Negative plate and battery

Abstract

The invention relates to a negative plate and a battery. The negative plate comprises a negative current collector and a negative coating arranged on at least one side surface of the negative current collector; a negative electrode active material in the negative electrode coating comprises a silicon carbon material and graphite; the negative plate meets the following relational expression: 1 < (D90C-D50SiC) / (D50SiC-D10C) < 25; 0.5 lt; (D90SiC-D50SiC) / (D50SiC-D10SiC) < lt >; 2; wherein the particle size D90 of the graphite is D90C, and the unit is [mu] m; the particle size D10 of the graphite is D10C, and the unit is mu m; the particle size D90 of the silicon carbon material is D90SiC, and the unit is mu m; the particle size D50 of the silicon carbon material is D50SiC, and the unit is mu m; the particle size D10 of the silicon carbon material is D10SiC, and the unit is mu m. According to the scheme provided by the invention, the battery can present high cycle performance and rate capability.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to negative electrode sheets and batteries. Background Technology

[0002] Lithium-ion batteries, with their advantages of high specific energy, no memory effect, and long cycle life, have become key energy devices in fields such as 3C digital products, power tools, electric vehicles, and energy storage systems. With the rapid development of electronic information technology and consumer products, the market is placing higher demands on the energy density and operating life of lithium-ion batteries.

[0003] Among various anode materials, silicon-based graphite blends have gradually become one of the mainstream technologies due to their effective balance between capacity and cost. However, silicon-based materials still have certain limitations: silicon-oxygen materials suffer from large volume expansion and low initial coulombic efficiency, while elemental silicon particles suffer from severe expansion and poor conductivity. In contrast, silicon-carbon composites prepared by vapor deposition using porous carbon as a substrate exhibit smaller volume expansion, higher initial coulombic efficiency, and better conductivity. Their physical properties are closer to those of graphite, allowing for good compatibility. Nevertheless, in practical applications, the mixing of silicon-carbon materials with graphite still results in insufficient electrolyte wetting, unstable conductive networks, and volume expansion of the anode coating, leading to a significant decrease in battery cycle performance and rate performance.

[0004] Therefore, developing a novel silicon-carbon-graphite composite anode sheet is of great significance for achieving long-cycle stability and high-rate performance of high-capacity lithium-ion batteries. Summary of the Invention

[0005] To solve or partially solve the problems existing in the related technologies, this application provides a negative electrode and a battery. The negative electrode can effectively control its volume expansion rate and exhibit high conductivity and good electrolyte wettability, which significantly improves the cycle performance and rate performance of the battery.

[0006] The first aspect of this application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode coating disposed on at least one side surface of the negative electrode current collector; the negative electrode active material in the negative electrode coating includes silicon-carbon material and graphite; The negative electrode sheet satisfies the following relationship: 1 < |(D90) C -D50 SiC ) / (D50 SiC -D10 C )|<25; 0.5<|(D90 SiC -D50 SiC ) / (D50 SiC -D10SiC )|<2; Among them, D90 C The particle size D90 of the graphite is in μm; D10 C The particle size D10 of the graphite is in μm; D90 SiC The particle size D90 of the silicon-carbon material is in μm; D50 SiC The particle size D50 of the silicon-carbon material is in μm; D10 SiC D10 represents the particle size of the silicon-carbon material, in μm.

[0007] As described in the first aspect, the negative electrode has 6μm < D50. SiC <10μm; And / or, 3μm < D10 SiC <6μm; And / or, 11μm < D90 SiC <18μm.

[0008] As described in the first aspect, the negative electrode sheet contains 0.7 g / cm³. 3 <TD SiC <1.3g / cm 3 Among them, TD SiC The tap density of the silicon-carbon material is expressed in g / cm³. 3 ; and / or, 0.9m 2 / g<SSA SiC <1.7m 2 / g; where SSA SiC The specific surface area of ​​the silicon-carbon material is given in m². 2 / g.

[0009] As described in the first aspect, the negative electrode sheet contains silicon in the silicon-carbon material at a mass percentage of 40% to 55%.

[0010] As described in the first aspect, the negative electrode has 7μm < D50. C <12μm, where D50 C The particle size D50 of the graphite is in μm; and / or, 3μm<D10 C <7μm; and / or, 16μm <D90 C <25μm.

[0011] As described in the first aspect, the negative electrode sheet contains 0.8 g / cm³. 3 <TD C <1.2g / cm 3 Among them, TD CThe tap density of the graphite is given in g / cm³. 3 ; And / or, 1m 2 / g<SSA C <2.8m 2 / g; where SSA C The specific surface area of ​​the graphite is given in m². 2 / g.

[0012] The negative electrode as described in the first aspect, wherein the graphitization degree of the graphite is greater than or equal to 94%.

[0013] As described in the first aspect, the negative electrode sheet contains, by mass percentage, 5% to 30% silicon-carbon material in the negative electrode active material.

[0014] As described in the first aspect, the negative electrode sheet contains, by mass percentage, 92% to 98% of the negative electrode active material in the negative electrode coating; And / or, the negative electrode coating further includes a conductive agent, the conductive agent including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes; preferably, the conductive agent in the negative electrode coating has a mass percentage content of 0.2% to 0.7%; And / or, the negative electrode coating further includes a binder, the binder comprising at least one selected from polyacrylic acid, polyacrylonitrile, polyacrylamide, and styrene-butadiene rubber; preferably, the binder comprises 1.5% to 6.5% by mass in the negative electrode coating; And / or, the negative electrode coating further includes a dispersant, the dispersant including at least one of lithium carboxymethyl cellulose and sodium carboxymethyl cellulose; preferably, the mass percentage of the dispersant in the negative electrode coating is 0.3% to 0.8%.

[0015] A second aspect of this application provides a battery, wherein the battery includes a negative electrode as described in the first aspect.

[0016] The technical solution provided in this application can include the following beneficial effects: On the one hand, silicon-carbon materials and graphite are tightly bonded to form a stable composite structure. The graphite skeleton can not only effectively buffer the volume expansion of silicon materials during cycling, but also synergistically construct a continuous and efficient conductive network, thereby taking into account both the structural stability and conductivity of the negative electrode sheet, and thus improving the cycle performance and rate performance of the battery. On the other hand, by precisely controlling the particle size matching relationship between graphite and silicon-carbon materials, functionalized gradient filling is achieved: large graphite particles are mainly responsible for constructing the macroscopic conductive skeleton, while small graphite particles can more fully contact silicon-carbon materials and fill the gaps, thereby simultaneously optimizing the electronic conduction path and electrolyte wetting channel, and thus significantly improving the fast charging performance and cycle life of the battery. In addition, by optimizing and controlling the particle size distribution of silicon-carbon materials themselves, the blockage of electrode pores due to excessive small particles is avoided, which affects ion transport. At the same time, the local volume expansion stress concentration caused by excessive large particles is also prevented, which would damage the integrity of the electrode structure, further improving the rate performance and long-cycle stability of the battery.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0018] To facilitate understanding of this application, it will be described in detail below. However, before describing this application in detail, it should be understood that this application is not limited to the specific embodiments described. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be restrictive.

[0019] Where a numerical range is provided, it should be understood that every intermediate value between the upper and lower limits of the range and any other specified or intermediate value within the specified range is covered within this application. The upper and lower limits of these smaller ranges may be independently included in the smaller range and are also covered within this application, subject to any explicitly excluded limits within the specified range. Where the specified range includes one or two limits, the range excluding any or both of those included limits is also included within this application.

[0020] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While the methods and materials described herein, or any equivalent methods and materials, may also be used in the implementation or testing of this application, preferred methods and materials are now described.

[0021] Among various anode materials, silicon-based graphite blends have gradually become one of the mainstream technologies due to their effective balance between capacity and cost. However, silicon-based materials still have certain limitations: silicon-oxygen materials suffer from large volume expansion and low initial coulombic efficiency, while elemental silicon particles suffer from severe expansion and poor conductivity. In contrast, silicon-carbon composites prepared by vapor deposition using porous carbon as a substrate exhibit smaller volume expansion, higher initial coulombic efficiency, and better conductivity. Their physical properties are closer to those of graphite, allowing for good compatibility. Nevertheless, in practical applications, the mixing of silicon-carbon materials with graphite still results in insufficient electrolyte wetting, unstable conductive networks, and volume expansion of the anode coating, leading to a significant decrease in battery cycle performance and rate performance.

[0022] To address the aforementioned issues, this application provides a negative electrode sheet, which includes a negative current collector and a negative electrode coating disposed on at least one side of the negative current collector; the negative electrode active material in the negative electrode coating includes silicon-carbon material and graphite.

[0023] This application does not limit the choice of negative electrode current collector; it can be selected according to actual needs, such as copper foil. The negative electrode active materials of this application include silicon-carbon materials and graphite. The silicon-carbon material of this application is a silicon-carbon composite material prepared by vapor deposition using porous carbon as a substrate. The graphite of this application includes, but is not limited to, natural graphite or artificial graphite.

[0024] The negative electrode sheet of this application satisfies the following relationship: 1 < |(D90) C -D50 SiC ) / (D50 SiC -D10 C )|<25; 0.5<|(D90 SiC -D50 SiC ) / (D50 SiC -D10 SiC )|<2; Among them, D90 C The particle size of graphite is D90, in μm; D10 C D10 is the particle size of graphite, in μm; D90 SiC The particle size D90 of silicon-carbon materials is measured in μm; D50 SiC D50 refers to the particle size of silicon-carbon materials, in μm; D10 SiC D10 represents the particle size of silicon-carbon materials, in μm.

[0025] D10, D50, and D90 are derived from particle size distribution curves. D10 refers to the particle size corresponding to a cumulative percentage of 10%. D50 refers to the particle size corresponding to a cumulative percentage of 50%. D90 refers to the particle size corresponding to a cumulative percentage of 90%.

[0026] (D90 C -D50 SiC ) / (D50 SiC -D10 C The absolute value of ) is less than 25 and greater than 1, for example, |(D90) C -D50 SiC ) / (D50 SiC -D10 C | Can be 2, 5, 10, 15, 20, 24, etc. (D90) SiC -D50 SiC ) / (D50 SiC -D10 SiC The absolute value of ) is less than 2 and greater than 0.5, for example, |(D90) SiC -D50 SiC ) / (D50 SiC -D10 SiC )| can be 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8 or 1.9, etc.

[0027] Understandable, D90 C The particle sizes D90 and D50 represent graphite. SiC The particle size D50 represents silicon-carbon materials. Therefore, the difference D90 C -D50 SiC The physical significance of D10 lies in reflecting the degree of matching between the larger graphite particles and the central particle size of silicon-carbon materials. Similarly, D10... C D10 represents the particle size of graphite. Therefore, the difference is D50. SiC -D10 C The physical significance of this ratio lies in reflecting the degree of matching between the central particle size of silicon-carbon materials and the smaller particle size of graphite particles. In summary, the ratio |(D90) C -D50 SiC ) / (D50 SiC -D10 C The physical meaning of )| is to evaluate the matching uniformity of the overall particle size distribution between graphite and silicon carbide materials.

[0028] D90 SiC D50 SiC and D10 SiC These represent the particle sizes D90, D50, and D10 of silicon-carbon materials, respectively. Therefore, the difference D90SiC -D50 SiC This reflects the size difference between larger particles and centrally located particles in silicon-carbon materials; while the difference D50 SiC -D10 SiC This reflects the size difference between the central-sized particles and the smaller particles. In summary, the ratio |(D90) SiC -D50 SiC ) / (D50 SiC -D10 SiC The physical meaning of )| is to characterize the symmetry and concentration of the particle size distribution of silicon-carbon materials.

[0029] According to the above-described scheme provided in this application, after the negative electrode is applied to the battery, the battery exhibits excellent cycle performance and rate performance. The applicant analyzed the principle behind this, believing that the reasons are as follows: Firstly, silicon-carbon materials and graphite form a stable composite structure through close bonding. The graphite skeleton not only effectively buffers the volume expansion of silicon materials during cycling but also collaboratively constructs a continuous and efficient conductive network, thus balancing the structural stability and conductivity of the negative electrode, thereby improving the battery's cycle performance and rate performance. Secondly, by precisely controlling the particle size matching relationship between graphite and silicon-carbon materials, functionalized gradient filling is achieved: large graphite particles are mainly responsible for constructing the macroscopic conductive skeleton, while small graphite particles can more fully contact silicon-carbon materials and fill the gaps, thereby simultaneously optimizing the electronic conduction path and electrolyte wetting channel, significantly improving the battery's fast-charging performance and cycle life. In addition, by optimizing and controlling the particle size distribution of silicon-carbon materials, the blockage of electrode pores by excessive small particles is avoided, which would affect ion transport. At the same time, the local volume expansion stress concentration caused by excessive large particles is also prevented, which would damage the integrity of the electrode structure, further improving the battery's rate performance and long-cycle stability.

[0030] In one specific implementation, 6μm < D50 SiC <10μm, for example, D50 SiCThe particle size can be 6.1μm, 7μm, 8μm, 9μm, 9.9μm, etc. This particle size range ensures that the silicon-carbon material can form a good particle size gradient match with graphite, allowing the silicon-carbon particles to effectively fill the graphite gaps, thereby improving the electrode's compaction density and lithium-ion transport efficiency. Simultaneously, this range optimizes electrode processing performance, avoiding the high viscosity and poor dispersibility of the slurry due to excessively small particle size, which leads to agglomeration. It also avoids the stress concentration caused by the dramatic increase in absolute expansion due to excessively large particle size, which can damage the electrode structure. This size also controls the specific surface area of ​​the silicon-carbon material within a reasonable range, avoiding the initial efficiency loss and increased difficulty in electrolyte wetting caused by excessively large particle size due to excessively large specific surface area. It also avoids the problems caused by excessively large particle size, such as excessively long lithium-ion diffusion paths, decreased rate performance, and the formation of rough spots on the electrode surface leading to localized lithium plating. Thus, it synergistically balances processing performance, structural stability, and electrochemical performance. Preferably, 7.7μm ≤ D50. SiC ≤9.4μm.

[0031] In one specific implementation, 3μm < D10 SiC <6μm, for example, D10 SiC It can be 3.1μm, 4μm, 5μm, 5.9μm, etc. When D10 SiC Within the aforementioned range, small-particle silicon-carbon materials can fill the gaps between graphite and larger silicon-carbon particles, improving the packing density and structural uniformity of the negative electrode coating. This ensures good ion transport channels while optimizing the electrode's interfacial stability and cycle life. Simultaneously, it avoids the presence of excessively small powder particles in the system, preventing problems such as difficulty in dispersion during slurry preparation, poor electrolyte wetting, or exacerbated side reactions during charge-discharge, leading to deterioration in the battery's initial efficiency and energy density. Preferably, 4.6 μm ≤ D10 SiC ≤5.3μm.

[0032] In one specific implementation, 11 μm < D90 SiC <18μm, for example, D90 SiC The particle size can be 11.1μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 17.9μm, etc. Controlling the particle size D90 of the silicon-carbon material within the range of 11μm to 18μm allows for effective size synergy between the silicon-carbon material and graphite, jointly constructing a stable electrode framework. This avoids the reduction in compaction density caused by excessively fine particles, thereby improving the electrolyte wettability of the negative electrode. It also prevents excessively large silicon-carbon particles from causing a significant increase in absolute volume expansion during lithiation, which could lead to huge internal stress causing particle breakage and active material shedding. This improves the structural stability of the negative electrode, ultimately significantly enhancing the cycle performance and rate performance of the battery. Preferably, 12.3μm ≤ D90 SiC ≤16.7μm.

[0033] In one specific implementation, 0.7 g / cm 3 <TD SiC <1.3g / cm 3 Among them, TD SiC This refers to the tap density of silicon carbide materials, expressed in g / cm³. 3 For example, TD SiC It can be 0.71 g / cm³ 3 0.8g / cm 3 0.9g / cm 3 1g / cm 3 1.1g / cm 3 1.2g / cm 3 1.29g / cm 3 By controlling the tap density of silicon-carbon materials within the aforementioned range, it is possible to balance high energy density, excellent fast-charging capability, and long cycle life of the battery. If TD... SiC <0.7g / cm 3 This indicates that the loose and irregular particle structure of silicon-carbon materials requires more binders and conductive agents to maintain structural integrity during electrode fabrication. This significantly reduces the proportion of active material and impairs the battery's energy density. Furthermore, the loose structure hinders close contact between particles, weakening the electrode's conductive network and degrading the battery's cycle performance and rate performance. Conversely, if TD… SiC >1.3g / cm 3 This indicates that the silicon-carbon particles are too dense, which is detrimental to the penetration and storage of the electrolyte, thus deteriorating the lithium-ion transport kinetics and affecting the battery's fast-charging performance. Furthermore, overly hard and dense particles are prone to stress concentration during the electrode rolling process, and may even damage the more fragile silicon-carbon particles mixed with them, affecting the integrity of the electrode structure. Preferably, 0.81 g / cm³ 3 ≤TD SiC ≤1.1g / cm 3 .

[0034] In one specific implementation, 0.9m 2 / g<SSA SiC <1.7m 2 / g; where SSA SiC The specific surface area of ​​silicon-carbon materials, in m². 2 / g; for example, SSA SiC It can be 0.91m 2 / g, 1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.69m 2 / g etc. When the specific surface area of ​​silicon-carbon materials is within the above range, the silicon-carbon materials can provide sufficient and moderate electrochemically active interfaces, which is conducive to the rapid insertion and extraction of lithium ions, thereby effectively ensuring the excellent rate performance and fast charging capability of the electrode. At the same time, the moderate specific surface area effectively balances the interfacial reactivity, which can both support the formation of a stable SEI film and significantly reduce lithium consumption and gas generation caused by excessive side reactions, laying the foundation for achieving high initial coulombic efficiency and excellent cycle stability. Preferably, 1.21m 2 / g≤SSA SiC ≤1.5m 2 / g.

[0035] In one specific embodiment, the mass percentage of silicon in the silicon-carbon material is 40% to 55%, for example, the mass percentage of silicon in the silicon-carbon material can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, etc. When the mass percentage of silicon is within the above range, it can ensure that the silicon-carbon-graphite composite anode exhibits a significantly higher specific capacity than the pure graphite anode, while also allowing the graphite skeleton to effectively bind and buffer the volume change of the silicon phase, maintaining the relative integrity of the electrode microstructure and interface stability, thereby achieving both high specific capacity and long cycle stability of the lithium-ion battery.

[0036] In one specific implementation, 7μm < D50 C <12μm, where D50 C D50 is the particle size of graphite, expressed in μm; for example, D50 C The particle size can be 7.1μm, 8μm, 9μm, 10μm, 11μm, 11.9μm, etc. When the median particle size of graphite is within the above range, the size gradient of graphite and silicon-carbon materials forms a good match, allowing graphite to act as a framework to build a conductive network, while silicon-carbon particles effectively fill the gaps, jointly improving the electrode compaction density and energy density. Moreover, this size can ensure excellent processing performance. If the particle size is too small, it will increase the specific surface area, block the electrode pores, and lead to poor electrolyte wetting, ultimately reducing energy density and cycle performance. If the particle size is too large, it will affect the mixing uniformity of graphite and silicon-carbon, increase the risk of rolling breakage, and make the lithium-ion migration path longer, reducing the rate performance of the battery. Preferably, 8.2μm ≤ D50 C ≤10.5μm.

[0037] In one specific implementation, 3μm < D10 C <7μm; e.g., D10C The D10 of graphite can be 3.1 μm, 4 μm, 7 μm, 6 μm, 6.9 μm, etc. When the D10 of graphite is within the above range, it ensures that the graphite composition contains an appropriate amount of fine particles of suitable size. These fine particles can effectively fill the gaps in the electrode skeleton constructed from larger graphite particles and silicon-carbon materials, thereby improving the contact tightness between active materials and the compaction density of the electrode. This is beneficial for forming a more uniform conductive network, thereby improving the conductivity of the negative electrode and ultimately improving the cycle performance and rate performance of the battery. Preferably, 4.1 μm ≤ D10 C ≤6μm.

[0038] In one specific implementation, 16μm < D90 C <25μm, for example, D90 C The particle size can be 16.1μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 24.9μm, etc. Graphite particles within this size range can effectively construct a stable macroscopic electrode framework, providing reliable support for silicon-carbon materials and facilitating the efficient transport of lithium ions and electrons within the electrode. Simultaneously, this size range ensures an optimized particle size gradient distribution between graphite and silicon-carbon materials, thereby improving the electrode's compaction density and energy density. Furthermore, the suitable particle size balances formability and structural stability during electrode processing, laying the foundation for excellent rate performance and long cycle life in the battery. Preferably, 18.8μm ≤ D90 C ≤23μm.

[0039] In one specific embodiment, 0.8 g / cm 3 <TD C <1.2g / cm 3 Among them, TD C This is the tap density of graphite, expressed in g / cm³. 3 For example, TD C It can be 0.81 g / cm³ 3 0.9g / cm 3 1g / cm 3 1.1g / cm 3 1.19 g / cm 3 The moderate tap density indicates that the graphite particles have a regular morphology and suitable particle size distribution, enabling a compact and porous optimized packing structure during electrode fabrication. This not only improves the electrode's compaction density and volumetric energy density but also provides smooth channels for electrolyte wetting and lithium-ion migration, thus ensuring excellent rate performance of the battery. Simultaneously, graphite with this tap density helps form a stable conductive network in the electrode and achieves good structural compatibility with silicon-carbon materials, jointly improving the battery's cycle stability. Preferably, 1.1 g / cm³3 ≤TD C ≤1.18g / cm 3 .

[0040] In one specific implementation, 1m 2 / g<SSA C <2.8m 2 / g; where SSA C The specific surface area of ​​graphite, in m². 2 / g; for example, SSA C It can be 1.01m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g、2m 2 / g、2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 2.6m 2 / g, 2.7m 2 / g, 2.79m 2 / g etc. When the specific surface area of ​​graphite is within the above range, it can provide sufficient electrochemically active interfaces, ensuring efficient and reversible insertion and extraction of lithium ions, thereby guaranteeing excellent rate performance and fast charging capability of the electrode. Simultaneously, this moderate specific surface area is conducive to the formation of a dense and stable solid electrolyte interphase (SEI) film, effectively balancing interfacial reaction kinetics and stability, laying a solid foundation for achieving high initial coulombic efficiency and long cycle life. This characteristic also allows graphite to form good interfacial compatibility with silicon-carbon materials, jointly improving the overall performance of the composite electrode. Preferably, 1.14m 2 / g≤SSA C ≤2.4m 2 / g.

[0041] In one specific embodiment, the graphitization degree of graphite is greater than or equal to 94%, for example, the graphitization degree of graphite can be 94%, 95%, 96%, 97%, 98%, 99%, or 100%. The highly graphitized crystal structure has a highly ordered layered arrangement, which provides extremely efficient migration channels for electrons within and between graphite particles. This significantly reduces the internal resistance of the electrodes, greatly improves the rate performance and fast charging capability of the battery, and at the same time, this stable crystal structure effectively reduces irreversible side reactions caused by lattice defects, promoting the formation of a thinner and more stable solid electrolyte interface film, thereby achieving higher initial coulombic efficiency and superior cycle life.

[0042] In one specific embodiment, the mass percentage of silicon-carbon material in the negative electrode active material is 5% to 30%, for example, the mass percentage of silicon-carbon material in the negative electrode active material can be 5%, 10%, 15%, 20%, 25%, or 30%, etc. When the proportion of silicon-carbon material reaches more than 5%, its high specific capacity characteristic can be effectively utilized, which can significantly improve the overall energy density of the battery, making it superior to the traditional pure graphite negative electrode system. When the content of silicon-carbon material is controlled below 30%, it can be ensured that the graphite matrix always serves as the main framework of the negative electrode. Utilizing its excellent structural stability and conductivity, it can effectively buffer and disperse the volume expansion stress of silicon-carbon material during cycling, maintaining the integrity of the electrode structure. This ratio allows the battery to achieve a significantly improved energy density while maintaining cycle stability similar to that of the pure graphite negative electrode system, avoiding the problem of rapid capacity decay caused by excessive silicon-carbon content.

[0043] In one specific embodiment, the mass percentage of the negative electrode active material in the negative electrode coating is 92% to 98%. When the mass percentage of the negative electrode active material is within the above range, the negative electrode coating can maintain a high proportion of active material, ensuring the high energy density of the battery. At the same time, it also leaves room for the necessary conductive agents and binders in the negative electrode coating to construct an efficient conductive network and ensure the structural stability of the negative electrode coating, ultimately improving the cycle performance and rate performance of the battery to a greater extent.

[0044] In one specific embodiment, the negative electrode coating further includes a conductive agent, which includes at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. Adding a conductive agent to the negative electrode active material layer can improve the conductivity of the negative electrode active material layer, which is beneficial for the rapid migration of lithium ions within the negative electrode active material layer and helps improve the cycle performance and rate performance of the battery.

[0045] In a preferred embodiment, the conductive agent has a mass percentage content of 0.2% to 0.7% in the negative electrode coating.

[0046] In one specific embodiment, the negative electrode coating further includes a binder, which includes at least one of polyacrylic acid, polyacrylonitrile, polyacrylamide, and styrene-butadiene rubber. Adding a binder to the negative electrode active material layer enables the negative electrode active material to be firmly bonded to the conductive agent through the adhesion and bonding of the polymer materials, and to stably adhere to the current collector surface. This not only effectively prevents the pulverization of the negative electrode coating, but also significantly improves the overall structural stability of the electrode through strong cohesion, contributing to improved battery cycle performance and rate performance.

[0047] In a preferred embodiment, the binder has a mass percentage content of 1.5% to 6.5% in the negative electrode coating.

[0048] In one specific embodiment, the negative electrode coating further includes a dispersant, which includes at least one of lithium carboxymethyl cellulose and sodium carboxymethyl cellulose. The dispersant, by adsorbing onto the surface of the silicon-carbon material and graphite, effectively prevents the agglomeration tendency between active particles through steric hindrance or electrostatic stabilization, thereby ensuring uniform nanoscale distribution in the slurry and electrode. This not only forms a stable and uniform slurry system but also significantly enhances the structural stability of the negative electrode coating, reduces sedimentation and secondary agglomeration of active materials during cyclic charging and discharging, and ultimately significantly improves the battery's cycle life and rate performance.

[0049] In a preferred embodiment, the dispersant has a mass percentage content of 0.3% to 0.8% in the negative electrode coating.

[0050] A second aspect of this application provides a battery comprising the aforementioned negative electrode. This battery exhibits excellent cycle performance and rate performance.

[0051] In one specific embodiment, the battery of this application further includes a positive electrode sheet, which comprises a positive current collector and a positive electrode coating coated on the positive current collector. The positive electrode coating comprises a positive electrode active material, which includes at least one of lithium manganese oxide, lithium nickel cobalt manganese oxide ternary materials, lithium nickel manganese oxide, lithium-rich manganese-based materials, and nickel cobalt aluminum ternary materials. When the above-mentioned compounds are selected as the positive electrode active material, the positive electrode active material can fully exert its performance and improve the electrochemical performance of the lithium-ion battery.

[0052] In this application embodiment, there is no particular limitation on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper. Preferably, the positive electrode current collector is a metallic material.

[0053] In one specific embodiment, the positive electrode coating further includes a conductive agent and a binder. The conductive agent includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, graphene, and vapor-grown carbon fiber (VGCF). The binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, polyvinylidene fluoride, and polytetrafluoroethylene.

[0054] In one specific embodiment, the battery of this application further includes an electrolyte, which is an electrolyte known in the art that can be used in batteries and makes the battery have excellent electrochemical performance, including lithium salts and organic solvents, and can be specifically set as needed.

[0055] In one specific embodiment, the lithium-ion battery further includes a separator. The embodiments of this application do not have any particular restrictions on the material and shape of the separator, as long as it does not significantly impair the effect of this application. It may include porous sheet-like or non-woven fabric-like materials with excellent liquid retention. The materials of the resin or glass fiber separator include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc., and can be set according to needs.

[0056] In one embodiment, the battery may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte.

[0057] In one specific embodiment, the outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0058] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0059] This application does not impose any particular restrictions on the application fields of lithium-ion batteries, and they can be used in fields such as consumer batteries, power batteries for new energy vehicles, and energy storage batteries.

[0060] The present application will be further described in detail below through specific embodiments.

[0061] Example 1 1. Preparation of negative electrode sheet Silicon carbon material, graphite, conductive agent (SP), binder, and carboxymethyl cellulose were stirred for 15 minutes at a mass ratio of 14.45:81.9:0.25:3:0.4. Then, water was added to adjust the solid content to 55%, and a secondary dispersion was performed for 60 minutes to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on one surface of a 6 μm thick negative electrode current collector copper foil and dried to obtain a negative electrode coating. The above operation was repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet.

[0062] Among them: D10 of silicon carbide materials SiC It is 4.6μm, D50 SiC It is 7.7μm, D90 SiC It is 12.3μm, tap density TD SiC It is 0.91 g / cm³ 3 Specific surface area SSA SiC It is 1.21m 2 / g, the mass percentage of silicon in silicon-carbon materials is 45.96%, and the mass percentage of silicon-carbon materials in anode active materials is 15%; D10 of graphite C It is 5.4μm, D50 C It is 10.5μm, D90 C It is 18.8μm, tap density TD C It is 1.12 g / cm³ 3 Specific surface area SSA C It is 1.140m 2 / g, with a graphitization degree of 95%.

[0063] Therefore, |(D90) C -D50 SiC ) / (D50 SiC -D10 C )|=4.83; |(D90 SiC -D50 SiC ) / (D50 SiC -D10 SiC )|=1.48.

[0064] 2. Preparation of the positive electrode sheet Lithium cobalt oxide (CCO), conductive carbon black (SP), and polyvinylidene fluoride (PVDF) binder were mixed uniformly at a mass ratio of 97.5:1.5:1. The mixture was then thoroughly stirred in N-methylpyrrolidone solvent to prepare a slurry with a solid content of 75%. This slurry was then uniformly coated onto one surface of a 9 μm thick aluminum foil, dried at 90°C, and cold-pressed to obtain a positive electrode sheet with a 93 μm thick coating. The above steps were repeated on the other surface of this positive electrode sheet to obtain a positive electrode sheet with a double-sided coating. The positive electrode sheet was then cut to a size of 76 mm × 851 mm and tabs were welded on for later use.

[0065] 3. Preparation of electrolyte Under conditions with a water content of less than 10 ppm, propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed in a mass ratio of 1:3:6. Based on the total mass of the electrolyte, 8% butyl butyrate was added. Then, lithium hexafluorophosphate (LiPF6) was added to the solvent, dissolved, and mixed thoroughly. Finally, vinylene carbonate (VC) was added to obtain the electrolyte. The molar concentration of LiPF6 in the electrolyte was 1.15 mol / L, and the mass concentration of VC in the electrolyte was 1%.

[0066] 4. Manufacturing of lithium-ion batteries The positive and negative electrode sheets are stacked in sequence, and the stacked electrode sheets are wound with a separator to obtain an electrode assembly. The electrode assembly is placed in a pre-formed aluminum-plastic film and dehydrated at 80°C. The prepared electrolyte is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, and shaping processes.

[0067] The main difference between Examples 2-38, Comparative Examples 1-7 and Example 1 is the different parameters of silicon-carbon material and graphite, as shown in Tables 1 and 2.

[0068] Table 1

[0069] Table 2

[0070] Test case 1. Cyclic performance test In a constant temperature chamber at (25±2)℃, the lithium-ion battery was charged at a constant current and constant voltage of 2.5C to 4.53V, then charged at a constant voltage to 0.05C, and after resting for 5 minutes, discharged at 0.7C to 2.75V. The capacity obtained in this step was taken as the initial capacity. Cyclic tests were performed using 2.5C charging / 0.7C discharging, and the capacity retention rate of the battery after 200 cycles was calculated.

[0071] Cycle capacity retention (%) = Discharge capacity at 200th cycle (mAh) / Discharge capacity at first cycle (mAh) × 100% Cyclic thickness expansion rate (%) = (Cell thickness at 100% SOC after the 200th cycle (mm) / Cell thickness at 100% SOC in the first cycle (mm) - 1) × 100%.

[0072] The average values ​​of cycle life and cycle expansion rate for each group of 5 batteries are recorded in Table 3.

[0073] 2. Ratio Performance Test Rate performance test: The lithium-ion batteries were charged to 4.53V at a constant current and constant voltage of 0.8C in a constant temperature chamber at 25±2℃, and then discharged to 2.75V at a cutoff current of 0.05C. The batteries were then discharged to 2.75V at a rate of 0.2C / 0.5C / 1.0C / 2.0C / 3.0C / 4.0C. The cycle discharge capacity of the batteries was recorded. There were 5 batteries in each group.

[0074] 4C discharge capacity retention rate (%) = 4C discharge capacity (mAh) / discharge capacity of 0.2C rate cycle (mAh) × 100%.

[0075] Five batteries were used in each group. The average capacity retention rate at 4C was taken and the results are recorded in Table 3.

[0076] Table 3

[0077] Experimental data show that the particle size matching relationship between graphite and silicon-carbon materials is |(D90) C -D50 SiC ) / (D50 SiC -D10 C | and the particle size distribution concentration of silicon-carbon materials themselves | (D90) SiC -D50 SiC ) / (D50 SiC -D10 SiC The anode material is the primary structural parameter that determines the performance of the negative electrode.

[0078] Meeting the core parameters is a prerequisite for excellent performance: When 1 < |(D90) C -D50 SiC ) / (D50 SiC -D10 C )|<25 and 0.5<|(D90) SiC -D50 SiC) / (D50 SiC -D10 SiC When |<2 (as in Examples 1, 2, 5, 8, 9), the negative electrode exhibits high cycle stability and rate performance (capacity retention of 96.35%~97.03%, 4C retention of 90.50%~93.0%), verifying that the optimized gradient filling structure can synergistically improve conductivity, wetting and expansion buffering capabilities.

[0079] Failure to meet core parameters directly leads to performance degradation: If any of the above ratios exceeds the range (such as |(D90) in Comparative Example 6), C -D50 SiC ) / (D50 SiC -D10 C )|<1, compared to |(D90) in examples 1, 2, and 7 C -D50 SiC ) / (D50 SiC -D10 C )|>25, compared to |(D90) in examples 3~5 SiC -D50 SiC ) / (D50 SiC -D10 SiC (2) Even with other good material parameters, the performance still declined significantly (capacity retention rate 91.50%~93.00%), proving that the undesirable particle size matching was the direct cause of the performance decline.

[0080] When the core parameters meet the standards, the synergistic effect of other parameters is crucial: Even if the core particle size distribution meets the requirements, if the key physical properties of silicon-carbon or graphite (such as tap density, specific surface area, silicon content, etc.) exceed the preferred range of the claims, a noticeable decrease in performance will still occur (e.g., the capacity retention rate in Examples 10 and 23 drops to 92.00%~95.50%). This indicates that the setting of each preferred range in the claims is synergistically necessary.

[0081] Comparative examples demonstrate the criticality of the core parameters: Comparative Examples 1, 2, and 7 (|(D90) C -D50 SiC ) / (D50 SiC -D10 C (25) Due to the severe imbalance in particle size matching, the performance was even worse (capacity retention rate of 91.50%~92.50%), which strongly confirmed the necessity and non-obviousness of controlling the core particle size matching relationship from the opposite perspective.

[0082] The effectiveness of this invention is first guaranteed by the core particle size matching parameters, and is ultimately achieved through systematic synergistic optimization with the intrinsic parameters of the material.

[0083] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode coating disposed on at least one side surface of the negative electrode current collector; the negative electrode active material in the negative electrode coating includes silicon-carbon material and graphite; The negative electrode sheet satisfies the following relationship: 1<|(D90 C -D50 SiC ) / (D50 SiC -D10 C )|<25; 0.5<|(D90 SiC -D50 SiC ) / (D50 SiC -D10 SiC )|<2; Among them, D90 C The particle size D90 of the graphite is in μm; D10 C The particle size D10 of the graphite is in μm; D90 SiC The particle size D90 of the silicon-carbon material is in μm; D50 SiC The particle size D50 of the silicon-carbon material is in μm; D10 SiC D10 represents the particle size of the silicon-carbon material, in μm.

2. The negative electrode sheet according to claim 1, characterized in that: 6μm<D50 SiC <10μm; And / or, 3μm < D10 SiC <6μm; And / or, 11μm < D90 SiC <18μm.

3. The negative electrode sheet according to claim 1, characterized in that: 0.7g / cm 3 <TD SiC <1.3g / cm 3 Among them, TD SiC The tap density of the silicon-carbon material is expressed in g / cm³. 3 ; and / or, 0.9m 2 / g<SSA SiC <1.7m 2 / g; where SSA SiC The specific surface area of ​​the silicon-carbon material is given in m². 2 / g.

4. The negative electrode sheet according to claim 1, characterized in that, The silicon element in the silicon-carbon material has a mass percentage content of 40% to 55%.

5. The negative electrode sheet according to claim 1, characterized in that: 7μm<D50 C <12μm, where D50 C D50 is the particle size of the graphite, in μm; And / or, 3μm < D10 C <7μm; And / or, 16μm < D90 C <25μm.

6. The negative electrode sheet according to claim 1, characterized in that: 0.8g / cm 3 <TD C <1.2g / cm 3 Among them, TD C The tap density of the graphite is given in g / cm³. 3 ; And / or, 1m 2 / g<SSA C <2.8m 2 / g; where SSA C The specific surface area of ​​the graphite is given in m². 2 / g.

7. The negative electrode sheet according to claim 1, characterized in that, The graphite has a graphitization degree greater than or equal to 94%.

8. The negative electrode sheet according to claim 1, characterized in that, The silicon-carbon material has a mass percentage of 5% to 30% in the negative electrode active material.

9. The negative electrode sheet according to claim 1, characterized in that, The negative electrode active material has a mass percentage content of 92%~98% in the negative electrode coating; And / or, the negative electrode coating further includes a conductive agent, the conductive agent including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes; preferably, the conductive agent in the negative electrode coating has a mass percentage content of 0.2% to 0.7%; And / or, the negative electrode coating further includes a binder, the binder comprising at least one selected from polyacrylic acid, polyacrylonitrile, polyacrylamide, and styrene-butadiene rubber; preferably, the binder comprises 1.5% to 6.5% by mass in the negative electrode coating; And / or, the negative electrode coating further includes a dispersant, the dispersant including at least one of lithium carboxymethyl cellulose and sodium carboxymethyl cellulose; preferably, the mass percentage of the dispersant in the negative electrode coating is 0.3% to 0.8%.

10. A battery, characterized in that, The battery includes the negative electrode sheet as described in any one of claims 1 to 9.

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