Electrode material and preparation method thereof, electrode plate and preparation method thereof, and lithium ion battery

Abstract

The invention discloses an electrode material and a preparation method thereof, the preparation method comprises: providing initial carbon matrix powder, the initial carbon matrix powder comprising initial carbon matrix particles, the initial carbon matrix particles having a porous structure; silicon embedding treatment is conducted on the initial carbon matrix powder, carbon-silicon composite powder is obtained, the carbon-silicon composite powder comprises a plurality of carbon-silicon composite particles, and the carbon-silicon composite particles comprise the initial carbon matrix particles with nanometer silicon; the carbon-silicon composite powder is subjected to titanium coating treatment, the electrode material is obtained, the electrode material comprises a plurality of electrode material particles, and each electrode material particle comprises a carbon-silicon composite particle and a TiSi2 protection shell coating the carbon-silicon composite particle. The invention also discloses an electrode, a preparation method thereof and a lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, specifically to an electrode material and its preparation method, an electrode sheet and its preparation method, and a lithium-ion battery. Background Technology

[0002] With the widespread adoption of electric vehicles, large-scale energy storage electronic devices, and portable electronic devices, higher demands are being placed on the energy density of lithium-ion batteries. Silicon-based materials, due to their extremely high theoretical specific capacity and abundant natural reserves, are considered the most promising anode materials for next-generation high-energy-density lithium-ion batteries. However, electrode structures made from silicon-based materials are prone to collapse, ultimately leading to a sharp decline in capacity.

[0003] Improving the stability of electrode structures made of silicon-based materials has become a pressing technical problem in this field. Summary of the Invention

[0004] This invention aims to address, to a certain extent, one of the technical problems in related technologies. To this end, this invention provides an electrode material and its preparation method, an electrode sheet and its preparation method, and a lithium-ion battery.

[0005] As a first aspect of the present invention, a method for preparing an electrode material is disclosed, the method comprising: An initial carbon matrix powder is provided, the initial carbon matrix powder comprising initial carbon matrix particles, wherein the initial carbon matrix particles have a porous structure; The initial carbon matrix powder is subjected to silicon inlay treatment to obtain carbon-silicon composite powder, wherein the carbon-silicon composite powder includes a plurality of carbon-silicon composite particles, and the carbon-silicon composite particles include the initial carbon matrix particles with nano-silicon formed thereon. A titanium-coated carbon-silicon composite powder is used to obtain an electrode material, wherein the electrode material comprises multiple electrode material particles, and the electrode material particles include carbon-silicon composite particles and a TiSi2 protective shell covering the carbon-silicon composite particles.

[0006] Further, the step of performing silicon inlay treatment on the initial carbon matrix powder to obtain carbon-silicon composite powder includes: introducing silicon source gas into a process chamber containing the initial carbon matrix powder.

[0007] Further, the step of introducing silicon source gas into the process chamber containing the initial carbon matrix powder includes: The initial carbon matrix is ​​fluidized in a reactor using an inert gas at a first temperature, which is between 450°C and 600°C. A mixed gas, comprising silane and an inert gas, is introduced into the reactor for a reaction time of 0.5 to 5 hours, wherein the silane constitutes 3% to 7% of the volume of the mixed gas.

[0008] Furthermore, the titanium coating treatment of the carbon-silicon composite powder to obtain the electrode material includes: Titanium source gas and silicon source gas are introduced into a process chamber containing the carbon-silicon composite powder at a set temperature; the carbon-silicon composite powder is cooled and collected in the process chamber to obtain the electrode material.

[0009] Furthermore, in the step of introducing titanium source gas and silicon source gas into the process chamber containing the silicon carbide composite powder, the partial pressure ratio of the titanium source gas to the silicon source gas is between 1:1 and 1:3, the set temperature is between 500°C and 700°C, and the introduction time is between 0.5 hours and 5 hours.

[0010] Furthermore, in the step of introducing titanium source gas and silicon source gas into the process chamber containing the silicon carbide composite powder, the preset thickness D of the TiSi2 protective shell satisfies: D = G × t, where G is the effective film thickness growth rate and t is the reaction time. The effective film thickness growth rate satisfies the following relationship:

[0011] Where r is the deposition flux, M is the molar mass of the TiSi2 protective shell, and ρ is the density of the TiSi2 protective shell. The deposition flux r is determined by the surface coverage and surface reaction rate of the titanium source gas and silicon source gas on the carbon-silicon composite particles at a set temperature.

[0012] Furthermore, the deposition flux r satisfies the following relationship:

[0013] Where k is the surface reaction rate constant. k0 is the pre-exponential factor for surface reaction, Ea is the activation energy of surface reaction of the titanium source gas and silicon source gas, R is the gas constant, and T is the reaction temperature; θ Ti The coverage of the titanium source gas on the surface of the carbon-silicon composite particles. θ Si The coverage of the silicon source gas on the surface of the silicon-carbon composite particles. P Ti P is the partial pressure of the titanium source gas. Si K is the partial pressure of the silicon source gas. Ti K is the adsorption constant of the titanium source gas. SiLet be the adsorption constant of the silicon source gas. , K Ti,0 The pre-exponential factor of the adsorption constant of the titanium source gas, ΔH ads,Ti The heat of adsorption of the titanium source gas, K Si,0 The pre-exponential factor of the adsorption constant of the silicon source gas, ΔH ads,Si This is the heat of adsorption of the silicon source gas.

[0014] Furthermore, an initial carbon matrix powder is provided, comprising: The initial carbon matrix powder is heated to between 800°C and 1000°C, wherein the initial carbon matrix powder includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, graphene, and carbon nanotubes.

[0015] As a second aspect of the present invention, an electrode material is disclosed, which is prepared by the preparation method described above.

[0016] Furthermore, the thickness of the TiSi2 protective shell is between 2 nm and 50 nm.

[0017] As a third aspect of the present invention, a method for preparing an electrode sheet is disclosed, which involves using the above-mentioned electrode material, mixing the electrode material, conductive agent, binder and solvent to prepare an electrode slurry; The electrode paste is coated onto a metal foil and dried to obtain an initial electrode sheet; The initial electrode sheet is subjected to a pressing and punching process to obtain the electrode sheet.

[0018] As a fourth aspect of the present invention, an electrode sheet is disclosed, which is prepared by the above-described preparation method.

[0019] As a fifth aspect of the present invention, a lithium-ion battery is disclosed, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode adopts the electrode sheet described above.

[0020] Compared with existing technologies, this invention has the following significant advantages: By embedding nano-silicon into initial carbon matrix particles with a porous structure to form a silicon-carbon composite, and further coating the composite surface with a TiSi2 protective shell, volume expansion is effectively buffered, and structural stability is improved. This method, through a two-step vapor-phase treatment of silicon embedding and titanium coating, can generate a TiSi2 shell layer in situ and uniformly on the surface of a complex porous silicon-carbon composite. The coating layer is chemically bonded to the substrate, with a bonding force far stronger than that of physical mixing or post-attachment methods, ensuring that the coating layer does not detach under drastic volume changes. Simultaneously, by precisely controlling process parameters, the thickness of the TiSi2 shell layer can be controlled at the nanoscale, taking into account both ion transport and mechanical protection requirements. This shell possesses excellent mechanical strength and density, effectively constraining the overall deformation of the particles from the outside. This dual mechanism works synergistically to greatly suppress the cracking and pulverization of the active material, ensuring the long-term integrity of the electrode structure. Furthermore, the in-situ generated TiSi2 is an intermetallic compound with extremely high intrinsic electronic conductivity. The TiSi2 protective shell forms a continuous, highly conductive coating layer on the particle surface, which integrates well with the internal carbon-silicon composite, forming a stable three-dimensional high-speed electron conduction path. This significantly reduces the internal resistance and polarization of the electrode, enabling the material to possess excellent fast charge and discharge capabilities. Moreover, the dense TiSi2 protective shell reduces the direct contact between silicon and the electrolyte, thereby effectively suppressing the continuous growth, thickening, and damage of the solid electrolyte interface film during cycling. This reduces the irreversible consumption of active lithium and electrolyte, thus significantly improving the material's initial coulombic efficiency and long-cycle capacity retention.

[0021] The electrode sheet prepared by this invention combines the advantages of high capacity of silicon, buffering capacity of carbon, and high conductivity and high strength of titanium silicide, exhibiting extremely long cycle life and excellent rate performance while maintaining high specific capacity.

[0022] These features and advantages of the present invention will be disclosed in detail in the following specific embodiments and accompanying drawings. The preferred embodiments or means of the present invention will be shown in detail in conjunction with the accompanying drawings, but are not intended to limit the technical solutions of the present invention. In addition, each of these features, elements and components appearing in the following text and drawings is a plurality of, and different symbols or numbers are used for convenience of representation, but all represent parts with the same or similar construction or function. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a schematic flowchart of one embodiment of the preparation method provided by the present invention; Figure 2 This is a SEM micrograph of the electrode material provided in Embodiment 1 of the present invention.

[0024] Explanation of reference numerals in the attached figures 1: Titanium silicide coating layer; 2: Carbon matrix. Detailed Implementation

[0025] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described are intended to explain the present invention and should not be construed as limiting the invention.

[0026] The terms "an embodiment," "example," or "example" used in this specification refer to a particular feature, structure, or characteristic described in connection with the embodiment itself that may be included in at least one embodiment disclosed in this application. The phrase "in an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0027] With the rapid development of electric vehicles, large-scale energy storage, and portable electronic devices, higher demands are being placed on the energy density of lithium-ion batteries. Silicon-based materials, due to their extremely high theoretical specific capacity (Li0.05 at room temperature), possess this advantage. 15 With its abundant natural reserves (approximately 3579 mAh / g), Si4 is considered the most promising anode material for next-generation high-energy-density lithium-ion batteries. However, silicon materials undergo significant volume changes (>300%) during charge and discharge, leading to the breakage and pulverization of active material particles, as well as the continuous growth and destruction of the solid electrolyte interphase (SEI) film. This results in the collapse of the electrode structure and a sharp decline in capacity, severely limiting its commercial application.

[0028] To overcome these problems, researchers typically employ nano-sizing and composite strategies. Among these, constructing silicon-carbon composites is currently the most mainstream technical approach, utilizing the excellent conductivity and buffering capacity of the carbon matrix to improve the performance of silicon. However, simple carbon coating or compositing still has shortcomings: carbon materials have limited mechanical strength, making it difficult to completely suppress the volume expansion of silicon during long-term cycling; at the same time, the conductivity of carbon materials is still lower than that of metallic materials, limiting further improvements in electrode rate performance.

[0029] In related technologies, industry researchers have used methods such as carbon coating with hydrocarbon compounds directly after silicon deposition. The main drawback of this method is insufficient rigidity of the coating material, which cannot effectively suppress the expansion effect of silicon during long-term charge-discharge processes, leading to material pulverization and failure. Another example is the use of metals or metal nitrides for coating, but this typically involves physical mixing, hydrothermal reactions, magnetron sputtering, or subsequent heat treatment. These methods suffer from uneven coating, weak adhesion to the substrate, complex processes, or high costs.

[0030] Therefore, developing a new method to achieve a uniform, dense, robust coating with high conductivity and high strength is crucial for promoting the practical application of silicon-carbon anodes.

[0031] This invention relates to the field of lithium-ion battery materials technology, specifically to a high-capacity, long-cycle-life silicon-carbon composite anode material for lithium-ion batteries, and more particularly to a method for coating silicon-carbon composite materials with a conductive, high-strength TiSi2 protective layer generated in situ using chemical vapor deposition (CVD) technology, and the resulting product.

[0032] The biggest bottleneck of silicon-carbon anode materials is the huge volume expansion (~300%) of silicon during charging and discharging, which leads to: particle breakage, continuous growth of the solid electrolyte interface (SEI film), consumption of electrolyte and lithium source, electrical contact failure, and rapid capacity decay.

[0033] In the study of titanium-silicon compounds, TiSi2 is an intermetallic compound with very high electronic conductivity, which can significantly improve the overall conductivity of the anode material and enhance rate performance. The rigid and dense TiSi2 film acts as a mechanical framework, constraining the volume expansion of silicon particles and preventing their pulverization and detachment from the conductive network. TiSi2 is chemically stable within the battery's operating voltage range, forming a stable and uniform physical barrier that prevents direct contact between the electrolyte and the silicon core, thereby generating a thinner and more stable SEI film.

[0034] However, TiSi2 prepared by gas deposition is unstable and produces many undesirable secondary phase products. Furthermore, due to the influence of gas dissociation and adsorption, the reaction rate of the deposited TiSi2 layer cannot be accurately detected and controlled, which leads to inconsistent preparation results and unstable process.

[0035] The primary objective of this invention is to provide a method for preparing a TiSi2-coated silicon-carbon composite anode material, which enables the in-situ formation of a uniform, dense, and strongly bonded TiSi2 protective layer on the surface of the silicon-carbon composite material. Another objective of this invention is to provide the TiSi2-coated silicon-carbon composite anode material obtained by the above method. A further objective of this invention is to provide the application of the above-mentioned TiSi2-coated silicon-carbon composite anode material in lithium-ion batteries.

[0036] As a first aspect of the present invention, a method for preparing an electrode material is disclosed, such as... Figure 1 The preparation method shown includes: S100. Provide initial carbon matrix powder, the initial carbon matrix powder comprising initial carbon matrix particles, wherein the initial carbon matrix particles have a porous structure; S200. The initial carbon matrix powder is subjected to silicon inlay treatment to obtain carbon silicon composite powder, wherein the carbon silicon composite powder includes multiple carbon silicon composite particles, and the carbon silicon composite particles include the initial carbon matrix particles with nano-silicon formed thereon. S300. The carbon silicon composite powder is subjected to titanium coating treatment to obtain electrode material, wherein the electrode material includes multiple electrode material particles, and the electrode material particles include carbon silicon composite particles and TiSi2 protective shells coating the carbon silicon composite particles.

[0037] Compared with existing technologies, this invention has the following significant advantages: By embedding nano-silicon into initial carbon matrix particles with a porous structure to form a silicon-carbon composite, and further coating the composite surface with a TiSi2 protective shell, volume expansion is effectively buffered, and structural stability is improved. This method, through a two-step vapor-phase treatment of silicon embedding and titanium coating, can generate a TiSi2 shell layer in situ and uniformly on the surface of a complex porous silicon-carbon composite. The coating layer is chemically bonded to the substrate, with a bonding force far stronger than that of physical mixing or post-attachment methods, ensuring that the coating layer does not detach under drastic volume changes. Simultaneously, by precisely controlling process parameters, the thickness of the TiSi2 shell layer can be controlled at the nanoscale, taking into account both ion transport and mechanical protection requirements. This shell possesses excellent mechanical strength and density, effectively constraining the overall deformation of the particles from the outside. This dual mechanism works synergistically to greatly suppress the cracking and pulverization of the active material, ensuring the long-term integrity of the electrode structure. Furthermore, the in-situ generated TiSi2 is an intermetallic compound with extremely high intrinsic electronic conductivity. The TiSi2 protective shell forms a continuous, highly conductive coating layer on the particle surface, which integrates well with the internal carbon-silicon composite, forming a stable three-dimensional high-speed electron conduction path. This significantly reduces the internal resistance and polarization of the electrode, enabling the material to possess excellent fast charge and discharge capabilities. Moreover, the dense TiSi2 protective shell reduces the direct contact between silicon and the electrolyte, thereby effectively suppressing the continuous growth, thickening, and damage of the solid electrolyte interface film during cycling. This reduces the irreversible consumption of active lithium and electrolyte, thus significantly improving the material's initial coulombic efficiency and long-cycle capacity retention.

[0038] In step S100, this application does not specifically limit the source of the initial carbon matrix powder; it can be purchased externally or made in-house. To improve the deposition efficiency of subsequent silicon particles and to enable deposition within the pores of the initial carbon matrix particles, as a preferred embodiment, the initial carbon matrix powder is provided, comprising: The initial carbon matrix powder is heated to between 800°C and 1000°C. The initial carbon matrix powder includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, graphene, and carbon nanotubes. Artificial graphite, hard carbon, mesoporous carbon, or graphene microspheres with high specific surface area and abundant pore structure are used. The particle size is typically controlled between 10 μm and 50 μm to ensure good fluidization and a strong and stable carbon skeleton that is less prone to collapse during subsequent deposition. This provides a matrix carbon skeleton for the anode material. Heating the carbon matrix removes surface-adsorbed moisture and functional groups, ensuring the purity and strong bonding of the subsequently deposited silicon. Pore expansion facilitates the entry of silicon source from the surface, promoting the formation of silicon-carbon composites. In some embodiments, the selected porous carbon material is first heated to 800°C to 1000°C under vacuum or an inert atmosphere; then, the pretreated carbon material is loaded into a fluidized bed reactor. The system was shut down, and argon gas was repeatedly used to purge and replace the oxygen and water content in the reactor to ensure that the oxygen and water content dropped below 100 ppm (to prevent spontaneous combustion of SiH4 and hydrolysis of TiCl4). Finally, argon gas was introduced at a constant flow rate, and the gas flow rate was precisely controlled to make the carbon particles in the bed enter a uniform "fluidized state", with the particles tumbling up and down, exhibiting a fluid-like state.

[0039] In step S200, this application does not specifically limit how the silicon-carbon composite particles are formed; they can be obtained through chemical vapor deposition. To obtain uniformly distributed nano-silicon within the initial carbon matrix particles, thereby reducing local volume expansion, preferably, the initial carbon matrix powder undergoes silicon inlay treatment to obtain silicon-carbon composite powder. This includes: introducing silicon source gas into a process chamber containing the initial carbon matrix powder. The silicon source gas can penetrate into the porous structure, uniformly depositing on the surface and inside the carbon particles.

[0040] In some specific embodiments, the initial carbon matrix powder is first fluidized in the reactor using an inert gas at a first temperature between 450°C and 600°C. The fluidized carbon matrix powder can fully contact the subsequent silicon source gas, improving reaction efficiency and distribution area. If the temperature is too low, decomposition is incomplete; if the temperature is too high, the silicon grains become too large and may clog the carbon pores. Next, a mixed gas, including silane and an inert gas, is introduced into the reactor for reaction. The introduction time is between 0.5 hours and 5 hours, and the volume fraction of silane in the mixed gas is between 3% and 7%.

[0041] In some embodiments, the inert gas is typically diluted to a safe concentration (e.g., 5%-20%) using high-purity argon (Ar) or hydrogen (H2). The mixed gas enters the fluidized bed through a gas distribution plate and comes into contact with the incandescent carbon particles in a fluidized state.

[0042] Reaction and Deposition: Silane gas undergoes the following thermal decomposition reaction on the surface and within the pores of carbon particles: SiH4=Si+2H2 Nanocrystalline silicon preferentially nucleates and grows within the pores of carbon in an amorphous or microcrystalline form. This process lasts between 0.5 and 5 hours, and the loading and grain size of the deposited silicon can be precisely controlled by adjusting the silane concentration, reaction time, and temperature.

[0043] After silicon precipitation is complete, the silane mixture is stopped and switched back to pure argon gas to purge the reaction chamber, completely removing any residual silane and byproduct hydrogen gas, in preparation for the next reaction step.

[0044] Preferably, the gas mixture is introduced over a period of 0.5 to 5 hours, and the volume fraction of silane in the mixture is between 3% and 7%. A specific ratio of silane to inert gas prevents oxidation of carbon and silicon. High-capacity silicon-carbon composite particles are constructed by depositing nano-silicon within the pores and on the surface of porous carbon particles through the thermal decomposition of silane (SiH4).

[0045] In step S300, this application does not specifically limit how the titanium coating is performed. To achieve a uniform surface coating effect, it is preferred to perform titanium coating treatment on the silicon carbide composite powder to obtain the electrode material, comprising: Titanium source gas and silicon source gas are introduced into a process chamber containing silicon-carbon composite powder at a set temperature. The silicon-carbon composite powder is then cooled and collected in the process chamber to obtain electrode material. The gas introduction method causes the titanium and silicon sources to dissociate and adsorb on the surface of the silicon-carbon composite particles, forming a protective shell on the surface through a diffusion chemical reaction. Preferably, in the step of introducing titanium and silicon source gases into the process chamber containing the silicon-carbon composite powder, the partial pressure ratio of the titanium source gas to the silicon source gas is between 1:1 and 1:3, the set temperature is between 500°C and 700°C, and the introduction time is between 0.5 hours and 5 hours.

[0046] In some embodiments, after silicon embedding is completed, the reaction temperature is increased in the same reactor to perform titanium coating, providing sufficient activation energy for the reaction. The titanium and silicon source gases are mixed in a fluidized bed and diffused onto the surface of the fluidized carbon-silicon composite particles, maintaining a partial pressure ratio of titanium to silicon gas between 1:1 and 1:3, and a second temperature between 500°C and 700°C. This ensures the reaction proceeds stoichiometrically, generating pure-phase TiSi2, and allows for precise control of the deposition thickness and crystallinity of the TiSi2 protective shell.

[0047] In step S300, the set temperature and gas partial pressure in this application are not chosen arbitrarily, but are determined efficiently and accurately through theoretical calculations and scientific derivation under the guidance of the reaction kinetic model. Specifically, this application adopts the Langmuir and Arrhenius reaction mechanisms to establish a kinetic model of "adsorption of two substances" and "surface reaction rate control." To establish an accurate model, this application uses numerous temperature-varying adsorption reaction experiments and simulations to perform regression fitting on the experimental data to obtain model-related parameters, such as the adsorption heat ΔH. ads Pre-exponential factor K0, activation energy E a Surface active site density N s In addition, the pre-exponential factor of the adsorption constant can be derived. Furthermore, the adsorption constant, coverage, and surface reaction rate constant can be derived, and the deposition flux can be obtained to determine the theoretical film thickness growth rate. This can be used to predict film deposition under specific operating conditions to guide experiments, reducing the blind spots and workload of experiments.

[0048] Compared with existing technologies, this invention has the following significant advantages: Through extensive experiments and theoretical verification, it has been found that at a specific temperature, using the gas-phase reaction of titanium and silicon sources, dense, uniform, and controllable TiS can be generated in situ on the surface of carbon-silicon composite particles. i2 The protective shell, formed by growing nanoscale single particles, exhibits excellent conductivity and higher strength, effectively constraining the volume expansion of silicon during lithium intercalation, preventing particle breakage and pulverization, and significantly improving the structural stability of the electrode. This invention first pre-prepares silicon particles in a carbon matrix to obtain a precursor structure of silicon-carbon composite particles. A titanium silicide coating layer is further formed on the surface of this porous, complex structure. The chemical bonding with the surface enhances the adhesion, which is far stronger than that of physical mixing or post-deposition methods, ensuring that the coating layer does not detach during long-term cycling. Furthermore, the process is simple, avoiding material transfer and contamination during multi-step deposition.

[0049] The reaction kinetics model of this application will be explained below.

[0050] In the step of introducing titanium source gas and silicon source gas into the process chamber containing silicon carbide composite powder, the preset thickness D of the TiSi2 protective shell satisfies the following relationship: D = G × t, where G is the effective film thickness growth rate and t is the reaction time. The effective film thickness growth rate satisfies the following relationship:

[0051] Where r is the deposition flux, M is the molar mass of the TiSi2 protective shell, and ρ is the density of the TiSi2 protective shell. The deposition flux r is determined by the coverage of the titanium source gas and silicon source gas on the surface of the carbon-silicon composite particles and the surface reaction rate at a set temperature.

[0052] The deposition flux r satisfies the following relationship:

[0053] Where k is the surface reaction rate constant. k0 is the pre-exponential factor for surface reaction, Ea is the activation energy of surface reaction for titanium source gas and silicon source gas, R is the gas constant, and T is the reaction temperature; θ Ti The coverage of titanium source gas on the surface of carbon-silicon composite particles. θ Si The coverage of silicon source gas on the surface of silicon-carbon composite particles. P Ti P is the partial pressure of the titanium source gas. Si K is the partial pressure of the silicon source gas. Ti K is the adsorption constant of the titanium source gas. Si Let be the adsorption constant of the silicon source gas. , K Ti,0 The pre-exponential factor of the adsorption constant of the titanium source gas, ΔH ads,Ti The heat of adsorption of the titanium source gas, K Si,0 The pre-exponential factor of the adsorption constant of the silicon source gas, ΔH ads,Si This is the heat of adsorption of the silicon source gas.

[0054] The model in this application can predict the nonlinear effects of temperature and partial pressure changes on the deposition rate (which ultimately affects the coating thickness and uniformity). Generally, as temperature increases, the surface reaction rate accelerates, but this may cause surface desorption, and the deposition rate will not increase. In order to obtain the deposition rate in the optimal range, parameters such as temperature and partial pressure need to be controlled within the optimization range of this application. In addition, it is very difficult to achieve uniform, dense and thickness-controllable (nanoscale) coatings on silicon-carbon materials, especially porous materials. The reaction must be controlled to proceed mainly in the manner of adsorption-surface diffusion reaction in order to form a coating deposition on the surface. Therefore, the relevant temperature and partial pressure also need to satisfy the above reaction kinetic model.

[0055] The following is a specific example of the reaction kinetic model of this application. The temperature is set to 923K, the titanium source gas is TiCl4 with a corresponding partial pressure of 5000Pa, and the silicon source gas is SiH4 with a corresponding partial pressure of 10000Pa. The kinetic parameters are shown in Table 1 below, obtained by fitting and regressing multiple variable-temperature experiments.

[0056] Table 1 Dynamic parameters

[0057] Universal gas constant: R = 8.314 J mol -1 K -1 .

[0058] TiCl4 adsorption constant:

[0059] SiH4 adsorption constant:

[0060] Surface coverage:

[0061]

[0062]

[0063]

[0064] Surface reaction rate constant:

[0065] Sediment flux:

[0066] Assume the molar mass of TiSi2 is M = 0.104 kg / mol and the density is ρ = 4500 kg / m³. 3 Effective film thickness growth rate:

[0067] Based on the above calculations, at a temperature of 923 K, using a gas distribution with a TiCl4 partial pressure of 5000 Pa and a SiH4 partial pressure of 10000 Pa, the effective growth rate of the TiSi2 film is 0.155 nm / min.

[0068] In some embodiments, the fluidized bed CVD reaction system includes a reactor body, a gas distribution plate, a preheating system, a precision temperature control system, a multi-channel gas mass flow controller (MFC), a TiCl4 bubbler, and a tail gas treatment system (alkali scrubbing tower for treating HCl and unreacted SiH4). The step of introducing titanium source gas and silicon source gas into a process chamber containing the silicon-carbon composite powder includes: A titanium source gas is introduced into the reactor using a carrier gas, and a silicon source gas is introduced into the reactor. The titanium source gas and silicon source gas are used to fluidize the carbon-silicon composite particles. Specifically, the titanium source gas is placed in a bubbler, and the titanium source gas includes TiCl4. An inert gas is introduced into the bubbler, so that the inert gas carries TiCl4 into the reactor. The inert gas includes nitrogen and / or argon.

[0069] Preferably, the molar flow ratio of TiCl4 to silicon source gas in the reactor is between 1:2 and 1:2.5, and the reaction time is between 0.5 hours and 5 hours, so that a TiSi2 protective shell can be formed on the surface of the carbon-silicon composite particles.

[0070] The two reactant gases are mixed in a fluidized bed and diffuse onto the surface of the fluidized, turbulent silicon-carbon composite particles. The following gas-phase reaction occurs on the particle surface: SiH4 + 2TiCl4 → TiSi2 + 4HCl + 2H2 The generated TiSi2 is directly deposited on the surface of silicon-carbon composite particles. Due to the uniformity of the fluidized bed, each particle can be uniformly coated to form a continuous TiSi2 shell. By controlling the reaction time, gas partial pressure, and ratio (usually controlling a slight excess of SiH4), the thickness of the TiSi2 shell can be precisely controlled between 5 nm and 20 nm, ensuring crystallinity.

[0071] In a specific embodiment where silicon-carbon composite powder is cooled and collected in a process chamber to obtain electrode material, after the preset coating time is reached, the flow of TiCl4 and SiH4 is stopped, and pure argon gas is switched back to purge the system, carrying away residual reaction gases and byproducts (HCl, H2). Under continuous argon gas flow protection, the reactor is naturally cooled or programmed to room temperature. After cooling, the material is discharged under an inert atmosphere (such as in a glove box) to obtain the final TiSi2-coated silicon-carbon composite anode material. The collected material can be directly used for the preparation of battery electrodes.

[0072] As a second aspect of the present invention, an electrode material is disclosed, which is prepared by the above-described preparation method.

[0073] The electrode material comprises multiple electrode material particles, wherein the electrode material particles include silicon carbide composite particles and a TiSi2 protective shell covering the silicon carbide composite particles. Preferably, the thickness of the TiSi2 protective shell is between 2 nm and 50 nm.

[0074] As a third aspect of the present invention, a method for preparing an electrode sheet is disclosed, which involves using the above-mentioned electrode material, mixing the electrode material, conductive agent, binder and solvent to prepare an electrode slurry; The electrode paste is coated onto a metal foil and dried to obtain the initial electrode sheet; The initial electrode sheet is pressed and punched to obtain the electrode sheet.

[0075] As a fourth aspect of the present invention, an electrode sheet is disclosed, which is prepared by the above-described preparation method.

[0076] As a fifth aspect of the present invention, a lithium-ion battery is disclosed, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode adopts the aforementioned electrode sheet.

[0077] The electrode sheets and lithium-ion batteries prepared by this invention combine the advantages of silicon's high capacity, carbon's buffering capacity, and TiSi2's high conductivity and strong mechanical protection, and are expected to exhibit extremely long cycle life and excellent rate performance while maintaining high specific capacity. Experiments show that half-cells assembled using the materials of this invention can retain more than 85% of their capacity after 200 cycles at 0.5C rate, which is far superior to uncoated or carbon-coated silicon-carbon materials.

[0078] The present invention will be further described below with reference to preparation examples and embodiments.

[0079] Example 1 Weigh 5g of porous artificial graphite as a carbon matrix precursor and place it in a CVD reaction tube.

[0080] Evacuate the furnace and introduce argon gas to raise the furnace temperature to 550℃ (T1).

[0081] A silane / argon mixture (5% silane by volume) was introduced at a flow rate of 200 sccm and reacted for 2 hours to induce silicon precipitation.

[0082] After silicon deposition is completed, stop the silane supply and adjust the furnace temperature to 580℃ (T2).

[0083] The vapor of TiCl4 liquid (maintained at 80°C) was introduced into the reaction tube by argon bubbling (flow rate 100 sccm), while a silane / argon mixture (silane volume fraction 5%) was introduced at a flow rate of 250 sccm. The reaction pressure was maintained at atmospheric pressure, and the reaction time was 1.5 hours.

[0084] After the reaction was completed, heating and gas supply were stopped, and the mixture was cooled to room temperature under an argon atmosphere to obtain the final product, a silicon-carbon composite material coated with TiSi2.

[0085] Characterization revealed that a continuous and dense TiSi2 coating layer approximately 15 nm thick was formed on the material surface.

[0086] Comparative Example 1 By performing only the steps in Example 1 up to the Ti coating stage, an uncoated TiSi2 silicon-carbon composite material was obtained.

[0087] Electrochemical performance testing The materials obtained in Example 1 and Comparative Example 1 were used as working electrodes, and lithium metal as the counter electrode, respectively, and assembled into button cells for testing. Charge-discharge cycle tests were conducted at a 0.5C rate.

[0088] The results are as follows: the material in Comparative Example 1 had a capacity retention rate of only 45% after 200 cycles, while the material in Example 1 had a capacity retention rate as high as 88%, demonstrating the significant performance advantage brought by the method of the present invention.

[0089] Example 2 and Example 3 By varying the reaction temperature, time, and gas ratio in the TiSi2 coating step (specific parameters are shown in Table 2), the resulting materials all exhibited superior cycling performance compared to Comparative Example 1.

[0090] Table 2. Performance comparison under different TiSi2 coating process parameters

[0091] Test case The electrode material of Example 1 was photographed by SEM and tested by EDS. The results are shown in the figure. Figure 2 And Table 3, Figure 2 As can be seen in the figure, the material covering the surface layer is a titanium silicide coating layer 1, and the matrix below the titanium silicide coating layer 1 is a carbon matrix 2. The titanium silicon compound on the surface exhibits a typical lamellar coating state. Table 3 shows the surface elemental analysis (EDS analysis results) of the microstructure photograph of the electrode material provided in Example 1 of this invention.

[0092] Table 3

[0093] According to the EDS results in Table 3, the surface of the electrode material of this application is completely covered by titanium silicon compound, and the content of titanium silicon compound on the surface meets the ratio of TiSi2.

[0094] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A method for preparing an electrode material, characterized in that, The preparation method includes: An initial carbon matrix powder is provided, the initial carbon matrix powder comprising initial carbon matrix particles, wherein the initial carbon matrix particles have a porous structure; The initial carbon matrix powder is subjected to silicon inlay treatment to obtain carbon-silicon composite powder, wherein the carbon-silicon composite powder includes a plurality of carbon-silicon composite particles, and the carbon-silicon composite particles include the initial carbon matrix particles with nano-silicon formed thereon. A titanium-coated carbon-silicon composite powder is used to obtain an electrode material, wherein the electrode material comprises multiple electrode material particles, and the electrode material particles include carbon-silicon composite particles and a TiSi2 protective shell covering the carbon-silicon composite particles.

2. The preparation method according to claim 1, characterized in that, The process of performing silicon intercalation treatment on the initial carbon matrix powder to obtain carbon-silicon composite powder includes: Silicon source gas is introduced into the process chamber containing the initial carbon matrix powder.

3. The preparation method according to claim 2, characterized in that, The step of introducing silicon source gas into the process chamber containing the initial carbon matrix powder includes: The initial carbon matrix powder is fluidized in a reactor at a first temperature, which is between 450°C and 600°C, using an inert gas. A mixed gas, comprising silane and an inert gas, is introduced into the reactor for a reaction time of 0.5 to 5 hours, wherein the silane constitutes 3% to 7% of the volume of the mixed gas.

4. The preparation method according to claim 1, characterized in that, The titanium coating treatment of the carbon-silicon composite powder yields the electrode material, comprising: Titanium source gas and silicon source gas are introduced into the process chamber containing the carbon-silicon composite powder at a set temperature; The carbon-silicon composite powder is cooled and collected in a process chamber to obtain the electrode material.

5. The preparation method according to claim 4, characterized in that, In the step of introducing titanium source gas and silicon source gas into the process chamber containing the silicon-carbon composite powder, the partial pressure ratio of the titanium source gas to the silicon source gas is between 1:1 and 1:3, the set temperature is between 500°C and 700°C, and the introduction time is between 0.5 hours and 5 hours.

6. The preparation method according to claim 4, characterized in that, In the step of introducing titanium source gas and silicon source gas into the process chamber containing the silicon carbide composite powder, the preset thickness D of the TiSi2 protective shell satisfies: D = G × t, where G is the effective film thickness growth rate of TiSi2, and t is the reaction time. The effective film thickness growth rate of TiSi2 satisfies the following relationship: Where r is the deposition flux, M is the molar mass of the TiSi2 protective shell, and ρ is the density of the TiSi2 protective shell. The deposition flux r is determined by the surface coverage and surface reaction rate of the titanium source gas and silicon source gas on the carbon-silicon composite particles at a set temperature.

7. The preparation method according to claim 6, characterized in that, The deposition flux r satisfies the following relationship: Where k is the surface reaction rate constant. k0 is the pre-exponential factor for surface reaction, Ea is the activation energy of surface reaction of the titanium source gas and silicon source gas, R is the gas constant, and T is the reaction temperature; θ Ti The coverage of the titanium source gas on the surface of the carbon-silicon composite particles. θ Si The coverage of the silicon source gas on the surface of the silicon-carbon composite particles. P Ti P is the partial pressure of the titanium source gas. Si K is the partial pressure of the silicon source gas. Ti K is the adsorption constant of the titanium source gas. Si Let be the adsorption constant of the silicon source gas. , K Ti,0 The pre-exponential factor of the adsorption constant of the titanium source gas, ΔH ads,Ti The heat of adsorption of the titanium source gas, K Si,0 The pre-exponential factor of the adsorption constant of the silicon source gas, ΔH ads,Si This is the heat of adsorption of the silicon source gas.

8. The preparation method according to any one of claims 1 to 7, characterized in that, Provide initial carbon matrix powder, including: The initial carbon matrix powder is heated to between 800°C and 1000°C, wherein the initial carbon matrix powder includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, graphene, and carbon nanotubes.

9. An electrode material, characterized in that, The electrode material is prepared using the preparation method described in any one of claims 1 to 8.

10. The electrode material according to claim 9, characterized in that, The thickness of the TiSi2 protective shell is between 2 nm and 50 nm.

11. A method for preparing an electrode sheet, characterized in that, Using the electrode material described in any one of claims 9 or 10, an electrode slurry is prepared by mixing the electrode material, a conductive agent, a binder, and a solvent. The electrode paste is coated onto a metal foil and dried to obtain an initial electrode sheet; The initial electrode sheet is subjected to a pressing and punching process to obtain the electrode sheet.

12. An electrode sheet, characterized in that, The electrode sheet is prepared using the preparation method described in claim 11.

13. A lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, characterized in that, The negative electrode is the electrode sheet described in claim 12.

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