Multi-level densified silicon-carbon negative electrode material, and preparation method and application thereof

Abstract

The present application relates to a kind of multi-level densification silicon-carbon negative electrode material and its preparation method and application.Silicon-carbon negative electrode material includes: porous carbon matrix;Multi-layer composite shell, is loaded on the surface and pore of porous carbon matrix;Multi-layer composite shell includes the multi-layer silicon layer and the multi-layer carbon layer that are sequentially arranged alternately from inside to outside, wherein, the outermost one is outer carbon layer;Each silicon layer includes at least part of silicon layer and the micro-nano void structure formed by selective etching of fluorine-containing gas, micro-nano void structure includes the recess, hole or columnar gap formed in the surface and / or inside of silicon layer, and, at least part of micro-nano void structure is not filled with silicon material, is reserved as the reserved space for buffering the volume expansion of silicon layer;The carbon layer in multi-layer composite shell is gradient densification structure;Gradient densification structure is specifically: along radial direction, from the inner carbon layer closest to porous carbon matrix to outer carbon layer, the density of each carbon layer is gradually increased, and the porosity is gradually decreased.

Description

Technical Field

[0001] This invention relates to the field of new energy battery technology, and in particular to a multi-layered densified silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of the electric vehicle and energy storage industries, higher demands are being placed on the energy density of lithium-ion batteries. Silicon, due to its extremely high theoretical specific capacity, is considered an important choice for next-generation lithium-ion battery anode materials. However, silicon undergoes dramatic volume expansion during charging and discharging, which can easily lead to material pulverization, electrode structure damage, and instability of the solid electrolyte interface film, severely limiting the practical application of silicon-based anode materials.

[0003] To alleviate the aforementioned problems, existing technologies typically employ silicon nanostructuring, silicon / carbon composites, and porous structure designs to improve the cycle stability of silicon anode materials. Among these, the technique of using porous carbon as a framework and depositing silicon on the surface or within the pores of the porous carbon has attracted attention. Carbon materials can provide a conductive network and, to some extent, buffer the volume changes of silicon, thus they are often used to construct silicon-carbon composite anode materials.

[0004] However, the single-layer or simple double-layer carbon coating structures commonly found in existing silicon-carbon anode materials still have significant shortcomings. If the carbon layer is too dense, although it can provide good conductivity and interface protection, it is difficult to accommodate the volume expansion of the inner silicon layer during lithium intercalation, which can easily lead to cracking of the outer carbon shell. If the carbon layer is relatively loose, although it can reserve some space for silicon expansion, its conductivity and structural strength are insufficient, and the electrolyte can easily penetrate into the interior, continuously reacting with the silicon material, resulting in repeated formation and rupture of the solid electrolyte interface film.

[0005] Furthermore, the formation of reserved spaces in existing technologies typically relies on template-based pore creation or simple porous structure design, which involves complex processes and makes it difficult to precisely control the location, size, and distribution density of the reserved spaces, thus failing to match the expansion behavior of different silicon layers. Simultaneously, a single carbon coating layer cannot provide gradient protection for the internal multi-level porous structure. After long-term cycling, localized stress concentration can easily lead to carbon layer cracking, interlayer delamination, and further electrolyte penetration, thereby exacerbating side reactions and reducing cycle life. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a multi-layered densified silicon-carbon anode material, its preparation method, and its applications. The silicon-carbon anode material of this invention has a composite structure with alternating layers of silicon and carbon. The silicon layers retain micro-nano void structures to buffer volume expansion, while the carbon layers exhibit a gradient densification distribution from the inside out. This structure provides the inner layer region with good expansion buffering capacity and the outer layer region with high structural protection and conductivity, thereby reducing material pulverization, carbon layer cracking, and interfacial side reactions caused by silicon layer expansion, and improving the cycle stability, structural integrity, and electrochemical performance of the silicon-carbon anode material. To achieve the above objectives, in a first aspect, the present invention provides a multi-layered densified silicon-carbon anode material, comprising: Porous carbon matrix, serving as a supporting framework; A multi-layered composite shell is loaded on the surface and within the pores of the porous carbon matrix; The multilayer composite shell includes multiple silicon layers and multiple carbon layers arranged alternately from the inside to the outside, wherein the outermost layer is the outer carbon layer; the remaining carbon layers other than the outer carbon layer are the inner carbon layers. Each silicon layer includes at least a portion of the silicon layer formed by selective etching with a fluorine-containing gas to form micro-nano void structures. The micro-nano void structures include depressions, pores, or columnar gaps formed on the surface and / or inside the silicon layer. Furthermore, at least a portion of the micro-nano void structures are not filled with silicon material and are reserved as space to buffer the volume expansion of the silicon layer. The carbon layers in the multilayer composite shell have a gradient densification structure; specifically, the gradient densification structure means that, along the radial direction, from the inner carbon layer closest to the porous carbon matrix to the outer carbon layer, the density of each carbon layer increases and the porosity decreases layer by layer.

[0007] Preferably, the average depth of the micro / nano void structure in each layer is 5 nm to 100 nm, accounting for 10% to 50% of the thickness of the corresponding silicon layer; The etching degree of each silicon layer is different. Along the radial direction from the inside to the outside, the etching degree gradually decreases, the micro-nano void structure decreases layer by layer, and the reserved space decreases layer by layer.

[0008] Preferably, the porosity of the outer carbon layer is less than 5%, and the porosity of the inner carbon layer is 30% to 60%. The density variation rate between two adjacent inner carbon layers is 5% to 20%.

[0009] Preferably, the thickness of a single silicon layer is 10 nm to 200 nm, the thickness of a single inner carbon layer is 20 nm to 300 nm, and the thickness of an outer carbon layer is 10 nm to 100 nm; the total number of silicon and carbon layers in the multilayer composite shell is less than or equal to 10 layers.

[0010] Preferably, the silicon layer is an amorphous silicon layer or a nanocrystalline silicon layer; the porous carbon matrix includes one or more of activated carbon, porous expanded graphite, graphene, carbon nanotubes, hard carbon, soft carbon, or carbon fiber.

[0011] Secondly, embodiments of the present invention provide a method for preparing the multi-layered densified silicon-carbon anode material described in the first aspect above, comprising: Step 1: In an inert atmosphere, a porous carbon matrix is ​​placed into a reactor, and a first mixed gas of silicon source gas and inert gas is introduced to deposit a silicon layer on the surface and in the pores of the porous carbon matrix. Step 2: A second mixed gas containing fluorine etching gas and inert gas is introduced to selectively etch the silicon layer, forming depressions, holes or columnar gaps on the surface and / or inside the silicon layer. Step 3: A third mixed gas containing carbon source gas and inert gas is introduced to deposit a carbon layer on the etched silicon layer surface; after the deposition, at least some of the depressions, holes or columnar gaps are not filled by carbon material, and are reserved as reserved space for buffering the volume expansion of the silicon layer. Step 4: Repeat steps 1 to 3 for N times to alternately deposit silicon and carbon layers. Each time step 2 is repeated, the etching time is gradually shortened to form a structure in which the etching degree gradually decreases from the inside to the outside in the radial direction, the micro-nano void structure decreases layer by layer, and the reserved space decreases layer by layer. Furthermore, each time step 3 is performed, the reaction temperature and / or the volume ratio of carbon source gas to inert gas in the third mixed gas and / or the deposition time are changed to form a structure in which the density of each carbon layer increases layer by layer and the porosity decreases layer by layer in the radial direction from the inside to the outside. N is an integer greater than or equal to 1.

[0012] Preferably, in step 1, the silicon source gas includes one or more of silane, silane, propane, trichlorosilane, or silicon tetrachloride; the inert gas includes one or more of nitrogen, argon, or helium; the silicon deposition temperature is 300℃~650℃, and the deposition time is 3 h~24 h. In step 2, the fluorine-containing etching gas includes one or more of nitrogen trifluoride, sulfur hexafluoride, carbon tetrafluoride, or fluoromethane; the inert gas includes one or more of argon, nitrogen, or helium; the etching temperature is 400℃~600℃, and the etching time is 30 min~200 min; the volume ratio of the fluorine-containing etching gas to the inert gas is 1:5~1:40. In step 3, the carbon source gas includes one or more of methane, propane, or acetylene; the inert gas includes one or more of nitrogen, argon, or helium; the deposition temperature is 500-800℃, and the reaction time is 2-12h. The changes in reaction temperature and / or the volume ratio of carbon source gas to inert gas in the third mixture and / or deposition time specifically include: controlling the deposition temperature of the carbon layer to be increased by 50-100°C compared to the deposition temperature of the previous carbon layer, and / or extending the deposition time by 20-100 min, and / or increasing the volume ratio of carbon source gas to inert gas in the third mixture.

[0013] Preferably, the method further includes: carbon coating on the outermost layer, so that the carbon coating layer obtained by deposition and the carbon layer formed in the last step 3 together constitute the outer carbon layer.

[0014] Thirdly, embodiments of the present invention provide a negative electrode sheet comprising the multi-layered densified silicon-carbon negative electrode material described in the first aspect above, or comprising the multi-layered densified silicon-carbon negative electrode material prepared by the preparation method described in the second aspect above.

[0015] Fourthly, embodiments of the present invention provide an energy storage device comprising the multi-layered densified silicon-carbon anode material described in the first aspect above, or the multi-layered densified silicon-carbon anode material prepared by the preparation method described in the second aspect above, or the anode sheet described in the third aspect above.

[0016] The multi-layered densified silicon-carbon anode material provided in this invention includes a porous carbon matrix and a multi-layered composite shell loaded on the surface and within the pores of the porous carbon matrix. In the multi-layered composite shell, multiple silicon layers and multiple carbon layers are alternately arranged from the inside out, dispersing the silicon material within the multi-layered structure and reducing localized stress concentration caused by the concentrated expansion of a single silicon layer. Each silicon layer retains a micro-nano void structure formed by selective etching with fluorine-containing gas. This micro-nano void structure serves as a reserved space, providing a buffer for the volume expansion of the silicon layer during charging and discharging, reducing silicon layer pulverization and composite shell cracking. Simultaneously, the multi-layered carbon layers exhibit a gradient densification structure from the inside out along the radial direction. The inner carbon layer has higher porosity, which is beneficial for accommodating silicon layer expansion; the outer carbon layer has higher density, which is beneficial for forming a stable external protective layer and conductive network, preventing the electrolyte from continuously penetrating into the interior. Therefore, this silicon-carbon anode material can simultaneously achieve volume expansion buffering, structural protection, conductive transport, and interface stability, improving the material's cycle stability and structural integrity. Attached Figure Description

[0017] Figure 1 A flowchart illustrating the preparation method of multi-layered densified silicon-carbon anode material provided in this embodiment of the invention; Figure 2 This is a partial structural schematic diagram of the multi-layered densified silicon-carbon anode material provided in Embodiment 1 of the present invention. Figure 3The charge-discharge curves are for the half-cell assembled in Embodiment 1 of the present invention. Detailed Implementation

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0019] This invention provides a multi-layered densified silicon-carbon anode material. The multi-layered densified silicon-carbon anode material of this invention comprises: a porous carbon matrix and a multi-layered composite shell.

[0020] A porous carbon matrix serves as the supporting framework. Preferably, the porous carbon matrix includes: activated carbon, porous expanded graphite, graphene, carbon nanotubes, hard carbon, soft carbon, or carbon fiber.

[0021] Porous carbon matrix can provide a stable load-bearing foundation for multilayer composite shells, and can also form an electron transport framework, so that the subsequently deposited silicon and carbon layers can distribute the load on the surface and in the pores of the porous carbon matrix, thereby reducing the expansion stress caused by local concentration of silicon materials.

[0022] A multilayer composite shell is loaded onto the surface and within the pores of a porous carbon matrix. The multilayer composite shell comprises multiple silicon layers and multiple carbon layers arranged alternately from the inside out, with the outermost layer being the outer carbon layer. The silicon layers are amorphous silicon layers or nanocrystalline silicon layers. The thickness of each inner carbon layer (excluding the outer carbon layer) is 20 nm to 300 nm, and the thickness of the outer carbon layer is 10 nm to 100 nm.

[0023] By alternating silicon and carbon layers, silicon material is dispersed in a multi-layered composite shell, which avoids excessive concentrated expansion stress generated by a single thick silicon layer during charging and discharging. The carbon layers form conductive connections and structural constraints between the silicon layers, which helps maintain the overall integrity of the composite shell.

[0024] In each silicon layer, at least a portion of the silicon layer is selectively etched with a fluorine-containing gas to form micro / nano-void structures. These micro / nano-void structures include depressions, pores, or columnar gaps formed on the surface and / or inside the silicon layer. Furthermore, at least a portion of these micro / nano-void structures are not filled with silicon material, but are reserved as space to buffer the volume expansion of the silicon layer. The etching degree varies in each silicon layer, gradually decreasing from the inside to the outside in the radial direction, resulting in a progressively smaller micro / nano-void structure and a progressively smaller reserved space. The average depth of the micro / nano-void structures in each layer ranges from 5 nm to 100 nm, accounting for 10% to 50% of the corresponding silicon layer thickness. The thickness of a single silicon layer ranges from 10 nm to 200 nm.

[0025] The aforementioned selective etching using fluorine-containing gases refers to the fact that the etching rate of silicon by fluorine-containing gases is much higher than that of carbon, allowing selective etching of the silicon layer without damaging the carbon framework in the presence of a porous carbon matrix. Consequently, micro- and nano-void structures are primarily formed in the silicon layer region, serving as a buffer space for subsequent volume expansion of the silicon layer. Simultaneously, the increased surface roughness of the etched silicon layer facilitates mechanical interlocking with the subsequent carbon layer, enhancing interlayer bonding.

[0026] Furthermore, the etching depth gradually decreases from the inside to the outside in the radial direction, which allows the inner silicon layer to have a larger reserved space to accommodate the strong expansion buffering requirements of the inner region; the reserved space of the outer silicon layer is relatively smaller, which is conducive to maintaining the structural strength near the outer region, thereby achieving a balance between buffering expansion and maintaining structural integrity.

[0027] The carbon layers in the multilayer composite shell exhibit a gradient densification structure. Specifically, along the radial direction, from the innermost carbon layer closest to the porous carbon matrix to the outermost carbon layer, the density of each carbon layer increases while the porosity decreases layer by layer. The porosity of the outer carbon layer is less than 5%, while the porosity of the inner carbon layers is 30%–60%; the density variation rate between adjacent inner carbon layers is 5%–20%.

[0028] The gradient densification structure gives the inner carbon layers higher porosity and better deformation adaptability, which can buffer the volume expansion of the silicon layer by utilizing the reserved space in the silicon layer. The outer carbon layers, especially the outermost carbon layer, have higher density, which can form a continuous outer protective layer, inhibiting the continuous penetration of electrolyte into the interior and improving the conductivity and interfacial stability of the material. At the same time, the density of adjacent carbon layers changes layer by layer, which can avoid interlayer stress concentration and interfacial delamination caused by abrupt changes in density. This allows the multilayer composite shell to maintain good structural integrity during cycling, thereby improving the cycling stability of the silicon-carbon anode material.

[0029] It is understood that the "multilayer" in the multilayer composite shell of the present invention is not limited to a specific number of layers, as long as a structure can be formed in which silicon layers and carbon layers are alternately arranged from the inside to the outside, and the carbon layers are gradually densified from the inside to the outside. For example, in some embodiments, the multilayer composite shell may include a structure in which two etched silicon layers and two inner carbon layers are alternately arranged, or it may include a structure in which three etched silicon layers and three carbon layers are alternately arranged, or it may include a structure in which more layers of etched silicon layers and carbon layers are alternately arranged. However, the total number of silicon and carbon layers is preferably no more than 10 layers to avoid the increased complexity of the fabrication process, the excessive deposition thickness, and the increase in ion transport paths caused by too many layers.

[0030] In one specific example, the multilayer composite shell can also include an etched silicon layer and two carbon layers. Specifically, an inner composite unit is formed by an etched silicon layer and an inner carbon layer outside the silicon layer, with an outer carbon layer covering the outer side of the inner composite unit. The inner carbon layer has a lower density and higher porosity than the outer carbon layer, serving to buffer the volume expansion of the etched silicon layer by utilizing the reserved space within it. The outer carbon layer has a higher density and lower porosity, forming an outer protective layer and providing a conductive network. Thus, even with only one etched silicon layer, a gradient densification structure from the inside out can be formed through the density difference between the inner and outer carbon layers.

[0031] The multi-layered densified silicon-carbon anode material proposed in this invention can be obtained by the following preparation method, the main steps of which include: Step 1: In an inert atmosphere, a porous carbon matrix is ​​placed into a reactor, and a first mixed gas of silicon source gas and inert gas is introduced to deposit a silicon layer on the surface and in the pores of the porous carbon matrix.

[0032] The silicon source gas includes one or more of silane, silane, propane, trichlorosilane, or silicon tetrachloride; the inert gas includes one or more of nitrogen, argon, or helium; the silicon deposition temperature is 300℃~650℃, and the deposition time is 3 h~24 h.

[0033] The silicon source gas decomposes or reacts at the deposition temperature to generate silicon, which is then deposited on the surface and within the pores of the porous carbon matrix to form a silicon layer. Due to the high specific surface area and pore structure of the porous carbon matrix, the silicon layer can be dispersed and formed on the surface and within the pores of the porous carbon matrix, thereby avoiding the concentrated accumulation of silicon material and providing a basis for the subsequent formation of a multilayer alternating structure of silicon and carbon layers.

[0034] Step 2: A second mixed gas containing fluorine etching gas and inert gas is introduced to selectively etch the silicon layer, forming depressions, holes or columnar gaps on the surface and / or inside the silicon layer.

[0035] The fluorine-containing etching gas includes one or more of nitrogen trifluoride, sulfur hexafluoride, carbon tetrafluoride, or fluoromethane; the inert gas includes one or more of argon, nitrogen, or helium; the etching temperature is 400℃~600℃, the etching time is 30 min~200 min; and the volume ratio of the fluorine-containing etching gas to the inert gas is 1:5~1:40.

[0036] Selective etching refers to the process where fluorinated etching gases have a higher etching rate on silicon than on carbon. Therefore, in the presence of a porous carbon matrix, the fluorinated etching gas can preferentially etch the silicon layer, partially etching it while largely preserving the porous carbon matrix. This etching process creates micro / nano void structures such as depressions, pores, or columnar gaps on the surface and / or inside the silicon layer, providing space for subsequent volume expansion of the silicon layer.

[0037] The etching degree can be adjusted by etching time, concentration of fluorine-containing etching gas, volume ratio of fluorine-containing etching gas to inert gas, and etching temperature. A higher etching degree results in larger and more numerous depressions, pores, or columnar gaps; a lower etching degree results in smaller and less dense micro / nano void structures.

[0038] Step 3: A third mixed gas containing carbon source gas and inert gas is introduced to deposit a carbon layer on the etched silicon layer surface; after deposition, at least some depressions, pores or columnar gaps are not filled by carbon material, which are reserved as space to buffer the volume expansion of the silicon layer.

[0039] The carbon source gas includes one or more of methane, propane, or acetylene; the inert gas includes one or more of nitrogen, argon, or helium; the deposition temperature is 500-800℃, and the reaction time is 2-12h.

[0040] The carbon source gas decomposes at the deposition temperature and deposits on the etched silicon surface to form a carbon layer. On the one hand, the carbon layer covers the silicon surface to improve the conductivity and interface stability of the silicon layer; on the other hand, the carbon layer does not completely fill the depressions, pores or columnar gaps formed by etching, so that at least part of the micro-nano void structure is preserved, thereby forming a reserved space between the silicon layer and the carbon layer or in a local part of the silicon layer that can accommodate the expansion of the silicon layer.

[0041] By controlling the carbon source gas concentration, deposition temperature, and deposition time, the deposition thickness, density, and porosity of the carbon layer can be adjusted. When the carbon layer is relatively loose, it can provide good deformation adaptability together with the reserved space; when the carbon layer is relatively dense, it can provide good external protection and a conductive network.

[0042] Step 4: Repeat steps 1 to 3 for N times to alternately deposit silicon and carbon layers.

[0043] In each repetition of step 2, by gradually shortening the etching time, a structure is formed in which the etching degree gradually decreases from the inside to the outside in the radial direction, the micro-nano void structure decreases layer by layer, and the reserved space decreases layer by layer; and in each execution of step 3, by changing the reaction temperature and / or the volume ratio of carbon source gas to inert gas in the third mixed gas and / or the deposition time, a structure is formed in which the density of each carbon layer increases layer by layer and the porosity decreases layer by layer in the radial direction from the inside to the outside; N is an integer greater than or equal to 1.

[0044] The changes mentioned here, such as altering the reaction temperature and / or the volume ratio of carbon source gas to inert gas in the third mixture and / or the deposition time, specifically include: controlling the deposition temperature of the carbon layer to be increased by 50-100°C compared to the deposition temperature of the previous carbon layer, and / or extending the deposition time by 20-100 min, and / or increasing the volume ratio of carbon source gas to inert gas in the third mixture.

[0045] Optionally, after step 140, a supplementary carbon coating deposition can be performed so that the resulting supplementary carbon coating layer together with the outermost carbon layer obtained in the last repeated step constitutes the outer carbon layer.

[0046] By repeating steps 1 to 3, a composite shell layer consisting of alternating silicon and carbon layers can be sequentially formed on the surface and within the pores of a porous carbon substrate. Each silicon layer is treated with a fluorine-containing etching gas to form a micro-nano void structure, and each carbon layer is deposited on the corresponding etched silicon layer surface, thereby forming a structure in which multiple silicon layers, multiple reserved spaces, and multiple carbon layers cooperate with each other.

[0047] During the repeated etching process, the etching time is gradually shortened, resulting in a higher degree of etching and a larger allowance for the silicon layer near the inner side, while the silicon layer near the outer side has a lower degree of etching and a smaller allowance. This arrangement allows the inner region to have better expansion buffering capacity, while maintaining a high degree of structural integrity in the outer region.

[0048] Simultaneously, by gradually increasing the carbon layer deposition temperature, extending the deposition time, and / or increasing the proportion of carbon source gas in the third mixed gas, the subsequently formed carbon layers become denser than the previous carbon layers, thus creating a gradient densification structure with increasing density and decreasing porosity from the inside out. This structure makes the inner carbon layer more suitable for buffering the expansion of the silicon layer with reserved space, while the outer carbon layer is more suitable for forming a dense protective layer, preventing electrolyte penetration, and improving conductivity stability.

[0049] Therefore, by controlling the etching degree layer by layer and the carbon layer density layer by layer, the present invention makes the reserved space gradient in the silicon layer match the gradient densification structure of the carbon layer, thereby simultaneously achieving buffering of silicon layer volume expansion, protection of composite shell structure and stability of silicon / electrolyte interface.

[0050] The multi-layered densified silicon-carbon anode material proposed in this invention can be used as an anode material in energy storage devices such as lithium-ion batteries and lithium-ion capacitors.

[0051] 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 merely some embodiments of this invention, and not all embodiments. 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.

[0052] Example 1 This embodiment provides a multi-layered, dense silicon-carbon composite anode material composed of alternating three silicon layers and three carbon layers, and its preparation process is as follows: Step 1): Weigh 1 kg of commercially available biomass porous carbon and place it in a chemical vapor deposition (CVD) reaction chamber. CVD is performed under nitrogen protection. The nitrogen flow rate is 10 L / min, and the reaction system is heated to 500°C at a rate of 5°C / min and maintained stable. Subsequently, a mixture of silane and nitrogen is introduced for CVD for 200 min, with the total gas flow rate controlled at 20 L / min and the silane volume concentration at 30%. After deposition, the silane supply is stopped, and nitrogen is continuously purged for 30 min to obtain a porous carbon matrix loaded with a first silicon layer.

[0053] Step 2) Continue in the fluidized bed reactor under a nitrogen protective atmosphere, maintaining the system temperature at 500℃. Introduce a mixture of sulfur hexafluoride (SF6) and nitrogen to selectively etch the first silicon layer obtained in Step 1) for 120 min. The total gas flow rate is controlled at 60 L / min, and the volume ratio of SF6 to nitrogen is 1:24, i.e., the SF6 volume concentration is approximately 4%. After etching, purge with pure nitrogen for 2 h to fully remove residual fluorine-containing gases and gaseous etching products from the equipment. After etching, depressions, pores, and some columnar gaps are formed on and inside the first silicon layer, creating the first layer's reserved space.

[0054] Step 3): A mixture of acetylene and nitrogen gas is continuously introduced into the fluidized bed reactor at 450°C, with a total gas flow rate controlled at 80 L / min and a volume ratio of acetylene to nitrogen of 1:10. Carbon deposition is performed on the material obtained in Step 2), depositing a first carbon layer on the etched surface of the first silicon layer for 50 min. Under the conditions of lower deposition temperature, lower acetylene concentration, and shorter deposition time, the homogeneous reaction of the carbon source in the gas phase is suppressed, with surface deposition becoming dominant, thus forming a first carbon layer with high porosity and low density. After deposition, some of the depressions, pores, or columnar gaps formed by etching are filled with carbon material, while the unfilled depressions, pores, or columnar gaps are reserved as buffer space for the volume expansion of the silicon layer.

[0055] Step 4) Adjust the system temperature to 500℃, and introduce a mixture of silane and nitrogen again, with the process conditions the same as in Step 1) to deposit a second silicon layer on the outside of the first carbon layer.

[0056] Step 5) uses the same etching gas and etching temperature as in Step 2) to selectively etch the second silicon layer, but the etching time is shortened to 90 min, resulting in the second layer reserved space. Because the etching time is shorter than that of the first silicon layer, the etching degree in the second silicon layer is lower than that of the first silicon layer, and the resulting micro-nano void structure and reserved space are relatively smaller.

[0057] Step 6): A mixture of acetylene and nitrogen gas is continuously introduced into the fluidized bed reactor at 500°C, with a total gas flow rate controlled at 80 L / min and a volume ratio of acetylene to nitrogen of 1:8. Carbon deposition is then performed on the material obtained in Step 5), depositing a second carbon layer on the etched surface of the second silicon layer for 100 min. Compared to the deposition process of the first carbon layer, the increased acetylene proportion and extended deposition time in this step result in a higher degree of carbon layer deposition, forming a second carbon layer with a higher density and lower porosity than the first carbon layer.

[0058] Step 7), adjust the system temperature to 500℃, and introduce a mixture of silane and nitrogen again, with the process conditions the same as in Step 1), and deposit the third silicon layer on the outside of the second carbon layer.

[0059] Step 8) uses the same etching gas and etching temperature as in Step 2) to selectively etch the third silicon layer, but the etching time is further shortened to 60 min, resulting in the reserved space of the third layer. Because the etching time of the third silicon layer is further shortened, the etching degree in the third silicon layer is lower than that in the second silicon layer, and the resulting micro / nano void structure and reserved space are further reduced.

[0060] Step 9): A mixture of acetylene and nitrogen gas is continuously introduced into the fluidized bed reactor at 550°C, with a total gas flow rate controlled at 80 L / min and a volume ratio of acetylene to nitrogen of 1:5. Carbon deposition is then performed on the material obtained in Step 8), depositing a third carbon layer on the etched third silicon layer surface for 150 min. Compared to the first and second carbon layers, this step further increases the deposition temperature, the acetylene ratio, and the deposition time, thereby enhancing the degree of acetylene decomposition and promoting the deposition of carbon materials on the material surface, resulting in a third carbon layer with further increased density and reduced porosity.

[0061] Step 10): The material obtained in Step 9) is transferred to a rotary kiln and heated to 540°C at a heating rate of 3°C / min under nitrogen protection. Then, a mixture of acetylene and nitrogen gas is introduced for supplementary carbon coating of the outer layer, with a total gas flow rate of 8 L / min and an acetylene to nitrogen volume ratio of 1:1, for a coating time of 5 h. After coating, the material is naturally cooled to room temperature under a nitrogen atmosphere to obtain the final multi-layered densified silicon-carbon composite anode material.

[0062] Figure 2 This is a magnified view of a pore structure of the multi-layered densified silicon-carbon composite anode material obtained in Example 1.

[0063] In this embodiment, the third carbon layer formed in step 9) and the outer supplementary carbon coating layer formed in step 10) together constitute the outermost carbon layer. Step 10) is not to form new silicon / carbon alternation units, but to further improve the continuity and density of the outermost carbon layer, so that the final outer carbon layer has lower porosity and better protection.

[0064] Step 11): Weigh the above-mentioned silicon-carbon composite negative electrode material, conductive carbon black, and binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a 1:1 mass ratio) at a mass ratio of 8:1:1 and at a mass ratio of 95:2:3. Grind them in a mortar at room temperature, then add deionized water and slurry using a pulper to form a negative electrode slurry. Coat the negative electrode slurry onto a copper foil current collector. Then, dry it in a vacuum oven at 80°C for 12 hours to remove the solvent. Subsequently, cut the dried electrode into 12mm diameter discs and transfer them to a glove box for later use in battery assembly.

[0065] Step 12): Assemble the above-mentioned circular electrode sheets into a CR2032 coin cell in an argon-filled glove box. The electrolyte of the CR2032 coin cell is a 1 mol / L lithium hexafluorophosphate (LiPF6) electrolyte, and the solvent of the electrolyte is a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of EC to DMC of 1:1. The counter electrode is a lithium sheet.

[0066] Step 13): After allowing the CR2032 coin cell to stand for 8 hours, charge-discharge tests were performed at room temperature using a Blue Battery Testing System (CT2001A). The test conditions were: first-cycle coulombic efficiency at 0.1 C rate and coin cell expansion at 0.8 V. The test data are recorded in Table 1. The electrochemical test curves are shown below. Figure 3 As shown.

[0067] In this embodiment, the etching times for the first, second, and third silicon layers are 120 min, 90 min, and 60 min, respectively, so that the etching degree of the silicon layers gradually decreases from the inside to the outside in the radial direction, and the micro-nano void structure and reserved space decrease layer by layer. The deposition conditions for the first, second, and outer carbon layers are gradually improved, so that the density of the carbon layers increases layer by layer from the inside to the outside in the radial direction, and the porosity decreases layer by layer. As a result, the obtained silicon-carbon composite anode material has a reserved space structure and a gradient-densified carbon layer structure that change from the inside to the outside.

[0068] Example 2 This embodiment provides a multi-layered densified silicon-carbon composite anode material with two silicon layers and two carbon layers, and its preparation process is as follows: Step 1): Weigh 1 kg of commercially available biomass porous carbon and place it in a chemical vapor deposition (CVD) reaction chamber. CVD is performed under nitrogen protection. The nitrogen flow rate is 10 L / min, and the reaction system is heated to 500°C at a rate of 5°C / min and maintained stable. Subsequently, a mixture of silane and nitrogen is introduced for CVD for 300 min, with the total gas flow rate controlled at 20 L / min and the silane volume concentration at 30%. After deposition, the silane supply is stopped, and nitrogen is continuously purged for 30 min to obtain a porous carbon matrix loaded with a first silicon layer.

[0069] Step 2): Continue etching the first silicon layer obtained in Step 1) in the fluidized bed reactor under a nitrogen protective atmosphere, maintaining the system temperature at 500°C. Introduce a mixture of sulfur hexafluoride (SF6) and nitrogen to selectively etch the layer for 120 min. The total gas flow rate is controlled at 60 L / min, and the volume ratio of SF6 to nitrogen is 1:24, i.e., the SF6 volume concentration is approximately 4%. After etching, purge with pure nitrogen for 2 h to fully remove residual fluorine-containing gases and gaseous etching products, thus obtaining the first reserved space layer.

[0070] Step 3): Continue to introduce a mixture of acetylene and nitrogen gas into the fluidized bed reactor at 500°C, with a total gas flow rate controlled at 100 L / min and a volume ratio of acetylene to nitrogen of 1:10. Perform carbon deposition on the material obtained in Step 2), depositing a first carbon layer on the surface of the etched first silicon layer for 50 min. Under these conditions, a first carbon layer with high porosity and low density is formed, and at least part of the depressions, pores, or columnar gaps formed by etching are reserved as space to buffer the volume expansion of the silicon layer.

[0071] Step 4) Adjust the system temperature to 500℃, and introduce a mixture of silane and nitrogen again, with the process conditions the same as in Step 1) to deposit a second silicon layer on the outside of the first carbon layer.

[0072] Step 5) uses the same etching gas and etching temperature as in Step 2) to selectively etch the second silicon layer, but the etching time is shortened to 90 min, resulting in the second layer reserved space. Because the etching time of the second silicon layer is shorter than that of the first silicon layer, the etching degree in the second silicon layer is lower than that in the first silicon layer, and the resulting micro / nano void structure and reserved space are relatively smaller.

[0073] Step 6): A mixture of acetylene and nitrogen is continuously introduced into the fluidized bed reactor at 550°C, with a total gas flow rate controlled at 100 L / min and a volume ratio of acetylene to nitrogen of 1:5. Carbon deposition is then performed on the material obtained in Step 5), depositing a second carbon layer on the etched second silicon layer surface for 100 min. Compared to the first carbon layer, this step involves increased deposition temperature, increased acetylene ratio, and prolonged deposition time, resulting in a higher density and lower porosity for the second carbon layer compared to the first carbon layer.

[0074] Step 7): The material obtained in Step 6) is transferred to a rotary kiln and heated to 540°C at a heating rate of 3°C / min under nitrogen protection. Then, a mixture of acetylene and nitrogen gas is introduced for supplementary carbon coating, with a total gas flow rate of 8 L / min and an acetylene to nitrogen volume ratio of 1:1, for a coating time of 5 h. After coating, the material is naturally cooled to room temperature under a nitrogen atmosphere to obtain the final multi-layered densified silicon-carbon composite anode material.

[0075] In this embodiment, the second carbon layer formed in step 6) and the outer supplementary carbon coating layer formed in step 7) together constitute the outermost carbon layer. Compared with embodiment 1, this embodiment reduces one set of silicon layer deposition, etching and carbon layer deposition processes, forming a multilayer composite shell structure with two silicon layers and two main carbon layers.

[0076] Steps 8)-10) are the same as in Example 1. Test data are recorded in Table 1.

[0077] Example 3 This embodiment provides a multi-layered densified silicon-carbon composite anode material using carbon tetrafluoride as the fluorine-containing etching gas. Except for the different fluorine-containing etching gas, the raw materials, process steps, and testing methods are the same as in Example 1.

[0078] Specifically, in steps 2), 5), and 8) of Example 3, the fluorine-containing etching gas sulfur hexafluoride (SF6) is replaced with carbon tetrafluoride (CF4), and a mixed gas of CF4 and nitrogen is used to selectively etch the corresponding silicon layers. The volume ratio of CF4 to nitrogen is 1:24, and the etching temperature is 500°C; wherein the etching time for the first silicon layer is 120 min, the etching time for the second silicon layer is 90 min, and the etching time for the third silicon layer is 60 min.

[0079] After the above treatment, depressions, pores, or columnar gaps are formed on the surface and / or inside of each silicon layer, and the etching degree gradually decreases from the inside to the outside in the radial direction, with the reserved space decreasing layer by layer. Subsequently, the final multi-layered densified silicon-carbon composite anode material was prepared according to the carbon layer deposition and outer layer supplementary carbon coating conditions of Example 1, and the anode sheet and CR2032 coin cell were prepared according to the method of Example 1, and electrochemical performance was tested. The test data are recorded in Table 1.

[0080] This embodiment illustrates that fluorine-containing etching gases are not limited to sulfur hexafluoride; carbon tetrafluoride can also be used to selectively etch silicon layers and form micro-nano void structures to buffer the volume expansion of silicon layers.

[0081] Comparative Example 1 This comparative example illustrates the impact of not performing fluorine-containing gas etching on the structure and performance of silicon-carbon composite anode materials.

[0082] This comparative example is basically the same as Example 2, except that steps 2) and 5) in Example 2 are omitted. That is, after the first and second silicon layers are deposited, fluorine-containing etching gas is not introduced for selective etching, but the subsequent carbon layer is directly deposited. Specifically, after the first silicon layer is deposited on the surface and in the pores of the porous carbon substrate, the first carbon layer is directly deposited on the surface of the first silicon layer; then the second silicon layer is deposited, and the second carbon layer is directly deposited on the surface of the second silicon layer, and finally, an outer carbon coating is added.

[0083] Because this comparative example did not perform fluorine-containing gas etching on the silicon layer, no obvious micro / nano void structures such as depressions, pores, or columnar gaps were formed on the surface and / or inside of the silicon layer. There was a lack of pre-set, reserved space between the silicon and carbon layers to buffer the volume expansion of the silicon layer. During charging and discharging, the volume expansion of the silicon layer is difficult to buffer effectively, easily leading to carbon layer cracking, material pulverization, and an increase in interfacial side reactions.

[0084] Following the same method as in Example 2, the silicon-carbon composite anode material obtained in this comparative example was prepared into a negative electrode sheet and assembled into a CR2032 coin cell. Electrochemical performance was tested under the same test conditions. The test data are recorded in Table 1.

[0085] Comparative Example 2 This comparative example illustrates the impact of the lack of a gradient densification structure on the structure and performance of silicon-carbon composite anode materials.

[0086] This comparative example is basically the same as Example 2, except that: the fluorine gas etching step in Example 2 is retained, so that micro-nano void structures and reserved spaces are formed in both the first silicon layer and the second silicon layer; however, all carbon layers are prepared using the deposition conditions of the outer supplementary carbon coating layer, that is, the first carbon layer, the second carbon layer and the outer supplementary carbon coating layer are all prepared using high-density carbon deposition conditions, so that the resulting carbon layers are all dense carbon layers, and a gradient densification structure with increasing density and decreasing porosity from the inside to the outside is not formed.

[0087] Specifically, after the first and second silicon layers are etched with fluorine-containing gas, carbon layers are deposited under the same conditions as in step 7) of Example 2, so that the inner carbon layer no longer has high porosity and deformation adaptability. The remaining preparation steps, electrode preparation steps, and coin cell testing steps are the same as in Example 2.

[0088] Although this comparative example retains the reserved space in the silicon layer, each carbon layer is a dense structure. The inner carbon layer cannot easily deform appropriately to accommodate the reserved space. When the silicon layer expands, it easily generates large local stresses at the silicon / carbon layer interface, leading to interlayer delamination or carbon layer cracking. Therefore, this comparative example can be used to illustrate the role of gradient-densified carbon layer structures in buffering stress transfer and maintaining structural integrity. Test data are recorded in Table 1.

[0089] Comparative Example 3 This comparative example illustrates the impact of using only a single layer of dense carbon coating without a gradient design on the structure and performance of silicon-carbon composite anode materials.

[0090] In this comparative example, 1 kg of commercially available biomass porous carbon was weighed and placed in a chemical vapor deposition reaction chamber. Under nitrogen protection, the temperature was increased to 500°C at a rate of 5°C / min and maintained stable. Subsequently, a mixture of silane and nitrogen gas was introduced to deposit a silicon layer on the surface and within the pores of the porous carbon matrix. After the silicon layer deposition was completed, instead of multiple alternating silicon / carbon layer depositions or the formation of a carbon layer structure that gradually changes from the inside out, a single-layer dense carbon coating was directly applied to the outside of the obtained silicon layer according to the process parameters of step 7) in Example 2, but the coating time was extended so that the total thickness of the obtained carbon coating layer was comparable to the total thickness of each carbon layer in Example 2. After coating, the material was naturally cooled to room temperature under a nitrogen atmosphere to obtain a single-layer dense carbon-coated silicon-carbon composite anode material.

[0091] Following the same method as in the examples, the silicon-carbon composite anode material obtained in this comparative example was prepared into a negative electrode sheet and assembled into a CR2032 coin cell. Electrochemical performance was then tested under the same test conditions. The test data are recorded in Table 1.

[0092] Because this comparative example only has a single-layer dense carbon coating structure, it lacks a multi-layer composite shell with alternating silicon and carbon layers, as well as a reserved space structure with gradually changing layers from the inside out and a carbon layer gradient densification structure. Therefore, the volume expansion of the silicon layer during charging and discharging mainly affects the single-layer dense carbon shell, which can easily lead to carbon shell cracking, silicon material pulverization, and continuous contact between the electrolyte and silicon material, thus affecting cycle stability.

[0093] Table 1 A comparison of Comparative Example 1 and Example 2 reveals that both employ a double-layer silicon / carbon structure, and both carbon layers feature a gradient densification design. The only difference lies in Comparative Example 1, which did not undergo fluorine-containing gas etching. In Example 2, fluorine-containing gas etching creates a reserved space within the silicon layer. This reserved space provides a buffer for the volume expansion of the silicon layer during charging and discharging, significantly suppressing electrode expansion and reducing the electrode expansion rate by 22%. Simultaneously, the reserved space alleviates structural damage and interfacial side reactions caused by silicon layer expansion, reducing irreversible capacity loss and improving the initial coulombic efficiency by 4.2 percentage points. Therefore, etching to create a reserved space is a key factor in improving the initial coulombic efficiency and suppressing electrode expansion.

[0094] A comparison of Comparative Example 2 and Example 2 reveals that both employ a double-layer silicon / carbon structure and retain the fluorine-containing gas etching step. The difference lies in whether the carbon layer possesses a gradient densification structure. In Example 2, the inner carbon layer is a low-density, high-porosity porous carbon layer, providing mechanical elastic buffering to prevent the expansion stress of the silicon layer from directly acting on the outer dense carbon layer. The outer carbon layer, on the other hand, is a high-density, low-porosity dense carbon layer, providing rigid protection and a stable conductive network. The inner buffer and outer protection work together to reduce the electrode expansion rate by 17% and improve the initial coulombic efficiency by 3.8 percentage points. This demonstrates that the carbon layer densification gradient is a crucial factor in suppressing volume expansion and maintaining the integrity of the composite structure.

[0095] Further analysis of the test results from Example 2 and the three comparative examples reveals that simply setting a reserved space or simply changing the carbon layer structure can improve material performance to some extent. However, when both the reserved space gradient and the carbon layer density gradient exist simultaneously, the resulting performance improvement is not a simple summation of their contributions, but rather exhibits a more significant synergistic enhancement effect. This is because the reserved space gradient and the carbon layer density gradient are spatially staggered and functionally matched: the reserved space in the silicon layer is mainly used to absorb volume expansion, the inner porous carbon layer is used to provide elastic buffering in conjunction with the reserved space, and the outer dense carbon layer is used to provide structural constraints and interface protection. This synergistic effect of the structure enables the material to simultaneously achieve expansion buffering, stress dispersion, conductivity maintenance, and interface stability during charging and discharging.

[0096] Furthermore, a comparison of Examples 1 and 2 reveals that the three-layer silicon / carbon structure, compared to the two-layer silicon / carbon structure, exhibits a 1.2 percentage point improvement in initial coulombic efficiency and a 6 percentage point reduction in electrode expansion rate. However, the reversible capacity decreases slightly, by approximately 11 mAh / g. This is because the three-layer structure possesses more interface layers and a smoother mechanical gradient, dispersing the total volume expansion across more layers, thereby further alleviating local stress concentration and reducing electrode expansion. However, the relatively increased carbon content in the three-layer structure leads to a slight decrease in the proportion of active silicon, resulting in a slight sacrifice in reversible capacity. This indicates that three-layer or even multi-layer structures are more suitable for applications requiring long cycle life and low expansion rate, while two-layer structures are more suitable for applications that balance structural stability and further pursue higher capacity.

[0097] 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. A multi-layered densified silicon-carbon anode material, characterized in that, The silicon-carbon anode material includes: Porous carbon matrix, serving as a supporting framework; A multi-layered composite shell is loaded on the surface and within the pores of the porous carbon matrix; The multilayer composite shell includes multiple silicon layers and multiple carbon layers arranged alternately from the inside to the outside, wherein the outermost layer is the outer carbon layer; the remaining carbon layers other than the outer carbon layer are the inner carbon layers. Each silicon layer includes at least a portion of the silicon layer formed by selective etching with a fluorine-containing gas to form micro-nano void structures. The micro-nano void structures include depressions, pores, or columnar gaps formed on the surface and / or inside the silicon layer. Furthermore, at least a portion of the micro-nano void structures are not filled with silicon material and are reserved as space to buffer the volume expansion of the silicon layer. The carbon layers in the multilayer composite shell have a gradient densification structure; specifically, the gradient densification structure means that, along the radial direction, from the inner carbon layer closest to the porous carbon matrix to the outer carbon layer, the density of each carbon layer increases and the porosity decreases layer by layer.

2. The silicon-carbon anode material according to claim 1, characterized in that, The average depth of the micro-nano void structures in each layer is 5 nm to 100 nm, accounting for 10% to 50% of the thickness of the corresponding silicon layer, respectively. The etching degree of each silicon layer is different. Along the radial direction from the inside to the outside, the etching degree gradually decreases, the micro-nano void structure decreases layer by layer, and the reserved space decreases layer by layer.

3. The silicon-carbon anode material according to claim 1, characterized in that, The porosity of the outer carbon layer is less than 5%, and the porosity of the inner carbon layer is 30% to 60%. The density variation rate between two adjacent inner carbon layers is 5% to 20%.

4. The silicon-carbon anode material according to claim 1, characterized in that, The thickness of a single silicon layer is 10 nm to 200 nm, the thickness of a single inner carbon layer is 20 nm to 300 nm, and the thickness of an outer carbon layer is 10 nm to 100 nm; the total number of silicon and carbon layers in the multilayer composite shell is less than or equal to 10.

5. The silicon-carbon anode material according to claim 1, characterized in that, The silicon layer is an amorphous silicon layer or a nanocrystalline silicon layer; the porous carbon matrix includes one or more of activated carbon, porous expanded graphite, graphene, carbon nanotubes, hard carbon, soft carbon, or carbon fiber.

6. A method for preparing a multi-layered densified silicon-carbon anode material as described in any one of claims 1-5, characterized in that, The preparation method includes: Step 1: In an inert atmosphere, a porous carbon matrix is ​​placed into a reactor, and a first mixed gas of silicon source gas and inert gas is introduced to deposit a silicon layer on the surface and in the pores of the porous carbon matrix. Step 2: A second mixed gas containing fluorine etching gas and inert gas is introduced to selectively etch the silicon layer, forming depressions, holes or columnar gaps on the surface and / or inside the silicon layer. Step 3: A third mixed gas containing carbon source gas and inert gas is introduced to deposit a carbon layer on the etched silicon layer surface; after the deposition, at least some of the depressions, holes or columnar gaps are not filled by carbon material, and are reserved as reserved space for buffering the volume expansion of the silicon layer. Step 4: Repeat steps 1 to 3 for N times to alternately deposit silicon and carbon layers. Each time step 2 is repeated, the etching time is gradually shortened to form a structure in which the etching degree gradually decreases from the inside to the outside in the radial direction, the micro-nano void structure decreases layer by layer, and the reserved space decreases layer by layer. Furthermore, each time step 3 is performed, the reaction temperature and / or the volume ratio of carbon source gas to inert gas in the third mixed gas and / or the deposition time are changed to form a structure in which the density of each carbon layer increases layer by layer and the porosity decreases layer by layer in the radial direction from the inside to the outside. N is an integer greater than or equal to 1.

7. The method according to claim 6, characterized in that, In step 1, the silicon source gas includes one or more of silane, silane, propane, trichlorosilane, or silicon tetrachloride; the inert gas includes one or more of nitrogen, argon, or helium; the silicon deposition temperature is 300℃~650℃, and the deposition time is 3 h~24 h. In step 2, the fluorine-containing etching gas includes one or more of nitrogen trifluoride, sulfur hexafluoride, carbon tetrafluoride, or fluoromethane; the inert gas includes one or more of argon, nitrogen, or helium; the etching temperature is 400℃~600℃, and the etching time is 30 min~200 min; the volume ratio of the fluorine-containing etching gas to the inert gas is 1:5~1:

40. In step 3, the carbon source gas includes one or more of methane, propane, or acetylene; the inert gas includes one or more of nitrogen, argon, or helium; the deposition temperature is 500-800℃, and the reaction time is 2-12h. The changes in reaction temperature and / or the volume ratio of carbon source gas to inert gas in the third mixture and / or deposition time specifically include: controlling the deposition temperature of the carbon layer to be increased by 50-100°C compared to the deposition temperature of the previous carbon layer, and / or extending the deposition time by 20-100 min, and / or increasing the volume ratio of carbon source gas to inert gas in the third mixture.

8. The method according to claim 6, characterized in that, The method further includes: applying carbon coating to the outermost layer, so that the carbon coating layer obtained by deposition and the carbon layer formed by the last execution of step 3 together constitute the outer carbon layer.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the multi-layered densified silicon-carbon negative electrode material as described in any one of claims 1-5, or the multi-layered densified silicon-carbon negative electrode material prepared by the preparation method described in any one of claims 6-8.

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 multi-layered densified silicon-carbon anode material as described in any one of claims 1-5, or the multi-layered densified silicon-carbon anode material prepared by the preparation method described in any one of claims 6-8, or the anode sheet as described in claim 9.

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