Silicon-carbon composite material electrode surface modification method

Abstract

The invention discloses a surface modification method for a silicon-carbon composite material electrode, which belongs to the technical field of lithium ion battery negative electrode materials, and mainly comprises the following steps: modifying the surface of the silicon-carbon composite material electrode by magnetron sputtering; wherein the modification material comprises a metal material and / or a solid electrolyte material; the metal material is selected from Al, Cu or In; the solid electrolyte material is selected from titanium aluminum lithium phosphate or gallium-doped lithium lanthanum zirconium tantalum oxide. The method solves the problems of poor conductivity, unstable SEI film and volume effect of the silicon-carbon electrode, and after the prepared electrode is assembled into a battery, the performance of the battery is superior to that of an unmodified electrode, the battery is adaptive to a solid-state battery, and the electrode has industrialization potential and application value.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, and particularly relates to a method for modifying the surface of a silicon-carbon composite electrode. Background Technology

[0002] In the field of lithium-ion battery anode materials, silicon is considered one of the most promising anode materials due to its ability to efficiently intercalate lithium by forming lithium-silicon alloys, resulting in extremely high theoretical specific capacity. However, silicon faces a severe volume effect problem during electrochemical cycling: the formation of lithium-silicon alloys during lithium intercalation is accompanied by huge volume expansion, while delithiation and dealloying processes result in drastic volume contraction, with volume changes reaching up to 300%. Such significant volume fluctuations easily lead to the pulverization and fragmentation of silicon material particles, damaging the integrity of the electrode structure and severely weakening the cycle stability of the battery, becoming a core bottleneck restricting the practical application of silicon-based anodes.

[0003] To alleviate the pulverization problem of silicon materials, existing technologies often optimize their structural stability by preparing nano-silicon powder with specific particle sizes. While this can reduce particle pulverization during electrochemical cycling to some extent, significant volume changes still occur after lithium intercalation into nano-silicon. As the number of cycles increases, the electrode continuously experiences repeated expansion and contraction, making it easy for nano-silicon particles to lose electrical contact and causing secondary pulverization. Ultimately, this leads to continuous capacity decay in the battery, and the cycle life fails to meet the requirements of practical applications.

[0004] Based on this, the industry has proposed a technical approach of using mature graphite-based anode materials as a framework and combining them with nano-silicon to form silicon-carbon composite materials. This approach aims to leverage the excellent structural stability and conductivity of graphite to compensate for the inherent defects of silicon-based materials, such as significant volume effects and poor cycle performance. The goal is to obtain a novel composite anode material whose specific capacity and cycle life can meet the requirements of lithium-ion batteries. Moreover, this method is cost-effective and has good industrialization potential.

[0005] However, new technical problems emerge after combining nano-silicon with graphite: On the one hand, nano-silicon itself has poor conductivity, and the overall conductive network after combining with graphite still has defects, limiting electron transport efficiency; on the other hand, there is a significant difference in the lithium insertion / extraction expansion and contraction rates of nano-silicon and graphite, and stress cracking easily occurs at the interface between the two during cycling, causing nano-silicon particles to detach from the conductive framework and lose electrical contact, resulting in capacity loss. At the same time, the solid electrolyte interphase (SEI) film formed on the surface of silicon-carbon composite materials has insufficient stability and is prone to cracking and regeneration under repeated volume changes, continuously consuming electrolyte and lithium ions, further aggravating the decline in battery cycle life. Summary of the Invention

[0006] This invention proposes a method for modifying the surface of silicon-carbon composite electrode, which aims to enhance the conductivity of nano-silicon particles, stabilize the SEI film, and mitigate volume changes, ultimately obtaining a silicon-carbon composite electrode with high cycle life and high rate performance, providing a new technical path and solution for the construction of solid-state battery electrodes.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for modifying the surface of a silicon-carbon composite electrode involves using magnetron sputtering to modify the surface of the silicon-carbon composite electrode. The modifying material includes a metallic material and / or a solid electrolyte material. The metallic material is selected from Al, Cu, or In. The solid electrolyte material is selected from lithium aluminum titanium phosphate (LATP) or gallium-doped lithium lanthanum zirconium tantalum oxide (Ga-LLZTO).

[0008] This invention modifies the electrode surface with metal materials such as Al, Cu, and In using magnetron sputtering. The excellent conductivity of these metals is utilized to construct a continuous conductive network, compensating for the reduced electron transport efficiency of nano-silicon and graphite composites and improving the overall conductivity of the electrode. The modified solid electrolyte material (lithium aluminum titanium phosphate, gallium-doped lithium lanthanum zirconium tantalum oxide) forms a dense and stable protective layer on the electrode surface. This layer inhibits the rupture and regeneration of the SEI film during cycling, reducing electrolyte and lithium-ion consumption. Furthermore, it buffers the volume expansion and contraction during silicon intercalation / deintercalation, lowering the risk of electrode structure breakage. The invention supports modification with individual metal materials, solid electrolyte materials, or a combination of both, allowing for adjustments based on actual needs (such as prioritizing conductivity or cycle stability) to adapt to different lithium-ion battery application scenarios.

[0009] Furthermore, the specific steps include: 1) Prepare silicon-carbon composite materials and fabricate them into electrode sheets; 2) Press the modification material into a target and mount it on the target of the magnetron sputtering equipment, and mount the electrode sheet on the substrate; 3) Evacuate the magnetron sputtering equipment, then introduce argon gas, adjust the gas pressure, adjust the target baffle to the closed state, and start the magnetron sputtering equipment for pre-sputtering; 4) After the pre-sputtering is completed, the target baffle is opened for formal sputtering to form a modification layer on the surface of the silicon-carbon composite electrode.

[0010] This invention breaks down the modification process into four steps: "electrode preparation → target mounting → vacuum pre-sputtering → formal sputtering." It clarifies the operational logic of each step, avoiding variations in modification effects caused by random fluctuations in process parameters and improving product consistency during mass production. The pre-sputtering step removes impurities (such as oxide layers and contaminants) from the target surface, preventing impurities from depositing on the electrode surface during formal sputtering, ensuring the purity of the modified layer, and reducing the negative impact of impurities on the electrode's electrochemical performance. The "target pressing and mounting + electrode substrate fixing" operation ensures the correct alignment between the target and the electrode, laying the structural foundation for the subsequent formal sputtering to form a uniform and fully covered modified layer.

[0011] Furthermore, the preparation method of the silicon-carbon composite material is selected from one of the following methods: Method 1: Weigh a certain amount of sodium carboxymethyl cellulose (CMC) powder and add it to deionized water and stir to disperse it, obtaining a CMC aqueous solution. Weigh a certain amount of spherical nano-silicon powder and add it to the CMC aqueous solution, stir and disperse it to obtain a nano-silicon powder suspension. Stir the suspension at high speed and add a certain amount of expanded graphite powder at the same time, stir and mix thoroughly to obtain a uniform slurry with a certain solid content. Place the uniform slurry obtained in the above steps into a freezer for pre-freezing. Then transfer the pre-frozen sample into a vacuum freeze dryer and control the freeze-drying time and temperature to obtain a nano-silicon-expanded graphite composite material precursor. Then transfer it into a vacuum furnace for high-temperature carbonization. After cooling, take it out, crush and sieve it to obtain a nano-silicon-expanded graphite composite anode material.

[0012] Beneficial effects: The vacuum environment in the above-mentioned vacuum carbonization process can prevent the precursor from reacting with oxygen in the air during carbonization, thus preventing the oxidation of nano-silicon and expanded graphite and ensuring that the material's performance is not affected by oxidation. This is especially crucial for easily oxidized materials like nano-silicon. Furthermore, vacuum carbonization causes the pyrolysis of sodium carboxymethyl cellulose to form a conductive network, which can more firmly bond nano-silicon and expanded graphite together, improving their conductivity, enhancing the structural stability of the composite material, and reducing particle shedding during cycling.

[0013] Method 2: Place ultrafine graphite powder in a fluidized bed reactor, purge the reactor with nitrogen and heat it to a certain temperature, then introduce a mixture of silane and nitrogen. Under constant temperature fluidization, deposit nano-silicon on the surface of the ultrafine graphite powder. After silicon deposition, raise the reactor temperature and further introduce a mixture of acetylene and nitrogen for carbon coating. After coating, silicon-carbon composite anode material is obtained.

[0014] Beneficial effects: The fluidized bed process allows for more uniform deposition of silicon nanoparticles on the graphite surface, resulting in more uniform material expansion. Furthermore, the deposition of carbon to coat the surface protects the deposited silicon nanoparticles from oxidation, improving the material's conductivity and maintaining structural stability.

[0015] Furthermore, the vacuuming is performed to a vacuum level of 5.0 × 10⁻⁶. -4 Pa.

[0016] This vacuum level effectively eliminates air (such as oxygen and nitrogen) and other impurity gases from the magnetron sputtering chamber, preventing these gases from reacting with target atoms during sputtering to form oxides, nitrides, and other impurities. This ensures the purity of the modified layer and guarantees its electrochemical activity. The low vacuum level also reduces the probability of gas molecule collisions, leading to a more stable argon (working gas) plasma state and more controllable deposition paths for target atoms. This reduces problems such as uneven modified layer thickness and high porosity caused by gas disturbances.

[0017] Furthermore, the flow rate of the argon gas is 20-40 sccm; the gas pressure is 0.3-1.3 Pa.

[0018] The flow rate of 20-40 sccm set in this invention maintains a stable plasma density. Too low a flow rate can lead to plasma instability (low deposition efficiency), while too high a flow rate may exacerbate target atom scattering (resulting in a porous modified layer). This range achieves a balance between "high-efficiency deposition" and "dense modified layer." A gas pressure of 0.3-1.3 Pa controls the collision frequency between target atoms and argon molecules, thereby adjusting the grain size and density of the modified layer. This avoids problems caused by excessively low pressure (excessive atomic kinetic energy leading to poor adhesion) or excessively high pressure (insufficient atomic kinetic energy leading to numerous porosity in the modified layer). This parameter range is compatible with the sputtering requirements of both metal (Al / Cu / In) and solid electrolyte (LATP / Ga-LLZTO) modified materials, eliminating the need for significant adjustments to gas parameters due to material changes and improving process versatility.

[0019] Furthermore, the parameters for the pre-sputtering are: power of 20-200W and sputtering time of 5min; the parameters for the formal sputtering are: power of 20-200W and sputtering time of 3-30min.

[0020] The 20-200W power setting of this invention is adaptable to different target materials (lower power is required for metal targets, and higher power is required for solid electrolyte targets), avoiding excessively low power (ineffective removal of target impurities) or excessively high power (target overheating and damage). A 5-minute pre-sputtering time thoroughly cleans the target surface while avoiding excessive pre-sputtering that could lead to target waste. The final sputtering power is consistent with the pre-sputtering power, ensuring the continuity and stability of the sputtering process and preventing fluctuations in the modified layer thickness due to sudden power changes. A sputtering time of 3-30 minutes allows for flexible control of the modified layer thickness (e.g., for metal modification requiring a thin, highly conductive layer, the time can be shortened; for solid electrolyte modification requiring a thicker layer to prevent volume effects, the time can be extended), meeting the electrode designs with different performance requirements.

[0021] Furthermore, the electrode sheet rotates at a speed of 3 r / min during the sputtering process.

[0022] In a rotating state, the electrode sheet can uniformly receive target atomic deposition across all areas, avoiding the uneven thickness of the modified layer caused by deposition differences between the "target center and edge" in a fixed state. This is especially beneficial for 60mm×60mm square electrode sheets, eliminating weak points in the corner areas. The uniformly deposited modified layer has more sufficient contact with the electrode sheet surface, reducing the risk of cracking and peeling due to excessive local deposition, and enhancing the bonding strength between the modified layer and the electrode substrate.

[0023] Furthermore, a DC power supply or an RF power supply is used during the sputtering process.

[0024] This invention is compatible with highly conductive metal targets (Al / Cu / In), enabling efficient ion bombardment and target sputtering with fast deposition rates and high-purity modified layers. It is also compatible with insulating or semi-insulating solid electrolyte targets (LATP / Ga-LLZTO), allowing for plasma stability maintenance via a radio frequency electromagnetic field. This prevents charge accumulation due to target insulation, ensuring effective deposition of the solid electrolyte modified layer. Furthermore, this invention supports switching between two power sources, enabling flexible switching between "metal modification," "solid electrolyte modification," and "composite modification" without changing the magnetron sputtering equipment, reducing equipment investment costs and improving process applicability.

[0025] The present invention also provides a solid silicon-carbon composite electrode prepared by the above method, which is composed of silicon-carbon composite material and modifying material.

[0026] This electrode possesses the characteristics of "high conductivity (metal modification) + stable SEI film (solid electrolyte modification) + resistance to volume effect (modification layer buffer)," solving the core pain points of traditional silicon-carbon electrodes such as "short cycle life and poor rate performance."

[0027] The present invention also provides an application of the solid silicon-carbon composite electrode in a lithium-ion battery.

[0028] The electrode prepared by this invention, when applied to lithium-ion batteries, enables the batteries to possess higher initial charge-discharge capacity, longer cycle life (capacity retention up to 80.08% after 60 cycles), and superior rate performance (capacity retention up to 79.61% at 1A / g), meeting the demands of power batteries and energy storage batteries for high capacity and long lifespan. By solving the volume effect and cycle stability problems of silicon-based anodes, this invention promotes the transition of silicon-carbon composite anodes from laboratory research to industrial application, providing key technological support for improving the energy density of lithium-ion batteries.

[0029] Compared with the prior art, the present invention has the following advantages and technical effects: The solid silicon-carbon composite electrode prepared by this invention contains a solid electrolyte modification layer, which has higher compatibility with solid battery electrolyte systems. It can replace the silicon-carbon electrode in the traditional liquid electrolyte system, solve the problem of violent reaction between liquid electrolyte and silicon-based materials, provide a new path for electrode technology of solid lithium-ion batteries, and break through the limitation that the existing silicon-based anode is only suitable for liquid batteries. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The scan spectrum and energy dispersive spectroscopy (EDS) spectrum of the solid silicon-carbon composite electrode prepared in Example 1 are shown. Figure 2 Cycle life curves (a) and rate life curves (b) of the materials prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0033] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0034] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0035] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0036] This invention provides a method for modifying the surface of a silicon-carbon composite electrode, the specific steps of which are as follows: 1. Preparation of silicon-carbon composite materials and electrode sheet molding 1) Preparation of silicon-carbon composite materials (choose one of the following methods): Method 1: Using nano-silicon powder and graphite powder as raw materials, sodium carboxymethyl cellulose powder (CMC) was weighed and added to deionized water for dispersion to obtain a CMC aqueous solution. Spherical nano-silicon powder was weighed and added to the CMC aqueous solution for dispersion to obtain a nano-silicon powder suspension. The suspension was stirred at high speed, and expanded graphite powder was added simultaneously. The mixture was stirred thoroughly to obtain a uniform slurry with a solid content of 15 wt.%. The uniform slurry obtained in the above steps was placed in a freezer for pre-freezing. The pre-frozen sample was then transferred to a vacuum freeze dryer to obtain a nano-silicon-expanded graphite composite material precursor. The precursor was then transferred to a vacuum furnace for high-temperature carbonization. After cooling, the precursor was removed, crushed, and sieved to obtain a nano-silicon-expanded graphite composite anode material, thus preparing a silicon-carbon composite material. The mass ratio of sodium carboxymethyl cellulose powder, spherical nano-silicon powder, and expanded graphite powder was 15:180:105. The pre-freezing time was 6 hours. The vacuum freeze-drying time was 24 hours at -100℃. The high-temperature carbonization temperature was 1200℃ for 6 hours. Method 2: 1000g of ultrafine graphite powder was placed in a fluidized bed reactor. Nitrogen gas (10L / min) was introduced to clean the reactor and the temperature was raised to 480℃. Then, a mixture of silane (2L / min) and nitrogen (8L / min) was introduced for 270min. Nano-silicon was deposited on the surface of the ultrafine graphite powder under constant temperature fluidization. After the silicon deposition was completed, the reactor temperature was raised to 520℃, and a mixture of acetylene (2L / min) and nitrogen (8L / min) was introduced for 150min to perform carbon coating treatment. After the coating was completed, the reactor was cooled under nitrogen to obtain silicon-carbon composite anode material. 2) Preparation of electrode sheet: In the silicon-carbon composite material, take silicon-carbon negative electrode material, mix it with conductive carbon and binder in a mass ratio of 8:1:1 to form a uniform slurry, coat it on copper foil, place it in an oven at 80℃ and dry overnight to obtain the electrode, and finally cut it into square electrode sheets with a size of 60mm×60mm for later use. 2. Target material preparation and equipment installation Select a modifying material (any one of the metal materials Al, Cu, and In, or any one of the solid electrolyte materials lithium titanium aluminum phosphate and gallium-doped lithium lanthanum zirconium tantalum oxide, or a combination of metal materials and solid electrolyte materials), place its powder in a mold, and press it under a pressure of 5-7 MPa for 10-15 min to make a target material that matches the target body of the magnetron sputtering equipment. During the pressing process, ensure that the target material is free of cracks and has a smooth surface. Install the prepared target material on the corresponding target body of the magnetron sputtering equipment and cover it with a target material cover (the distance between the target material cover and the target material is controlled at 5-8 mm). At the same time, fix the square electrode sheet prepared in step 1 on the substrate of the equipment, ensuring that the surface of the electrode sheet is free of wrinkles and impurities and that it is in a straight position with the target material. 3. Equipment debugging and pre-sputtering before sputtering Close the magnetron sputtering chamber door and start the vacuum pump to evacuate the chamber until the vacuum level reaches 5.0 × 10⁻⁶. -4 After the vacuum level is reached, set the heating temperature to room temperature - 150℃ (if the modifier material contains solid electrolyte material, heat treatment is required, such as 100℃ or 150℃; if the metal material is used alone as the modifier material, room temperature is sufficient). Introduce argon gas as the working gas and adjust the argon flow rate to 20-40 sccm (exemplary values ​​include 20 sccm, 30 sccm, or 40 sccm). By adjusting the gate valve position, stabilize the working gas pressure in the chamber at 0.3-1.3 Pa (the purpose is to control the deposition rate and improve the film quality; exemplary values ​​include working gas pressures of 0.3 Pa, 0.5 Pa, 0.57 Pa, 0.8 Pa, 1 Pa, or 1.3 Pa). Select the power supply according to the type of modifier material (DC power supply for metal materials, [unspecified power supply] for solid electrolyte materials). For the RF power supply (DC power supply for metal materials and RF power supply for solid electrolyte materials during combined modification), after confirming that the target baffle is in the closed state, start the magnetron sputtering equipment and set the pre-sputtering power to 20-200W (20-60W for metal materials, for example, 20W, 30W or 60W; 100-200W for solid electrolyte materials, for example, 100W or 200W). Start with 10W as the initial power and gradually increase it to the target power in units of 5-20W (for example, 5W or 20W) to avoid damage to the target material from sudden power increases. After the power stabilizes, maintain the pre-sputtering state for 5 minutes. During the pre-sputtering process, start the substrate rotation device to rotate the electrode sheet at a speed of 3r / min to ensure uniform subsequent deposition. 4. Formal sputtering and sample removal After pre-sputtering, open the target baffle to begin formal sputtering. Keep the argon flow rate, working pressure, power supply type, and substrate rotation state unchanged. The formal sputtering power is the same as the pre-sputtering power. The sputtering time is controlled between 3-30 minutes depending on the type of modified material (3-20 minutes for metal materials alone, for example, 3 or 20 minutes; 20 minutes for solid electrolyte materials alone; and 10 minutes for a combination of metal and solid electrolyte materials). After the preset sputtering time is reached, first close the target baffle, then sequentially close the sputtering power, argon gas inlet valve, and substrate rotation device. After the temperature inside the equipment chamber naturally drops to room temperature, open the chamber door and remove the electrode sheet to obtain a solid silicon-carbon composite electrode with a surface-coated modification layer. If a battery needs to be assembled, the electrode sheet can be further cut into a circular electrode sheet with a diameter of 12 mm, and assembled using a CR2032 button cell, a Celgard2400 separator, and lithium foil as the counter electrode.

[0037] Unless otherwise specified, "room temperature" in this invention refers to 25±2℃.

[0038] All raw materials used in this invention were purchased from the market.

[0039] The technical solution of the present invention will be further illustrated by the following embodiments.

[0040] Example 1 A method for modifying the surface of a silicon-carbon composite electrode, comprising the following specific steps: 1. Preparation of silicon-carbon composite materials and electrode sheet molding 1) Preparation of silicon-carbon composite material: Using nano-silicon powder and graphite powder as raw materials, 15g of sodium carboxymethyl cellulose powder (CMC) was weighed and added to 1700g of deionized water and stirred to disperse, obtaining a CMC aqueous solution. 180g of spherical nano-silicon powder was weighed and added to the CMC aqueous solution and stirred to disperse, obtaining a suspension of nano-silicon powder. The suspension was stirred at high speed, and 105g of expanded graphite powder was added simultaneously. The mixture was stirred thoroughly and evenly to obtain a uniform slurry with a solid content of 15wt.%. The uniform slurry obtained in the above steps was placed in a freezer for pre-freezing for 6 hours. Then, the pre-frozen sample was transferred to a vacuum freeze dryer and the freeze-drying time was controlled at -100℃ for 24 hours to obtain a nano-silicon-expanded graphite composite material precursor. Then, it was transferred to a vacuum furnace for high-temperature carbonization at 1200℃ for 6 hours. After cooling, it was taken out, crushed, and sieved to obtain a nano-silicon-expanded graphite composite anode material, thus preparing a silicon-carbon composite material. 2) Preparation of electrode sheet: In the silicon-carbon composite material, take silicon-carbon negative electrode material, mix it with conductive carbon and binder in a mass ratio of 8:1:1 to form a uniform slurry, coat it on copper foil, and dry it overnight at 80°C in an oven to obtain the electrode. Finally, cut it into square electrode sheets with a size of 60mm×60mm for later use.

[0041] 2. Target material preparation and equipment installation Cu was selected as the modifying material. Cu powder was placed in a mold and pressed for 10-15 minutes under a pressure of 5-7 MPa to make a target material that matches the target body of the magnetron sputtering equipment. The prepared target material was installed on the target body corresponding to the magnetron sputtering equipment and covered with a target material cover. At the same time, the square electrode sheet prepared in step 1 was fixed on the substrate of the equipment. 3. Equipment debugging and pre-sputtering before sputtering Close the magnetron sputtering chamber door and start the vacuum pump to evacuate the chamber until the vacuum level reaches 5.0 × 10⁻⁶. -4 After the vacuum level reaches the standard, argon gas is introduced as the working gas, and the argon flow rate is adjusted to 20 sccm. By adjusting the position of the gate valve, the working gas pressure inside the chamber is stabilized at 1.3 Pa, and the electrode plate is rotated at a speed of 3 r / min. After selecting the DC power supply and confirming that the target baffle is in the closed state, the magnetron sputtering equipment is started, and the pre-sputtering power is set to 20W. The power is increased gradually to the target power in increments of 5W, starting with 10W. After the power stabilizes, the pre-sputtering state is maintained for 5 minutes. 4. Formal sputtering and sample removal After pre-sputtering, open the target baffle to begin formal sputtering, keeping the argon flow rate, working pressure, power supply type, and substrate rotation state unchanged. The formal sputtering power is the same as the pre-sputtering power, and sputtering lasts for 20 minutes. After the preset sputtering time is reached, first close the target baffle, then sequentially close the sputtering power, argon inlet valve, and substrate rotation device. After the temperature inside the equipment chamber naturally drops to room temperature, open the chamber door and remove the electrode sheet to obtain a solid silicon-carbon composite electrode with a surface-coated modification layer.

[0042] Example 2 A method for modifying the surface of a silicon-carbon composite electrode, comprising the following specific steps: 1. Preparation of silicon-carbon composite materials and electrode sheet molding: 1) Preparation of silicon-carbon composite material: The preparation method is the same as in Example 1; 2) Preparation of electrode sheets: The preparation method is the same as in Example 1; 2. Target material preparation and equipment installation Cu was selected as the modifying material. Cu powder was placed in a mold and pressed for 10-15 minutes under a pressure of 5-7 MPa to make a target material that matches the target body of the magnetron sputtering equipment. The prepared target material was installed on the target body corresponding to the magnetron sputtering equipment and covered with a target material cover. At the same time, the square electrode sheet prepared in step 1 was fixed on the substrate of the equipment. 3. Equipment debugging and pre-sputtering before sputtering Close the magnetron sputtering chamber door and start the vacuum pump to evacuate the chamber until the vacuum level reaches 5.0 × 10⁻⁶.-4 After the vacuum level reaches the standard, argon gas is introduced as the working gas, and the argon flow rate is adjusted to 20 sccm. By adjusting the position of the gate valve, the working gas pressure inside the chamber is stabilized at 1.3 Pa, and the electrode plate is rotated at a speed of 3 r / min. After selecting the DC power supply and confirming that the target baffle is in the closed state, the magnetron sputtering equipment is started, and the pre-sputtering power is set to 60W. The power is gradually increased to the target power in increments of 10W and 5W. After the power stabilizes, the pre-sputtering state is maintained for 5 minutes. 4. Formal sputtering and sample removal After pre-sputtering, open the target baffle to begin formal sputtering, keeping the argon flow rate, working pressure, power supply type, and substrate rotation state unchanged. The formal sputtering power is the same as the pre-sputtering power, and sputtering lasts for 3 minutes. After the preset sputtering time is reached, first close the target baffle, then sequentially close the sputtering power, argon inlet valve, and substrate rotation device. After the temperature inside the equipment chamber naturally drops to room temperature, open the chamber door and remove the electrode sheet to obtain a solid silicon-carbon composite electrode with a surface-coated modification layer.

[0043] Example 3 A method for modifying the surface of a silicon-carbon composite electrode, comprising the following specific steps: 1. Preparation of silicon-carbon composite materials and electrode sheet molding: 1) Preparation of silicon-carbon composite material: The preparation method is the same as in Example 1; 2) Preparation of electrode sheets: The preparation method is the same as in Example 1; 2. Target material preparation and equipment installation Lithium aluminum titanium phosphate (LATP) was selected as the modifying material. Lithium aluminum titanium phosphate (LATP) powder was placed in a mold and pressed under a pressure of 5-7 MPa for 10-15 min to prepare a target material that matches the target body of the magnetron sputtering equipment. The prepared target material was installed on the target body corresponding to the magnetron sputtering equipment and covered with a target material cover. At the same time, the square electrode sheet prepared in step 1 was fixed on the substrate of the equipment. 3. Equipment debugging and pre-sputtering before sputtering Close the magnetron sputtering chamber door and start the vacuum pump to evacuate the chamber until the vacuum level reaches 5.0 × 10⁻⁶. -4 Pa; After the vacuum level reaches the standard, set the heating temperature to 100℃, introduce argon gas as the working gas, and adjust the argon gas flow rate to 30 sccm; stabilize the working gas pressure in the chamber at 1 Pa by adjusting the gate valve position, and rotate the electrode plate at a speed of 3 r / min; select the radio frequency power supply, confirm that the target baffle is in the closed state, start the magnetron sputtering equipment, set the pre-sputtering power to 200W, start with 10W as the initial power, and gradually increase to the target power in 5W increments; after the power stabilizes, maintain the pre-sputtering state for 5 minutes; 4. Formal sputtering and sample removal After pre-sputtering, open the target baffle to begin formal sputtering, keeping the argon flow rate, working pressure, power supply type, and substrate rotation state unchanged. The formal sputtering power is the same as the pre-sputtering power, and sputtering lasts for 20 minutes. After the preset sputtering time is reached, first close the target baffle, then sequentially close the sputtering power, argon inlet valve, and substrate rotation device. After the temperature inside the equipment chamber naturally drops to room temperature, open the chamber door and remove the electrode sheet to obtain a solid silicon-carbon composite electrode with a surface-coated modification layer.

[0044] Example 4 A method for modifying the surface of a silicon-carbon composite electrode, comprising the following specific steps: 1. Preparation of silicon-carbon composite materials and electrode sheet molding: 1) Preparation of silicon-carbon composite material: The preparation method is the same as in Example 1; 2) Preparation of electrode sheets: The preparation method is the same as in Example 1; 2. Target material preparation and equipment installation Cu and lithium aluminum titanium phosphate (LATP) were selected as modification materials. Cu powder and LATP powder were placed in molds and pressed under a pressure of 5-7 MPa for 10-15 min to prepare a target material that matches the target body of the magnetron sputtering equipment. The prepared target material was installed on the target body corresponding to the magnetron sputtering equipment and covered with a target material cover. At the same time, the square electrode sheet prepared in step 1 was fixed on the substrate of the equipment. 3. Equipment debugging and pre-sputtering before sputtering Close the magnetron sputtering chamber door and start the vacuum pump to evacuate the chamber until the vacuum level reaches 5.0 × 10⁻⁶. -4 Pa; After the vacuum level reaches the standard, set the heating temperature to 100℃, introduce argon gas as the working gas, and adjust the argon gas flow rate to 30 sccm; stabilize the working gas pressure in the chamber at 1 Pa by adjusting the gate valve position, and rotate the electrode plate at a speed of 3 r / min; select DC power supply for Cu sputtering and RF power supply for LATP sputtering. After confirming that the target baffle is in the closed state, start the magnetron sputtering equipment, set the Cu pre-sputtering power to 60W and the LATP pre-sputtering power to 100W, and gradually increase the power to the target power in increments of 10W and 5W respectively; after the power stabilizes, maintain the pre-sputtering state for 5 minutes; 4. Formal sputtering and sample removal After pre-sputtering, open the target baffle to begin formal sputtering, keeping the argon flow rate, working pressure, power supply type, and substrate rotation state unchanged. The formal sputtering power is the same as the pre-sputtering power, and sputtering lasts for 10 minutes. After the preset sputtering time is reached, first close the target baffle, then sequentially close the sputtering power, argon inlet valve, and substrate rotation device. After the temperature inside the equipment chamber naturally drops to room temperature, open the chamber door and remove the electrode sheet to obtain a solid silicon-carbon composite electrode with a surface-coated modification layer.

[0045] Example 5 A method for modifying the surface of a silicon-carbon composite electrode, comprising the following specific steps: 1. Preparation of silicon-carbon composite materials and electrode sheet molding: 1) Preparation of silicon-carbon composite material: The preparation method is the same as in Example 1; 2) Preparation of electrode sheets: The preparation method is the same as in Example 1; 2. Target material preparation and equipment installation Al was selected as the modifying material. Al powder was placed in a mold and pressed for 10-15 minutes under a pressure of 5-7 MPa to make a target material that matches the target body of the magnetron sputtering equipment. The prepared target material was installed on the target body corresponding to the magnetron sputtering equipment and covered with a target material cover. At the same time, the square electrode sheet prepared in step 1 was fixed on the substrate of the equipment. 3. Equipment debugging and pre-sputtering before sputtering Close the magnetron sputtering chamber door and start the vacuum pump to evacuate the chamber until the vacuum level reaches 5.0 × 10⁻⁶. -4 After the vacuum level reaches the standard, argon gas is introduced as the working gas, and the argon flow rate is adjusted to 20 sccm. The working gas pressure inside the chamber is stabilized at 0.8 Pa by adjusting the position of the gate valve, and the electrode plate is rotated at a speed of 3 r / min. After selecting the DC power supply and confirming that the target baffle is in the closed state, the magnetron sputtering equipment is started, and the pre-sputtering power is set to 60 W. The power is gradually increased to the target power in increments of 10 W and 5 W. After the power stabilizes, the pre-sputtering state is maintained for 5 min. 4. Formal sputtering and sample removal After pre-sputtering, open the target baffle to begin formal sputtering, keeping the argon flow rate, working pressure, power supply type, and substrate rotation state unchanged. The formal sputtering power is the same as the pre-sputtering power, and sputtering lasts for 20 minutes. After the preset sputtering time is reached, first close the target baffle, then sequentially close the sputtering power, argon inlet valve, and substrate rotation device. After the temperature inside the equipment chamber naturally drops to room temperature, open the chamber door and remove the electrode sheet to obtain a solid silicon-carbon composite electrode with a surface-coated modification layer.

[0046] Example 6 A method for modifying the surface of a silicon-carbon composite electrode, comprising the following specific steps: 1. Preparation of silicon-carbon composite materials and electrode sheet molding: 1) Preparation of silicon-carbon composite material: 1000g of ultrafine graphite powder was placed in a fluidized bed reactor. Nitrogen gas (10L / min) was introduced to clean the reactor and the temperature was raised to 480℃. Then, a mixture of silane (2L / min) and nitrogen (8L / min) was introduced for 270min. Nano-silicon was deposited on the surface of ultrafine graphite powder under constant temperature fluidization. After silicon deposition, the reactor temperature was raised to 520℃ and a mixture of acetylene (2L / min) and nitrogen (8L / min) was introduced for 150min to perform carbon coating treatment. After coating, the mixture was cooled under nitrogen to obtain silicon-carbon composite anode material.

[0047] 2) Preparation of electrode sheets: The preparation method is the same as in Example 1; 2. Target material preparation and equipment installation In is selected as the modifying material. In powder is placed in a mold and pressed for 10-15 minutes under a pressure of 5-7 MPa to make a target material that matches the target body of the magnetron sputtering equipment. The prepared target material is installed on the target body corresponding to the magnetron sputtering equipment and covered with a target material cover. At the same time, the square electrode sheet prepared in step 1 is fixed on the substrate of the equipment. 3. Equipment debugging and pre-sputtering before sputtering Close the magnetron sputtering chamber door and start the vacuum pump to evacuate the chamber until the vacuum level reaches 5.0 × 10⁻⁶. -4 After the vacuum level reaches the standard, argon gas is introduced as the working gas, and the argon flow rate is adjusted to 40 sccm. The working gas pressure inside the chamber is stabilized at 0.5 Pa by adjusting the position of the gate valve, and the electrode plate is rotated at a speed of 3 r / min. After selecting the DC power supply and confirming that the target baffle is in the closed state, the magnetron sputtering equipment is started, and the pre-sputtering power is set to 30 W. The power is gradually increased to the target power in increments of 10 W and 5 W. After the power stabilizes, the pre-sputtering state is maintained for 5 min. 4. Formal sputtering and sample removal After pre-sputtering, open the target baffle to begin formal sputtering, keeping the argon flow rate, working pressure, power supply type, and substrate rotation state unchanged. The formal sputtering power is the same as the pre-sputtering power, and sputtering lasts for 3 minutes. After the preset sputtering time is reached, first close the target baffle, then sequentially close the sputtering power, argon inlet valve, and substrate rotation device. After the temperature inside the equipment chamber naturally drops to room temperature, open the chamber door and remove the electrode sheet to obtain a solid silicon-carbon composite electrode with a surface-coated modification layer.

[0048] Example 7 A method for modifying the surface of a silicon-carbon composite electrode, comprising the following specific steps: 1. Preparation of silicon-carbon composite materials and electrode sheet molding: 1) Preparation of silicon-carbon composite material: The preparation method is the same as in Example 6; 2) Preparation of electrode sheets: The preparation method is the same as in Example 1; 2. Target material preparation and equipment installation Gallium-doped lithium lanthanum zirconium tantalum oxide (Ga-LLZTO) was selected as the modification material. Ga-LLZTO powder was placed in a mold and pressed for 10-15 minutes under a pressure of 5-7 MPa to prepare a target material that matches the target body of the magnetron sputtering equipment. The prepared target material was installed on the target body corresponding to the magnetron sputtering equipment and covered with a target material cover. At the same time, the square electrode sheet prepared in step 1 was fixed on the substrate of the equipment. 3. Equipment debugging and pre-sputtering before sputtering Close the magnetron sputtering chamber door and start the vacuum pump to evacuate the chamber until the vacuum level reaches 5.0 × 10⁻⁶. -4 After the vacuum level reaches the standard, set the heating temperature to 150℃, introduce argon gas as the working gas, and adjust the argon gas flow rate to 40 sccm; stabilize the working gas pressure in the chamber at 0.57 Pa by adjusting the gate valve position, and rotate the electrode plate at a speed of 3 r / min; select the radio frequency power supply, confirm that the target baffle is in the closed state, start the magnetron sputtering equipment, set the pre-sputtering power to 100W, and gradually increase it to the target power in increments of 10W and 20W; after the power stabilizes, maintain the pre-sputtering state for 5 minutes; 4. Formal sputtering and sample removal After pre-sputtering, open the target baffle to begin formal sputtering, keeping the argon flow rate, working pressure, power supply type, and substrate rotation state unchanged. The formal sputtering power is the same as the pre-sputtering power, and sputtering lasts for 20 minutes. After the preset sputtering time is reached, first close the target baffle, then sequentially close the sputtering power, argon inlet valve, and substrate rotation device. After the temperature inside the equipment chamber naturally drops to room temperature, open the chamber door and remove the electrode sheet to obtain a solid silicon-carbon composite electrode with a surface-coated modification layer.

[0049] Comparative Example 1 A method for preparing a silicon-carbon composite electrode sheet without surface modification, the specific steps of which are as follows: 1) Preparation of silicon-carbon composite material: The preparation method is the same as in Example 1; 2) Preparation of electrode sheets: The preparation method is the same as in Example 1; 3) Cut the prepared electrode sheet into electrode sheets with a diameter of 12 mm.

[0050] Comparative Example 2 A method for preparing a silicon-carbon composite electrode sheet without surface modification, the specific steps of which are as follows: 1) Preparation of silicon-carbon composite material: The preparation method is the same as in Example 6; 2) Preparation of electrode sheets: The preparation method is the same as in Example 1; 3) Cut the prepared electrode sheet into electrode sheets with a diameter of 12 mm.

[0051] Figure 1 The scan spectrum and energy dispersive spectroscopy (EDS) of the solid silicon-carbon composite electrode prepared in Example 1 are shown below. Figure 1 The energy dispersive spectroscopy signal clearly detected elements such as Cu (copper), Si (silicon), and O (oxygen). Combined with the fact that the modification material in Example 1 was Cu, it was confirmed that a Cu modification layer was successfully deposited on the surface of the silicon-carbon composite electrode by magnetron sputtering, and the modification material was effectively attached to the electrode surface.

[0052] Performance testing: 1. The electrode materials prepared in Examples 1-7 and Comparative Examples 1-2 were assembled into 2032 coin cells, and their cycle life was tested. The specific test method was as follows: first, the cells were discharged to 0.01V at a current density of 100mA / g, then discharged to 0.005V at a current density of 10mA / g, allowed to stand for 3 minutes, and finally charged to 1.5V at a current density of 100mA / g. This constituted one cycle for testing the cycle performance. The test results are shown in Table 1. The cycle life curves of the materials prepared in Example 1 and Comparative Example 1 are shown below. Figure 2 As shown in a).

[0053]

[0054] As can be seen from Table 1, the capacity retention rates (62.9-80.08%) of all magnetron sputtered modified examples (1-7) were higher than those of unmodified Comparative Example 1 (60.4%) and Comparative Example 2 (63.3%), verifying that surface modification can effectively alleviate the capacity decay during silicon-carbon electrode cycling. Although Comparative Example 1 had a high initial capacity, it decayed the fastest, demonstrating the dual role of modification in "capacity retention + stable cycling".

[0055] Figure 2 In Figure a), the cycle life curves of the materials prepared in Example 1 and Comparative Example 1 are shown. As can be seen from the figure, compared with the unmodified Comparative Example 1, the charge / discharge specific capacity of Example 1 (Cu modified) decays significantly less within 60 cycles and maintains a higher specific capacity level throughout the process, indicating that magnetron sputtering modification of Cu can effectively improve the cycle stability of silicon-carbon composite electrodes.

[0056] 2. The materials prepared in Examples 1-7 and Comparative Examples 1-2 were assembled into 2032 coin cells, and their rate life performance was tested. The specific test method was as follows: charge-discharge tests were performed sequentially at current densities of 0.1 A / g, 0.2 A / g, 0.5 A / g, 0.8 A / g, and 1 A / g. The test results are shown in Table 2, and the rate life curves are shown in Table 2. Figure 2 As shown in b) of the diagram.

[0057]

[0058] As can be seen from Table 2, the capacity retention of all examples at a high current density of 1 A / g (69.65-79.61%) is much higher than that of Comparative Example 1 (41.49%), and most of them are higher than that of Comparative Example 2 (75.15%), proving that surface modification can significantly improve the rate adaptability of the electrode.

[0059] Figure 2 b) shows the rate lifetime curves of the materials prepared in Example 1 and Comparative Example 1. As can be seen from the figure, the charge-discharge specific capacity of Example 1 at different current densities (0.1A / g to 1A / g) is much higher than that of Comparative Example 1, especially at high current densities (1A / g), which shows that surface modification can improve the rate performance of the electrode and enhance the capacity retention capability during high current charge and discharge.

[0060] In summary, this invention significantly improves the cycle life (capacity retention) and rate performance of silicon-carbon composite electrodes by modifying the surface of the electrodes with metals (Al / Cu / In) or solid electrolytes (LATP / Ga-LLZTO) through magnetron sputtering. The combined effect of In and Ga-LLZTO single modification and Cu+LATP composite modification is even better. The unmodified silicon-carbon electrode shows poor performance in both cycle and rate performance, which verifies the effectiveness of the modification method of this invention.

[0061] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for modifying the surface of a silicon-carbon composite electrode, characterized in that, A solid silicon-carbon composite electrode is obtained by modifying the surface of the silicon-carbon composite electrode using magnetron sputtering; wherein the modifying material includes a metallic material and / or a solid electrolyte material. The metallic material is selected from Al, Cu, or In; The solid electrolyte material is selected from lithium titanium aluminum phosphate or gallium-doped lithium lanthanum zirconium tantalum oxide.

2. The method for modifying the surface of a silicon-carbon composite electrode according to claim 1, characterized in that, Specifically, the following steps are included: 1) Prepare silicon-carbon composite materials and fabricate them into electrode sheets; 2) Press the modification material into a target and mount it on the target of the magnetron sputtering equipment, and mount the electrode sheet on the substrate; 3) Evacuate the magnetron sputtering equipment, then introduce argon gas, adjust the gas pressure, adjust the target baffle to the closed state, and start the magnetron sputtering equipment for pre-sputtering; 4) After the pre-sputtering is completed, the target baffle is opened for formal sputtering, and a modification layer is formed on the surface of the silicon-carbon composite electrode to obtain a solid silicon-carbon composite electrode.

3. The method for modifying the surface of a silicon-carbon composite electrode according to claim 2, characterized in that, The silicon-carbon composite material is prepared by one of the following methods: Method 1: Add spherical nano-silicon powder to an aqueous solution of sodium carboxymethyl cellulose to obtain a nano-silicon powder suspension; continue to add expanded graphite powder to the nano-silicon powder suspension to obtain a slurry; subject the slurry to pre-freezing and vacuum freezing in sequence to obtain a nano-silicon-expanded graphite composite material precursor, then perform high-temperature carbonization, cool and remove, crush and sieve to obtain a nano-silicon-expanded graphite composite anode material. Method 2: Place ultrafine graphite powder in a fluidized bed reactor, introduce nitrogen gas and raise the temperature, then introduce a mixture of silane and nitrogen gas. Under constant temperature fluidization, deposit nano-silicon on the surface of ultrafine graphite powder. After silicon deposition is completed, raise the reactor temperature and introduce a mixture of acetylene and nitrogen gas again for carbon coating treatment. After coating, silicon-carbon composite anode material is obtained.

4. The method for modifying the surface of a silicon-carbon composite electrode according to claim 2, characterized in that, The vacuuming process refers to evacuating to a vacuum level of 5.0 × 10⁻⁶. -4 Pa.

5. The method for modifying the surface of a silicon-carbon composite electrode according to claim 2, characterized in that, The argon gas flow rate is 20-40 sccm; the gas pressure is 0.3-1.3 Pa.

6. The method for modifying the surface of a silicon-carbon composite electrode according to claim 2, characterized in that, The pre-sputtering parameters are: power of 20-200W, sputtering time of 5min; and / or, The parameters for the formal sputtering are: power of 20-200W and sputtering time of 3-30min.

7. The method for modifying the surface of a silicon-carbon composite electrode according to claim 2, characterized in that, The electrode sheet rotates at a speed of 3 r / min during the sputtering process.

8. The method for modifying the surface of a silicon-carbon composite electrode according to claim 2, characterized in that, The sputtering process uses a DC power supply or an RF power supply.

9. A solid silicon-carbon composite electrode prepared by the method according to any one of claims 1-8.

10. The application of a solid silicon-carbon composite electrode as described in claim 9 in a lithium-ion battery.

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