Battery cell and method for producing the same, battery device, electric device, energy storage device

Abstract

The application provides a battery monomer, a preparation method thereof, a battery device, a power utilization device and an energy storage device. The battery monomer comprises a positive electrode sheet, a diaphragm and a negative electrode sheet, the negative electrode sheet comprises a negative electrode material, the negative electrode material comprises a silicon-carbon composite negative electrode material, the silicon-carbon composite negative electrode material comprises a porous carbon matrix and silicon deposited in pores of the porous carbon matrix; a space region is divided by taking a geometric center of the porous carbon matrix as an origin and a radial distance with a radius R, an outer layer region from an outer surface of the porous carbon matrix to a depth of alpha R is defined, and an inner layer region from a depth of beta R to the geometric center of the porous carbon matrix is defined; wherein alpha is 0.10-0.35, beta is 0.40-0.60, the mass content of silicon in the outer layer region is 5-15%, and the mass content of silicon in the inner layer region is 30-50%. The battery monomer adopting the above silicon-carbon composite material has high energy density and good cycle stability.

Description

Technical Field

[0001] This invention relates to the field of batteries, and in particular to a battery cell and its preparation method, a battery device, an electrical device, and an energy storage device. Background Technology

[0002] With the rapid development of electric vehicles, portable electronic devices, and large-scale energy storage systems, the demand for the energy density of lithium-ion batteries continues to grow. In the field of anode materials, the theoretical specific capacity of traditional graphite anodes is only 372 mAh / g, which is insufficient to meet the requirements of high-energy-density battery systems. Silicon materials, with their theoretical specific capacity as high as 4200 mAh / g (corresponding to Li...),... 4.4 Si), and a moderate lithium intercalation potential (approximately 0.4 V vs. Li / Li). + With its abundant crustal reserves, it is widely regarded as the most promising next-generation high-capacity anode material.

[0003] However, silicon anodes undergo volume expansion and contraction of up to 300-400% during charge and discharge, and this inherent volume effect causes a series of problems. First, repeated volume changes lead to silicon particle pulverization and electrode structure collapse, causing electrical contact failure between the active material and the current collector. Second, the SEI film on the silicon surface repeatedly breaks and rebuilds during volume changes, continuously consuming lithium ions and solvents in the electrolyte, resulting in reduced coulombic efficiency (CE) and irreversible capacity loss. In addition, the accumulation of volume stress can also cause cracking and delamination at the electrode layer, seriously affecting the cycle life of the battery.

[0004] To address these issues, the silicon-carbon composite strategy has attracted considerable attention. This strategy primarily involves loading nano-silicon components onto a carbon matrix, utilizing the excellent conductivity, structural stability, and volume buffering capacity of carbon materials to compensate for the shortcomings of silicon. However, challenges remain, including the difficulty in precisely controlling silicon distribution and the weak interfacial bonding between silicon and carbon components. This results in poor cycle stability and interfacial compatibility of silicon-carbon composite anode materials, making it difficult to maintain high specific capacity while achieving excellent long-cycle performance. Summary of the Invention

[0005] The main objective of this invention is to provide a battery cell and its preparation method, battery device, power consumption device, and energy storage device, in order to solve the problems of poor cycle stability and interface compatibility of silicon-carbon anode composite materials in existing battery cells.

[0006] To achieve the above objectives, according to one aspect of the present invention, a battery cell is provided, comprising a positive electrode, a separator, and a negative electrode. The negative electrode comprises a negative electrode material, which includes a silicon-carbon composite negative electrode material. The silicon-carbon composite negative electrode material comprises a porous carbon matrix and silicon deposited within the pores of the porous carbon matrix. Spatial regions are divided with the geometric center of the porous carbon matrix as the origin and a radial distance of radius R. The region from the outer surface of the porous carbon matrix to a depth αR is defined as the outer layer region, and the region from a depth βR to the geometric center of the porous carbon matrix is ​​defined as the inner layer region. Wherein, α is 0.10~0.35, β is 0.40~0.60, the silicon mass content in the outer layer region is 5~15%, and the silicon mass content in the inner layer region is 30~50%.

[0007] Furthermore, the ratio of the mass content of silicon in the inner region to the mass content of silicon in the outer region is 2.2 to 10:1.

[0008] Furthermore, the total mass content of silicon in the silicon-carbon composite anode material is 15-40%.

[0009] Furthermore, the region from depth αR to depth βR is defined as the middle layer region; wherein, the silicon mass content in the middle layer region is 15~30%; and the silicon mass content in the middle layer region is less than the silicon mass content in the inner layer region, and the silicon mass content in the outer layer region is less than the silicon mass content in the middle layer region.

[0010] Furthermore, the porous carbon matrix has an interconnected hierarchical pore structure; the hierarchical pores include at least two types of micropores, mesopores and macropores; wherein, the pore size of micropores is <2nm; the pore size of mesopores is 2~50nm; and the pore size of macropores is >50nm.

[0011] Furthermore, the specific surface area of ​​the porous carbon matrix is ​​200~1500 m². 2 / g, the total pore volume of the porous carbon matrix is ​​0.3~1.5cm³. 3 / g; the volume of the mesopores in the porous carbon matrix accounts for 20-80% of the total pore volume of the porous carbon matrix; and / or, the porous carbon matrix is ​​biomass-derived porous carbon, which is obtained by carbonization and activation of biomass-based raw materials, and the biomass-based raw materials are selected from any one or more of coconut shell, bamboo, rice husk, lignin, starch and cellulose.

[0012] Furthermore, the outer surface of the silicon-carbon composite anode material is also coated with a carbon layer, the thickness of which is 1~20nm, and the carbon layer is an amorphous carbon layer.

[0013] According to another aspect of the present invention, a method for preparing a battery cell is provided, comprising preparing a negative electrode material and preparing a negative electrode sheet including the negative electrode material, wherein a positive electrode sheet, a separator, and a negative electrode sheet are sequentially stacked and assembled to obtain a battery cell, the negative electrode material comprising a silicon-carbon composite negative electrode material, the silicon-carbon composite negative electrode material comprising a porous carbon matrix and silicon deposited in the pores of the porous carbon matrix; the method for preparing the silicon-carbon composite negative electrode material comprises: dividing a spatial region with the geometric center of the porous carbon matrix as the origin and a radial distance of radius R, defining the region from the outer surface of the porous carbon matrix to a depth αR as the outer region. The inner layer region extends from depth βR to the geometric center of the porous carbon matrix; where α is 0.10~0.35 and β is 0.40~0.60. A raw material comprising the porous carbon matrix and a first silicon source is subjected to chemical vapor deposition (CVD) to deposit silicon in the inner layer region of the porous carbon matrix, yielding an intermediate. A raw material comprising the intermediate and a second silicon source is subjected to CVD to deposit silicon in the outer layer region of the porous carbon matrix, yielding a silicon-carbon composite anode material. The silicon content in the outer layer region is 5~15% by mass, and the silicon content in the inner layer region is 30~50% by mass.

[0014] Furthermore, the deposition temperature of chemical vapor infiltration is 400~600℃, the deposition time is 0.5~8h, and the pressure is 0.1~50kPa; the volume concentration of the first silicon source is 0.5~5vol%, and the flow rate of the first silicon source is 50~500mL / min; chemical vapor infiltration is carried out using a pulsed gas supply method, which includes: gas supply for 1~30min followed by vacuum diffusion for 1~30min, which constitutes one cycle, and a total of 5~50 cycles are performed.

[0015] Furthermore, the deposition temperature of chemical vapor deposition is 500~700℃, the deposition time of chemical vapor deposition is 0.5~4h, and the pressure of chemical vapor deposition is 50~200kPa; the volume concentration of the second silicon source is 3~20vol%, and the flow rate of the second silicon source is 100~1000mL / min.

[0016] Furthermore, the porous carbon matrix is ​​obtained by sequentially carbonizing and activating biomass-based raw materials; wherein, the carbonization temperature is 600~1000℃, the carbonization time is 1~6h, and the carbonization atmosphere is an inert gas; the activation method is physical activation and / or chemical activation; physical activation is water vapor activation and / or carbon dioxide activation, the physical activation temperature is 700~1000℃, and the physical activation time is 0.5~4h; chemical activation is carried out using an activating agent, which is selected from any one or more of KOH, NaOH, ZnCl2 and H3PO4, the mass ratio of activating agent to biomass-based raw material is 1~5:1, the chemical activation temperature is 600~900℃, and the chemical activation time is 1~4h.

[0017] Furthermore, the preparation method of silicon-carbon composite anode material also includes: surface coating of raw materials including chemical vapor deposition product and carbon source, forming a carbon layer on the outer surface of chemical vapor deposition product to obtain silicon-carbon composite anode material; wherein, the carbon source is selected from any one or more of methane, ethylene, acetylene and propylene; the surface coating method is chemical vapor deposition, the surface coating temperature is 600~900℃, and the surface coating time is 10~120min.

[0018] According to another aspect of the present invention, a battery device is provided, the battery device comprising the above-described battery cell, and the battery device comprising any one or more of a battery module, a battery pack, and an energy storage battery.

[0019] According to another aspect of the present invention, an electrical device is provided, which includes the battery device described above, the battery device being used to provide electrical energy.

[0020] According to another aspect of the present invention, an energy storage device is provided, which includes the battery device described above, the battery device being used to store electrical energy.

[0021] The technical solution of this application has the following beneficial effects: For traditional silicon-carbon anode materials with uniform silicon distribution, the battery cell of this application adopts a silicon-carbon anode material with a clearly defined functional partition and a silicon content gradient structure of "low outside, high inside." This allows the outer region of the carbon particles to assume structural stability and interface protection functions, while the inner region assumes high-capacity lithium storage functions. This significantly improves the cycle stability and interface compatibility of the silicon-carbon composite anode material, achieving excellent long-cycle performance while maintaining high specific capacity. This design shift enables silicon-carbon composite materials to adapt to spatially heterogeneous environments at the structural level for the first time, fundamentally changing the trade-off between capacity and stability. This application defines the aforementioned inner and outer regions and controls the silicon mass content in both regions within the aforementioned range, enabling systematic optimization of the synergistic effects of structural stability, interface compatibility, and capacity utilization in silicon-carbon composite anode materials. The outer region, acting as an "interface barrier layer" in direct contact with the electrolyte, significantly reduces the volume expansion rate during lithiation / delithiation processes due to its low silicon content. This effectively alleviates surface stress concentration, inhibits particle cracking and pulverization, and the repeated rupture and reconstruction of the SEI film, thereby greatly reducing the irreversible consumption of active lithium and electrolyte, improving the first-cycle coulombic efficiency, and extending battery life. Simultaneously, the inner region, as a "high-capacity energy storage core area," fully releases the ultra-high theoretical specific capacity of silicon under the three-dimensional confinement of the carbon skeleton and the buffer protection of the low-silicon outer region, achieving efficient utilization of the overall material specific capacity. Because the silicon in the inner region is encapsulated within a porous carbon network, its volume expansion is constrained by the elasticity of the surrounding carbon matrix and mechanically shielded by the outer structure, avoiding the severe interfacial side reactions caused by direct exposure to the electrolyte, thus maintaining structural integrity without sacrificing capacity. Therefore, battery cells using the aforementioned silicon-carbon composite material exhibit high energy density and good cycle stability, making them better suited for applications in electric vehicles, portable electronic devices, and large-scale energy storage systems. Attached Figure Description

[0022] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0023] Figure 1 A schematic flowchart of the method for preparing a single battery cell in Embodiment 1 of this application is shown;

[0024] Figure 2 A schematic diagram of the spatial region of the porous carbon matrix in this application is shown.

[0025] The above figures include the following reference numerals:

[0026] 1. Outer region; 2. Middle region; 3. Inner region. Detailed Implementation

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0028] As analyzed in the background section of this application, existing technologies suffer from problems such as poor cycle stability and interface compatibility of silicon-carbon anode composite materials in battery cells. To address these issues, this application provides a battery cell, its preparation method, a battery device, an electrical device, and an energy storage device.

[0029] In a typical embodiment of this application, a battery cell is provided, including a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative electrode material, which is a silicon-carbon composite negative electrode material. The silicon-carbon composite negative electrode material comprises a porous carbon matrix and silicon deposited within the pores of the porous carbon matrix. A spatial region is divided with the geometric center of the porous carbon matrix as the origin and a radial distance of radius R. The region from the outer surface of the porous carbon matrix to a depth αR is defined as the outer layer region, and the region from a depth βR to the geometric center of the porous carbon matrix is ​​defined as the inner layer region. Wherein, α is 0.10~0.35, β is 0.40~0.60, the silicon mass content in the outer layer region is 5~15%, and the silicon mass content in the inner layer region is 30~50%.

[0030] In contrast to traditional silicon-carbon anode materials with uniform silicon distribution, this application's battery cell employs a silicon-carbon anode material with a clearly defined functional partitioning and a "low outer, high inner" silicon content gradient structure. This allows the outer region of the carbon particles to provide structural stability and interface protection, while the inner region provides high-capacity lithium storage. This significantly improves the cycle stability and interface compatibility of the silicon-carbon composite anode material, achieving excellent long-cycle performance while maintaining high specific capacity. This design shift enables silicon-carbon composite materials to adapt to spatially heterogeneous environments at the structural level for the first time, fundamentally altering the trade-off between capacity and stability. This application defines the aforementioned inner and outer regions and controls the silicon mass content in both regions within the specified range, systematically achieving synergistic optimization of structural stability, interface compatibility, and capacity utilization in the silicon-carbon composite anode material. The outer region, acting as an "interface barrier layer" in direct contact with the electrolyte, significantly reduces the volume expansion rate during lithiation / delithiation processes due to its low silicon content. This effectively alleviates surface stress concentration, inhibits particle cracking and pulverization, and the repeated rupture and reconstruction of the SEI film, thereby greatly reducing the irreversible consumption of active lithium and electrolyte, improving the first-cycle coulombic efficiency, and extending battery life. Simultaneously, the inner region, as a "high-capacity energy storage core area," fully releases the ultra-high theoretical specific capacity of silicon under the three-dimensional confinement of the carbon skeleton and the buffer protection of the low-silicon outer region, achieving efficient utilization of the overall material specific capacity. Because the silicon in the inner region is encapsulated within a porous carbon network, its volume expansion is constrained by the elasticity of the surrounding carbon matrix and mechanically shielded by the outer structure, avoiding the severe interfacial side reactions caused by direct exposure to the electrolyte, thus maintaining structural integrity without sacrificing capacity. Therefore, battery cells using the aforementioned silicon-carbon composite material exhibit high energy density and good cycle stability, making them better suited for applications in electric vehicles, portable electronic devices, and large-scale energy storage systems.

[0031] R is the equivalent radius of the porous carbon matrix particles, and R is 1000~10000 nm; preferably, R is 2000~8000 nm; more preferably, R is 3000~6000 nm. The mass content of silicon in the outer layer region is based on the mass of the outer layer region, and the mass content of silicon in the inner layer region is based on the mass of the inner layer region.

[0032] In one embodiment of this application, the ratio of the mass content of silicon in the inner layer region to the mass content of silicon in the outer layer region is 2.2 to 10:1.

[0033] Controlling the ratio of silicon mass content in the inner layer region to that in the outer layer region within the aforementioned range helps to enhance the synergistic effect between the outer and inner layers. This allows the inner layer region to fully exert its "high capacity" function while simultaneously increasing the constraint of the outer layer region on the volume expansion of the inner layer, improving structural stability, and reducing reactions with the electrolyte. This, in turn, achieves cycle stability and interfacial compatibility of the silicon-carbon composite anode material, improving long-cycle performance while maintaining high specific capacity.

[0034] In one embodiment of this application, the total mass content of silicon in the silicon-carbon composite anode material is 15-40%.

[0035] The total mass content of silicon in the silicon-carbon composite anode material is based on the total mass of the silicon-carbon composite anode material. If the total mass content of silicon in the silicon-carbon composite anode material is too low, it is difficult to take advantage of the high energy density of silicon materials; if the total mass content of silicon in the silicon-carbon composite anode material is too high, the silicon phase will excessively aggregate, and the volume expansion stress will exceed the buffer limit of the carbon skeleton, resulting in intensified particle pulverization, continuous thickening of the SEI film, and reduced cycle life. Therefore, this application controls the total mass content of silicon in the silicon-carbon composite anode material within the above-mentioned range, which helps to fully utilize the high capacity and improve structural stability, thereby improving the energy density and cycle life of the battery cell.

[0036] In one embodiment of this application, the region from depth αR to depth βR is defined as the middle layer region; wherein, the silicon mass content in the middle layer region is 15~30%; and the silicon mass content in the middle layer region is less than the silicon mass content in the inner layer region, and the silicon mass content in the outer layer region is less than the silicon mass content in the middle layer region.

[0037] By setting up the aforementioned three silicon content regions, the middle region acts as a "buffer transition layer," which helps to achieve a smooth transition between stress and lithium-ion transport, thereby further improving the cycle stability of the silicon-carbon composite anode material. Preferably, α is 0.15~0.30, β is 0.45~0.55, the silicon mass content in the middle region is 12~20% lower than that in the inner region, and the silicon mass content in the outer region is 10~18% lower than that in the middle region. This helps maintain the connectivity of the ion transport channels and provides elastic support for the high-silicon region in the inner layer, reducing the local peak value of volumetric strain. This allows for the stable release of silicon expansion stress, improving cycle stability and enabling the battery cell to achieve high capacity, long lifespan, and high reliability.

[0038] A schematic diagram of the spatial regions of a porous carbon matrix is ​​shown below. Figure 2As shown, the spatial regions are divided with the geometric center of the porous carbon matrix as the origin and radial distances of radius R. The region from the outer surface of the porous carbon matrix to depth αR is the outer layer region 1, the region from depth βR to the geometric center of the porous carbon matrix is ​​the inner layer region 3, and the region from depth αR to depth βR is the middle layer region 2. The depth direction is the direction from the outer surface of the porous carbon matrix inward (towards the geometric center).

[0039] In one embodiment of this application, the porous carbon matrix has an interconnected hierarchical pore structure; the hierarchical pores include at least two types of micropores, mesopores and macropores; wherein, the pore size of the micropores is <2nm; the pore size of the mesopores is 2~50nm; and the pore size of the macropores is >50nm.

[0040] A porous carbon matrix with an interconnected hierarchical pore structure facilitates the gradient deposition of silicon. In this application, "interconnected hierarchical pore structure" refers to at least two types of pore structures—micropores, mesopores, and macropores—that are interconnected within a three-dimensional carbon framework or connected through a continuous pore network, allowing the gaseous silicon source to diffuse along the pores from the outer layer to the inner layer of the particle. Micropores provide high specific surface area and silicon nanonucleation sites, mesopores serve as the main channels for silicon precursor permeation and lithium-ion transport, and macropores mitigate volume expansion and improve electrolyte wettability. The hierarchical pore structure, including at least two of these types, helps to synergistically construct a "permeation-transport-buffering" interconnected network, thereby improving the structural stability of the silicon-carbon composite anode material.

[0041] In one embodiment of this application, the specific surface area of ​​the porous carbon matrix is ​​200~1500 m². 2 / g, the total pore volume of the porous carbon matrix is ​​0.3~1.5cm³. 3 / g; the volume of the mesopores in the porous carbon matrix accounts for 20-80% of the total pore volume of the porous carbon matrix; and / or, the porous carbon matrix is ​​biomass-derived porous carbon, which is obtained by carbonization and activation of biomass-based raw materials, and the biomass-based raw materials are selected from any one or more of coconut shell, bamboo, rice husk, lignin, starch and cellulose.

[0042] Preferred control of the specific surface area, total pore volume, and the proportion of the volume of mesopores in the porous carbon matrix to the total pore volume within the aforementioned ranges facilitates high silicon deposition in the inner layer and low silicon deposition in the outer layer, maintaining the mechanical strength of the electrode structure. The porous carbon matrix prepared using the above-mentioned raw materials is low-cost and environmentally friendly, and its hierarchical pore structure is conducive to silicon deposition.

[0043] When the porous carbon matrix includes micropores, mesopores and macropores, the pore volume ratio of micropores, mesopores and macropores is 5~40:20~80:5~50, preferably 10~30:40~70:10~30, which helps to synergistically construct a "permeation-transport-buffering" interconnected network, thereby improving the structural stability of silicon-carbon composite anode materials.

[0044] In one embodiment of this application, the outer surface of the silicon-carbon composite anode material is further coated with a carbon layer, the thickness of which is 1~20nm, and the carbon layer is an amorphous carbon layer.

[0045] The outer surface of the preferred silicon-carbon composite anode material is coated with a carbon layer, which helps to improve the conductivity of the silicon-carbon composite anode material and further enhance interface stability, thereby improving the electrochemical performance of the battery cell. If the carbon layer is too thin, the coverage is insufficient, making it difficult to suppress electrolyte penetration and excessive SEI film growth; if the carbon layer is too thick, it will increase lithium-ion transport resistance, reducing rate performance and active material utilization. Therefore, the preferred carbon layer thickness is within the above-mentioned range, which helps to improve its mechanical stability while further enhancing the conductivity of the particle surface.

[0046] The positive electrode of the battery cell of this application includes a positive current collector and a positive active layer. The positive active layer is formed by coating a positive electrode slurry onto the surface of the positive current collector. The positive electrode slurry includes a positive active material, a conductive agent, and a binder. The positive active material includes, but is not limited to: layered oxide positive electrode materials, such as lithium cobalt oxide (LiCoO2), ternary materials NCM (including NCM111, NCM523, NCM622, NCM811, etc.), nickel-cobalt-aluminum ternary materials NCA, etc.; polyanionic compound positive electrode materials, such as lithium iron phosphate (LiFePO4), lithium manganese iron phosphate, etc.; spinel structure positive electrode materials, such as lithium manganese oxide (LiMn2O4), high-voltage spinel, etc. The content of the positive active material is 85~98wt%. The conductive agent is selected from any one or more of Super P, Ketjen Black, carbon nanotubes, and graphene, and its content is 1~10wt%. The binder is polyvinylidene fluoride (PVDF) and / or polytetrafluoroethylene (PTFE), with a content of 2-8 wt%. The positive electrode current collector is aluminum foil or carbon-coated aluminum foil current collector.

[0047] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer. The negative electrode active layer is formed by coating the surface of the negative electrode current collector with a negative electrode slurry. The negative electrode slurry includes a negative electrode active material, a conductive agent, and a binder. The silicon-carbon composite negative electrode material of this application can be used alone or mixed with other negative electrode active materials (such as natural graphite, artificial graphite, soft carbon, hard carbon, etc.) in a certain mass ratio. The content of the negative electrode active material is 80~97wt%, and the conductive agent is Super P and / or carbon nanotubes, with a content of 0~5wt%. The binder is selected from any one or more of polyacrylic acid (PAA), polyimide (PI), a composite system of sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), and sodium alginate, with a content of 3~15wt%. The negative electrode current collector is a copper foil current collector. Optionally, when the silicon-carbon composite negative electrode material of this application is used as the main active component, the binder is preferably a polymer material with strong adhesion, such as PAA or PI, to accommodate the volume change of the silicon-carbon material.

[0048] Separators include polyolefin separators (such as polypropylene (PP) separators, polyethylene (PE) separators, PP / PE / PP three-layer composite separators, etc.), ceramic-coated separators (such as Al2O3-coated separators, SiO2-coated separators, etc.) and other high-performance separator materials.

[0049] The electrolyte system comprises an electrolyte formulation using carbonate solvents such as ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as the main solvent, lithium salts such as lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the conductive salt, and may add film-forming additives such as fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Preferably, the electrolyte contains 5-20 wt% FEC to form a high-quality SEI film rich in lithium fluoride (LiF) on the surface of the silicon-carbon anode.

[0050] The selection and combination of the above components can be optimized and matched according to specific battery design requirements. The silicon-carbon composite anode material of this application has good adaptability to different cathode systems and electrolyte formulations.

[0051] In another typical embodiment of this application, a method for preparing a battery cell is provided, including preparing a negative electrode material and preparing a negative electrode sheet including the negative electrode material. A positive electrode sheet, a separator, and a negative electrode sheet are sequentially stacked and assembled to obtain a battery cell. The negative electrode material includes a silicon-carbon composite negative electrode material, which comprises a porous carbon matrix and silicon deposited within the pores of the porous carbon matrix. The method for preparing the silicon-carbon composite negative electrode material includes: dividing a spatial region from the outer surface of the porous carbon matrix to a depth αR, with the geometric center of the porous carbon matrix as the origin and a radial distance of radius R. The outer layer region is defined as the region extending from depth βR to the geometric center of the porous carbon matrix, while the inner layer region is defined as the region extending from depth βR to the geometric center of the porous carbon matrix. Here, α is 0.10–0.35, and β is 0.40–0.60. A raw material comprising the porous carbon matrix and a first silicon source is subjected to chemical vapor deposition (CVD) to deposit silicon in the inner layer region of the porous carbon matrix, yielding an intermediate. A raw material comprising the intermediate and a second silicon source is then subjected to CVD to deposit silicon in the outer layer region of the porous carbon matrix, yielding a silicon-carbon composite anode material. The silicon content in the outer layer region is 5–15% by mass, and the silicon content in the inner layer region is 30–50% by mass.

[0052] Currently, the preparation of silicon-carbon composite anode materials mainly employs the following technical solutions. The first is the mechanical mixing method, which physically combines nano-silicon particles with carbon materials through mechanical means such as ball milling or high-speed mixing. This method only achieves physical contact between silicon and carbon components, lacking chemical bonding, and the uniformity of silicon particle distribution within the carbon matrix is ​​difficult to guarantee. The second is the liquid-phase deposition-thermal reduction method, which introduces silicon-containing precursors (such as tetraethyl orthosilicate, silicate solutions, etc.) into the pores of a porous carbon matrix through liquid-phase processes such as impregnation or sol-gel, followed by high-temperature carbothermic or magnesian reduction to convert the silicon-containing precursors into elemental silicon. This method can utilize the wetting and penetration effects of the liquid phase to introduce the silicon precursor into the carbon matrix, theoretically facilitating a more uniform silicon distribution. However, the liquid-phase method is prone to capillary migration and enrichment of the precursor during the drying process, making it difficult to precisely control the uniformity of silicon deposition; furthermore, the high-temperature conditions of the reduction process may alter the microstructure of the carbon matrix. The third type is chemical vapor deposition (CVD), which uses silane or other silicon-containing gaseous precursors as the silicon source. Under certain temperature conditions, these precursors undergo thermal decomposition reactions on the surface and within the pores of a porous carbon matrix, resulting in the in-situ deposition of a nanocrystalline silicon layer. The core advantage of CVD is that the deposition process occurs at the gas-solid interface, enabling uniform coverage and tight bonding of silicon on the pore walls of the carbon matrix. In a typical CVD process, silane gas (usually diluted to a certain volume concentration with nitrogen or argon) is introduced into the reaction chamber. The carbon matrix comes into contact with the silane gas under heating conditions, and the silane undergoes thermal decomposition reactions on the carbon surface, depositing an amorphous or nanocrystalline silicon layer. The total amount of silicon deposited can be adjusted by controlling parameters such as reaction temperature, silane concentration, reaction time, and gas flow rate. However, in the case of a porous carbon matrix, the gaseous precursor diffuses from the outer surface of the particles towards the internal pores while simultaneously being consumed by surface reactions. When the surface reaction rate is significantly higher than the diffusion rate within the pores (i.e., high Thiele modulus conditions), the precursor is largely consumed before reaching the deep pores, resulting in silicon being deposited mainly on the outer surface and in the shallow pores.

[0053] Both mechanical mixing and liquid phase deposition share a core drawback: weak interfacial bonding between silicon and carbon components. In mechanical mixing, silicon particles adhere to the carbon material surface only through physical contact, making them prone to detachment during repeated volume changes, leading to loss of active material and failure of electrical contacts. While liquid phase deposition can partially utilize the capillary action of pores to introduce precursors, the reduction product also lacks a strong interfacial bond with the carbon matrix. Furthermore, the liquid phase method inevitably suffers from silicon particle agglomeration and size inhomogeneity during drying and reduction. In addition, both methods struggle to achieve controlled, ordered distribution of silicon components in the radial direction of the carbon matrix.

[0054] For CVD, the root of its technical bottleneck lies in the dominance of Thiele modulus on the spatial distribution of silicon deposition. Under conventional CVD conditions (higher temperatures such as 600–800 °C and higher silane concentrations), the surface reaction rate constant k increases exponentially with temperature according to the Arrhenius equation, resulting in a significant increase in Thiele modulus. Under high Thiele modulus conditions, silane precursors are rapidly consumed at the outer surface of carbon particles and at shallow pores, forming a dense silicon deposition layer that further blocks the pores and hinders the inward diffusion of subsequent precursors. This positive feedback mechanism leads to a "high outer, low inner" silicon deposition distribution, meaning that the silicon content on the outer surface is much higher than that in the interior.

[0055] The aforementioned "high silicon content on the outside, low silicon content on the inside" distribution characteristic brings multiple negative effects. First, the high silicon content region on the outer surface bears the greatest volume expansion stress during lithiation / delithiation, becoming a preferential site for crack initiation and propagation, accelerating particle pulverization and structural failure. Second, the drastic volume change on the outer surface directly damages the SEI film in contact with the electrolyte, causing repeated fracture-reconstruction cycles of the SEI film, continuously consuming active lithium and electrolyte components, leading to a decrease in CE and a continuous increase in impedance. In addition, due to the insufficient silicon content in the internal pores, the overall lithium storage capacity of the material is not fully utilized, resulting in low capacity utilization efficiency. Currently, although some studies attempt to improve the uniformity of silicon distribution by adjusting CVD process parameters, these methods are essentially still optimizations under a homogenization paradigm, failing to fundamentally solve the problem of preferential surface deposition, let alone achieve the target gradient structure of "low silicon content on the outside, high silicon content on the inside".

[0056] Based on the physical nature of the reaction-diffusion competition in porous media, this application proposes a novel technical strategy to achieve radial gradient distribution of silicon components by controlling the Thiele modulus in stages. The core design is to actively construct a gradient structure with clearly defined functional zones—lower silicon content on the outside and higher on the inside—instead of pursuing traditional silicon uniformity. This allows the outer region of the carbon particles to provide structural stability and interface protection, while the inner region provides high-capacity lithium storage. This significantly improves the cycle stability and interface compatibility of silicon-carbon composite anode materials, achieving excellent long-cycle performance while maintaining high specific capacity. Compared to the homogenization optimization approach under single deposition conditions, this application adopts a staged deposition strategy of "inside first, then outside." The first stage uses chemical vapor infiltration (CVI) to control the Thiele modulus at an extremely low level, making the diffusion rate far exceed the surface reaction rate. This drives the first silicon source to penetrate deeply into the pores of the porous carbon matrix and deposit preferentially. The second stage employs a CVD process, utilizing the natural sealing effect of the deposited products from the first stage on the pores, allowing silicon to be deposited primarily in the outer region while maintaining a controllable content. This two-stage kinetic switching strategy cleverly utilizes the "outer-rich, inner-thin" deposition characteristic of traditional CVD in stages: the first stage avoids it, while the second stage utilizes it, ultimately achieving the spontaneous formation of the target silicon content distribution structure. Based on the above structural and fabrication method innovations, the silicon-carbon composite anode material in the battery cell of this application achieves systematic improvements in several key performance dimensions. In terms of cycle stability, the volume expansion of the low-silicon-content outer region is controlled at a low level, effectively suppressing stress concentration and crack formation on the outer surface of the particles, thereby significantly delaying the structural degradation rate during cycling. In terms of interface stability, the low volume change amplitude in the outer region ensures the mechanical integrity of the SEI film, reducing repeated rupture-reconstruction cycles of the SEI film, thereby improving CE and mitigating impedance growth. In terms of capacity utilization, the high-silicon content inner layer contributes the main lithium storage capacity of the material, and its volume change is constrained and buffered by the surrounding carbon skeleton and the low-silicon outer layer due to its location within the protective internal space of the porous carbon matrix. Regarding process economy, the entire preparation process can be continuously completed in the same equipment, requiring no additional nano-silicon synthesis and dispersion steps. The equipment has good compatibility, and process parameters can be precisely controlled, enabling large-scale production. In summary, this application systematically solves the cycle decay and interface degradation problems caused by surface silicon enrichment in existing silicon-carbon composite anode materials through a radial "low outer, high inner" gradient silicon content distribution structural design and a staged CVI+CVD process. Therefore, the silicon-carbon composite anode material obtained by the preparation method of this application has good cycle stability and interface compatibility, achieving excellent long-cycle performance while maintaining high specific capacity, thereby improving the energy density and cycle performance of lithium-ion batteries.

[0057] In one embodiment of this application, the deposition temperature of chemical vapor infiltration is 400~600℃, the deposition time of chemical vapor infiltration is 0.5~8h, and the pressure of chemical vapor infiltration is 0.1~50kPa; the volume concentration of the first silicon source is 0.5~5vol%, and the flow rate of the first silicon source is 50~500mL / min; chemical vapor infiltration is performed using a pulsed gas supply method, and the pulsed gas supply process includes: gas supply for 1~30min followed by vacuum diffusion for 1~30min, which constitutes one cycle, and a total of 5~50 cycles are performed.

[0058] Precisely controlling the deposition temperature, deposition time, pressure, and volume concentration and flow rate of the first silicon source within the aforementioned ranges for chemical vapor infiltration (CVD), along with low temperature, low silane partial pressure, and reduced pressure environment, helps to keep the Thiele modulus well below 1 in the reaction control range. This allows the first silicon source to diffuse sufficiently into the internal pores of the porous carbon matrix before being consumed by the surface reaction, achieving preferential silicon deposition in the inner layer region. Pulsed gas supply, through alternating cycles of "gas-vacuuming," utilizes the concentration gradient to drive the first silicon source to continuously diffuse inward during periods without new gas supply. This helps to reduce the effective Thiele modulus, thereby overcoming the diffusion limitations of traditional CVD and enabling silicon to preferentially deposit in the inner layer region.

[0059] In one embodiment of this application, the deposition temperature of chemical vapor deposition is 500~700℃, the deposition time of chemical vapor deposition is 0.5~4h, the pressure of chemical vapor deposition is 50~200kPa, the volume concentration of the second silicon source is 3~20vol%, and the flow rate of the second silicon source is 100~1000mL / min.

[0060] Since the silicon deposited in the first stage partially fills the internal pores, reducing the effective pore size and connectivity of the internal pores, further controlling the deposition temperature, deposition time, pressure, and the volume concentration and flow rate of the second silicon source within the aforementioned ranges during chemical vapor deposition helps the second stage, under higher Thiele modulus conditions, to allow the second silicon source to be deposited primarily in the residual pores and surface of the outer layer, forming a controlled low-silicon content region in the outer layer. The self-blocking effect between the two stages allows the silicon content gradient distribution between the inner and outer layers to form spontaneously.

[0061] In one embodiment of this application, the porous carbon matrix is ​​obtained by sequentially carbonizing and activating biomass-based raw materials; wherein, the carbonization temperature is 600~1000℃, the carbonization time is 1~6h, and the carbonization atmosphere is an inert gas; the activation method is physical activation and / or chemical activation; the physical activation is water vapor activation and / or carbon dioxide activation, the physical activation temperature is 700~1000℃, and the physical activation time is 0.5~4h; chemical activation is performed using an activating agent, which is selected from any one or more of KOH, NaOH, ZnCl2 and H3PO4, the mass ratio of the activating agent to the biomass-based raw material is 1~5:1, the chemical activation temperature is 600~900℃, and the chemical activation time is 1~4h.

[0062] The porous carbon matrix is ​​prepared by carbonizing biomass-based raw materials under the aforementioned conditions, which leads to the pyrolysis of organic components and the initial construction of the carbon framework, thereby improving the structural integrity and conductivity of the carbon matrix. Subsequent activation treatment under the same conditions helps to precisely control the pore structure. The above-mentioned methods for preparing porous carbon matrices facilitate the formation of interconnected hierarchical pore structures. Chemical activation helps optimize the specific surface area and mesopore ratio of the porous carbon matrix, while physical activation is more conducive to preserving the natural pore structure.

[0063] In one embodiment of this application, the preparation method of silicon-carbon composite anode material further includes: surface coating of raw materials including chemical vapor deposition product and carbon source, forming a carbon layer on the outer surface of chemical vapor deposition product to obtain silicon-carbon composite anode material; wherein, the carbon source is selected from any one or more of methane, ethylene, acetylene and propylene; the surface coating method is chemical vapor deposition, the surface coating temperature is 600~900℃, and the surface coating time is 10~120min.

[0064] The carbon layer is formed by the above preparation method. By controlling the type of carbon source, the surface coating temperature and time within the above range, it is helpful to form a uniform amorphous carbon coating layer on the outer surface of the product after chemical vapor deposition. This can serve as an interface protection layer and also help to improve the conductivity of silicon-carbon composite anode materials.

[0065] In another typical embodiment of this application, a battery device is provided, which includes the above-mentioned battery cell, and the battery device includes any one or more of battery modules, battery packs, and energy storage batteries.

[0066] Battery devices including the aforementioned battery cells have superior overall performance in terms of high power output, wide temperature range operation, and long cycle life, making them suitable for energy storage systems and power battery applications with high requirements for energy density, safety, and reliability.

[0067] In another typical embodiment of this application, an electrical device is provided, which includes the battery device described above, the battery device being used to provide electrical energy.

[0068] The aforementioned battery devices enable electrical devices to have higher energy efficiency, longer service life and more stable power output characteristics, making them suitable for energy storage systems and electric vehicle applications with stringent requirements for safety and cycle performance.

[0069] In another typical embodiment of this application, an energy storage device is provided, which includes the battery device described above, the battery device being used to store electrical energy.

[0070] Energy storage devices including the aforementioned battery devices can effectively reduce interface impedance, suppress dendrite growth, and improve the cycle life and rate performance of batteries in a wide temperature range environment. They are suitable for energy storage systems with comprehensive requirements for energy density, safety and low temperature adaptability, and are especially suitable for high-reliability energy storage application scenarios under solid-state battery architecture.

[0071] Furthermore, the gradient silicon content silicon-carbon composite anode prepared in this application not only maintains high specific capacity but also achieves excellent long-cycle performance, making it more suitable for the needs of long-term energy storage systems. This material possesses high volumetric energy density and excellent cycle stability (capacity retention >85% after >10,000 cycles), efficiently supporting the operation of large-scale energy storage power stations at 4-hour (4h) and 8-hour (8h) levels, meeting the stringent requirements for high-capacity batteries in application scenarios such as grid peak shaving and smooth output of renewable energy.

[0072] Energy storage devices including the aforementioned battery devices can effectively reduce interface impedance, suppress silicon particle pulverization and repeated SEI film rupture, and improve the cycle life and rate performance of batteries in a wide temperature range environment. They are suitable for energy storage systems with comprehensive requirements for energy density, safety and low temperature adaptability, and are especially suitable for high-reliability energy storage application scenarios.

[0073] Furthermore, the gradient silicon content silicon-carbon composite anode prepared in this application not only maintains high specific capacity but also achieves excellent long-cycle performance, making it more suitable for the needs of long-term energy storage systems. According to the test results of the examples, the material can still maintain a high capacity retention rate after 500 cycles in a half-cell and can achieve a good capacity retention rate of 200 cycles in a full cell. It can support the operation of large-scale energy storage power stations with a capacity of 4 hours (4h) and 8 hours (8h), meeting the requirements of high-capacity batteries for application scenarios such as grid peak shaving and smooth output of renewable energy.

[0074] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0075] Example 1

[0076] According to such Figure 1 The preparation method of the silicon-carbon composite anode material in the battery cell preparation method shown is as follows:

[0077] Preparation of porous carbon matrix: Cleaned and dried coconut shell fragments were placed in a tube furnace and carbonized at 800℃ for 3 hours under a nitrogen atmosphere with a heating rate of 5℃ / min. The carbonized product was cooled, pulverized, and sieved through a 200-mesh sieve to obtain carbonized coconut shell powder. The carbonized coconut shell powder was ground with activator KOH at a mass ratio of 1:3, placed in a nickel crucible, and chemically activated at 800℃ for 2 hours under a nitrogen atmosphere with a heating rate of 5℃ / min. After cooling, the activated product was washed sequentially with 1 mol / L hydrochloric acid solution and deionized water until the filtrate was neutral. It was then vacuum dried at 120℃ for 12 hours to obtain a porous carbon matrix with a connected hierarchical pore structure. The specific surface area of ​​the porous carbon matrix was 1000 m². 2 / g, total pore volume is 1cm³ 3 / g; The volume ratio of micropores (pore size < 2nm), mesopores (pore size 2~50nm) and macropores (pore size > 50nm) in the porous carbon matrix is ​​20:60:20.

[0078] Preparation of silicon-carbon composite anode materials: Spatial regions are divided with the geometric center of the porous carbon matrix as the origin and a radial distance of radius R (5000 nm), such as... Figure 2As shown, the region from the outer surface of the porous carbon matrix to depth αR is defined as outer region 1, the region from depth αR to depth βR is defined as middle region 2, and the region from depth βR to the geometric center of the porous carbon matrix is ​​defined as inner region 3; where α is 0.1 and β is 0.4. Porous carbon matrix powder is uniformly spread in a quartz boat to a thickness of 5 mm and placed in the isothermal zone of a tubular reactor. First stage CVI deposition: The reaction chamber is heated to 480℃ under an argon atmosphere while simultaneously being evacuated to 5 kPa. Chemical vapor infiltration (CVI) is performed using a pulsed gas supply mode. During the gas supply phase, a silane-argon mixture (with a first silicon source silane volume concentration of 2 vol%) is introduced into the reaction chamber at a flow rate of 200 mL / min for 10 min. During the diffusion phase, the gas supply is stopped and evacuation is continued to maintain a low-pressure state for 10 min. This pulsed cycle is repeated 20 times, with a total deposition time of 3 h, depositing silicon in the inner region of the porous carbon matrix to obtain an intermediate. Second-stage CVD deposition: After the first stage, without removing the intermediate, the temperature of the reaction chamber was raised to 600℃, and the chamber pressure was restored to atmospheric pressure (101 kPa). A silane-argon mixture (the volume concentration of the second silicon source silane was 10 vol%) was introduced at a flow rate of 500 mL / min, and chemical vapor deposition was continuously performed for 2 hours, depositing silicon in the outer layer region, resulting in a CVD product with a total silicon mass content of 30%. The silicon mass content in the outer layer region was 15%, in the middle layer region it was 30%, and in the inner layer region it was 50%. According to the three-layer division corresponding to α and β, the volume percentages of the outer, middle, and inner layers were 27.1%, 51.3%, and 21.6%, respectively. The weighted silicon content calculated based on the regional average silicon content was basically consistent with the total silicon content measured by ICP-OES. The silicon content in each region mentioned above is the local mass content of the corresponding region, and the total silicon mass content is the mass percentage based on the overall mass of the silicon-carbon composite anode material. After the second stage of CVD deposition is completed, the reaction temperature is adjusted to 800℃, and an acetylene-argon mixture (acetylene volume concentration of 10 vol%) is introduced. After deposition for 30 min, an amorphous carbon layer with a thickness of 5 nm is formed on the outer surface of the product after chemical vapor deposition, thus obtaining silicon-carbon composite anode material.

[0079] Example 2

[0080] The difference from Example 1 lies in the preparation of the silicon-carbon composite anode material: the spatial region is divided with the geometric center of the porous carbon matrix as the origin and a radial distance of radius R (5000 nm). The region from the outer surface of the porous carbon matrix to depth αR is defined as the outer layer region, and the region from depth βR to the geometric center of the porous carbon matrix is ​​defined as the inner layer region; where α is 0.10 and β is 0.40. The porous carbon matrix powder is uniformly spread in a quartz boat with a spreading thickness of 5 mm and placed in the isothermal zone of a tubular reactor. First stage CVI deposition: the reaction chamber is heated to 400°C under an argon atmosphere while being evacuated to 50 kPa. Chemical vapor infiltration is performed using a pulsed gas supply mode. During the gas supply stage, a silane-argon mixture (the volume concentration of the first silicon source silane is 5 vol%) is introduced into the reaction chamber at a flow rate of 500 mL / min for 1 min. During the diffusion stage, the gas supply is stopped and the vacuum is maintained at a low pressure for 30 min. The above pulse cycle was repeated 50 times, with a total deposition time of 3 hours, depositing silicon in the inner layer region of the porous carbon matrix to obtain an intermediate. Second-stage CVD deposition: After the first stage, without removing the intermediate, the temperature of the reaction chamber was raised to 600℃, and the chamber pressure was restored to atmospheric pressure (101 kPa). A silane-argon mixture (with a volume concentration of 10 vol% for the second silicon source silane) was introduced at a flow rate of 500 mL / min, and chemical vapor deposition was continuously performed for 4 hours, depositing silicon in the outer layer region to obtain a silicon-carbon composite anode material with a total silicon mass content of 30%. The silicon mass content in the outer layer region was 8%, and the silicon mass content in the inner layer region was 40%.

[0081] Example 3

[0082] The difference from Example 2 is that α is 0.20, β is 0.45, the mass content of silicon in the outer region is 7%, and the mass content of silicon in the inner region is 42%, ultimately resulting in a silicon-carbon composite material.

[0083] Example 4

[0084] The difference from Example 2 is that α is 0.35, β is 0.60, the mass content of silicon in the outer region is 12%, and the mass content of silicon in the inner region is 36%, ultimately resulting in a silicon-carbon composite material.

[0085] Example 5

[0086] The difference from Example 2 is that the mass content of silicon in the outer region is 5%, the mass content of silicon in the inner region is 50%, and the ratio of the mass content of silicon in the inner region to the mass content of silicon in the outer region is 10:1, thus obtaining a silicon-carbon composite material.

[0087] Example 6

[0088] The difference from Example 2 is that the mass content of silicon in the outer layer region is 15%, the mass content of silicon in the inner layer region is 30%, and the ratio of the mass content of silicon in the inner layer region to the mass content of silicon in the outer layer region is 2:1, thus obtaining a silicon-carbon composite material.

[0089] Example 7

[0090] The difference from Example 1 is that the total mass content of silicon in the silicon-carbon composite material is 40%, and the final product is a silicon-carbon composite material.

[0091] Example 8

[0092] The difference from Example 1 is that the total mass content of silicon in the silicon-carbon composite material is 50%, and the final product is a silicon-carbon composite material.

[0093] Example 9

[0094] The difference from Example 1 is that α is 0.30, β is 0.55, the mass content of silicon in the outer region is 12%, the mass content of silicon in the middle region is 22%, and the mass content of silicon in the inner region is 42%, ultimately yielding a silicon-carbon composite material.

[0095] Example 10

[0096] The difference from Example 1 is that α is 0.30, β is 0.55, the mass content of silicon in the outer region is 6%, the mass content of silicon in the middle region is 17%, and the mass content of silicon in the inner region is 42%, ultimately yielding a silicon-carbon composite material.

[0097] Example 11

[0098] The difference from Example 2 is that the chemical vapor infiltration pressure is 0.1 kPa, and a silicon-carbon composite material is finally obtained.

[0099] Example 12

[0100] The difference from Example 2 is that the chemical vapor infiltration pressure is 55 kPa, and a silicon-carbon composite material is finally obtained.

[0101] Example 13

[0102] The difference from Example 2 is that the temperature of chemical vapor infiltration is 600°C, and a silicon-carbon composite material is finally obtained.

[0103] Example 14

[0104] The difference from Example 2 is that the temperature of chemical vapor infiltration is 650°C, and a silicon-carbon composite material is finally obtained.

[0105] Example 15

[0106] The difference from Example 1 is that the volume concentration of the second silicon source is 20 vol%, the deposition time of chemical vapor deposition is 0.5 h, and a silicon-carbon composite material is finally obtained.

[0107] Example 16

[0108] The difference from Example 1 is that the volume concentration of the second silicon source is 25 vol%, the chemical vapor deposition time is 5 h, and a silicon-carbon composite material is finally obtained.

[0109] Example 17

[0110] The difference from Example 2 lies in the preparation of the porous carbon matrix: Cleaned and dried bamboo fragments were placed in a tube furnace and heated to 600°C at a rate of 5°C / min under a nitrogen atmosphere, and held at this temperature for 6 hours for carbonization. After cooling, the carbonized product was pulverized and passed through a 200-mesh sieve to obtain carbonized bamboo powder. The carbonized bamboo powder was ground with activator KOH at a mass ratio of 1:3, placed in a nickel crucible, and chemically activated at 600°C at a rate of 5°C / min under nitrogen protection for 4 hours. After cooling, the activated product was washed sequentially with 1 mol / L hydrochloric acid solution and deionized water until the filtrate was neutral, and then vacuum dried at 120°C for 12 hours to obtain a porous carbon matrix with a connected hierarchical pore structure. The specific surface area of ​​the porous carbon matrix was 1500 m². 2 / g, total pore volume is 1.5cm³ 3 / g; The volume ratio of micropores (pore size < 2nm), mesopores (pore size 2~50nm) and macropores (pore size > 50nm) in the porous carbon matrix is ​​10:80:10, and the final silicon-carbon composite material is obtained.

[0111] Example 18

[0112] The difference from Example 2 lies in the preparation of the porous carbon matrix: Washed and dried rice husk fragments were placed in a tube furnace and heated to 600°C at a rate of 5°C / min under a nitrogen protective atmosphere, and held at this temperature for 6 hours for carbonization. After cooling, the carbonized product was pulverized and passed through a 200-mesh sieve to obtain carbonized rice husk powder. This carbonized rice husk powder was then physically activated at 600°C for 5 hours to obtain a porous carbon matrix with an interconnected hierarchical pore structure. The specific surface area of ​​the porous carbon matrix was 10 m². 2 / g, total pore volume is 0.2cm³ 3 / g; the volume ratio of micropores (pore size < 2nm), mesopores (pore size 2~50nm) and macropores (pore size > 50nm) in the porous carbon matrix is ​​50:10:40, and the final silicon-carbon composite material is obtained.

[0113] Example 19

[0114] The difference from Example 1 is that the thickness of the carbon layer is 20 nm, resulting in a silicon-carbon composite material.

[0115] Example 20

[0116] The difference from Example 1 is that the thickness of the carbon layer is 25 nm, resulting in a silicon-carbon composite material.

[0117] Example 21

[0118] The difference from Example 1 is that the carbonization product is not chemically activated, the porous carbon matrix does not have a connected hierarchical pore structure, and a silicon-carbon composite material is finally obtained.

[0119] Example 22

[0120] The difference from Example 1 is that a continuous gas supply mode is used for chemical vapor infiltration, and the pressure of chemical vapor infiltration is 55 kPa, ultimately yielding a silicon-carbon composite material.

[0121] Comparative Example 1

[0122] The difference from Example 1 is that the porous carbon matrix is ​​placed directly in the reaction chamber, the temperature of the reaction chamber is raised to 650°C, the chamber pressure is kept at atmospheric pressure (101 kPa), a silane-argon mixture is introduced (the volume concentration of the second silicon source silane is 10 vol%), and chemical vapor deposition is continuously performed for 5 hours to obtain a chemical vapor deposition product with a high silicon content on the outside and a low silicon content on the inside, and a total silicon mass content of 30%, and finally obtains a silicon-carbon composite anode material.

[0123] Comparative Example 2

[0124] The difference from Example 2 is that chemical vapor deposition is not performed, and a silicon-carbon composite anode material with a total silicon mass content of 18% is finally obtained.

[0125] Comparative Example 3

[0126] The difference from Example 1 is that chemical vapor deposition is performed first, followed by chemical vapor infiltration, to finally obtain a silicon-carbon composite anode material.

[0127] Comparative Example 4

[0128] The difference from Comparative Example 1 is that there is no carbon layer, resulting in a silicon-carbon composite anode material.

[0129] Test method:

[0130] Total silicon content testing in silicon-carbon composite anode materials: The total silicon content of each sample was determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The silicon-carbon composite material was digested with acid, and the silicon element concentration in the solution was measured to calculate the mass percentage of silicon in the material.

[0131] Silicon content testing in the outer, middle, and inner layers: Cross-sectional samples of silicon-carbon composite particles were prepared (ion polishing or mechanical grinding after epoxy resin embedding). Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) was used to determine the silicon content in each radial region. The radial position was determined based on the geometric center and outer edge of the particle cross-section. Analysis areas were divided into outer, middle (for three-layer structures), and inner layers. EDS quantitative analysis was performed at corresponding positions on multiple particles within each region, and the average value of multiple particles was taken as the silicon content of that region.

[0132] Characterization of porous carbon matrix by BET and pore structure: The specific surface area, total pore volume, and pore size distribution of porous carbon matrix (before silicon deposition) were determined using N2 adsorption-desorption methods (BET and BJH methods). Samples were degassed under vacuum at 300℃ for 6 h before testing. Specific surface area, total pore volume, and the proportion of mesopore volume to total pore volume were recorded.

[0133] Half-cell testing was conducted using CR2032 coin cells. The negative electrode was prepared as follows: The silicon-carbon composite negative electrode material, Super P conductive agent, CNT conductive agent, and PAA binder were mixed in a mass ratio of 85:3:2:10, using deionized water as a solvent, and stirred in a planetary ball mill to obtain a uniform negative electrode slurry. The slurry was coated onto a copper foil current collector, vacuum dried at 80°C for 12 hours, and then rolled and punched into circular electrode sheets with a diameter of 12 mm. The areal density of the active material in the electrode sheet was 2.0 mg / cm³. 2 The coin cell assembly was completed in an argon-atmospheric glove box. A silicon-carbon composite negative electrode was used as the working electrode, lithium metal foil as the counter and reference electrodes, and a ceramic-coated PE separator as the separator. An electrolyte was injected, consisting of EC / DMC / EMC (volume ratio 1:1:1), 1 mol / L LiPF6, and 10 wt% FEC. After assembly, the cells were allowed to stand at 25°C for 12 hours to ensure adequate electrolyte wetting.

[0134] All half-cell performance data are based on the average of three parallel sample tests, with a typical error range of ±3 to ±5%. To avoid confusion regarding the charge and discharge directions in the context of full cells and half-cells, the following descriptions will uniformly use lithium insertion (corresponding to the lithiation process of silicon-carbon anodes, with the potential changing towards 0.01V) and lithium removal (corresponding to the delithiation process of silicon-carbon anodes, with the potential changing towards 1.5V).

[0135] First-week lithium insertion / extraction and coulombic efficiency tests: The CR2032 coin cell was tested for lithium insertion / extraction in its first week at 25°C. Lithium insertion was performed at a constant current rate of 0.1C to 0.01V, followed by constant voltage lithium insertion until the current dropped to 0.01C (cutoff). The first-week lithium insertion specific capacity was recorded. Subsequently, lithium extraction was performed at a constant current rate of 0.1C to 1.5V, and the first-week de-lithiation specific capacity was recorded. The first-week coulombic efficiency (ICE) (%) = (first-week de-lithiation capacity / first-week lithium insertion capacity) × 100%. The first-week coulombic efficiency is a key indicator for evaluating the degree of interfacial side reactions and irreversible lithium loss in silicon-carbon anode materials. A higher value indicates that less active lithium is consumed during the formation of the SEI film on the material surface.

[0136] 25℃ Cyclic Stability Test: A constant current lithium insertion / extraction cycle test was conducted at 25℃ with a 1C rate. Lithium insertion was performed to 0.01V (constant voltage to 0.01C cutoff), and lithium extraction was performed to 1.5V. The lithium extraction capacity was recorded on the 200th cycle, and the capacity retention rate (%) was calculated as (lithium extraction capacity on the 200th cycle / lithium extraction capacity on the 1st cycle) × 100%. Some samples were tested up to 500 cycles.

[0137] 25℃ Rate Performance Testing: At 25℃, lithium was first inserted at a constant current and voltage of 0.5C to 0.01V (0.05C cutoff), then delithiated at 0.2C, 0.5C, 1C, and 2C to 1.5V, respectively, for 5 cycles at each rate. The capacity retention rate of 2C / 0.2C delithiation was calculated using the 0.2C delithiation capacity as a baseline (100%). Rate performance is used to verify whether the gradient structure sacrifices ion transport kinetics while maintaining cycle stability.

[0138] 45℃ High-Temperature Cycling Test: Under 45℃ conditions, using the same lithium insertion / extraction regime (1C rate) as the 25℃ cycling test, the delithiation capacity was recorded after the 200th cycle, and the capacity retention was calculated. High-temperature conditions accelerate electrolyte decomposition and SEI film side reactions, effectively amplifying the differences in interface stability caused by variations in outer silicon content.

[0139] Electrochemical Impedance Spectroscopy (EIS) Testing: At 25°C, the coin cells were adjusted to a 50% state of charge (SOC) defined by the reversible capacity after the first formation cycle. Electrochemical impedance spectroscopy (EIS) testing was performed at frequencies ranging from 100 kHz to 0.01 Hz and AC amplitudes of 10 mV. Tests were performed once after the first formation cycle and again after 100 cycles, and the charge transfer resistance Rct (in ohms) was recorded. The change in Rct before and after cycling reflects the rate of increase in interfacial impedance and is an indirect indicator for evaluating the stability of the SEI film.

[0140] 60℃ Storage Stability Test: At 25℃, the coin cell was first lithium-intercalated to 0.01V at 0.1C (constant voltage to 0.01C cutoff), then delithiated to 1.5V at 1C, and the delithiated capacity was recorded as the initial capacity C1. Subsequently, lithium-intercalation was performed again under the same conditions to 0.01V, and the battery was transferred to a 60℃ constant temperature chamber for storage for 30 days. After storage, the battery was allowed to return to room temperature for at least 2 hours, then delithiated to 1.5V at 1C, and the delithiated capacity was recorded as C2. The capacity retention rate after storage (%) was calculated as (C2 / C1) × 100%.

[0141] Full cell 25℃ cycle test: A 3-5Ah NCM622 / silicon-carbon-graphite composite negative electrode stacked soft-pack battery was used. The positive electrode slurry formulation consisted of active material NCM622 (94wt%), conductive agent Super P (3wt%), and binder PVDF (3wt%). The positive electrode areal density was controlled at 18 mg / cm³. 2 Compacted density 3.2 g / cm³ 3 The negative electrode is a composite negative electrode made of silicon-carbon composite material and artificial graphite mixed at a mass ratio of 15:85. The total content of active material is 92wt%, Super P content is 1wt%, and CMC / SBR composite binder content is 7wt%. After battery assembly, it undergoes standard processes such as vacuum drying, electrolyte injection, static impregnation, formation, and capacity testing. It is charged at 25℃ with a 1C constant current rate to 4.2V (constant voltage to 0.05C cutoff), and discharged at a 1C constant current rate to 2.5V. The discharge capacity on the 200th cycle is recorded, and the capacity retention rate is calculated.

[0142] The results are shown in Tables 1 and 2.

[0143] Table 1

[0144]

[0145] Table 2

[0146]

[0147] It should be noted that Comparative Example 2, without the chemical vapor deposition step, only underwent a chemical vapor infiltration stage to deposit a silicon-carbon composite anode material with a total silicon content of approximately 18%, which is significantly lower than the other examples and comparative examples (approximately 30%). Although Comparative Example 2 has a higher first-week coulombic efficiency, this is due to the reduction of SEI side reaction pathways under low silicon content, which is different from the interface stability improvement mechanism achieved by the gradient structure sample of this application through "low outside and high inside" partitioning. Therefore, the first-week coulombic efficiency index of Comparative Example 2 is not directly compared with the gradient structure sample with high silicon content.

[0148] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0149] In contrast to traditional silicon-carbon anode materials with uniform silicon distribution, this application's battery cell employs a silicon-carbon anode material with a clearly defined functional partitioning and a "low outer, high inner" silicon content gradient structure. This allows the outer region of the carbon particles to provide structural stability and interface protection, while the inner region provides high-capacity lithium storage. This significantly improves the cycle stability and interface compatibility of the silicon-carbon composite anode material, achieving excellent long-cycle performance while maintaining high specific capacity. This design shift enables silicon-carbon composite materials to adapt to spatially heterogeneous environments at the structural level for the first time, fundamentally altering the trade-off between capacity and stability. This application defines the aforementioned inner and outer regions and controls the silicon mass content in both regions within the specified range, systematically achieving synergistic optimization of structural stability, interface compatibility, and capacity utilization in the silicon-carbon composite anode material. The outer region, acting as an "interface barrier layer" in direct contact with the electrolyte, significantly reduces the volume expansion rate during lithiation / delithiation processes due to its low silicon content. This effectively alleviates surface stress concentration, inhibits particle cracking and pulverization, and the repeated rupture and reconstruction of the SEI film, thereby greatly reducing the irreversible consumption of active lithium and electrolyte, improving the first-cycle coulombic efficiency, and extending battery life. Simultaneously, the inner region, as a "high-capacity energy storage core area," fully releases the ultra-high theoretical specific capacity of silicon under the three-dimensional confinement of the carbon skeleton and the buffer protection of the low-silicon outer region, achieving efficient utilization of the overall material specific capacity. Because the silicon in the inner region is encapsulated within a porous carbon network, its volume expansion is constrained by the elasticity of the surrounding carbon matrix and mechanically shielded by the outer structure, avoiding the severe interfacial side reactions caused by direct exposure to the electrolyte, thus maintaining structural integrity without sacrificing capacity. Therefore, battery cells using the aforementioned silicon-carbon composite material exhibit high energy density and good cycle stability, making them better suited for applications in electric vehicles, portable electronic devices, and large-scale energy storage systems.

[0150] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a battery cell, comprising preparing a negative electrode material and preparing a negative electrode sheet including the negative electrode material, wherein a positive electrode sheet, a separator, and the negative electrode sheet are sequentially stacked and assembled to obtain the battery cell, characterized in that, The negative electrode material includes a silicon-carbon composite negative electrode material, which comprises a porous carbon matrix and silicon deposited within the pores of the porous carbon matrix; the preparation method of the silicon-carbon composite negative electrode material includes: Using the geometric center of the porous carbon matrix as the origin, the spatial regions are divided by radial distances of radius R. The region from the outer surface of the porous carbon matrix to depth αR is defined as the outer layer region, the region from depth βR to the geometric center of the porous carbon matrix is ​​defined as the inner layer region, and the region from depth αR to depth βR is defined as the middle layer region; where α is 0.10~0.35, β is 0.40~0.60, and R is 1000~10000 nm. The raw material comprising the porous carbon matrix and the first silicon source is subjected to chemical vapor infiltration to deposit silicon in the inner layer region of the porous carbon matrix to obtain an intermediate. The raw materials, including the intermediate and the second silicon source, are subjected to chemical vapor deposition to deposit silicon in the outer layer region of the porous carbon matrix, thereby obtaining the silicon-carbon composite anode material. The silicon content in the outer layer region is 5-15% by mass, the silicon content in the inner layer region is 30-50% by mass, and the silicon content in the middle layer region is 15-30% by mass. The silicon content in the middle layer region is 12-20% lower than that in the inner layer region, and the silicon content in the outer layer region is 10-18% lower than that in the middle layer region. The deposition temperature of the chemical vapor infiltration is 400~600℃, and the pressure of the chemical vapor infiltration is 0.1~50kPa; the chemical vapor infiltration is carried out by a pulsed gas supply method, and the pulsed gas supply process includes: gas supply for 1~30min followed by vacuum diffusion for 1~30min, which constitutes one cycle; The deposition temperature of the chemical vapor deposition is 500~700℃, and the pressure of the chemical vapor deposition is 50~200kPa.

2. The method for preparing a single battery cell according to claim 1, characterized in that, The deposition time for the chemical vapor infiltration is 0.5 to 8 hours; the volume concentration of the first silicon source is 0.5 to 5 vol%, and the flow rate of the first silicon source is 50 to 500 mL / min. The pulsed gas supply process includes a total of 5 to 50 cycles.

3. The method for preparing a single battery cell according to claim 1, characterized in that, The deposition time for the chemical vapor deposition is 0.5 to 4 hours; the volume concentration of the second silicon source is 3 to 20 vol%, and the flow rate of the second silicon source is 100 to 1000 mL / min.

4. The method for preparing a battery cell according to any one of claims 1 to 3, characterized in that, The porous carbon matrix is ​​obtained by sequentially carbonizing and activating biomass-based raw materials; wherein the carbonization temperature is 600~1000℃, the carbonization time is 1~6h, and the carbonization atmosphere is an inert gas. The activation treatment is physical activation and / or chemical activation; the physical activation is water vapor activation and / or carbon dioxide activation, the temperature of the physical activation is 700~1000℃, and the time of the physical activation is 0.5~4h; The chemical activation is carried out using an activator selected from any one or more of KOH, NaOH, ZnCl2 and H3PO4. The mass ratio of the activator to the biomass-based raw material is 1~5:

1. The chemical activation temperature is 600~900℃ and the chemical activation time is 1~4h.

5. The method for preparing a battery cell according to any one of claims 1 to 3, characterized in that, The preparation method of the silicon-carbon composite anode material further includes: coating the raw materials including chemical vapor deposition products and carbon sources on the surface, forming a carbon layer on the outer surface of the chemical vapor deposition products, and obtaining the silicon-carbon composite anode material. The carbon source is selected from any one or more of methane, ethylene, acetylene, and propylene; the surface coating method is chemical vapor deposition; the surface coating temperature is 600~900℃; and the surface coating time is 10~120min.

6. A battery cell, comprising a positive electrode, a separator, and a negative electrode, wherein the negative electrode comprises a negative electrode material, characterized in that, The battery cell is prepared by the method for preparing the battery cell according to any one of claims 1 to 5; The negative electrode material includes a silicon-carbon composite negative electrode material, which comprises a porous carbon matrix and silicon deposited within the pores of the porous carbon matrix. Spatial regions are divided with the geometric center of the porous carbon matrix as the origin and a radial distance of radius R. The region from the outer surface of the porous carbon matrix to depth αR is defined as the outer layer region, the region from depth βR to the geometric center of the porous carbon matrix is ​​defined as the inner layer region, and the region from depth αR to depth βR is defined as the middle layer region. Wherein, α is 0.10~0.35, β is 0.40~0.60, and R is 1000~10000 nm. The silicon mass content in the outer layer region is 5~15%, the silicon mass content in the inner layer region is 30~50%, and the silicon mass content in the middle layer region is 15~30%. The silicon content in the middle layer region is 12-20% lower than that in the inner layer region, and the silicon content in the outer layer region is 10-18% lower than that in the middle layer region.

7. The battery cell according to claim 6, characterized in that, The ratio of the mass content of silicon in the inner layer region to the mass content of silicon in the outer layer region is 2.2 to 10:

1.

8. The battery cell according to claim 6, characterized in that, The total mass content of silicon in the silicon-carbon composite anode material is 15-40%.

9. The battery cell according to any one of claims 6 to 8, characterized in that, The porous carbon matrix has an interconnected hierarchical pore structure; the hierarchical pores include at least two types of micropores, mesopores and macropores; wherein the pore size of the micropores is <2nm; the pore size of the mesopores is 2~50nm; and the pore size of the macropores is >50nm.

10. The battery cell according to claim 9, characterized in that, The specific surface area of ​​the porous carbon matrix is ​​200~1500 m². 2 / g, the total pore volume of the porous carbon matrix is ​​0.3~1.5cm³. 3 / g; the volume of the mesopores in the porous carbon matrix accounts for 20-80% of the total pore volume of the porous carbon matrix; And / or, the porous carbon matrix is ​​biomass-derived porous carbon, which is obtained by carbonization and activation of biomass-based raw materials, wherein the biomass-based raw materials are selected from any one or more of coconut shell, bamboo, rice husk, lignin, starch and cellulose.

11. The battery cell according to any one of claims 6 to 8, characterized in that, The outer surface of the silicon-carbon composite anode material is also coated with a carbon layer, the thickness of which is 1~20nm, and the carbon layer is an amorphous carbon layer.

12. A battery device, characterized in that, The battery device includes the battery cell of any one of claims 6 to 8, and the battery device includes any one or more of the following: battery module, battery pack, and energy storage battery.

13. An electrical appliance, characterized in that, The electrical device includes the battery device of claim 12, the battery device being used to provide electrical energy.

14. An energy storage device, characterized in that, The energy storage device includes the battery device of claim 12, the battery device being used to store electrical energy.

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