Lithium ion secondary battery

Abstract

This invention relates to the field of battery technology, specifically to a lithium-ion secondary battery. It includes a positive electrode, a negative electrode, and a separator. The positive electrode comprises a ternary cathode material, and the negative electrode comprises a silicon-carbon material. The silicon-carbon material includes a shell and a cavity formed by the shell. The cross-sectional porosity θ of the silicon-carbon material is 1%-20%, and the maximum Feret diameter of the cavity is D1. The separator includes a substrate layer and a coating located on at least one surface of the substrate layer, the coating at least facing the negative electrode. The coating comprises barium titanate particles, the average particle size of which is D2; wherein 0.03 ≤ D2 / D1 ≤ 1. This invention can significantly improve the battery's cycle stability, high-temperature storage performance, and furnace temperature safety performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and specifically to a lithium-ion secondary battery. Background Technology

[0002] With the rapid development of electric vehicles and consumer electronics, higher demands are being placed on the energy density of lithium-ion batteries. Among these, ternary cathode materials and silicon-carbon materials have become research hotspots for cathode and anode materials due to their high theoretical specific capacity, and are considered key materials for improving energy density. However, silicon-carbon materials undergo dramatic volume expansion (exceeding 300%) during charge and discharge, leading to cracking of the anode active layer, pulverization of active particles, and repeated rupture and regrowth of the solid electrolyte interphase (SEI) film. This continuously consumes electrolyte and lithium source, severely impacting the battery's cycle life.

[0003] Existing technologies employ hollow silicon-carbon materials, which buffer volume expansion through pre-reserved cavities, effectively improving battery cycle stability. However, the surface of silicon-carbon materials is typically more hydrophilic than other conventional anode materials (such as graphite), and the cavities physically adsorb and "lock in" some moisture during electrode fabrication. This moisture cannot be completely removed by conventional vacuum baking processes and readily reacts with lithium salts (such as LiPF6) in the electrolyte to generate HF, which in turn corrodes the cathode, deteriorating the battery's high-temperature storage performance, high-temperature cycle performance, and furnace temperature safety performance. Summary of the Invention

[0004] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a lithium-ion secondary battery. The lithium-ion secondary battery of this invention (hereinafter referred to as the battery) improves the positive and negative electrode plates and the separator, effectively suppressing the damage to the battery caused by introduced moisture while utilizing the excellent expansion buffering capacity of the silicon-carbon material's cavity structure. This ensures that the battery simultaneously possesses excellent high-temperature storage performance, high-temperature cycle performance, and furnace temperature safety performance.

[0005] Based on the above problems, the inventors conducted extensive targeted research and discovered: By applying a coating containing barium titanate particles to the surface of the separator, a synergistic effect can be achieved with the cavity-containing silicon-carbon material. This effectively solves the problem of additional moisture introduced by the hydrophilicity of silicon-carbon material and the water-locking effect of the cavity, and inhibits the generation of HF and the occurrence of side reactions. The reason is that barium titanate particles (BTO), as a typical ferroelectric material, have highly polar titanate ions that can preferentially remove free water molecules migrating from the negative electrode side or remaining in the electrolyte through a combination of physical adsorption and chemical capture. Within the battery's operating or storage temperature range, barium titanate particles exhibit spontaneous polarization characteristics, and their internal permanent electric dipole moment can strongly anchor polar water molecules and harmful anions (such as OH-). - F -Furthermore, the weak alkalinity of barium titanate particles can locally neutralize small amounts of acidic substances (such as HF), reducing their concentration and minimizing their corrosion of the positive electrode and damage to the SEI film. Under high-temperature conditions, side reactions intensify, and BTO can continuously capture water molecules and byproducts that are more active at high temperatures, significantly improving the battery's high-temperature storage performance, high-temperature cycle performance, and furnace temperature safety performance.

[0006] Furthermore, this invention also regulates the average particle size D2 of barium titanate particles and the maximum Feret diameter D1 of the internal cavity of the silicon-carbon material, ensuring that their ratio meets a specific range to further improve the battery's high-temperature storage performance, high-temperature cycling performance, and furnace temperature safety performance. This is because the moisture released or remaining in the cavity region of the silicon-carbon material needs to be effectively captured by barium titanate particles with sufficiently small particle size and sufficiently large specific surface area. Therefore, D2 should be less than or equal to D1 to ensure that the size of the BTO particles matches the size of the cavity in the silicon-carbon material, allowing the BTO particles to enter or approach the opening of the cavity region for adsorption, ensuring that the BTO particles can effectively contact water molecules and HF, and exert their ferroelectric adsorption and chemical capture functions. If D2 / D1 is too large (e.g., >1), BTO particles, due to their excessive size and small specific surface area, cannot form a sufficiently dense adsorption layer, resulting in poor adsorption capacity. Moisture can penetrate the separator and migrate to the positive electrode side, exacerbating the side reactions between the positive electrode material and the electrolyte, and damaging the stability of the positive electrode structure. At the same time, HF will erode the SEI film, causing the SEI film to repeatedly repair and consume active lithium, ultimately affecting the battery's high-temperature cycle performance, storage life, and safety performance (such as increased risk of high-temperature bulging and thermal runaway). If D2 / D1 is too small (e.g., <0.03), BTO particles, due to their small size, are prone to dispersion and aggregation, blocking the separator pores and hindering lithium-ion transport, leading to increased battery internal resistance and decreased high-temperature cycle performance. In addition, aggregation will also cause uneven coating distribution, weakening the adsorption capacity in local areas, making it unable to effectively capture moisture and HF. Instead, local defects will trigger side reactions, leading to a deterioration in the battery's high-temperature storage performance.

[0007] Based on this, the inventors of this invention propose the following solution: This invention provides a lithium-ion secondary battery, characterized in that it comprises a positive electrode, a negative electrode, and a separator; the positive electrode comprises a positive current collector and a positive active layer located on at least one side surface of the positive current collector, the positive active layer comprising a ternary positive electrode material, the chemical formula of which is LiNi. x Co y M 1 1-x-y M 2 z O2, where 0.3 ≤ x < 1, 0 < y < 0.2, 0 ≤ z ≤ 0.05, M 1 Including Mn and / or Al, M 2The anode material includes at least one of Mg, Ti, Nb, Zr, B, W, P, Na, Fe, Y, La, and Sr; the negative electrode includes a negative current collector and a negative active layer located on at least one side of the negative current collector, the negative active layer comprising a silicon-carbon material, the silicon-carbon material comprising a shell and a cavity formed by the shell, the cross-sectional porosity θ of the silicon-carbon material being 1%-20%, and the maximum Ferete diameter of the cavity being D1; the separator includes a substrate layer and a coating located on at least one side of the substrate layer, the coating comprising barium titanate particles, the average particle size of the barium titanate particles being D2. Wherein, 0.03 ≤ D2 / D1 ≤ 1.

[0008] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: (1) By setting a coating containing barium titanate particles on the surface of the separator, the present invention can play a synergistic role with the cavity structure of silicon carbon material, effectively solving the problem of additional water introduced by the hydrophilicity of silicon carbon material and water locking of cavity, inhibiting the generation of HF, reducing its corrosion of the positive electrode and damage to the SEI film, and reducing the occurrence of side reactions; under high temperature conditions, barium titanate particles can be used to continuously capture water molecules and side reaction products with enhanced activity at high temperature, significantly improving the high temperature storage performance, high temperature cycle performance and furnace temperature safety performance of the battery; (2) By adjusting the average particle size D2 of barium titanate particles and the maximum Feret diameter D1 of the cavity inside the silicon-carbon material, the present invention ensures that the size of barium titanate particles matches the opening size of the cavity in the silicon-carbon material, thereby further improving the high-temperature storage performance, high-temperature cycle performance and furnace temperature safety performance of the battery.

[0009] 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. Attached Figure Description

[0010] Figure 1 The image shown is a scanning electron microscope (SEM) image of the cross-section of the negative electrode in an example of the present invention.

[0011] Figure 2 The image shown is a SEM image of the diaphragm cross section in an example of the present invention.

[0012] Figure 3 The image shown is a SEM image of the diaphragm surface in an example of the present invention. Detailed Implementation

[0013] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0014] This invention provides a lithium-ion secondary battery, comprising a positive electrode, a negative electrode, and a separator; the positive electrode includes a positive current collector and a positive active layer located on at least one side surface of the positive current collector, the positive active layer comprising a ternary positive electrode material with the chemical formula LiNi. x Co y M 1 1-x-y M 2 z O2, where 0.3 ≤ x < 1 (e.g., 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, or 0.99), 0 < y < 0.2 (e.g., 0.01, 0.03, 0.05, 0.07, 0.09, 0.11, 0.13, 0.15, 0.17, or 0.19), 0 ≤ z ≤ 0.05 (e.g., 0, 0.01, 0.02, 0.03, 0.04, or 0.05), M 1 Including Mn and / or Al, M 2 The anode material comprises at least one of Mg, Ti, Nb, Zr, B, W, P, Na, Fe, Y, La, and Sr. The anode sheet includes a negative electrode current collector and a negative electrode active layer located on at least one side of the surface of the negative electrode current collector. The negative electrode active layer comprises a silicon-carbon material, which includes a shell and a cavity formed by the shell. The cross-sectional porosity θ of the silicon-carbon material is 1%-20% (e.g., 1%, 3%, 5%, 7%, 9%, 11%, 13%, 15%, 17%, or 20%). The porosity θ reflects the relative proportion of cavities in the silicon-carbon material. If θ is too small (e.g., <1%), the volume expansion of the silicon-carbon material cannot be effectively buffered; if θ is too large (e.g., >20%), the structural strength of the silicon-carbon material decreases, and excessive moisture remains and locks in the cavities, exacerbating side reactions and affecting the thermal stability of the battery.

[0015] In one example, the cross-sectional porosity θ of the silicon-carbon material is 5%-15%.

[0016] In one instance, 0.8 ≤ x < 1.

[0017] Ternary cathode materials are extremely sensitive to moisture and have a high residual alkali content on their surface, especially high-nickel ternary cathode materials (0.8≤x<1). Compared to ordinary low- and medium-nickel ternary cathode materials, while increasing the nickel content can improve the specific capacity of the cathode material and the energy density of the battery, it also significantly increases the number of surface active sites, resulting in a higher residual alkali content, stronger hygroscopicity, and greater sensitivity to moisture. When moisture adsorbed in the cavities of silicon-carbon materials enters the battery system, it reacts chemically with lithium salts in the electrolyte to generate hydrogen fluoride (HF), which then interacts violently with the high-nickel ternary cathode material. This can easily lead to problems such as lattice collapse, metal ion dissolution, and interface film damage, further corroding the cathode material and current collector, and affecting the thermal stability of the battery. This invention, by using a combination of ternary cathode materials, silicon-carbon materials with cavity structures, and separators containing barium titanate particles, can better reduce the impact of moisture on the cathode, ensuring that the battery has excellent high-temperature cycle performance, furnace temperature safety performance, and high-temperature storage performance.

[0018] In this invention, the maximum Ferete diameter of the cavity is D1; ​​the diaphragm includes a substrate layer and a coating located on at least one side surface of the substrate layer, the coating including barium titanate particles, the average particle size of the barium titanate particles being D2; wherein, 0.03≤D2 / D1≤1 (e.g., 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1).

[0019] In one instance, D1 is 0.5μm-9μm (e.g., 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm or 9μm).

[0020] In one instance, D2 is 0.1μm-1μm (e.g., 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm or 1μm).

[0021] In this invention, the "maximum Feret diameter D1 of the cavity" refers to the perpendicular distance between two parallel lines tangent to the projected profile of the cavity drawn along any measurement direction (0°~180°). Since cavities are typically irregular, their Feret diameter varies with the measurement direction. The maximum Feret diameter D1 represents the maximum value of the Feret diameter measured in all possible measurement directions (0°~180°). Therefore, this value represents the absolute longest dimension that can be detected regardless of how the cavity rotates around its geometric center, accurately characterizing the maximum spatial scale of the cavity.

[0022] In this invention, D1 can be obtained by conventional methods in the art, such as taking microscopic morphology images of silicon-carbon materials using a scanning electron microscope (SEM), importing the images into professional image analysis software (such as Image-ProPlus), simulating the projected contour of the cavity, measuring and calculating the vertical distance between two parallel lines tangent to the cavity contour in each direction, and automatically selecting the maximum value, which is the maximum Feret diameter D1.

[0023] In this invention, D2 can be obtained by conventional methods in the art. For example, after discharging the battery to 0% SOC (e.g., discharging the battery to 2.5V), the separator is disassembled, soaked in dimethyl carbonate (DMC) solvent for 12 hours, and then rinsed with DMC solvent to remove lithium salts adhering to the separator. SEM is used for observation and measurement at 5K magnification. At least 10 barium titanate particles are randomly selected, and the particle size of each particle is measured, and the average value is taken. If the number of particles at 5K magnification is less than 10, more SEM images are taken until 10 barium titanate particles are measured. If the particle is a regular circle in the SEM image, then the particle size is the diameter of that circle. If the particle is not a "regular circle" in the SEM image, then the particle size is the diameter of an equivalent circle with the same area as the "regular circle".

[0024] In this invention, the void ratio θ of the cross-section of the silicon-carbon material refers to the ratio of the cross-sectional area of ​​the cavities to the total cross-sectional area of ​​the silicon-carbon material in a cross-sectional image of the silicon-carbon material. For example... Figure 1 The image shown is a scanning electron microscope (SEM) image of the cross-section of the negative electrode sheet in an example of the present invention. S1 represents the cross-sectional area of ​​the cavity, and S2 represents the cross-sectional area of ​​the entire silicon-carbon material, that is, the sum of the areas of the silicon-carbon material shell and the cavity on this cross-section.

[0025] In this invention, the void fraction θ of the cross-section of the silicon-carbon material can be obtained by conventional methods in the art. For example, after discharging the battery to 0% SOC, the negative electrode sheet is disassembled and removed. After soaking in DMC solvent for 12 hours, it is rinsed with DMC solvent to remove the lithium salt attached to the negative electrode sheet. Alternatively, the negative electrode sheet before soaking in electrolyte can be directly taken, and the negative electrode sheet can be cut with an argon ion milling machine using a CP laser. The projected profile of the cross-section of the silicon-carbon material can be simulated using SEM and Image-Pro Plus, and the void fraction θ of the cross-section of the silicon-carbon material can be calculated.

[0026] In one example, the silicon-carbon material in the negative electrode active layer has a mass content of 5%-50% (e.g., 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%).

[0027] In this invention, the coating is disposed facing the negative electrode and / or the positive electrode.

[0028] In one example, the coating is positioned facing the negative electrode.

[0029] In one example, the coating is positioned facing the positive electrode.

[0030] In one example, the coating is disposed facing both the negative electrode and the positive electrode.

[0031] Barium titanate particles, as a high dielectric constant ferroelectric material, can effectively adsorb water molecules on their polar surface when the coating faces the electrode (negative electrode and / or positive electrode), inhibiting the generation of HF and the occurrence of side reactions, reducing the corrosion of ternary cathode materials (especially high-nickel ternary materials) by HF and the damage to the interface film, thereby improving the high-temperature cycle performance and high-temperature safety performance of the battery.

[0032] In one example, the barium titanate particles have a specific surface area of ​​10 m². 2 / g-50m 2 / g (e.g., 10m) 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g、45m 2 / g or 50m 2 The surface area and pore size ( / g) can be obtained by methods conventional in the art, such as using a McMurray TriStar II 3020 Plus high-throughput surface area and pore size analyzer.

[0033] In this invention, the chemical formula of the barium titanate particles is (Ba 1-a Sr a (Ti) 1-b Zr b The doping of barium titanate particles with Sr and / or Zr can effectively improve their dielectric constant, structural stability, and water adsorption capacity. When Sr and Zr enter the crystal structure of barium titanate particles, Sr... 2+ It can partially replace Ba 2+ Site, Zr 4+ It can partially replace Ti 4+By controlling the degree of lattice distortion, the dielectric constant of barium titanate can be effectively increased, thereby enhancing the polarity of barium titanate particles to achieve the desired effect on polar water molecules and OH-containing molecules in the electrolyte. - F - It has a stronger adsorption capacity for harmful ions, which further improves the battery's high-temperature storage performance and cycle life.

[0034] In this invention, the coating comprises a porous structure with a porosity of 30%-60% (e.g., 30%, 35%, 40%, 45%, 50%, 55%, or 60%). An appropriate porosity provides sufficient specific surface area and adsorption sites for the coating, ensuring its adsorption function, while preventing excessively dense pores that could unduly increase lithium-ion transport resistance and hinder lithium-ion transport.

[0035] In this invention, the porosity of the coating can be tested using conventional methods in the art. For example, after discharging a lithium-ion secondary battery to 0% SOC, the separator is disassembled, dried, and then cut into 100mm diameter circular samples using a slicer. The thickness is measured at at least 5 different locations on the sample using a micrometer, and the average value is recorded as d. The sample is placed in an oven at 80°C for 2 hours to completely remove adsorbed moisture and solvent. It is then transferred to a desiccator and cooled to room temperature. The sample is weighed using a balance and recorded as W0. Subsequently, the sample is held by one corner with tweezers and slowly tilted and immersed in deionized water to ensure that the liquid fully enters the micropores. The sample is soaked for 30 minutes. The sample is then removed, and the surface free liquid is gently absorbed with filter paper. The wet weight is immediately recorded as W1. The porosity is calculated using the formula: porosity (%) = [(W1-W0) / ρ 水 ] / (A×d)×100% is calculated, where ρ 水 A is the density of deionized water at 25℃, and A is the area of ​​the disc sample.

[0036] In this invention, the coating further includes an adhesive, which includes at least one selected from polyvinylidene fluoride, a polymer of vinylidene fluoride-hexafluoropropylene, a polymer of vinylidene fluoride-trichloroethylene, polyvinyl acetate, polymethyl methacrylate, polyvinyl alcohol, polyethylene oxide, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0037] In one example, the adhesive comprises a polymer of vinylidene fluoride-hexafluoropropylene (PVDF-HFP) and / or polymethyl methacrylate (PMMA).

[0038] In one example, the coating further includes a dispersant, which includes polyvinylpyrrolidone (PVP), ammonium polyacrylate (PAA-NH4), and copolymers containing acidic groups (e.g., BYK-110 / BYK-111).

[0039] In one example, based on the total weight of the coating, the mass content w1 of the barium titanate particles is 70%-95% (e.g., 70%, 75%, 80%, 85%, 90% or 95%), and the mass content w2 of the binder is 5%-30% (e.g., 5%, 10%, 15%, 20%, 25% or 30%).

[0040] like Figure 2 The image shown is a SEM image of the diaphragm cross-section in an example of the present invention. Figure 3 The image shown is a SEM image of the separator surface in an example of the present invention. In the present invention, the thickness of the coating on one side of the separator surface is 0.5μm-5μm (e.g., 0.5μm, 1μm, 2μm, 3μm, 4μm, or 5μm). If the coating thickness is too large (e.g., >5μm), it will increase the lithium ion transport path, increase the battery internal resistance, lead to a decrease in the battery's ionic conductivity, increase the degree of polarization, and affect the battery's charge / discharge rate performance and cycle stability. At the same time, an excessively thick coating is prone to causing uneven internal stress, which can easily lead to cracks during electrode winding or pressing, and may even cause the coating to fall off in severe cases of powder shedding. This also reduces the coating's adsorption and capture of harmful substances such as moisture and HF, and worsens the K value. If the coating thickness is too small (e.g., <0.5μm), the effective adsorption area and active adsorption sites provided by the thin coating are insufficient, which cannot fully capture free water molecules and HF that migrate from the negative electrode side or remain in the electrolyte in the battery system. This will not effectively suppress the corrosion of the high-nickel positive electrode by HF and the damage to the SEI film, and the high-temperature storage performance of the battery will be difficult to improve substantially.

[0041] In this invention, the thickness of the coating on one side surface of the separator can be tested by conventional methods in the art. For example, the battery is discharged to 0% SOC, the separator is disassembled and removed, soaked in DMC solvent for 12 hours, and then rinsed with DMC solvent to remove the lithium salt attached to the separator. The separator is then cut along the thickness direction using an argon ion milling machine with a CP laser. Combined with SEM, at least 20 points are randomly selected on the coating, and the thickness of the coating at each point is measured and the average value is taken.

[0042] In one example, the coating further includes first particles comprising a nitrogen-containing heterocyclic compound, the nitrogen-containing heterocyclic compound comprising at least one of melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, melamine cyanurate, and melamine thiocyanate.

[0043] Because barium titanate particles are ferroelectrics with high electron conductivity, when they adsorb transition metals, transition metal ions (such as Mn)... 2+ Valence state changes may occur during charging and discharging (e.g., Mn). 2+ →Mn 3+This leads to repeated expansion and contraction of the lattice, causing cracks in the barium titanate particles and ultimately resulting in their fragmentation. When the coating contains the first particle, the nitrogen-containing heterocyclic compound has lone pairs of electrons and strong coordination ability, allowing it to preferentially adsorb transition metal ions (such as Mn) dissolved from the positive electrode through complexation. 2+ Ni 2+ This reduces the erosion and damage to the barium titanate lattice, effectively maintaining the long-term structural integrity of the coating and ensuring its continuous role in moisture capture and protection during long battery cycles. Furthermore, the nitrogen-containing material exhibits excellent thermal stability and mechanical strength, which can suppress thermal shrinkage of the separator at high temperatures, reduce the risk of internal short circuits caused by positive and negative electrode contact, and further improve the furnace temperature safety performance of the battery.

[0044] In one example, based on the total weight of the coating, the mass content w1 of the barium titanate particles is 50%-80% (e.g., 50%, 55%, 60%, 65%, 70%, 75%, or 80%), the mass content w2 of the binder is 10%-49% (e.g., 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 49%), and the mass content w3 of the first particles is 1%-10% (e.g., 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%).

[0045] In this invention, the diaphragm further includes an adhesive layer located on at least one outer surface of the diaphragm, the adhesive layer comprising second particles, the second particles comprising a polymer formed by polymerizing at least one monomer selected from acrylic acid, methyl methacrylate, butyl acrylate, butadiene, acrylonitrile, styrene, vinyl alcohol, methacrylamide, acrylamide, ethyl methacrylate, isooctyl acrylate, n-propyl acrylate, butyl acrylate, cyclohexyl acrylate, 2-hydroxyethyl acrylate, vinylidene fluoride, tetrafluoroethylene, hexafluoroethylene, and hexafluoropropylene.

[0046] In one example, the second particle comprises at least one of polymethyl methacrylate, polyvinyl alcohol, and styrene-butadiene rubber.

[0047] In one example, the average particle size of the second particle is 0.1 μm-2 μm (e.g., 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1.1 μm, 1.3 μm, 1.5 μm, 1.7 μm, or 2 μm), which can be obtained by conventional methods in the art. For example, after discharging the battery to 0% SOC, the separator is disassembled, soaked in DMC solvent for 12 hours, and then rinsed with DMC solvent to remove lithium salts adhering to the separator. The sample is then observed using SEM and measured at 5K magnification. At least 10 second particles are randomly selected, and the particle size of each particle is measured, and the average value is taken. If the number of particles at 5K magnification is less than 10, more electron microscope images are taken until 10 second particles are measured. If the particle appears as a regular circle in the electron microscope image, then the particle size is the diameter of that circle. If the particle appears as a non-regular circle in the electron microscope image, then the particle size is the diameter of an equivalent circle with the same area as the regular circle.

[0048] In one example, the adhesive layer covers 15%-70% of the membrane surface (e.g., 15%, 20%, 30%, 40%, 50%, 60% or 70%), and the adhesive layer is distributed in a dotted or island-like pattern on the membrane surface, which ensures adhesion while leaving sufficient interface for lithium-ion transport.

[0049] In this invention, the coverage of the adhesive layer on the diaphragm surface can be tested using conventional methods in the art, such as SEM combined with image analysis software.

[0050] In one example, the thickness of the adhesive layer is 0.5μm-5μm (e.g., 0.5μm, 1μm, 2μm, 3μm, 4μm or 5μm); the test method for the thickness of the adhesive layer is the same as that for the coating, and will not be repeated here.

[0051] In this invention, the ternary cathode material comprises single-crystal particles. Compared with polycrystalline particles (formed by secondary particle agglomeration), single-crystal particles have higher structural stability and voltage resistance, which can effectively suppress particle cracking, pulverization, and shedding caused by stress concentration during high-temperature charge-discharge cycles, reduce active material loss and electrolyte side reactions, and further improve the high-temperature storage performance of the battery.

[0052] In this invention, the average particle size of the ternary cathode material is 1μm-10μm (e.g., 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm), which can be obtained by SEM testing.

[0053] In one example, the average particle size of the ternary cathode material is 2 μm-7 μm.

[0054] In this invention, the positive electrode active layer further includes a positive electrode conductive agent and a positive electrode binder. The positive electrode conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes (including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes), and carbon fibers. The positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, polyethylene oxide, polyacrylic acid, and derivatives of the above substances. Based on the total weight of the positive electrode active layer, the mass content of the ternary positive electrode material is 80%-99.8%, the mass content of the positive electrode conductive agent is 0.1%-10%, and the mass content of the positive electrode binder is 0.1%-10%.

[0055] In this invention, the lithium-ion secondary battery further includes an electrolyte comprising fluoroethylene carbonate (FEC) and a sulfur-containing additive. FEC preferentially reduces on the negative electrode surface to form a dense and flexible SEI film, effectively accommodating the volume expansion of the silicon-carbon material and maintaining the stability of the negative electrode structure. By complementing the hollow silicon-carbon material, it further enhances the battery's high-temperature cycle performance. The sulfur-containing additive helps form a stable interface film on the positive and negative electrode surfaces. When the electrolyte contains both sulfur-based additives and FEC, a dense and highly flexible SEI film can form on the surface of the negative electrode material. This film effectively buffers the volume changes of silicon-carbon, efficiently conducts lithium ions, and prevents further erosion by solvent molecules, thereby greatly protecting the negative electrode structure.

[0056] In one example, the sulfur-containing additive includes , , and At least one of them.

[0057] In one example, the electrolyte comprises FEC and .

[0058] In one example, the mass content C1 of FEC in the electrolyte is 5%-20% (e.g., 5%, 7%, 9%, 11%, 13%, 15%, 17% or 20%).

[0059] In one example, the sulfur-containing additive in the electrolyte has a mass content C2 of 0.5%-3% (e.g., 0.5%, 1%, 1.5%, 2%, 2.5% or 3%).

[0060] In this invention, C1 and C2 can be obtained by methods conventional in the art, such as gas chromatography (GC), gas chromatography-mass spectrometry (GCMS), or liquid chromatography (LC).

[0061] In this invention, the electrolyte also includes other conventional choices in the art, such as, but not limited to, at least one of propylene carbonate (PC) and butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), and methyl butyrate (MB).

[0062] In this invention, the electrolyte further includes an electrolyte salt, which comprises at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium hexafluorophosphate (LiPF6). These lithium salts themselves can improve the lithium-ion conductivity of the electrolyte, ensuring that the battery has high lithium-ion conductivity under high-speed charging conditions, thereby improving the cycle stability of the battery. Among them, LiTFSI and LiFSI have high chemical and thermal stability and are not prone to hydrolysis.

[0063] In this invention, the negative electrode active layer includes a negative electrode material, which includes graphite material and silicon-carbon material; the average particle size of the graphite material is 5μm-25μm (e.g., 5μm, 7μm, 9μm, 11μm, 13μm, 15μm, 17μm, 20μm, 23μm or 25μm).

[0064] In one example, the average particle size of the silicon-carbon material is 5 μm-20 μm (e.g., 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, or 20 μm). The average particle size of the graphite material and the average particle size of the silicon-carbon material can be obtained by methods conventional in the art, such as SEM testing.

[0065] In this invention, the silicon-carbon material accounts for 3%-30% of the mass of the negative electrode material (e.g., 3%, 5%, 10%, 15%, 20%, 25%, or 30%). If the proportion of silicon-carbon material is too low (e.g., <3%), the effect on improving the battery energy density will be insignificant, making it difficult to fully utilize the advantage of the high theoretical specific capacity of silicon-carbon material. If the proportion of silicon-carbon material is too high (e.g., >30%), the severe volume expansion and water absorption problems generated by silicon-carbon material during charging and discharging will be difficult to control effectively, which will still aggravate the adverse effects such as cracking of the negative electrode active layer, repeated damage and regeneration of the SEI film, and corrosion of the positive electrode by HF, affecting the high-temperature cycle performance and high-temperature storage performance of the battery.

[0066] In one example, the specific surface area of ​​the silicon-carbon material is 0.5 m². 2 / g-5m 2 / g (e.g., 0.5m) 2 / g, 1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g or 5m 2 The surface area and pore size ( / g) can be obtained by methods conventional in the art, such as using a McMurray TriStar II 3020 Plus high-throughput surface area and pore size analyzer.

[0067] In one example, the sphericity of the silicon-carbon material is 0.8-1 (e.g., 0.8, 0.85, 0.9, 0.95, or 1). Using silicon-carbon materials with higher sphericity results in better flowability, which facilitates the uniform dispersion of silicon-carbon particles in the negative electrode slurry, effectively reducing internal stress concentration in the negative electrode sheet during the rolling process and further mitigating the volume expansion effect of the silicon-carbon negative electrode.

[0068] In this invention, the sphericity of the silicon-carbon material can be tested using conventional methods in the art. For example, the battery is discharged to 0% SOC, the negative electrode is disassembled and removed, or the negative electrode is directly removed. The cross-section of the negative electrode is polished using an argon-ion polisher, and then observed using backscatter imaging mode on a scanning electron microscope (SEM). Silicon-carbon material particles with continuous and smooth contours are found. Any two points on the edge of the particle are connected to form a straight line segment inside the particle. The longest straight line segment inside the particle is selected, and its length is denoted as Z1. The midpoint of this longest straight line segment is taken, and a straight line is drawn through this midpoint to form a straight line segment with both ends at the edge of the particle. The shortest straight line segment is selected, and its length is denoted as Z2. The sphericity of the particle is then Z2 / Z1. At least 10 silicon-carbon particles are selected, and the sphericity is measured and the average value is taken.

[0069] In this invention, the negative electrode active layer further includes a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes (including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes), and carbon fibers. The negative electrode binder includes at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, polyethylene oxide, polyacrylic acid, and derivatives of the above substances. Based on the total weight of the negative electrode active layer, the mass content of the negative electrode material is 80%-99.8%, the mass content of the negative electrode conductive agent is 0.1%-10%, and the mass content of the negative electrode binder is 0.1%-10%.

[0070] The batteries can all be assembled in accordance with conventional methods in the field.

[0071] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0072] 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.

[0073] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0074] The following examples illustrate the lithium-ion secondary battery of the present invention.

[0075] Example 1 Batteries are prepared according to the following method. (1) Preparation of positive electrode sheet LiNi cathode material 0.8 Co 0.1 Mn 0.1 O2 (single crystal particles with an average particle size of 3 μm), conductive carbon black and PVDF are mixed in a mass ratio of 96.5:2:1.5, and N-methylpyrrolidone is added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on the positive electrode current collector to form a positive electrode active layer, and then dried, rolled and slit to obtain a positive electrode sheet. (2) Preparation of negative electrode sheet A negative electrode material (artificial graphite and silicon carbide in a mass ratio of 85:15), conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber in a mass ratio of 94.5:1.5:1.5:1:2.5 were mixed, deionized water was added, and the mixture was stirred under vacuum to prepare a negative electrode slurry. This slurry was then uniformly coated onto both sides of a copper foil and dried in an oven at 80°C for 10 hours. After rolling and slitting, the negative electrode sheet was obtained. The silicon carbide material comprises an outer shell and a cavity formed by the outer shell. The cross-sectional porosity θ of the silicon carbide material is 8%, the maximum Freette diameter D1 of the cavity is 1.5 μm, the D2 / D1 ratio is 0.53, the average particle size of the silicon carbide material is 9 μm, and the specific surface area of ​​the silicon carbide material is 1.1 m². 2 / g, the sphericity of silicon carbide material is 0.8, and the average particle size of graphite material is 15.5μm; (3) Preparation of diaphragm Using 5μm polyethylene (PE) as the base film, barium titanate particles (Ba) with a thickness of 2μm are coated on the side of the base film facing the negative electrode. 0.8 Sr 0.2 (Ti) 0.9 Zr0.1 For coatings of O3, PVDF-HFP, and PVP, a 1μm thick layer of PMMA latex particles (average particle size 0.2μm) is sprayed onto both the surface of the coating and the opposite surface of the PE base film. The barium titanate particles have an average particle size D2 of 0.8μm and a specific surface area of ​​20.5m². 2 / g, the porosity of the coating is 45%, w1 is 89%, w2 is 11%, and the coverage of the adhesive layer on the diaphragm surface is 50%; (4) Preparation of electrolyte In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), EC / EMC / DEC were mixed thoroughly in a 1:1:1 volume ratio. Then, fully dried LiPF6 was quickly added to prepare a 1.2 mol / L solution. FEC and... After thorough mixing and passing tests for moisture and free acid, the desired electrolyte is obtained. Based on the total mass of the electrolyte, C1 comprises 10% and C2 comprises 2%. (5) Battery fabrication The positive electrode sheet prepared in step (1), the separator prepared in step (3), and the negative electrode sheet prepared in step (2) are stacked in order to ensure that the separator is between the positive and negative electrode sheets to play a role in isolation. Then, the bare battery is obtained by winding. The bare battery cell is placed in the outer packaging aluminum foil, and the electrolyte prepared in step (4) is injected into the outer packaging. After vacuum sealing, standing, formation, shaping, sorting and open circuit voltage testing, a lithium-ion secondary battery is obtained.

[0076] Example 2 group This set of embodiments follows the same procedure as Embodiment 1, except that the porosity θ of the cross-section of the silicon-carbon material is changed to verify the effect of the change in θ, as detailed below: Example 2-1, θ is 5%, the chemical formula of the ternary cathode material is LiNi 0.8 Co 0.1 Al 0.1 O2; Example 2-2, θ is 15%, the chemical formula of the ternary cathode material is LiNi 0.7 Co 0.1 Mn 0.15 Al 0.05 O2; Examples 2-3, θ is 1%; Examples 2-4, where θ is 20%.

[0077] Example 3 Group This set of embodiments follows the same procedure as Embodiment 1, except that the ratio D2 / D1 is adjusted by changing the maximum Ferete diameter D1 of the cavity and the average particle size D2 of the barium titanate particles. This is used to verify the effect of changing D2 / D1, as detailed below: Example 3-1: D2 / D1 is 1, D1 is 0.5 μm, D2 is 0.5 μm, and the specific surface area of ​​the barium titanate particles is 36.5 m². 2 / g; Example 3-2: D2 / D1 is 0.11, D1 is 9 μm, D2 is 1 μm, and the specific surface area of ​​the barium titanate particles is 10.5 m². 2 / g; In Examples 3-3, D2 / D1 was 0.25, D1 was 0.4 μm, D2 was 0.1 μm, and the specific surface area of ​​the barium titanate particles was 49.8 m². 2 / g; In Examples 3-4, D2 / D1 was 0.8, D1 was 1 μm, D2 was 0.8 μm, and the specific surface area of ​​the barium titanate particles was 20.6 m². 2 / g; Examples 3-5 show a D2 / D1 ratio of 0.16, a D1 value of 0.5 μm, a D2 value of 0.08 μm, and a specific surface area of ​​50.4 m² for the barium titanate particles. 2 / g; Examples 3-6 show that D2 / D1 is 0.73, D1 is 1.5 μm, D2 is 1.1 μm, and the specific surface area of ​​the barium titanate particles is 10 m². 2 / g; Examples 3-7 show a D2 / D1 ratio of 0.03, a D1 of 6 μm, a D2 of 0.2 μm, and a specific surface area of ​​41.5 m² for the barium titanate particles. 2 / g.

[0078] Example 4 group This set of examples follows the same procedure as Example 1, except that the chemical formula of the barium titanate particles is changed to verify the effect of the change in the chemical formula of the barium titanate particles, as detailed below: Example 4-1, the chemical formula of barium titanate particles is BaTi 0.9 Zr 0.1 O3; Example 4-2, the chemical formula of barium titanate particles is Ba 0.8 Sr 0.2 TiO3; In Examples 4-3, the chemical formula of the barium titanate particles is BaTiO3.

[0079] Example 5 group This set of embodiments follows the same procedure as Embodiment 1, except that the thickness of the diaphragm coating is changed to verify the effect of the change in diaphragm coating thickness, as detailed below: Example 5-1: The coating thickness is 0.5 μm; Example 5-2: The coating thickness is 5 μm.

[0080] Example 6 This embodiment is based on Embodiment 1, except that the diaphragm coating further includes a first particle of melamine cyanurate, wherein w1 is 86%, w2 is 11%, and w3 is 3%.

[0081] Example 7 group This set of examples follows the same format as Example 1, except that the composition of the electrolyte is changed to verify the effect of the change in electrolyte, as detailed below: Example 7-1, C1 is 0.5%; Example 7-2, C2 is 0%.

[0082] Example 8 This embodiment is based on Embodiment 1, except that the cathode material is LiNi. 0.8 Co 0.1 Mn 0.1 O2 includes polycrystalline particles.

[0083] Comparative Example 1 This comparative example is based on Example 1, except that the porosity θ of the cross-section of the silicon-carbon material is changed to verify the effect of the change in θ, as follows: Comparative Example 1, θ is 22%.

[0084] Comparative Example 2 This comparative example is based on Example 1, except that the barium titanate particles in the diaphragm coating are replaced with boehmite of the same mass content.

[0085] Comparative Example 3 Groups This comparative study was conducted in accordance with Example 1, except that the ratio D2 / D1 was adjusted by changing the maximum Ferete diameter D1 of the cavity and the average particle size D2 of the barium titanate particles. This was used to verify the effect of changing D2 / D1, as detailed below: Comparative Example 3-1: D2 / D1 is 1.33, D1 is 0.6 μm, and D2 is 0.8 μm; Comparative Example 3-2, D2 / D1 is 0.02, D1 is 8.9 μm, and D2 is 0.2 μm.

[0086] Test case (1) 45℃ cycle test The batteries prepared in the examples and comparative examples were subjected to a cycling test at 45°C. The specific test method is as follows: S1. Place the prepared battery in a constant-temperature environment at 45°C, charge it at a constant current of 1C and constant voltage up to 4.3V, with a cut-off current of 0.05C. After full charge, let it stand for 10 minutes, and then discharge it at a constant current of 5C until the cut-off voltage of 2.5V; conduct 3 complete charge-discharge cycles and take the discharge capacity of the 3rd cycle as the initial capacity C1; S2. Continue to cycle according to the charge-discharge regime in step S1 (1C charge / 5C discharge); when the number of cycles reaches 800, stop the test and record the discharge capacity of the 800th cycle as C2; then the capacity retention rate (%) = C2 / C1×100%, and record the results in Table 1.

[0087] (2)Furnace temperature safety test The batteries prepared in the examples and comparative examples were subjected to a furnace temperature safety test. The specific test method is as follows: Charge the batteries prepared in the examples and comparative examples at a constant current of 0.5C and constant voltage up to 4.3V at room temperature (25°C±2°C), with a cut-off current of 0.05C. Then place them horizontally in a temperature-rising oven and heat them at a heating rate of 5°C / min to 135°C, and keep the temperature for 1h. Observe the battery status. The evaluation criterion: when the battery does not catch fire and does not explode, it can be judged as passing. Test 15 samples for each example, record the passing rate of the samples, passing rate = number of passing batteries / total number of tested batteries, and record the results in Table 1.

[0088] (3)60°C high-temperature storage test The batteries prepared in the examples and comparative examples were subjected to a 60°C high-temperature storage test. The specific test method is as follows: In an environment of 25°C±3°C, use a PPG thickness gauge to measure the initial thickness of the battery, denoted as T1; then charge the battery at a constant current of 0.5C and constant voltage up to 4.3V, with a cut-off current of 0.05C to make it in a fully charged state; place the fully charged battery in a test chamber at 60°C±2°C and let it stand for storage for 30 days. Immediately take it out after storage and use a PPG to measure the thickness of the battery, denoted as T2; then the thickness expansion rate (%) = (T2 - T1) / T1×100%, and record the results in Table 1.

[0089] Table 1 As can be seen from Table 1, compared with the comparative examples, the batteries of the present invention have excellent high-temperature cycling performance and furnace temperature safety performance, and have a lower thickness expansion rate after high-temperature storage.

[0090] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A lithium-ion secondary battery, characterized in that, Includes positive electrode, negative electrode, and separator; The positive electrode includes a positive current collector and a positive active layer located on at least one side of the surface of the positive current collector. The positive active layer includes a ternary positive electrode material with the chemical formula LiNi. x Co y M 1 1-x-y M 2 z O2, where 0.3 ≤ x < 1, 0 < y < 0.2, 0 ≤ z ≤ 0.05, M 1 Including Mn and / or Al, M 2 Including at least one of Mg, Ti, Nb, Zr, B, W, P, Na, Fe, Y, La and Sr; The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector. The negative electrode active layer includes a silicon-carbon material. The silicon-carbon material includes a shell and a cavity formed by the shell. The cross-sectional porosity θ of the silicon-carbon material is 1%-20%, and the maximum Freette diameter of the cavity is D1. The diaphragm includes a substrate layer and a coating located on at least one side of the substrate layer, the coating including barium titanate particles with an average particle size of D2; Where 0.03≤D2 / D1≤1.

2. The lithium-ion secondary battery according to claim 1, wherein, D1 ranges from 0.5 μm to 9 μm; And / or, D2 is 0.1μm-1μm; And / or, θ is 5%-15%; And / or, the coating is disposed facing the negative electrode and / or the positive electrode.

3. The lithium-ion secondary battery according to claim 1 or 2, wherein, The barium titanate particles have a specific surface area of ​​10 m². 2 / g-50m 2 / g; And / or, the chemical formula of the barium titanate particles is (Ba 1-a Sr a (Ti) 1-b Zr b O3, where 0 ≤ a ≤ 0.3, 0 ≤ b ≤ 0.15; And / or, the porosity of the coating is 30%-60%.

4. The lithium-ion secondary battery according to claim 1 or 2, wherein, The coating further includes an adhesive, which includes at least one of polyvinylidene fluoride, a polymer of vinylidene fluoride-hexafluoropropylene, a polymer of vinylidene fluoride-trichloroethylene, polyvinyl acetate, polymethyl methacrylate, polyvinyl alcohol, polyethylene oxide, polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. Preferably, the adhesive comprises a polymer of vinylidene fluoride-hexafluoropropylene and / or polymethyl methacrylate; Preferably, based on the total weight of the coating, the mass content w1 of the barium titanate particles is 70%-95%, and the mass content w2 of the binder is 5%-30%. And / or, the thickness of the coating on one side surface of the diaphragm is 0.5μm-5μm.

5. The lithium-ion secondary battery according to claim 4, wherein, The coating further includes first particles, the first particles comprising a nitrogen-containing heterocyclic compound, the nitrogen-containing heterocyclic compound comprising at least one of melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, melamine cyanurate, and melamine trithiocyanate; Preferably, based on the total weight of the coating, the mass content w1 of the barium titanate particles is 50%-80%, the mass content w2 of the binder is 10%-49%, and the mass content w3 of the first particles is 1%-10%.

6. The lithium-ion secondary battery according to claim 1 or 2, wherein, The diaphragm further includes an adhesive layer located on at least one outer surface of the diaphragm, the adhesive layer comprising second particles, the second particles comprising a polymer formed by polymerizing at least one monomer selected from acrylic acid, methyl methacrylate, butyl acrylate, butadiene, acrylonitrile, styrene, vinyl alcohol, methacrylamide, acrylamide, ethyl methacrylate, isooctyl acrylate, n-propyl acrylate, butyl acrylate, cyclohexyl acrylate, 2-hydroxyethyl acrylate, vinylidene fluoride, tetrafluoroethylene, hexafluoroethylene, and hexafluoropropylene; Preferably, the second particle comprises at least one of polymethyl methacrylate, polyvinyl alcohol, and styrene-butadiene rubber; Preferably, the average particle size of the second particle is 0.1 μm-2 μm; Preferably, the adhesive layer covers 15%-70% of the diaphragm surface; Preferably, the thickness of the adhesive layer is 0.5μm-5μm.

7. The lithium-ion secondary battery according to claim 1 or 2, wherein, The lithium-ion secondary battery further includes an electrolyte, which comprises fluoroethylene carbonate and a sulfur-containing additive, wherein the sulfur-containing additive comprises... , , and At least one of them; Preferably, the electrolyte comprises fluoroethylene carbonate and ; Preferably, the mass content (C1) of the fluoroethylene carbonate in the electrolyte is 5%-20%; Preferably, the sulfur-containing additive in the electrolyte has a mass content of 0.5%-3% (C2).

8. The lithium-ion secondary battery according to claim 1 or 2, wherein, The ternary cathode material includes single-crystal particles; And / or, the average particle size of the ternary cathode material is 1μm-10μm; preferably 2μm-7μm.

9. The lithium-ion secondary battery according to claim 1 or 2, wherein, The average particle size of the silicon-carbon material is 5μm-20μm; And / or, the specific surface area of ​​the silicon-carbon material is 0.5 m². 2 / g-5m 2 / g; And / or, the sphericity of the silicon-carbon material is 0.8-1.

10. The lithium-ion secondary battery according to claim 1 or 2, wherein, The negative electrode active layer also includes graphite material; Preferably, the average particle size of the graphite material is 5μm-25μm.

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