Silicon-carbon composite material, preparation method thereof and secondary battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a silicon-carbon composite material, a preparation method thereof and a secondary battery. The silicon-carbon composite material comprises a shell and an inner core, wherein the mass ratio of the shell to the inner core is (1-5): 100; the inner core comprises mesoporous carbon, and nano silicon and heteroatoms are deposited in pores and on the surface of the mesoporous carbon; the shell is composed of amorphous carbon and solid electrolyte. The preparation method comprises the following steps: preparing modified mesoporous carbon by adopting a double-template method; sequentially introducing silane mixed gas and carbon source mixed gas into the fluidized bed, and depositing nano silicon and amorphous carbon on the surface of the mesoporous carbon; and finally, depositing a solid electrolyte coating layer on the surface of the material by adopting a magnetron sputtering method. According to the invention, through the synergistic effect of the design of the hierarchical pore structure, co-doping of heteroatoms and lithium and coating of the solid electrolyte, the ion diffusion rate, the electronic conductivity and the structural stability of the material are remarkably improved, and the prepared silicon-carbon composite material has high specific capacity, high first efficiency, low resistance and excellent cycle performance.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a silicon-carbon composite material and its preparation method, and a secondary battery. Background Technology

[0002] When existing silicon-carbon composite materials are used as anodes in lithium-ion batteries, there are still significant shortcomings in terms of cycle stability and rate performance. The root cause lies mainly in the structural and property limitations of carbon matrix materials.

[0003] Specifically, on the one hand, commonly used porous carbon materials, due to their wide pore size distribution and poor pore connectivity, result in uneven distribution of the loaded silicon nanoparticles, making them prone to failure during cycling due to localized stress concentration, leading to rapid capacity decay. On the other hand, porous carbon itself has low electronic conductivity, which severely limits the charge / discharge rate and power performance of the electrodes.

[0004] Although using mesoporous carbon with a more regular structure as a carrier can improve the uniformity of silicon distribution and buffer volume expansion to some extent, thereby improving cycle life, the rate performance of silicon-carbon composites based on mesoporous carbon still needs further improvement. Simultaneously optimizing its electron and ion transport efficiency is key to enhancing the overall performance of this material. Summary of the Invention

[0005] In view of this, this application provides a silicon-carbon composite material and its preparation method, as well as a secondary battery, to solve the technical problems of low electronic / ionic conductivity and poor cycle performance of silicon-carbon composite materials.

[0006] To achieve one or more of the above objectives or other objectives, the first aspect of this application provides a silicon-carbon composite material comprising a core and a shell, wherein the mass ratio of the shell to the core is (1-5):100. The core comprises mesoporous carbon, the pores and surface of which are deposited with nano-silicon and heteroatoms; the outer shell is composed of amorphous carbon and solid electrolyte.

[0007] The silicon-carbon composite material described in this application has a mesoporous carbon core. The numerous nanoscale pores inside the mesoporous carbon provide space for the expansion of nano-silicon during lithium intercalation, effectively improving the cycle performance of the anode material.

[0008] Preferably, based on a 100% total mass ratio of the core, the core consists of 40-45% mesoporous carbon, 40-45% nano-silicon, and 10-20% heteroatoms. This ratio is designed to allow the mesoporous carbon, nano-silicon, and heteroatoms to work synergistically.

[0009] Mesoporous carbon provides a rigid framework and conductive network for the negative electrode of silicon-carbon composite materials. Too low a mesoporous carbon content will lead to a decrease in conductivity and mechanical strength, while too high a content will lead to a decrease in tap density and volumetric energy density. Therefore, this application controls the mesoporous carbon content within a reasonable range of 40-45%.

[0010] The addition of nano-silicon can provide higher energy density, but excessive content can cause the collapse of mesoporous carbon structures and agglomeration of silicon particles, accelerating pulverization. Therefore, this application controls the nano-silicon content within a reasonable range of 40%-45% to achieve better overall performance.

[0011] Doping heteroatoms in silicon-carbon composites can improve electronic conductivity and provide active sites. However, if the doping amount is too low, the effect will be insignificant, while if the doping amount is too high, it will introduce too many defects and reduce the conductivity of the material.

[0012] Preferably, the amorphous carbon is lithium-doped amorphous carbon.

[0013] Preferably, the outer shell consists of amorphous carbon and solid electrolyte from the inside out. Based on a total mass ratio of 100%, the outer shell is composed of 30-50% solid electrolyte and 50-70% amorphous carbon.

[0014] This application uses lithium-doped amorphous carbon, which helps to reduce carbon framework defects, improve ionic conductivity, and alleviate the damage to the structure caused by the volume effect of active materials during cycling, thereby improving the cycling stability of the material.

[0015] A second aspect of this application provides a method for preparing a silicon-carbon composite material, the method comprising the following steps: Step S1 Inorganic template, organic template, and coupling agent are added to a carbohydrate compound solution and dispersed evenly. After spray drying, a precursor is obtained. The precursor is transferred to a tube furnace and heated to 900-1100°C. Steam is introduced for activation for at least 1 hour. After cooling, a mixture of heteroatom gas and crosslinking gas is introduced to obtain modified mesoporous carbon.

[0016] Step S2 The modified mesoporous carbon is added to a fluidized bed, an inert gas is introduced to purge the air from the tube, the temperature is raised to 450-600°C, a silane mixed gas is introduced for no more than 1 hour, and then the temperature is raised to 500-900°C, a carbon source mixed gas is introduced for no more than 1 hour, to obtain an intermediate material with amorphous carbon deposited on the surface.

[0017] Step S3 A solid electrolyte is deposited on the surface of the intermediate material to obtain a solid electrolyte-coated silicon-carbon composite material.

[0018] This application describes the creation of pores in carbohydrate compounds under dual-template conditions (organic template and inorganic template) to prepare a uniform nano- or micro-sized pore structure, resulting in mesoporous carbon materials. Compared with porous carbon, mesoporous carbon materials have advantages such as uniform pore size and strong compressive strength. Furthermore, heteroatom doping is performed to improve the electronic conductivity of the materials and enhance rate performance.

[0019] In step S1, during precursor activation, water vapor is typically introduced at a flow rate of 100-500 SCCM for 60-600 minutes. By controlling the water vapor flow rate, activation time, and subsequent doping temperature, the mesoporous carbon structure is optimized.

[0020] After activation, the temperature is usually lowered to 500-800℃ before heteroatom gas and cross-linking gas are introduced. The temperature is precisely controlled at 500-800℃ to achieve efficient and stable heteroatom doping through a controllable gas phase reaction without damaging the excellent pore structure and conductive framework created in the first step.

[0021] In step S2, the flow rate of the silane mixed gas is typically controlled at 10-100 SCCM for 10-60 minutes. Under suitable flow rate and temperature conditions, the silane decomposition rate is moderate, which is beneficial for forming uniformly distributed ultrafine nanoparticles and achieving uniform deposition.

[0022] During amorphous carbon deposition, the carbon source mixed gas flow rate is 5-20 SCCM and the time is 10-60 minutes. By controlling the temperature, flow rate, and time, the carbon cracking rate, nucleation rate during deposition, and deposition amount are moderate, so that the final silicon-carbon composite material has better comprehensive electrochemical performance.

[0023] In step S3, the solid electrolyte suitable for this application is preferably a garnet-type electrolyte (such as LLZO, i.e., lithium lanthanum zirconate, with the chemical formula Li7La3Zr2O). 12 NASICON-type electrolytes (such as LATP, i.e., lithium aluminum titanate phosphate, chemical formula Li) 1+X Al X Ti 2-X (PO4)3 (x value between 0 and 0.5), and lithium aluminum phosphate germanate (LAGP, chemical formula Li). 1+y Al y Ge 2-y At least one of (PO4)3 (y value between 0 and 0.8) is used in the preparation of the silicon-carbon composite material of this application. The synergistic effect of the materials is better, resulting in better overall performance of the final silicon-carbon composite material.

[0024] Preferably, step S1 satisfies one or more of the following conditions ag: a. The inorganic template is at least one of sodium carbonate, potassium carbonate, and magnesium carbonate; b. The organic template is an organic compound containing lithium; preferably, the organic template is at least one of lithium gluconate, lithium lactate, and lithium citrate; c. The mass ratio of the inorganic template, the organic template, the coupling agent, and the carbohydrate compound is (5-15):(5-15):(1-5):100; d. The carbohydrate compound is at least one selected from glucose, sucrose, fructose, galactose, ribose, maltose, or lactose, and the concentration of the carbohydrate compound solution is 1-10 wt%. e. The heteroatom gas is one of nitrogen, sulfur, phosphorus, and boron; f. The crosslinking gas is at least one of peracetic acid peroxide, butanone peroxide, cyclohexanone peroxide, and benzoic acid peroxide; g. The volume ratio of the heteroatom gas and the crosslinking gas is heteroatom gas: crosslinking gas = 10: (1-5).

[0025] In this application, the organic template is an organic compound containing lithium. After carbonization, it generates lithium-doped amorphous carbon, reducing defects in porous carbon and improving ionic conductivity. The organic template generates smaller pores, while the inorganic template generates larger pores. The two work synergistically to generate abundant nano- and micro-pores, which increases the amount of active silicon deposited and avoids silicon agglomeration.

[0026] Inorganic templates can create large pores. If the content is too high, it will create too many and too large pores, which will reduce mechanical strength. If it is too low, it will result in insufficient large pores, which will reduce the rate performance level and cycle stability.

[0027] Excessive organic template content leads to decomposition and the generation of excessive amorphous carbon, which blocks the valuable macropores created by the inorganic template, resulting in a decrease in specific surface area and pore volume, while also causing uneven lithium doping. Insufficient content prevents the formation of a well-developed porous structure, resulting in carbon materials with fewer channels, smaller pore volume, and lower specific surface area.

[0028] Carbohydrate solutions can act as dispersants and binders in the initial stage of mesoporous carbon formation, uniformly dispersing organic templates, inorganic templates, and coupling agents. At the same time, the carbonization of carbohydrates releases small molecule gases, forming a large number of micropores, which can work synergistically with the template to form a hierarchical porous structure in the final carbon structure. Furthermore, carbohydrates can generate porous carbon precursor materials with smaller particle sizes, reducing impedance.

[0029] Setting the volume ratio of heteroatom gas to crosslinking gas to 10:(1-5) allows the heteroatom gas to dominate the reaction atmosphere, preferentially achieving efficient doping of the carbon skeleton, thereby significantly improving the electronic conductivity of the material; at the same time, a small amount of crosslinking gas is used to crosslink and stabilize the new defect sites generated by doping in situ, enhancing the mechanical strength of the carbon skeleton and the durability of the doped structure without excessively blocking the pores.

[0030] If the crosslinking gas content is too high, amorphous carbon will be excessively deposited, which will not only compete with and inhibit the doping efficiency of heteroatoms, but also block the mesopore channels, resulting in a decrease in specific surface area and obstruction of ion transport. If the crosslinking gas content is too low, it will not be able to effectively repair the lattice defects introduced by doping, resulting in insufficient stability of the carbon skeleton. During cycling, the doped structure is prone to degradation, affecting the long-term performance of the material.

[0031] Preferably, the silane mixed gas is a mixture of at least one of silane, silane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane with nitrogen, and the volume ratio is 1:(1-3).

[0032] Alternatively, the carbon source gas mixture is a mixture of at least one of methane, ethane, ethylene, acetylene, and propane with nitrogen, in a volume ratio of 1:(1-3).

[0033] An appropriate nitrogen content can effectively dilute the silane mixture and carbon source gas, making their reaction on the mesoporous carbon surface more gentle. At the same time, it also acts as a carrier gas, enhancing the flowability and permeability of the silane mixture and carbon source gas.

[0034] This application achieves synergistic effects among components by screening organic templates, inorganic templates, coupling agents, crosslinking gases, heteroatom gases, and carbohydrate compounds, and by rationally configuring the mass / volume ratios, thereby significantly improving the rate performance and cycle performance of the prepared silicon-carbon composite.

[0035] Preferably, in step S3, the mass ratio of solid electrolyte to intermediate material is (1-5):100; Preferably, the solid electrolyte is deposited on the surface of the intermediate material using magnetron sputtering. The magnetron sputtering parameters are: power 10-50W, time 10-100s, and vacuum degree (1-10)×10⁻⁶. -4 Pa, self-bias pressure ≤1Pa, gas source is either argon or helium.

[0036] For many solid electrolyte materials, grain boundaries are a major obstacle to ion migration. Preparing highly oriented or even epitaxially grown thin films via magnetron sputtering can reduce or even eliminate grain boundaries, thereby achieving high ionic conductivity close to theoretical values. Therefore, by depositing a solid electrolyte thin film on the surface of the intermediate material using magnetron sputtering technology, the ionic conductivity of the material can be further improved, thus enhancing rate performance.

[0037] Furthermore, magnetron sputtering technology enables the solid electrolyte film to form strong chemical bonds and mechanical interlocks with the substrate, resulting in strong adhesion. This reduces interfacial impedance and allows the film to withstand the stress caused by changes in electrode volume during battery cycling, thus maintaining interfacial stability.

[0038] A third aspect of this application provides a secondary battery made of the aforementioned silicon-carbon composite material. The secondary battery is obtained by assembling a negative electrode sheet made of the silicon-carbon composite material with an electrolyte, a separator, and a positive electrode sheet. The secondary battery includes button cells and pouch cells.

[0039] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will be further illustrated by the embodiments and drawings. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] in: Figure 1 This is a schematic diagram of a scanning electron microscope image of a silicon-carbon composite material in one embodiment. Detailed Implementation

[0042] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0044] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0045] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0046] In this application, if the unit of a data range is only followed by the right endpoint, it means that the units of the left and right endpoints are the same.

[0047] In this application, terms such as "multiple," "various," and "repeatedly" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "multiple" means two or more. This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0048] The "scope" disclosed in this application is defined by a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way may include end values ​​or not.

[0049] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows for temperature fluctuations within the precision range controlled by the instrument.

[0050] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0051] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but sequentially is preferred.

[0052] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0053] Example 1 This embodiment provides a method for preparing a silicon-carbon composite material, including the following steps: Step S1 Inorganic template, organic template, and coupling agent are added to a carbohydrate compound solution and dispersed evenly. After spray drying, a precursor is obtained. The precursor is transferred to a tube furnace and heated to 900-1100°C. Steam is introduced for activation for at least 1 hour. After cooling, a mixture of heteroatom gas and crosslinking gas is introduced to obtain modified mesoporous carbon.

[0054] The carbohydrate compound is at least one of glucose, sucrose, fructose, galactose, ribose, maltose, or lactose, and the concentration of the carbohydrate compound solution is 1-10 wt%.

[0055] The heteroatom gas is one of nitrogen, sulfur, phosphorus, and boron; the crosslinking gas is at least one of peracetic acid peroxide, butanone peroxide, cyclohexanone peroxide, and benzoic acid peroxide; the volume ratio of the heteroatom gas and the crosslinking gas is 10:(1-5).

[0056] The inorganic template is at least one of sodium carbonate, potassium carbonate, and magnesium carbonate. The organic template is at least one of lithium gluconate, lithium lactate, and lithium citrate.

[0057] Step S2 Modified mesoporous carbon is added to a fluidized bed, inert gas is introduced to purge the air from the tube, the temperature is raised to 450-600℃, and a silane mixed gas is introduced for no more than 1 hour. Then the temperature is raised to 500-900℃ and a carbon source mixed gas is introduced for no more than 1 hour to obtain an intermediate material with amorphous carbon deposited on the surface.

[0058] The silane mixture is a mixture of at least one of methanesilane, ethylsilane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane with nitrogen, and the volume ratio is 1:(1-3). The carbon source gas mixture is a mixture of at least one of methane, ethane, ethylene, acetylene, and propane with nitrogen, in a volume ratio of 1:(1-3).

[0059] Step S3 A solid electrolyte is deposited on the surface of an intermediate material to obtain a silicon-carbon composite material coated with a solid electrolyte.

[0060] This application describes the creation of pores in carbohydrate compounds under dual-template conditions (organic template and inorganic template) to prepare a uniform nano- or micro-sized pore structure, resulting in mesoporous carbon materials. Compared with porous carbon, mesoporous carbon materials have advantages such as uniform pore size and strong compressive strength. Furthermore, heteroatom doping is performed to improve the electronic conductivity of the materials and enhance rate performance.

[0061] Example 2 This embodiment prepares a silicon-carbon composite material, and the specific steps are as follows.

[0062] Step S1 10g of sodium carbonate, 10g of lithium gluconate, and 3g of tetrabutyl titanate were added to 2000g of a 5wt% glucose aqueous solution (i.e., 100g of glucose) and dispersed evenly. The precursor was then obtained by spray drying.

[0063] The precursor was transferred to a tube furnace and heated to 1000°C. Then, steam gas was introduced and activated for 300 minutes at a flow rate of 300 SCCM.

[0064] After activation, the temperature was lowered to 650℃, and a mixture of ammonia gas and peracetic acid gas (volume ratio: ammonia gas: peracetic acid gas = 10: 3) was introduced at a flow rate of 30 SCCM to obtain modified mesoporous carbon.

[0065] Step S2 The modified mesoporous carbon obtained in step S1 is added to a fluidized bed, and argon inert gas is introduced to purge the air from the tube. The temperature is then raised to 500°C, and a silane mixed gas (volume ratio, silane:nitrogen = 1:2) is introduced at a flow rate of 50 SCCM for 30 minutes.

[0066] After the silane mixture is introduced, the temperature is raised to 700°C, and then an ethylene mixture (volume ratio: ethylene:nitrogen = 1:2) is introduced. The flow rate of the silane mixture is 10 SCCM, and the introduction time is 30 minutes, to obtain the intermediate material.

[0067] Step S3 A solid electrolyte LLZO was deposited on the surface of an intermediate material using magnetron sputtering with 3g of garnet-type lithium lanthanum zirconium oxide (LLZO) solid electrolyte as the target and 100g of intermediate material as the matrix, to obtain a silicon-carbon composite material coated with solid electrolyte.

[0068] The magnetron sputtering parameters were: power 30W, time 50s, vacuum degree 5×10⁻⁶. -4 Pa, self-bias pressure ≤1 Pa, gas source is argon.

[0069] The silicon-carbon composite material obtained in this embodiment was imaged using a scanning electron microscope (SEM), showing the following: Figure 1 As shown, from Figure 1 It can be seen that the obtained composite material exhibits a regular spherical structure with a particle size between 5-10 μm, uniform size distribution, and rough small particles on the surface, indicating it is a solid electrolyte material.

[0070] Example 3 This embodiment describes a method for preparing a silicon-carbon composite material according to this application, comprising the following steps: Step S1: 10g of sodium carbonate, 10g of lithium gluconate, and 3g of tetrabutyl titanate were added to 2000g of a 5wt% glucose aqueous solution (i.e., 100g of glucose) and dispersed evenly. The precursor was obtained by spray drying.

[0071] The precursor material was transferred to a tube furnace and heated to 1000°C. Steam was then introduced to activate the precursor at a flow rate of 300 SCCM for 300 minutes.

[0072] After activation, the temperature was lowered to 650℃, and a mixture of ammonia gas and peracetic acid gas was introduced at a flow rate of 30 SCCM, with a volume ratio of ammonia gas to peracetic acid gas of 10:3, to obtain modified mesoporous carbon.

[0073] Step S2: Modified mesoporous carbon was added to the fluidized bed, and argon inert gas was introduced to purge the air from the tube. After the air was purged, the temperature was raised to 500°C, and a mixture of silane and nitrogen was introduced at a flow rate of 50 SCCM. The volume ratio of silane to nitrogen was 1:2, and the gas introduction time was 30 minutes.

[0074] After the mixed gas is introduced, the temperature is raised to 700℃, and ethylene mixed gas is introduced at a flow rate of 10 SCCM. The volume ratio of ethylene to nitrogen is 1:2, and the gas introduction time is 30 minutes to obtain the intermediate material.

[0075] Step S3: A solid electrolyte-coated silicon-carbon composite material was obtained by magnetron sputtering, using 3g of LLZO solid electrolyte as the target and 100g of intermediate material as the matrix. The magnetron sputtering parameters were: power 30W, time 50s, vacuum degree 5×10-4Pa, self-bias voltage ≤1Pa, and argon gas source.

[0076] Example 3 This embodiment describes a method for preparing a silicon-carbon composite material according to this application, comprising the following steps: Step S1: 15g of potassium carbonate, 15g of lithium citrate, and 5g of tetraethyl titanate were added to 1000g of a 10wt% fructose aqueous solution (i.e., 100g of fructose) and dispersed evenly. The precursor was then obtained by spray drying.

[0077] The precursor material was transferred to a tube furnace and heated to 1100°C. Water vapor was introduced at 1100°C to activate the precursor material. The water vapor flow rate was 500 SCCM and the activation time was 60 minutes.

[0078] After activation, the temperature was lowered to 800℃, and a mixture of phosphine gas and cyclohexanone peroxide gas was introduced at a flow rate of 50 SCCM. The volume ratio of the mixed gas was phosphine gas:cyclohexanone peroxide gas = 10:5, thus obtaining modified mesoporous carbon.

[0079] Step S2: Modified mesoporous carbon was added to the fluidized bed, and argon inert gas was introduced to purge the air from the tube. After the air was purged, the temperature was raised to 600°C, and a monochlorosilane mixed gas was introduced at a flow rate of 100 SCCM. The volume ratio of the mixed gas was monochlorosilane to nitrogen = 1:3, and the gas introduction time was 10 minutes.

[0080] After the mixed gas is introduced, the temperature is raised to 900℃, and acetylene mixed gas is introduced at a flow rate of 20 SCCM. The volume ratio of acetylene to nitrogen is 1:3, and the gas introduction time is 10 minutes to obtain the intermediate material.

[0081] Step S3: A solid electrolyte was deposited on the surface of the intermediate material using magnetron sputtering with 5g of lithium aluminum Germanium phosphate (LAGP) as the target and 100g of intermediate material as the matrix, to obtain a solid electrolyte-coated silicon-carbon composite material.

[0082] The parameters for magnetron sputtering technology are: power 50W, time 100S, vacuum degree 10×10-4Pa, self-bias voltage ≤1Pa, and gas source is helium.

[0083] Comparative Example 1 Unlike Example 2, sodium carbonate and lithium gluconate are not added in step S1, but everything else is the same as in Example 1.

[0084] Comparative Example 2 Unlike Example 2, sodium carbonate is not added in step S1, but everything else is the same as in Example 1.

[0085] Comparative Example 3 Unlike Example 2, lithium gluconate is not added in step S1, but everything else is the same as in Example 1.

[0086] Comparative Example 4 Unlike Example 2, 50g of sodium carbonate and 50g of lithium gluconate were added in step S1, while the rest was the same as in Example 1.

[0087] Comparative Example 5 Unlike Example 2, peracetic acid gas is not introduced in step S1, but otherwise it is the same as Example 1.

[0088] Comparative Example 6 Unlike Example 2, in step S1, the volume ratio of ammonia gas to acetic acid peroxide gas is 10:10, while the rest is the same as in Example 1.

[0089] Physicochemical performance testing The physicochemical properties of the silicon-carbon composite materials prepared in each embodiment and comparative example were tested: the pore size and specific surface area of ​​each mesoporous carbon were tested according to the national standards GB / T-38949-2020 "Determination of Pore Size of Porous Membranes - Standard Particle Method" and GB / T7702.20-2008 "Detection of Pore Volume of Coal-based Activated Carbon"; the specific surface area and tap density of each silicon-carbon composite material were tested according to the national standard GB / T38823-2020 "Silicon-Carbon"; and the powder resistivity of each mesoporous carbon and its silicon-carbon composite material was tested using a four-probe tester. The test results are shown in Table 1.

[0090] Table 1 As shown in Table 1, compared with the comparative example, the mesoporous carbon components in the silicon-carbon composite materials prepared in each embodiment exhibit significant advantages in pore size distribution, specific surface area, and powder resistivity: specifically, larger pore size, higher specific surface area, and lower powder resistivity. The silicon-carbon composite materials prepared from mesoporous carbon show significant performance advantages in tap density, powder resistivity, and specific surface area, specifically: higher tap density, lower powder resistivity, and larger specific surface area.

[0091] Structural features collectively contribute to the overall improvement of the material's electrochemical performance, as detailed below.

[0092] 1. Synergistic effect of pore size and specific surface area: The examples employ a dual-activator pore-forming strategy to construct a carbon framework with larger pore sizes and a well-developed microporous / mesoporous network. Larger pore sizes facilitate rapid ion transport in the electrolyte, thereby improving rate performance; simultaneously, the high specific surface area shortens the ion diffusion path, further enhancing reaction kinetics. Furthermore, the optimized pore structure provides an effective buffer for the volume expansion of silicon during cycling, contributing to improved cycling stability.

[0093] 2. Improved conductivity: The materials in the examples exhibit lower powder resistivity, indicating stronger electronic conductivity. This is due, in part, to the effective reduction of lattice defects in the carbon framework through doping with elements such as lithium, thereby improving intrinsic electronic conductivity; and in part, to the further improvement of interfacial conductivity by depositing a solid electrolyte layer on the material surface using magnetron sputtering, which together reduce the overall resistance.

[0094] 3. Tap Density and Volumetric Energy Density: The materials in the examples achieved higher tap densities while possessing high specific surface area and excellent conductivity. This indicates that the materials have both well-developed porosity and dense particle packing in their microstructure, which helps to improve the volumetric energy density of the electrodes, thereby storing more energy in a limited space.

[0095] In summary, the embodiments achieved breakthroughs in comprehensive performance in terms of ion transport, electronic conductivity, and volumetric energy density through the synergistic optimization of porous structure design, element doping, and surface modification.

[0096] Example 5 This embodiment prepares a secondary battery, specifically a coin cell battery. The silicon-carbon composite material prepared in Examples 2-4 is used to prepare electrodes and then assembled into a battery. The specific method is as follows.

[0097] Electrode preparation: Silicon-carbon composite material, binder (LA136D), and conductive agent (SP, conductive carbon black) were mixed in a mass ratio of 70:15:15. 300 mL of N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred to form a uniform slurry. This slurry was then coated onto a copper foil current collector, dried, and rolled to obtain the negative electrode sheet.

[0098] Battery assembly: In an argon-atmospheric glove box, the battery was assembled using the prepared negative electrode as the working electrode, a lithium metal sheet as the counter electrode, and a polypropylene (PP) membrane as the separator. The electrolyte used was a 1 mol / L LiPF6 solution, and the solvent was a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1:1).

[0099] Subsequently, the prepared coin cells were subjected to the following performance tests.

[0100] (1) Electrochemical performance testing: The Wuhan Landian CT2001A battery testing system was used to conduct charge-discharge tests at a rate of 0.1C within a voltage range of 0.005 V to 2.0 V to evaluate its discharge specific capacity and initial coulombic efficiency. At the same time, 100 cycles were conducted at a charge-discharge rate of 0.1C / 0.1C within the same voltage window to evaluate its cycle performance.

[0101] (2) Full charge expansion test: Measure the initial thickness (D1) of the electrode after rolling. After the battery is charged to 100% SOC, measure the electrode thickness (D2) again. Calculate the relative thickness change of the electrode according to the formula: Full charge expansion rate = (D2 - D1) / D1 × 100%.

[0102] (3) Lithium-ion diffusion coefficient test: The lithium-ion diffusion coefficient of the material was determined by constant current intermittent titration (GITT).

[0103] The test results are summarized in Table 2.

[0104] Table 2 As shown in Table 2, compared with the comparative examples, the solid electrolyte-coated silicon-carbon composite material prepared in the embodiments of the present invention exhibits significant advantages in specific capacity, initial coulombic efficiency, and ion diffusion coefficient. This performance improvement mainly stems from the following synergistic mechanism.

[0105] Bulk doping optimizes electrochemical performance: By co-doping lithium (pre-lithiation) and heteroatoms into the material core, the intrinsic electronic and ionic conductivity of the material is effectively improved. This reduces the polarization of the electrode reaction, allowing the discharge specific capacity to be fully utilized; on the other hand, pre-lithiation directly compensates for the active lithium consumed in forming the solid electrolyte interphase (SEI) film, thereby significantly improving the first coulombic efficiency.

[0106] Surface coating enhances structural stability: The solid electrolyte coating layer constructed on the surface of the intermediate plays a dual role: First, as an interface layer for ion conductors, it further improves the overall ionic conductivity, thereby improving the rate performance of the battery; Second, as a robust mechanical confinement framework, the coating layer effectively suppresses the volume expansion of the core nano-silicon during cycling, maintains the integrity of the electrode structure, and thus significantly enhances the cycling stability of the material.

[0107] Soft-pack battery testing The solid electrolytes prepared in each embodiment and each comparative example were coated with silicon-carbon composite materials to prepare negative electrode sheets, using ternary materials LiNi 0.8 Co 0.1 Mn 0.1 O2 was used as the positive electrode material; LiPF6 was used as the electrolyte, and a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 volume ratio was used as the solvent; a Celgard 2400 membrane was used as the separator to prepare 5Ah pouch cells. The following performance tests were then conducted on each pouch cell.

[0108] 1. Cyclic performance test: The battery is subjected to constant current charge and discharge cycles at a 1C rate within a voltage range of 2.5V-4.2V at an environment of 25±3°C to evaluate its cycle performance.

[0109] 2. HPPC Performance Test: Using pulse currents for 3C charging and 4C discharging, the DC internal resistance (DCR) of the battery under different states of charge (SOC: 10%, 30%, 50%, 70%, 90%) is measured.

[0110] The test results for the pouch batteries are shown in Table 3.

[0111] Table 3 As shown in Table 3, the solid electrolyte-coated intermediates prepared in each embodiment of the present invention exhibit significantly better cycle performance and rate performance in pouch cells than the comparative examples. This performance advantage stems from the synergistic effect of material design and solid electrolyte coating, the core working principle of which is as follows.

[0112] 1. Solid electrolyte coating: mechanical confinement and interfacial stability Suppressing Volume Expansion: The silicon-carbon composite core undergoes a significant volume change (~300%) during charge and discharge, leading to particle breakage and continuous thickening of the solid electrolyte interface film. In this embodiment, the surface-coated solid electrolyte layer constitutes a robust "mechanical restraint," effectively confining the core expansion, maintaining the structural integrity of the particles, and thus significantly improving cycle life.

[0113] Building a stable interface: This coating layer directly avoids direct contact between the silicon-carbon composite material and the liquid electrolyte, reducing the occurrence of side reactions from the source, promoting the formation of a thinner and more stable solid electrolyte interface film, and reducing the consumption of active lithium, which is the key to long-cycle performance.

[0114] 2. Large-pore mesoporous carbon framework: buffer space and ion channel Providing expansion buffer space: The mesoporous carbon template used in this embodiment has the characteristics of large pore size and high pore volume. This provides ample internal space for the volume expansion of silicon particles, like a "nano-reaction chamber", which can effectively buffer stress, prevent the carbon skeleton from breaking due to expansion, and further improve the cycle stability of the structure.

[0115] Ensuring rapid ion transport: Even after coating and cycling, the well-developed macroporous structure remains unobstructed, ensuring rapid transport of lithium ions within the material, which is the foundation for achieving excellent rate performance.

[0116] 3. Core pre-lithiation design: improving kinetics and compensating for lithium consumption Reduced internal resistance: The embodiment introduces additional lithium sources and active sites into the lattice beforehand by doping the material core with lithium atoms (pre-lithiation). This not only significantly improves the solid-phase diffusion rate of lithium ions, but also directly results in a reduction in the battery's DC internal resistance, thus improving rate performance.

[0117] Compensating for initial lithium loss: The additional lithium source provided by pre-lithiation can effectively compensate for the lithium consumed in the formation of the solid electrolyte interface film during the first charge and discharge process, thereby improving the battery's initial coulombic efficiency and reversible capacity, laying a solid foundation for long cycle life.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material includes an outer shell and a core, wherein the mass ratio of the outer shell to the core is (1-5):100; The core comprises mesoporous carbon, the pores and surface of which are deposited with nano-silicon and heteroatoms; The outer shell is composed of amorphous carbon and solid electrolyte.

2. The silicon-carbon composite material as described in claim 1, characterized in that, Based on the total mass ratio of the core being 100%, the core is composed of 40-45% mesoporous carbon, 40-45% nano-silicon, and 10-20% heteroatoms.

3. The silicon-carbon composite material as described in claim 1, characterized in that, The outer shell consists of amorphous carbon and solid electrolyte from the inside out. Based on a total mass ratio of 100%, the outer shell is composed of 30-50% solid electrolyte and 50-70% amorphous carbon.

4. The silicon-carbon composite material according to any one of claims 1 to 3, characterized in that, The amorphous carbon is lithium-doped amorphous carbon.

5. A method for preparing a silicon-carbon composite material, characterized in that, The silicon-carbon composite material is the silicon-carbon composite material according to any one of claims 1 to 4, and the preparation method includes the following steps: Step S1: Inorganic template, organic template, and coupling agent are added to a carbohydrate compound solution and dispersed evenly. After spray drying, a precursor is obtained. The precursor is transferred to a tube furnace and heated to 900-1100°C. Steam is introduced for activation for at least 1 hour. After cooling, a mixture of heteroatom gas and crosslinking gas is introduced to obtain modified mesoporous carbon. Step S2: The modified mesoporous carbon is added to a fluidized bed, an inert gas is introduced to purge the air from the tube, the temperature is raised to 450-600℃ and then a silane mixed gas is introduced for no more than 1 hour, and then the temperature is raised to 500-900℃ and then a carbon source mixed gas is introduced for no more than 1 hour to obtain an intermediate material with amorphous carbon deposited on the surface. Step S3: A solid electrolyte is deposited on the surface of the intermediate material to obtain a solid electrolyte-coated silicon-carbon composite material.

6. The method for preparing the silicon-carbon composite material as described in claim 5, characterized in that, Step S1 satisfies one or more of the following conditions ag: a. The inorganic template is at least one of sodium carbonate, potassium carbonate, and magnesium carbonate; b. The organic template is an organic compound containing lithium; preferably, the organic template is at least one of lithium gluconate, lithium lactate, and lithium citrate; c. The mass ratio of the inorganic template, the organic template, the coupling agent, and the carbohydrate compound is (5-15):(5-15):(1-5):100; d. The carbohydrate compound is at least one selected from glucose, sucrose, fructose, galactose, ribose, maltose, or lactose, and the concentration of the carbohydrate compound solution is 1-10 wt%. e. The heteroatom gas is one of nitrogen, sulfur, phosphorus, and boron; f. The crosslinking gas is at least one of peracetic acid peroxide, butanone peroxide, cyclohexanone peroxide, and benzoic acid peroxide; g. The volume ratio of the heteroatom gas and the crosslinking gas is heteroatom gas: crosslinking gas = 10: (1-5).

7. The method for preparing the silicon-carbon composite material as described in claim 5, characterized in that, The silane mixture is a mixture of at least one of silane, silane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane with nitrogen, and the volume ratio is 1:(1-3). Alternatively, the carbon source gas mixture is a mixture of at least one of methane, ethane, ethylene, acetylene, and propane with nitrogen, in a volume ratio of 1:(1-3).

8. The method for preparing the silicon-carbon composite material as described in claim 5, characterized in that, In step S3, the mass ratio of the solid electrolyte to the intermediate material is (1-5):

100.

9. The method for preparing the silicon-carbon composite material as described in claim 5, characterized in that, In step S3, the solid electrolyte is deposited on the surface of the intermediate material using magnetron sputtering. The magnetron sputtering parameters are: power 10-50W, time 10-100s, and vacuum degree (1-10)×10⁻⁶. -4 Pa, self-bias pressure ≤1Pa, gas source is either argon or helium.

10. A secondary battery, characterized in that, The secondary battery is made of the silicon-carbon composite material according to any one of claims 1-9. The negative electrode sheet made of the silicon-carbon composite material is assembled with an electrolyte, a separator and a positive electrode sheet to obtain the secondary battery. The secondary battery includes button cells and pouch cells.

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