. For example, in some nucleophilic substitution reactions, polar solvents such as tetrahydrofuran can promote the dissolution and reaction of ionic reactants; while in some reactions requiring rate control, nonpolar solvents such as n-hexane can reduce reactivity, making the reaction more controllable.

[0020] Preferably, in this embodiment, a catalyst is also added to the reaction system. The catalyst is a transition metal catalyst and / or an organic small molecule catalyst. It should be noted that, in specific implementation, a suitable catalyst is selected according to different reaction types and raw material characteristics. Specifically, the transition metal catalyst can be palladium, platinum, etc., which have high catalytic activity in reactions that form carbon-carbon bonds and carbon-heteroatom bonds. The organic small molecule catalyst can be proline, triethylamine, etc. Preferably, in this embodiment, the amount of catalyst added is 0.01-0.2 times the molar amount of the phosphorus source or boron source, preferably 0.02-0.06 times.

[0021] Preferably, in this embodiment, the molar ratio of the ligand to the phosphorus source or boron source is 2-5 times, more preferably 2.5-3 times; preferably, in this embodiment, the amount of organic solvent added is 1.5-3 times, more preferably 2-3 times, the molar ratio of the ligand; preferably, in this embodiment, the reaction temperature is set at 60-110℃, more preferably 80-100℃, and the reaction time is 3-10 hours, more preferably 4-8 hours. Preferably, in this embodiment, the reaction apparatus can be selected according to the specific circumstances of the reaction. For example, a distillation and water separation device can be built to disperse the phosphorus source or boron source and its corresponding ligand in an organic solvent, and the temperature is raised to reflux for reaction, continuously separating the water generated in the system during the reaction; alternatively, the phosphorus source or boron source can be pre-dispersed in an organic solvent, and then the liquid ligand is slowly added dropwise to the mixture of phosphorus source or boron source and organic solution, and finally the temperature is raised for reaction. In this embodiment, the post-processing involved in this application mainly refers to the fine separation (using known separation processes) and / or purification (using known purification processes) of the reaction products (in a mixture state) after the reaction is completed. For example, firstly, solid or liquid products are initially separated using methods such as filtration and extraction to remove unreacted raw materials, by-products, and catalysts. During filtration, appropriate filter media and filtration methods are selected based on differences in particle size and solubility of the products and impurities, such as vacuum filtration and centrifugal filtration. Extraction involves selecting appropriate extractants and extraction conditions based on the differences in solubility of the products in different solvents to achieve preliminary enrichment of the products. These all fall within the scope of the art. Based on the content described in this application, conventional technical means can be used by those skilled in the art; then, further purification is carried out through processes such as recrystallization and column chromatography to obtain high-purity target cyclic phosphorus and boron compounds. In the recrystallization process, appropriate solvent systems and crystallization conditions, such as cooling rate and stirring speed, can be selected to improve the purity and crystallinity of the product; column chromatography utilizes the difference in the partition coefficients of different substances in the stationary and mobile phases to achieve fine separation of the product. These are all conventional technical means that can be used by those skilled in the art based on the content described in this application; finally, known analytical methods such as nuclear magnetic resonance (NMR) are used to accurately characterize the purity and structure of the final product to ensure that the target product that meets the requirements is obtained.

[0022] Preferably, this embodiment also proposes an application of the cyclic compound described above, wherein the cyclic compound is added to the electrolyte of the battery, and the amount of the cyclic compound added to the electrolyte is 0.05-3 wt%, more preferably 0.1-2 wt%; further preferably, in this embodiment, the battery can be a lithium-ion battery or a sodium-ion battery.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] Example 1: A distillation and water separation apparatus was constructed. A certain amount of pyrophosphate and paraformaldehyde (as a ligand for pyrophosphate) were dispersed in toluene. The mixture was heated (set at 110°C) to reflux, and water generated in the system was continuously separated during the reaction. In this Example 1, toluene, as the reaction solvent, has good solubility and a suitable boiling point, which allows the reactants to come into full contact and promotes the reaction. The reflux water separation operation can remove the water generated in the reaction in a timely manner, break the reaction equilibrium, and promote the reaction in the forward direction. The molar ratio of paraformaldehyde to pyrophosphate was 2:1, and the molar ratio of toluene to paraformaldehyde was 2.5:1. The reaction time was 6 hours. After the reaction was completed, the mixture was distilled under reduced pressure until it reached a viscous state, effectively removing most of the solvent and reducing the workload of subsequent processing. Then, a mixture of petroleum ether / ethyl acetate in a ratio of 3:1 was added for extraction and further concentration, finally yielding the cyclic phosphorus compound represented by the following structural formula: ; The cyclic phosphorus compounds obtained in Example 1 were characterized by NMR (¹H, ¹³C, ³¹P): 1 ¹H NMR: δ 5.76 (4H, s); 13 C NMR: δ 93.6 (2C, s); 31P NMR: δ 3.25.

[0027] Example 2: A certain amount of potassium pyrophosphate was dispersed in dichloromethane, and a solid phosgene solution (specifically bis(trichloromethyl) carbonate, abbreviated as BTC) was slowly added dropwise as a ligand. After the addition was completed, the temperature was raised to 85°C and the reaction was continued for 5 hours. In this Example 2, dichloromethane was used as a solvent to dissolve potassium pyrophosphate and solid phosgene, providing a homogeneous environment for the reaction. The slow addition of the solid phosgene solution could control the reaction rate and avoid an overly vigorous reaction. The molar ratio of bis(trichloromethyl) carbonate to potassium pyrophosphate was 2.5:1, and the molar ratio of dichloromethane to bis(trichloromethyl) carbonate was 2:1. After the reaction, potassium chloride was removed by filtration. Inorganic salt impurities generated during the reaction were removed by simple solid-liquid separation. The filtrate was rotary evaporated until viscous, and the product was further concentrated. Ether was added for extraction, utilizing the good solubility of the target product in ether to enrich the product and achieve further concentration, ultimately obtaining the cyclic phosphorus compound represented by the following structural formula: ; The cyclic phosphorus compounds obtained in Example 2 were characterized by NMR (13C, 31P): 13C NMR: δ 149.1 (2C, s); 31P NMR: δ 0.56.

[0028] Example 3: A certain amount of potassium pyrophosphate was dispersed in dichloromethane, and thionyl chloride, acting as a ligand, was slowly added dropwise. After the addition was complete, the temperature was raised to 90°C and the reaction continued for 5 hours. In this Example 3, dichloromethane was used as an organic solvent to ensure thorough mixing of the reactants and smooth reaction. Thionyl chloride, as a ligand, participated in the reaction to form the specific structure of the target compound. The molar ratio of thionyl chloride to potassium pyrophosphate was 3:1, and the molar ratio of dichloromethane to thionyl chloride was 2.5:1. After the reaction, potassium chloride was removed by filtration. Inorganic salt impurities generated during the reaction were removed by simple solid-liquid separation. The filtrate was rotary evaporated until viscous, and the product was further concentrated. Ether was added for extraction, utilizing the good solubility of the target product in ether to enrich the product and achieve further concentration, ultimately obtaining the cyclic phosphorus compound represented by the following structural formula: ; The cyclic phosphorus compounds obtained in Example 3 were characterized by NMR (31P): 31P NMR: δ -1.55.

[0029] Example 4: A certain amount of potassium pyrophosphate was dispersed in dimethyl sulfoxide, a certain amount of dibromofluoromethane as a ligand was added, and 18-crown ether-6 catalyst was added. The reaction was carried out at 95±5℃ for 4 hours. In this Example 4, dimethyl sulfoxide has good solubility and a high boiling point, can exist stably at the reaction temperature, and promotes the dissolution of reactants and the reaction. Catalyst 18-crown ether-6, as a small organic molecule catalyst, can form stable complexes with metal ions, promote the reaction, and improve the reaction rate and selectivity. The reaction temperature of 90-100℃ provides a suitable activation energy for the reaction, ensuring that the reaction is completed within a reasonable time. The molar ratio of dibromofluoromethane to potassium pyrophosphate is 2:1, the molar ratio of dimethyl sulfoxide to dibromofluoromethane is 3:1, and the molar ratio of 18-crown ether-6 to potassium pyrophosphate is 0.1:1. After the reaction was complete, potassium bromide was removed by filtration, and the filtrate was rotary evaporated until it became viscous. Petroleum ether was added for extraction, and the extract was further concentrated to finally obtain the cyclic phosphorus compound represented by the following structural formula: ; The cyclic phosphorus compounds obtained in Example 4 were characterized by NMR (¹H, ¹³C, ³¹P): 1H NMR: δ 6.74 (2H, s); 13C NMR: δ 73.2 (2C, s); 31P NMR: δ 3.03.

[0030] Example 5: A distillation and water separation apparatus was constructed. A certain amount of phosphorous pyrophosphoric acid and paraformaldehyde were dispersed in toluene. The mixture was heated (set at 110°C) to reflux reaction. During the reaction, water generated in the system was continuously separated, promoting the reaction in the forward direction. The molar ratio of paraformaldehyde to phosphoric acid was 2.5:1, and the molar ratio of toluene to paraformaldehyde was 2.5:1. The reaction time was 10 hours. After the reaction was completed, the mixture was distilled under reduced pressure until it reached a viscous state, effectively removing most of the solvent and reducing the workload of subsequent processing. Then, a mixture of petroleum ether / ethyl acetate in a ratio of 3:1 was added for extraction and further concentration, finally yielding the cyclic phosphorus compound represented by the following structural formula: ; The cyclic phosphorus compounds obtained in Example 5 were characterized by NMR (1H, 13C, 31P): 1H NMR: δ 5.55-5.73 (4H, m); 13C NMR: δ 93.6 (2C, s); 31P NMR: δ 4.0.

[0031] Example 6: A distillation apparatus was constructed to separate water. A certain amount of boric acid was dispersed in chlorobenzene, and the mixture was heated (set at 150°C) to reflux. During the reaction, water generated in the system was continuously separated. After about 1 equivalent of water was separated, paraformaldehyde was added to continue the water separation reaction until no more water was generated in the system. The molar ratio of paraformaldehyde to boric acid was 2.5:2, and the molar ratio of toluene to paraformaldehyde was 2.5:1. The reaction time was 4.5 hours. After the reaction was complete, the mixture was distilled under reduced pressure until it reached a viscous state, effectively removing most of the solvent and reducing the workload of subsequent processing. Then, DMC was added for extraction and further concentration, finally yielding the cyclic boron compound represented by the following structural formula: ; The cyclic phosphorus compound obtained in Example 6 was characterized by NMR (1H, 13C, 31P): 1H NMR: δ 5.42 (4H, m); 13C NMR: δ 93.6 (2C, s).

[0032] Comparative Example 1: This Comparative Example 1 uses B03 as the cyclic borooxane compound as used in the example of the prior patent CN114512721B.

[0033] For the purity and yield of the products from Examples 1-6, please refer to Table 1 below: ; As can be seen from Table 1 above, the yield of Example 6 is significantly low, and it is not recommended as a preferred example. To further verify the application effects achieved in Embodiments 1-5 of this application, the following comparative application experiments were conducted on the products provided in Embodiments 1-5 and Comparative Example 1 respectively: The pouch cells corresponding to Examples 1-5 and Comparative Example 1 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 78% is specifically composed of ethylene carbonate EC: 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 1-6 and Comparative Example 1 were selected respectively, and the product accounted for 1% of the electrolyte by mass. The rest are other additives, specifically composed of vinyl sulfate DTD: fluorovinyl carbonate FEC: propanesulfonate lactone PS = 4:2:1 (wt%); After the raw materials of the organic solvent system are mixed evenly in a fixed ratio, the mixture is cooled to a freezing temperature of 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 1-6 and Comparative Example 1, as well as other additives, are added and mixed evenly for later use.

[0034] 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 example 2: Comparative Example 2: The rest of the technical solutions of Comparative Example 2 are the same as those of Example 1, except that the product in Example 1 is replaced with the additive propanesulfonic acid lactone PS.

[0035] Therefore, we obtained pouch cells assembled using electrolytes provided in Examples 1-5 and Comparative Examples 1-2 as specific additives, respectively, with each pouch cell using an electrolyte concentration of 3.5-4.5 g / Ah. The following performance comparison tests were then conducted on each pouch cell: Three groups of each soft-pack battery corresponding to Examples 1-5 and Comparative Examples 1-2 were made. Each group was cycled 200 times at 25°C, 45°C and 60°C respectively. The charge and discharge conditions used for each cycle test were: charge and discharge rate of 1C / 1C and voltage range of 2.5V-4.2V. The measured capacity retention rates of the lithium-ion batteries are shown in Table 2 below: ;

[0036] To further enhance the effectiveness of the cyclic compounds proposed in the above embodiments of this application in lithium-ion batteries, this embodiment also proposes an electrolyte for a ternary lithium-ion battery, comprising an organic solvent system, a lithium salt system, and an additive system; the organic solvent system consists of at least one cyclic carbonate and at least one chain carbonate; the lithium salt system comprises 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, lithium perchlorate LiClO4, lithium trifluoromethanesulfonate LiOTf, and lithium tetrafluoroborate LiBF4; the additive system comprises cyclic compounds, wherein the cyclic compounds are those described above in this embodiment.

[0037] Preferably, in this embodiment, the organic solvent system accounts for 60-90% of the mass fraction of the electrolyte in the ternary lithium-ion battery, more preferably 65.5-87.9%; even more preferably, in this embodiment, cyclic carbonates account for 15-35% of the mass fraction of the electrolyte in the ternary lithium-ion battery, and chain carbonates account for 45-75% of the mass fraction of the electrolyte in the ternary lithium-ion battery.

[0038] Preferably, in this embodiment, the cyclic carbonate is ethylene carbonate (EC) and / or propylene carbonate (PC); the chain carbonate is dimethyl carbonate (DMC) and / or ethyl methyl carbonate (EMC) and / or diethyl carbonate (DEC).

[0039] Preferably, in this embodiment, the concentration of the lithium salt system in the electrolyte of the ternary lithium-ion battery is 0.5-2 mol·L⁻¹.-1 ; and / or preferably, in this embodiment, the cyclic compound accounts for 0.08-3% of the mass fraction of the electrolyte in the ternary lithium-ion battery, more preferably 0.1-2%.

[0040] Preferably, in this embodiment, the additive system accounts for 0.2-6% of the mass fraction of the electrolyte in the ternary lithium-ion battery; the additive system also includes the combined use of at least two of the following: ethylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and propanesulfonate lactone (PS).

[0041] This embodiment also proposes a method for preparing the electrolyte of a ternary lithium-ion battery as described above. The method involves mixing the raw materials of the organic solvent system to obtain an organic solvent mixture, freezing the organic solvent mixture for 1-3 hours (preferably 1.5-2 hours), adding the lithium salt system to the organic solvent mixture for mixing, and finally adding the additive system for mixing to obtain the electrolyte of the ternary lithium-ion battery.

[0042] This embodiment also proposes a ternary lithium-ion battery, which uses the electrolyte of the ternary lithium-ion battery as described above; its positive electrode active material includes lithium nickel cobalt manganese oxide (NCM) and / or lithium nickel cobalt aluminum oxide (NCA) as ternary positive electrode materials; preferably, in this embodiment, the negative electrode active material of the ternary lithium-ion battery includes graphite.

[0043] 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 7: An electrolyte for a ternary lithium-ion battery, comprising: The organic solvent system with a mass fraction of 78% is specifically composed of ethylene carbonate EC: ethyl methyl carbonate EMC: dimethyl carbonate DMC = 3:5:2 (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 1%; The remainder consists of other additives, specifically ethylene sulfate DTD: fluoroethylene carbonate FEC: propanesulfonate lactone PS = 4:2:1 (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.

[0044] Example 8: The remaining technical solutions of Example 8 are the same as those of Example 7, except that in Example 8, the product provided in Example 2 is used instead of the product provided in Example 1.

[0045] Example 9: The remaining technical solutions of Example 9 are the same as those of Example 7, except that in Example 9, the product provided in Example 3 is used instead of the product provided in Example 1.

[0046] Example 10: The remaining technical solutions of Example 10 are the same as those of Example 7, except that in Example 10, the product provided in Example 4 is used instead of the product provided in Example 1.

[0047] Example 11: The remaining technical solutions of Example 11 are the same as those of Example 7, except that in Example 11, the product provided in Example 5 is used instead of the product provided in Example 1.

[0048] Comparative Example 3: The remaining technical solutions of Comparative Example 3 are the same as those of Example 7, except that in Comparative Example 3, the product provided by Comparative Example 1 is used instead of the product provided by Example 1.

[0049] Comparative Example 4: The remaining technical solutions of Comparative Example 4 are the same as those of Example 7, except that the implementation scheme of Comparative Example 2 is adopted in Comparative Example 4, that is, the product in Example 1 is replaced with the additive propanesulfonic acid lactone PS.

[0050] Comparative Example 5: The remaining technical solutions of Comparative Example 5 are the same as those of Example 7, except that in Comparative Example 5, the organic solvent system is specifically composed of dimethyl carbonate (DMC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) = 1:1:1 (wt%).

[0051] Comparative Example 6: The remaining technical solutions of Comparative Example 6 are the same as those of Example 7, except that in Comparative Example 6, the organic solvent system is specifically composed of propylene carbonate PC: ethylene carbonate EC = 1:1 (wt%).

[0052] Comparative Example 7: The remaining technical solutions of Comparative Example 7 are the same as those of Example 7, except that in Comparative Example 7, the organic solvent system is specifically composed of ethyl propionate EP: fluoroethylene carbonate FEC = 1:1 (wt%).

[0053] Then, the pouch cells corresponding to Examples 7-11 and Comparative Examples 3-7 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 (specifically, a ternary system NCM622) 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 NCM622|| graphite pouch cells assembled using electrolytes provided as specific additives in Examples 7-11 and Comparative Examples 3-7, respectively. The electrolyte usage of each pouch cell was 3.5-4.5 g / Ah. The following performance comparison tests were then conducted on each pouch cell: Three groups of each soft-pack battery corresponding to Examples 7-11 and Comparative Examples 3-7 were made. Each group was cycled 200 times at 25°C, 45°C and 60°C respectively. The charge and discharge conditions used for each cycle test were: charge and discharge rate of 1C / 1C and voltage range of 2.5V-4.2V. The measured capacity retention rates of the lithium-ion batteries are shown in Table 3 below: ; To further demonstrate the performance of this embodiment, this application also conducted flame retardancy tests (using UL 94 rating standards) and limiting oxygen index tests (referring to ISO 4589-2:2017) on the cyclic compound materials corresponding to Examples 7-11 and Comparative Examples 3-7; this application also conducted overcharge protection performance tests on each pouch battery corresponding to Examples 7-11 and Comparative Examples 3-7, and the test results are shown in Table 4 below: ; 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.

[0054] 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. An electrolyte for a ternary lithium-ion battery, 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 lithium salt system comprises any one or a mixture of several of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium perchlorate (LiClO4), lithium trifluoromethanesulfonate (LiOTf), and lithium tetrafluoroborate (LiBF4); the additive system comprises cyclic compounds, wherein the cyclic compounds contain the following structural formula: Where X is any one of P, B, or P=O; Y is a C1-C6 carbon chain containing an alkylene group, carbonyl group, sulfinyl group, sulfonyl group, or fluoroalkylene group.

2. The electrolyte of the ternary lithium-ion battery according to claim 1, characterized in that, The organic solvent system accounts for 60%-90% of the mass fraction of the electrolyte in the ternary lithium-ion battery, preferably 65.5%-87.9%.

3. The electrolyte of the ternary lithium-ion battery according to claim 2, characterized in that, The cyclic carbonate accounts for 15%-35% of the mass fraction of the electrolyte in the ternary lithium-ion battery; the chain carbonate accounts for 45%-75% of the mass fraction of the electrolyte in the ternary lithium-ion battery.

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

5. The electrolyte of the ternary lithium-ion battery according to claim 1, characterized in that, The lithium salt system accounts for 0.5-2 mol·L⁻¹ of the electrolyte in the ternary lithium-ion battery. -1 ; and / or the cyclic compound accounts for 0.08%-3% of the mass fraction of the electrolyte in the ternary lithium-ion battery, preferably 0.1%-2%.

6. The electrolyte of the ternary lithium-ion battery according to claim 1, characterized in that, The cyclic compound comprises the following structure: , , , , Any one or a mixture of several of them.

7. The electrolyte of the ternary lithium-ion battery according to claim 1, characterized in that, The additive system accounts for 0.2%-6% of the mass fraction of the electrolyte in the ternary lithium-ion battery; the additive system also includes the combined use of at least two of the following: ethylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and propanesulfonate lactone (PS).

8. A method for preparing the electrolyte of a ternary lithium-ion battery 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 ternary lithium-ion battery.

9. A ternary lithium-ion battery, characterized in that, The electrolyte of the ternary lithium-ion battery according to any one of claims 1-7 is used; the positive electrode active material includes lithium nickel cobalt manganese oxide (Li(NiCoMn)O2) and / or lithium nickel cobalt aluminum oxide as ternary positive electrode materials.

10. The ternary lithium-ion battery according to claim 9, characterized in that, The negative electrode active material of the ternary lithium-ion battery includes graphite.

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