Battery

Abstract

The invention provides a battery, which comprises a negative plate and an electrolyte, the negative plate comprises a negative active material, the negative active material comprises a silicon-carbon composite material, the silicon-carbon composite material comprises a silicon-carbon core and a shell coated on the surface of the silicon-carbon core, the shell comprises an amorphous carbon layer and a graphene layer, and the amorphous carbon layer is coated on the surface of the silicon-carbon core. The amorphous carbon layer is located between the silicon carbon inner core and the graphene layer; in the Raman spectrum of the silicon-carbon composite material, the I2D / IG value k is more than or equal to 0.4 and less than or equal to 0.8; the electrolyte comprises acetic acid 2, 2-difluoroethyl ester, and the mass percentage m% of the acetic acid 2, 2-difluoroethyl ester in the electrolyte meets the condition that m% is larger than or equal to 5% and smaller than or equal to 65%, and k / m meets the condition that k / m is larger than or equal to 0.008 and smaller than or equal to 0.1. According to the battery, the amorphous carbon layer buffers expansion, and the graphene layer conducts electricity and obstructs; in the electrolyte, acetic acid 2, 2-difluoroethyl ester and graphene cooperate to construct a self-adaptive SEI film; parameter optimization is matched to enhance structural stability and ion transmission, and the performance is comprehensively improved.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, and particularly relates to a battery. Background Technology

[0002] Since their commercialization, lithium-ion batteries have been widely used in consumer electronics, electric vehicles, and other fields due to their advantages such as long lifespan, high specific capacity, and absence of memory effect. In recent years, with the increasing market demand for battery energy density and power performance, high areal density and high compaction design have become the mainstream development trend. However, this has also led to a series of overall performance challenges, including increased battery polarization, accelerated capacity decay, shortened cycle life, decreased rate performance, and increased safety risks.

[0003] Silicon-carbon composite materials, as a key anode system for improving battery energy density, possess theoretically high capacity advantages, but still face significant bottlenecks in practical battery applications. Especially under long-term cycling and high-rate operating conditions, batteries often exhibit a decline in rate performance, making it difficult to meet the requirements of high-performance battery systems.

[0004] Currently, various material-level improvement strategies have been developed for silicon-carbon anodes. However, while these strategies improve rate performance, they often exacerbate interfacial side reactions and the risk of lithium plating, leaving the battery's cycle life issue unresolved. Therefore, how to significantly improve the long-cycle stability of batteries while maintaining excellent rate performance has become a key technical challenge restricting the further development of high-energy-density lithium-ion batteries. Summary of the Invention

[0005] This invention provides a battery with excellent cycle performance and rate performance.

[0006] The first aspect of the present invention provides a battery, including a negative electrode sheet and an electrolyte, wherein the negative electrode sheet includes a negative electrode active material, the negative electrode active material includes a silicon-carbon composite material, the silicon-carbon composite material includes a silicon-carbon core and a shell covering the surface of the silicon-carbon core, the shell includes an amorphous carbon layer and a graphene layer, the amorphous carbon layer being located between the silicon-carbon core and the graphene layer;

[0007] In the Raman spectrum of the silicon-carbon composite material, the I2D / IG value k satisfies: 0.4 ≤ k ≤ 0.8;

[0008] The electrolyte comprises 2,2-difluoroethyl acetate, and the mass percentage (m%) of 2,2-difluoroethyl acetate in the electrolyte satisfies the following condition: 5% ≤ m% ≤ 65%.

[0009] k / m satisfies: 0.008≤k / m≤0.1.

[0010] In the battery described above, the full width at half maximum (FWHM) of the 2D peak in the Raman spectrum of the silicon-carbon composite material is no greater than 65 cm⁻¹. -1 The preferred size is 45-65cm. -1 .

[0011] In the battery described above, the thickness of the amorphous carbon layer is 2-20 nm; and / or,

[0012] The thickness of the graphene layer is 1-10 nm.

[0013] In the battery described above, the amorphous carbon layer further includes at least one of nitrogen, phosphorus, and boron, preferably nitrogen.

[0014] Preferably, the nitrogen element accounts for 0.2-1% of the mass of the silicon-carbon composite material.

[0015] In the battery described above, the particle size Dv50 of the silicon-carbon composite material is 5-15 μm; and / or,

[0016] The sphericity of the silicon-carbon composite material is 0.7-1; and / or,

[0017] The specific surface area of ​​the silicon-carbon composite material is 0.1-10 m². 2 / g; and / or,

[0018] The pore volume of the silicon-carbon composite material is 0.0005-0.002 cm³. 3 / g; and / or,

[0019] The true density of the silicon-carbon composite material is 1.5-2.4 cm³. 3 / g; and / or,

[0020] The silicon-carbon core comprises a porous carbon material and silicon material deposited within the porous carbon material, wherein the average particle size of the silicon material is 0.1-2000 nm; and / or,

[0021] The silicon-carbon composite material contains 28-72% silicon by mass.

[0022] In the battery described above, the cross-section of the silicon-carbon composite material has a first region and a second region. The mass content of silicon in the first region is c1, and the mass content of silicon in the second region is c2. The absolute difference between c2 and c1 is ≤10%. The perpendicular line to the tangent at any point on the edge of the cross-section has a dimension L on the cross-section. The region 0.3L away from the edge of the cross-section on the perpendicular line constitutes the first region, and the remaining regions of the cross-section other than the first region constitute the second region.

[0023] In the battery described above, the negative electrode active material further includes graphite material, wherein the OI value of the graphite material is ≥15, and the particle size Dv50 of the graphite material is 8-18μm;

[0024] In the thickness direction of the negative electrode sheet, the negative electrode sheet sequentially includes a negative electrode current collector, a first negative electrode active layer and a second negative electrode active layer, wherein the first negative electrode active layer includes the silicon-carbon composite material and the second negative electrode active layer includes the graphite material.

[0025] The battery as described above further includes a separator, the separator comprising a separator substrate and an adhesive layer coated on the surface of the separator substrate, the adhesive layer having a coverage of 15-45% on the separator substrate;

[0026] The diaphragm further includes a functional layer located between the adhesive layer and the diaphragm substrate. The functional layer includes first particles, which include at least one of 1,3,5-triazine-2,4,6-triamine, melamine cyanurate, melamine thiocyanate, polyacrylonitrile, or nitrile rubber. The aspect ratio of the first particles is 2-8.

[0027] The battery as described above further includes a positive electrode, the positive electrode comprising a positive electrode active material;

[0028] The positive electrode active material includes tellurium, preferably, the tellurium content is 10-50 ppm by mass percentage.

[0029] In the battery described above, the electrolyte further includes adiponitrile, and the adiponitrile has a mass percentage of 0.5-8% in the electrolyte.

[0030] The battery of this invention exhibits excellent cycle performance and rate performance due to a multi-layered synergistic effect. First, the amorphous carbon layer in the silicon-carbon composite material fills the surface defects of the core, providing good interfacial compatibility and buffering performance, effectively suppressing the volume change of silicon during charging and discharging, thereby improving cycle stability. The graphene layer constructs a highly conductive network and simultaneously coats the material surface to block electrolyte penetration, reducing active lithium loss and repeated SEI film formation, significantly improving the initial coulombic efficiency. Second, the 2,2-difluoroethyl acetate added to the electrolyte forms a stable SEI film, enhancing interfacial chemical stability and compensating for structural defects in the graphene layer. The graphene layer provides more film-forming active sites for this ester and strengthens the SEI film's adaptability to silicon volume expansion; the two work synergistically to further improve cycle performance. Furthermore, by optimizing parameters k and m, the structural stability and active ion transport efficiency of the composite material are further enhanced, resulting in a significant improvement in the overall electrochemical performance of the battery. Attached Figure Description

[0031] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0032] Figure 1 This is a schematic diagram of the structure of the silicon-carbon composite material provided in an embodiment of the present invention.

[0033] Figure label:

[0034] 1-Silicon-carbon core; 2-Amorphous carbon layer; 3-Graphene layer.

[0035] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0037] To balance the rate performance and cycle performance of high-energy-density batteries, the inventors conducted in-depth research on the performance of existing silicon-carbon composite materials. Currently, the main improvement method is to coat the surface of silicon-carbon materials with amorphous carbon. While this method can improve the rate performance of the battery, a single amorphous carbon coating is still insufficient to completely suppress the drastic volume changes of silicon during charge and discharge. Furthermore, the carbon coating layer is prone to cracking after multiple cycles, leading to an increase in side reactions between the electrode and the electrolyte.

[0038] Based on this, the inventors proposed the battery solution of the present invention with the goal of simultaneously suppressing the drastic volume change of silicon during charging and discharging and maintaining the active ion transport efficiency.

[0039] like Figure 1 As shown, the first aspect of the present invention provides a battery, including a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative electrode active material, which includes a silicon-carbon composite material. The silicon-carbon composite material includes a silicon-carbon core 1 and a shell covering the surface of the silicon-carbon core. The shell includes an amorphous carbon layer 2 and a graphene layer 3, with the amorphous carbon layer 2 located between the silicon-carbon core 1 and the graphene layer 3.

[0040] In the Raman spectrum of silicon-carbon composite materials, the I2D / IG value k satisfies: 0.4 ≤ k ≤ 0.8;

[0041] The electrolyte includes 2,2-difluoroethyl acetate, and the mass percentage (m%) of 2,2-difluoroethyl acetate in the electrolyte satisfies the following condition: 5% ≤ m% ≤ 65%.

[0042] k / m satisfies: 0.008≤k / m≤0.1.

[0043] For example, k is 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, or 0.8, or a range of any two of these values.

[0044] For example, m% is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or 65%, or a range of any two of these values.

[0045] For example, k / m is 0.008, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1, or a range of any two of these values.

[0046] The battery provided by this invention exhibits excellent cycle performance and rate performance. The reason is as follows:

[0047] On the one hand, the amorphous carbon layer of the silicon-carbon composite material can effectively fill the surface defects of the silicon-carbon core, providing excellent interfacial compatibility and buffering performance, effectively buffering the volume changes of silicon during lithiation / delithiation, and improving the cycle stability of the battery. The graphene layer constructs a highly conductive network, and since it is located on the outermost layer, it blocks the electrolyte from penetrating into the interior, reducing the consumption of active ions and the repeated formation of the SEI film, thereby significantly improving the battery's initial coulombic efficiency. On the other hand, the addition of 2,2-difluoroethyl acetate to the electrolyte helps to form a stable SEI film, improving the chemical stability of the electrode interface, and effectively compensating for any structural defects that may exist in the graphene coating layer. The graphene layer not only provides more film-forming active sites for 2,2-difluoroethyl acetate, but also enhances the adaptability of the formed SEI film to the volume changes of silicon materials during charge and discharge. Through synergistic effects, the two jointly improve the cycle performance of the secondary battery. In addition, by optimizing the range of parameters k and m, the structural stability and active ion transport efficiency of the silicon-carbon composite material are further enhanced, resulting in a significant improvement in the battery's cycle performance and rate performance.

[0048] In the Raman spectrum of silicon-carbon composite materials, the I²D / IG value k satisfies: 0.4 ≤ k ≤ 0.8. In the Raman spectrum of silicon-carbon composite materials, graphene exhibits characteristics at ~1580 cm⁻¹.-1 There is a G peak at ~2700 cm. -1 The presence of a 2D peak and its intensity ratio (I2D / IG) is key to identifying the number of layers and quality. A k value within the above range indicates that the silicon-carbon core is coated with a graphene layer that is uniformly covered on the particle surface. This layer acts as a supportive and protective framework for the silicon-carbon material, improving the compressive strength of the silicon-carbon particles. In addition, it can effectively suppress the expansion of silicon particles, thereby effectively improving the battery's initial efficiency and energy density.

[0049] The present invention does not specifically limit the mass percentage of oxygen in the silicon-carbon composite material. In one embodiment, the mass percentage of oxygen in the silicon-carbon composite material is less than 1.2%.

[0050] This invention uses X-ray fluorescence spectroscopy under an inert atmosphere to test and analyze the mass percentage of oxygen in silicon-carbon composite materials.

[0051] The negative electrode sheet of the present invention further includes a negative electrode current collector, a conductive agent and a binder, wherein the negative electrode current collector, the negative electrode active material, the conductive agent and the binder constitute a negative electrode active layer.

[0052] The negative electrode current collector layer can be made of at least one of copper foil, nickel foam, and copper foam; the conductive agent can be made of at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene; and the binder can be made of at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0053] In the specific preparation of the negative electrode sheet, the negative electrode active material, conductive agent, and binder can be dispersed in an appropriate amount of deionized water and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, the negative electrode sheet is obtained. In one embodiment, based on the total mass of the negative electrode active layer, the content of the negative electrode active material can be 80-99.8 wt%, the content of the conductive agent can be 0.1-10 wt%, the content of the binder can be 0.1-5 wt%, and the compaction density is 1.2-1.8 g / cm³. 3The conductive agents include carbon black and carbon nanotubes. The carbon nanotubes are multi-walled carbon nanotubes with diameters of 5-50 nm and aspect ratios of 500-2000. The high aspect ratio of carbon nanotubes results in higher mechanical strength, which is beneficial for buffering the intercalation and expansion of silicon-carbon particles. Simultaneously, the long carbon nanotubes can connect silicon-carbon particles, graphite, binders, etc., to form a dense conductive network, improving the overall conductivity of the negative electrode. Because silicon-carbon composite materials have stronger adhesion than conventional silicon-carbon materials, the amount of binder added can be appropriately reduced, increasing the proportion of active materials in the negative electrode, thereby improving the battery's energy density.

[0054] In one specific embodiment, the full width at half maximum (FWHM) of the 2D peak in the Raman spectrum of the silicon-carbon composite material is no greater than 65 cm⁻¹. -1 The preferred size is 45-65cm. -1 The fact that the half-maximum width of the 2D peak is within this range indicates that the graphene layer has high crystallinity and good structural order, which can improve the electronic conductivity and structural stability of silicon-carbon composite materials, thereby improving the rate performance and cycle performance of the battery.

[0055] For example, the full width at half maximum (FWHM) of the 2D peak in the Raman spectrum of the silicon-carbon composite material is 65 cm⁻¹. -1 64cm -1 63cm -1 62cm -1 61cm -1 60cm -1 Or below, or a range consisting of any two of these values.

[0056] In one specific embodiment, the thickness of the amorphous carbon layer is 2-20 nm. Within this range, the thickness of the amorphous carbon layer can balance the expansion effect of the buffer silicon material and the content of active materials, thereby balancing the cycle performance and energy density of the battery.

[0057] For example, the thickness of the amorphous carbon layer is 2 nm, 4 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm or 20 nm, or a range of any two of these values.

[0058] In one specific embodiment, the thickness of the graphene layer is 1-10 nm. Within this range, the thickness of the graphene layer effectively blocks the penetration of the electrolyte while ensuring the active ion conduction efficiency, thus balancing the cycle performance and rate performance of the battery.

[0059] For example, the thickness of the graphene layer is 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm, or a range of any two of these values.

[0060] To further improve the electronic conductivity and electrode interface bonding of silicon-carbon composite materials, heterogeneous elements can be introduced into the amorphous carbon layer.

[0061] In one specific embodiment, the amorphous carbon layer further includes at least one of nitrogen, phosphorus, and boron, preferably nitrogen. Introducing these elements provides more active sites for the active ions and enhances the interfacial bonding between the amorphous carbon layer and the graphene layer, thereby improving the rate performance and cycle performance of the battery. With the introduction of nitrogen, when the amorphous carbon layer and the graphene layer are in close contact, strong π-π stacking interactions occur between the large, electron-rich sp² carbon planes. The lone pairs of electrons in pyridine nitrogen and its electron-withdrawing properties can generate local dipoles at the interface. These dipoles generate additional electrostatic attraction between themselves or with the π electron cloud of the graphene layer, making the surface energy of the amorphous carbon layer closer to that of the graphene layer, thus facilitating a closer bonding between the two.

[0062] In one specific embodiment, the nitrogen content in the silicon-carbon composite material is 0.2-1% by mass. Within this range, the nitrogen content further suppresses shell cracking during cycling, maintains the structural stability of the silicon-carbon composite material, and ensures the bonding force between the amorphous carbon layer and the graphene layer, thus contributing to improved battery cycle life.

[0063] For example, the mass percentage of nitrogen in the silicon-carbon composite material is 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%, or a range of any two of these values.

[0064] In one specific embodiment, the particle size Dv50 of the silicon-carbon composite material is 5-15 μm. Within this range, the particle size Dv50 of the silicon-carbon composite material can suppress side reactions while maintaining active ion diffusion efficiency, thereby improving both the cycle performance and rate performance of the secondary battery.

[0065] For example, the particle size Dv50 of the silicon-carbon composite material is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, or a range of any two of these values.

[0066] The particle size Dv50 of silicon-carbon composite materials refers to the particle size when the cumulative volume distribution of silicon-based materials is 50%. This parameter is measured by a Malvern laser particle size analyzer.

[0067] In one specific embodiment, the sphericity of the silicon-carbon composite material is 0.7-1. Controlling the sphericity within this range achieves a synergistic improvement in both structural and interfacial stability of the silicon-carbon composite material, significantly improving the battery's cycle performance and thickness expansion rate. Simultaneously, the silicon-carbon composite material within this sphericity range possesses moderate surface roughness, ensuring both effective adhesion of the SEI film and interfacial stability.

[0068] The sphericity of silicon-carbon composite materials can be tested using conventional methods in the art. For example, after a cycled battery is disassembled, the negative electrode is removed, cleaned and dried with dimethyl carbonate, and then its cross-section is polished using an argon-ion polishing machine. The cross-sectional morphology is observed using a scanning electron microscope in backscatter mode to identify the white spherical silicon-carbon composite material particles. The maximum diameter d1 and minimum diameter d2 of each particle's cross-section are measured, and the d1 / d2 ratio is calculated as the sphericity of a single particle. At least 30 particles are selected for testing, and the average value is taken to obtain the average sphericity of the silicon-carbon composite material.

[0069] For example, the sphericity of the silicon-carbon composite material is 0.7, 0.8, 0.9 or 1, or a range of any two of these values.

[0070] In one specific embodiment, the specific surface area of ​​the silicon-carbon composite material is 0.1-10 m². 2 / g. The specific surface area of ​​the silicon-carbon composite material is within this range, which allows the negative electrode active material to have a high specific capacity while effectively reducing the contact between the negative electrode active material and the electrolyte, reducing the formation of the SEI film, thereby improving the battery's initial efficiency and cycle performance.

[0071] For example, the specific surface area of ​​the silicon-carbon composite material is 0.1 m². 2 / g、1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g or 10m 2 / g, or a range consisting of any two of these values.

[0072] The specific surface area of ​​the silicon-carbon composite material was determined by N2 adsorption-desorption test.

[0073] In one specific embodiment, the pore volume of the silicon-carbon composite material is 0.0005-0.002 cm³. 3 / g. The specific surface area of ​​the silicon-carbon composite material is within this range, which allows the negative electrode active material to have a high specific capacity while effectively reducing the contact between the negative electrode active material and the electrolyte, reducing the formation of the SEI film, thereby improving the battery's initial efficiency and cycle performance.

[0074] For example, the pore volume of the silicon-carbon composite material is 0.0005 cm³. 3 / g, 0.0007cm 3 / g, 0.0009cm 3 / g, 0.0011cm 3 / g, 0.0013cm 3 / g, 0.0015cm 3 / g, 0.0017cm 3 / g, 0.0019cm 3 / g or 0.002cm 3 / g, or a range consisting of any two of these values.

[0075] The method for testing the pore volume of the silicon-carbon composite material in this invention is as follows: the low-temperature nitrogen adsorption method is used for testing, and the testing instrument is a Tri Star II surface area analyzer.

[0076] In one specific embodiment, the true density of the silicon-carbon composite material is 1.5-2.4 cm³. 3 / g. The true density of silicon-carbon composite materials, within a specific range, can ensure that the negative electrode active material has a high specific capacity while providing sufficient buffer space for the volume expansion of silicon materials during charging, thereby avoiding the failure of the negative electrode active material due to excessive volume expansion.

[0077] For example, the true density of the silicon-carbon composite material is 1.5 cm³. 3 / g, 1.6cm 3 / g, 1.7cm 3 / g, 1.8cm 3 / g, 1.9cm 3 / g, 2.0cm 3 / g, 2.1cm 3 / g, 2.2cm 3 / g, 2.3cm 3 / g or 2.4cm 3 / g, or a range consisting of any two of these values.

[0078] The method for testing the true density of silicon-carbon composite materials in this invention is as follows: The test is conducted using a JW M100A fully automatic true density tester. The test gas is helium. The silicon-carbon composite material powder is placed in the true density tester, and the pressure in the measuring chamber is gradually increased to a specified value. Then, the helium expands and enters the expansion chamber. The equilibrium pressure of the two processes is automatically recorded by the instrument. According to the law of conservation of mass, the volumes of the measuring chamber and the expansion chamber are calibrated by a standard sphere, and then the volume of the silicon-carbon composite material powder is determined to calculate the true density.

[0079] In one specific embodiment, the silicon-carbon core comprises a porous carbon material and silicon material deposited within the porous carbon material, wherein the average particle size of the silicon material is 0.1-2000 nm. When the silicon material is dispersed within the porous carbon material, it can distribute the stress generated by the expansion of the silicon material to various parts of the silicon-carbon composite material, thereby mitigating particle breakage failure caused by excessive local stress. The average particle size of the silicon material within this range balances the contact area between the silicon material and the electrolyte with the transport efficiency of active ions, thus balancing the battery's initial efficiency and rate performance.

[0080] For example, the average particle size of the silicon material is 0.1 nm, 200 nm, 400 nm, 600 nm, 800 nm, 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm or 2000 nm, or a range of any two of these values.

[0081] This invention does not specifically limit the content of porous carbon material and silicon material in silicon-carbon composite materials. In one embodiment, based on the total mass of the silicon-carbon composite material, the content of porous carbon material is 38-65%, the content of silicon material is 30-60%, and the content of SiO2 is 30-60%. x The content is 2-5%; where 0≤x≤2, SiO x This is formed during the preparation of silicon-carbon composite materials. When the content of each component in a silicon-carbon composite material satisfies the above relationship, the silicon-carbon composite material has the advantages of high specific capacity, high initial efficiency, and low expansion rate.

[0082] In one specific embodiment, the silicon content in the silicon-carbon composite material is 28-72% by mass. This range of silicon content balances the battery's energy density and cycle performance.

[0083] For example, the mass percentage of silicon in the silicon-carbon composite material is 28%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 72%, or a range of any two of these values.

[0084] In one specific embodiment, the cross-section of the silicon-carbon composite material has a first region and a second region. The mass content of silicon in the first region is c1, and the mass content of silicon in the second region is c2. The absolute difference between c2 and c1 is ≤10%. The perpendicular line to the tangent at any point on the edge of the cross-section has a dimension L on the cross-section. The region 0.3L from the edge of the cross-section on this perpendicular line constitutes the first region, and the remaining regions of the cross-section excluding the first region constitute the second region. The absolute difference between c2 and c1 falling within this range indicates that silicon material can be uniformly deposited in the pores of the porous carbon material, and there is no silicon particle agglomeration on the surface of the silicon-carbon composite material. When silicon material is uniformly dispersed in the pores of the porous carbon material, the stress generated by the expansion of silicon material during lithium intercalation can be uniformly distributed to various parts of the silicon-carbon composite material, thereby alleviating particle breakage failure caused by excessive local stress and improving the cycle performance of the battery.

[0085] For example, the absolute difference between c2 and c1 is 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2% or less, or a range of any two of these values.

[0086] The silicon mass content in both the first and second regions can be determined using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). In EDS point scanning mode, 5-10 points are selected in the first region, and the silicon mass content at each point is measured. The average value is the silicon mass content of the first region. The method for testing the silicon mass content in the second region is similar.

[0087] In one specific embodiment, the negative electrode active material further includes graphite material, wherein the OI value of the graphite material is ≥15 and the particle size Dv50 of the graphite material is 8-18μm;

[0088] In the thickness direction of the negative electrode sheet, the negative electrode sheet sequentially includes a negative electrode current collector, a first negative electrode active layer, and a second negative electrode active layer. The first negative electrode active layer comprises a silicon-carbon composite material, and the second negative electrode active layer comprises graphite material. The OI value of the graphite material is within this range, indicating that the graphite sheets exhibit a strong preferred arrangement or highly oriented structural feature within the material, which is beneficial for rapid electron conduction. The use of this graphite material in the second negative electrode active layer improves the rate performance of the battery, while the separate placement of the first and second negative electrode active layers further ensures the energy density of the battery. The Dv50 particle size of the graphite material is within this range, balancing the contact area with the electrolyte and the diffusion efficiency of active ions, thus balancing the battery's initial efficiency and rate performance.

[0089] For example, the OI value of the graphite material is 15, 16, 17, 18, 19, 20 or above, or a range of any two of these values.

[0090] For example, the particle size Dv50 of the graphite material is 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm or 18 μm, or a range of any two of these values.

[0091] In one specific embodiment, the battery further includes a separator, which comprises a separator substrate and an adhesive layer coated on the surface of the separator substrate, wherein the adhesive layer has a coverage of 15-45% on the separator substrate. Within this range, the coverage of the adhesive layer on the separator substrate ensures both the adhesion of the separator and the internal resistance of the battery.

[0092] For example, the coverage of the adhesive layer on the membrane substrate is 15%, 18%, 21%, 24%, 27%, 30%, 33%, 36%, 39%, 42%, or 45%, or a range of any two of these values.

[0093] The adhesive layer of the present invention is formed by discontinuous adhesive dots. The present invention does not specifically limit the size and spacing of the adhesive dots. In one embodiment, the size of the adhesive dots is 50-200μm and the spacing between the adhesive dots is 200-500μm.

[0094] This invention does not strictly limit the choice of material for the separator substrate. It can be one of the separator substrate materials commonly used in batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), and cellulose nonwoven fabric separator.

[0095] In one specific embodiment, the separator further includes a functional layer located between the adhesive layer and the separator substrate. The functional layer includes first particles, which comprise at least one of 1,3,5-triazine-2,4,6-triamine, melamine cyanurate, melamine trithiocyanate, polyacrylonitrile, or nitrile rubber. The aspect ratio of the first particles is 2-8. The negative polar groups of the aforementioned first particles are beneficial for increasing the active ion transport rate on the negative electrode side, reducing electrochemical polarization, and improving the constant current charge ratio of the battery cell. Simultaneously, the first particles can also suppress Co in the positive electrode active material. 3+ Dissolution further stabilizes the structure of the positive electrode active material and improves battery cycle performance. The aspect ratio of the first particle is within the aforementioned range, which is beneficial for constructing a continuous and dense coating structure, enhancing the physical interlocking and bonding strength between the coating and the adhesive layer and the separator substrate, improving the overall mechanical integrity of the separator, and thus improving battery cycle performance.

[0096] For example, the aspect ratio of the first particle is 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5 or 8, or a range of any two of these values.

[0097] When the first particles mentioned above are mixtures of the aforementioned substances, the present invention does not specifically limit the proportion of each specific substance in the mixture.

[0098] The separator of the present invention also includes polyvinylidene fluoride (PVDF), which swells in ethylene carbonate (EC) / dimethyl carbonate (DMC) solvent to form a gel network that promotes active ion transport and improves the cell dynamics performance.

[0099] In one specific embodiment, the battery further includes a positive electrode sheet, which includes a positive electrode active material;

[0100] The positive electrode active material includes tellurium, preferably with a tellurium content of 10-50 ppm by mass. Adding tellurium to the positive electrode active material improves the battery's cycle performance and reduces lithium plating. Within the aforementioned range, the tellurium content effectively stabilizes the crystal structure of the positive electrode active material, forming a more stable positive and negative electrode with the negative electrode active materials, thus improving the battery's cycle performance. Furthermore, tellurium doping improves electronic conductivity and reduces positive electrode polarization, complementing the improved conductivity of graphene and ensuring a dynamic match between the active ions shuttling between the positive and negative electrodes, thereby reducing lithium plating.

[0101] For example, the tellurium content, expressed as a percentage by mass, is 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, or 50 ppm, or a range of any two of these values.

[0102] The positive electrode active material of this invention also includes Al, Y, and La elements; wherein the Al content is ≤500ppm, the Y content is ≤200ppm, and the La content is ≤100ppm. These elements, within their respective ranges, further enhance the structural stability of the positive electrode active material, thereby improving the cycle performance of the battery.

[0103] The positive electrode active material in this invention includes both monocrystalline and polycrystalline particles. Monocrystalline particles, due to their uniform internal crystal structure and consistent grain orientation, exhibit excellent structural stability. Polycrystalline particles have smaller primary particle sizes, significantly shortening the transport distance of active ions and thus improving battery rate performance. Therefore, when monocrystalline and polycrystalline particles are used in combination, they offer good structural stability and rate performance. Furthermore, when the positive electrode active material comprises both monocrystalline and polycrystalline particles, it exhibits a lower discharge temperature rise. Reducing the battery temperature during charging and discharging effectively suppresses silicon volume expansion, resulting in higher cycle performance and energy density. Therefore, when the positive electrode active material meets specific characteristics, its use in conjunction with the negative electrode active material provided in this invention can further enhance the overall energy density, rate performance, and cycle performance of the battery.

[0104] The positive electrode sheet of the present invention specifically includes a positive electrode current collector and a positive electrode active layer formed of a positive electrode active material disposed on the surface of the positive electrode current collector. The positive electrode active material may include at least one of lithium cobalt oxide (LCO), nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), nickel cobalt manganese aluminum quaternary material (NCMA), lithium iron phosphate (LFP), lithium manganese phosphate (LMP), lithium vanadium phosphate (LVP), lithium manganese oxide (LMO), lithium nickel oxide, lithium nickel manganese oxide binary material, lithium-rich manganese-based material, and lithium manganese iron phosphate.

[0105] In the specific preparation of the positive electrode sheet, for example, the positive electrode active material of the present invention can be dispersed with a conductive agent and a binder in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling and slitting, the positive electrode sheet is obtained. In one specific embodiment, the positive electrode active layer comprises, by weight percentage, 70-99 wt% of positive electrode active material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder, and further comprises 80-98 wt% of positive electrode active material, 1-10 wt% of conductive agent, and 1-10 wt% of binder.

[0106] The positive current collector can be made of at least one of aluminum foil or nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; and the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0107] In one specific embodiment, the electrolyte further includes adiponitrile, with the adiponitrile comprising 0.5-8% by mass. Adiponitrile can form an elastic SEI on the surface of the silicon-carbon composite material, mitigating volume expansion, while also reducing surface tension and promoting wetting between the electrolyte and the silicon-carbon composite material. Within this range of adiponitrile mass percentage in the electrolyte, both rate performance and cycle performance of the battery can be balanced.

[0108] For example, the mass percentage of adiponitrile in the electrolyte is 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%, or a range of any two of these values.

[0109] This invention does not specifically limit the other components and contents of the electrolyte. In one embodiment, the electrolyte further includes a solvent, a lithium salt, and other additives. The solvent can be a mixture of EC and chain carbonates (DMC, EMC, etc.), with a volume ratio of EC to chain carbonates of 3:7, and the solvent accounting for 70-85% of the total electrolyte mass. The lithium salt can be one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), accounting for 10-15% of the total electrolyte mass. The additives include at least one of carbonate additives and nitrile additives. The carbonate additive can be at least one of fluoroethylene carbonate (FEC) and vinylene carbonate (VC). FEC accounts for 10-20% of the total electrolyte mass, and VC accounts for 1-3% of the total electrolyte mass. The addition of VC is beneficial for improving the SEI film quality on the negative electrode surface and further improving the cycle stability of the silicon-carbon composite material.

[0110] This invention does not strictly limit the battery manufacturing method. In one embodiment, a bare cell is obtained by winding or stacking a positive electrode sheet, a separator, and a negative electrode sheet, and then packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried at 85°C, electrolyte is injected into the dried battery. The battery is then placed, formed, and resealed to complete the battery manufacturing process.

[0111] In this invention, the mass ratio of positive electrode active material per unit area in the positive electrode sheet to negative electrode active material per unit area in the negative electrode sheet is preferably controlled between 2.3 and 8.0. This method is particularly suitable for battery systems composed of cobalt-containing positive electrode active material and silicon-doped negative electrode active material. By setting a higher positive-to-negative electrode mass ratio, it effectively compensates for the irreversible capacity loss caused by the low initial coulombic efficiency of the silicon-doped negative electrode, thereby significantly suppressing lithium plating during charging and improving the charging safety and cycle stability of the battery.

[0112] The present invention will be further described below through specific embodiments.

[0113] Example 1

[0114] The battery preparation method in this embodiment includes:

[0115] (1) Preparation of negative electrode

[0116] 1) Amorphous carbon coating: 100g of silicon-carbon material was weighed and placed in a 2L reactor. 1500ml of a 6.8wt% phenolic resin ethanol solution was added. The mixture was mechanically stirred at 300rpm for 10h at a constant temperature of 45℃ to ensure complete resin impregnation and adsorption. Subsequently, the ethanol solvent was slowly removed using a rotary evaporator at a water bath temperature of 60℃ to obtain a pre-coated powder. The obtained powder was placed in a muffle furnace and heated to 250℃ at 2℃ / min under air atmosphere, and held for 1.5h to complete cross-linking and curing. Then, it was transferred to a tube furnace and heated to 600℃ at 5℃ / min under argon protection, and held for 2h for carbonization. After natural cooling, an amorphous carbon-coated intermediate product was obtained, denoted as Si / C@aC.

[0117] 2) Graphene layer coating: In an argon glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), 8 g of reduced graphene oxide powder was weighed and added to 1000 ml of anhydrous NMP solvent. The mixture was ultrasonically broken up at 400 W for 45 min under ice-water bath conditions to form a uniformly dispersed rGO / NMP suspension (concentration 8 mg / ml). 100 g of Si / C@aC from step 1) was added to this suspension and transferred to a three-necked flask equipped with a reflux condenser. Under argon protection and a 70°C oil bath, the mixture was mechanically stirred at 500 rpm for 8 h to complete the self-assembly coating of the graphene layer, resulting in the coated slurry.

[0118] 3) Post-processing: The coated slurry was treated in an argon atmosphere using a spray dryer with an inlet temperature of 200℃, an outlet temperature of 105℃, and a material flow rate of 10ml / min to obtain precursor powder. Finally, the precursor powder was placed in a tube furnace and heat-treated in an Ar / H2 mixed gas atmosphere (95:5 volume ratio) at a rate of 3℃ / min to 550℃, held for 2 hours, and then allowed to cool naturally to obtain the silicon-carbon composite material, denoted as Si / C@aC@rGO.

[0119] 4) Negative electrode materials: The prepared silicon-carbon composite material, graphite, conductive agent, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and water are added to a planetary mixing tank, wherein the mass ratio of active materials is 7:90:0.5:1.2:1.3, and the negative electrode slurry is prepared by rotating at 500 r / min and revolving at 2000 r / min.

[0120] 5) Negative electrode coating: A negative electrode slurry is coated on the surface of the negative electrode current collector with a coating thickness of 50μm. The coating is then dried in an oven at 80℃ to obtain the negative electrode sheet.

[0121] (2) Preparation of positive electrode sheet

[0122] Positive electrode preparation and coating: Lithium cobalt oxide, conductive agent and PVDF are mixed in NMP solvent at a mass ratio of 97:2:1 and stirred at a rotation speed of 800 r / min and a revolution speed of 2500 r / min to prepare positive electrode slurry. The slurry is then coated on 10 μm aluminum foil and dried in an oven at 120℃.

[0123] (3) Battery preparation

[0124] A positive electrode, separator, and negative electrode are fabricated and wound into a battery. The electrolyte includes LiPF6 (1 mol / L), ethylene carbonate (EC), dimethyl carbonate (DMC), 2,2-difluoroethyl acetate (DFEA), and adiponitrile. The adiponitrile content in the electrolyte is 4% by mass, EC content is 30% by mass, DMC content is 23.5% by mass, and DFEA content is 30% by mass. Relevant parameters for Example 1 are shown in Tables 1A, 1B, 2A, and 2B.

[0125] The relevant parameters for Examples 2-23 and Comparative Examples 1-7 are shown in Tables 1A, 1B, 1C, 2A, and 2B.

[0126] Experimental Example 1

[0127] 1. The I2D / IG value, half-peak width of the 2D peak, thickness of the amorphous carbon layer, thickness of the graphene layer, mass percentage of nitrogen in the amorphous carbon layer of the silicon-carbon composite material (abbreviated as nitrogen content), particle size Dv50, sphericity, specific surface area, pore volume, true density of the silicon-carbon composite material, average particle size of silicon material, mass percentage of silicon in the silicon-carbon composite material, and absolute difference between c2 and c1 were tested for the silicon-carbon composite material in the examples and comparative examples; the tellurium content in the positive electrode active material of the batteries in the examples and comparative examples, and the content of 2,2-difluoroethyl acetate and adiponitrile in the electrolyte of the batteries in the examples and comparative examples; see Tables 1A, 1B, 1C, 2A, and 2B.

[0128] 2. Testing Methods

[0129] 1) Test methods for the thickness of amorphous carbon layers and graphene layers

[0130] The battery was discharged to 0% SOC, the negative electrode was disassembled and removed, and then soaked in dimethyl carbonate (DMC) solvent for 12 hours. Afterward, it was rinsed with DMC solvent to remove lithium salt adhering to the negative electrode. After drying, the silicon material was cut using an argon ion milling machine (CP). TEM was used to observe and determine the positions of the amorphous carbon layer and graphene layer. Ten test sites were randomly selected on the surface of each amorphous carbon layer and graphene layer, and the thickness of each site was measured, with the average value taken. At least 10 silicon material particles were selected for measurement, and the final average value was taken.

[0131] 2) Test method for determining the mass percentage of nitrogen in the amorphous carbon layer of silicon-carbon composite material

[0132] Nitrogen element determination: A carbon, sulfur and nitrogen element analyzer is used to measure nitrogen. A certain mass of sample is taken and placed on a ceramic boat for complete combustion in a high temperature and oxygen-rich environment. Nitrogen oxides are converted into nitrogen gas, which is then directly introduced into the gas separation system along with the carrier gas for adsorption and detection.

[0133] 3) Test methods for particle size Dv50, sphericity, specific surface area, pore volume, and true density of silicon-carbon composite materials; test methods for the average particle size of silicon materials.

[0134] The particle size Dv50 of the silicon-carbon composite material was measured using a Malvern laser particle size analyzer.

[0135] Sphericity of silicon-carbon composite materials: After cycling, the battery was disassembled, the negative electrode was removed, cleaned and dried with dimethyl carbonate, and then the cross-section of the electrode was polished using an argon-ion polishing machine. The cross-sectional morphology was observed using a scanning electron microscope in backscatter mode to identify the white spherical silicon-carbon composite material particles. The maximum diameter d1 and minimum diameter d2 of each particle's cross-section were measured, and the d1 / d2 ratio was calculated as the sphericity of a single particle. At least 30 particles were selected for testing, and the average value was taken to obtain the average sphericity of the silicon-carbon composite material.

[0136] The specific surface area of ​​the silicon-carbon composite material was determined by N2 adsorption-desorption test.

[0137] The pore volume of silicon-carbon composite materials was tested using a low-temperature nitrogen adsorption method, and the instrument used was a Tri Star II surface area analyzer.

[0138] The true density test method for silicon-carbon composite materials is as follows: The test is conducted using a JW M100A fully automatic true density tester. The test gas is helium. The silicon-carbon composite material powder is placed in the true density tester, and the pressure in the measuring chamber is gradually increased to a specified value. Then, the helium expands and enters the expansion chamber. The equilibrium pressure of the two processes is automatically recorded by the instrument. According to the law of conservation of mass, the volumes of the measuring chamber and the expansion chamber are calibrated by a standard sphere, and then the volume of the silicon-carbon composite material powder is determined to calculate the true density.

[0139] 4) Test methods for the mass percentage of silicon in silicon-carbon composite materials and the absolute difference between c2 and c1.

[0140] The silicon content was determined by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). In EDS point scanning mode, 5-10 points were selected in the silicon-carbon composite material, and the silicon mass content at each point was measured. The average value was taken as the silicon mass content in the silicon-carbon composite material.

[0141] The silicon mass content in both regions can be determined using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). In EDS point scanning mode, 5-10 points are selected in the first region, and the silicon mass content at each point is measured. The average value is the silicon mass content of the first region. The method for testing the silicon mass content in the second region is similar. The absolute difference between c2 and c1 represents the absolute difference between the silicon mass content in the first and second regions.

[0142] Table 1A

[0143]

[0144] Table 1B

[0145]

[0146] Table 1C

[0147]

[0148] Table 2A

[0149]

[0150] Table 2B

[0151]

[0152] Experimental Example 2

[0153] 1. The batteries of the examples and comparative examples were tested for first-efficiency performance, rate performance, cycle performance and energy density. The results are shown in Tables 3A and 3B.

[0154] 2. Testing Methods

[0155] 1) First-effect testing method

[0156] The silicon-carbon composite material, carbon nanotubes, styrene-butadiene rubber, and conductive carbon black (SuperP) prepared in each embodiment and comparative example were mixed at a mass ratio of 90:1:5:4, and deionized water was added. The mixture was ultrasonically treated for 30 min and then vacuum stirred (1000 rpm, 4 h) to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto copper foil using a 200 μm scraper, and then vacuum dried in a vacuum oven at 100 °C for 10 h to obtain a negative electrode sheet. Under drying conditions, the negative electrode sheet was formed into a negative electrode disc with a diameter of 12 mm using a die-casting machine. In a glove box, the negative electrode disc was used as the working electrode, a lithium metal sheet was used as the counter electrode, and a polyethylene membrane with a thickness of 20 μm was used as the separator. Electrolyte was added to assemble a coin cell half-cell.

[0157] After the coin cell half-cell is allowed to rest and reach equilibrium, it undergoes a stepped discharge (0.1C → 0.05C) to 5mV, followed by a constant current charge of 0.05C to 1.5V. Initial coulombic efficiency (%) = charge capacity / total discharge capacity × 100%.

[0158] 2) Test methods for rate performance

[0159] Charged to 4.53V at 0.2C current, and then cut off at 0.02C current, constant current discharge tests were performed at 0.2C and 1C rates (cutoff voltage 3.0V). Rate performance = 1C capacity / 0.2C capacity × 100%.

[0160] 3) Cyclic performance testing methods

[0161] Cyclic performance (%) = C 1000 / C0×100%, where C 1000 C0 represents the capacity retained after 1000 cycles at 25°C, and C0 represents the initial discharge capacity. The testing method is as follows: The lithium-ion secondary batteries prepared in the embodiments and comparative examples of this invention are tested in the LAND testing system: They are charged at a constant current of 1.5C to 4.53V, then charged at a constant voltage of 0.1C, left to stand for 10 minutes, and then discharged at 1C to 3V, left to stand for 10 minutes; this cycle is repeated 1000 times. The battery cycle capacity is calculated based on the initial discharge capacity and the discharge capacity per cycle.

[0162] 4) Test method for volumetric energy density

[0163] The volumetric energy density of the batteries prepared in the examples and comparative examples was tested using the following specific methods:

[0164] The battery was charged at a current of 0.2C to its upper limit voltage (4.53V), then charged at a constant voltage until the current dropped to 0.02C. It was then discharged at a current of 0.2C until it reached 3.0V. The energy discharged is denoted as E. The battery's thickness, width, and length were measured, and their product was calculated to obtain the battery's volume, denoted as V. The formula for calculating volumetric energy density is V0. ED =E / V.

[0165] Table 3A

[0166]

[0167] Table 3B

[0168]

[0169] As shown in Tables 3A and 3B, compared with the comparative example, the battery of the present invention has excellent first-efficiency performance, rate performance, cycle performance, and high volumetric energy density.

[0170] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A battery, characterized by, The battery comprises a negative electrode sheet and an electrolyte, the negative electrode sheet comprises a negative electrode active material, the negative electrode active material comprises a silicon-carbon composite material, the silicon-carbon composite material comprises a silicon-carbon inner core and a shell coated on the surface of the silicon-carbon inner core, the shell comprises an amorphous carbon layer and a graphene layer, and the amorphous carbon layer is located between the silicon-carbon inner core and the graphene layer. In the Raman spectrum of the silicon-carbon composite material, the value k of I2D / IG satisfies 0.4≤k≤0.

8. The electrolyte comprises 2,2-difluoroethyl acetate, the mass percentage m% of the 2,2-difluoroethyl acetate in the electrolyte satisfies 5%≤m%≤65%, and k / m satisfies 0.008≤k / m≤0.

1.

3. The battery according to claim 1 or 2, wherein the thickness of the amorphous carbon layer is 2-20 nm; and / or the thickness of the graphene layer is 1-10 nm.

2. The battery of claim 1, wherein, The half-peak width of the 2D peak in the Raman spectrum of the silicon-carbon composite material is not greater than 65 cm -1 , preferably 45-65 cm -1 . The amorphous carbon layer further comprises at least one of nitrogen element, phosphorus element and boron element, and preferably the nitrogen element. Preferably, the mass percentage of the nitrogen element in the silicon-carbon composite material is 0.2-1%. The particle size Dv50 of the silicon-carbon composite material is 5-15 μm; and / or the sphericity of the silicon-carbon composite material is 0.7-1; and / or the silicon-carbon inner core comprises a porous carbon material and a silicon material deposited in the interior of the porous carbon material, and the average particle size of the silicon material is 0.1-2000 nm; and / or the mass percentage of silicon element in the silicon-carbon composite material is 28-72%.

4. The battery according to any one of claims 1 to 3, characterized in that The silicon-carbon composite material has a first region and a second region on the cross section, the mass content of silicon element in the first region is c1, the mass content of silicon element in the second region is c2, and the absolute difference between c2 and c1 is ≤10%; wherein the perpendicular line of the tangent line of any point on the edge of the cross section has a size L on the cross section, and the region 0.3L away from the edge of the cross section on the perpendicular line constitutes the first region, and the remaining region of the cross section except the first region constitutes the second region. The negative electrode active material further comprises a graphite material, the OI value of the graphite material is ≥15, and the particle size Dv50 of the graphite material is 8-18 μm.

5. The battery according to any one of claims 1 to 4, characterized in that, In the thickness direction of the negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector, a first negative electrode active layer and a second negative electrode active layer in sequence, wherein the first negative electrode active layer comprises the silicon-carbon composite material, and the second negative electrode active layer comprises the graphite material. The battery further comprises a separator, the separator comprises a separator base and a glue layer coated on the surface of the separator base, and the coverage of the glue layer on the separator base is 15-45%; and the separator further comprises a functional layer between the glue layer and the separator base, the functional layer comprises first particles, the first particles comprise at least one of 1,3,5-triazine-2,4,6-triamine, melamine cyanurate, melamine trimer thiocyanate, polyacrylonitrile or butyronitrile rubber, and the aspect ratio of the first particles is 2-8. The specific surface area of the silicon-carbon composite material is 0.1-10 m 2 / g; and / or, The silicon-carbon composite has a pore volume of 0.0005-0.002 cm 3 / g; and / or, The silicon-carbon composite material has a true density of 1.5-2.4 cm 3 / g; and / or, ​ ​ 6. The battery according to any one of claims 1 to 5, characterized in that, ​ 7. The battery according to any one of claims 1 to 6, wherein ​ ​ 8. The battery according to any one of claims 1 to 7, characterized in that ​ ​ 9. The battery according to any one of claims 1 to 8, characterized in that, The battery further comprises a positive electrode sheet comprising a positive electrode active material; The positive electrode active material comprises tellurium, preferably the content of the tellurium is 10-50 ppm in mass percentage.

10. The battery of any one of claims 1-9, wherein, The electrolyte further comprises hexanedinitrile, and the mass percentage content of the hexanedinitrile in the electrolyte is 0.5-8%.

Images