Silicon-carbon composite material, silicon-carbon composite material preparation method and negative electrode sheet

Abstract

The application provides a silicon-carbon composite material, a silicon-carbon composite material preparation method and a negative electrode sheet, and comprises a core and a metal organic framework pyrolysis layer, the core is a silicon-carbon core, the metal organic framework pyrolysis layer coats the core, the metal organic framework pyrolysis layer comprises metal oxide and carbon, the metal organic framework pyrolysis layer comprises a metal oxide layer, a transition layer and a porous carbon layer from inside to outside in sequence, and the content of the metal oxide decreases in sequence from the metal oxide layer, the transition layer to the porous carbon layer. The silicon-carbon composite material provided by the application forms a gradient distribution with decreasing content of metal oxide, the high-content metal oxide in the metal oxide layer can inhibit the initial stress of volume expansion through the close combination with the silicon-carbon core, the transition layer realizes the step-by-step buffering and dispersion of stress through the mixing ratio of metal oxide and carbon, and the outermost porous carbon layer provides space for the volume change of the silicon-carbon core and maintains the overall structural integrity by virtue of its flexibility and porous structure.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a silicon-carbon composite material, a method for preparing the silicon-carbon composite material, and a negative electrode sheet. Background Technology

[0002] Silicon-carbon composite materials prepared by chemical vapor deposition (CVD) have shown certain application potential in the field of lithium-ion batteries, but many problems still exist. Silicon can expand by more than 300% during charge and discharge. Even with nanoscale dispersion of silicon particles using CVD, it is difficult to completely avoid structural breakage due to silicon volume expansion, leading to poorer contact between the active material and the current collector, and increased electrode resistance. Simultaneously, the volume change of silicon in the silicon-carbon composite material causes the solid electrolyte interphase (SEI) film to continuously break and reform, triggering side reactions, consuming active lithium and electrolyte, reducing the battery's initial efficiency and cycle life, and the thickened SEI film increases lithium-ion transport resistance. Furthermore, traditional carbon coatings suffer from problems such as difficulty in ensuring integrity, limited bonding strength with silicon, and inherent volume changes, failing to effectively buffer and protect the composite material, thus affecting its structural stability and electrochemical performance. Therefore, there is an urgent need to develop a novel silicon-carbon composite material and its preparation method to solve these problems. Summary of the Invention

[0003] To address the problem that excessive expansion of silicon volume in silicon-carbon lithium-ion batteries affects the structural stability and electrical performance of silicon-carbon composite materials, this paper provides a silicon-carbon composite material, a method for preparing the silicon-carbon composite material, and a negative electrode sheet.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0005] On one hand, the present invention provides a silicon-carbon composite material, comprising a core and a metal-organic framework pyrolysis layer, wherein the core is a silicon-carbon core, the metal-organic framework pyrolysis layer covers the core, the metal-organic framework pyrolysis layer comprises metal oxides and carbon, and the metal-organic framework pyrolysis layer comprises, from the inside to the outside, a metal oxide layer, a transition layer and a porous carbon layer, wherein the content of the metal oxide decreases sequentially from the metal oxide layer, the transition layer to the porous carbon layer.

[0006] Optionally, the metal oxide layer has a metal oxide content of 70%-90% by mass, the transition layer has a metal oxide content of 30%-70% by mass, and the porous carbon layer has a metal oxide content of 0%-30% by mass.

[0007] Optionally, the carbon content increases sequentially from the metal oxide layer, the transition layer to the porous carbon layer.

[0008] Optionally, the carbon content of the metal oxide layer is 10%-30% by mass, the carbon content of the transition layer is 30%-70% by mass, and the carbon content of the porous carbon layer is 70%-100% by mass.

[0009] Optionally, the metal-organic framework pyrolysis layer is obtained by pyrolysis of a metal-organic framework material, wherein the metal element in the metal-organic framework material includes one or more of Zr, Zn, Fe, and Cr.

[0010] Optionally, the metal-organic framework material includes one or more of UiO-66, ZIF-8, and MIL-101.

[0011] Optionally, the thickness of the metal-organic framework pyrolysis layer is 30-100 nm.

[0012] Optionally, the thickness of the metal oxide layer is 5-15 nm;

[0013] The thickness of the transition layer is 10-40 nm;

[0014] The thickness of the porous carbon layer is 15-45 nm.

[0015] Optionally, the silicon-carbon core includes a porous carbon framework, nano-silicon, and a carbon deposition layer, wherein the nano-silicon is dispersed on the porous carbon framework and the carbon deposition layer covers the porous carbon framework.

[0016] Optionally, the particle size of the nano-silicon is 1-50 nm;

[0017] The thickness of the carbon deposition layer is 5-20 nm.

[0018] Optionally, the method for preparing the silicon-carbon composite material as described above includes the following operations:

[0019] Obtaining silicon-carbon cores;

[0020] A first precursor solution and a second precursor solution containing a metal-organic framework material are obtained, wherein the metal-organic framework material is obtained by coordination of a metal salt and an organic ligand.

[0021] The silicon-carbon core is placed in the first precursor solution and then heat-treated to obtain the first precursor.

[0022] The first precursor was placed in a solution of the second precursor and then heat-treated to obtain the second precursor.

[0023] The molar ratio of metal salt to organic ligand in the first precursor solution is greater than that in the second precursor solution;

[0024] The second precursor was heat-treated in an inert atmosphere to obtain a precursor with a metal oxide layer.

[0025] A precursor with a metal oxide layer is heat-treated in a reducing atmosphere to form a porous carbon layer, and a transition layer is formed between the metal oxide layer and the porous carbon layer to obtain a silicon-carbon composite material.

[0026] Optionally, the silicon-carbon core is prepared by the following method:

[0027] A silicon source was introduced into the reaction chamber, and under high temperature conditions, a porous carbon framework with nano-silicon deposition was obtained.

[0028] A carbon source is introduced and, under high-temperature catalytic conditions, a carbon deposition layer is formed on a porous carbon framework with nano-silicon deposits through chemical vapor deposition.

[0029] Optionally, in the first precursor solution, the molar ratio of the metal salt to the organic ligand is 1:0.5 to 1:1.5; and / or,

[0030] In the second precursor solution, the molar ratio of metal salt to organic ligand is 1:3 to 1:10.

[0031] Optionally, the metal-organic framework material in the first precursor solution comprises 4%-10% by mass; and / or,

[0032] In the second precursor solution, the mass percentage of metal-organic framework material is 0.5%-4%.

[0033] Optionally, the metal salt is selected from Zr salt. After heat treatment in an inert atmosphere and a reducing atmosphere, the Zr salt forms ZrO2 and is dispersed in the metal oxide layer, the transition layer and the porous carbon layer.

[0034] Optionally, the metal salt is selected from Zn salt. After heat treatment in an inert atmosphere, the Zn salt forms ZnO and is dispersed in the metal oxide layer, transition layer and porous carbon layer. After heat treatment in a reducing atmosphere, at least part of the ZnO is reduced to Zn and volatilized, forming pores in the metal oxide layer, transition layer and porous carbon layer.

[0035] Optionally, metal salts and organic ligands are dissolved in a solvent, and a catalyst is added to react, to obtain a first precursor solution and a second precursor solution with a metal-organic framework material.

[0036] The metal salt includes one or more of ZrCl4, Zn(NO3)2, and FeCl3; and / or,

[0037] The organic ligand includes one or more of terephthalic acid and 2-methylimidazole; and / or

[0038] The catalyst includes one or more of hydrochloric acid and acetic acid; and / or,

[0039] The solvent includes one or more of N,N-dimethylformamide and methanol.

[0040] Optionally, when the second precursor is heat-treated in an inert atmosphere, the heat treatment time is 1-5 hours, the heat treatment temperature is 300-500℃, and the heating rate is 2-10℃ / min.

[0041] When heat treatment is performed in the reducing atmosphere, the heat treatment time is 1-5 hours, the heat treatment temperature is 600-900℃, and the heating rate is 2-10℃ / min.

[0042] Optionally, when preparing the first precursor, the heat treatment time is 1-6 hours and the heat treatment temperature is 30-50℃;

[0043] When preparing the second precursor, the heat treatment time is 6-12 hours and the heat treatment temperature is 50-80℃.

[0044] On the other hand, the present invention provides a negative electrode sheet, including a negative electrode material layer, wherein the negative electrode material layer includes a binder, a conductive agent and the silicon-carbon composite material, or a silicon-carbon composite material prepared by the method for preparing the silicon-carbon composite material.

[0045] The beneficial effects of this application are as follows:

[0046] The silicon-carbon composite material provided in this application includes a core and a metal-organic framework pyrolysis layer. The metal-organic framework pyrolysis layer comprises, from the inside out, a metal oxide layer, a transition layer, and a porous carbon layer. The content of the metal oxide decreases sequentially from the metal oxide layer to the transition layer and then to the porous carbon layer, forming a gradient distribution with decreasing metal oxide content. The high metal oxide content in the metal oxide layer can suppress the initial stress of volume expansion through close bonding with the silicon-carbon core. The transition layer achieves gradual buffering and dispersion of stress through the mixing ratio of metal oxide and carbon. The outermost porous carbon layer, with its flexibility and porous structure, provides space for volume changes in the silicon-carbon core and maintains the overall structural integrity. Furthermore, the synergistic effect of the metal oxide and carbon guides the formation of a uniform and stable SEI film, reducing side reactions and ensuring the continuity of electron and ion transport channels, thus avoiding electrical performance degradation due to structural breakage. In other words, the silicon-carbon composite material provided in this application suppresses silicon volume expansion while simultaneously ensuring the structural stability and electrochemical performance of the material. Detailed Implementation

[0047] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0048] This invention provides a silicon-carbon composite material, comprising a core and a metal-organic framework pyrolysis layer. The core is a silicon-carbon core, and the metal-organic framework pyrolysis layer covers the core. The metal-organic framework pyrolysis layer comprises metal oxides and carbon. The metal-organic framework pyrolysis layer comprises, from the inside out, a metal oxide layer, a transition layer, and a porous carbon layer. The content of the metal oxide decreases sequentially from the metal oxide layer, the transition layer to the porous carbon layer.

[0049] Specifically, the silicon-carbon composite material provided in this application includes a core and a metal-organic framework pyrolysis layer. The metal-organic framework pyrolysis layer is sequentially composed of a metal oxide layer, a transition layer, and a porous carbon layer from the inside out. The content of the metal oxide decreases sequentially from the metal oxide layer and the transition layer to the porous carbon layer, forming a gradient distribution with decreasing metal oxide content. The high metal oxide content in the metal oxide layer can suppress the initial stress of volume expansion through close bonding with the silicon-carbon core. The transition layer achieves gradual buffering and dispersion of stress through the mixing ratio of metal oxide and carbon. The outermost porous carbon layer, with its flexibility and porous structure, provides space for volume changes in the silicon-carbon core and maintains the overall structural integrity. Furthermore, the synergistic effect of the metal oxide and carbon guides the formation of a uniform and stable SEI film, reducing side reactions and ensuring the continuity of electron and ion transport channels, thus avoiding electrical performance degradation due to structural breakage. In other words, the silicon-carbon composite material provided in this application suppresses silicon volume expansion while simultaneously ensuring the structural stability and electrochemical performance of the material.

[0050] Specifically, the metal oxide layer is tightly bonded to the silicon-carbon core through COM bonds, forming a strong interface constraint that directly suppresses the excessive expansion of silicon particles; the transition layer achieves a smooth transition of elastic modulus from the rigidity of metal oxide to the flexibility of carbon through a gradient change in metal oxide content, gradually dissipating the stress generated by volume expansion and preventing the structure from cracking due to stress concentration; the porous carbon layer plays multiple roles, with its high porosity providing a short-distance lithium-ion diffusion path and continuous carbon phase ensuring efficient electron transport and improving rate performance.

[0051] In some embodiments, the mass percentage of metal oxide in the metal oxide layer is 70%-90%, the mass percentage of metal oxide in the transition layer is 30%-70%, and the mass percentage of metal oxide in the porous carbon layer is 0%-30%.

[0052] Specifically, when the metal oxide content of the high-metal oxide layer is 70%-90% by mass, it can tightly bond with the silicon-carbon core due to its large amount of metal oxides, strengthening the interface constraint ability and effectively suppressing the initial expansion of silicon particles. When the metal oxide content of the transition layer is 30%-70% by mass, the elastic modulus is smoothly transitioned from rigid to flexible through a step-by-step decrease in mass percentage, gradually dispersing and buffering the expansion stress to avoid structural breakage due to stress abrupt changes. When the metal oxide concentration of the porous carbon layer is 0-30%, the carbon phase is dominant, and the high porosity and continuous carbon network ensure rapid lithium-ion transport and efficient electron conduction. At the same time, a small amount of metal oxide particles can still synergistically stabilize the SEI film. That is, the setting of the metal oxide content gradient ensures the rigid support of the inner layer to suppress expansion, the gradient transition of the transition layer to buffer stress, and also takes into account the flexible function of the outer porous carbon layer to optimize electrochemical performance, ultimately achieving a synergistic improvement in the structural stability of silicon-carbon composite materials and the overall performance of the battery.

[0053] In some embodiments, the carbon content increases sequentially from the metal oxide layer, the transition layer to the porous carbon layer.

[0054] Specifically, the carbon content gradually increases from the metal oxide layer to the transition layer, achieving a smooth transition in the elastic modulus of the material from the rigidity of the metal oxide to the flexibility of the carbon. This gradually disperses the stress caused by volume expansion, preventing structural breakage due to sudden stress changes. The high carbon content of the porous carbon layer fully leverages the advantages of carbon materials. The continuous carbon phase constructs efficient electron transport channels, and the porous structure provides short-distance lithium-ion diffusion paths, significantly improving electrochemical kinetic performance. At the same time, the flexibility of high carbon can act as an elastic shell, further absorbing the impact of volume changes to maintain the integrity of the overall structure. This gradient increase in carbon content not only achieves layered protection of structural stability through compositional transition but also optimizes electrochemical performance by utilizing the characteristics of carbon materials. Together with the synergistic effect of the metal oxide, it stabilizes the SEI film, ultimately achieving a balance between suppressing volume expansion and improving the overall performance of the battery in the silicon-carbon composite material.

[0055] In some embodiments, the carbon content of the metal oxide layer is 10%-30% by mass, the carbon content of the transition layer is 30%-70% by mass, and the carbon content of the porous carbon layer is 70%-100% by mass.

[0056] In some embodiments, the metal-organic framework pyrolysis layer is obtained by pyrolysis of a metal-organic framework material, wherein the metal element in the metal-organic framework material includes one or more of Zr, Zn, Fe, and Cr.

[0057] Specifically, the metal oxides formed by the aforementioned metal elements, such as ZrO2, ZnO, Fe2O3, and Cr2O3, exhibit various advantages. ZrO2 possesses high chemical stability and strong mechanical strength, enhancing its bonding with the silicon-carbon core through CO-Zr bonds and effectively suppressing volume expansion. ZnO undergoes at least partial reduction and volatilization during pyrolysis, contributing to the formation of a porous carbon structure and optimizing ion transport pathways. Fe2O3 and Cr2O3 possess excellent electrical conductivity and chemical activity, synergistically enhancing the material's electronic conductivity and stabilizing the SEI film. The flexibility in selecting multiple metal elements allows for the enhancement of a specific function through the characteristics of a single metal oxide (such as the rigid support of ZrO2), or the achievement of complementary functions through the combination of multiple metal elements (such as the combination of ZnO regulating the porous structure and Fe2O3 enhancing conductivity). This adapts to the requirements of different gradient structures, forming a synergistic effect in suppressing silicon volume expansion, improving structural stability, and enhancing electrochemical performance.

[0058] In some embodiments, the metal-organic framework material includes one or more of UiO-66, ZIF-8, and MIL-101.

[0059] Specifically, the controllable ratio of metal nodes (such as Zr in UiO-66, Zn in ZIF-8, and Fe / Cr in MIL-101) to organic ligands in the aforementioned metal-organic framework (MOF) materials, through adjustment of concentration and reaction conditions, facilitates the precise construction of a gradient pyrolysis layer with decreasing metal oxide content from the inside out. After pyrolysis, the ZrO2 derived from UiO-66 has high mechanical strength, which can strengthen the bonding between the inner layer and the silicon-carbon core to suppress expansion; the ZnO derived from ZIF-8 is easily volatilized to form a porous carbon structure, which is beneficial for optimizing the outer layer ion transport; and the Fe2O3 derived from MIL-101 can enhance conductivity and stabilize the SEI film. At the same time, the aforementioned metal-organic framework materials have good solubility in organic solvents and controllable pyrolysis behavior, which can stably prepare organic framework pyrolysis layers with a clear gradient structure, thereby synergistically improving the structural stability of silicon-carbon composite materials and the electrochemical performance of lithium-ion batteries.

[0060] In some embodiments, the thickness of the metal-organic framework pyrolysis layer is 30-100 nm.

[0061] Specifically, setting the thickness of the metal-organic framework pyrolysis layer to a range of 30-100 nm ensures that each component of the gradient structure (metal oxide layer, transition layer, porous carbon layer) fully performs its corresponding function, while avoiding problems such as insufficient structural support and poor buffering due to excessive thickness, or increased ion diffusion resistance and reduced overall conductivity of the material due to excessive thickness of the metal-organic framework pyrolysis layer. The metal-organic framework pyrolysis layer within this thickness range can achieve a good balance between structural stability and electrochemical performance, providing a suitable buffer space for silicon volume expansion and ensuring efficient lithium-ion transport.

[0062] Specifically, the thickness of the metal-organic framework pyrolysis layer can be 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm.

[0063] In some embodiments, the thickness of the metal oxide layer is 5-15 nm;

[0064] The thickness of the transition layer is 10-40 nm;

[0065] The thickness of the porous carbon layer is 15-45 nm.

[0066] Specifically, the thickness of the metal oxide layer can be 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm or 15nm, and more specifically, the thickness of the metal oxide layer can be 5nm, 6nm, 7nm, 8nm, 9nm or 10nm.

[0067] The thickness of the transition layer can be 10nm, 15nm, 20nm, 25nm, 26nm, 28nm, 29nm, 30nm, 32nm, 36nm or 40nm;

[0068] The thickness of the porous carbon layer can be 15nm, 20nm, 25nm, 29nm, 30nm, 35nm, 41nm or 45nm;

[0069] Furthermore, in some embodiments of this application, the thickness of the porous carbon layer in the obtained organic framework pyrolysis layer is greater than the thickness of the metal oxide layer.

[0070] It should be noted that the thicker porous carbon layer can provide more space for silicon volume expansion. In addition, the flexibility of the porous carbon layer is also conducive to enhancing the overall buffering capacity against silicon volume expansion. Its high porosity and continuous carbon phase can further widen the lithium-ion diffusion channels, extend the efficient electron transport path, and improve rate performance. At the same time, the thicker porous carbon layer, as an outer protective shell, can more effectively maintain the integrity of the material structure and reduce the risk of outer layer cracking caused by silicon expansion.

[0071] The relatively thin metal oxide layer, while ensuring a strong bond with the silicon-carbon core to suppress initial expansion, avoids increasing ion transport resistance due to excessive thickness. The differential thickness setting between the porous carbon layer and the metal oxide layer is beneficial to synergistically improving the structural stability and electrochemical performance of the silicon-carbon composite material.

[0072] In some embodiments, the silicon-carbon core includes a porous carbon framework, nano-silicon, and a carbon deposition layer, wherein the nano-silicon is dispersed on the porous carbon framework and the carbon deposition layer covers the porous carbon framework.

[0073] Specifically, the porous carbon framework provides a dispersion carrier for nano-silicon, which can reduce the aggregation of nano-silicon through spatial separation effect. At the same time, the porous structure of the porous carbon framework itself can reserve buffer space for silicon volume expansion. The nano-silicon dispersed on the framework can shorten the lithium ion diffusion distance. The carbon deposition layer covering the porous carbon framework can not only enhance the overall conductivity through continuous carbon phase, but also form a tighter interface bond with the metal oxide layer of the outer metal-organic framework pyrolysis layer, further strengthening the constraint on silicon expansion.

[0074] In some embodiments, the particle size of the nano-silicon is 1-50 nm;

[0075] The thickness of the carbon deposition layer is 5-20 nm.

[0076] Specifically, the 1-50nm nano-silicon particle size can reduce the stress caused by the volume expansion of a single particle and reduce the risk of structural breakage by utilizing the nano-size, while also shortening the lithium-ion diffusion distance and avoiding the problems of excessive surface energy and agglomeration caused by excessively small particle size; the 5-20nm carbon deposition layer thickness ensures complete coating of the porous carbon framework and nano-silicon and the construction of continuous electron transport channels, while avoiding excessive thickness that hinders lithium-ion migration.

[0077] Furthermore, the thickness of the carbon deposition layer can be 5 nm, 10 nm, 15 nm or 20 nm.

[0078] In some embodiments, the method for preparing the silicon-carbon composite material as described above includes the following operations:

[0079] Obtaining silicon-carbon cores;

[0080] A first precursor solution and a second precursor solution containing a metal-organic framework material are obtained, wherein the metal-organic framework material is obtained by coordination of a metal salt and an organic ligand.

[0081] The silicon-carbon core is placed in the first precursor solution and then heat-treated to obtain the first precursor.

[0082] The first precursor was placed in a solution of the second precursor and then heat-treated to obtain the second precursor.

[0083] The molar ratio of metal salt to organic ligand in the first precursor solution is greater than that in the second precursor solution;

[0084] The second precursor was heat-treated in an inert atmosphere to obtain a precursor with a metal oxide layer.

[0085] A precursor with a metal oxide layer is heat-treated in a reducing atmosphere to form a porous carbon layer, and a transition layer is formed between the metal oxide layer and the porous carbon layer to obtain a silicon-carbon composite material.

[0086] Specifically, in this operation, a metal-rich substrate is first formed on the surface of a silicon-carbon core using a first precursor solution with a high molar ratio of metal salt and organic ligand. This substrate is then heat-treated in an inert atmosphere to transform it into a metal oxide layer, ensuring strong interfacial bonding with the silicon-carbon core. Next, an outer layer is deposited using a second precursor solution with a low molar ratio of metal salt and organic ligand. This outer layer is then heat-treated in a reducing atmosphere to transform more of it into porous carbon. Meanwhile, a transition layer is formed in the middle region due to the gradient distribution of metal and carbon, ultimately resulting in a gradient structure where the metal oxide content decreases from the inside to the outside.

[0087] In some embodiments, the silicon-carbon core is prepared by means of:

[0088] A silicon source was introduced into the reaction chamber, and a porous carbon framework with nano-silicon deposition was obtained under high temperature conditions.

[0089] A carbon source is introduced and, under high-temperature catalytic conditions, a carbon deposition layer is formed on a porous carbon framework with nano-silicon deposits through chemical vapor deposition.

[0090] Specifically, porous carbon material is placed in a sintering furnace, and silane gas is introduced into an inert atmosphere at 400-800°C to deposit silicon material inside the porous carbon material. After deposition, the silane gas is switched to acetylene gas, and the temperature is increased to 600-1000°C to coat the surface of the porous carbon material with amorphous carbon, thus obtaining a silicon-carbon core.

[0091] Porous carbon frameworks have good compatibility with silicon-carbon materials and can provide a stable support framework for the growth of silicon-carbon cores. Their porous or layered structure is conducive to the uniform dispersion of nano-silicon and reserves space for subsequent volume expansion.

[0092] Under high-temperature catalytic conditions, the deposition rate and distribution of carbon and silicon sources can be precisely controlled, allowing nano-silicon to be uniformly loaded onto the carbon framework and form a continuous carbon deposition layer. This helps to ensure the integrity of electron transport channels. Furthermore, the chemical vapor deposition (CVD) process enables nanoscale composites of silicon and carbon, thereby reducing the concentration effect of silicon particle agglomeration and volume expansion from the source.

[0093] In some embodiments, the molar ratio of the metal salt to the organic ligand in the first precursor solution is 1:0.5 to 1:1.5; and / or,

[0094] In the second precursor solution, the molar ratio of metal salt to organic ligand is 1:3 to 1:10.

[0095] In some embodiments, the metal-organic framework material in the first precursor solution comprises 4%-10% by mass; and / or,

[0096] In the second precursor solution, the mass percentage of metal-organic framework material is 0.5%-4%.

[0097] Specifically, setting the mass percentage of metal-organic framework material in the first precursor solution within the range of 4%-10% ensures the formation of sufficient metal-rich component deposition on the silicon-carbon core surface, providing ample precursor material for subsequent conversion into a dense metal oxide layer. Setting the mass percentage of metal-organic framework material in the second precursor solution within the range of 0.5-4% controls the deposition amount of the outer metal-organic framework material, resulting in a thinner and more porous carbon layer after subsequent pyrolysis, reducing ion transport resistance. Simultaneously, by adjusting the concentration difference in conjunction with the ratio of metal salt to ligand, a gradient change in metal oxide content from the inside to the outside is formed, ensuring that the transition layer plays a buffering role in the silicon volume expansion. The above concentration settings not only ensure the effective formation of each layer structure in the metal-organic framework pyrolysis layer but also enhance the synergistic function of each layer through gradient differences.

[0098] In some embodiments, the metal salt is selected from Zr salt. After heat treatment in an inert atmosphere and a reducing atmosphere, the Zr salt forms ZrO2 and is dispersed in the metal oxide layer, the transition layer and the porous carbon layer.

[0099] Specifically, when the metal salt is selected from Zr salt, ZrO2 is formed. ZrO2 has high chemical stability and forms a strong interfacial bond with the silicon-carbon core in the metal oxide layer, which strengthens the initial constraint on the volume expansion of silicon. In the transition layer, ZrO2 is distributed with the content gradient, which helps the elastic modulus to transition smoothly from rigid to flexible and enhances the stress buffering capacity. In the porous carbon layer, the dispersed ZrO2 nanoparticles can guide the formation of a stable SEI film to reduce side reactions, while its chemical inertness does not affect the electron transport efficiency of the carbon layer.

[0100] Specifically, when the metal salt is selected from Zr salts, the process of forming ZrO2 from Zr salts includes:

[0101] The second precursor was heated to 400°C in the low-temperature range under an Ar inert atmosphere at a heating rate of 5°C / min and held for 3 hours for heat treatment. During this process, the inner layer of the MOF material in the second precursor preferentially decomposed, and the metal nodes were oxidized to Zr metal oxide. 4+ →ZrO2, the ligands are partially carbonized to form a mixed layer, thus obtaining a precursor with a metal oxide layer;

[0102] The precursor with the metal oxide layer was heated to 800°C in the high-temperature section at a heating rate of 10°C / min under H2 reducing atmosphere and held for 4 hours for heat treatment. The outer layer of MOF was completely carbonized, the metal oxide part was uniformly dispersed in the carbon matrix, and ZrO2 was stably present in the carbon layer to form a porous carbon layer. A transition layer was formed between the metal oxide layer and the porous carbon layer, thus obtaining a silicon-carbon composite material.

[0103] In some embodiments, the metal salt is selected from Zn salt. After heat treatment in an inert atmosphere, the Zn salt forms ZnO and is dispersed in the metal oxide layer, the transition layer and the porous carbon layer. After heat treatment in a reducing atmosphere, at least part of the ZnO is reduced to Zn and volatilized, forming pores in the metal oxide layer, the transition layer and the porous carbon layer.

[0104] Specifically, the ZnO formed after heat treatment in an inert atmosphere is dispersed in each layer of the metal-organic framework pyrolysis layer. In the metal oxide layer, it can help suppress silicon expansion through interfacial interaction, and in the transition layer, it participates in the construction of gradient structure to buffer stress. Under a reducing atmosphere, some ZnO is reduced to Zn and volatilizes, which can form abundant pores in each layer, providing additional buffer space for silicon volume expansion, while shortening the lithium ion diffusion path and improving electrolyte wettability.

[0105] Specifically, when the metal salt is selected from Zn salts, the operations of forming ZnO from the Zn salt and at least partially reducing ZnO to Zn include:

[0106] The second precursor was heated to 400°C in the low-temperature range under an Ar inert atmosphere at a heating rate of 5°C / min and held for 3 hours for heat treatment. During this process, the inner layer of the MOF material in the second precursor preferentially decomposed, and the metal nodes were oxidized to the metal oxide Zn. 2 +→ZnO, the ligands are partially carbonized to form a mixed layer, and then heated to 800℃ in the high-temperature section at a heating rate of 10℃ / min under H2 reducing atmosphere, and held for 4 hours for heat treatment. The outer layer of MOF is completely carbonized, the metal oxide part is uniformly dispersed in the carbon matrix, ZnO is reduced to Zn and volatilized, and pores are formed in the metal oxide layer, transition layer and porous carbon layer, thus obtaining silicon-carbon composite material.

[0107] In some embodiments, metal salts and organic ligands are dissolved in a solvent, and a catalyst is added to react, resulting in a first precursor solution and a second precursor solution having a metal-organic framework material.

[0108] The metal salt includes one or more of ZrCl4, Zn(NO3)2, and FeCl3; and / or,

[0109] The organic ligand includes one or more of terephthalic acid and 2-methylimidazole; and / or

[0110] The catalyst includes one or more of hydrochloric acid and acetic acid; and / or,

[0111] The solvent includes one or more of N,N-dimethylformamide and methanol.

[0112] Specifically, dissolving metal salts and organic ligands in a solvent, combined with a catalyst, can accelerate the reaction and improve the crystallinity and dispersibility of metal-organic framework (MOF) materials, ensuring uniform MOF particle size and structural stability in the precursor solution. By controlling the ratio and concentration of metal salts and organic ligands, first and second precursor solutions with different compositions can be precisely prepared. The morphology and content of MOF materials can be flexibly adjusted by controlling the reaction time and temperature, ensuring that the MOF layer is uniformly coated on the core surface. Through subsequent pyrolysis, it is transformed into a gradient coating layer with controllable structure, thereby achieving the regulation of material properties.

[0113] In some embodiments, when the second precursor is heat-treated in an inert atmosphere, the heat treatment time is 1-5 hours, the heat treatment temperature is 300-500℃, and the heating rate is 2-10℃ / min.

[0114] When heat treatment is performed in the reducing atmosphere, the heat treatment time is 1-5 hours, the heat treatment temperature is 600-900℃, and the heating rate is 2-10℃ / min.

[0115] In some embodiments, when preparing the first precursor, the heat treatment time is 1-6 hours and the heat treatment temperature is 30-50°C;

[0116] When preparing the second precursor, the heat treatment time is 6-12 hours and the heat treatment temperature is 50-80℃.

[0117] In another embodiment of the present invention, a negative electrode sheet is provided, comprising a negative electrode material layer, wherein the negative electrode material layer comprises a binder, a conductive agent, and the aforementioned silicon-carbon composite material, or a silicon-carbon composite material prepared by the method for preparing the aforementioned silicon-carbon composite material.

[0118] Specifically, the negative electrode includes the silicon-carbon composite material provided in this application. This silicon-carbon composite material includes a core and a metal-organic framework pyrolysis layer. The metal-organic framework pyrolysis layer is sequentially composed of a metal oxide layer, a transition layer, and a porous carbon layer from the inside out. The content of the metal oxide decreases sequentially from the metal oxide layer and the transition layer to the porous carbon layer, forming a gradient distribution with decreasing metal oxide content. The high metal oxide content in the metal oxide layer can suppress the initial stress of volume expansion through close bonding with the silicon-carbon core. The transition layer achieves gradual buffering and dispersion of stress through the mixing ratio of metal oxide and carbon. The outermost porous carbon layer, with its flexibility and porous structure, provides space for volume changes in the silicon-carbon core and maintains the overall structural integrity. Furthermore, the synergistic effect of the metal oxide and carbon guides the formation of a uniform and stable SEI film, reducing side reactions and ensuring the continuity of electron and ion transport channels, thus avoiding electrical performance degradation due to structural breakage. In other words, the silicon-carbon composite material provided in this application suppresses silicon volume expansion while simultaneously ensuring the structural stability and electrochemical performance of the material.

[0119] The present invention will be further illustrated by the following examples.

[0120] Table 1

[0121]

[0122]

[0123] Table 2

[0124]

[0125] Example 1

[0126] This embodiment illustrates the silicon-carbon composite material, its preparation method, and the negative electrode sheet disclosed in this invention, and includes the following steps:

[0127] Porous carbon material is placed in a sintering furnace, and silane gas is introduced in an inert atmosphere at 400°C to deposit silicon material inside the porous carbon material. After deposition, the silane gas is switched to acetylene gas, and the temperature is increased to 600°C to coat the surface of the porous carbon material with amorphous carbon to obtain a silicon-carbon core.

[0128] 4.64 g of metal salt ZrCl4 and 3.32 g of organic ligand terephthalic acid were dissolved in 100 mL of N,N-dimethylformamide solvent. After adding 5 mL of concentrated hydrochloric acid catalyst, the first precursor solution with metal-organic framework material was obtained.

[0129] 4.64 g of metal salt ZrCl4 and 9.96 g of organic ligand terephthalic acid were dissolved in 100 mL of N,N-dimethylformamide solvent. After adding 5 mL of concentrated hydrochloric acid catalyst, a second precursor solution with metal-organic framework material was obtained.

[0130] The silicon-carbon core was placed in the first precursor solution and stirred at 40°C for 3 hours. After the reaction was completed, the precursor was separated, washed and dried to obtain the first precursor.

[0131] The first precursor was placed in the second precursor solution and stirred at 70°C for 9 hours. After the reaction was completed, the precursor was separated, washed and dried to obtain the second precursor (silicon-carbon core coated with MOF material).

[0132] The second precursor was heated to 400°C in the low-temperature range under an Ar inert atmosphere at a heating rate of 5°C / min and held for 3 hours for heat treatment. During this process, the inner layer of the MOF material in the second precursor preferentially decomposed, and the metal nodes were oxidized to Zr metal oxide. 4+ →ZrO2, the ligands are partially carbonized to form a mixed layer, thus obtaining a precursor with a metal oxide layer;

[0133] The precursor with a metal oxide layer was heated to 800℃ in the high-temperature section at a heating rate of 10℃ / min under a H2 reducing atmosphere and held for 4 hours for heat treatment. The outer layer of MOF was completely carbonized, the metal oxide part was uniformly dispersed in the carbon matrix, and ZrO2 was stably present in the carbon layer to form a porous carbon layer. A transition layer was formed between the metal oxide layer and the porous carbon layer, thus obtaining a silicon-carbon composite material. The metal oxide and carbon contents of the metal oxide layer, the transition layer and the porous carbon layer were detected and recorded in Table 1. The thickness of the metal oxide layer (nm), the thickness of the transition layer (nm), the thickness of the porous carbon layer (nm), and the thickness of the metal-organic framework pyrolysis layer (nm) were detected and recorded in Table 2.

[0134] Silicon-carbon composite material, polyvinylidene fluoride (PVDF), and acetylene black are mixed in a mass ratio of 80:10:10, and an appropriate amount of N-methylpyrrolidone (NMP) solvent is added and stirred evenly to form a negative electrode slurry.

[0135] The negative electrode slurry is coated onto a copper foil current collector, dried at 120°C for 8 hours, and then rolled to form a negative electrode sheet.

[0136] Example 2

[0137] This embodiment illustrates the silicon-carbon composite material, the method for preparing the silicon-carbon composite material, and the negative electrode sheet disclosed in this invention. It includes most of the operations in Example 1, but differs in that:

[0138] 5.95 g of metal salt Zn(NO3)2・6H2O and 1.64 g of organic ligand 2-methylimidazole were dissolved in 100 mL of methanol solvent, and 5 mL of concentrated hydrochloric acid catalyst was added to react and obtain the first precursor solution with metal-organic framework material.

[0139] 5.95 g of metal salt Zn(NO3)2・6H2O and 4.92 g of organic ligand 2-methylimidazole were dissolved in 100 mL of methanol solvent, and 5 mL of concentrated hydrochloric acid catalyst was added to react and obtain a second precursor solution with metal-organic framework material.

[0140] The second precursor was heated to 400°C in the low-temperature range under an Ar inert atmosphere at a heating rate of 5°C / min and held for 3 hours for heat treatment. During this process, the inner layer of the MOF material in the second precursor preferentially decomposed, and the metal nodes were oxidized to the metal oxide Zn. 2+ →ZnO, the ligands are partially carbonized to form a mixed layer, thus obtaining a precursor with a metal oxide layer;

[0141] The precursor with a metal oxide layer was heated to 800℃ in a high-temperature zone at a heating rate of 10℃ / min under a H2 reducing atmosphere and held for 4 hours for heat treatment. The outer layer of the MOF was completely carbonized, ZnO was reduced to elemental Zn and volatilized, leaving porous carbon to form a porous carbon layer. A transition layer was formed between the metal oxide layer and the porous carbon layer, thus obtaining a silicon-carbon composite material. The metal oxide and carbon contents of the metal oxide layer, transition layer and porous carbon layer were detected and recorded in Table 1. The thickness of the metal oxide layer (nm), the thickness of the transition layer (nm), the thickness of the porous carbon layer (nm), and the thickness of the metal-organic framework pyrolysis layer (nm) were detected and recorded in Table 2.

[0142] Example 3-12

[0143] Examples 3-12 illustrate the silicon-carbon composite material, the method for preparing the silicon-carbon composite material, and the negative electrode sheet disclosed in this invention. They include most of the operations in Example 1, except that:

[0144] According to Table 2, the ratio of metal salt to organic ligand in the first precursor solution, the ratio of metal salt to organic ligand in the second precursor solution, the nano-silicon particle size (nm), and the thickness of the carbon deposition layer (nm) are as follows.

[0145] The metal oxide and carbon contents of the metal oxide layer, transition layer and porous carbon layer were detected and recorded in Table 1. The thicknesses of the metal oxide layer (nm), transition layer (nm), porous carbon layer (nm), and metal-organic framework pyrolysis layer (nm) were detected and recorded in Table 2.

[0146] Comparative Example 1

[0147] This comparative example is used to illustrate the silicon-carbon composite material, the method for preparing the silicon-carbon composite material, and the negative electrode sheet disclosed in this invention. It includes most of the operations in Example 1, with the following differences:

[0148] The anode slurry is prepared directly using a silicon-carbon core without the preparation of a metal-organic framework pyrolysis layer.

[0149] Comparative Example 2

[0150] This comparative example is used to illustrate the silicon-carbon composite material, the method for preparing the silicon-carbon composite material, and the negative electrode sheet disclosed in this invention. It includes most of the operations in Example 1, but the difference is:

[0151] The silicon-carbon core is not treated with the first precursor solution. Instead, it is placed directly in the second precursor solution and stirred at 70°C for 9 hours. After the reaction is completed, it is separated, washed and dried to obtain the second precursor (silicon-carbon core coated with MOF material).

[0152] Comparative Example 3

[0153] This comparative example is used to illustrate the silicon-carbon composite material, the method for preparing the silicon-carbon composite material, and the negative electrode sheet disclosed in this invention. It includes most of the operations in Example 1, but the difference is:

[0154] The first precursor obtained is not treated with the second precursor solution; the first precursor is used instead of the second precursor for subsequent operations.

[0155] Comparative Example 4

[0156] This comparative example is used to illustrate the silicon-carbon composite material, the method for preparing the silicon-carbon composite material, and the negative electrode sheet disclosed in this invention. It includes most of the operations in Example 1, but the difference is:

[0157] After obtaining the precursor with the metal oxide layer, no H2 reduction treatment is performed, and the negative electrode slurry is directly prepared using the precursor with the metal oxide layer.

[0158] Comparative Example 5

[0159] This comparative example is used to illustrate the silicon-carbon composite material, the method for preparing the silicon-carbon composite material, and the negative electrode sheet disclosed in this invention. It includes most of the operations in Example 2, but the difference is:

[0160] After obtaining the precursor with the metal oxide layer, no H2 reduction treatment is performed, and the negative electrode slurry is directly prepared using the precursor with the metal oxide layer.

[0161] Performance testing

[0162] The following performance tests were performed on Examples 1-12 and Comparative Examples 1-5 prepared above:

[0163] The prepared negative electrode sheet is assembled into a lithium-ion battery.

[0164] Test method: The battery was subjected to 1C / 1C charge-discharge cycle test at 25℃ and within the range of 2.8V-4.5V (1C=1800 mAh / g).

[0165] First charge / discharge efficiency = First discharge specific capacity / First charge specific capacity;

[0166] Capacity retention rate after 100 cycles = discharge specific capacity after 100 cycles / initial discharge specific capacity;

[0167] The test results are entered into Table 3.

[0168] Table 3

[0169]

[0170] As can be seen from the test results in Table 3, the first charge-discharge efficiency of Examples 1-12 is significantly higher than that of Comparative Example 1 without a metal-organic framework pyrolysis layer, indicating that the metal-organic framework pyrolysis layer provided in this application can effectively suppress silicon volume expansion.

[0171] In Example 1, the metal oxide layer has a metal oxide content of 80% by mass and a retention rate of 91.5% after 100 cycles. The transition layer has 50% metal oxide. The gradient of metal oxide content achieves a smooth transition of elastic modulus from rigid to flexible, avoiding stress concentration. Furthermore, the transition layer in Example 1 has 50% metal oxide and 50% carbon, and its retention rate is higher than that of Example 6, where the transition layer has 30% metal oxide.

[0172] Example 3 showed the highest initial charge-discharge efficiency at 92.1%, while Example 10 showed the lowest at 86.2%. This is presumably because in Example 3, the total thickness of the metal-organic framework pyrolysis layer was 100 nm, with thicker transition layers (40 nm) and porous carbon layers (45 nm), which better buffered stress and provided space for volume expansion. The large difference in the molar ratio of the first precursor solution's metal salt to organic ligand (1:0.5) and the second precursor's (1:10) resulted in a more significant gradient in metal oxide content after pyrolysis, with a more reasonable carbon content gradient (15%, 50%, 90%) between the metal oxide layer (85%), transition layer (50%), and porous carbon layer (10%), thus enhancing electron transport and structural flexibility. In contrast, Example 10... The total thickness is 92nm, with the transition layer (36nm) and porous carbon layer (41nm) being relatively thin. The ratio of the first and second precursors is 1:1 and 1:3, with little difference. The content of metal oxides (90%, 62%, 28%) and carbon content (10%, 38%, 72%) have a gentle gradient, and the carbon deposition layer is only 5nm thick. The relatively thin carbon deposition layer may weaken the protection of the core and electron conduction.

[0173] Example 4 exhibited the highest initial discharge specific capacity at 1768 mAh / g, while Example 12 showed the lowest at 1656 mAh / g. In Example 4, the total thickness of the metal-organic framework pyrolysis layer was 30 nm, with relatively thin metal oxide layer (5 nm), transition layer (10 nm), and porous carbon layer (15 nm). The molar ratio of metal salt to organic ligand in the first precursor solution was 1:1.5, and that of the second precursor was 1:3. The gradient of metal oxide content in the metal oxide layer (70%), transition layer (70%), and porous carbon layer (30%) was not significant, while the gradient of carbon content was not obvious. The thickness of the silicon nanoparticles (30%, 30%, 70%) is relatively flat, but the 10nm silicon nanoparticle size and the 10nm carbon deposition layer are conducive to ion transport. In Example 12, the total thickness is 64nm, with a relatively thick metal oxide layer (9nm), transition layer (25nm), and porous carbon layer (30nm). The ratio of the first and second precursors is 1:1 and 1:3, and the gradient of metal oxide content (71%, 38%, 19%) and carbon content (29%, 62%, 81%) is more reasonable. Although the 20nm carbon deposition layer enhances protection, with a silicon nanoparticle size of 10nm, an excessively thick carbon layer may increase the resistance to ion transport.

[0174] The test results of Comparative Examples 1-5 show that Comparative Example 1, which did not prepare a metal-organic framework pyrolysis layer, had the worst performance in all aspects, with an initial charge-discharge efficiency of only 68.5% and a capacity retention rate of 65.2% after 100 cycles. This demonstrates the importance of the metal-organic framework pyrolysis layer provided in this application for improving electrical performance.

[0175] Comparative Example 2 uses only the second precursor solution to treat the silicon-carbon core, without the first precursor solution treatment. Although its performance is better than that of Comparative Example 1, it is still worse than the example with a complete metal-organic framework pyrolysis layer (first charge-discharge efficiency 75.2%, cycle retention 74.8%). This shows that the complete metal-organic framework pyrolysis layer is beneficial to alleviate the expansion of the silicon-carbon core.

[0176] Comparative Example 3 was treated with only the first precursor solution and did not use the second precursor solution. Its performance was slightly better than that of Comparative Example 2 (initial charge-discharge efficiency of 78.3% and cycle retention of 72.3%), but due to the lack of an outer porous carbon layer, its structural buffering and ion transport capabilities were insufficient.

[0177] Of Comparative Examples 4 and 5, Comparative Example 4 performed relatively better, with an initial charge-discharge efficiency of 82.4% and a cycle retention rate of 81.2%. However, neither of them underwent heat treatment in a reducing atmosphere after obtaining the precursor with the metal oxide layer during the preparation process. This prevented the formation of a porous carbon layer and a transition layer between the metal oxide layer and the porous carbon layer. Consequently, the gradient structure of the metal-organic framework pyrolysis layer was incomplete. Without a transition layer, it was impossible to achieve gradual buffering and dispersion of stress. Without a porous carbon layer, it was impossible to provide sufficient space for changes in the volume of the silicon-carbon core, making it difficult to maintain the integrity of the overall structure.

[0178] The test results from the above embodiments and comparative examples show that the silicon-carbon composite material with a core and a metal-organic framework pyrolysis layer provided by the present invention improves the performance of lithium-ion batteries through the multi-layer structure of its metal-organic framework pyrolysis layer and the synergistic effect of the core.

[0179] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that, The device includes a core and a metal-organic framework pyrolysis layer. The core is a silicon-carbon core. The metal-organic framework pyrolysis layer covers the core and includes metal oxides and carbon. The metal-organic framework pyrolysis layer includes a metal oxide layer, a transition layer and a porous carbon layer from the inside to the outside. The content of the metal oxide decreases sequentially from the metal oxide layer and the transition layer to the porous carbon layer. The metal oxide layer has a metal oxide content of 70%-90% by mass, the transition layer has a metal oxide content of 30%-70% by mass, and the porous carbon layer has a metal oxide content of 2%-30% by mass. The carbon content increases sequentially from the metal oxide layer, the transition layer to the porous carbon layer; The mass percentage of carbon in the metal oxide layer is 10%-30%, the mass percentage of carbon in the transition layer is 30%-70%, and the mass percentage of carbon in the porous carbon layer is 70%-100%. The silicon-carbon core includes a porous carbon framework, nano-silicon, and a carbon deposition layer. The nano-silicon is dispersed on the porous carbon framework, and the carbon deposition layer covers the porous carbon framework.

2. The silicon-carbon composite material according to claim 1, characterized in that, The metal-organic framework pyrolysis layer is obtained by pyrolysis of metal-organic framework material, and the metal elements in the metal-organic framework material include one or more of Zr, Zn, Fe, and Cr.

3. The silicon-carbon composite material according to claim 2, characterized in that, The metal-organic framework material includes one or more of UiO-66, ZIF-8, and MIL-101.

4. The silicon-carbon composite material according to claim 1, characterized in that, The thickness of the metal-organic framework pyrolysis layer is 30-100 nm.

5. The silicon-carbon composite material according to claim 1, characterized in that, The thickness of the metal oxide layer is 5-15 nm; The thickness of the transition layer is 10-40 nm; The thickness of the porous carbon layer is 15-45 nm.

6. The silicon-carbon composite material according to claim 1, characterized in that, The particle size of the nano-silicon is 1-50 nm; The thickness of the carbon deposition layer is 5-20 nm.

7. The method for preparing the silicon-carbon composite material according to any one of claims 1-6, characterized in that, Includes the following operations: Obtaining silicon-carbon cores; A first precursor solution and a second precursor solution containing a metal-organic framework material are obtained, wherein the metal-organic framework material is obtained by coordination of a metal salt and an organic ligand. The silicon-carbon core is placed in the first precursor solution and then heat-treated to obtain the first precursor. The first precursor was placed in a solution of the second precursor and then heat-treated to obtain the second precursor. The molar ratio of metal salt to organic ligand in the first precursor solution is greater than that in the second precursor solution; The second precursor was heat-treated in an inert atmosphere to obtain a precursor with a metal oxide layer. A precursor with a metal oxide layer is heat-treated in a reducing atmosphere to form a porous carbon layer, and a transition layer is formed between the metal oxide layer and the porous carbon layer to obtain a silicon-carbon composite material.

8. The method for preparing the silicon-carbon composite material according to claim 7, characterized in that, The silicon-carbon core is prepared by the following method: A silicon source was introduced into the reaction chamber, and a porous carbon framework with nano-silicon deposition was obtained under high temperature conditions of 400-800℃. A carbon deposit layer is formed on a porous carbon framework with nano-silicon deposits by introducing a carbon source and catalyzing at a high temperature of 600-1000℃.

9. The method for preparing the silicon-carbon composite material according to claim 7, characterized in that, In the first precursor solution, the molar ratio of the metal salt to the organic ligand is 1:0.5 to 1:1.5; and / or, In the second precursor solution, the molar ratio of metal salt to organic ligand is 1:3 to 1:

10.

10. The method for preparing the silicon-carbon composite material according to claim 7, characterized in that, In the first precursor solution, the mass percentage of the metal-organic framework material is 4%-10%; and / or, In the second precursor solution, the mass percentage of metal-organic framework material is 0.5%-4%.

11. The method for preparing the silicon-carbon composite material according to claim 7, characterized in that, The metal salt is selected from Zr salt. After heat treatment in an inert atmosphere and a reducing atmosphere, the Zr salt forms ZrO2 and is dispersed in the metal oxide layer, the transition layer and the porous carbon layer.

12. The method for preparing the silicon-carbon composite material according to claim 7, characterized in that, The metal salt is selected from Zn salt. After heat treatment in an inert atmosphere, the Zn salt forms ZnO and is dispersed in the metal oxide layer, transition layer and porous carbon layer. After heat treatment in a reducing atmosphere, at least part of the ZnO is reduced to Zn and volatilized, forming pores in the metal oxide layer, transition layer and porous carbon layer.

13. The method for preparing the silicon-carbon composite material according to claim 7, characterized in that, Metal salts and organic ligands are dissolved in a solvent, and a catalyst is added to react, resulting in a first precursor solution and a second precursor solution with a metal-organic framework material. The metal salt includes one or more of ZrCl4, Zn(NO3)2, and FeCl3; and / or, The organic ligand comprises one or more of terephthalic acid and 2-methylimidazole; and / or The catalyst includes one or more of hydrochloric acid and acetic acid; and / or, The solvent includes one or more of N,N-dimethylformamide and methanol.

14. The method for preparing the silicon-carbon composite material according to claim 7, characterized in that, When the second precursor is heat-treated in an inert atmosphere, the heat treatment time is 1-5 hours, the heat treatment temperature is 300-500℃, and the heating rate is 2-10℃ / min. When heat treatment is performed in the reducing atmosphere, the heat treatment time is 1-5 hours, the heat treatment temperature is 600-900℃, and the heating rate is 2-10℃ / min.

15. The method for preparing the silicon-carbon composite material according to claim 7, characterized in that, When preparing the first precursor, the heat treatment time is 1-6 hours and the heat treatment temperature is 30-50℃; When preparing the second precursor, the heat treatment time is 6-12 hours and the heat treatment temperature is 50-80℃.

16. A negative electrode sheet, characterized in that, The material includes a negative electrode material layer, which comprises a binder, a conductive agent, and a silicon-carbon composite material as described in any one of claims 1-6, or a silicon-carbon composite material prepared by the method described in any one of claims 7-15.

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