Near-zero expansion silicon-carbon negative electrode material and preparation method and application thereof

Abstract

The application belongs to the field of battery materials, and discloses a near-zero expansion silicon-carbon negative electrode material and a preparation method and application thereof. The negative electrode material comprises, from inside to outside, an inner composite region, an outer composite region and an encapsulation layer. The inner composite region comprises a first carbon framework and nano silicon particles, and the nano silicon particles are distributed in the mesopores of the first carbon framework. The outer composite region comprises a second carbon framework and nano silicon particles, and the nano silicon particles are distributed in the micropores of the second carbon framework. The encapsulation layer is a functional polymer encapsulation layer, and the encapsulation layer at least coats part of the surface of the particles formed by the outer composite region and the inner composite region. The mesoporous carbon framework of the inner composite region provides a buffer for silicon volume expansion and guarantees ion transmission, the microporous carbon framework of the outer composite region limits silicon deformation, and the encapsulation layer has the functions of isolating electrolyte, anchoring reinforcement and electrical conductivity. The three form a gradient protection, realize near-zero expansion, balance capacity performance, expansion performance and cycle stability, obtain relatively optimal capacity and cycle performance, and have a relatively low expansion rate.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, and relates to a negative electrode material, specifically a near-zero expansion silicon-carbon negative electrode material and its preparation method and application. Background Technology

[0002] With the continuous upgrading of demand for high-energy-density batteries in fields such as new energy vehicles, consumer electronics, and solid-state batteries, silicon-based anode materials, due to their ultra-high theoretical specific capacity of 4200 mAh / g (far exceeding the 372 mAh / g of commercial graphite), have become the core research and development direction for next-generation lithium battery anodes. Currently, silicon-carbon anodes, represented by CVD vapor deposition technology, have achieved commercial applications and are suitable for consumer electronics scenarios such as smartphones and laptops. However, the problem of up to 300% volume expansion of silicon materials during lithiation remains a key bottleneck restricting its large-scale application, resulting in short battery cycle life and rapid capacity decay, failing to meet the stringent stability requirements of high-end applications. To mitigate the volume effect of silicon, existing technologies generally employ silicon-carbon composite structure designs, which are broadly categorized into two types: coated structures and embedded structures. Coated structures achieve protection and buffering by constructing a carbon layer on the surface of silicon particles. These include core-shell structures with no voids, yolk-shell structures with reserved expansion space, and double-shell / multi-shell structures that enhance mechanical properties. Embedded structures, on the other hand, use processes such as chemical vapor deposition (CVD) to load nano-silicon into a three-dimensional porous carbon framework, utilizing the porosity of the carbon matrix to provide buffering space for expansion. A typical example is the "porous carbon framework + CVD silicon deposition + secondary carbon coating" structure. Furthermore, some solutions further optimize interface compatibility and structural stability by introducing a SiO2 interlayer or a fluorine-doped carbon source. The existing structural designs of silicon-carbon composite materials still have fundamental flaws: First, the mechanical properties and buffering capacity of the carbon matrix are mismatched. Traditional carbon materials such as hard carbon and graphite are rigid but lack toughness. The pore walls of porous carbon skeletons are prone to fatigue cracking during repeated expansion and contraction. Although the double-shell structure can enhance support, it cannot completely offset cyclic stress. Second, structural integrity is difficult to maintain in the long term. The dense carbon layer of the core-shell type is prone to direct rupture due to silicon expansion. If the pore design of the yolk-shell type is not precisely matched with the expansion amount, it will still lead to the carbon shell being damaged under pressure, eventually exposing the internal silicon again. This causes repeated rupture and regeneration of the SEI film, continuously consuming active lithium and electrolyte, resulting in rapid capacity decay. These flaws prevent existing solutions from simultaneously meeting the core requirements of high capacity, low expansion, and long cycle life, leading to a performance trade-off dilemma. Summary of the Invention In view of the defects and deficiencies of the existing technology, the present invention provides, firstly, a near-zero expansion silicon-carbon anode material; secondly, a method for preparing the near-zero expansion silicon-carbon anode material; and thirdly, a battery.

[0003] In a first aspect, a near-zero expansion silicon-carbon anode material includes an inner composite region, an outer composite region, and an encapsulation layer. The inner composite region includes a first carbon framework and nano-silicon particles, wherein the nano-silicon particles are distributed within the pores of the first carbon framework, which are mainly mesoporous. The outer composite region covers at least a portion of the surface of the inner composite region. The outer composite region includes a second carbon framework and nano-silicon particles. The nano-silicon particles are distributed within the pores of the second carbon framework, which are mainly micropores. The encapsulation layer is a functional polymer encapsulation layer, and the encapsulation layer covers at least a portion of the surface of the particles formed by the outer composite region and the inner composite region.

[0004] Preferably, the silicon content in the near-zero expansion silicon-carbon anode material is 40wt%~60wt%, and the specific surface area is 0.1~10m². 2 / g, with a particle size of 2~30μm and a powder resistivity of 5~100Ω·cm.

[0005] Preferably, the particle size D50 of the first carbon skeleton is 2~30μm; the thickness of the outer composite region is 20~100nm; and the thickness of the encapsulation layer is 5~50nm.

[0006] Preferably, the specific surface area of ​​the first carbon skeleton and the specific surface area of ​​the second carbon skeleton satisfy the following condition: 0.22 ≤ specific surface area of ​​the first carbon skeleton / specific surface area of ​​the second carbon skeleton ≤ 0.70.

[0007] Preferably, the specific surface area of ​​the first carbon skeleton is 400~700 m². 2 / g, the pore volume of the first carbon framework is 1.0~2.0cm³. 3 / g, the average pore size of the first carbon skeleton is 2~50nm, and the proportion of mesopores with a pore size of 2~50nm to the total pore volume of the first carbon skeleton is ≥65%.

[0008] Preferably, the specific surface area of ​​the second carbon skeleton is 1000~1800 m². 2 / g, the pore volume of the second carbon framework is 0.4~1.2cm³. 3 / g, the micropore size of the second carbon skeleton is 0.1~2nm, and the proportion of micropores with a pore size of 0.1~2nm to the total pore volume of the second carbon skeleton is ≥75%.

[0009] Preferably, the silicon content of the inner composite region is 35% to 60%, and the silicon content of the outer composite region is 0.5% to 5%.

[0010] Preferably, the particle size of the silicon nanoparticles in the inner composite region is 1~30nm, and the silicon nanoparticles in the outer composite region are any one or both of highly dispersed island-shaped and cluster-shaped, and the size of the silicon nanoparticles in the outer composite region is 1~10nm.

[0011] Preferably, the density of the encapsulation layer gradually decreases from the inside to the outside; the side of the encapsulation layer closer to the outer composite region is the inner side of the encapsulation, and the side of the encapsulation layer farther from the outer composite region is the outer side of the encapsulation, with the conductivity of the inner side of the encapsulation being higher than that of the outer side of the encapsulation.

[0012] Preferably, the outer side of the package is flexible; the outer side of the package has a porous morphology.

[0013] Preferably, the encapsulation layer also contains carbon material, which is any one or more of carbon nanotubes, graphene, and carbon nanofibers.

[0014] Secondly, the present invention provides a method for preparing a near-zero expansion silicon-carbon anode material, comprising the following steps: Step 1, Preparation of the first carbon framework: The first carbon precursor particles are carbonized and heat-treated under a protective atmosphere, and then activated to obtain the first carbon framework. Step 2, Preparation of bilayer carbon porous particles: The second carbon precursor material is coated on the surface of the first carbon skeleton, carbonized and heat-treated under a protective atmosphere, and then activated to form bilayer carbon porous particles with hierarchical pore structure. Step 3, Chemical vapor deposition silicon infiltration: Place the double carbon layer porous particles in a reactor, introduce silicon source gas to perform silicon infiltration treatment, and obtain silicon carbon particles. Step 4, Construction of the functional polymer encapsulation layer: Silicon carbon particles are dispersed in a dopamine hydrochloride-tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution and subjected to staged temperature-controlled polymerization. After the polymerization reaction is completed, the particles are filtered, washed and dried sequentially to obtain a near-zero expansion silicon carbon anode material. The phased temperature-controlled polymerization includes the first stage: low-temperature static infiltration; and the second stage: heating and continuous introduction of oxygen-containing gas for bubbling reaction.

[0015] Preferably, in step 1, the first carbon precursor is any one or more of phenolic resin, sucrose, and cellulose.

[0016] Preferably, in step 2, the second carbon precursor is any one or more of mesophase pitch, petroleum pitch, and polyamic acid.

[0017] Preferably, in step 2, the specific operation of coating the surface of the first carbon skeleton with the second carbon precursor material is as follows: dissolve the second carbon precursor in an organic solvent to obtain solution A, then add the first carbon skeleton to solution A and stir to disperse, then dry to remove the organic solvent, ball mill to disperse, and complete the coating.

[0018] Preferably, in step 2, the measurement is based on the raw materials, and the mass ratio of the first carbon precursor to the second carbon precursor is 1: (0.05~0.3).

[0019] Preferably, in step 2, the particle size of the first carbon precursor is 3~35μm.

[0020] Preferably, in steps 1 and 2, the temperature of the carbonization heat treatment is 800~1200℃, and the time of the carbonization heat treatment is 1~5h.

[0021] Preferably, in steps 1 and 2, during the activation treatment, the activation atmosphere is a water-containing oxidizing atmosphere, wherein the volume concentration of water vapor is 5 vol% to 40 vol.

[0022] Preferably, in steps 1 and 2, the activation temperature is 750~950℃ and the activation time is 0.5~4h.

[0023] Preferably, in step 3, the silicon source gas is any one or more of silane, chlorosilane, and organosiloxane.

[0024] Preferably, in step 3, the silicon content in the near-zero expansion silicon-carbon anode material is controlled by controlling the flow rate of the silicon source gas and the silicon infiltration time.

[0025] Preferably, in step 4, the concentration of dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloride buffer is 0.5~5.0 mg / mL; wherein the pH value of tris(hydroxymethyl)aminomethane-hydrochloride buffer is 8.0~9.0.

[0026] Preferably, in step 4, the first stage involves static infiltration at 5~15℃ for 0.5~2 hours.

[0027] Preferably, in step 4, the second stage involves introducing air or oxygen at 25-35°C for bubbling and stirring reaction for 2-10 hours; the aeration rate is 0.5-2 L / min.

[0028] Preferably, in step 4, the drying temperature is 60~100℃ and the time is 6-24h.

[0029] Preferably, in step 4, an additive is added during the construction of the polydopamine encapsulation layer. The additive is any one or more of carbon nanotubes, graphene, and carbon nanofibers; the mass ratio of silicon carbon particles to additives is 1: (0.01~0.1).

[0030] Thirdly, the present invention provides a battery comprising the near-zero expansion silicon-carbon anode material described in the first aspect or the near-zero expansion silicon-carbon anode material prepared by the preparation method provided in the second aspect.

[0031] Compared with the prior art, one or more technical solutions provided by the present invention have at least one of the following beneficial effects: (1) The mesoporous carbon skeleton in the inner composite region of the negative electrode material provided by the present invention provides a buffer for silicon volume expansion and ensures ion transport. The microporous carbon skeleton in the outer composite region further restricts silicon deformation. The encapsulation layer has the functions of isolating electrolyte, anchoring and strengthening and conducting electricity. The three form a gradient protection to achieve near-zero expansion and balance capacity performance, expansion performance and cycle stability. When applied to batteries, it can obtain better capacity and cycle performance and lower electrode expansion rate.

[0032] (2) The high conductivity inside the package creates an efficient electronic pathway, while the low conductivity on the outside prevents excessive electrolyte penetration. Combined with the flexible porous morphology and internal and external density gradient, it balances electron transport efficiency, side reaction suppression and structural stability, reduces polarization and extends service life.

[0033] (3) First, carbonization and activation are used to prepare bilayer carbon particles with mesoporous and microporous hierarchical structure. Silicon is then uniformly dispersed by chemical vapor deposition and silicon infiltration. Finally, a functional polymer encapsulation layer is constructed by staged temperature-controlled polymerization. The process is mild and controllable, forming a multi-level conductive and elastic constraint structure, which has both performance advantages and industrialization potential. Attached Figure Description

[0034] Figure 1 The charge-discharge curves of the battery composed of the negative electrode material prepared in Example 1 are shown. Figure 2 The image shows the cycle curve of the battery composed of the negative electrode material prepared in Example 1. Detailed Implementation

[0035] The present invention provides the following specific technical solutions.

[0036] In a first aspect, a near-zero expansion silicon-carbon anode material includes an inner composite region, an outer composite region, and an encapsulation layer. The inner composite region includes a first carbon framework and nano-silicon particles, wherein the nano-silicon particles are distributed within the pores of the first carbon framework, which are mainly mesoporous. The outer composite region covers at least a portion of the surface of the inner composite region. The outer composite region includes a second carbon framework and nano-silicon particles. The nano-silicon particles are distributed within the pores of the second carbon framework, which are mainly micropores. The encapsulation layer is a functional polymer encapsulation layer, and the encapsulation layer covers at least a portion of the surface of the particles formed by the outer composite region and the inner composite region; The encapsulation layer is a functional polymer encapsulation layer, which covers at least part of the surface of the particles formed by the outer composite region and the inner composite region, and the encapsulation layer penetrates into the pore structure of the outer composite region to form an anchoring structure.

[0037] Research has revealed that this near-zero expansion silicon-carbon anode material employs a gradient multi-level structural design consisting of an inner composite region, an outer composite region, and a conductive polymer encapsulation layer. Utilizing gradient pore size distribution, differentiated silicon load, interface anchoring, and synergistic confinement mechanisms, it achieves a balance between high capacity and near-zero expansion. From the inside out, the material forms a gradient synergistic system of mesopore buffer expansion, precise micropore confinement, and surface encapsulation anchoring. The inner layer is responsible for capacity release and volume buffering, the middle layer for structural reinforcement and expansion suppression, and the outer layer for conductivity stability and interface protection. These three layers work together to maximize the high capacity characteristics of silicon while fundamentally suppressing volume expansion, pulverization failure, and conductivity degradation, ultimately achieving near-zero expansion. Simultaneously, it improves lithium-ion transport efficiency, electronic conductivity, structural integrity, and long-term cycle stability, giving the material excellent comprehensive electrochemical performance and application potential in high-energy-density power battery systems.

[0038] In actual production, the morphology of the inner composite zone is any one or two of the following: spherical, near-spherical, and blocky.

[0039] Preferably, the silicon content in the near-zero expansion silicon-carbon anode material is 40wt%~60wt%, and the specific surface area of ​​the near-zero expansion silicon-carbon anode material is 0.1~10m². 2 / g, the particle size of the near-zero expansion silicon-carbon anode material is 2~30μm, and the powder resistivity of the near-zero expansion silicon-carbon anode material is 5~100Ω·cm.

[0040] Research has shown that a silicon content of 40wt%~60wt% in the anode material ensures high reversible capacity and fully leverages the high energy density of silicon while avoiding uncontrolled volume expansion due to excessive silicon content, thus balancing capacity and structural stability. Controlling the specific surface area effectively reduces side reactions at the electrolyte-material interface, lowers initial irreversible capacity loss, inhibits excessive formation of unstable SEI films, and ensures compact particle structure. Controlling particle size balances electrode processing performance and ion transport efficiency, avoiding both uneven dispersion and increased expansion caused by excessive fine powder, and excessive large particles that lead to excessively long lithium-ion diffusion paths and reduced rate performance. The anode material provided by this invention has a powder resistivity in the range of 5~100Ω·cm, enabling efficient electron conduction, ensuring stable electrical contact during charging and discharging, reducing electrode polarization, improving rate performance and cycle stability, while avoiding energy density reduction due to excessive space occupied by conductive agents.

[0041] Preferably, the particle size D50 of the inner composite region is 2~30μm; the thickness of the outer composite region is 20~100nm; and the thickness of the encapsulation layer is 5~50nm.

[0042] Research has shown that controlling the particle size D50 of the inner composite region to 2-30 μm ensures that the material has suitable particle size and tap density; the thickness of the outer composite region is 20-100 nm, which can effectively confine the internal silicon-based region while maintaining appropriate structural flexibility and ion transport channels; the thickness of the encapsulation layer is 5-50 nm, which can stabilize the electrode interface, suppress electrolyte side reactions and excessive SEI film growth through a thin and dense coating layer, and the anchoring structure formed between the encapsulation layer and the outer composite region can strengthen the bonding strength between the encapsulation layer and the outer composite region, build a continuous and efficient conductive network, improve electron conduction efficiency, and further constrain volume deformation, ultimately achieving a unity of near-zero expansion, high cycle stability and excellent rate performance.

[0043] Preferably, the specific surface area of ​​the first carbon skeleton and the specific surface area of ​​the second carbon skeleton satisfy the following condition: 0.22 ≤ specific surface area of ​​the first carbon skeleton / specific surface area of ​​the second carbon skeleton ≤ 0.70.

[0044] Preferably, the specific surface area of ​​the first carbon skeleton is 400~700 m². 2 / g, pore volume 1.0~2.0cm³ 3 / g, with mesopores having a pore size of 2~50nm, and the proportion of mesopores with a pore size of 2~50nm to the total pore volume of the first carbon framework being ≥65%.

[0045] Research has shown that the aforementioned optimized parameters provide sufficient and uniformly distributed silicon deposition sites, enabling highly dispersed nano-silicon within the framework and preventing agglomeration. Simultaneously, the ample mesoporous space provides an efficient buffer for the volume expansion of silicon during lithium insertion / extraction, significantly reducing structural stress and the risk of pulverization. A high proportion of mesoporous structures facilitates rapid lithium-ion transport and uniform silicon source gas permeation, improving rate performance and silicon loading uniformity. Appropriate specific surface area and pore volume ensure sufficient active sites while avoiding problems such as electrolyte side reactions and decreased initial coulombic efficiency caused by excessively high specific surface area. This allows the internal composite region to achieve high silicon loading and high specific capacity while also possessing excellent structural stability and electrochemical kinetic performance.

[0046] Preferably, the specific surface area of ​​the second carbon skeleton is 1000~1800 m². 2 / g, the pore volume of the second carbon framework is 0.4~1.2cm³. 3 / g, the micropore size of the second carbon skeleton is <2nm, and the proportion of micropores with a pore size <2nm to the total pore volume of the second carbon skeleton is ≥75%.

[0047] Research has shown that the high proportion of micropores in the outer composite region can effectively confine the volume expansion of silicon, constrain expansion deformation, reduce the overall electrode expansion rate, and enhance structural rigidity and stability. The moderate pore volume ensures rapid ion transport without reducing the material's tap density due to excessive pore size. It can also form a gradient pore structure with the inner mesoporous carbon, and together with the subsequent conductive polymer encapsulation, form an anchoring structure, further improving interfacial bonding and electronic conductivity. Ultimately, it suppresses expansion, stabilizes the structure, and improves cycle life while balancing rate performance and energy density.

[0048] Preferably, the silicon content of the inner composite region is 35% to 60%, and the silicon content of the outer composite region is 0.5% to 5%.

[0049] Research has shown that forming a gradient distribution structure with high silicon content in the inner layer and low silicon content in the outer layer allows the high capacity characteristics of silicon to be fully utilized, ensuring the overall high energy density of the material. At the same time, the mesoporous carbon framework provides sufficient buffer space for the volume expansion of silicon. The extremely low silicon content in the outer layer significantly reduces the volume deformation of the outer region, avoiding excessive expansion of the outer layer that could lead to structural cracking, pulverization, and interface instability.

[0050] Preferably, the particle size of the silicon nanoparticles in the inner composite region is 1~30nm, and the silicon nanoparticles in the outer composite region are any one or both of highly dispersed island-shaped and cluster-shaped, and the size of the silicon nanoparticles in the outer composite region is less than 10nm.

[0051] Preferably, the density of the encapsulation layer gradually decreases from the inside to the outside; the side of the encapsulation layer closer to the outer composite region is the inner side of the encapsulation, and the side of the encapsulation layer farther from the outer composite region is the outer side of the encapsulation, with the conductivity of the inner side of the encapsulation being higher than that of the outer side of the encapsulation.

[0052] Research has revealed that the inner side of the package exhibits higher conductivity, enabling rapid electron extraction from silicon particles during charging and discharging. This significantly reduces interfacial impedance and improves rate performance and charge / discharge efficiency. Simultaneously, the high-density inner structure forms a strong anchoring effect with the pores of the outer composite region, enhancing interlayer bonding and preventing structural delamination and pulverization during cycling. The gradual decrease in density and conductivity from the inside out provides the package layer with superior flexibility and elasticity. This allows for further buffering of internal silicon volume expansion without significantly sacrificing conductivity, preventing the rigid coating from cracking due to excessive stress. Furthermore, the gradient structure optimizes lithium-ion penetration and interfacial mass transfer, stabilizes SEI film formation, and reduces electrolyte side reactions. Ultimately, by improving electron conduction and strengthening structural constraints, it achieves efficient buffering and interfacial protection, further ensuring the material's near-zero expansion characteristics and long-cycle stability.

[0053] Preferably, the outer side of the package is flexible.

[0054] Research has revealed that the flexible outer layer of the package allows for elastic deformation during charging and discharging, adapting to the volume changes of the internal silicon particles. This effectively absorbs and dissipates expansion stress, preventing the rigid coating from cracking and failing due to repeated stress. Simultaneously, the flexible outer layer does not impede lithium-ion transport, complementing the strong mechanical constraints of the dense inner layer. This synergistic protection of an inner rigid and outer flexible structure further reduces electrode expansion and extends cycle life.

[0055] Preferably, the outer side of the package has a porous morphology.

[0056] Research has revealed that the porous morphology on the outer side of the package provides a rapid transport channel for lithium ions, reduces interfacial charge transfer impedance, and is beneficial for improving rate performance. Simultaneously, the porous structure increases the contact area between the package layer and the electrolyte, promoting the formation of a uniform and stable SEI film on the outer side of the package layer, rather than directly contacting the internal silicon, thus protecting the inner silicon active material.

[0057] Preferably, the encapsulation layer also contains carbon material, which is any one or more of carbon nanotubes, graphene, and carbon nanofibers.

[0058] Research has revealed that carbon materials, with their high aspect ratio or two-dimensional layered structure, form a three-dimensional conductive network framework within the encapsulation layer, significantly improving the overall electronic conductivity of the encapsulation layer, reducing interfacial charge transfer impedance, and enhancing the material's rate performance. Simultaneously, the carbon material, PDA, and carbon framework form a strong interfacial bond through π-π conjugation and physical entanglement, strengthening the mechanical strength and structural integrity of the encapsulation layer.

[0059] Secondly, the present invention provides a method for preparing a near-zero expansion silicon-carbon anode material, comprising the following steps: Step 1, Preparation of the first carbon framework: The first carbon precursor particles are carbonized and heat-treated under a protective atmosphere, and then activated to obtain the first carbon framework. Step 2, Preparation of bilayer carbon porous particles: The second carbon precursor material is coated on the surface of the first carbon skeleton, carbonized and heat-treated under a protective atmosphere, and then activated to form bilayer carbon porous particles with hierarchical pore structure. Step 3, Chemical vapor deposition silicon infiltration: The double-carbon porous particles are placed in a reactor and silicon source-argon gas mixture is introduced for silicon infiltration treatment to obtain silicon-carbon particles. Step 4, Construction of the functional polymer encapsulation layer: Silicon carbon particles are dispersed in a dopamine hydrochloride-tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution and subjected to staged temperature-controlled polymerization. After the polymerization reaction is completed, the particles are filtered, washed and dried in sequence to obtain the near-zero expansion silicon carbon anode material. The phased temperature-controlled polymerization includes the first stage: low-temperature static infiltration; and the second stage: heating and continuous introduction of oxygen-containing gas for bubbling reaction.

[0060] Research has revealed that this preparation process first forms primary particles with a double-layer carbon structure through coating and carbonization, and then activates them in an aqueous oxidizing atmosphere to precisely construct a hierarchical porous carbon framework with an inner layer dominated by mesopores and an outer layer dominated by micropores, reserving buffer space for the uniform loading and volume expansion of silicon in the subsequent process. The use of chemical vapor deposition for silicon infiltration allows the silicon source to fully penetrate and generate nano-silicon in situ within the pores, achieving high dispersion, high loading, and resistance to agglomeration of silicon particles. Finally, the swelling and in-situ polymerization of functional polymer solutions not only forms a complete coating layer on the particle surface but also penetrates into the outer pores to form an anchoring structure, improving conductivity and structural stability.

[0061] Using dopamine hydrochloride as a precursor, dopamine monomers undergo oxidative self-polymerization in a weakly alkaline aerobic environment provided by Tris-HCl buffer, generating polydopamine (PDA) in situ on the surface of silicon carbon particles and in the pores of the outer porous carbon layer. Through a low-temperature permeation stage, dopamine monomers infiltrate into the pores of the outer composite zone via capillary action through the micropores and mesopores of the second carbon framework, forming a strongly anchored structure. During subsequent heating polymerization, the high monomer concentration and rapid polymerization on the inner side result in a dense PDA inner layer strongly anchored to the carbon framework, while the low monomer concentration and oxygen diffusion-controlled polymerization on the outer open solution result in a relatively loose and porous PDA outer layer. The resulting gradient encapsulation layer exhibits decreasing density and conductivity from the inside out. The dense inner layer effectively blocks electrolyte penetration and strengthens interfacial bonding, while the flexible porous outer layer promotes lithium-ion transport and provides buffer space, synergistically achieving a balance between interfacial stability, efficient mass transfer, and structural integrity.

[0062] The overall process steps are clear, the conditions are mild, and the parameters are adjustable. It can accurately achieve a near-zero expansion structure with internal high silicon buffer, external low silicon confinement, and surface conductive encapsulation. It effectively suppresses the volume expansion and pulverization of silicon anodes during charging and discharging, while ensuring smooth ion and electron transport. The resulting material has high capacity, long cycle life, and excellent rate performance. Moreover, the process route is easy to scale up and has good potential for industrial application.

[0063] Preferably, in step 1, the first carbon precursor is any one or more of phenolic resin, sucrose, and cellulose.

[0064] Preferably, in step 1, the temperature of the carbonization heat treatment is 800~1200℃, and the time of the carbonization heat treatment is 1~5h.

[0065] Preferably, in step 2, the second carbon precursor is any one or more of mesophase pitch, petroleum pitch, and polyimide.

[0066] Preferably, in step 2, the specific operation of coating the surface of the first carbon skeleton with the second carbon precursor material is as follows: dissolve the second carbon precursor in an organic solvent to obtain solution A, then add the first carbon skeleton to solution A and stir to disperse, then dry to remove the organic solvent, and ball mill to disperse, thus completing the coating.

[0067] In actual production, the organic solvent used in mesophase asphalt is any one or more of quinoline, pyridine, toluene, and xylene; the organic solvent used in petroleum asphalt is any one or more of chloroform, toluene, xylene, benzene, petroleum ether, and ethyl acetate; and the solvent used in polyamic acid is any one or two of N-methylpyrrolidone and N,N-dimethylacetamide.

[0068] In step 2, when the second carbon source precursor is mesophase asphalt or petroleum asphalt, the first carbon precursor particles are dispersed in solution A (the concentration of the second carbon precursor in solution A is 5wt%~20wt%). After stirring and mixing evenly, the mixture is heated to 80~120℃ in air atmosphere to dry and remove the solvent. Then, under a protective atmosphere, the temperature is raised to 300~350℃ at 2~10℃ / min and held for 1~3h. The temperature is then raised to 800~1200℃ and held for 2~4h for carbonization treatment, that is, the second carbon skeleton is coated on the surface of the first carbon skeleton. When the second carbon source precursor is polyimide, polyamic acid (PAA) is dispersed in solution A, a crosslinking agent is added, and the reaction is allowed to stand. After that, the mixture is filtered sequentially, and then dried at 80~120℃ in air to remove the solvent. Subsequently, the temperature is increased to 300~350℃ at 2~10℃ / min under a protective atmosphere and held for 1~3h. Then, the temperature is increased to 800~1200℃ and held for 1~3h for carbonization treatment, that is, the second carbon skeleton is coated on the surface of the first carbon skeleton.

[0069] The crosslinking agent is any one or more of bis(3-(trimethoxysilyl)propyl)amine, p-phenylenediamine, pyromellitic dianhydride, and epichlorohydrin; the molar ratio of the crosslinking agent to the anhydride group in the polyamic acid is (0.1~0.5):1. In actual production, the second carbon precursor is first subjected to thermosetting crosslinking transformation at 300~350℃ to prevent it from melting and flowing at subsequent high temperatures, thus blocking the pores of the first carbon skeleton or destroying the coating layer structure. Then, the temperature is raised to 800~1200℃ for full carbonization, forming a uniform and stable second carbon skeleton coating layer. After subsequent activation treatment, this coating layer can obtain a hierarchical pore structure.

[0070] Preferably, in step 2, the mass ratio of the first carbon precursor to the second carbon precursor in solution A is 1:(0.05~0.3).

[0071] Preferably, in step 2, the particle size of the first carbon precursor is 3~35μm.

[0072] Preferably, in steps 1 and 2, during the activation treatment, the activation atmosphere is a water-containing oxidizing atmosphere, wherein the volume concentration of water vapor is 5 vol% to 40 vol.

[0073] Preferably, in steps 1 and 2, the activation temperature is 750~950℃ and the activation time is 0.5~4h.

[0074] Research has shown that even if the same activation process is used in steps 1 and 2, the carbon matrix formed after carbonization of the first carbon precursor and the second carbon precursor has significant differences in density and etching resistance. The former has a loose structure and is easily etched to form large-diameter mesopores, while the latter has a dense structure and is not easy to expand to form small-diameter micropores. Therefore, it is still possible to stably form a hierarchical pore bilayer carbon material with large inner pores and small outer pores.

[0075] Preferably, in step 3, the silicon source gas is any one or more of silane, chlorosilane, and organosiloxane.

[0076] Preferably, in step 3, the partial pressure of the silicon source in the reaction chamber is 0.5~8 kPa, and the deposition temperature is 450~550℃.

[0077] Further preferably, in step 3, the partial pressure of the silicon source in the reaction chamber is 1~5 kPa; even more preferably, the partial pressure of the silicon source in the reaction chamber is 2~3 kPa.

[0078] Research revealed that silane gas can freely diffuse through micropores into the inner mesopores. Due to the strong capillary condensation effect and long gas residence time, the silicon deposition rate in the inner mesopores is much higher than that in the outer micropores; the outer micropores only contain trace atomic-level adsorption and deposition, without occupying effective pore space. By limiting the silicon source partial pressure and medium-low temperature to further reduce the outer deposition rate and ensure sufficient gas diffusion inward, the micropores remain unobstructed throughout the process, ultimately forming a gradient structure with high silicon content in the inner composite region and low silicon content in the outer composite region.

[0079] In practical applications, the silicon infiltration process parameters provided in step 3 directly determine the total amount of silicon deposited and the distribution of silicon elements within the silicon-carbon composite particles. Ideally, the ratio of silicon packing volume to material pore volume should be controlled within a reasonable range, reserving sufficient mesoporous buffer space to effectively accommodate the volume expansion of silicon during charging and discharging, reducing internal stress within the particles, preventing particle pulverization, and thus balancing high specific capacity with excellent cycle stability. This allows silicon to naturally form a content gradient from the inside out during the CVD process, with the outer micropores fully exerting their confinement effect on near-surface silicon, inhibiting silicon migration and exposure to the particle surface, reducing side reactions with the electrolyte, and improving initial coulombic efficiency and long-term cycle performance.

[0080] Preferably, in step 3, the silicon content in the near-zero expansion silicon-carbon anode material is controlled by controlling the flow rate of the silicon source gas and the silicon infiltration time.

[0081] In existing technologies, the flow rate of the silicon source gas and the silicon infiltration time both affect the silicon content in the anode material. This invention, by synergistically regulating the flow rate of the silicon source gas and the silicon infiltration time, achieves precise and stable control over the overall silicon content of the material, maintaining the silicon loading within the target range, ensuring uniform dispersion of silicon particles in the hierarchical porous carbon framework, and simultaneously balancing high capacity utilization with structural expansion suppression, thereby improving batch consistency and electrochemical performance stability.

[0082] Preferably, in step 4, the construction process of the polydopamine encapsulation layer is as follows: silicon carbon particles are dispersed in a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution containing dopamine hydrochloride, and then allowed to stand at a low temperature of 5~15℃ for 0.5~2h to allow the dopamine monomer solution to fully penetrate and accumulate in the near-surface pores of the outer composite region by utilizing the capillary action of the micropores and micromesoporosis of the second carbon skeleton; then the temperature is raised to 25~35℃ and air or oxygen is continuously introduced and stirred for 2~10h; after the reaction is completed, the mixture is filtered, washed and dried in sequence to obtain the near-zero expansion silicon carbon anode material.

[0083] Research has shown that this staged temperature-controlled polymerization process, combined with a gradient design of first low-temperature static infiltration and then high-temperature bubbling polymerization, can achieve a polydopamine encapsulation layer with decreasing density and conductivity from the inside out, and precise and controllable structure. Static infiltration at a low temperature of 5-15℃ effectively inhibits the spontaneous polymerization of dopamine monomers in the bulk solution, allowing the monomers to fully infiltrate and accumulate in the near-surface pores of the outer composite zone through the capillary action of the micropores and mesopores of the second carbon framework. The absence of stirring avoids disturbance to the particle surface, ensuring the directional enrichment of monomers within a confined space. The temperature is then raised to 25-35°C and air is introduced for bubbling and stirring. The dopamine monomers enriched in the confined space undergo rapid oxidative self-polymerization due to their high concentration and strong reaction driving force, forming a dense PDA inner layer that is strongly anchored to the carbon skeleton. Meanwhile, the open solution region on the outermost side of the particles, due to its lower monomer concentration and the fact that the polymerization reaction is controlled by oxygen diffusion, slowly forms a relatively loose and porous PDA outer layer. The low monomer concentration and the slow reaction due to oxygen diffusion control result in a flexible outer layer with low cross-linking degree and high molecular chain fluidity, thus constructing an encapsulation layer with a density gradient decreasing from the inside to the outside.

[0084] Overall, this phased polymerization method ensures that PDA fully penetrates the pores to form a strong anchoring structure, while also constructing a gradient encapsulation layer with a dense inner layer and a sparse outer layer on the particle surface. The dense inner layer effectively blocks electrolyte penetration and strengthens interfacial bonding, while the flexible porous outer layer promotes lithium-ion transport and provides buffer space. This synergistically suppresses silicon volume expansion and prevents the encapsulation layer from falling off, while optimizing lithium-ion transport and electron conduction, ultimately achieving a balance between near-zero expansion, high cycle stability, and excellent rate performance.

[0085] Preferably, in step 4, the concentration of the dopamine hydrochloride solution is 0.5~5.0 mg / mL.

[0086] Preferably, in step 4, the dopamine hydrochloride solution is specifically a tris(hydroxymethyl)aminomethane-hydrochloride buffer solution for dopamine hydrochloride, wherein the pH value of the tris(hydroxymethyl)aminomethane-hydrochloride buffer solution is 8.0~9.0.

[0087] Preferably, in step 4, an additive is added during the construction of the polydopamine encapsulation layer. The additive is any one or more of carbon nanotubes, graphene, and carbon nanofibers; the mass ratio of silicon carbon particles to additives is 1: (0.01~0.1).

[0088] Preferably, in step 4, the drying temperature is 60~100℃ and the drying time is 6~24h.

[0089] Thirdly, the present invention provides a battery comprising the near-zero expansion silicon-carbon anode material described in the first aspect or the near-zero expansion silicon-carbon anode material prepared by the preparation method provided in the second aspect.

[0090] To make the technical problems, technical solutions and technical advantages of the present invention clearer, a detailed description will be given below with reference to specific examples. However, the scope of protection of the present invention is not limited to the following specific embodiments.

[0091] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0092] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0093] Example 1: A method for preparing a near-zero expansion silicon-carbon anode material includes the following steps: Step 1, Preparation of the first carbon framework: Phenolic resin particles with a D50 of 10 μm were selected as the first carbon precursor. Under a nitrogen protective atmosphere, the temperature was increased to 1000℃ at 5℃ / min and held for 2h for carbonization heat treatment. Subsequently, in a water-containing oxidizing atmosphere with a water vapor volume concentration of 25 vol%, the first carbon framework with mesoporous structure was obtained for 2h. The D50 of the first carbon framework was 9 μm.

[0094] Step 2, Preparation of bilayer carbon porous particles: Mesophase pitch is dissolved in an organic solvent to obtain solution A. The first carbon framework is then added to solution A and stirred to disperse. After uniform mixing, the mixture is dried in air at 80-120°C to remove the solvent. The particles are then ball-milled (300 r / min, 1 h) to coat the second carbon precursor, maintaining a mass ratio of 1:0.1 between the first and second carbon precursors. The coated particles are placed in a nitrogen atmosphere and heated to 300°C at 5°C / min for 2 h. The temperature is then increased to 1000°C and held for 2 h for carbonization. Finally, the particles are placed in a 25 vol% aqueous oxidizing atmosphere and activated at 850°C for 2 h, forming a hierarchical bilayer carbon porous particle with a mesoporous inner layer and a microporous outer layer. The thickness of the outer composite region is 40-50 nm.

[0095] Step 3, Chemical Vapor Deposition for Silicon Infiltration: The above-mentioned double-carbon porous particles are transferred to a CVD reactor and heated to 550°C in an argon atmosphere. Then, a silane-argon mixture is introduced for silicon infiltration. The partial pressure of the silicon source in the reaction chamber is controlled at 6 kPa and the deposition temperature is controlled at 500°C. By adjusting the silicon infiltration time, the total silicon content in the material is controlled at 46 wt%. The difference in pore structure between the inner and outer layers is used to achieve a gradient distribution of silicon, so that the silicon content in the inner composite zone is significantly higher than that in the outer composite zone, thus obtaining silicon-carbon particles.

[0096] Step 4, Construction of the functional polymer encapsulation layer: 1.0 g of the obtained silicon carbon particles were dispersed in 200 mL of a 2.0 mg / mL dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution (pH 8.5). The solution was first allowed to stand at 10 °C for 1 h without stirring. The dopamine monomer solution was fully permeated and enriched in the near-surface pores of the outer composite region by utilizing the capillary action of the micropores and mesopores of the second carbon skeleton. Then, the temperature was raised to 30 °C and air was continuously introduced and stirred for 6 h. After the reaction, the solution was filtered, washed with deionized water, and vacuum dried at 80 °C for 12 h to obtain the near-zero expansion silicon carbon anode material. The encapsulation layer thickness of the near-zero expansion silicon carbon anode material was 10-20 nm.

[0097] Example 2: A method for preparing a near-zero expansion silicon-carbon anode material includes the following steps: Step 1, Preparation of the first carbon framework: Sucrose particles with a D50 of 5 μm were selected as the first carbon precursor. Under a nitrogen protective atmosphere, the temperature was increased to 800℃ at 5℃ / min and held for 1 h for carbonization heat treatment. Subsequently, in a water-containing oxidizing atmosphere with a water vapor volume concentration of 5 vol%, the first carbon framework was activated at 750℃ for 0.5 h to obtain a first carbon framework mainly composed of mesoporous structures with a D50 of 4 μm.

[0098] Step 2, Preparation of bilayer carbon porous particles: Polyimide prepolymer solution (polyamic acid PAA dissolved in N-methylpyrrolidone, concentration 15wt%) was used as the second carbon precursor solution. The first carbon skeleton was added to the polyimide prepolymer solution and stirred and dispersed for 3h (mass ratio of the first carbon skeleton to the anhydride group in polyamic acid was 1:0.05). The crosslinking agent bis(3-(trimethoxysilyl)propyl)amine was added (molar ratio of the crosslinking agent to the anhydride group in polyamic acid was 0.3:1). The crosslinking reaction was completed by standing at room temperature of 25℃ for 6h. Then, the particles were filtered, and the obtained solid particles were dried at 80℃ in air atmosphere to remove organic solvent. They were then dispersed by ball milling (ball milling speed 200r / min, ball milling time 0.5h) to complete the coating of the second carbon precursor. The coated particles were placed in a nitrogen atmosphere and heated to 300℃ at a rate of 5℃ / min and held for 3 hours. Then, the temperature was increased to 800℃ and held for 3 hours for carbonization heat treatment. The particles were then transferred to a water-containing oxidizing atmosphere with a water vapor volume concentration of 5 vol% and activated at 750℃ for 0.5 hours to form a hierarchical pore structure of double carbon layer porous particles with a mesoporous inner layer and a microporous outer layer. The thickness of the outer composite region was about 20~30 nm.

[0099] Step 3, Chemical Vapor Deposition for Silicon Infiltration: The double-carbon porous particles are transferred to a CVD reactor and heated to 450°C in an argon atmosphere. Then, a silane-argon mixture is introduced for silicon infiltration. The partial pressure of the silicon source in the reaction chamber is controlled to be 1 kPa. By adjusting the silicon infiltration time, the total silicon content of the material is controlled to be 40 wt%, and silicon-carbon particles are obtained.

[0100] Step 4, Construction of the functional polymer encapsulation layer: 1.0 g of the obtained silicon carbon particles were dispersed in 500 mL of a 0.5 mg / mL dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution (pH 8.0). The solution was first allowed to stand at 5 °C for 0.5 h without stirring. The dopamine monomer solution was fully permeated and enriched in the near-surface pores of the outer composite region by utilizing the capillary action of the micropores and mesopores of the second carbon skeleton. Then, the temperature was raised to 25 °C and air was continuously introduced and stirred for 2 h. After the reaction, the solution was filtered, washed with deionized water, and vacuum dried at 60 °C for 6 h to obtain the near-zero expansion silicon carbon anode material. The encapsulation layer thickness of the near-zero expansion silicon carbon anode material was 5-10 nm.

[0101] Example 3: A method for preparing a near-zero expansion silicon-carbon anode material includes the following steps: Step 1, Preparation of the first carbon framework: Cellulose particles with a D50 of 30 μm were selected as the first carbon precursor. Under a nitrogen protective atmosphere, the temperature was increased to 1200℃ at 5℃ / min and held for 4h for carbonization heat treatment. Subsequently, in a water-containing oxidizing atmosphere with a water vapor volume concentration of 40 vol%, the first carbon framework with mesoporous structure was obtained for 4h. The D50 of the first carbon framework was 28 μm.

[0102] Step 2, Preparation of bilayer carbon porous particles: Petroleum asphalt was dissolved in an organic solvent to obtain solution A. The first carbon framework was added to solution A and stirred to disperse. After drying at 120℃ to remove the organic solvent, the particles were ball-milled (400 r / min for 2 h) to complete the coating of the second carbon precursor. The mass ratio of the first carbon precursor to the second carbon precursor was 1:0.3. The coated particles were heated to 350℃ at 5℃ / min and held for 1 h under a nitrogen protective atmosphere, and then heated to 1200℃ and held for 1 h for carbonization heat treatment. Then, the particles were placed in an aqueous oxidizing atmosphere with a water vapor volume concentration of 40 vol% and activated at 950℃ for 4 h to form a hierarchical pore structure of bilayer carbon porous particles with a mesoporous inner layer and a microporous outer layer. The thickness of the outer composite region was 80 nm. Step 3, Chemical Vapor Deposition for Silicon Infiltration: The above-mentioned double-carbon porous particles are transferred to a CVD reactor and heated to 550°C in an argon atmosphere. Then, a silane-argon mixture is introduced for silicon infiltration. The partial pressure of the silicon source in the reaction chamber is controlled at 3 kPa. By adjusting the silicon infiltration time, the total silicon content of the material is controlled at 60 wt%. The difference in pore structure between the inner and outer layers is used to achieve a gradient distribution of silicon, so that the silicon content in the inner composite zone is significantly higher than that in the outer composite zone, thus obtaining silicon-carbon particles. Step 4, Construction of the functional polymer encapsulation layer: 1.0 g of the obtained silicon carbon particles were dispersed in 50 mL of a 5.0 mg / mL dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution (pH 9.0). The solution was first allowed to stand at 15 °C for 2 h without stirring. The dopamine monomer solution was fully permeated and enriched in the near-surface pores of the outer composite region by utilizing the capillary action of the micropores and mesopores of the second carbon framework. Subsequently, the temperature was raised to 35 °C and air was continuously introduced and stirred for 10 h. After the reaction, the solution was filtered, washed with deionized water, and vacuum dried at 100 °C for 24 h to obtain the near-zero expansion silicon carbon anode material. The encapsulation layer thickness of the near-zero expansion silicon carbon anode material was 40-50 nm.

[0103] Example 4: A method for preparing a near-zero expansion silicon-carbon anode material differs from Example 1 in that, in step 4, carbon nanotubes are added to the dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution, and 0.05 g of carbon nanotubes are contained in 200 mL of the dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a concentration of 2.0 mg / mL.

[0104] Example 5: A method for preparing a near-zero expansion silicon-carbon anode material differs from Example 1 in that, in step 4, graphene is added to the dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution, and 0.05 g of graphene is contained in 200 mL of the dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a concentration of 2.0 mg / mL.

[0105] Comparative Example 1: A method for preparing a negative electrode material includes the following steps: Step 1, Preparation of the first carbon framework: Phenolic resin particles with a D50 of about 10 μm were selected as the first carbon precursor. Under a nitrogen protective atmosphere, the temperature was increased to 1000℃ at 5℃ / min and held for 2h for carbonization heat treatment. Subsequently, in a water-containing oxidizing atmosphere with a water vapor volume concentration of 25 vol%, the first carbon framework with mesoporous structure was obtained.

[0106] Step 2, Chemical Vapor Deposition for Silicon Infiltration: The first carbon skeleton is transferred to the CVD reactor and heated to 550°C in an argon atmosphere. Then, silane gas is introduced for silicon infiltration. By adjusting the silane flow rate and silicon infiltration time, the total silicon content of the material is controlled to be 46 wt%.

[0107] Step 3, Construction of the functional polymer encapsulation layer: 1.0 g of the obtained silicon carbon particles were dispersed in 200 mL of a 2.0 mg / mL dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution (pH 8.5). The mixture was first allowed to stand at 10 °C for 1 h without stirring, and then the temperature was raised to 30 °C and air was continuously introduced and stirred for 6 h. After the reaction was completed, the mixture was filtered, washed with deionized water, and vacuum dried at 80 °C for 12 h to obtain a silicon carbon anode material with a total thickness of about 10-20 nm of polydopamine encapsulation layer.

[0108] Comparative Example 2: A method for preparing a negative electrode material includes the following steps: Step 1, Preparation of the second carbon framework: Polyimide particles with a D50 of 5 μm were selected as the second carbon precursor. Under a nitrogen protective atmosphere, the temperature was increased to 800℃ at 5℃ / min and held for 1 h for carbonization heat treatment. Then, the particles were placed under a water vapor volume concentration of 5 vol% and activated at 750℃ for 0.5 h to obtain the second carbon framework.

[0109] Step 2, Chemical Vapor Deposition for Silicon Infiltration: The double-carbon porous particles are transferred to the CVD reactor and heated to 450°C in an argon atmosphere. Then, silane gas is introduced for silicon infiltration. By adjusting the silane flow rate and silicon infiltration time, the total silicon content of the material is controlled to be 40 wt%.

[0110] Step 3, Construction of the functional polymer encapsulation layer: 1.0 g of the obtained silicon carbon particles were dispersed in 200 mL of a 0.5 mg / mL dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution (pH 8.0). The solution was first allowed to stand at 5 °C for 0.5 h without stirring, and then heated to 25 °C and continuously bubbled and stirred with air for 2 h. After the reaction was completed, the solution was filtered, washed with deionized water, and vacuum dried at 60 °C for 6 h to obtain a silicon carbon anode material with a total thickness of about 5-10 nm polydopamine encapsulation layer.

[0111] Comparative Example 3: A method for preparing a negative electrode material includes the following steps: Steps 1 to 3 are the same as in Example 1.

[0112] Step 4, Construction of the functional polymer encapsulation layer: 1.0 g of the obtained silicon carbon particles were dispersed in 200 mL of a 2.0 mg / mL dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution (pH 8.5), and the reaction was carried out by bubbling and stirring with air continuously at 30 °C for 7 h. After the reaction was completed, the mixture was filtered, washed with deionized water, and vacuum dried at 80 °C for 12 h to obtain a silicon carbon anode material with a total thickness of about 10-20 nm of polydopamine encapsulation layer.

[0113] Comparative Example 4: A method for preparing a negative electrode material includes the following steps: Steps 1 to 3 are the same as in Example 1.

[0114] Step 4, Construction of the functional polymer encapsulation layer: 1.0 g of the obtained silicon carbon particles were dispersed in 200 mL of a 2.0 mg / mL dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution (pH 8.5). The solution was first allowed to stand at 10 °C for 1 h for infiltration, and then heated to 25 °C and allowed to stand for 2 h for reaction. After the reaction was completed, the solution was filtered, washed with deionized water, and vacuum dried at 60 °C for 6 h to obtain a near-zero expansion silicon carbon anode material with a total encapsulation layer thickness of about 2-5 nm.

[0115] Comparative Example 5: A method for preparing a negative electrode material includes the following steps: Steps 1-3 are the same as steps 1-3 in Example 1.

[0116] Step 4, Construction of the carbon coating layer: The silicon-carbon particles obtained in Step 3 are placed in a chemical vapor deposition reactor and heated to 700°C under an argon atmosphere. Then, a mixture of acetylene and argon is introduced for carbon deposition. The volumetric flow rate ratio of acetylene to argon is 1:10 (acetylene flow rate 50 sccm, argon flow rate 500 sccm), the deposition time is 1.5 h, and the deposition temperature is 700°C. After deposition, the material is cooled to room temperature under an argon atmosphere to obtain the carbon-coated silicon-carbon anode material. The thickness of the carbon coating layer is approximately 10~20 nm.

[0117] Based on the preparation process provided in Examples 1-3 above, characterization data of the first carbon skeleton and the second carbon skeleton were tested. The test sample of the first carbon skeleton was the first carbon skeleton prepared in step 1 of Examples 1-3. The second carbon skeleton sample was obtained by preparing the second carbon precursor alone (without adding the first carbon skeleton) under the same carbonization and activation conditions as in step 2.

[0118] Nitrogen adsorption-desorption tests were conducted using a fully automated specific surface area and porosity analyzer; the specific test method is as follows: (1) Sample pretreatment: Take an appropriate amount of carbon skeleton sample and degas it under vacuum at 300℃ for 6 hours to remove the moisture and gas impurities adsorbed on the sample surface and in the pores. (2) Specific surface area calculation: The total specific surface area was calculated using the Brunauer-Emmett-Teller (BET) multi-point method, and data points with relative pressure P / P0 in the range of 0.05~0.30 were used for linear fitting; (3) Average pore size: determined by the peak value of the pore size distribution curve of the BJH desorption branch; (4) Calculation of mesopore proportion: The cumulative mesopore volume obtained by the BJH method is divided by the total pore volume of single-point adsorption at relative pressure P / P0≈0.99 × 100% to obtain the proportion of mesopores in the total pore volume; (5) Micropore ratio: The cumulative pore volume of micropores (<2nm) obtained by the t-plot method or HK method is divided by the total pore volume.

[0119] (6) Silicon content of inner and outer composite layers: The cross-section of silicon-carbon composite particles was prepared by argon ion polishing. The cross-sectional morphology of the particles was observed by SEM and combined with EDS line scan analysis to calculate the proportion of silicon mass contributed by the inner composite layer to the total silicon mass of the particles, and the proportion of silicon mass contributed by the outer composite layer to the total silicon mass of the particles.

[0120] (7) Using nitrogen adsorption method, let the volume of the nano-silicon particles in the first carbon framework be V1, the total pore volume of the first carbon framework be V2, and the volume of the nano-silicon particles in the silicon-carbon particles obtained in step 3 be V3. (8) The pore volume occupied by silicon particles is V1=V2 V3 can be obtained by calculating the ratio of V1 to V2.

[0121] The test data for the specific surface area, mesoporous specific surface area, pore volume, average mesoporous pore diameter, and mesoporous percentage of the first carbon skeleton are shown in Table 1.

[0122] Table 1 Characterization data of the first carbon skeletons obtained in Examples 1-3 The test data for the specific surface area, microporous specific surface area, pore volume, average micropore diameter, and micropore percentage of the second carbon skeleton are shown in Table 2.

[0123] Table 2 Characterization data of the second carbon skeletons obtained in Examples 1-3 As shown in Tables 1 and 2, the present invention successfully constructed a hierarchical pore double carbon layer structure dominated by mesopores in the inner layer and micropores in the outer layer, and the pore size, pore volume, specific surface area and pore type ratio can all be controlled by selecting different carbon precursors.

[0124] Comparing the data in Tables 1 and 2, the pore volume of the first carbon framework is only about twice that of the second carbon framework. However, the amount of silicon in the first carbon framework is far greater than that in the second carbon framework. The first carbon framework is mainly mesoporous, and the silicon source gas undergoes capillary condensation within the mesopores, resulting in a large amount of silicon deposition in a "filling" manner, with the loading amount depending on the pore volume. The second carbon framework is mainly microporous, with extremely small pore sizes that prevent capillary condensation. Silicon can only be adsorbed and dispersed on the surface of the micropores at the atomic level, and the loading amount depends on the specific surface area, with the adsorption capacity per unit volume being far lower than that of the volumetric filling. Furthermore, the inner composite zone is the main particle group, and its total pore volume is much larger than that of the outer composite zone. Therefore, the deposition mechanism and the material composition together determine that the silicon content in the inner composite zone is much higher than that in the outer composite zone.

[0125] The silicon-carbon composite materials obtained in Examples 1-5 and Comparative Examples 1-3 were tested using the following testing methods.

[0126] Silicon content: determined by gravimetric method. Weigh approximately 1g of sample and ignite it in air at 1000℃ to constant weight. Calculate the carbon content from the mass difference before and after ignition, and the remainder is the silicon content.

[0127] Average particle size: determined using a laser particle size analyzer. The sample was dispersed in ethanol and ultrasonically dispersed for 3 minutes. The volumetric particle size distribution was then measured using water as the medium, and the Dv50 value was recorded.

[0128] Specific surface area: determined by nitrogen adsorption method. A suitable amount of sample was degassed under vacuum at 300℃ for 6h. High-purity nitrogen was used as the adsorbate, and the nitrogen adsorption isotherm was measured at liquid nitrogen temperature of 77K. The specific surface area was calculated using the BET multipoint method.

[0129] Powder resistivity: Measured using the four-probe method. Approximately 1g of powder was placed into a mold and pressed into a disc under a pressure of 10MPa. The resistance was measured using a four-probe resistivity meter, and the resistivity (Ω·cm) was calculated. The test data are shown in Table 3. Table 3 Performance tests of the negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-4 As shown in Table 3, by adjusting the carbon skeleton pore size, CVD silicon infiltration conditions (partial pressure, temperature, time) and encapsulation layer thickness, the silicon loading, specific surface area and electronic conductivity of the final product can be flexibly adjusted to meet different energy density and rate performance requirements.

[0130] Compared to Example 1, the resistivity of Example 4 (with added carbon nanotubes) decreased from 24.6 Ω·cm to 18.8 Ω·cm (a decrease of 23.6%), and the resistivity of Example 5 (with added graphene) decreased to 16.4 Ω·cm (a decrease of 33.3%), while the specific surface area only slightly increased from 2.8 to 3.2 and 3.0 m² / g, respectively, and the silicon content remained essentially unchanged. This demonstrates that carbon nanotubes or graphene can be embedded in the polydopamine encapsulation layer to construct a three-dimensional conductive network, significantly reducing interfacial impedance without compromising the density of the encapsulation layer.

[0131] Comparing Example 1 and Comparative Example 1, Comparative Example 1 has no external composite region and its specific surface area is as high as 5.8 m². 2 / g, the resistivity increased to 32.5Ω·cm, proving that the micropore confinement structure of the outer composite region can effectively reduce the exposure of surface pores, while also helping to build a more complete conductive network.

[0132] Comparing Example 2 with Comparative Example 2, Comparative Example 2 has no internal recombination region and its resistivity is as high as 45.3 Ω·cm, which proves that the high porosity mesoporous structure of the internal recombination region provides a continuous carbon framework for silicon deposition and electronic conduction, and its absence will lead to deterioration of conductivity.

[0133] Comparing Example 1 and Comparative Example 3, the encapsulation layer of Comparative Example 3 has no gradient structure and its resistivity of 27.2 Ω·cm is slightly higher than that of Example 1. This proves that the low-temperature infiltration step helps the encapsulation layer penetrate into the pores to form an anchoring structure and improve the electronic contact at the interface.

[0134] Comparing Example 1 and Comparative Example 4, the encapsulation layer of Comparative Example 4 had no gradient structure and was not subjected to bubble polymerization, resulting in a specific surface area of ​​4.2 m². 2 / g, the resistivity increased to 28.5Ω·cm. This indicates that: only low-temperature infiltration without bubbling polymerization resulted in an extremely thin and loose discontinuous PDA layer, which could not effectively cover the pores on the particle surface, leading to a higher specific surface area; at the same time, the conductive pathways were discontinuous, and the interfacial electronic contact was weaker than that of the dense gradient encapsulation layer in Example 1.

[0135] Comparing Example 1 and Comparative Example 4, Comparative Example 5 uses a traditional CVD carbon coating layer instead of a polymer encapsulation layer, resulting in a reduced specific surface area of ​​1.8 m². 2 / g, the resistivity decreased to 15.0 Ω·cm. This indicates that the rigid carbon coating can densely cover the surface pores and reduce the resistivity by virtue of the intrinsic high conductivity of carbon materials, but it lacks elastic buffering capacity. Once it cracks during long-term cycling, it will fail irreversibly. It is necessary to comprehensively evaluate its advantages and disadvantages with the flexible gradient encapsulation layer of the present invention by combining the electrochemical data in Table 4.

[0136] Electrode and half-cell preparation and electrochemical performance testing: Using the negative electrode materials prepared in the above embodiments and comparative examples as negative electrode active materials, negative electrode sheets were prepared respectively. The electrode sheet composition was as follows: active material accounted for 90 wt%, binder SBR accounted for 5 wt%, conductive agent SP accounted for 4.9 wt%, and SWCNT accounted for 0.1 wt%. The negative electrode sheets were used to prepare CR2032 coin cells using conventional methods, and the electrical performance of the cells was tested. (1) Half-cell assembly: Assemble CR2032 button cells in a glove box, with lithium metal sheet as counter electrode, polypropylene microporous membrane as separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC=1∶1), wherein the concentration of LiPF6 is 1mol / L.

[0137] (2) Use the LAND battery test system to perform charge and discharge tests on the battery.

[0138] Capacity test: After the CR2032 button cell was left to stand for 6 hours, it was discharged at 0.1C to 0.005V, then discharged at a constant voltage of 0.005V until the current cutoff was 0.01C. After standing for 5 minutes, it was charged at a constant current of 0.1C to 1.5V, and the capacity was recorded. Capacity retention test: After resting for 5 minutes, repeat the above charge and discharge steps twice; then discharge to 0.005V at 0.5C; after resting for 5 minutes, charge to 1.5V at 0.5C constant current, cycle 300 times; calculate the capacity retention rate by dividing the specific capacity of the 300th cycle by the charging capacity of the 1st cycle by 100%. Electrode expansion rate: After the CR2032 coin cell was left to stand for 6 hours, it was discharged at 0.05C to 0.005V, and then discharged at 0.01C to 0.005V. Then the coin cell was disassembled in the glove box, the electrode was cleaned with DMC and the thickness of the electrode was measured. The expansion rate was calculated as: (first fully charged electrode thickness - original electrode thickness) / original electrode thickness × 100%. The test data are shown in Table 4.

[0139] Figure 1The image shows the charge-discharge curves of the battery composed of the anode material prepared in Example 1. The silicon-carbon anode material prepared in Example 1 has an initial discharge specific capacity of 1568 mAh / g, an initial charge specific capacity (lithiation process) of 1391 mAh / g, and an initial coulombic efficiency as high as 88.7%, exhibiting a high reversible lithium storage capacity. This indicates that the material's "core mesoporous buffer - outer shell microporous confinement - surface PDA gradient anchoring encapsulation" structure effectively reduces the irreversible capacity loss during the initial lithium insertion process and has excellent interface stability.

[0140] Figure 2 This is a cycle curve diagram of the battery composed of the negative electrode material prepared in Example 1. Figure 2 It can be seen that the silicon-carbon anode material prepared in Example 1 still retains 87.3% capacity after 300 cycles at 0.5C rate, and the overall capacity decay is gradual. This indicates that the "core mesoporous buffer-shell micropore confinement-surface PDA gradient anchoring encapsulation" structure of the material effectively suppresses the volume expansion of silicon, maintains the stability of the electrode structure and interface, and exhibits excellent long-cycle stability.

[0141] Table 4 Electrochemical performance of batteries assembled from the negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-5 As shown in Table 4, Examples 1-3 all adopt an integrated design of "core mesoporous buffer - outer shell micropore confinement - surface PDA gradient anchoring encapsulation". The performance of silicon-based materials is optimized through a three-level confinement mechanism. The carbon skeleton inside the mesopores provides expansion buffer space, the carbon layer outside the micropores strengthens the spatial confinement of near-surface silicon, and the PDA gradient encapsulation layer takes into account both mechanical constraints and interface stability. The three work together to promote the formation of a stable SEI film. Among them, Example 3 has the highest silicon content (60wt%) and the largest thickness of the outer composite region (80nm). Although the specific capacity of 1718mAh / g is the best among the three, the volume expansion rate (72%) is also the highest, and the capacity retention rate (79.4%) is relatively low. The electrical performance of the anode material prepared in Example 3 is still at the top level in the industry.

[0142] Compared to Example 1, Examples 4 and 5 showed a slight increase in specific capacity, significantly higher initial coulombic efficiency, a substantial improvement in capacity retention, and a significantly lower electrode expansion rate. This indicates that introducing carbon nanotubes or graphene into the polydopamine encapsulation layer can construct a three-dimensional conductive network and enhance the mechanical strength and interfacial anchoring effect of the encapsulation layer, thereby further improving cycle stability and reducing expansion rate. Among these, graphene is slightly more effective than carbon nanotubes.

[0143] Compared to Example 1, Comparative Example 1 has a similar specific capacity, but its initial coulombic efficiency is significantly lower, capacity retention is greatly reduced, and electrode expansion rate is significantly higher. This indicates that the lack of a microporous confinement layer in the external composite region leads to the exposure of nano-silicon to the particle surface, resulting in severe volume expansion during charge and discharge, repeated rupture and regeneration of the SEI film, serious deterioration of initial efficiency and cycle life, and uncontrolled electrode expansion.

[0144] Compared to Example 3, Comparative Example 2 exhibits significantly lower specific capacity, lower initial coulombic efficiency, higher expansion rate, and lower capacity retention. This indicates that the lack of a mesoporous buffer layer with an inner recombination region drastically limits the loading capacity of silicon. Furthermore, the absence of internal buffer space allows volume expansion stress to be directly transferred to the outer layers, leading to rapid structural failure.

[0145] Compared to Example 1, Comparative Example 3 had a similar specific capacity, but lower initial coulombic efficiency, lower capacity retention, and higher expansion rate. This indicates that omitting the low-temperature static infiltration step prevents polydopamine from penetrating into the pores to form an anchoring structure. The encapsulation layer only adheres to the particle surface, resulting in weak interfacial bonding, easy peeling failure during cycling, increased expansion, and accelerated capacity decay.

[0146] Comparing Example 1 and Comparative Example 4, the specific capacity was similar, but the initial coulombic efficiency was significantly lower, the capacity retention rate decreased sharply, and the electrode expansion rate was significantly higher. This indicates that: with only low-temperature infiltration without bubbling polymerization, dopamine cannot be effectively oxidized and self-polymerized. The resulting PDA layer is extremely thin and loosely discontinuous, making it impossible to construct a dense gradient encapsulation layer. The constraint on silicon volume expansion and the interface protection are severely insufficient, and the encapsulation layer is prone to failure during cycling, leading to increased expansion and accelerated capacity decay.

[0147] Comparing Example 1 and Comparative Example 4, the specific capacity and initial coulombic efficiency were similar, but the capacity retention rate was significantly lower and the electrode expansion rate was higher. This indicates that although the traditional CVD carbon coating layer has excellent initial conductivity and can isolate the electrolyte, the rigid carbon layer lacks elastic buffering capacity and is prone to cracking during the repeated expansion and contraction of silicon. Once cracked, it loses its protective function, leading to continuous regeneration of the SEI film and accelerated capacity decay. In contrast, the flexible gradient polymer encapsulation layer of the present invention can elastically deform with the change of silicon volume, exhibiting better structural integrity and more durable expansion suppression effect during long-term cycling.

[0148] The above-described embodiments are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope of the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A near-zero expansion silicon-carbon anode material, characterized in that, It includes an inner composite region, an outer composite region, and an encapsulation layer. The inner composite region includes a first carbon framework and nano-silicon particles, with the nano-silicon particles distributed within the mesoporous channels of the first carbon framework. The outer composite region covers at least a portion of the surface of the inner composite region. The outer composite region includes a second carbon framework and nano-silicon particles. The nano-silicon particles are distributed within the pores of the second carbon framework, which are mainly micropores. The encapsulation layer is a functional polymer encapsulation layer, and the encapsulation layer covers at least a portion of the surface of the particles formed by the outer composite region and the inner composite region; The density of the encapsulation layer gradually decreases from the inside to the outside; the side of the encapsulation layer closer to the outer composite region is the inner side of the encapsulation, and the side of the encapsulation layer farther from the outer composite region is the outer side of the encapsulation; the conductivity of the inner side of the encapsulation is higher than that of the outer side of the encapsulation.

2. The near-zero expansion silicon-carbon anode material as described in claim 1, characterized in that, The outer side of the package is flexible; The outer side of the package has a porous morphology.

3. The near-zero expansion silicon-carbon anode material as described in claim 1 or 2, characterized in that, The encapsulation layer also contains carbon materials, which are any one or more of carbon nanotubes, graphene, and carbon nanofibers.

4. The near-zero expansion silicon-carbon anode material as described in claim 1 or 2, characterized in that, The near-zero expansion silicon-carbon anode material has a silicon content of 40wt%~60wt% and a specific surface area of ​​0.1~10m². 2 / g, with a particle size of 2~30μm and a powder resistivity of 5~100Ω·cm; The particle size D50 of the first carbon skeleton is 2~30μm; the thickness of the outer composite region is 20~100nm; and the thickness of the encapsulation layer is 5~50nm. The specific surface area of ​​the first carbon framework is 400~700 m². 2 / g, the pore volume of the first carbon framework is 1.0~2.0cm³. 3 / g, the average pore size of the first carbon skeleton is 2~50nm, and the proportion of mesopores with a pore size of 2~50nm to the total pore volume of the first carbon skeleton is ≥65%; The specific surface area of ​​the second carbon skeleton is 1000~1800 m². 2 / g, the pore volume of the second carbon framework is 0.4~1.2cm³. 3 / g, the micropore size of the second carbon skeleton is 0.1~2nm, and the proportion of micropores with a pore size of 0.1~2nm to the total pore volume of the second carbon skeleton is ≥75%.

5. The near-zero expansion silicon-carbon anode material as described in claim 1, characterized in that, The silicon content of the inner composite region is 35% to 60%, and the silicon content of the outer composite region is 0.5% to 5%. The specific surface area of ​​the first carbon skeleton and the specific surface area of ​​the second carbon skeleton satisfy the following condition: 0.22 ≤ specific surface area of ​​the first carbon skeleton / specific surface area of ​​the second carbon skeleton ≤ 0.

70.

6. A method for preparing a near-zero expansion silicon-carbon anode material, characterized in that, Used to prepare the near-zero expansion silicon-carbon anode material according to any one of claims 1 to 5 The preparation method includes the following steps: Step 1, Preparation of the first carbon framework: The first carbon precursor particles are carbonized and heat-treated under a protective atmosphere, and then activated to obtain the first carbon framework. Step 2, Preparation of bilayer carbon porous particles: The second carbon precursor material is coated on the surface of the first carbon skeleton, carbonized and heat-treated under a protective atmosphere, and then activated to form bilayer carbon porous particles with hierarchical pore structure. Step 3, Chemical vapor deposition silicon infiltration: Place the double carbon layer porous particles in a reactor, introduce silicon source gas to perform silicon infiltration treatment, and obtain silicon carbon particles. Step 4, Construction of the functional polymer encapsulation layer: Silicon carbon particles are dispersed in a dopamine hydrochloride-tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution and subjected to staged temperature-controlled polymerization. After the polymerization reaction is completed, the particles are filtered, washed and dried in sequence to obtain the near-zero expansion silicon carbon anode material. The phased temperature-controlled polymerization includes the first stage: low-temperature static infiltration; and the second stage: heating and continuous introduction of oxygen-containing gas for bubbling reaction.

7. The method for preparing the near-zero expansion silicon-carbon anode material as described in claim 6, characterized in that, In step 4, the concentration of dopamine hydrochloride tris(hydroxymethyl)aminomethane-hydrochloric acid buffer is 0.5~5.0 mg / mL; wherein the pH value of tris(hydroxymethyl)aminomethane-hydrochloric acid buffer is 8.0~9.0; The first stage involves static infiltration at 5~15℃ for 0.5~2 hours; The second stage involves bubbling and stirring at 25-35°C with air or oxygen introduced for 2-10 hours; the aeration rate is 0.5-2 L / min.

8. The method for preparing the near-zero expansion silicon-carbon anode material as described in claim 6 or 7, characterized in that, In step 4, additives are added during the construction of the polydopamine encapsulation layer. The additives are any one or more of carbon nanotubes, graphene, and carbon nanofibers. The mass ratio of silicon carbon particles to additives is 1: (0.01~0.1).

9. The method for preparing the near-zero expansion silicon-carbon anode material as described in claim 6 or 7, characterized in that, The first carbon precursor is any one or more of phenolic resin, sucrose, and cellulose. The second carbon precursor is any one or more of mesophase pitch, petroleum pitch, and polyamic acid. The mass ratio of the first carbon precursor to the second carbon precursor is 1: (0.05~0.3) based on the raw materials. In steps 1 and 2, the carbonization heat treatment temperature is 800~1200℃, and the carbonization heat treatment time is 1~5h; during the activation treatment, the activation atmosphere is a water-containing oxidizing atmosphere, in which the volume concentration of water vapor is 5vol%~40vol%; the activation temperature is 750~950℃, and the activation time is 0.5~4h.

10. A battery, characterized in that, This includes the near-zero expansion silicon-carbon anode material as described in any one of claims 1 to 5, or the near-zero expansion silicon-carbon anode material prepared by the preparation method described in any one of claims 6 to 9.

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