Electrolyte additive and preparation method thereof, electrolyte and lithium ion battery

Abstract

This invention relates to electrolyte additives and their preparation methods, electrolytes, and lithium-ion batteries. The chemical formula of the electrolyte additives satisfies aM + 【A(Q) b 】 a‑ Q and A are linked by coordinate bonds, where a is an integer from 1 to 10 and b is an integer from 1 to 4; M + Selected from metal ions or onium ions; A is selected from at least one of AlCl4, AlBr4, GaCl4, and GaBr4; Q has the structure shown in formula (Ⅰ); Y1 is selected from one of B and P; R1, R2, and R3 are independently selected from A'(Q'). c c is an integer from 0 to 3, halogen, unsubstituted, or substituted by at least one R a Substituted C1-C8 alkyl or phenyl groups; R a Selected from halogens; A' selected from at least one of AlCl4, AlBr4, GaCl4, and GaBr4; Q' having the structure shown in formula (II); Y2 selected from one of B and P; R4, R5, and R6 independently selected from A'', halogens, unsubstituted compounds, or compounds substituted by at least one R b Substituted C1-C8 alkyl or phenyl groups; R b Selected from halogens; A'' selected from at least one of AlCl4, AlBr4, GaCl4, and GaBr4. Formula (I); Formula (II).

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more particularly to electrolyte additives and their preparation methods, electrolytes, and lithium-ion batteries. Background Technology

[0002] Traditional carbonate electrolytes suffer from instability under high-voltage conditions. For example, at ≥4.4V, the HOMO (Highest Occupied Molecular Orbital) energy level of carbonate solvents shifts upward, making them prone to reacting with the high-valence Ni on the surface of layered cathode active materials. 4+ Co 4+ Direct single-electron oxidation occurs, leading to lithium extraction, accompanied by oxygen oxidation and the generation of gases such as O2, CO2, and C2H4. Furthermore, the interfacial layer continuously accumulates byproducts due to the chain reaction of free radicals, causing the CEI (Cathode Electrolyte Interface) film to thicken continuously. This results in an exponential increase in impedance mass transfer during long-term cycling, ultimately leading to a sharp drop in capacity. In addition, LiPF6 in the electrolyte inevitably hydrolyzes to generate HF due to trace amounts of water. Transition metal ions dissolved from the positive electrode by HF etching migrate to the negative electrode and are reduced and adsorbed on the electrode surface, continuously catalyzing electrolyte reduction. This ultimately damages the stability of the SEI (Solid Electrolyte Interface) film and continuously consumes active lithium for interfacial phase reconstruction, causing unnecessary consumption of active lithium ions.

[0003] Therefore, there is an urgent need to provide an electrolyte additive that can solve the above problems. Summary of the Invention

[0004] This invention provides an electrolyte additive and its preparation method, an electrolyte, and a lithium-ion battery. This electrolyte additive preferentially adsorbs on the positive electrode side of the battery, preferentially forming a passivation layer and regulating the construction of the positive electrode CEI film. While improving the oxidation stability of the electrolyte, it significantly reduces the probability of oxidation chain reactions under high voltage (≥4.45V), thereby effectively alleviating the gas generation and degradation cycle problems caused by side reactions on the positive electrode side, ultimately achieving long-term cycle stability of the battery under high voltage.

[0005] The first aspect of this invention provides an electrolyte additive, wherein the chemical formula of the electrolyte additive satisfies aM +

A(Q) b

[0006] This invention provides a novel complex-type electrolyte additive. The A portion of this additive (i.e., AlCl4, AlBr4, GaCl4, GaBr4) is a Lewis base, while the Q portion (i.e., a compound containing B or P) is a Lewis acid. Therefore, the A and Q portions can coordinate to form ion-pair complexes. A can coordinate with multiple Q portions, and Q can further coordinate with more A portions to form more complex clusters. The entire [A(Q)] complex... b Partially negatively charged, M in the additive + (i.e., metal ions or onium ions) exist in solvent separation or contact ion pairs, eventually forming a complete complex-type additive.

[0007] Because the metal center (i.e., Al or Ga) of part A in the additive is electron-deficient, and part Q is also electron-deficient, during the initial charging stage of the battery, the additive preferentially oriented and adsorbed onto the positive electrode surface due to electrostatic attraction, preferentially forming a passivation layer. Subsequently, an ultrathin CEI film rich in components such as Al-F-Cl is induced on the positive electrode surface. This "adsorption-film formation" method reduces the contact between the solvent and the positive electrode surface, thus minimizing oxidation. Furthermore, the introduction of this additive can increase the oxidation potential of the carbonate solvent, greatly reducing the probability of oxidation chain reactions, thereby effectively alleviating the gas generation and degradation cycle problems caused by positive electrode side reactions. In addition, during long-term battery cycling, the positive electrode active material (e.g., NCM, NCA, etc.) undergoes bulk Ni oxidation. 3+ / Ni 4+The Jahn-Teller distortion and Li / Ni mixing lead to lattice stress, causing structural damage and ion dissolution. However, after the additive is adsorbed and formed into a film on the cathode surface, it still retains some of the bridging Q component (e.g., BF3 component). The bridging Lewis acid component can react with the dissolved Ni. 2+ / Co 2+ Formation of stable complex ions (e.g., Ni) 2+ / Co 2+ -FB), thereby achieving the effect of depositing and sealing the dissolved metal ions on the positive electrode surface, preventing them from migrating to the negative electrode and damaging the negative electrode SEI film. Simultaneously, Al 3+ or Ga 3+ It can redeposit a protective layer containing components such as Al2O3, AlF3, Ga2O3, and GaF3 on the surface of the positive electrode, enhance the stability of the positive electrode CEI film, protect the structural integrity of the positive electrode active material to a certain extent, inhibit the further dissolution of transition metal ions and the harmful gases generated by the oxidation and decomposition of the electrolyte, and ultimately improve the long-term cycle stability of the battery under high voltage conditions.

[0008] Specifically, the term is explained as follows: "Jahn-Teller distortion," also known as the Young-Teller effect, is a special case of ion energy level splitting in a crystal field. When an ion is in a degenerate electronic state, if a small geometric distortion (i.e., a change in the position of each atom) occurs in the system, causing degeneracy to split and occupying a lower energy state, then the energy decrease will be proportional to the distortion.

[0009] According to an embodiment of the present invention, the M + It includes one of the following ions: Li ions, Na ions, K ions, Mg ions, Zn ions, and quaternary ammonium ions. This allows the electrolyte additive to possess suitable charge density and solubility.

[0010] According to an embodiment of the present invention, the electrolyte additive includes (Ⅰ-1) (Ⅰ-2) (Ⅰ-3) (Ⅰ-4) (Ⅰ-5) (Ⅰ-6) (Ⅰ-7) (Ⅰ-8) (Ⅰ-9) (Ⅰ-10) (Ⅰ-11) (Ⅰ-12) (Ⅰ-13) (Ⅰ-14) (Ⅰ-15) (Ⅰ-16) (Ⅰ-17) (Ⅰ-18) (Ⅰ-19) (Ⅰ-20) (Ⅰ-21) (Ⅰ-22) (Ⅰ-23) (Ⅰ-24) (Ⅰ-25) (Ⅰ-26) At least one of (Ⅰ-27). Thus, electrolyte additives can effectively improve the long-term cycle stability of batteries under high-voltage conditions.

[0011] A second aspect of the present invention provides a method for preparing the electrolyte additive described in the first aspect, comprising: mixing MA and Q in a solvent to perform a complexation reaction to obtain the electrolyte additive; wherein, M in MA... + Selected from metal ions or onium ions; A in the MA - Selected from AlCl4 - AlBr4 - GaCl4 - GaBr4 - At least one of them; the Q has the structure shown in formula (I), Formula (I). Thus, the aforementioned electrolyte additive can be prepared. The preparation method provided by this invention is simple and convenient, and has the potential for large-scale industrial production.

[0012] According to an embodiment of the present invention, the complexation reaction is carried out at a temperature of 20°C-35°C for 6-12 hours. Thus, MA and Q can fully undergo the complexation reaction to form the aforementioned electrolyte additive.

[0013] According to an embodiment of the present invention, the MA includes at least one of LiAlCl4, LiAlBr4, LiGaCl4, LiGaBr4, NaAlCl4, Mg(AlCl4)2, and Me4N(AlCl4).

[0014] According to an embodiment of the present invention, Q includes BF3, BF2CH3, BF(C6H5)2, BF(C6F5)2, BF2C6H5, BF2C6F5, B(CH3)3, B(C6H5)3, B(C6F5)3, BF2C4H9, and BF2C8H. 17 At least one of PF3.

[0015] A third aspect of the present invention provides an electrolyte comprising the electrolyte additive described in the first aspect, or an electrolyte additive prepared according to the method described in the second aspect. Therefore, using this electrolyte can improve the long-term cycle stability of the manufactured lithium-ion battery under high voltage.

[0016] According to an embodiment of the present invention, the mass percentage of the electrolyte additive is 0.01wt%-5wt% based on the total mass of the electrolyte. Thus, the additive, when used in a suitable amount, effectively improves the high-voltage stability of the battery while suppressing impedance growth and reducing costs.

[0017] According to embodiments of the present invention, the electrolyte further includes a solvent, wherein the solvent comprises a carbonate solvent. Therefore, the electrolyte additive provided by the present invention can significantly improve the problem of poor stability of electrolytes containing carbonate solvents under high-voltage conditions.

[0018] A fourth aspect of the present invention provides a lithium-ion battery comprising the electrolyte described in the third aspect. Consequently, this lithium-ion battery exhibits excellent long-term cycle stability under high-voltage conditions.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0020] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0021] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] To facilitate understanding of the invention, certain technical and scientific terms are specifically defined below. Unless otherwise expressly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0025] In this document, the terms “optionally,” “optionally,” or “optionally” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0026] Currently, in order to improve the long-term stability of carbonate electrolytes under high-pressure environments, related technologies often involve adding high-pressure organic small molecule additives (such as phosphate esters, boron-based, nitrile, and sulfur-based additives). Although these additives can increase the oxidation potential of the electrolyte, they cannot form a stable interfacial film to prevent the continuous occurrence of side reactions when used in small amounts. If the amount is increased, problems such as gas generation or impedance surge are likely to occur. Furthermore, they are sensitive to water and are prone to premature oxidation and failure, ultimately damaging the electrochemical performance of the battery.

[0027] Based on this, the first aspect of the present invention provides an electrolyte additive, wherein the chemical formula of the electrolyte additive satisfies aM +

A(Q) b

[0028] This invention provides a novel complex-type electrolyte additive. The A portion of this additive (i.e., AlCl4, AlBr4, GaCl4, GaBr4) is a Lewis base, while the Q portion (i.e., a compound containing B or P) is a Lewis acid. Therefore, the A and Q portions can coordinate to form ion-pair complexes. A can coordinate with multiple Q portions, and Q can further coordinate with more A portions to form more complex clusters. The entire [A(Q)] complex... b Partially negatively charged, M in the additive + (i.e., metal ions or onium ions) exist in solvent separation or contact ion pairs, eventually forming a complete complex-type additive.

[0029] Because the metal center (i.e., Al or Ga) of part A in the additive is electron-deficient, and part Q is also electron-deficient, during the initial charging stage of the battery, the additive preferentially oriented and adsorbed onto the positive electrode surface due to electrostatic attraction, preferentially forming a passivation layer. Subsequently, an ultrathin CEI film rich in components such as Al-F-Cl is induced on the positive electrode surface. This "adsorption-film formation" method reduces the contact between the solvent and the positive electrode surface, thus minimizing oxidation. Furthermore, the introduction of this additive can increase the oxidation potential of the carbonate solvent, greatly reducing the probability of oxidation chain reactions, thereby effectively alleviating the gas generation and degradation cycle problems caused by positive electrode side reactions. In addition, during long-term battery cycling, the positive electrode active material (e.g., NCM, NCA, etc.) undergoes bulk Ni oxidation. 3+ / Ni 4+ The Jahn-Teller distortion and Li / Ni mixing lead to lattice stress, causing structural damage and ion dissolution. However, after the additive is adsorbed and formed into a film on the cathode surface, it still retains some of the bridging Q component (e.g., BF3 component). The bridging Lewis acid component can react with the dissolved Ni. 2+ / Co 2+ Formation of stable complex ions (e.g., Ni) 2+ / Co 2+ -FB), thereby achieving the effect of depositing and sealing the dissolved metal ions on the positive electrode surface, preventing them from migrating to the negative electrode and damaging the negative electrode SEI film. Simultaneously, Al 3+ or Ga 3+ It can redeposit a protective layer containing components such as Al2O3, AlF3, Ga2O3, and GaF3 on the surface of the positive electrode, enhance the stability of the positive electrode CEI film, protect the structural integrity of the positive electrode active material to a certain extent, inhibit the further dissolution of transition metal ions and the harmful gases generated by the oxidation and decomposition of the electrolyte, and ultimately improve the long-term cycle stability of the battery under high voltage conditions.

[0030] Specifically, the term is explained as follows: "Jahn-Teller distortion," also known as the Young-Teller effect, is a special case of ion energy level splitting in a crystal field. When an ion is in a degenerate electronic state, if a small geometric distortion (i.e., a change in the position of each atom) occurs in the system, causing degeneracy to split and occupying a lower energy state, then the energy decrease will be proportional to the distortion.

[0031] According to a specific embodiment of the present invention, the M + It includes one of the following ions: Li ions, Na ions, K ions, Mg ions, Zn ions, and quaternary ammonium ions. This allows the electrolyte additive to possess suitable charge density and solubility.

[0032] According to a specific embodiment of the present invention, the electrolyte additive includes (Ⅰ-1) (Ⅰ-2) (Ⅰ-3) (Ⅰ-4) (Ⅰ-5) (Ⅰ-6) (Ⅰ-7) (Ⅰ-8) (Ⅰ-9) (Ⅰ-10) (Ⅰ-11) (Ⅰ-12) (Ⅰ-13) (Ⅰ-14) (Ⅰ-15) (Ⅰ-16) (Ⅰ-17) (Ⅰ-18) (Ⅰ-19) (Ⅰ-20) (Ⅰ-21) (Ⅰ-22) (Ⅰ-23) (Ⅰ-24) (Ⅰ-25) (Ⅰ-26) At least one of (Ⅰ-27). Thus, electrolyte additives can effectively improve the long-term cycle stability of batteries under high-voltage conditions.

[0033] A second aspect of the present invention provides a method for preparing the electrolyte additive described in the first aspect, comprising: mixing MA and Q in a solvent to perform a complexation reaction to obtain the electrolyte additive; wherein, M in MA... +Selected from metal ions or onium ions; A in the MA - Selected from AlCl4 - AlBr4 - GaCl4 - GaBr4 - At least one of them; the Q has the structure shown in formula (I), Formula (I). Thus, the aforementioned electrolyte additive can be prepared. The preparation method provided by this invention is simple and convenient, and has the potential for large-scale industrial production.

[0034] According to specific embodiments of the present invention, the type of solvent is not particularly limited, and those skilled in the art can select it as needed, for example, carbonate solvents can be used directly.

[0035] According to a specific embodiment of the present invention, the temperature of the complexation reaction is 20℃-35℃, and the time is 6h-12h.

[0036] As specific examples, the temperature of the complexation reaction can be 20°C, 25°C, 30°C, 35°C, etc., and the time can be 6h, 8h, 10h, 12h, etc. Thus, MA and Q can fully undergo the complexation reaction to form the aforementioned electrolyte additive.

[0037] According to a specific embodiment of the present invention, the MA includes at least one of LiAlCl4, LiAlBr4, LiGaCl4, LiGaBr4, NaAlCl4, Mg(AlCl4)2, and Me4N(AlCl4).

[0038] According to a specific embodiment of the present invention, Q includes BF3, BF2CH3, BF(C6H5)2, BF(C6F5)2, BF2C6H5, BF2C6F5, B(CH3)3, B(C6H5)3, B(C6F5)3, BF2C4H9, and BF2C8H. 17 At least one of PF3.

[0039] A third aspect of the present invention provides an electrolyte comprising the electrolyte additive described in the first aspect, or an electrolyte additive prepared according to the method described in the second aspect. Therefore, using this electrolyte can improve the long-term cycle stability of the manufactured lithium-ion battery under high voltage.

[0040] According to a specific embodiment of the present invention, the mass percentage of the electrolyte additive is 0.01wt%-5wt% based on the total mass of the electrolyte.

[0041] As specific examples, the mass percentage of the additive can be 0.01wt%, 0.02wt%, 0.05wt%, 0.1wt%, 0.2wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, etc. Thus, with appropriate dosage, the additive effectively improves the high-voltage stability of the battery while suppressing impedance growth and reducing costs.

[0042] According to a specific embodiment of the present invention, the electrolyte further includes a solvent, which includes a carbonate solvent. Therefore, the electrolyte additive provided by the present invention can significantly improve the problem of poor stability of electrolytes containing carbonate solvents under high pressure conditions.

[0043] According to specific embodiments of the present invention, the amount of solvent is not particularly limited, and those skilled in the art can select it according to actual conditions. For example, based on the total mass of the electrolyte, the mass ratio of the solvent can be 77%-89.9%.

[0044] According to specific embodiments of the present invention, the type of carbonate solvent is not particularly limited, and some specific examples include at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, methyltrifluoromethylethyl carbonate, bis(2,2,2)-trifluoroethyl carbonate, and 3,3,3-trifluoropropylene carbonate.

[0045] According to specific embodiments of the present invention, the electrolyte further includes a lithium salt, the type of which is not particularly limited, and some specific examples include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluorooxalate phosphate, lithium difluorobis(oxalate) phosphate, lithium difluorooxalate borate, and lithium tri(oxalate) phosphate.

[0046] According to specific embodiments of the present invention, the amount of lithium salt is not particularly limited, and those skilled in the art can select it according to actual conditions. For example, based on the total mass of the electrolyte, the mass ratio of lithium salt can be 10%-20%.

[0047] A fourth aspect of the present invention provides a lithium-ion battery comprising the electrolyte described in the third aspect. Consequently, this lithium-ion battery exhibits excellent long-term cycle stability under high-voltage conditions.

[0048] According to a specific embodiment of the present invention, the lithium-ion battery further includes a positive electrode sheet, a negative electrode sheet, and a separator; the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, the positive active material layer including a positive active material;

[0049] The positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, and nickel-cobalt-manganese ternary materials. Typically, a battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through.

[0050] In some embodiments of the present invention, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. For example, the composite positive electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0051] In some embodiments of the present invention, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0052] In some embodiments of the present invention, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0053] In some embodiments of the present invention, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, and binder, in a solvent (e.g., N-methylpyrrolidone, NMP) to form a positive electrode slurry; coating the positive electrode slurry onto a positive current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0054] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0055] In some embodiments of the present invention, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0056] In some embodiments of the present invention, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, nano-carbon, elemental silicon, silicon oxide, silicon-carbon composite, silicon alloy, elemental tin, tin oxide, tin-carbon composite, tin alloy, and lithium titanate.

[0057] In some embodiments of the present invention, the negative electrode active material layer may optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0058] In some embodiments of the present invention, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0059] In some embodiments of the present invention, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0060] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0061] Example 1

[0062] This embodiment provides a lithium-ion battery and its preparation method, the specific steps of which are as follows:

[0063] (1) Preparation of electrolyte additives

[0064] Inside a glove box, 0.3 mol of BF3 was first dissolved in 25.3 mL of dimethyl carbonate (DMC) solvent, followed by the addition of 4.074 g (0.3 mol) of anhydrous LiAlCl4 and magnetic stirring. The mixture was stirred continuously at 25 °C for 8 h to obtain the electrolyte additive. .

[0065] (2) Preparation of electrolyte

[0066] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed evenly in a mass ratio of 55:30:15 (the mass percentage of DMC here includes the portion used as solvent in step (1)) to obtain a basic mixed solvent. Then, LiPF6 and the electrolyte additive prepared in step (1) are added, dissolved, and mixed evenly to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage of LiPF6 is 12%, and the mass percentage of the electrolyte additive is 1%.

[0067] (3) Preparation of positive electrode sheet

[0068] The positive electrode active material NCM613, conductive agent Super P, conductive agent carbon nanotubes (CNTs), and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:3:0.5:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 65wt%. After vacuum stirring, the slurry was obtained. The positive electrode slurry was uniformly coated on both surfaces of the positive electrode current collector aluminum foil, dried at 85℃, and then cold-pressed to obtain a positive electrode sheet with a double-sided coated positive electrode material layer. The thickness of the single-sided positive electrode material layer was 125μm. The sheet was then trimmed, cut, and slit. After slitting, it was dried at 85℃ under vacuum for 4 hours, and tabs were welded to obtain a positive electrode sheet with a size of 540mm×50mm for later use.

[0069] (4) Preparation of negative electrode sheet

[0070] Silicon carbide (SiC550, manufactured by Liyang Tianmu Pioneer Battery Materials Technology Co., Ltd.), conductive agent Super P, styrene-butadiene rubber (SBR), and binder sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95:1.5:2:1.5. Deionized water was added as a solvent to prepare a slurry with a solid content of 49wt%. The slurry was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated on both surfaces of a 9μm thick copper foil current collector. After drying at 85℃, it was cold-pressed to obtain a negative electrode sheet with a double-sided coated negative electrode material layer. The thickness of the single-sided negative electrode material layer was 73μm. The sheet was then trimmed, cut, and slit. After slitting, it was dried at 85℃ under vacuum for 4 hours. The tabs were then welded to obtain a negative electrode sheet with a size of 660mm×59mm for later use.

[0071] (5) Preparation of the diaphragm

[0072] The diaphragm is a polyethylene (PE) ceramic-coated diaphragm, which was purchased from Shenzhen Xingyuan Material Technology Co., Ltd., model PE ceramic 10+2, with a total thickness of 12μm.

[0073] (6) Preparation of lithium-ion batteries

[0074] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to act as a separator. The stacked battery is then assembled, with the positive tab connected to the positive electrode and the negative tab connected to the negative electrode, resulting in an electrode assembly. The electrode assembly is placed in an aluminum foil packaging bag, with the positive and negative tabs extended from the inside to the outside of the bag. It is then vacuum-dried at 85°C for 48 hours, and the electrolyte prepared above is injected at an injection rate of 3.0 g / Ah. After vacuum sealing, formation, aging, and capacity testing, a lithium-ion battery is obtained. The formation voltage limit is 3.9V, the formation temperature is 45℃, and the formation resting time is 2 hours; the aging temperature is 45℃, and the aging resting time is 16 hours; the capacity test involves charging to 4.45V at 0.1C, resting for 5 minutes, then discharging to 3.0V at 0.1C, and repeating the above steps twice. Then, the voltage is charged to 4.45V at 1C, rested for 5 minutes, and then discharged to 3.0V at 0.1C, and the above steps are repeated three times.

[0075] Compared with Example 1, the other examples and comparative examples only made adjustments to some features, as shown in Table 1.

[0076] Table 1

[0077]

[0078] Test case

[0079] The performance of the lithium-ion batteries prepared in the above embodiments and comparative examples was tested using the following methods:

[0080] (1) Testing of the oxidation potential of the electrolyte

[0081] The oxidation potential of the electrolyte was measured using linear sweep voltammetry. A three-electrode system was assembled with platinum (Pt) as the working electrode and lithium metal as the counter and reference electrodes; the working area of ​​the Pt electrode was 0.0314 cm². 2 During the test, the scan voltage range was from open-circuit voltage to 5.5V (vs. Li / Li). + The scan rate was 1 mV / s. The current density on the polarization curve was taken as 0.001 mA / cm².2 The corresponding potential value is taken as the oxidation potential of the electrolyte.

[0082] (2) DC Impedance (DCR) Test

[0083] The internal resistance is calculated using Ohm's law by measuring the voltage change after applying an instantaneous DC current to the lithium-ion battery. The specific test method is as follows: After capacity formation, the lithium-ion battery is placed in a 25°C constant temperature chamber and charged at a constant current of 1C until the voltage reaches 4.45V. Then, it is charged at a constant voltage of 4.45V until the current reaches 0.05C. After resting for 30 minutes, it is discharged at a constant current of 1C for 30 minutes (adjusted to 50% SOC, where SOC refers to the battery's state of charge). It is then left to stand in the 25°C constant temperature chamber for 1 hour, and the voltage of the lithium-ion battery at this point is recorded as V0. Then, it is discharged at a constant current of 2C for 10 seconds, left to stand for 5 minutes, and the voltage of the lithium-ion battery at this point is recorded as V1.

[0084] The DCR of a lithium-ion battery is calculated as (V0 - V1) / 2C. The smaller the DCR value, the lower the impedance of the lithium-ion battery.

[0085] (3) Cyclic performance test at 25℃

[0086] The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 2 hours to allow it to reach a constant temperature. It was then charged at a constant current of 1C until the voltage reached 4.45V, followed by constant voltage charging at 4.45V until the cutoff current reached 0.05C. Finally, it was discharged at a constant current of 1.0C until the voltage reached 3.0V. The initial discharge capacity was recorded as C1. This constituted one charge-discharge cycle. This process was repeated 500 times, and the discharge capacity after the 500th cycle was recorded as C2.

[0087] Capacity retention rate at 25℃ (%) = C2 / C1 × 100%; The capacity retention rate at 25℃ is used to evaluate the room temperature cycle performance of lithium-ion batteries at high rates. The higher the capacity retention rate at 25℃, the better the room temperature cycle performance of lithium-ion batteries at high rates.

[0088] (4) High-temperature storage performance test at 60℃

[0089] The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 2 hours to allow it to reach a constant temperature. It was then charged at a constant current of 1.0C to a voltage of 4.45V, followed by constant voltage charging at 4.45V until the cutoff current was 0.05C. Afterward, it was discharged at a constant current of 1.0C to a voltage of 3.0V. This cycle was repeated 5 times. Then, the battery was charged at a constant current of 1.0C to a voltage of 4.45V, followed by constant voltage charging at 4.45V until the cutoff current was 0.05C. The thickness d1 of the lithium-ion battery at this point was measured. The fully charged battery was then placed in a 60°C constant temperature chamber for 30 days. After storage, the lithium-ion battery was left to stand in a 25°C constant temperature chamber for 2 hours. After this period, the thickness d2 of the lithium-ion battery was measured.

[0090] Thickness expansion rate (%) after 30 days of storage at 60℃ = (d2-d1) / d1×100%. The lower the thickness expansion rate, the fewer side reactions the lithium-ion battery has during high-temperature storage, and the better the high-temperature storage performance of the lithium-ion battery.

[0091] The performance test results of the lithium-ion batteries prepared in the aforementioned embodiments and comparative examples are shown in Table 2.

[0092] Table 2

[0093]

[0094] Results analysis:

[0095] Comparative Example 1 used no additives, Comparative Example 2 used conventional phosphate ester additives, and Comparative Example 3 used conventional sulfur-based additives. As shown in Table 2, compared with the comparative examples, the lithium-ion batteries prepared in Examples 1-37 all exhibited higher oxidation potentials, lower DCRs, and better cycle performance, demonstrating the superior performance of the novel additives provided in this application.

[0096] In Example 28, the amount of additive used was relatively low, which slightly reduced the effect of the additive on improving battery performance. In Example 35, the amount of additive used was relatively high. Although it increased the oxidation potential of the electrolyte to a certain extent, the additive's participation in film formation increased the battery impedance, thereby slightly reducing the battery performance.

[0097] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0098] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An electrolyte with high-voltage stability, characterized in that, The electrolyte comprises a solvent and an electrolyte additive. The solvent includes a carbonate solvent. Based on the total mass of the electrolyte, the electrolyte additive accounts for 0.01 wt% to 5 wt% of the total mass of the electrolyte. The chemical formula of the electrolyte additive satisfies aM + 【A(Q) b 】 a- Q and A are linked by a coordinate bond, where a is a positive integer from 1 to 10 and b is a positive integer from 1 to 4, where: M + Selected from metal ions or onium ions; A is selected from at least one of AlCl4, AlBr4, GaCl4, and GaBr4; Q has the structure shown in equation (Ⅰ). Equation (I); Among them, Y1 is selected from either B or P; R1, R2, and R3 are each independently selected from A'(Q'). c c is an integer between 0 and 3, halogen, unsubstituted, or subjected to at least one R a Substituted C1-C8 alkyl or phenyl groups; R a Selected from halogens; A' is selected from at least one of AlCl4, AlBr4, GaCl4, and GaBr4; Q' has the structure shown in equation (II), Formula (II); Among them, Y2 is selected from either B or P; R4, R5, and R6 are each independently selected from A'', halogens, unsubstituted compounds, or compounds modified by at least one R. b Substituted C1-C8 alkyl or phenyl groups; R b Selected from halogens; A'' is selected from at least one of AlCl4, AlBr4, GaCl4, and GaBr4.

2. The electrolyte with high-voltage stability according to claim 1, characterized in that, The M + It includes one of the following: Li ion, Na ion, K ion, Mg ion, Zn ion, and quaternary ammonium ion.

3. The electrolyte with high-voltage stability according to claim 1, characterized in that, The electrolyte additive includes (Ⅰ-1) (Ⅰ-2) (Ⅰ-3) (Ⅰ-4) (Ⅰ-5) (Ⅰ-6) (Ⅰ-7) (Ⅰ-8) (Ⅰ-9) (Ⅰ-10) (Ⅰ-11) (Ⅰ-12) (Ⅰ-13) (Ⅰ-14) (Ⅰ-15) (Ⅰ-16) (Ⅰ-17) (Ⅰ-18) (Ⅰ-19) (Ⅰ-20) (Ⅰ-21) (Ⅰ-22) (Ⅰ-23) (Ⅰ-24) (Ⅰ-25) (Ⅰ-26) At least one of (Ⅰ-27).

4. The electrolyte with high-voltage stability according to claim 1, characterized in that, The preparation method of the electrolyte additive includes: MA and Q are mixed in a solvent to carry out a complexation reaction, thereby obtaining the electrolyte additive. Wherein, M in MA + Selected from metal ions or onium ions; A in MA - Selected from AlCl4 - AlBr4 - GaCl4 - GaBr4 - At least one of them; The Q has the structure shown in equation (Ⅰ). Equation (Ⅰ).

5. The electrolyte with high-voltage stability according to claim 4, characterized in that, The complexation reaction is carried out at a temperature of 20℃-35℃ for a time of 6h-12h.

6. The electrolyte with high-voltage stability according to claim 4, characterized in that, The MA includes at least one of LiAlCl4, LiAlBr4, LiGaCl4, LiGaBr4, NaAlCl4, Mg(AlCl4)2, and Me4N(AlCl4); and / or, The Q includes BF3, BF2CH3, BF(C6H5)2, BF(C6F5)2, BF2C6H5, BF2C6F5, B(CH3)3, B(C6H5)3, B(C6F5)3, BF2C4H9, and BF2C8H. 17 At least one of PF3.

7. A lithium-ion battery, characterized in that, Includes the electrolyte with high-voltage stability as described in any one of claims 1-6.

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