In-situ hetero-doped multi-stage random-pore silicon-carbon composite materials, preparation and applications

Abstract

This invention relates to an in-situ hetero-doped multi-level random porous silicon-carbon composite material, its preparation, and its application. It comprises: a porous carbon matrix as a supporting framework; multiple stacked in-situ hetero-doped porous silicon unit layers loaded on the surface and within the pores of the porous carbon matrix; each unit layer includes silicon material and a dopant element material hetero-doped in the silicon material in situ; each unit layer has interconnected channels, and the channels of each unit layer are interconnected, forming a continuous three-dimensional random porous interconnection network within the composite material; wherein each unit layer is prepared by gas-phase co-deposition of a gaseous silicon source and a dopant source precursor to form a silicon-doped composite material, followed by masking and selective etching; in the silicon-doped composite material, the dopant element is randomly distributed in the silicon matrix, and the atomic percentage of the dopant element in silicon is 0.2-20 wt%; the dopant element is used to induce random channel formation; and a masking layer is discretely distributed on the surface of each unit layer and the inner wall of the channels.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and in particular to an in-situ hetero-doped multi-level random porous silicon-carbon composite material, its preparation and application. Background Technology

[0002] With the rapid development of the electric vehicle and energy storage industries, higher requirements have been placed on the energy density of lithium-ion batteries. Silicon-based anode materials have become a research focus due to their extremely high theoretical specific capacity (4200 mAh / g), but they exhibit huge volume expansion (>300%) during charge and discharge, which easily leads to material pulverization, repeated rupture of the solid electrolyte interphase (SEI) film, and electrode structure failure, severely restricting their practical application.

[0003] To address this issue, researchers have developed various porous silicon structures that can accommodate volume expansion through internal pores, thereby mitigating mechanical stress.

[0004] Currently, common methods for preparing porous silicon include electrochemical etching, metal-assisted chemical etching, template methods, and magnesothermic reduction. Electrochemical etching typically requires a single-crystal silicon wafer as a substrate, making it difficult to prepare powder materials at low cost. Metal-assisted chemical etching involves heavy metal contamination, and the pore orientation is limited by crystal orientation. Although template methods can control the pore size, the template removal step is cumbersome, and the resulting pores are mostly isolated or in a regular array, easily leading to localized stress concentrations during cycling. Magnesothermic reduction involves a violent reaction, making it difficult to control the pore structure, and residual magnesium phase is difficult to completely remove. These methods generally suffer from problems such as complex processes, unsuitability for large-scale production, uniform pore morphology, and uneven stress distribution.

[0005] In recent years, fluidized bed chemical vapor deposition (CVD), combined with a mask and fluorine-containing etching gas, has been considered a promising route for the fabrication of porous silicon powder. This technique first deposits a silicon layer on the particle surface, then deposits a mask layer, and uses a fluorine-containing gas to selectively etch the unmasked areas. However, this route faces a core bottleneck: the penetration depth of the fluorine-containing etching gas is limited. For example... Figure 1 As shown, in conventional etching processes, the etching gas has difficulty penetrating the silicon material, and the etching reaction mainly occurs on the surface of the particles. This results in pore structures concentrated on the surface, while the internal regions remain dense, making it difficult to form interconnected pore structures. Therefore, in a single thick-layer silicon etching process, the gas cannot reach the interior, resulting in pores confined to the surface. If the amount of etching gas is forcibly increased or the etching time is extended, the surface silicon will be excessively consumed or even completely removed, and interconnected pores will still not be formed internally. This may also lead to pore wall collapse and particle breakage. Furthermore, the pores formed by conventional mask etching often exhibit directional alignment. During multiple charge-discharge cycles, stress tends to concentrate along the pore direction, accelerating material pulverization.

[0006] To improve the electrochemical kinetics of silicon anodes, researchers have attempted to dope silicon with elements such as carbon, nitrogen, and phosphorus to enhance electronic conductivity or provide additional capacity. However, existing doping methods (such as liquid-phase mixing, mechanical ball milling, and high-temperature solid-phase diffusion) struggle to achieve uniform distribution within nanoscale channels, and cannot utilize the reaction differences between the dopant phase and the etching gas to aid channel formation. Therefore, overcoming the mass transfer limit of etching gases to construct a stress-dispersed, highly conductive, and controllable three-dimensional porous network within powder particles, while simultaneously achieving in-situ uniform introduction of dopant elements, remains a critical technical challenge to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing an in-situ hetero-doped multi-level random porous silicon-carbon composite material, its preparation, and its application. By constructing layer by layer and utilizing the random distribution of etch-resistant doped phases to guide the spontaneous formation of a three-dimensional interconnected random network of channels, the problems of mass transfer limitation, stress concentration, and insufficient electrochemical performance are simultaneously solved. This achieves high specific capacity while significantly improving the material's cycling stability and structural integrity.

[0008] To achieve the above objectives, in a first aspect, the present invention provides an in-situ hetero-doped multi-level random porous silicon-carbon composite material, comprising: Porous carbon matrix serves as a supporting framework; Multilayered, in-situ hetero-doped porous silicon unit layers are loaded onto the surface and pores of a porous carbon matrix. Each in-situ hetero-doped porous silicon unit layer comprises silicon material and a dopant element material hetero-doped in the silicon material. The in-situ hetero-doped porous silicon unit layers have interconnected channels, forming a continuous three-dimensional random channel interconnection network within the composite material. Each in-situ hetero-doped porous silicon unit layer is prepared by gas-phase co-deposition of a gaseous silicon source and a dopant source precursor to form a silicon-doped composite material, followed by masking and selective etching. The dopant element includes at least one of C, N, O, P, and B. In the silicon-doped composite material, the dopant element is randomly distributed in the silicon matrix, and the atomic percentage of the dopant element in silicon is 0.2-20 wt%. The dopant element is used to induce random channel formation. The masking layer is discretely distributed on the surface of each unit layer and the inner wall of the pores.

[0009] Preferably, the porous carbon matrix comprises one or more of activated carbon, porous expanded graphite, graphene, or carbon fiber; the specific surface area of ​​the porous carbon matrix is ​​500-2500 m². 2 / g, pore volume 0.3-5.0 cm³ 3 / g, pore size 0.6-10 nm, ash content less than 0.5%; The diameter of the through-hole is 0.15-1.2 nm; the total porosity of the multilayer stacked in-situ hetero-doped porous silicon unit layer is 5%-60%; the number of stacked layers of the in-situ hetero-doped porous silicon unit layer is 2-6. The material of the mask modification layer includes one or more of silicon oxide, silicon nitride, aluminum oxide, or silicon carbide; the thickness of the mask modification layer is 1-20 nm.

[0010] Preferably, the composite material further includes a pre-coating layer on the outer layer and a carbon coating layer on the outermost layer; the pre-coating layer is a pre-coated carbon layer or a pre-coated alumina layer.

[0011] Secondly, embodiments of the present invention provide a method for preparing an in-situ hetero-doped multi-level random porous silicon-carbon composite material, the method comprising: Step 1: Place the porous carbon matrix in a reactor and heat it to the silicon deposition temperature under a protective atmosphere. Then, introduce a first mixed gas containing a gaseous silicon source and a dopant source precursor to perform chemical vapor deposition. Deposit a silicon-doped composite material layer in the pores of the porous carbon matrix to obtain a composite material with a silicon-doped composite material layer. In the silicon-doped composite material, the dopant elements are randomly distributed in the silicon matrix. Step 2: Adjust the temperature inside the reactor to the mask deposition temperature under a protective atmosphere, introduce a second mixed gas containing the mask precursor, and deposit island-shaped and / or block-shaped discontinuous mask modification layers on the surface and pores of the composite material with silicon-doped composite material layer to obtain a composite material with mask coverage. Step 3: Under a protective atmosphere, adjust the temperature inside the reactor to the etching temperature, and introduce a third mixed gas containing fluorine-containing etching gas to selectively etch the composite material covered by the mask. The etching gas is guided by the mask modification layer to etch silicon along the thickness direction on the silicon-doped composite material layer in the area not covered by the mask modification layer. The etching selectivity of the etching gas for silicon is higher than that for the dopant element. The dopant element induces the random formation of the pores etched in the silicon-doped composite material layer, thereby forming a first in-situ heterogeneous doped porous silicon unit layer with through-holes in the composite material. At the same time, part of the mask modification layer is retained on the inner wall and surface of the pores. Step 4: Repeat steps 1 to 3 for N times, sequentially forming a second in-situ hetero-doped porous silicon unit layer to an (N+1)th in-situ hetero-doped porous silicon unit layer with through-holes in the composite material, and the pores of each unit layer are interconnected to form a through-hole three-dimensional random pore interconnection network in the composite material; N is an integer greater than or equal to 1.

[0012] Preferably, the protective atmosphere includes one or more of argon, nitrogen, or helium; In step 1, the silicon deposition temperature is 300-700 ℃, and the deposition time is 10-120 min; the gaseous silicon source includes one or more of silane, dichlorosilane, trichlorosilane, or silicon tetrachloride; the doping source precursor includes one or more of methane, acetylene, ammonia, oxygen, carbon dioxide, carbon monoxide, phosphine, or diborane; the first mixed gas also includes a carrier gas, which includes one or more of argon, nitrogen, or helium. In step 2, the mask deposition temperature is 300-750 ℃, and the deposition time is 5-200 min; the mask precursor includes one or more of oxygen, water vapor, carbon dioxide, carbon monoxide, ammonia, methane, ethylene or acetylene, and one or more of aluminum isopropoxide, trimethylaluminum or gaseous silicon source; the second mixed gas also includes a carrier gas, which includes one or more of argon, nitrogen or helium; In step 3, the etching temperature is 400-600 ℃, and the etching time is 30-300 min; the fluorine-containing etching gas includes one or more of carbon tetrafluoride, fluoromethane, sulfur hexafluoride, or nitrogen trifluoride; the third mixed gas also includes a carrier gas, which includes one or more of argon, nitrogen, or helium; the volume ratio of the fluorine-containing etching gas to the carrier gas is 1:10-1:100.

[0013] Preferably, the method further includes: The composite material with a three-dimensional random channel interconnection network obtained in step 4 is pre-coated after being purged with inert gas. The pre-coated composite material is subjected to secondary carbon coating by chemical vapor deposition or liquid phase impregnation-pyrolysis to obtain the porous silicon / carbon composite material with three-dimensional through channels.

[0014] More preferably, the pre-coating treatment specifically involves: forming a pre-coated carbon layer or a pre-coated alumina layer by chemical vapor deposition; wherein the carbon source gas for forming the pre-coated carbon layer includes one or more of methane, ethylene, or acetylene; the precursor for forming the pre-coated alumina layer includes trimethylaluminum or aluminum isopropoxide, and an oxidizing gas is simultaneously introduced; the pre-coating treatment time is 5-60 min; The process conditions for the chemical vapor deposition method are as follows: a carbon source for vapor deposition is introduced at a temperature of 500-750 °C for 1-4 h; the carbon source for vapor deposition includes one or more of methane, ethylene, or acetylene. The process conditions for the liquid phase impregnation-pyrolysis method are as follows: the pre-coated composite material is impregnated in a carbon precursor solution for 3-8 hours, then removed and dried, and carbonized at 800-1100 °C for 1-4 hours under a protective atmosphere; the carbon precursor includes one or more of sucrose, glucose, phenolic resin or asphalt.

[0015] Preferably, in step 3, the etching is performed using plasma-assisted etching, which involves introducing a radio frequency power supply or a microwave power supply into the reactor to excite the fluorine-containing etching gas to form plasma, thereby increasing the concentration of etching active particles.

[0016] Thirdly, embodiments of the present invention provide a negative electrode sheet comprising the in-situ hetero-doped multi-level random porous silicon-carbon composite material described in the first aspect above, or comprising the in-situ hetero-doped multi-level random porous silicon-carbon composite material prepared by the preparation method described in the second aspect above.

[0017] Fourthly, embodiments of the present invention provide an energy storage device, the energy storage device comprising: a lithium-ion battery or a lithium-ion capacitor; the energy storage device comprising the in-situ hetero-doped multi-level random porous silicon-carbon composite material described in the first aspect above, or comprising the in-situ hetero-doped multi-level random porous silicon-carbon composite material prepared by the preparation method described in the second aspect above, or comprising the negative electrode sheet described in the third aspect above.

[0018] The in-situ hetero-doped multi-level random porous silicon-carbon composite material provided in this embodiment of the invention constructs a cyclic control mechanism of "in-situ hetero-doped silicon deposition-mask-etching and inducing random pore formation". This decomposes the one-step etching process of traditional thick silicon materials into a layer-by-layer construction and pore-forming process of multiple thin-layer in-situ hetero-doped porous silicon unit layers. In-situ hetero-doped porous silicon unit layers are formed in-situ on the surface and inside the pores of the porous carbon matrix. Through the interconnection and communication of the randomly formed pores in each layer, a three-dimensional random pore interconnection network that is completely interconnected from the inside to the outside is constructed inside the composite material.

[0019] This structural design effectively overcomes the mass transfer limitation of fluorine-containing etching gases penetrating deep into the material during traditional etching processes. It also solves the technical bottlenecks of traditional processes, such as porous structures being limited to the surface, prone to over-etching or lack of internal pores, and structural collapse. Simultaneously, the randomly distributed etching-resistant doped phases act as in-situ blocking sites during etching, inducing disordered pore growth and avoiding the stress concentration problem caused by the uniform orientation of traditional regular pores, significantly improving the material's resistance to powdering. Furthermore, the multi-interface protection system composed of discretely distributed mask modification layers and an outermost continuous carbon shell effectively stabilizes the silicon-electrolyte interface, inhibiting the continuous growth and rupture of the solid electrolyte interphase (SEI) film.

[0020] Based on the above structural features, on the one hand, the three-dimensional random pore interconnection network constructed in this invention significantly shortens the lithium-ion diffusion path, improves the electrolyte wetting ability and ion transport efficiency, thereby enhancing the rate performance of the material; on the other hand, the randomly formed pore structure provides an effective buffer space for the volume expansion of silicon material during charging and discharging, reducing internal stress accumulation and inhibiting particle pulverization and structural cracking. Simultaneously, the synergistic effect of the outer continuous carbon coating layer and the internal mask residual structure effectively stabilizes the silicon / electrolyte interface, inhibits the repeated formation and cracking of the SEI, reduces irreversible capacity loss, and thus significantly improves the cycling stability and coulombic efficiency of the material.

[0021] Therefore, this invention, through the synergistic effect of an "internal porous and external stable" dual mechanism, significantly improves the material's cycle stability, structural integrity, and interfacial electrochemical stability while maintaining high specific capacity. The in-situ hetero-doped multi-level random porous silicon-carbon composite material is suitable for next-generation high-energy-density lithium-ion batteries, especially meeting the requirements of power batteries and energy storage systems for long-life, low-expansion anodes, and possesses promising prospects for industrial application. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of porous silicon materials prepared using conventional etching methods in the prior art. Figure 2 This is a partial structural schematic diagram of the in-situ hetero-doped multi-level random channel silicon-carbon composite material provided in an embodiment of the present invention; Figure 3 The charge-discharge curves are for the half-cell assembled in Embodiment 1 of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0024] This invention provides an in-situ hetero-doped multi-level random channel silicon-carbon composite material.

[0025] Figure 2 This is a magnified view of a pore structure in an in-situ hetero-doped multi-level random channel silicon-carbon composite material provided in an embodiment of the present invention. The following is a detailed description in conjunction with... Figure 2 The technical solution of the present invention will be described below.

[0026] The in-situ hetero-doped multi-level random channel silicon-carbon composite material of the present invention comprises: Porous carbon matrix serves as the supporting framework for composite materials.

[0027] Preferably, the porous carbon matrix comprises one or more of activated carbon, porous expanded graphite, graphene, or carbon fiber; the specific surface area of ​​the porous carbon matrix is ​​500-2500 m². 2 / g, pore volume 0.3-5.0 cm³ 3 / g, pore size 0.6-10 nm, ash content less than 0.5%.

[0028] Multilayered, in-situ hetero-doped porous silicon unit layers are loaded onto the surface and pores of a porous carbon matrix. Each in-situ hetero-doped porous silicon unit layer comprises silicon material and a dopant element material hetero-doped in the silicon material. Each in-situ hetero-doped porous silicon unit layer has interconnected channels, and the channels of each unit layer are interconnected, forming a continuous three-dimensional random channel interconnection network inside the composite material. Each in-situ hetero-doped porous silicon unit layer is prepared by gas-phase co-deposition of a gaseous silicon source and a dopant source precursor to form a silicon-doped composite material, followed by masking and selective etching. The dopant element includes at least one of C, N, O, P, and B. In the silicon-doped composite material, the dopant element is randomly distributed in the silicon matrix, and the atomic percentage of the dopant element in silicon is 0.2-20 wt%. The dopant element is used to induce random channel formation.

[0029] Preferably, the pore size of the through-channels in each unit layer is 0.15-1.2 nm; the total porosity of each unit layer is 5%-60%; and the number of stacked unit layers is 2-6. Figure 2 The image shows a 4-layer stack.

[0030] In this invention, the pore size of the through-channels refers to the pore size of the internal pore structure of the silicon-doped composite material, a meaning known in the art. The pore size of the through-channels within the unit layer in the embodiments of this invention can be determined using instruments and conventional methods known in the art. Specifically, the Brunauer-Emmet-Teller (BET) gas adsorption method can be used, and the measuring instrument is a Micromeritics ASAP2460 specific surface area and pore size analyzer from McMuritics (Shanghai) Instruments Co., Ltd., USA.

[0031] The mask modification layer is discretely distributed on the surface and inner wall of the pores of each porous silicon unit layer.

[0032] Preferably, the material of the mask modification layer includes one or more of silicon oxide, silicon nitride, aluminum oxide, or silicon carbide; the thickness of the mask modification layer is 1-20 nm.

[0033] Furthermore, the composite material may also include a pre-coating layer on the outer layer and a carbon coating layer on the outermost layer; the pre-coating layer is a pre-coated carbon layer or a pre-coated alumina layer.

[0034] This invention Figure 2 This diagram only shows a local structure within a single pore of a porous carbon matrix to illustrate the stacking of in-situ hetero-doped porous silicon unit layers and the connectivity of three-dimensional random interconnected channels. Those skilled in the art will understand that in actual materials, the aforementioned structure can be repeatedly distributed on the surface of the porous carbon matrix and within each pore. Of course, although the aforementioned structure can be formed on the surface of the porous carbon matrix and within multiple pores, due to the mass transfer behavior and interfacial energy differences during vapor deposition and etching, silicon deposition and the subsequent formation of porous structures mainly occur within the pores of the porous carbon matrix.

[0035] The preparation method of in-situ hetero-doped multi-level random porous silicon-carbon composite material is introduced below.

[0036] The preparation method proposed in this invention includes: Step 1: Place the porous carbon matrix in a reactor and heat it to the silicon deposition temperature under a protective atmosphere. Then, introduce a first mixed gas containing a gaseous silicon source and a dopant source precursor to perform chemical vapor deposition. Deposit a silicon-doped composite material layer in the pores of the porous carbon matrix to obtain a composite material with a silicon-doped composite material layer.

[0037] In step 1, a thin layer of silicon-doped composite material is uniformly deposited within the high specific surface area pores of a porous carbon matrix, providing a foundation for subsequent construction of unit layers. In the silicon-doped composite material, the dopant elements are randomly distributed within the silicon matrix.

[0038] Specifically, the porous carbon matrix includes one or more of the following: activated carbon, porous expanded graphite, graphene, or carbon fiber; the specific surface area of ​​the porous carbon matrix is ​​500-2500 m². 2 / g, pore volume 0.3-5.0 cm³ 3 / g, pore size 0.6-10 nm, ash content less than 0.5%.

[0039] The porous carbon substrate can be placed in a chemical vapor deposition (CVD) apparatus (such as a fluidized bed or rotary kiln) and heated to the vapor-phase silicon deposition temperature of 300-700 °C at a heating rate of 3-10 °C / min under a protective atmosphere. Then, a reactive gas is introduced for CVD deposition, with a deposition time of 10-120 min.

[0040] The protective atmosphere includes one or more of argon, nitrogen, or helium. The reaction gas is a first mixed gas, including a gaseous silicon source, a dopant source precursor, and a carrier gas. The gaseous silicon source includes one or more of silane, dichlorosilane, trichlorosilane, or silicon tetrachloride; the dopant source precursor includes one or more of methane, acetylene, ammonia, oxygen, carbon dioxide, carbon monoxide, phosphine, or diborane; the carrier gas includes one or more of argon, nitrogen, or helium. The oxygen content in the nitrogen is less than 5 ppm. In a specific embodiment of the invention, the total gas flow rate of the first mixed gas, consisting of the carrier gas, the gaseous silicon source, and the dopant source precursor, is controlled at 0.5-5 L / min, wherein the volume concentration of the gaseous silicon source is 0.1%-60%, and the volume concentration of the dopant source precursor is 0.01%-10%.

[0041] In this step, porous carbon serves as a conductive support framework. By depositing doped silicon in situ on the surface of the porous carbon framework, uniform deposition of the silicon layer, random distribution of dopant elements, and uniform and complete coating of the surface and pores of the porous carbon framework can be achieved. This ensures close contact between the silicon-doped composite material layer and the carbon framework, providing a pathway for electron transport.

[0042] Taking silane as the gaseous silicon source and acetylene as the dopant source as an example: silane and acetylene undergo thermal decomposition reactions at high temperatures: SiH4(g) → Si(s) + 2H2(g), C2H2(g) → 2C(s) + H2(g). The generated silicon atoms undergo heterogeneous nucleation and growth on the surface and pore surfaces of the porous carbon matrix, and the dopant element carbon is randomly distributed in the deposited silicon matrix, forming a thin silicon-doped composite material layer covering the surface of the porous carbon framework.

[0043] Step 2: Under a protective atmosphere, adjust the temperature inside the reactor to the mask deposition temperature, introduce a second mixed gas containing the mask precursor, and deposit island-shaped and / or block-shaped discontinuous mask modification layers on the surface and pores of the composite material with silicon-doped composite material layer to obtain a composite material with mask coverage.

[0044] Step 2 forms discrete mask modification layers with high etch selectivity on the surface of the thin silicon-doped composite material layer deposited in the previous step, providing guidance for subsequent etching positions and enabling selective and preferential etching of areas not covered by the mask modification layer.

[0045] In this step, the mask deposition temperature is 300-750 ℃, and the deposition time is 5-200 min. The protective atmosphere includes one or more of argon, nitrogen, or helium. The reaction gas is a second mixed gas, including the mask precursor and the carrier gas. The mask precursor includes one or more of oxygen, water vapor, carbon dioxide, carbon monoxide, ammonia, methane, ethylene, or acetylene, and one or more of aluminum isopropoxide, trimethylaluminum, or gaseous silicon sources. The carrier gas includes one or more of argon, nitrogen, or helium.

[0046] The introduced mask precursors react with each other to form a mask modification layer. The material of the mask modification layer includes one or more of silicon oxide, silicon nitride, aluminum oxide, or silicon carbide. Specifically, the choice of mask precursor can be determined based on the material of the desired mask modification layer. For example, when the mask modification layer is silicon oxide, the mask precursor can be a combination of oxygen, water vapor, carbon dioxide, or carbon monoxide with a gaseous silicon source; when the mask modification layer is silicon nitride, the mask precursor can be a combination of ammonia with a gaseous silicon source; when the mask modification layer is aluminum oxide, the mask precursor can be a combination of trimethylaluminum or aluminum isopropoxide with an oxidizing gas (such as water vapor or oxygen); when the mask modification layer is silicon carbide, the mask precursor can be a combination of methane, ethylene, or acetylene with a silicon source gas.

[0047] In this step, the formation of the mask modification layer is a vapor-phase heterogeneous deposition process performed on the surface of the silicon-doped composite material layer. Because the nucleation and growth behavior of the mask precursor on the silicon surface is influenced by interfacial energy differences and the distribution of surface active sites, its nucleation process exhibits non-uniform characteristics. Consequently, discrete nucleation points are preferentially formed in localized areas, gradually growing into island-like or blocky structures rather than a continuous, dense thin film.

[0048] Simultaneously, by controlling the deposition time and the proportions of reactants in the mask precursors, incomplete reactions can occur between the mask precursors, or their surface diffusion and coalescence processes can be restricted, thereby inhibiting the formation of continuous films and promoting the formation of discontinuous mask structures with spatial intervals. Those skilled in the art can rationally select and optimize the deposition time and the proportions of reactants through conventional experiments, based on the desired coverage and structural morphology of the mask modification layer, to obtain the desired discontinuous mask structure.

[0049] The mask modification layer obtained in this step can provide more obvious selective protection in the subsequent etching process, so that the silicon-doped composite material layer in the uncovered area is preferentially etched.

[0050] Step 3: Under a protective atmosphere, adjust the temperature inside the reactor to the etching temperature, and introduce a third mixed gas containing fluorine-containing etching gas to selectively etch the composite material covered by the mask. The etching gas is guided by the mask modification layer to etch silicon along the thickness direction on the silicon-doped composite material layer in the area not covered by the mask modification layer. The channels formed by etching in the silicon-doped composite material layer are randomly shaped by the doping element, thereby forming a first in-situ hetero-doped porous silicon unit layer with through channels in the composite material. At the same time, part of the mask modification layer is retained on the inner wall and surface of the channels.

[0051] The etching rate of silicon by fluorine-containing etching gases is significantly higher than that of mask-modified layer materials (such as silicon oxide, silicon nitride, aluminum oxide, or silicon carbide), and also significantly higher than that of doped elements. During the etching reaction, the mask-modified layer acts as a barrier to protect the underlying structure, guiding the etching gas to preferentially attack the silicon-doped composite layer not covered by the mask-modified layer. It first deeply etches the silicon material along the thickness direction. Simultaneously, the randomly distributed doped elements within the silicon-doped composite layer act as in-situ blocking points, forcing the etching path to randomly detour, thus spontaneously forming a network of curved, branching, and interconnected random channels. In other words, through the inductive effect of the doped elements, the channels etched in the silicon-doped composite layer are randomly shaped. After etching, some of the mask-modified layer remains on the inner walls and surface of the channels, which can further control the channel morphology and suppress lateral expansion, thereby forming a unit layer with randomly shaped through-channels within the silicon layer.

[0052] Optionally, etching can also be carried out using plasma-assisted etching, which involves introducing a radio frequency power supply or a microwave power supply into the reactor to excite fluorine-containing etching gas to form plasma, thereby increasing the concentration of etching active particles.

[0053] The etching temperature is 400-600 ℃, and the etching time is 30-300 min; the protective atmosphere includes one or more of argon, nitrogen, or helium. The third mixed gas includes a fluorine-containing etching gas and a carrier gas. The fluorine-containing etching gas includes one or more of carbon tetrafluoride, fluoromethane, sulfur hexafluoride, or nitrogen trifluoride; the carrier gas includes one or more of argon, nitrogen, or helium; preferably, the volume ratio of the fluorine-containing etching gas to the carrier gas is 1:10-1:100.

[0054] Step 4: Repeat steps 1 to 3 for N times, sequentially forming the second in-situ hetero-doped porous silicon unit layer to the (N+1)th in-situ hetero-doped porous silicon unit layer with through-channels in the composite material, and the channels of each unit layer are interconnected to form a through-channel three-dimensional random channel interconnection network in the composite material; N is an integer greater than or equal to 1.

[0055] This invention employs a repeated cycle of in-situ hetero-doped silicon deposition-masking-etching, inducing random channel formation. Each time, only one thin layer of in-situ hetero-doped porous silicon unit is deposited and etched, creating a layer-by-layer progression. The etching depth is controllable, specifically less than or equal to the thickness of the silicon deposition layer, thus avoiding the possibility of etching through the current layer and damaging the underlying structure. The channels formed by each etching layer have a randomly formed structure and are interconnected, ultimately forming a fully interconnected three-dimensional random channel network from the inside out, effectively overcoming the mass transfer limitations of fluorine-containing etching gases.

[0056] Preferably, the number of repetitions N is 1-5 times, and the total number of unit layers is 2-6 layers. The deposition temperature and time of silicon-doped composite material, the deposition temperature and time of mask modification layer, the etching temperature and time, as well as the selection of gas type and flow rate in each cycle can be the same or different, and each layer can be independently adjusted according to the required pore structure, etc.

[0057] Furthermore, since the preparation method of this invention combines vapor deposition and selective etching, during the deposition process, the gaseous silicon source and dopant source have a longer residence time and a higher effective collision probability inside the pores of the porous carbon matrix, thus preferentially forming a silicon-doped composite material layer inside the pores. During mask deposition, the inner surface of the pores, due to its curvature structure and interfacial energy characteristics, is more conducive to the nucleation and island aggregation of the mask precursor, making the mask modification layer more fully distributed within the pores. During etching, the pore structure restricts the diffusion path of the etching gas, causing the etching process to occur preferentially along the thickness direction, thus making it easier to form through-channels inside the pores. Therefore, under multiple deposition and etching cycles, the unit layer and its through-channel structure are mainly formed inside the pores of the porous carbon matrix and connected layer by layer, ultimately constructing a three-dimensional random pore interconnection network, while only a small amount or discontinuous structures are formed on the outer surface.

[0058] After step 4 above, the composite material with a three-dimensional random interconnected pore network obtained in step 4 can be pre-coated after being purged with an inert gas; the pre-coated composite material can be carbon-coated again by chemical vapor deposition or liquid phase impregnation-pyrolysis to obtain a porous silicon / carbon composite material with three-dimensional interconnected pores.

[0059] Specifically, the pre-coating process involves forming a pre-coated carbon layer or a pre-coated alumina layer through chemical vapor deposition. The carbon source gas for forming the pre-coated carbon layer includes one or more of methane, ethylene, or acetylene. The precursor for forming the pre-coated alumina layer includes trimethylaluminum or aluminum isopropoxide, and an oxidizing gas is introduced simultaneously. The pre-coating process takes 5-60 minutes and is carried out at a temperature of 400℃-600℃.

[0060] The process conditions for chemical vapor deposition are as follows: under a protective atmosphere, the temperature is increased to 500-750 ℃ ​​at a heating rate of 3-10 ℃ / min, and a mixture of gaseous carbon source and inert gas is introduced for chemical vapor deposition treatment for 1-4 h. The gaseous carbon source includes one or more of methane, ethylene or acetylene; the inert gas includes one or more of argon, nitrogen or helium, and the oxygen content in the nitrogen is less than 5 ppm.

[0061] The process conditions for the liquid phase impregnation-pyrolysis method are as follows: the pre-coated composite material is impregnated in a carbon precursor solution for 3-8 h, removed and dried, and then heated to 800-1100 ℃ at a heating rate of 3-10 ℃ / min under a protective atmosphere for carbonization treatment for 1-4 h; the carbon precursor includes one or more of sucrose, glucose, phenolic resin or asphalt, and the concentration of the carbon precursor solution is 5 wt%-30 wt%.

[0062] Because porous silicon materials have a high specific surface area and abundant surface active sites, they are prone to reacting with oxygen or moisture in the air, leading to reduced material stability and even self-heating under localized conditions. Therefore, a pre-coating treatment is performed after step 4. By forming a dense or semi-dense protective layer on the material surface, the surface active sites are passivated, thereby reducing the probability of contact and reaction with active components in the air. This improves the safety and stability of the material when it is removed, transferred, or exposed to short-term environments before the secondary carbon coating step.

[0063] Through secondary carbon coating, a complete external conductive and mechanical constraint layer is formed on the outermost layer. The continuous and complete carbon coating layer formed undertakes the following three functions: (1) Conductive network: provides an efficient electron transport path; (2) Mechanical constraint: restricts the overall volume expansion of particles from the outside and maintains the integrity of the electrode structure; (3) Interface stability: the carbon material itself can form a stable SEI film, further improving interface compatibility.

[0064] Through the above preparation method, a silicon-carbon composite material with a multi-layered structure consisting of a porous carbon matrix, multiple stacked in-situ hetero-doped porous silicon unit layers, a mask modification layer, and a carbon coating layer was finally formed. This multi-layered structure synergistically achieves internal stress dissipation and external interface stability, enabling the material to simultaneously possess high specific capacity, low volume expansion, and long cycle life.

[0065] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0066] Example 1 This embodiment prepares a silicon-carbon composite material with four stacked unit layers.

[0067] Step 110, take 500g of material with a specific surface area of ​​2000 m². 2 / g, pore volume 1.5 cm 3 A porous activated carbon matrix with an average pore size of 2.5 nm was placed in a fluidized bed reactor and heated to 520 °C at a rate of 5 °C / min under a nitrogen protective atmosphere. A mixture of silane gas (flow rate 3 L / min), NH3 (flow rate 0.2 L / min), and nitrogen gas (flow rate 7 L / min) was introduced and chemical vapor deposition was performed for 50 min. Silicon-doped composite material was deposited on the surface and within the pores of the porous carbon matrix to obtain a doped silicon deposit.

[0068] Step 120: Under a nitrogen protective atmosphere, the temperature is reduced to 500°C, and nitrogen is used as a carrier gas to enter the molten aluminum isopropoxide. The aluminum isopropoxide vapor is carried into the reactor by bubbling, while oxygen is introduced. The nitrogen flow rate is 10 L / min, the oxygen flow rate is 1 L / min, and the deposition time is 100 min, forming a discontinuous aluminum oxide mask modification layer on the silicon surface.

[0069] Step 130: Under a nitrogen protective atmosphere, the temperature is reduced to 350°C, and a mixed gas of nitrogen trifluoride (1 L / min) and nitrogen (9 L / min) is introduced for etching for 45 min. The alumina mask layer guides the etching gas to selectively etch silicon along the thickness direction, and the nitrogen doping element induces random formation of etching channels inside the silicon-doped composite material layer, forming a unit layer with through channels. Part of the mask layer remains on the inner wall and surface of the channels, resulting in a porous silicon / carbon composite material with the first unit layer.

[0070] Step 140: On the porous silicon / carbon composite material with the first unit layer, steps 110 to 130 are repeated three times to form the second, third, and fourth unit layers, respectively. The pores of each porous silicon unit layer are interconnected, forming a three-dimensional random pore interconnection network that runs from the inside out.

[0071] Step 150: After purging the obtained material with argon, acetylene gas (2 L / min) and nitrogen gas (8 L / min) are introduced and treated at 540°C for 60 min to form a thin carbon coating to prevent spontaneous combustion during discharge.

[0072] Step 160: The pre-coated material is transferred to a chemical vapor deposition (CVD) reactor, heated to 540°C, and ethylene gas (4 L / min) and nitrogen gas (6 L / min) are introduced. Chemical vapor deposition is carried out for 2 h to form a complete carbon coating layer on the outermost layer, and finally the porous silicon-carbon composite material prepared in this embodiment is obtained.

[0073] The total carbon content of the silicon-carbon composite anode material prepared in this embodiment was determined to be 41.23 wt% using a carbon-sulfur analyzer (CS-2800G); the silicon content was calculated to be 56.02 wt% using X-ray fluorescence spectroscopy (XRF); the nitrogen content was found to be 1.98 wt% using an oxygen-nitrogen-hydrogen analyzer, with nitrogen accounting for 3.41 wt% of silicon; and the specific surface area of ​​the silicon-carbon composite anode material prepared in this embodiment was determined to be 2.18 m² using a specific surface area and pore size analyzer (BSD-660S) via nitrogen adsorption-desorption method. 2 / g.

[0074] The specific process for assembling a half-cell (CR2032 coin cell) using the porous silicon / carbon composite material prepared in this embodiment is as follows: Electrode preparation: The silicon-carbon composite material, conductive additive carbon black, and binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:1) prepared in this embodiment are weighed at a mass ratio of 95:2:3 and placed in a pulping machine at room temperature to prepare slurry; the prepared slurry is evenly coated on copper foil and dried in a forced-air drying oven at 50°C for 2 hours, then cut into 8×8mm electrode sheets and placed in a vacuum drying oven at 100°C for 10 hours; the dried electrode sheets are then transferred to a glove box for later use in battery assembly.

[0075] Assemble the half-cell: The assembly is carried out in a glove box containing a high-purity Ar atmosphere. Lithium metal is used as the counter electrode, and a solution of ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v=1:1) containing 1 mol / L LiPF6 is used as the electrolyte. Polyethylene is used as the separator, and the half-cell is assembled together with the electrode prepared in the previous step.

[0076] The assembled half-cells were tested using a Blue Electricity tester in constant current charge-discharge mode. The discharge cutoff voltage was 0.005V, and the charge cutoff voltage was 2V. Charge-discharge testing was conducted at a 0.1C rate. At 0.8V, the charging specific capacity was 1919.83 mAh / g, with an initial coulombic efficiency of 81.50%; the intercalation-discharge specific capacity was 2355.62 mAh / g. "Intercalation-discharge specific capacity" represents the reversible lithium intercalation capacity per unit mass of material during discharge in the test system.

[0077] The charge-discharge curve of the half-cell assembled in this embodiment is as follows: Figure 3 As shown, the horizontal axis represents specific capacity (mAh / g), and the vertical axis represents voltage (V).

[0078] The half-cell was disassembled after testing, and the electrode thickness expansion rate was measured to be 65.23%. The formula for calculating the electrode thickness expansion rate is: Electrode thickness expansion rate = (Electrode thickness after testing - Electrode thickness before testing) × 100%.

[0079] The unit lithium intercalation expansion rate was calculated as: Unit lithium intercalation expansion rate = Electrode sheet thickness expansion rate / Lithium intercalation capacity × 100%. Detailed data are shown in Table 1. In this application, "lithium intercalation capacity" under the electrochemical test conditions of this embodiment is equivalent to "intercalation-discharge specific capacity," both representing the reversible lithium intercalation capacity per unit mass of the material during discharge in the test system.

[0080] Example 2 This embodiment prepares a silicon-carbon composite material with four stacked unit layers.

[0081] The difference from Example 1 is that the doping source precursor used in step 110 is phosphine (PH3). The remaining process conditions and methods are the same as in Example 1.

[0082] The total carbon content of the silicon-carbon composite anode material prepared in this embodiment was determined to be 42.09 wt% using a carbon-sulfur analyzer (CS-2800G). Combined with X-ray fluorescence spectroscopy (XRF) analysis, the silicon content was calculated to be 55.31 wt%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) revealed a phosphorus content of 2.03 wt%, representing 3.54 wt% of silicon, and an aluminum content of 980 ppm. The specific surface area of ​​the silicon-carbon composite anode material prepared in this embodiment was determined to be 2.03 m² using a nitrogen adsorption-desorption method and a specific surface area and pore size analyzer (BSD-660S). 2 / g.

[0083] The assembled half-cells were tested using a Blue Electricity tester in constant current charge-discharge mode. The discharge cutoff voltage was 0.005V, and the charge cutoff voltage was 2V. Charge-discharge testing was conducted at a 0.1C rate. At 0.8V, the charging specific capacity was 1950.98 mAh / g, with an initial coulombic efficiency of 82.20%; the intercalation-discharge specific capacity was 2373.45 mAh / g. The electrode sheet thickness expansion rate was measured to be 60.45%.

[0084] Example 3 This embodiment prepares a silicon-carbon composite material with four stacked unit layers.

[0085] The difference from Example 1 is that the doping source precursor used in step 110 is acetylene (C2H2). The remaining process conditions and methods are the same as in Example 1.

[0086] The total carbon content of the silicon-carbon composite anode material prepared in this embodiment was determined to be 43.43 wt% using a carbon-sulfur analyzer (CS-2800G). Combined with X-ray fluorescence spectroscopy (XRF) analysis, the silicon content was calculated to be 55.42 wt%, and the aluminum content to be 1020 ppm. The specific surface area of ​​the silicon-carbon composite anode material prepared in this embodiment was determined to be 2.42 m² using a nitrogen adsorption-desorption method and a specific surface area and pore size analyzer (BSD-660S). 2 / g.

[0087] The assembled half-cells were tested using a Blue Electric Tester in constant current charge-discharge mode. The discharge cutoff voltage was 0.005V, and the charge cutoff voltage was 2V. Charge-discharge tests were conducted at a 0.1C rate. At 0.8V, the charging specific capacity was 1904.19 mAh / g, with an initial coulombic efficiency of 81.60%; the intercalation-discharge specific capacity was 2333.57 mAh / g. The electrode sheet thickness expansion rate was measured to be 72.18%. Example 4 This embodiment prepares a silicon-carbon composite material with four layers of multi-unit stacked layers.

[0088] The difference from Example 1 is that the doping source precursor used in step 110 is CO2. The remaining process conditions and methods are the same as in Example 1.

[0089] The total carbon content of the silicon-carbon composite anode material prepared in this embodiment was determined to be 41.59 wt% using a carbon-sulfur analyzer (CS-2800G). Combined with X-ray fluorescence spectroscopy (XRF) analysis, the silicon content was calculated to be 54.35 wt%, and the aluminum content to be 990 ppm. The specific surface area of ​​the silicon-carbon composite anode material prepared in this embodiment was determined to be 2.30 m² using a nitrogen adsorption-desorption method and a specific surface area and pore size analyzer (BSD-660S). 2 / g.

[0090] The assembled half-cells were tested using a Blue Electricity tester in constant current charge-discharge mode. The discharge cutoff voltage was 0.005V, and the charge cutoff voltage was 2V. Charge-discharge tests were conducted at a 0.1C rate. At 0.8V, the charging specific capacity was 1864.10 mAh / g, with an initial coulombic efficiency of 80.30%; the intercalation-discharge specific capacity was 2321.42 mAh / g. The electrode sheet thickness expansion rate was measured to be 68.76%.

[0091] Example 5 This embodiment prepares a silicon-carbon composite material with two stacked unit layers.

[0092] The difference from Example 1 is that the chemical vapor deposition time in step 110 is 100 min, and the number of repetitions in step 140 is 1. The remaining process conditions and methods are the same as in Example 1.

[0093] The total carbon content of the silicon-carbon composite anode material prepared in this embodiment was determined to be 41.29 wt% using a carbon-sulfur analyzer (CS-2800G). Combined with X-ray fluorescence spectroscopy (XRF) analysis, the silicon content was calculated to be 55.63 wt%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) yielded a phosphorus content of 2.01 wt%, representing 3.49 wt% of silicon, and an aluminum content of 1010 ppm. The specific surface area of ​​the silicon-carbon composite anode material prepared in this embodiment was determined to be 2.12 m² using a nitrogen adsorption-desorption method and a specific surface area and pore size analyzer (BSD-660S). 2 / g.

[0094] The assembled half-cells were tested using a Blue Electricity tester in constant current charge-discharge mode. The discharge cutoff voltage was 0.005V, and the charge cutoff voltage was 2V. Charge-discharge tests were conducted at a 0.1C rate. At 0.8V, the charging specific capacity was 1934.94 mAh / g, with an initial coulombic efficiency of 83.00%; the intercalation-discharge specific capacity was 2331.25 mAh / g. The electrode sheet thickness expansion rate was measured to be 98.52%.

[0095] Example 6 This embodiment prepares a silicon-carbon composite material with 6 stacked unit layers.

[0096] The difference from Example 1 is that the chemical vapor deposition time in step 110 is 33 min, and the number of repetitions in step 140 is 5. The remaining process conditions and methods are the same as in Example 1.

[0097] The total carbon content of the silicon-carbon composite anode material prepared in this embodiment was determined to be 41.45 wt% using a carbon-sulfur analyzer (CS-2800G). Combined with X-ray fluorescence spectroscopy (XRF) analysis, the silicon content was calculated to be 55.83 wt%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) yielded a phosphorus content of 2.05 wt%, representing 3.54 wt% of silicon. The aluminum content was 1040 ppm. The specific surface area of ​​the silicon-carbon composite anode material prepared in this embodiment was determined to be 2.48 m² using a nitrogen adsorption-desorption method and a specific surface area and pore size analyzer (BSD-660S). 2 / g.

[0098] The assembled half-cells were tested using a Blue Electricity tester in constant current charge-discharge mode. The discharge cutoff voltage was 0.005V, and the charge cutoff voltage was 2V. Charge-discharge tests were conducted at a 0.1C rate. At 0.8V, the charging specific capacity was 1920.04 mAh / g, with an initial coulombic efficiency of 80.90%; the intercalation-discharge specific capacity was 2373.35 mAh / g. The electrode sheet thickness expansion rate was measured to be 47.33%.

[0099] Comparative Example 1 Step 110, take 500g of material with a specific surface area of ​​2000 m². 2 / g, pore volume 1.5 cm 3 A porous activated carbon matrix with an average pore size of 2.5 nm was placed in a fluidized bed reactor and heated to 520 °C at a rate of 5 °C / min under a nitrogen protective atmosphere. A mixture of silane gas (flow rate 3 L / min) and nitrogen gas (flow rate 7 L / min) was introduced, and chemical vapor deposition was performed for 50 min to deposit silicon on the surface and within the pores of the porous carbon matrix, thus obtaining a silicon deposit.

[0100] Steps 120-160 are the same as in Example 1.

[0101] The total carbon content of the silicon-carbon composite anode material prepared in this embodiment was determined to be 41.68 wt% using a carbon-sulfur analyzer (CS-2800G). Combined with X-ray fluorescence spectroscopy (XRF) analysis, the silicon content was calculated to be 57.45 wt%, and the aluminum content to be 960 ppm. The specific surface area of ​​the silicon-carbon composite anode material prepared in this embodiment was determined to be 2.01 m² using a nitrogen adsorption-desorption method and a specific surface area and pore size analyzer (BSD-660S). 2 / g.

[0102] The assembled half-cells were tested using a Blue Electricity tester in constant current charge-discharge mode. The discharge cutoff voltage was 0.005V, and the charge cutoff voltage was 2V. Charge-discharge tests were conducted at a 0.1C rate. At 0.8V, the charging specific capacity was 2022.44 mAh / g, with an initial coulombic efficiency of 83.80%; the intercalation-discharge specific capacity was 2413.41 mAh / g. The electrode sheet thickness expansion rate was measured to be 138.27%.

[0103] Comparative Example 2 Step 110, take 500g of material with a specific surface area of ​​2000 m². 2 / g, pore volume 1.5 cm 3A porous activated carbon matrix with an average pore size of 2.5 nm was placed in a fluidized bed reactor and heated to 520 °C at a rate of 5 °C / min under a nitrogen protective atmosphere. A mixture of silane gas (flow rate 3 L / min), PH3 (flow rate 0.2 L / min), and nitrogen gas (flow rate 7 L / min) was introduced, and chemical vapor deposition was performed for 200 min to deposit silicon-doped composite material on the surface and within the pores of the porous carbon matrix, resulting in a doped silicon deposit.

[0104] Step 120: Under a nitrogen protective atmosphere, the temperature is reduced to 500°C, and nitrogen is used as a carrier gas to enter the molten aluminum isopropoxide. The aluminum isopropoxide vapor is carried into the reactor by bubbling, while oxygen is introduced. The nitrogen flow rate is 10 L / min, the oxygen flow rate is 1 L / min, and the deposition time is 100 min, forming a discontinuous aluminum oxide mask modification layer on the silicon surface.

[0105] Step 130: Under a nitrogen protective atmosphere, the temperature is reduced to 350°C, and a mixed gas of nitrogen trifluoride (1 L / min) and nitrogen (9 L / min) is introduced for etching for 180 min. The alumina mask layer guides the etching gas to selectively etch silicon along the thickness direction, and the doped nitrogen element induces random formation of etching channels inside the silicon-doped composite material layer, forming a unit layer with through channels. Part of the mask layer remains on the inner wall and surface of the channels, resulting in a porous silicon / carbon composite material with the first unit layer.

[0106] Step 140: After purging the obtained material with argon, acetylene gas (2 L / min) and nitrogen gas (8 L / min) are introduced and treated at 540℃ for 60 min to form a thin carbon coating to prevent spontaneous combustion during discharge.

[0107] Step 150: The pre-coated material is transferred to a chemical vapor deposition (CVD) reactor, heated to 540°C, and ethylene gas (4 L / min) and nitrogen gas (6 L / min) are introduced. Chemical vapor deposition is carried out for 2 h to form a complete carbon coating layer on the outermost layer, and finally the porous silicon / carbon composite material prepared in this comparative example is obtained.

[0108] The total carbon content of the silicon-carbon composite anode material prepared in this embodiment was determined to be 41.76 wt% using a carbon-sulfur analyzer (CS-2800G). Combined with X-ray fluorescence spectroscopy (XRF) analysis, the silicon content was calculated to be 55.61 wt%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) yielded a phosphorus content of 1.97 wt%, representing 3.42 wt% of silicon, and an aluminum content of 990 ppm. The specific surface area of ​​the silicon-carbon composite anode material prepared in this embodiment was determined to be 2.23 m² using a nitrogen adsorption-desorption method and a specific surface area and pore size analyzer (BSD-660S). 2 / g.

[0109] The assembled half-cells were tested using a Blue Electricity tester in constant current charge-discharge mode. The discharge cutoff voltage was 0.005V, and the charge cutoff voltage was 2V. Charge-discharge tests were conducted at a 0.1C rate. At 0.8V, the charging specific capacity was 1871.11 mAh / g, with an initial coulombic efficiency of 80.10%; the intercalation-discharge specific capacity was 2335.97 mAh / g. The electrode sheet thickness expansion rate was measured to be 162.84%.

[0110] Comparative Example 3 Step 110, take 500g of material with a specific surface area of ​​2000 m². 2 / g, pore volume 1.5 cm 3 A porous activated carbon matrix with an average pore size of 2.5 nm was placed in a fluidized bed reactor and heated to 520 °C at a rate of 5 °C / min under a nitrogen protective atmosphere. A mixture of silane gas (flow rate 3 L / min), PH3 (flow rate 0.2 L / min), and nitrogen gas (flow rate 7 L / min) was introduced and chemical vapor deposition was performed for 50 min. Silicon-doped composite material was deposited on the surface and in the pores of the porous carbon matrix to obtain a doped silicon deposit.

[0111] Step 120: Under a nitrogen protective atmosphere, the temperature is reduced to 350°C, and a mixed gas of nitrogen trifluoride (1 L / min) and nitrogen (9 L / min) is introduced for etching for 45 min. The alumina mask layer guides the etching gas to selectively etch silicon along the thickness direction, and the nitrogen doping element induces random formation of etching channels inside the silicon-doped composite material layer, forming a unit layer with through channels. Part of the mask layer remains on the inner wall and surface of the channels, resulting in a porous silicon / carbon composite material with the first unit layer.

[0112] Step 130: On the porous silicon / carbon composite material having the first unit layer, repeat steps 110 to 120 three times to form the second, third and fourth unit layers respectively.

[0113] Step 140: After purging the obtained material with argon, acetylene gas (2 L / min) and nitrogen gas (8 L / min) are introduced and treated at 540℃ for 60 min to form a thin carbon coating to prevent spontaneous combustion during discharge.

[0114] Step 150: The pre-coated material is transferred to a chemical vapor deposition (CVD) reactor, heated to 540°C, and ethylene gas (4 L / min) and nitrogen gas (6 L / min) are introduced. Chemical vapor deposition is carried out for 2 h to form a complete carbon coating layer on the outermost layer, and finally the porous silicon-carbon composite material prepared in this comparative example is obtained.

[0115] The total carbon content of the silicon-carbon composite anode material prepared in this embodiment was determined to be 41.79 wt% using a carbon-sulfur analyzer (CS-2800G). Combined with X-ray fluorescence spectroscopy (XRF) analysis, the silicon content was calculated to be 55.18 wt%. Inductively coupled plasma atomic emission spectrometry (ICP-AES) yielded a phosphorus content of 2.02 wt%, representing 3.53 wt% of silicon, and an aluminum content of 25 ppm. The specific surface area of ​​the silicon-carbon composite anode material prepared in this embodiment was determined to be 2.38 m² using a nitrogen adsorption-desorption method and a specific surface area and pore size analyzer (BSD-660S). 2 / g.

[0116] The assembled half-cells were tested using a Blue Electricity tester in constant current charge-discharge mode. The discharge cutoff voltage was 0.005V, and the charge cutoff voltage was 2V. Charge-discharge tests were conducted at a 0.1C rate. At 0.8V, the charging specific capacity was 1852.33 mAh / g, with an initial coulombic efficiency of 79.90%; the intercalation-discharge specific capacity was 2318.31 mAh / g. The electrode sheet thickness expansion rate was measured to be 145.91%.

[0117] The materials and batteries prepared in the above embodiments and comparative examples were subjected to performance tests, and the test results are recorded in Table 1.

[0118] Table 1 The test data in Table 1 show that the initial coulombic efficiency of Examples 1-4 is higher than that of Comparative Examples 1-3, and the coin cell expansion rate of Examples 1-4 is lower than that of Comparative Examples 1-3. Example 2 (phosphorus doping, 4-layer stacked in-situ hetero-doped porous silicon unit layer) is then compared and analyzed with each comparative example.

[0119] Comparative Example 1 used undoped pure silicon (4-layer cyclic stacking) without introducing an etch-resistant dopant phase. The coin cell expansion rates of Example 2 and Comparative Example 1 were 60.45% and 138.27%, respectively, with Comparative Example 1 showing a significantly higher expansion rate than Example 2. This is because Comparative Example 1 lacked randomly distributed dopant phases as etch-blocking sites, resulting in regularly oriented etched channels. During charging and discharging, stress concentrated along the channel direction, leading to material pulverization. In contrast, Example 2 introduced phosphorus through co-deposition, generating etch-resistant SiP in situ. x During the etching process, the phase forms randomly distributed blocking sites, forcing the channels to bend and interconnect, effectively dispersing stress, and thus significantly reducing the expansion rate.

[0120] Comparative Example 2 used phosphorus doping but without multi-layer cyclic stacking (single-layer thick silicon deposition). The coin cell expansion rate of Comparative Example 2 was 162.84%, which was much higher than that of Example 2 (60.45%). This shows that if only a single thick silicon deposition and etching is performed, the fluorine-containing etching gas cannot penetrate into the interior of the particles, and the channels are limited to the surface, while the interior remains dense silicon. Even if the etching time is extended, the surface silicon is excessively consumed or even collapses, and a network of channels that runs from the inside out cannot be formed. In contrast, Example 2, through four-layer cyclic stacking (etching immediately after each thin layer deposition), constructs through channels layer by layer, which uniformly distributes the expansion stress and significantly improves the structural integrity.

[0121] Comparative Example 3 employed phosphorus doping and a 4-layer cyclic stack, but omitted the mask deposition step. The coin cell expansion rate of Comparative Example 3 was 145.91%, and the first-cycle coulombic efficiency was only 79.90%, both inferior to Example 2 (expansion rate 60.45%, first-cycle efficiency 82.20%). The aluminum content in Comparative Example 3 was only 25 ppm (far lower than the 980 ppm in Example 2), confirming the absence of a mask layer. Without a mask, etching lost its directional control, and the fluorine-containing gas excessively expanded laterally, leading to severe hole wall collapse and a significant decrease in capacity and first-cycle efficiency. Example 2 used an Al2O3 mask (approximately 3 nm thick), which preferentially guided the gas along the mask's weak points during etching, while simultaneously suppressing lateral expansion, thereby forming structurally intact and stress-dispersed random channels.

[0122] In this invention, a balance exists between silicon loading and performance: Examples 1-4 demonstrate that the dopant content can be adjusted by controlling the co-deposition time, thereby achieving a balance between capacity and expansion rate. Example 2 (phosphorus doping) exhibits the best overall performance (expansion rate 60.45%, first-time efficiency 82.20%), while Example 3 (carbon doping) provides a higher discharge specific capacity (2333.57 mAh / g) but a slightly higher expansion rate (72.18%). Examples 5 (2-layer cyclic stacking) and 6 (6-layer cyclic stacking) further demonstrate that increasing the number of layers reduces the expansion rate (98.52%→60.45%→47.33%), but with a slight sacrifice in capacity. This proves that the preparation method has good controllability and can be directionally designed according to the needs of different application scenarios (e.g., high energy density or long cycle life).

[0123] Examples 1-4 of this invention demonstrate initial coulombic efficiency (80.30%–82.20%) comparable to all comparative examples (initial efficiency 79.90%–83.80%), and superior volume expansion (60.45%–72.18%) control compared to all comparative examples (138.27%–162.84%). This indicates that the silicon-carbon composite anode material provided by these embodiments exhibits outstanding comprehensive performance advantages. This is attributed to the synergistic effect of "in-situ heterogeneous doping-induced random channels," "cyclic stacking layer-by-layer pore formation," and "Al2O3 mask + pre-coating + secondary carbon coating." The randomly distributed etch-resistant doped phases enable the channels to bend and interconnect, avoiding stress concentration; the cyclic stacking structure overcomes the limitations of etching gas mass transfer, achieving uniform through-channels from the inside out; the Al2O3 mask precisely guides the etching direction, while the pre-coating and secondary carbon coating construct a robust interface protective layer. This structural design, characterized by "internal sparseness and external stability with doping assistance," systematically solves the three core problems of silicon anodes—volume expansion, stress concentration, and interface instability—from the material source.

[0124] The in-situ hetero-doped multi-level random porous silicon-carbon composite material provided in this embodiment of the invention achieves a significant improvement in material structural stability and electrochemical performance.

[0125] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. 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. An in-situ hetero-doped multi-level random porous silicon-carbon composite material, characterized in that, The composite material includes: Porous carbon matrix serves as a supporting framework; Multilayered, in-situ hetero-doped porous silicon unit layers are loaded onto the surface and pores of a porous carbon matrix. Each in-situ hetero-doped porous silicon unit layer comprises silicon material and a dopant element material hetero-doped in the silicon material. The in-situ hetero-doped porous silicon unit layers have interconnected channels, forming a continuous three-dimensional random channel interconnection network within the composite material. Each in-situ hetero-doped porous silicon unit layer is prepared by gas-phase co-deposition of a gaseous silicon source and a dopant source precursor to form a silicon-doped composite material, followed by masking and selective etching. The dopant element includes at least one of C, N, O, P, and B. In the silicon-doped composite material, the dopant element is randomly distributed in the silicon matrix, and the atomic percentage of the dopant element in silicon is 0.2-20 wt%. The dopant element is used to induce random channel formation. The mask modification layer is discretely distributed on the surface of each unit layer and the inner wall of the pores.

2. The composite material of claim 1, wherein, The porous carbon matrix comprises one or more of activated carbon, porous expanded graphite, graphene, or carbon fiber; the specific surface area of ​​the porous carbon matrix is ​​500-2500 m². 2 / g, pore volume 0.3-5.0 cm³ 3 / g, pore size 0.6-10 nm, ash content less than 0.5%; The diameter of the through-hole is 0.15-1.2 nm; the total porosity of the multilayer stacked in-situ hetero-doped porous silicon unit layer is 5%-60%; the number of stacked layers of the in-situ hetero-doped porous silicon unit layer is 2-6. The material of the mask modification layer includes one or more of silicon oxide, silicon nitride, aluminum oxide, or silicon carbide; the thickness of the mask modification layer is 1-20 nm.

3. The composite material of claim 1, wherein, The composite material also includes a pre-coating layer on the outer layer and a carbon coating layer on the outermost layer; the pre-coating layer is a pre-coated carbon layer or a pre-coated alumina layer.

4. A method for preparing in-situ hetero-doped multi-stage random-pore silicon-carbon composite material, characterized in that, The preparation method includes: Step 1: Place the porous carbon matrix in a reactor and heat it to the silicon deposition temperature under a protective atmosphere. Then, introduce a first mixed gas containing a gaseous silicon source and a dopant source precursor to perform chemical vapor deposition. Deposit a silicon-doped composite material layer in the pores of the porous carbon matrix to obtain a composite material with a silicon-doped composite material layer. In the silicon-doped composite material, the dopant elements are randomly distributed in the silicon matrix. Step 2: Adjust the temperature inside the reactor to the mask deposition temperature under a protective atmosphere, introduce a second mixed gas containing the mask precursor, and deposit island-shaped and / or block-shaped discontinuous mask modification layers on the surface and pores of the composite material with silicon-doped composite material layer to obtain a composite material with mask coverage. Step 3: Under a protective atmosphere, adjust the temperature inside the reactor to the etching temperature, and introduce a third mixed gas containing fluorine-containing etching gas to selectively etch the composite material covered by the mask. The etching gas is guided by the mask modification layer to etch silicon along the thickness direction on the silicon-doped composite material layer in the area not covered by the mask modification layer. The etching selectivity of the etching gas for silicon is higher than that for the dopant element. The dopant element induces the random formation of the pores etched in the silicon-doped composite material layer, thereby forming a first in-situ heterogeneous doped porous silicon unit layer with through-holes in the composite material. At the same time, part of the mask modification layer is retained on the inner wall and surface of the pores. Step 4: Repeat steps 1 to 3 for N times, sequentially forming a second in-situ hetero-doped porous silicon unit layer to an (N+1)th in-situ hetero-doped porous silicon unit layer with through-holes in the composite material, and the pores of each unit layer are interconnected to form a through-hole three-dimensional random pore interconnection network in the composite material; N is an integer greater than or equal to 1.

5. The preparation method according to claim 4, characterized in that, The protective atmosphere includes one or more of argon, nitrogen, or helium; In step 1, the silicon deposition temperature is 300-700 ℃, and the deposition time is 10-120 min; the gaseous silicon source includes one or more of silane, dichlorosilane, trichlorosilane, or silicon tetrachloride; the doping source precursor includes one or more of methane, acetylene, ammonia, oxygen, carbon dioxide, carbon monoxide, phosphine, or diborane; the first mixed gas also includes a carrier gas, which includes one or more of argon, nitrogen, or helium. In step 2, the mask deposition temperature is 300-750 ℃, and the deposition time is 5-200 min; the mask precursor includes one or more of oxygen, water vapor, carbon dioxide, carbon monoxide, ammonia, methane, ethylene or acetylene, and one or more of aluminum isopropoxide, trimethylaluminum or gaseous silicon source; the second mixed gas also includes a carrier gas, which includes one or more of argon, nitrogen or helium; In step 3, the etching temperature is 400-600 ℃, and the etching time is 30-300 min; the fluorine-containing etching gas includes one or more of carbon tetrafluoride, fluoromethane, sulfur hexafluoride, or nitrogen trifluoride; the third mixed gas also includes a carrier gas, which includes one or more of argon, nitrogen, or helium; the volume ratio of the fluorine-containing etching gas to the carrier gas is 1:10-1:

100.

6. The preparation method according to claim 4, characterized in that, The method further includes: The composite material with a three-dimensional random channel interconnection network obtained in step 4 is pre-coated after being purged with inert gas. The pre-coated composite material is subjected to secondary carbon coating by chemical vapor deposition or liquid phase impregnation-pyrolysis to obtain the porous silicon / carbon composite material with three-dimensional through channels.

7. The preparation method according to claim 6, characterized in that, The pre-coating process specifically involves forming a pre-coated carbon layer or a pre-coated alumina layer through chemical vapor deposition; wherein the carbon source gas for forming the pre-coated carbon layer includes one or more of methane, ethylene, or acetylene; the precursor for forming the pre-coated alumina layer includes trimethylaluminum or aluminum isopropoxide, and an oxidizing gas is simultaneously introduced; the pre-coating process takes 5-60 minutes. The process conditions for the chemical vapor deposition method are as follows: a carbon source for vapor deposition is introduced at a temperature of 500-750 °C for 1-4 h; the carbon source for vapor deposition includes one or more of methane, ethylene, or acetylene. The process conditions for the liquid phase impregnation-pyrolysis method are as follows: the pre-coated composite material is impregnated in a carbon precursor solution for 3-8 hours, then removed and dried, and carbonized at 800-1100 °C for 1-4 hours under a protective atmosphere; the carbon precursor includes one or more of sucrose, glucose, phenolic resin or asphalt.

8. The preparation method according to claim 4, characterized in that, In step 3, the etching is performed using plasma-assisted etching, which involves introducing a radio frequency power supply or a microwave power supply into the reactor to excite the fluorine-containing etching gas to form plasma, thereby increasing the concentration of etching active particles.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the in-situ hetero-doped multi-level random channel silicon-carbon composite material according to any one of claims 1-3, or the in-situ hetero-doped multi-level random channel silicon-carbon composite material prepared by the preparation method according to any one of claims 4-8.

10. An energy storage device, characterized in that, The energy storage device includes: a lithium-ion battery or a lithium-ion capacitor; the energy storage device includes the in-situ hetero-doped multi-level random channel silicon-carbon composite material according to any one of claims 1-3, or includes the in-situ hetero-doped multi-level random channel silicon-carbon composite material prepared by the preparation method according to any one of claims 4-8, or includes the negative electrode sheet according to claim 9.

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