battery

Abstract

The application relates to the technical field of batteries, in particular to a battery. The battery comprises an electrode assembly formed by laminating and winding a positive electrode sheet, a separator and a negative electrode sheet, the negative electrode sheet comprises 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 comprises a negative electrode active material, the negative electrode active material comprises a silicon-carbon material, at least one included angle exists on a cross-section profile of the silicon-carbon material, and the average angle of the included angle is 10 DEG to 150 DEG; the separator comprises a base material layer and a glue layer located on at least one side surface of the base material layer, the glue layer comprises glue particles, the glue particles protrude to form protrusions on a side away from the base material layer, the glue particles comprise a first polymer, the average height of the protrusions is h, and h is 1 micrometer to 6 micrometers; and the glue layer is arranged opposite to the negative electrode sheet. The battery has good cycle stability and rate performance, and the lithium precipitation of the negative electrode is improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a battery. Background Technology

[0002] As the demand for electric vehicles with longer driving ranges and longer lifespans continues to increase, the demand for high-energy-density, long-cycle, and high-safety lithium-ion batteries is growing. Silicon materials, due to their environmental friendliness and high capacity, are gradually partially replacing traditional graphite. With the increasing demand for energy density, the silicon content in silicon-based anodes is constantly increasing. However, silicon-based materials undergo significant volume expansion during charging and discharging, especially in wound-structured batteries. The curved areas naturally experience greater bending stress, which is further exacerbated by the expansion stress of the silicon-based anode. This leads to decreased adhesion and insufficient interface stability at the anode-separator interface, resulting in a loose battery structure and interrupted ion transport paths between interfaces. Furthermore, the electrolyte often has more difficulty wetting the electrodes located at the curved areas, leading to poor ion transport in these regions. During battery cycling, the anodes located at the curved areas are prone to lithium plating, resulting in poor rate performance and cycle stability. Summary of the Invention

[0003] The purpose of this invention is to provide a battery that uses a separator with raised surfaces and a silicon-carbon material with an angled cross-sectional profile, which improves the rate performance and cycle stability of the battery while suppressing lithium deposition in the arc-shaped negative electrode.

[0004] Due to its structural characteristics, the electrode at the arc of a wound battery is prone to local stress concentration under the combined effects of curling stress and negative electrode expansion stress. At the same time, the arc area is also a weak area for electrolyte wetting. All of these factors increase the resistance to lithium ion transport at the interface, reduce lithium ion transport efficiency, and lead to lithium plating in the arc area, affecting the rate performance and cycle stability of the battery. In related technologies, while near-spherical silicon-carbon materials have better compressive strength, their small contact area with the conductive agents, binders, and graphite particles in the negative electrode active layer affects the electron and ion transport of the negative electrode active material. At the same time, the small contact area between near-spherical silicon-carbon materials and the negative electrode current collector reduces the peel strength of the negative electrode active layer, making it easier for the negative electrode active material to detach or peel off from the surface of the negative electrode sheet under stress, which is not conducive to improving lithium plating in the arc region. On the other hand, irregular blocky silicon-carbon materials are limited by the existence of their particle edges and corners, resulting in low strength. They are easily broken under external pressure and puncture the separator, causing battery self-discharge. At the same time, the specific surface area of ​​the broken silicon-carbon material increases, which intensifies the side reactions with the electrolyte and is not conducive to improving the cycle stability of the battery.

[0005] The inventors of this invention have discovered that using a separator with raised surfaces in combination with a silicon-carbon material whose interface contour has an angle within a certain range can significantly improve the interfacial adhesion between the electrode and the separator, increase the porosity of the negative electrode, and reserve storage space for the electrolyte. This promotes the wetting of the electrode and separator in the arc-shaped area by the electrolyte, thereby improving the rate performance and cycle stability of the battery while suppressing the lithium plating problem in the arc-shaped area.

[0006] First, the negative electrode uses silicon-carbon material with at least one included angle in its cross-sectional profile, ranging from 10° to 150°. Compared to near-spherical silicon-carbon material, this material has more grooves on its surface, resulting in a relatively increased specific surface area. This increases the effective contact area between the silicon-carbon material and the conductive agent, binder, and graphite particles in the negative electrode active layer, improving the peeling force of the negative electrode active layer. It also possesses sufficient strength to resist external stress and maintain its structural stability. Compared to blocky silicon-carbon material, its surface has fewer sharp edges, reducing the risk of particle breakage and pulverization, as well as membrane puncture, and exhibiting higher compressive strength. Specifically, the included angle in the cross-sectional profile of the silicon-carbon material creates a certain electrolyte storage space between the silicon-carbon material on the negative electrode surface and the membrane, improving electrolyte flow and facilitating rapid lithium-ion transport, thereby alleviating the lithium plating problem in the arc-shaped region of the negative electrode.

[0007] Secondly, the separator employs a special structure with several protrusions formed on at least one surface. These protrusions create a gap between the separator and the negative electrode, further increasing the electrolyte storage space. Simultaneously, the protrusions form several support points between the separator and the negative electrode, maintaining the bonding strength between them while increasing the electrolyte storage space, ensuring stable interfacial contact. Furthermore, adjusting the average height h of the protrusions to the range of 1μm to 6μm not only ensures that the electrolyte particles in the separator can expand the negative electrode to create sufficient space for electrolyte storage, but also reduces the impact on battery energy density and maintains the interfacial contact between the separator and the negative electrode.

[0008] Finally, the combination of a protruding separator and a silicon-carbon material with an angled cross-sectional profile significantly suppresses lithium plating in the arc region, improving battery rate performance and cycle stability. This is because: First, the angled area of ​​the silicon-carbon material macroscopically manifests as a trench structure on its surface, with a high radius of curvature, which enhances the local electric field. Lithium ions tend to rapidly embed from the trench walls, shortening the solid-phase diffusion distance compared to the near-spherical shape of the silicon-carbon material and improving kinetics. Second, the trench structure of the silicon-carbon material matches the protrusions of the separator, reducing the separator-negative electrode interface slippage caused by the expansion of the negative electrode during charging and discharging. First, the surface trenches of the silicon-carbon material can store a portion of the electrolyte, enabling localized electrolyte replenishment and preventing interface drying that could lead to lithium plating on the negative electrode. The separator surface has abundant carboxylic acid functional groups, which can form a high-density hydrogen bond network with some oxygen-containing functional groups on the surface of the silicon-carbon material. Combined with the abundant electrolyte storage, this helps to form a thinner, denser, and more stable SEI film on the surface of the silicon-carbon material, thereby restricting the volume expansion of the silicon-based negative electrode, reducing electrolyte side reactions, improving the cycle stability and rate performance of the battery, and suppressing lithium plating on the negative electrode.

[0009] Based on this, the present invention proposes the following technical solution: This invention provides a battery comprising an electrode assembly formed by stacking and winding a positive electrode, a separator, and a negative electrode. 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 includes a negative active material, which is a silicon-carbon material. At least one included angle exists on the cross-sectional profile of the silicon-carbon material, and the average angle of the included angle is 10° to 150°. The separator includes a substrate layer and an adhesive layer located on at least one side of the substrate layer. The adhesive layer includes adhesive particles, which protrude on the side opposite to the substrate layer to form protrusions. The adhesive particles include a first polymer, and the average height of the protrusions is h, which is 1 μm to 6 μm. The adhesive layer is disposed opposite to the negative electrode.

[0010] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: The battery of the present invention improves the rate performance and cycle stability of the battery while suppressing lithium plating in the arc region.

[0011] 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

[0012] Figure 1 The figure shown is a cross-sectional schematic diagram of the negative electrode active layer in one embodiment 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] The present invention provides a battery comprising an electrode assembly formed by stacking and winding a positive electrode, a separator, and a negative electrode. The negative electrode comprises a negative current collector and a negative active layer located on at least one side surface of the negative current collector. The negative active layer comprises a negative active material, which comprises a silicon-carbon material. At least one included angle exists on the cross-sectional profile of the silicon-carbon material, and the average angle of the included angle is 10° to 150°, for example, 10°, 25°, 40°, 55°, 70°, 85°, 100°, 115°, 130°, 145°, or 150°.

[0015] In one embodiment, the average angle of the included angle is 45° to 120°.

[0016] It is understood that the included angle located in the cross-sectional profile of the silicon-carbon material refers to: among all points on the cross-sectional profile of the silicon-carbon material, the single point with a vertical distance of more than 0.25 μm from its convex hull segment is taken as the vertex, and a straight line tangent to the cross-sectional profile of the silicon-carbon material is drawn. At this time, there are two different tangent lines, and the angle formed by the two tangent lines outside the cross-section of the silicon-carbon material is the included angle.

[0017] like Figure 1 The figure shown is a cross-sectional schematic diagram of the negative electrode active layer in one embodiment of the present invention, where ∠1 and ∠2 are the included angles.

[0018] In this invention, the diaphragm includes a substrate layer and an adhesive layer located on at least one side of the substrate layer. The adhesive layer includes adhesive particles, which protrude on the side opposite to the substrate layer to form protrusions. The adhesive particles include a first polymer. The average height of the protrusions is h, which is 1 μm to 6 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm.

[0019] In this invention, the adhesive layer is positioned directly opposite the negative electrode sheet.

[0020] When the average angle of the included electrode is within the range of 10° to 150°, more electrolyte can be stored, improving electrolyte flow and promoting lithium-ion transport, thus alleviating the lithium plating problem of the negative electrode in the arc region. When the average angle of the included electrode is too small (e.g., less than 10°), the angle is too sharp, reducing the contact area between the silicon-carbon material and components such as graphite and conductive agents, affecting electron and ion transport, and hindering the improvement of battery cycle stability and the lithium plating problem in the arc region. When the average angle of the included electrode is too large (e.g., greater than 150°), the surface of the silicon-carbon material particles tends to be smooth, making it difficult to form trenches with effective volume to store electrolyte, resulting in an insignificant electrolyte storage effect and failing to effectively supplement the additional electrolyte demand in the arc region.

[0021] The protrusion height refers to the height space created by the gel particles at the separator-negative electrode interface after hot pressing of the battery cell. When the average protrusion height is within this range, the impact on battery energy density is relatively low, and it can provide additional liquid storage space while maintaining stable interface contact, thus improving the problem of lithium plating at electrode arcs. When h is too small (e.g., less than 1 μm), the protrusion is difficult to form an effective liquid storage gap space at the negative electrode-separator interface, and the liquid storage effect is not obvious. When h is too large (e.g., greater than 6 μm), although the protrusion can provide a larger space, the matching degree with the silicon-carbon material angle region is poor, and problems such as interface slippage are prone to occur during battery cycling, resulting in decreased interface stability. This is not conducive to further improvement of battery cycle stability and increases the risk of lithium plating.

[0022] In this invention, the average angle of the included angle can be obtained by conventional testing methods in the art, such as by SEM measurement, specifically as follows: Discharge the battery to 0% SOC, disassemble and remove the negative electrode sheet, or directly remove the negative electrode sheet, polish its cross-section with an argon ion mill, and image the obtained cross-section using backscatter imaging mode in an SEM device. Find the point on the outline of the silicon-carbon material particle that is more than 0.25 μm away from its convex hull line segment as the vertex. Draw two tangent lines through the vertex to the outline of the silicon-carbon material cross-section, and use image processing software to measure the angle between the two tangent lines outside the cross-section. A total of 10 different first silicon-carbon material particles are measured, and the average value is taken as the average angle of the included angle.

[0023] In this invention, h can be obtained by conventional testing methods in the art. For example, after discharging the battery to 0% SOC, the separator is disassembled, cleaned with anhydrous ethanol to remove electrolyte and residual lithium salt, and the height of the protrusions on the separator surface is tested using a 3D profilometer. The average value is then taken as h.

[0024] In this invention, the first polymer comprises at least one of the following monomers polymerized together: methyl acrylate, methyl methacrylate, ethyl methacrylate, ethyl acrylate, and butyl acrylate.

[0025] In this invention, the adhesive layer further includes a second polymer, which includes at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, and sodium alginate.

[0026] In this invention, the average particle size of the adhesive particles is 1μm to 10μm, for example, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm.

[0027] In one embodiment, the average particle size of the colloidal particles is 4 μm to 8 μm.

[0028] In this invention, the colloidal particle is formed by the accumulation of a plurality of primary particles, wherein "a plurality of" refers to the number of primary particles constituting the colloidal particle being greater than or equal to 2. The average particle size of the primary particles is 100nm to 1000nm, for example, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 800nm ​​or 1000nm.

[0029] It is understood that the protrusion is formed by the adhesive particles protruding on the side away from the substrate layer. Taking into account the deformation of the substrate layer, the height of the protrusion is determined based on the distance from the vertex of the protrusion away from the substrate layer to the surface of the substrate layer.

[0030] In this invention, the area of ​​the orthographic projection of the colloidal particles with an average particle size greater than or equal to 4 μm on the surface of the diaphragm accounts for 5% to 15%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

[0031] When the average particle size of the colloidal particles is within this range, the particle size is close to that of the positive and negative electrode active materials, which can effectively construct the liquid storage space without adversely affecting the electrode structure. When the average particle size of the colloidal particles is too small (e.g., less than 1 μm), the height of the colloidal particles is limited, making it difficult to effectively expand the electrode sheet. The resulting gap space is limited, and the liquid storage effect is not obvious. At the same time, the colloidal particles cannot form protrusions of sufficient height to form effective support points at the interface, which is not conducive to improving the cycle stability and rate performance of the battery, nor is it conducive to further mitigating the lithium plating problem of the negative electrode sheet in the arc area. When the average particle size of the colloidal particles is too large (e.g., greater than 10 μm), the protrusions formed by the colloidal particles can support a larger space, but the excessively large particles block the reaction sites on the surface of the negative electrode active material, which is not conducive to the effective transport of lithium ions and increases the risk of lithium plating.

[0032] The area ratio of the projected surface area of ​​particles with an average particle size greater than or equal to 4 μm on the separator reflects the coverage of particles (≥4 μm) on the separator surface. When the coverage is in the range of 5% to 15%, it can provide sufficient interfacial support points and additional electrolyte storage space without severely clogging the separator pores and affecting ionic conductivity. When the coverage is too small (e.g., less than 5%), the support distribution at the interface is sparse, the spatial distribution between the negative electrode and the separator is uneven, the electrolyte storage effect and distribution uniformity are poor, and it is easy to lead to excessively high local lithium-ion concentration or excessive local electrolyte side reactions, which is not conducive to improving the rate performance of the battery and improving lithium plating in the arc region. When the coverage is too large (e.g., greater than 15%), the support points at the interface are more dense. Although the bonding strength will be improved and the electrolyte storage space is larger, the air permeability of the separator will be significantly reduced, leading to blockage of ion transport channels, which may increase the internal resistance of the battery, which is not conducive to improving the rate performance of the battery and improving lithium plating in the arc region.

[0033] In this invention, the average particle size of the gel particles can be obtained using conventional testing methods in the art, for example, by discharging the battery to 0% SOC, disassembling and removing the separator, cleaning with anhydrous ethanol to remove surface lithium salt and electrolyte, drying, and then using SEM to obtain a scanning image of the separator's adhesive layer surface. Using image analysis software such as Image Pro Plus, the maximum diameter of any 30 gel particles in the obtained scanning image is measured, and the average of these measurements is taken as the average diameter. It should be noted that if 30 gel particles are observable in the captured image, the average of the maximum diameters of any 30 gel particles in that image is taken as the average particle size. If no 30 gel particles are observed in the image, multiple images are captured, and the average of the total maximum diameters of the 30 gel particles is taken as the average diameter.

[0034] In this invention, the area percentage of the orthographic projection of the particles with an average particle size greater than or equal to 4 μm on the surface of the separator can be obtained by conventional testing methods in the art, for example, by the following method: discharge the battery to 0% SOC, disassemble and remove the separator, clean it with anhydrous ethanol to remove the surface lithium salt and electrolyte, dry it and use SEM to obtain a scanning image of the separator adhesive layer surface, use image analysis software such as Image Pro Plus to draw any 50 μm × 50 μm area (denoted as S1) on the obtained scanning image, count the orthographic projection area of ​​the particles with a particle size greater than or equal to 4 μm and record it as S2, calculate S2 / S1 × 100%, and take the average value after counting and calculating at least 5 different areas.

[0035] In this invention, the average particle size of the silicon-carbon material is 3μm to 15μm. The average particle size of the silicon-carbon material can be obtained by conventional testing methods in the art, such as the following method: discharge the battery to 0% SOC, disassemble and remove the negative electrode, or directly remove the negative electrode, clean it with anhydrous ethanol to remove the surface lithium salt and electrolyte, dry it, and then use SEM with backscatter imaging mode to obtain a scanning image of the surface of the negative electrode. In the image, the silicon-carbon particles appear grayish-white. Then, use electron microscopy image analysis software such as ImageJ to count the orthographic projection area of ​​the silicon-carbon material, and calculate the equivalent diameter, which is the particle size of the silicon-carbon material. Count the particle sizes of at least 15 silicon-carbon materials and take the average value. It can be understood that the "equivalent diameter" refers to converting the orthographic projection area of ​​the silicon-carbon material into the diameter of a regular circle that is equivalent to it.

[0036] In one embodiment, the average particle size of the silicon-carbon material is 5 μm to 11 μm.

[0037] When the average particle size of silicon-carbon materials is within the aforementioned range, it is beneficial to improve the consistency of lithium-ion insertion / extraction and transport within the battery, thereby enhancing the battery's cycle stability. When the average particle size of silicon-carbon materials is too small (e.g., less than 3 μm), the silicon-carbon materials have a large specific surface area, which consumes too much electrolyte to form a solid electrolyte interface film during the first charge, resulting in more irreversible loss of active lithium. This is detrimental to improving the battery's first-cycle coulombic efficiency. In addition, an excessively large specific surface area also increases the contact area between the electrolyte and the silicon-carbon materials, leading to aggravated electrolyte side reactions and hindering the improvement of battery cycle stability. When the average particle size of silicon-carbon materials is too large (e.g., greater than 15 μm), the solid-phase diffusion path of lithium ions within the silicon-carbon particles is longer, resulting in poorer kinetic performance of the negative electrode active material and hindering the improvement of battery rate performance.

[0038] In this invention, the area of ​​the positive projection of the silicon-carbon material on the surface of the negative electrode is 10% to 40%. This percentage can be obtained using conventional testing methods in the art, such as the following: discharge the battery to 0% SOC, disassemble and remove the negative electrode, or directly remove the negative electrode, clean it with anhydrous ethanol to remove surface lithium salt and electrolyte, dry it, and then use SEM in backscatter imaging mode to obtain a scanned image of the negative electrode surface. In the image, the silicon-carbon particles appear grayish-white. At 1000x magnification, select a 100μm × 100μm region (area S3), and use electron microscopy image analysis software such as ImageJ to calculate the positive projection area S4 of the silicon-carbon material in this region. Calculate S4 / S3 × 100%, and repeat this process at least 5 different selected areas and take the average value to obtain the percentage of the positive projection area of ​​the silicon-carbon material on the surface of the negative electrode.

[0039] When the proportion of the projected area of ​​silicon-carbon material on the surface of the negative electrode is within the above-mentioned range, it can provide sufficient additional electrolyte storage sites formed by the grooves formed by the silicon-carbon material, improving electrolyte flow and rapid ion transport, and alleviating lithium plating in the arc region of the negative electrode. When this proportion is small (e.g., less than 10%), the total amount of silicon-carbon material is small, providing too few electrolyte storage sites, especially contributing little to local electrolyte replenishment in the arc region. The problem of poor wetting in the arc region cannot be effectively solved, which is not conducive to improving lithium plating in the arc region of the negative electrode. When the proportion is large (e.g., greater than 40%), the proportion of silicon-carbon material in the negative electrode is too high, and the cumulative effect of volume expansion during the overall charge and discharge process increases, which may lead to an increase in battery thickness expansion, which is not conducive to further improving the cycle stability of the battery.

[0040] In this invention, based on the total mass of the silicon-carbon material, the mass content of silicon element is 30% to 70%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%.

[0041] In this invention, based on the total mass of the negative electrode active layer, the mass content of silicon element is 3% to 50%, for example, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%. The mass content of silicon element in the negative electrode active layer can be tested 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 dimethyl carbonate (DMC) solvent for 12 hours, it is rinsed with DMC solvent to remove the lithium salt attached to the negative electrode sheet. After drying, the negative electrode sheet is subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours (for example, in a tube furnace under nitrogen or argon atmosphere). The negative electrode active layer can then be peeled off from the negative electrode current collector and collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA550 thermogravimetric analyzer), the sample size is 5-15 mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25°C) to 900°C at a rate of 10°C / min, and held at 900°C for 40 min. This allows the non-silicon components in the negative electrode active layer to volatilize while the silicon is fully oxidized to silicon dioxide. The remaining substance is the ash content of the negative electrode active layer. The mass content of silicon in the negative electrode active layer can be calculated based on the mass of the ash, using the following formula: Mass content of silicon in the negative electrode active layer = 7 × mass of ash / (15 × mass of test sample).

[0042] In this invention, the silicon-carbon material comprises a porous carbon matrix and silicon particles located in the pores within the porous carbon matrix.

[0043] During charging and discharging, silicon provides high capacity, while the carbon matrix buffers the volume expansion of silicon and provides an electron conduction pathway. Adjusting the silicon content in the silicon-carbon material and / or the silicon content in the negative electrode active layer can strike a balance between increasing capacity and mitigating volume expansion. When the silicon content in the negative electrode active layer is too high (e.g., greater than 50%), the silicon-carbon material as a whole has a large volume expansion rate, which can easily lead to electrode structure damage and is detrimental to improving the cycle stability of the battery. When the silicon content is too low (e.g., less than 3%), the low proportion of silicon-carbon material contributes less to the battery capacity and is not conducive to improving the overall energy density of the battery.

[0044] In this invention, the specific surface area of ​​the silicon-carbon material is 0.01 m². 2 / g~8m 2 / g, for example, 0.01m 2 / g, 0.5m 2 / g、1m 2 / g, 1.5m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g or 8m 2 / g. The specific surface area of ​​the silicon-carbon material can be determined by conventional testing methods in the art, such as the Brunauer-Emmett-Teller (BET) test method, or by measuring it using a TriStar II specific surface area analyzer, with N2 as the adsorbed gas.

[0045] In one embodiment, the specific surface area of ​​the silicon-carbon material is 0.01 m². 2 / g~4m 2 / g.

[0046] A smaller specific surface area can better prevent the electrolyte from excessively entering the structure of silicon-carbon materials, reducing the amount of SEI film formed due to electrolyte decomposition, thereby reducing the overall consumption of electrolyte. This helps maintain the electrolyte content in the negative electrode active layer and works in conjunction with the trench storage space on the surface of silicon-carbon particles to continuously supply electrolyte to the arc-shaped area, thus alleviating the lithium plating problem of the negative electrode in the arc-shaped area.

[0047] In this invention, the negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer, wherein the second negative electrode active layer is located between the first negative electrode active layer and the negative electrode current collector.

[0048] In this invention, the ratio of the thickness of the second negative electrode active layer to the thickness of the first negative electrode active layer is (1~9):1, for example, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, 2.5:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or 9:1.

[0049] In one embodiment, the thickness ratio of the second negative electrode active layer to the thickness of the first negative electrode active layer is (2~4):1.

[0050] In one embodiment, the first negative electrode active layer and the second negative electrode active layer comprise the silicon-carbon material.

[0051] In another embodiment, the first negative electrode active layer comprises the silicon-carbon material.

[0052] In this invention, the first negative electrode active layer includes a first graphite, which includes element B. Based on the total mass of the first negative electrode active layer, the mass content of element B is 0.1% to 10%, for example, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. The mass content of element B in the first negative electrode active layer can be determined by conventional testing methods in the art, such as by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), specifically as follows: the battery is discharged to 0% SOC, the negative electrode sheet 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 negative electrode sheet. After drying the negative electrode sheet, it is cut into appropriate sizes, and its surface is imaged using backscatter imaging mode in an SEM device. Then, elemental distribution information is obtained by EDS surface scanning, and the mass content of element B in the first negative electrode active layer is obtained.

[0053] In this invention, the second negative electrode active layer comprises a second graphite, which includes artificial graphite and / or natural graphite.

[0054] In one embodiment, the first graphite comprises boron carbide and / or boron carbide.

[0055] In this invention, the boron carbide and / or boron carbide can be introduced into the first graphite by doping or by coating.

[0056] Research has found that the kinetic behavior of negative electrode active material particles during charge and discharge is mainly limited by the diffusion path of lithium ions and the conduction path of electrons. Along the thickness of the negative electrode sheet, the ion and electron transport environments of the active material at different depths differ. The surface active material is in direct contact with the electrolyte, resulting in a short ion transport path, while the bottom active material is limited by a longer solid-phase diffusion and liquid-phase penetration path. Furthermore, the negative electrode sheet can adopt a double-layer coating structure, and a first graphite containing element B can be introduced into the first negative electrode active layer located on the surface. After modification with boron carbide and / or boron nitride, the first graphite exhibits excellent lithium-ion diffusion performance. Introducing first graphite with excellent lithium-ion diffusion capabilities into the surface layer can improve the overall apparent kinetics of the battery, enabling rapid reception and release of lithium ions, thereby widening the lithium plating window and further improving circular lithium plating. Meanwhile, the second negative electrode active layer located at the bottom can be fitted with high-capacity or high-density graphite to ensure the overall energy density of the battery.

[0057] Meanwhile, at least the first negative electrode active layer contains the silicon-carbon material, which, when placed on the surface, not only provides additional space for electrolyte storage and increases the effective contact area with the conductive agent, binder, and graphite particles, but also maintains the mechanical stability of the surface active layer by its own strength, maintains good contact with the interface support points formed by the membrane protrusions, further increases the electrolyte storage space, improves the fluidity of the electrolyte, and facilitates the rapid transport of lithium ions, thereby alleviating the lithium plating problem of the negative electrode sheet in the arc region.

[0058] Adjusting the thickness ratio of the second negative electrode active layer to the first negative electrode active layer can ensure better electrochemical performance of the battery, improve the lithium plating window, and significantly improve the circular lithium plating effect. When the thickness ratio is too small (e.g., less than 1:1), the thickness of the first negative electrode active layer is too large compared to the second negative electrode active layer, which is not conducive to further improving the overall energy density of the battery; when the thickness ratio is too large (e.g., greater than 9:1), the thickness of the first negative electrode active layer is too small compared to the second negative electrode active layer, which is not conducive to further improving the rate performance of the battery.

[0059] In this invention, the negative electrode active layer further includes a negative electrode binder. Based on the total mass of the negative electrode active layer, the mass content of the negative electrode binder is 0.5% to 3%, for example, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8% or 3%.

[0060] In this invention, the average particle size of the negative electrode binder is 0.2 μm to 5 μm, for example, 0.2 μm, 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm. The average particle size of the negative electrode binder can be obtained by conventional testing methods in the art, for example, by the following method: discharging the battery to 0% SOC, disassembling and removing the negative electrode sheet, immersing it in DMC solvent for 12 hours, then rinsing it with DMC solvent to remove the lithium salt adhering to the negative electrode sheet, drying the negative electrode sheet, polishing its cross-section with an argon ion mill, imaging the obtained cross-section using backscatter imaging mode in an SEM device, magnifying it to a certain multiple (e.g., 20,000 times), and measuring the maximum size of at least 10 negative electrode binder particles, taking the average value as the average particle size of the negative electrode binder.

[0061] In this invention, the particles of the negative electrode binder have a shell and a cavity region formed by the shell.

[0062] In this invention, the average thickness of the outer shell is 100nm~300nm, for example, 100nm, 120nm, 140nm, 160nm, 180nm, 200nm, 220nm, 240nm, 260nm, 280nm or 300nm. The average thickness of the outer shell can be obtained by conventional testing methods in the art, for example by the following method: discharging the battery to 0% SOC, disassembling and removing the negative electrode sheet, immersing it in DMC solvent for 12 hours, then rinsing it with DMC solvent to remove the lithium salt attached to the negative electrode sheet, drying the negative electrode sheet and polishing its cross-section with an argon ion mill, imaging the obtained cross-section using backscatter imaging mode in an SEM device, magnifying it to a certain multiple (e.g., 20,000 times), and measuring the shell thickness of at least 10 negative electrode binder particles that have been cut to form cross-sections, and taking the average value as the average particle size of the negative electrode binder. If there are no negative electrode particles in the cross section that can be cut to form the cross section, repeat the above operation to cut the polished cross section of the negative electrode multiple times until the shell thickness of at least 10 particles is measured cumulatively.

[0063] In this invention, the negative electrode binder comprises polymethyl methacrylate (PMMA) and / or acrylate copolymers. For example, the negative electrode binder may be hollow PMMA microspheres and / or hollow acrylate copolymer microspheres. It is understood that the term "acrylate copolymer" refers to a polymer generated by copolymerizing acrylates (such as methyl acrylate, ethyl acrylate, butyl acrylate, etc.) with other unsaturated compounds containing double bonds (such as styrene, vinyl acetate, etc.).

[0064] In some embodiments, the negative electrode binder may further include at least one of polyacrylic acid (PAA), sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), polyimide, styrene-butadiene rubber (SBR), and polyvinylidene fluoride (PVDF).

[0065] The negative electrode binder of this invention has a hollow structure with numerous pores, possessing both liquid absorption and retention capabilities. It provides liquid storage space within the negative electrode sheet and exhibits strong deformation resistance, adapting to the expansion of silicon-carbon materials. Under compression, it releases more electrolyte, improving the overall liquid retention and ion transport efficiency of the electrode system. Adjusting the mass content of the negative electrode binder in the active layer provides ample liquid storage space, improving the overall liquid retention and ion transport efficiency of the electrode system while maintaining good structural strength of the negative electrode sheet. When the mass content of the negative electrode binder is too low (e.g., less than 0.5%), the additional liquid storage space provided by the binder is limited, hindering further improvement in battery rate performance and the reduction of lithium plating in the arc region. When the mass content of the negative electrode binder is too high (e.g., greater than 3%), the binder excessively occupies the connection areas between active material particles, affecting the overall structural strength and electron conduction network of the negative electrode sheet, thus negatively impacting battery cycle stability.

[0066] Furthermore, adjusting the average particle size of the negative electrode binder and the average thickness of the outer shell can balance the liquid storage capacity and the structural stability of the binder particles. When the average particle size of the negative electrode binder is too large and / or the average thickness of the outer shell is too small, although the negative electrode binder provides sufficient liquid storage space, which helps to improve the liquid retention capacity of the electrode, the thin outer shell results in low strength of the negative electrode binder. Under expansion stress during electrode rolling or battery cycling, the binder particles are prone to breakage and failure. When the average particle size of the negative electrode binder is too small and / or the average thickness of the outer shell is too large, the internal cavity structure of the binder is compressed, even approaching solidity, which cannot effectively provide more liquid storage space and is not conducive to improving the liquid retention capacity and ion transport efficiency of the electrode system.

[0067] In this invention, the battery further includes an electrolyte, which in turn includes a solvent, a lithium salt, and additives. The lithium salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(trifluorosulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium dioxolane borate (LiBOB), lithium difluorooxolane borate (LiDFOB), and lithium perchlorate (LiClO4). The solvent may include at least one of cyclic carbonates (such as ethylene carbonate (EC), propylene carbonate (PC), etc.), chain carbonates (such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc.), carboxylic acid esters (such as methyl acetate (MA), ethyl acetate (EA), propyl acetate (MP), ethyl propionate (EP), etc.) and other solvents (such as sulfolane (SL), fluoroethylene vinyl carbonate (FEC), vinylene carbonate (VC), etc.). The additive may include at least one of vinylene carbonate (VC), ethyl difluorocarbonate (DFEA), fluoroethylene carbonate (FEC), ethylene sulfate (PS), trimethyl phosphate (TMP), adiponitrile (AND), succinic anionyl (SN), and 1,3,6-hexanetrionitrile (HTCN).

[0068] In this invention, the term "0% SOC" refers to discharging the battery to a lower limit voltage (e.g., 2.8V) at 0.1C.

[0069] 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.

[0070] 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.

[0071] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0072] The following examples illustrate the battery of the present invention.

[0073] Example 1: (1) Preparation of the positive electrode: Lithium cobalt oxide, polyvinylidene fluoride (PVDF), acetylene black, and carbon nanotubes (CNTs) were mixed in a mass ratio of 96.6:2:1.1:0.3, and then N-methylpyrrolidone (NMP) solvent was added. The mixture was stirred under vacuum until it was homogeneous to obtain a positive electrode slurry. This slurry was coated on both sides of an aluminum foil and dried in a vacuum drying oven at 150°C for 12 hours. After rolling and slitting, the positive electrode sheet was obtained.

[0074] (2) Preparation of the negative electrode: Silicon carbon material, first graphite containing boron nitride and boron nitride, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), Super P, and hollow PMMA microspheres (average particle size 3.5 μm, shell thickness 185 nm) were mixed in a mass ratio of 15:80.5:1.5:0.5:1.5:1, and deionized water was added and stirred to obtain the first negative electrode slurry; silicon carbon material, artificial graphite, CMC-Na, SBR, and Super P were then mixed... P and hollow PMMA microspheres were mixed in a mass ratio of 15:80.5:1.5:0.5:1.5:1, and deionized water was added and stirred to obtain a second negative electrode slurry. The second negative electrode slurry was uniformly coated on both sides of a negative electrode current collector with a thickness of 8 μm. After coating, the negative electrode sheet was transferred to an 80℃ oven and dried for 5 hours to obtain a second negative electrode active layer. The first negative electrode slurry was uniformly coated on the outer surface of the second negative electrode active layer. After coating, the negative electrode sheet was transferred to an 80℃ oven and dried for 5 hours to obtain a first negative electrode active layer. After rolling and slitting, the negative electrode sheet was obtained.

[0075] The silicon-carbon material has an average included angle of 98°, an average particle size of 8.4 μm, a projected area of ​​28.4% on the negative electrode surface, a silicon content of 7.5% in the negative electrode active layer, and a specific surface area of ​​2.34 m². 2 / g, the ratio of the thickness of the second negative electrode active layer to the thickness of the first negative electrode active layer is 3:1, and the mass content of element B in the first negative electrode active layer is 5.7%.

[0076] (3) Preparation of electrolyte: Under the protection of argon atmosphere, PC, EP, PP and DEC are mixed in a weight ratio of 2:1:3:3 to obtain a solvent. Based on the total weight of the electrolyte, 10% FEC, 1.5% HTCN and 12% lithium hexafluorophosphate (LiPF6) are added and stirred evenly to obtain the electrolyte.

[0077] (4) Preparation of the diaphragm: PVDF, SBR, polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA) copolymer granules, and deionized water were mixed in a ratio of 25:10:8:15:42 and dispersed in a high-speed disperser at 3000 rpm for 90 minutes to obtain a uniform and stable aqueous slurry. An 8μm polyethylene membrane was selected as the substrate layer, and the prepared slurry was coated onto one side of the substrate layer using extrusion coating to obtain an adhesive layer. After drying, a diaphragm was obtained.

[0078] The average particle size of the colloidal particles is 5.5 μm, the projected area of ​​colloidal particles with an average particle size greater than or equal to 4 μm accounts for 6.8%, and the protrusion height h is 3.3 μm.

[0079] (5) Battery fabrication: The obtained positive electrode, separator and negative electrode are stacked in sequence, with the separator adhesive layer facing the negative electrode. After being wound into a bare cell, it is loaded into an aluminum-plastic composite film and sealed. Electrolyte is injected under vacuum conditions and vacuum sealed. The battery is obtained through standing, formation and sorting processes.

[0080] Example 2: Based on Example 1, the difference lies in the preparation of the negative electrode. The first negative electrode slurry is prepared by mixing silicon-carbon material, first graphite containing boron nitride and boron nitride, CMC-Na, SBR, Super P, and hollow PMMA microspheres (average particle size 0.2 μm, shell thickness 100 nm) in a mass ratio of 15:80.5:1.5:1:1.5:0.5, and then adding deionized water and stirring. The second negative electrode slurry is prepared by mixing silicon-carbon material, artificial graphite, CMC-Na, SBR, Super P, and hollow PMMA microspheres in a mass ratio of 15:80.5:1.5:1:1.5:0.5, and then adding deionized water and stirring. The average included angle of the silicon-carbon material is 46°, the average particle size of the silicon-carbon material is 5.2 μm, the area of ​​the positive projection of the silicon-carbon material onto the surface of the negative electrode is 12.7%, and the specific surface area of ​​the silicon-carbon material is 3.76 m². 2 / g, the ratio of the thickness of the second negative electrode active layer to the thickness of the first negative electrode active layer is 2:1, and the mass content of element B in the first negative electrode active layer is 0.3%; In the preparation of the diaphragm, the average particle size of the colloidal particles is 7.9 μm, the proportion of the projected area of ​​colloidal particles with an average particle size greater than or equal to 4 μm is 12.6%, and the protrusion height h is 4.8 μm.

[0081] Example 3: Based on Example 1, the difference lies in the preparation of the negative electrode sheet. The first negative electrode slurry is prepared by mixing silicon carbon material, first graphite containing boron nitride and boron nitride, CMC-Na, SBR, Super P, and hollow acrylate copolymer (average particle size 4.8 μm, shell thickness 297 nm) in a mass ratio of 15:80.5:0.5:0.5:0.5:3, and then adding deionized water and stirring. The second negative electrode slurry is prepared by mixing silicon carbon material, artificial graphite, CMC-Na, SBR, Super P, and hollow acrylate copolymer in a mass ratio of 15:80.5:0.5:0.5:0.5:3, and then adding deionized water and stirring. The average included angle of the silicon carbon material is 117°, the average particle size of the silicon carbon material is 10.7 μm, the area of ​​the positive projection of the silicon carbon material onto the surface of the negative electrode sheet is 36.5%, and the specific surface area of ​​the silicon carbon material is 1.06 m². 2 / g, the ratio of the thickness of the second negative electrode active layer to the thickness of the first negative electrode active layer is 4:1, and the mass content of element B in the first negative electrode active layer is 9.8%; In the preparation of the diaphragm, the average particle size of the colloidal particles is 4.3 μm, the proportion of the projected area of ​​colloidal particles with an average particle size greater than or equal to 4 μm is 5.2%, and the protrusion height h is 2.1 μm.

[0082] Example 4 group: This set of examples is used to verify the impact of changes in the "average included angle of silicon-carbon materials", as detailed below: Example 4a is based on Example 1, except that the average included angle of the silicon-carbon material is 12° and the specific surface area of ​​the silicon-carbon material is 2.31 m². 2 / g; Example 4b is based on Example 1, except that the average included angle of the silicon-carbon material is 149° and the specific surface area of ​​the silicon-carbon material is 2.38 m². 2 / g.

[0083] Example 5 group: This set of examples is used to verify the impact of changes in "h", as detailed below: Example 5a is based on Example 1, except that h is 5.9 μm, the average particle size is 9.7 μm, and the projected area of ​​particles with an average particle size greater than or equal to 4 μm accounts for 14.8%. Example 5b is based on Example 1, except that h is 1.2 μm, the average particle size is 1.5 μm, and the projected area of ​​particles with an average particle size greater than or equal to 4 μm accounts for 0.2%.

[0084] Example 6 group: This set of examples is used to verify the impact of changes in the "average particle size of silicon-carbon materials", as detailed below: Example 6a, based on Example 1, differs in that the average particle size of the silicon-carbon material is 3.3 μm, the area of ​​the silicon-carbon material projected onto the negative electrode surface is 10.4%, and the specific surface area of ​​the silicon-carbon material is 5.12 m². 2 / g; Example 6b is based on Example 1, except that the average particle size of the silicon-carbon material is 14.9 μm, the area of ​​the silicon-carbon material projected onto the surface of the negative electrode is 39.5%, and the specific surface area of ​​the silicon-carbon material is 0.73 m². 2 / g.

[0085] Example 7 group: This set of examples is used to verify the impact of changes in the "mass content of silicon in the negative electrode active layer", as detailed below: Example 7a, based on the example, differs in that the first negative electrode slurry is obtained by mixing silicon-carbon material, first graphite, CMC-Na, SBR, Super P, and hollow PMMA microspheres in a mass ratio of 10:85.5:1.5:0.5:1.5:1, and then adding deionized water and stirring; the second negative electrode slurry is obtained by mixing silicon-carbon material, artificial graphite, CMC-Na, SBR, Super P, and hollow PMMA microspheres in a mass ratio of 10:85.5:1.5:0.5:1.5:1, and then adding deionized water and stirring; the area of ​​the silicon-carbon material projected onto the surface of the negative electrode is 15.2%, the silicon content in the negative electrode active layer is 3%, and the specific surface area of ​​the silicon-carbon material is 2.41 m². 2 / g; Example 7b, based on the example, differs in that the first negative electrode slurry is obtained by mixing silicon-carbon material, first graphite, CMC-Na, SBR, Super P, and hollow PMMA microspheres in a mass ratio of 70:25.5:1.5:0.5:1.5:1, and then adding deionized water and stirring; the second negative electrode slurry is obtained by mixing silicon-carbon material, artificial graphite, CMC-Na, SBR, Super P, and hollow PMMA microspheres in a mass ratio of 70:25.5:1.5:0.5:1.5:1, and then adding deionized water and stirring; the area of ​​the silicon-carbon material projected onto the surface of the negative electrode is 45.5%, the silicon content in the negative electrode active layer is 49%, and the specific surface area of ​​the silicon-carbon material is 2.29 m². 2 / g.

[0086] Example 8 group: This set of examples is used to verify the impact of changes in the "negative electrode active layer", as detailed below: Example 8a is based on Example 1, except that the ratio of the thickness of the second negative electrode active layer to the thickness of the first negative electrode active layer is 1:1. Example 8b is based on Example 1, except that the ratio of the thickness of the second negative electrode active layer to the thickness of the first negative electrode active layer is 9:1. Example 8c is based on Example 1, except that only the first negative electrode active layer is provided; Example 8d is based on Example 1, except that only a second negative electrode active layer is provided; Example 8e is based on Example 1, except that the mass content of element B in the first negative electrode active layer is 10.5%.

[0087] Example 9 group: This set of examples is used to verify the impact of changes in the "negative electrode binder", as detailed below: Example 9a is based on Example 1, except that the first negative electrode slurry is obtained by mixing silicon carbon material, first graphite, CMC-Na, SBR and Super P in a mass ratio of 15:80.5:1.5:1:2 and adding deionized water and stirring; the second negative electrode slurry is obtained by mixing silicon carbon material, artificial graphite, CMC-Na, SBR and Super P in a mass ratio of 15:80.5:1.5:1:2 and adding deionized water and stirring. Example 9b is based on Example 1, except that the first negative electrode slurry is obtained by mixing silicon carbon material, first graphite, CMC-Na, SBR, Super P and PMMA in a mass ratio of 15:80.5:1.5:0.5:1.5:1 and adding deionized water and stirring; the second negative electrode slurry is obtained by mixing silicon carbon material, artificial graphite, CMC-Na, SBR, Super P and PMMA in a mass ratio of 15:80.5:1.5:0.5:1.5:1 and adding deionized water and stirring. Example 9c is based on Example 1, except that the shell thickness of the negative electrode binder is 97 nm; Example 9d is based on Example 1, except that the shell thickness of the negative electrode binder is 320 nm.

[0088] Example 10 group: This set of embodiments is used to verify the impact of changes in the "first graphite", as detailed below: Example 10a is based on Example 1, except that the first graphite is replaced with a first graphite containing boron nitride of the same mass fraction; Example 10b is based on Example 1, except that the first graphite is replaced with a first graphite containing boron carbide of the same mass fraction.

[0089] Comparative Example 1: This set of comparative models is used to verify the impact of changes in "silicon-carbon materials", as detailed below: Comparative Example 1a is based on Example 1, except that the silicon-carbon material without an included angle is replaced with spherical silicon-carbon material of equal mass, the average included angle of the silicon-carbon material is 0°, and the specific surface area of ​​the silicon-carbon material is 2.22 m². 2 / g, the area of ​​the silicon-carbon material projected onto the surface of the negative electrode is 25.6%, and the spherical silicon-carbon material is a conventional material used in this field; Comparative Example 1b is based on Example 1, except that the average included angle of the silicon-carbon material is 158° and the specific surface area of ​​the silicon-carbon material is 2.41 m². 2 / g, the area of ​​the silicon-carbon material projected onto the surface of the negative electrode is 30.1%; Comparative Example 1c is based on Example 1, except that the silicon-carbon material is replaced with an equal mass of blocky silicon-carbon material, the specific surface area of ​​which is 2.29 m². 2 / g, the area of ​​the silicon-carbon material projected onto the surface of the negative electrode is 27.3%, and the bulk silicon-carbon material is a conventional material used in this field.

[0090] Comparative Example 2: This set of scales is used to verify the impact of changes in the "protrusion and its height h", as follows: Comparative Example 2a is based on Example 1, except that h is 0.8 μm and the average particle size of the colloidal particles is 1 μm; Comparative Example 2b is based on Example 1, except that h is 6.3 μm and the average particle size of the colloidal particles is 6.4 μm.

[0091] Comparative Example 3: Based on Example 1, the difference is that the adhesive layer and the positive electrode are arranged facing each other.

[0092] Test example: (1) Cyclic stability test: The batteries obtained in the embodiments and comparative examples of this invention were charged at 0.7C constant current and constant voltage to 4.53V at 25℃±2℃, cut off at 0.05C, and then discharged at 0.2C constant current to 2.8V. The initial discharge capacity was recorded as Q0. After resting for 10 minutes, the cycle was as follows: 3C constant current and constant voltage charging to 4.25V, cut off at 2C, then 2C constant current and constant voltage charging to 4.48V, cut off at 1.5C, then 1.5C constant current and constant voltage charging to 4.53V, cut off at 0.18C, rested for 5 minutes, and then discharged at 0.7C to 2.8V. After 800T cycles, the batteries were charged at 0.7C constant current and constant voltage to 4.53V, cut off at 0.05C, and then discharged at 0.2C constant current to 2.8V. The discharge capacity at this point was recorded as Q1. Capacity retention rate: Q=(Q1 / Q0)×100%. The test results are recorded in Table 1.

[0093] (2) Ratio performance test: The batteries obtained in the embodiments and comparative examples of the present invention were tested for rate performance using a Xinwei battery tester at an environment of 25℃±2℃, according to the following steps: (i) Charge at 0.2C to the upper limit voltage of 4.53V (cutoff at 0.02C), discharge at 0.2C to the lower limit voltage of 2.8V, and record the discharge capacity as C1; (ii) Charge at 0.2C to the upper limit voltage of 4.53V (cut off at 0.02C), discharge at 1C to the lower limit voltage of 2.8V, and record the discharge capacity as C2; (iii) The capacity retention rate of the battery at a 1C discharge rate is C2 / C1. The higher the capacity retention rate, the better the battery's rate performance. The test results are recorded in Table 1.

[0094] (3) Lithium plating test: The batteries obtained in the embodiments and comparative examples of this invention were subjected to a 0.2C discharge to the lower limit voltage of 2.8V at 25℃±2℃, allowed to stand for 10 minutes, charged at 0.7C to the upper limit voltage of 4.53V, and allowed to stand for 10 minutes. Subsequently, they were charged at a constant current and constant voltage of 3.5C to full charge (cutoff at 0.02C), and discharged at 0.7C. This charge-discharge cycle was repeated for 50T cycles. The batteries were then disassembled to observe the lithium plating state on the surface of the negative electrode. The criteria for judging the lithium plating phenomenon on the negative electrode were as follows: "0" for no lithium plating; "1" for the lithium plating area being less than 3% of the total negative electrode area; "2" for the lithium plating area being 3%-5% of the total negative electrode area; "3" for the lithium plating area being greater than 5% and less than or equal to 10% of the total negative electrode area; and "4" for the lithium plating area being greater than 15% of the total negative electrode area. The test results are recorded in Table 1.

[0095] Table 1: As can be seen from Table 1, the battery prepared by the present invention has both rate performance and cycle stability compared to the comparative example, while suppressing lithium deposition on the negative electrode.

[0096] 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 battery, characterized in that, The battery includes an electrode assembly formed by stacking and winding a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative current collector and a negative active layer located on at least one side surface of the negative current collector. The negative active layer includes a negative active material, which includes a silicon-carbon material. At least one included angle exists on the cross-sectional profile of the silicon-carbon material, and the average angle of the included angle is 10° to 150°. The diaphragm includes a substrate layer and an adhesive layer located on at least one side of the substrate layer. The adhesive layer includes adhesive particles, which protrude on the side opposite to the substrate layer to form protrusions. The adhesive particles include a first polymer, and the average height of the protrusions is h, where h is 1 μm to 6 μm. The adhesive layer is positioned directly opposite the negative electrode sheet.

2. The battery according to claim 1, wherein, The average angle of the included angle is 45°~120°; And / or, the first polymer comprises at least one polymer formed by polymerizing one or more of the following monomers: methyl acrylate, methyl methacrylate, ethyl methacrylate, ethyl acrylate, and butyl acrylate; And / or, the adhesive layer further includes a second polymer, the second polymer including at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, and sodium alginate.

3. The battery according to claim 1 or 2, wherein, The average particle size of the colloidal particles is 1μm~10μm; And / or, the area of ​​the orthographic projection of the colloidal particles with an average particle size greater than or equal to 4 μm on the surface of the diaphragm accounts for 5% to 15%; Preferably, the average particle size of the adhesive particles is 4μm to 8μm.

4. The battery according to claim 1 or 2, wherein, The average particle size of the silicon-carbon material is 3μm~15μm; preferably 5μm~11μm. And / or, the area of ​​the positive projection of the silicon-carbon material accounts for 10% to 40% of the surface of the negative electrode.

5. The battery according to claim 1 or 2, wherein, Based on the total mass of the silicon-carbon material, the mass content of silicon element is 30% to 70%; And / or, based on the total mass of the negative electrode active layer, the mass content of silicon element is 3% to 50%.

6. The battery according to claim 1 or 2, wherein, The specific surface area of ​​the silicon-carbon material is 0.01 m². 2 / g~8m 2 / g; Preferably, the specific surface area of ​​the silicon-carbon material is 0.01 m². 2 / g~4m 2 / g.

7. The battery according to claim 1 or 2, wherein, The negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer, wherein the second negative electrode active layer is located between the first negative electrode active layer and the negative electrode current collector; Preferably, the ratio of the thickness of the second negative electrode active layer to the thickness of the first negative electrode active layer is (1~9):1; More preferably, the ratio of the thickness of the second negative electrode active layer to the thickness of the first negative electrode active layer is (2~4):

1.

8. The battery according to claim 7, wherein, The first negative electrode active layer includes a first graphite, which includes element B. Based on the total mass of the first negative electrode active layer, the mass content of element B is 0.1% to 10%. And / or, the second negative electrode active layer includes a second graphite, which includes artificial graphite and / or natural graphite; Preferably, the first graphite comprises boron carbide and / or boron carbide.

9. The battery according to claim 1 or 2, wherein, The negative electrode active layer further includes a negative electrode binder, and the mass content of the negative electrode binder is 0.5% to 3% based on the total mass of the negative electrode active layer; And / or, the average particle size of the negative electrode binder is 0.2 μm to 5 μm.

10. The battery according to claim 9, wherein, The particles of the negative electrode binder have a shell and a cavity region formed by the shell; And / or, the average thickness of the outer shell is 100nm~300nm; Preferably, the negative electrode binder comprises polymethyl methacrylate and / or acrylate copolymers.

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