Electrolyte for ternary lithium ion battery and battery

Abstract

The invention relates to the technical field of batteries, in particular to an electrolyte for a ternary lithium ion battery and the battery. The electrolyte comprises a solvent, a lithium salt and a first additive; the first additive comprises a nitrile compound and acesulfamide lithium; the mass content of the nitrile compound in the electrolyte is marked as A%, the mass content of the acesulfamide lithium in the electrolyte is marked as B%, and A is greater than B. The electrolyte provided by the invention can better improve the high-temperature storage stability and cycling stability of the battery under high voltage, and realizes comprehensive improvement of the comprehensive performance of the high-voltage ternary battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to an electrolyte and battery for ternary lithium-ion batteries. Background Technology

[0002] Ternary lithium-ion batteries (such as NCM and NCA) are a key technology in the power and energy storage fields due to their high energy density. However, when high-voltage (≥4.35V) charging strategies are adopted in pursuit of higher energy density, the battery cycle life faces severe challenges.

[0003] High potentials can drastically catalyze the oxidative decomposition of the electrolyte at the cathode surface. After oxidation, the base solvent (such as ethylene carbonate EC) forms an incomplete and unstable cathode-electrolyte interface (CEI) film with high impedance and prone to rupture, failing to effectively prevent ongoing interfacial side reactions. This leads to the absorption of transition metal ions (especially high-valence Ni). 4+ Transition metal ions dissolve from the crystal lattice, accompanied by irreversible loss of lattice oxygen, triggering a transformation of the bulk structure of the cathode material from layered to spinel or rock salt phases, resulting in irreversible capacity loss. The dissolved transition metal ions migrate to the anode, catalyzing the decomposition and regeneration of the solid electrolyte interphase (SEI) film, consuming active lithium, and increasing interfacial impedance, forming a vicious cycle. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and provide an electrolyte and battery for ternary lithium-ion batteries. The electrolyte can stabilize the high-voltage positive electrode and protect the graphite negative electrode, thereby improving the high-temperature storage stability and cycle stability of the battery.

[0005] Introducing nitrile compounds is an effective strategy for stabilizing the high-voltage cathode interface. Nitriles possess high highest occupied molecular orbital (HOMO) energy levels, preferentially undergoing oxidative decomposition over the base solvent at high potentials to generate a dense CEI film rich in nitrides, organic cyanides, and other components, effectively inhibiting continuous electrolyte oxidation and transition metal dissolution. However, this invention has found that nitrile compounds, due to their high lowest unoccupied molecular orbital (LUMO) energy levels, also preferentially undergo reduction reactions over solvents such as ethylene carbonate (EC) at low potentials in the anode (e.g., graphite anode). The reduction products are mainly cyano-containing polymers, resulting in a porous and poorly conductive SEI film that severely hinders lithium-ion transport and accelerates anode capacity decay. Therefore, how to leverage the protective role of nitrile compounds at the cathode without damaging the anode is the core challenge in high-voltage electrolyte design.

[0006] To achieve the above objectives, a first aspect of the present invention provides an electrolyte for a ternary lithium-ion battery, comprising a solvent, a lithium salt, and a first additive; the first additive comprises a nitrile compound and lithium acesulfame potassium; the mass content of the nitrile compound in the electrolyte is denoted as A%, and the mass content of the lithium acesulfame potassium in the electrolyte is denoted as B%, A > B.

[0007] In some of these implementations, A is 5-15.

[0008] In some of these implementations, B is 0.3-1.5.

[0009] In some of these implementations, the ratio of A to B is 5-20.

[0010] In some of these embodiments, the mass content A% of the nitrile compound in the electrolyte satisfies formula (1). Equation (1), In equation (1), C represents the proportion of the number of moles of nickel in the ternary positive electrode active material of the ternary lithium-ion battery to the total number of moles of all metal elements other than lithium.

[0011] In some of these embodiments, the mass content B% of the lithium acesulfame potassium in the electrolyte satisfies equation (2). B=[0.07+0.02sin(πC)]A+γ(C−0.5) 2 Equation (2), In formula (2), C is the proportion of the number of moles of nickel in the ternary positive electrode active material contained in the ternary lithium-ion battery to the total number of moles of all metal elements other than lithium. When C≤0.7, γ=2; when C>0.7, γ=3.

[0012] The mass content B% of lithium acesulfame potassium in the electrolyte satisfies equation (2). B=[0.07+0.02sin(πC)]A+γ(C−0.5) 2 Equation (2), In formula (2), C is the proportion of the number of moles of nickel in the ternary positive electrode active material contained in the ternary lithium-ion battery to the total number of moles of all metal elements other than lithium. When C≤0.7, γ=2; when C>0.7, γ=3.

[0013] In some embodiments, the electrolyte also includes a second additive.

[0014] In some of these embodiments, the second additive comprises at least one selected from vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, vinyl sulfate, propylene sulfite, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, methanedisulfonate, tris(trimethylsilyl)boronic acid ester, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, and tetravinylsilane.

[0015] In some embodiments, the second additive has a mass content of 0.5%-5% in the electrolyte.

[0016] In some of these embodiments, the nitrile compound contains 1-3 nitrile groups.

[0017] In some of these embodiments, the nitrile compounds include chain-like aliphatic cyanoethyl ethers and / or alkane nitriles.

[0018] In some of these embodiments, the chain-like aliphatic cyanoethyl ether comprises 1,2-di(cyanoethoxy)ethane and / or glycerol trinitrile.

[0019] In some of these embodiments, the alkane nitrile includes C2-C10 alkane nitrile.

[0020] In some embodiments, the lithium salt includes at least one of LiPF6, LiN(SO2F)2, LiBF4, LiN(CF3SO2)2, LiClO4, LiAsF6, LiB(C2O4)2, LiBF2C2O4, and lithium difluorodioxazophosphate.

[0021] In some embodiments, the concentration of lithium salt in the electrolyte is 0.9 mol / L to 1.2 mol / L.

[0022] In some embodiments, the solvent comprises carbonate compounds, including cyclic carbonates and / or chain carbonates.

[0023] In some of these embodiments, the cyclic carbonate includes ethylene carbonate and / or propylene carbonate.

[0024] In some of these embodiments, the chain carbonate includes at least one of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

[0025] A second aspect of the present invention provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte provided in any of the above embodiments; wherein the positive electrode comprises a ternary positive electrode active material.

[0026] In some embodiments, the ternary cathode active material is LiNi.x Co y Mn z O2, where, 0.5≤x≤0.8, y>0, z>0, x+y+z=1.

[0027] Implementing the technical solution of the present invention has at least the following beneficial effects: The electrolyte in this invention can better improve the high-temperature storage stability and cycle stability of the battery under high voltage, and achieve a comprehensive improvement in the overall performance of high-voltage ternary batteries.

[0028] Although the mechanism is not yet clear, it is preliminarily speculated that by combining nitrile compounds with lithium acesulfame potassium and controlling the content of nitrile compounds in the electrolyte to be greater than the content of acesulfame potassium in the electrolyte, the problem of battery interface synergistic failure can be solved, the interface film performance can be optimized, and thus the overall performance of the battery can be improved. Detailed Implementation

[0029] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such 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.

[0030] The first aspect of the present invention provides an electrolyte for a ternary lithium-ion battery, comprising a solvent, a lithium salt, and a first additive; The first additive contains nitrile compounds and lithium acesulfame potassium; The mass content of the nitrile compound in the electrolyte is denoted as A%, and the mass content of the lithium acesulfame potassium in the electrolyte is denoted as B%, where A > B.

[0031] The electrolyte in this invention can better improve the high-temperature storage stability and cycle stability of the battery, achieving a comprehensive improvement in the overall performance of high-voltage ternary batteries. Specifically, in this invention, under high voltage, nitrile compounds have a high HOMO energy level and can preferentially undergo electrochemical oxidation decomposition on the cathode surface compared to the basic solvent (such as EC). Their decomposition products (such as cyanides, nitrides, unsaturated nitrile polymers, etc.) are co-deposited on the surface of the cathode material particles, forming a dense, stable, nitrogen-rich CEI film. This film has excellent electronic insulation and ion conductivity, effectively isolating the electrolyte from direct contact with the highly active delithiated cathode material, significantly suppressing the continuous oxidation decomposition of the electrolyte, the dissolution of transition metal ions, and the resulting lattice oxygen loss and phase transition, thereby stabilizing the cathode interface structure.

[0032] The molecular structural formula of lithium acesulfame potassium is: .

[0033] Furthermore, during the initial charging process, when the potential drops to the operating range of the negative electrode, lithium acesulfame potassium, with its higher LUMO energy level (i.e., lower reduction potential) compared to nitrile compounds, preferentially undergoes a reduction reaction on the negative electrode surface. The sulfonyl group (-SO2-) in its molecule breaks down, generating inorganic lithium salts such as Li2SO3 and Li2S. Simultaneously, its nitrogen-containing heterocyclic structure participates in the reaction, forming components with high ionic conductivity, such as Li3N. These products collectively construct a dense and robust primary SEI film dominated by high ionic conductivity inorganic lithium salts. This high-quality primary SEI film is not only thermodynamically and kinetically stable but also serves as a "physical barrier" and "template," fundamentally altering the reaction pathway of subsequent nitrile compounds at the negative electrode interface. When nitrile compound molecules diffuse to the negative electrode, their reduction and decomposition reactions are confined to the outside or pores of the already formed dense primary SEI film. Therefore, the cyano-containing polymers generated from the reduction of nitrile compounds no longer serve as the main body for SEI film formation (otherwise, a poor-quality film would be formed), but instead act as a filler and reinforcing material, deposited on the framework or within the pores of the primary SEI film. This "sacrificial preferential film formation" mechanism successfully transforms the negative decomposition of nitrile compounds on the negative electrode side into a benign modification and enhancement of the existing high-quality SEI film, ultimately synergistically constructing a composite SEI layer with high ionic conductivity, good mechanical strength, and a dense and uniform structure.

[0034] Furthermore, during long-term cycling, especially in the later stages of high-voltage cycling, the positive electrode CEI film may experience localized rupture, leading to the release of transition metal ions (such as Ni). 2+ Co 2+ Mn 2+ Dissolution. The decomposition products of lithium acesulfame potassium or their residual nitrogen-containing heterocyclic structures can effectively complex these dissolved transition metal ions through coordination, "anchoring" them to the positive electrode side or the electrolyte, significantly inhibiting their migration to the negative electrode. This mechanism can cut off the pathway of transition metal ions catalyzing the destruction of the SEI film at the negative electrode, providing another dimension of protection.

[0035] The high dielectric constant of nitrile compounds can simultaneously address the low solubility of lithium acesulfame in carbonate solvents. Furthermore, controlling the content of nitrile compounds in the electrolyte to be greater than that of acesulfame can ensure a sufficient dosage of nitrile compounds, the main film-forming material at the positive electrode, thereby constructing a sufficiently dense and stable CEI film and suppressing high-voltage oxidation side reactions and metal ion dissolution at the source. Simultaneously, the preferentially reduced lithium acesulfame forms a high-quality inorganic primary SEI film as a "skeleton template," while the reduction products of the larger amount of nitrile compounds can fully serve as "filling materials," reinforcing and modifying the skeleton, ultimately forming a high-performance composite SEI layer with an ideal gradient structure. Therefore, controlling the content of nitrile compounds in the electrolyte to be greater than that of acesulfame can construct a high-voltage stable positive electrode CEI and negative electrode composite SEI, fundamentally solving the problem of interfacial synergistic failure.

[0036] According to the present invention, in some embodiments, A is 5-15, for example, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a range consisting of any two of the above values.

[0037] By controlling the value of A within the above-mentioned range in this invention, the continuous oxidative decomposition of the electrolyte can be more effectively suppressed, thereby improving the stability of the battery interface and the cycle life.

[0038] According to the present invention, in some embodiments, B is 0.3-1.5, for example, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, or a range consisting of any two of the above values.

[0039] By controlling the value of B within the above-mentioned range in this invention, the cycle stability and safety performance of the battery can be significantly improved, while ensuring that the battery has low impedance, thereby achieving higher energy density and better charge and discharge performance.

[0040] According to the present invention, in some embodiments, the ratio of A to B is 5-20, for example 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, preferably 8-15.

[0041] In this invention, by controlling the ratio of A to B within the aforementioned range, the electrolyte can better construct a stable positive electrode CEI and a negative electrode composite SEI in ternary lithium-ion batteries. It can achieve a balance between interface protection performance and battery long-cycle stability within a wide range of nickel content, thereby better increasing the overall performance of the battery.

[0042] According to some embodiments of the present invention, the mass content A% of the nitrile compound in the electrolyte satisfies formula (1). Equation (1), In equation (1), C represents the proportion of the number of moles of nickel in the ternary positive electrode active material of the ternary lithium-ion battery to the total number of moles of all metal elements other than lithium.

[0043] Although the mechanism is not yet clear, this invention unexpectedly discovered that controlling the amount of nitrile compound added (A%) and the nickel content (C) of the cathode to satisfy the above-mentioned formula allows for maximizing the interface stability of high-voltage ternary batteries and significantly increasing cycle life in high-voltage electrolysis across a wide range of nickel contents. The above formula is an S-shaped function, specifically defining the allowable range of A as a function of C. Its lower limit ensures the minimum effective protection strength for the cathode, with the lower limit value increasing rapidly near the medium nickel region (C~0.65) to cope with the significant increase in oxidation. The upper limit prevents excessive nitrile compounds from causing excessively high electrolyte viscosity and decreased conductivity, and avoids excessive decomposition that is difficult to manage even in the presence of acesulfame potassium, leading to excessively thick interfacial films and increased lithium-ion migration resistance.

[0044] According to the present invention, in some embodiments, C in formula (1) is 0.5-0.8, for example, 0.5, 0.6, 0.7, 0.8, and there is no specific limitation.

[0045] The electrolyte in this invention ensures balanced and optimal interfacial stability and cycle life for all battery models, from basic nickel to ultra-high nickel. For example, it can cover ternary cathode active materials such as LiNi. 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.7 Co 0.1 Mn 0.2 O2 (NCM712), LiNi 0.8 Co 0.1 Mn 0.1 Mainstream materials such as O2 (NCM811). That is, the above formula provided by this invention can guide high-voltage electrolytes with a wide nickel content range from NCM523 to NCM811 to achieve excellent cycle life.

[0046] According to some embodiments of the present invention, the mass content B% of the lithium acesulfame potassium in the electrolyte satisfies formula (2). B=[0.07+0.02sin(πC)]A+γ(C−0.5) 2 Equation (2), In formula (2), C is the proportion of the number of moles of nickel in the ternary positive electrode active material contained in the ternary lithium-ion battery to the total number of moles of all metal elements other than lithium. When C≤0.7, γ=2; when C>0.7, γ=3.

[0047] Although the mechanism is not yet clear, this invention unexpectedly discovered that controlling the addition amount of lithium acesulfame potassium (B%), the addition amount of nitrile compounds (A%), and the nickel content of the cathode (C) to satisfy the above-mentioned relationship formula allows for the maximization of interface stability and a significant increase in cycle life of high-voltage ternary batteries in high-voltage electrolytes across a wide range of nickel content. In formula (2), the dynamic proportional term [0.07+0.03sin(πC)]A reflects the influence of the periodic oscillation of the electronic structure of the cathode material with C on the coupling strength of the positive and negative electrode interfaces, and needs to be further dynamically fine-tuned in conjunction with the ratio of B to A. γ can be called the dissolution risk coefficient, and the nickel risk square term γ(C-0.5) 2 Nonlinear quantification of transition metal leaching risk: When C>0.7 enters the high nickel region, the coefficient γ jumps from 2 to 3, marking a shift in protection strategy from "conventional suppression" to "enhanced anchoring" mode to cope with the suddenly increased leaching damage.

[0048] According to the present invention, in some embodiments, C in formula (2) is 0.5-0.8, for example, 0.5, 0.6, 0.7, 0.8, and there is no specific limitation.

[0049] Furthermore, in some embodiments, it is preferred that the mass content of the nitrile compound in the electrolyte in the present invention is denoted as A%, and the mass content of lithium acesulfame potassium in the electrolyte is B%, both satisfying equations (1) and (2). Based on the precise design system of nonlinearly customized additives (A, B) for the positive electrode nickel content (C), the electrolyte and electrode materials can be adapted at the "genetic level". Through the sequential reaction and functional synergy of the addition amount A%, B% corresponding to the first additive, a high-voltage stable positive electrode CEI and a negative electrode composite SEI are constructed simultaneously, fundamentally solving the problem of interface synergistic failure. Thus, the electrolyte in the present invention can accurately guide the formulation of high-voltage electrolytes within a wide range of nickel content, and all can achieve excellent cycle life.

[0050] According to the present invention, "nitrile compound" refers to a compound containing a nitrile group (-CN), that is, a nitrile compound contains at least one nitrile group. In some embodiments, the nitrile compound contains 1-3 nitrile groups; in some embodiments, the nitrile compound includes chain-like aliphatic cyanoethyl ethers and / or alkane nitriles. The nitrile compounds of the present invention have sufficiently high HOMO energy levels, enabling them to preferably undergo electrochemical oxidative decomposition on the cathode surface. Simultaneously, they exhibit excellent solubility and chemical stability in the electrolyte, and better compatibility with the primary SEI film formed with lithium acesulfame potassium, thereby achieving better synergistic film formation and increasing the overall performance of the battery.

[0051] According to the present invention, in some embodiments, the chain-like aliphatic cyanoethyl ether comprises 1,2-di(cyanoethoxy)ethane and / or glycerol trinitrile.

[0052] According to the present invention, in some embodiments, the alkane nitrile includes C2-C10 alkane nitrile, preferably including at least one of acetonitrile, butadiene nitrile and adiponitrile.

[0053] According to the present invention, conventional additives in the art can be introduced into the electrolyte as needed to further enhance battery performance. In some embodiments, the electrolyte further includes a second additive, which includes at least one selected from the following: vinylene carbonate (VC), ethylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinyl sulfate (DTD), propylene sulfite, 1,3-propanesulfonate lactone (PS), 1,4-butanesulfonate lactone (BS), methanedisulfonate methylene ester (MMDS), tris(trimethylsilyl)boronic acid ester, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, and tetravinylsilane. The second additive can further optimize the composition and properties of the SEI / CEI membrane, synergistically enhancing the overall performance of the battery in conjunction with the first additive system of the present invention.

[0054] According to the present invention, the content of the second additive in the electrolyte can be a conventional content in the art. In some embodiments, the mass content of the second additive in the electrolyte is 0.5%-5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. Controlling the appropriate amount of the second additive can further optimize the composition and properties of the SEI / CEI film, thereby improving the electrochemical performance of the battery.

[0055] As an example, the second additive is vinylene carbonate (VC) and vinyl sulfate (DTD) in a mass ratio of 1:2.

[0056] According to the present invention, lithium salt refers to a lithium salt used to provide lithium ions in an electrolyte. The specific selection of lithium salt is not particularly limited as long as the purpose of the present invention is achieved; it can be any lithium salt known in the art. In some embodiments, the lithium salt includes at least one of LiPF6, LiN(SO2F)2 (LiFSI), LiBF4, LiN(CF3SO2)2 (LiTFSI), LiClO4, LiAsF6, LiB(C2O4)2 (LiBOB), LiBF2C2O4 (LiDFOB), and lithium difluorodioxalate phosphate (LiDFOP).

[0057] The use of the above-mentioned lithium salt in this invention can better improve the electrochemical performance of the battery.

[0058] As an example, the lithium salt is LiPF6.

[0059] According to the present invention, the lithium salt content in the electrolyte can be selected within a wide range, as long as the objective of the present invention is achieved. In some embodiments, the concentration of lithium salt in the electrolyte is 0.9 mol / L-1.2 mol / L, for example, 0.90 mol / L, 0.95 mol / L, 1 mol / L, 1.05 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, etc., and there is no specific limitation. Controlling the lithium salt within a suitable range can ensure that the battery has a stable and efficient ion transport environment, thereby improving the overall performance of the battery.

[0060] According to the present invention, the type of solvent in the electrolyte is not particularly limited and can be any non-aqueous solvent in the art. In some embodiments, the solvent includes carbonate compounds.

[0061] According to the present invention, in some embodiments, the carbonate compounds include cyclic carbonates and / or chain carbonates.

[0062] According to the present invention, in some embodiments, the cyclic carbonate includes ethylene carbonate (EC) and / or propylene carbonate (PC).

[0063] According to some embodiments of the present invention, the chain carbonate includes at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC).

[0064] The solvent described above in this invention is beneficial to the stability of the battery during operation, thereby improving the overall performance of the battery.

[0065] As an example, the solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), wherein the volume percentage of ethylene carbonate (EC) in the solvent is 15%-25%, the volume percentage of ethyl methyl carbonate (EMC) in the solvent is 50%-70%, and the volume percentage of diethyl carbonate (DEC) in the solvent is 5%-15%.

[0066] The preparation method of the electrolyte in this invention is not particularly limited; it is sufficient to mix the various components of the electrolyte evenly.

[0067] According to the present invention, in some embodiments, the voltage range of the electrolyte is: the upper limit cutoff voltage of the lithium-ion battery is 4.3V-4.5V, for example 4.3V, 4.35V, 4.4V, 4.45V, 4.5V.

[0068] A second aspect of the present invention provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte provided in any of the above embodiments; wherein the positive electrode comprises a ternary positive electrode active material.

[0069] The battery of this invention contains the above-mentioned electrolyte and has excellent high-temperature storage stability and cycle life.

[0070] According to the present invention, those skilled in the art will understand that "ternary cathode active material" refers to a layered oxide composed of lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), or aluminum (Al), with common systems being lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA). In some embodiments, the ternary cathode active material is LiNi x Co y Mn z O2, where 0.5 ≤ x ≤ 0.8, y > 0, z > 0, and x + y + z = 1. Examples of ternary cathode active materials include LiNi. 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.7 Co 0.1 Mn 0.2 O2 (NCM712), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), etc.

[0071] The materials and preparation methods of the battery described in this invention, excluding the electrolyte and ternary cathode active material, can be carried out in accordance with the practices in this field, and all can achieve high cycle stability and low expansion rate.

[0072] According to the present invention, in some embodiments, the positive electrode sheet includes a positive current collector and a positive active layer comprising a ternary positive active material located on one or both sides of the surface of the positive current collector.

[0073] According to some embodiments of the present invention, the ternary positive electrode active material has a mass content of 80%-99.8% in the positive electrode active layer.

[0074] According to the present invention, in some embodiments, the positive electrode active layer further includes a positive electrode conductive agent and a positive electrode binder. Both the positive electrode conductive agent and the positive electrode binder can be materials known in the art. As examples, the positive electrode conductive agent includes, but is not limited to, at least one of graphite, carbon nanotubes, nanofibers, conductive carbon black, and graphene. As examples, the positive electrode binder includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), hydrogenated nitrile rubber, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and sodium polyacrylate (PAAS).

[0075] According to the present invention, in some embodiments, the mass content of the positive electrode conductive agent in the positive electrode active layer is 0.1%-10%, for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, and there is no specific limitation.

[0076] According to the present invention, in some embodiments, the mass content of the positive electrode binder in the positive electrode active layer is 0.1%-10%, for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, and there is no specific limitation.

[0077] According to the present invention, the positive current collector can be a metal foil or a composite current collector known in the art. For example, aluminum foil can be used as the metal foil.

[0078] According to the present invention, in some embodiments, the method for preparing the positive electrode sheet includes: dispersing a ternary positive electrode active material, optionally a positive electrode conductive agent and optionally a positive electrode binder in a solvent (e.g., N-methylpyrrolidone NMP) to obtain a positive electrode slurry with a solid content of 50wt%-70wt%, then coating the positive electrode slurry onto at least one surface of a positive electrode current collector, and obtaining the positive electrode sheet through processes such as drying and cold pressing.

[0079] According to the present invention, in some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer containing a negative electrode active material located on one or both sides of the surface of the negative electrode current collector. The aforementioned negative electrode active material can be any negative electrode active material known in the art, including graphite-based materials such as artificial graphite and natural graphite.

[0080] According to the present invention, in some embodiments, the mass content of the negative electrode active material in the negative electrode active layer is 70%-99.8%, for example, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.8%, and there is no specific limitation.

[0081] According to the present invention, in some embodiments, the negative electrode active layer further includes a negative electrode conductive agent and a negative electrode binder. Both the negative electrode conductive agent and the negative electrode binder can be materials known in the art. As an example, the negative electrode conductive agent includes, but is not limited to, at least one of graphite, carbon nanotubes, nanofibers, conductive carbon black, and graphene. As an example, the negative electrode binder includes, but is not limited to, at least one of styrene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), and polymethacrylic acid (PMAA).

[0082] According to the present invention, in some embodiments, the mass content of the negative electrode conductive agent in the negative electrode active layer is 0.1%-10%, for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, and there is no specific limitation.

[0083] According to the present invention, in some embodiments, the mass content of the negative electrode binder in the negative electrode active layer is 0.1%-10%, for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, and there is no specific limitation.

[0084] According to the present invention, in some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners, such as carboxymethyl cellulose (CMC). The mass content of the other additives in the negative electrode active layer is 0%-10%.

[0085] According to the present invention, the negative electrode current collector can be a metal foil or a composite current collector known in the art. For example, copper foil can be used as the metal foil.

[0086] According to some embodiments of the present invention, the method for preparing the negative electrode sheet includes: mixing a negative electrode active material, optionally a negative electrode conductive agent, optionally a negative electrode binder, optionally a thickener and water (preferably deionized water) uniformly to obtain a negative electrode slurry with a solid content of 40wt%-55wt%, then coating the negative electrode slurry onto at least one surface of a negative electrode current collector, and obtaining a negative electrode sheet through processes such as drying and cold pressing.

[0087] According to the present invention, the separator is disposed between the positive electrode and the negative electrode. The separator in the present invention can be any porous structure separator with good chemical and mechanical stability known in the art, including but not limited to: polyethylene separator.

[0088] According to the present invention, the battery can be assembled according to assembly methods known in the art. As an example, the positive electrode, negative electrode, and separator can be formed into an electrode assembly by a winding process or a stacking process; the battery may include an outer packaging for encapsulating the aforementioned electrode assembly and electrolyte, and the outer packaging of the battery can be a hard plastic shell or a soft pack.

[0089] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0090] Example 1 Preparation of positive electrode sheet: The ternary positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) in a mass ratio of 98:1:1 are mixed evenly to obtain a positive electrode slurry with a solid content of 65wt%. The positive electrode slurry is coated on two surfaces of a 10μm aluminum foil, and the positive electrode sheet is obtained by drying, cold pressing and other processes.

[0091] Preparation of negative electrode sheet: The negative electrode active materials artificial graphite, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNT) and carboxymethyl cellulose (CMC) are mixed in a mass ratio of 96:2.4:0.5:0.5:0.6. Then, deionized water is added as a solvent and stirred evenly to obtain a negative electrode slurry with a solid content of 45wt%. The negative electrode slurry is coated on two surfaces of a 6μm thick copper foil. After drying, cold pressing and other processes, the negative electrode sheet is obtained.

[0092] Separator: Polyethylene diaphragm.

[0093] Electrolyte: EC:EMC:DEC in a volume ratio of 20:65:15 is used as the solvent. The electrolyte contains 0.5 wt% vinylene carbonate (VC), 1 wt% vinyl sulfate (DTD), a certain amount of nitrile compounds, and a certain amount of lithium acesulfame potassium.

[0094] Battery fabrication: Using the above-mentioned positive electrode, negative electrode, separator and electrolyte, a soft-pack full battery with a rated capacity of 2Ah is assembled according to the battery assembly process.

[0095] Examples 2-11, Comparative Examples 1-3 Batteries were prepared using a method similar to that of Example 1, except that the electrolyte compositions in Examples 2-11 differed from those in Example 1, and the types of ternary cathode active materials in some examples also differed from those in Example 1. Table 1 shows the types of nitrile compounds, their content in the electrolyte, the content of lithium acesulfame potassium in the electrolyte, and the types of ternary cathode active materials in Examples 2-11, Comparative Examples 1-3.

[0096] Table 1 Performance testing The following performance tests were performed on the batteries in Examples 1-11 and Comparative Examples 1-3 respectively: 1. Cyclic performance: At a cutoff voltage of 4.35V, 1C / 1C charge-discharge cycle tests were conducted at 25℃, and the capacity retention rate was recorded after 1000 cycles.

[0097] 2. High-Temperature Storage Performance: The battery was charged to 4.35V at a constant current of 1C at 25℃, and then stored at a high temperature of 60℃ for 7 days. After storage, the battery volume expansion rate at full charge was measured at 25℃, and then discharged to 2.8V at 1C to calculate the capacity recovery rate.

[0098] The test results are shown in Table 2.

[0099] Table 2 As shown in Table 2, the battery of this invention exhibits optimal cycle performance while maintaining the highest high-temperature storage capacity recovery rate. Furthermore, the electrolyte of this invention maintains excellent performance under high nickel and high voltage conditions. Comparative Examples 1-3 demonstrate that the battery performance deteriorates comprehensively when nitrile compounds and / or lithium acesulfame potassium are lacking in the electrolyte, confirming the indispensability of the synergistic mechanism between nitrile compounds and lithium acesulfame potassium. In particular, the batteries in Examples 1-4 of this invention exhibit optimal cycle performance while also demonstrating better high-temperature storage capacity recovery rates (90.3%-94.1%) and the smallest volume expansion rate (8.5%-11.2%). This directly proves that the CEI / SEI composite interface layer constructed in this invention possesses excellent thermal stability and structural integrity, effectively suppressing the continuous decomposition and gas generation of the electrolyte at high temperatures. For the verification of high-temperature storage performance: high-temperature storage tests rigorously evaluated the thermal stability and gas generation behavior of the interface film. The batteries in the examples, especially Examples 1-4, exhibited the highest capacity recovery rate and the lowest thickness expansion rate, indicating that the interface film formed by the present invention can effectively suppress the continuous decomposition and gas generation of the electrolyte at high temperatures. Conversely, insufficient protection or excessively thick interfaces resulted in lower capacity recovery and greater swelling.

[0100] In Examples 5 and 6, the mass content of nitrile compounds in the electrolyte that does not satisfy the above formula (1) is not met. The storage performance of the batteries was worse than that of Examples 1-4, which proves that the upper and lower limits of the mass content A% of nitrile compounds in the electrolyte can better balance the positive electrode protection and the overall interface stability. The reason is that if the value of A is lower than the lower limit of the above formula, it will lead to insufficient positive electrode protection, resulting in increased dissolution and decreased storage performance; if the value of A is higher than the upper limit of the above formula, it will lead to an excessively thick interface film, increased gas generation during storage, and decreased performance.

[0101] In Example 7, the mass content (B%) of lithium acesulfame potassium in the electrolyte was insufficient, resulting in a decrease in the battery's storage performance compared to Examples 1-4. This indicates that precise fine-tuning of the dynamic ratio term is necessary for constructing the optimal negative electrode interface. The reason for this is that the insufficient mass content (B%) of lithium acesulfame potassium in the electrolyte weakens the confinement effect on nitrile compounds, leading to a decrease in the quality of the negative electrode SEI.

[0102] In Example 8, the mass content B% of lithium acesulfame potassium in the electrolyte does not satisfy B=[0.07+0.02sin(πC)]A+γ(C−0.5) 2 Specifically, the nickel risk square term γ(C-0.5) is missing. 2 The battery performance is reduced to some extent because the cumulative effect of dissolved ions appears in the later stages of cycling, and the capacity recovery after storage is slightly lower.

[0103] In Example 9, the mass content of lithium acesulfame potassium in the electrolyte was B%, where B = [0.07 + 0.02sin(πC)]A + γ(C − 0.5). 2 B was calculated using the γ value (0.2) in the low-nickel region. The battery performance deteriorated to some extent compared to Examples 1-4. This was attributed to insufficient complexation capacity at high nickel levels, leading to dissolved ions damaging the SEI, resulting in severe gas generation during storage and poor capacity recovery. Furthermore, for high-nickel materials with C > 0.7, B = [0.07 + 0.02sin(πC)]A + γ(C − 0.5) 2 The jump in the γ coefficient from 2 to 3 in the formula is a decisive design feature to ensure the stability of high-temperature storage, and is by no means a simple adjustment.

[0104] Examples 10 and 11 simply fixed the ratio of the mass content A% of nitrile compounds in the electrolyte to the mass content B% of lithium acesulfame potassium in the electrolyte, and the performance of their batteries was worse than that of Examples 1 to 4.

Claims

1. An electrolyte for ternary lithium-ion batteries, characterized in that, The electrolyte contains a solvent, a lithium salt, and a first additive; the first additive contains a nitrile compound and lithium acesulfame potassium; the mass content of the nitrile compound in the electrolyte is denoted as A%, and the mass content of the lithium acesulfame potassium in the electrolyte is denoted as B%, where A > B.

2. The electrolyte according to claim 1, characterized in that, A is 5-15; And / or, B is 0.3-1.5; And / or, the ratio of A to B is 5-20.

3. The electrolyte according to claim 1 or 2, characterized in that, The mass content A% of the nitrile compound in the electrolyte satisfies formula (1). Equation (1), Equation (1), C is the proportion of the number of moles of nickel in the ternary positive electrode active material contained in the ternary lithium-ion battery to the total number of moles of all metal elements other than lithium. And / or, the mass content B% of the lithium acesulfame potassium in the electrolyte satisfies equation (2). B=[0.07+0.02sin(πC)]A+γ(C−0.5) 2 formula (2), In formula (2), C is the proportion of the number of moles of nickel in the ternary positive electrode active material contained in the ternary lithium-ion battery to the total number of moles of all metal elements other than lithium. When C≤0.7, γ=2; when C>0.7, γ=3.

4. The electrolyte according to claim 1 or 2, characterized in that, The electrolyte also includes a second additive; The second additive includes at least one of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, vinyl sulfate, propylene sulfite, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, methanedisulfonate methylene, tris(trimethylsilyl)boronic acid ester, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, and tetravinylsilane. The second additive has a mass content of 0.5%-5% in the electrolyte.

5. The electrolyte according to claim 1 or 2, characterized in that, The nitrile compounds contain 1-3 nitrile groups; And / or, the nitrile compounds include chain-like aliphatic cyanoethyl ethers and / or alkane nitriles.

6. The electrolyte according to claim 5, characterized in that, The chain-like aliphatic cyanoethyl ether comprises 1,2-di(cyanoethoxy)ethane and / or triglycerides; And / or, the alkane nitrile includes C2-C10 alkane nitrile.

7. The electrolyte according to claim 1 or 2, characterized in that, The lithium salt includes at least one of LiPF6, LiN(SO2F)2, LiBF4, LiN(CF3SO2)2, LiClO4, LiAsF6, LiB(C2O4)2, LiBF2C2O4 and lithium difluorodioxanol phosphate; And / or, the concentration of lithium salt in the electrolyte is 0.9 mol / L-1.2 mol / L; And / or, the solvent includes carbonate compounds, which include cyclic carbonates and / or chain carbonates.

8. The electrolyte according to claim 7, characterized in that, The cyclic carbonates include ethylene carbonate and / or propylene carbonate; And / or, the chain carbonate includes at least one of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

9. A battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of claims 1-8; the positive electrode comprises a ternary positive electrode active material.

10. The battery according to claim 9, characterized in that, The ternary cathode active material is LiNi. x Co y Mn z O2, where, 0.5≤x≤0.8, y>0, z>0, x+y+z=1.

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