Preparation method of boron-doped modified silicon composite negative electrode material

Abstract

The application provides a preparation method of boron-doped modified silicon composite negative electrode material and relates to the technical field of battery negative electrode material preparation. The method comprises the following steps: S1, boron-doped silicon nanowire preparation; S2, preparation of multilayer MXene, wherein the size of the multilayer MXene is 5-10 mu m; S3, dispersing the boron-doped silicon nanowire material and the multilayer MXene material in a solvent, and performing ultra-low temperature freeze drying on the obtained solution to obtain a boron-doped silicon nanowire / multilayer MXene composite negative electrode material. The boron-doped silicon nanowire / multilayer MXene composite negative electrode material can reduce the rapid capacity attenuation of the material in the charging and discharging process.

Description

Technical Field

[0001] This invention relates to the field of battery anode material preparation technology, specifically to a method for preparing a boron-doped modified silicon composite anode material. Background Technology

[0002] Silicon-based anodes have attracted considerable attention due to their high theoretical specific capacity (~4212 mAh / g). As a material that can form alloys with lithium, each silicon atom can react with 4.4 lithium ions, which is a huge improvement over the capacity of commercial graphite (~372 mAh / g). This makes it regarded as the next generation of anode materials. At the same time, silicon is one of the most abundant elements on Earth, and its low cost is also one of the reasons for its attention.

[0003] However, silicon-based anode materials undergo significant volume expansion and contraction during charging and discharging. Repeated volume expansion and contraction can cause the anode material to detach, resulting in a rapid decrease in the anode material's capacity. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing boron-doped modified silicon composite anode materials, which solves the technical problem that silicon-based anode materials experience significant volume expansion and contraction during charging and discharging, leading to rapid capacity decay.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing a boron-doped modified silicon composite anode material, comprising the following steps:

[0009] S1, Preparation of boron-doped silicon nanowires

[0010] S11. Provide a silicon substrate, and after cleaning, use aluminum as the plating source to form an aluminum film with a thickness of 5 to 20 μm on the surface of the silicon substrate to obtain an aluminum film modified silicon substrate.

[0011] S12. Create holes in the aluminum film-modified silicon substrate to prepare a porous alumina film-modified silicon substrate.

[0012] S13. An Au (gold) layer is deposited on the surface of the porous alumina film modified silicon substrate to obtain a gold layer porous alumina film modified silicon substrate. Then, silane, borane and hydrogen are used as reaction gases to co-deposit on the gold layer porous alumina film modified silicon substrate. After deposition, acid washing is performed to obtain a boron-doped silicon nanowire array.

[0013] S2. Prepare multilayer MXene material, wherein the size of the multilayer MXene is 5μm to 10μm;

[0014] S3. Disperse the boron-doped silicon nanowire material and the multilayer MXene material in a solvent, and freeze-dry the resulting solution at -100℃ to -50℃ to obtain a boron-doped silicon nanowire / multilayer MXene composite anode material.

[0015] In the preparation method of boron-doped modified silicon composite anode materials, boron doping can increase the intrinsic conductivity of silicon, improve the atomic mixing degree in silicon-based unit cells, and reduce the volume expansion rate of the anode material during charge-discharge cycles. Simultaneously, boron coating effectively isolates silicon powder particles from direct contact with the electrolyte, avoiding side reactions and electrolyte consumption. MXene material improves the conductivity and lithium-ion diffusion rate of the anode material, thereby reducing electrode polarization. Its open structure provides space for the volume expansion of the anode material, preventing it from detaching due to volume expansion, thus improving the cycle performance of the anode material.

[0016] Preferably, the hole-forming process in S12 includes the following steps: placing the aluminum film-modified silicon substrate in an electrolyte, controlling a constant voltage of 1-20V and a constant current of 0.3-2.5A to form holes on the aluminum film-modified silicon substrate by anodizing, thereby forming a porous aluminum oxide film-modified silicon substrate with a pore size of 100-300nm.

[0017] Preferably, the electrolyte comprises an acid and a solvent, wherein the acid is selected from one or two of concentrated phosphoric acid and oxalic acid, and the solvent is selected from at least one of ethanol, ethylene glycol, and deionized water.

[0018] Preferably, the process prior to creating the aperture further includes polishing the aluminum film-modified silicon substrate, specifically including the following steps:

[0019] Remove the oxide layer on the surface of the aluminum-modified silicon substrate, and then perform a current density of 50–200 mA·cm⁻¹. -2 The aluminum film-modified silicon substrate is electrochemically polished under a polishing time of 50-100s to obtain a polished aluminum film-modified silicon substrate. The electrolyte for electrochemical polishing includes phosphoric acid, chromium trioxide, and water, and the mass ratio of phosphoric acid, chromium trioxide, and water is 80:5-12:8-15.

[0020] Preferably, the aluminum film-modified silicon substrate is placed in a sodium hydroxide solution to remove the surface oxide layer, wherein the concentration of the sodium hydroxide solution is 0.02wt% to 10wt% and the temperature is 50 to 80°C.

[0021] Preferably, the co-deposition in S13 includes the following steps:

[0022] Borane, silane, and hydrogen are co-deposited under a protective atmosphere at a gas flow ratio of 0.5–5:60:1–5. The deposition temperature is 500°C–1000°C, and the deposition time is 1–5 hours. The protective atmosphere is selected from nitrogen, argon, or an argon-hydrogen mixture.

[0023] Preferably, in S13, the acid used for pickling is selected from one or two of dilute hydrochloric acid, dilute sulfuric acid, and dilute nitric acid.

[0024] Preferably, in step S11, the silicon substrate is cleaned by ultrasonic treatment with acetone, ethanol, hydrofluoric acid, and deionized water for 15 to 20 minutes in sequence to initially remove organic and inorganic impurities. Then, it is dried at 50 to 70°C, and aluminum is used as the plating source to form an aluminum film on the surface of the silicon substrate.

[0025] Preferably, step S2 includes the following steps: preparing multilayer MXene material by hydrofluoric acid etching, with an etching temperature of 45℃~80℃, a hydrofluoric acid concentration of 10%~20%, and an etching time of 36h~72h.

[0026] Preferably, the solvent in S3 is selected from any one of ethanol, ethylene glycol, and propanol.

[0027] Preferably, S3 satisfies at least one of the following conditions:

[0028] The mass ratio of boron-doped silicon nanowires to multilayer MXene materials is 5:0.5–2;

[0029] The mass-to-volume ratio of the total mass of boron-doped silicon nanowires and multilayer MXene materials to the solvent is 1:3 to 10. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 SEM image of the boron-doped silicon nanowire / multilayer MXene composite anode material prepared in Example 1;

[0032] Figure 2 SEM images of the pore structure of porous alumina films on silicon substrates prepared under different voltages;

[0033] Where (a) is 10V and (b) is 4V. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] This application provides a method for preparing boron-doped modified silicon composite anode materials, which solves the technical problem that silicon-based anode materials experience significant volume expansion and contraction during charging and discharging, leading to rapid capacity decay.

[0036] The technical solution in this application is to solve the above-mentioned technical problems, and the general idea is as follows:

[0037] The purpose of this invention is to provide a method for preparing boron-doped modified silicon composite anode material. Boron-doped silicon nanowires are prepared using a template method and ultra-vacuum CVD deposition technology, while multilayer MXene is prepared by wet etching with hydrogen fluoride (HF). After mixing, a silicon nanowire / multilayer MXene anode material is prepared.

[0038] Using silicon wafers as the raw material for silicon nanowires, the silicon wafers were cleaned using the RCA method and then etched to obtain silicon nanowires. An aluminum film of a certain thickness was deposited on the silicon substrate surface using electron beam evaporation. The aluminum film was then subjected to surface oxide treatment and electrochemical polishing. The polished aluminum film was then used to modify the silicon substrate, followed by anodic oxidation to prepare a porous aluminum film. Finally, the porous alumina film containing the nanoporous structure was placed in an ultra-vacuum CVD furnace for silane and borane co-deposition. The porous alumina film on the boron-coated silicon nanowire substrate was then acid-washed to obtain a boron-doped silicon nanowire array.

[0039] The MXene precursor was etched using hydrochloric acid or hydrofluoric acid as the etching solution, with hydrofluoric acid being preferred. The MXene precursor was placed in a heated hydrofluoric acid solution and etched at a higher temperature. After etching, the acid was removed until the solution was neutral, and the solution was filtered and collected to obtain MXene with an open structure. This MXene was then stirred and mixed with boron-doped silicon nanowires to obtain a boron-doped silicon nanowire / multilayer MXene composite anode material. This material was coated, dried, sliced, and then placed in a glove box for half-cell assembly using a CR2032 battery case. Battery cycle performance was tested using a Newwell BST3000 testing system, and all tests were conducted at room temperature.

[0040] Compared to other silicon anode fabrication methods, this method allows for better control over the size and growth direction of silicon nanowires. Boron doping increases the intrinsic conductivity of the silicon-based anode material, improves atomic mixing within the silicon unit cell, and reduces the material's expansion rate during charge-discharge cycles. Furthermore, boron doping effectively isolates silicon particles from direct contact with the electrolyte, preventing side reactions and electrolyte consumption. While silicon's poor conductivity hinders its application in rate performance, highly conductive MXene is well-suited for semiconductor silicon anodes. MXene significantly improves conductivity, enhances lithium-ion diffusion rates, reduces electrode polarization, and its open structure is well-suited to the expansion and contraction of silicon anodes, improving cycle performance. To adapt to the development of next-generation silicon-based anode materials and further reduce costs, the high nanoscale size, high conductivity, and high performance of silicon nanowire anodes are essential development directions for next-generation silicon-based anode materials.

[0041] The nanowires retain numerous structural gaps, which effectively accommodate the volume changes induced by the anode material during charging and discharging. This reduces internal stress buildup on the electrode surface and lowers the risk of electrode breakage, thus facilitating the further industrial production and commercialization of silicon anodes.

[0042] The method for preparing boron-doped modified silicon composite anode material in this application employs a template-co-deposition method to prepare silicon nanowires. First, a porous oxide template is prepared using anodizing, and then silicon nanowires are prepared using the template. During the growth of the silicon nanowires, borane is co-deposited to change the atomic arrangement structure inside the silicon-based nanowires. At the same time, the surface of the silicon nanowires is modified with boron. Then, the prepared silicon nanowire material is composite-mixed with MXene material to obtain the boron-doped modified silicon composite anode material.

[0043] The equipment used in this application is relatively simple and the preparation is rapid. The material possesses characteristics such as controllable size and excellent cycle performance. This provides a relatively reliable solution for next-generation silicon-based anodes with high nanoscale, high conductivity, and high performance.

[0044] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0045] Example 1

[0046] This embodiment provides a method for preparing a boron-doped modified silicon composite anode material, including the following steps:

[0047] S1, Preparation of boron-doped silicon nanowires

[0048] S11. The silicon wafer was ultrasonically cleaned sequentially with acetone, anhydrous ethanol, hydrofluoric acid, and deionized water for 20 minutes to remove organic and inorganic impurities from the surface. The cleaned silicon wafer was then dried in a forced-air drying oven at 60°C. Using an aluminum block as the deposition source, a 10 μm thick aluminum film was deposited on the silicon wafer surface via electron beam evaporation to prepare an aluminum-modified silicon substrate. The deposition time was 5 hours.

[0049] S12. Place the obtained aluminum film-modified silicon substrate into a 2wt% sodium hydroxide solution and clean it at 60°C for 2 minutes to remove the aluminum oxide impurity layer on the surface.

[0050] S13. Electrochemically polish the aluminum-film-modified silicon substrate with the surface oxide layer removed using an electrolyte composed of phosphoric acid, chromium trioxide, and water at 120 mA·cm⁻¹. -2 Constant current electrochemical polishing was performed at a specific current density to achieve a bright mirror finish on the aluminum foil surface, resulting in a polished aluminum film that modifies the silicon substrate. Since the aluminum film undergoes alkaline cleaning in S12, surface defects may remain; polishing removes these defects, leading to more uniform subsequent reactions. The polished aluminum film is then washed with deionized water and dried for later use. The mass ratio of phosphoric acid, chromium trioxide, and water is 80:12:8, and the polishing time is 50 seconds.

[0051] S14. The polished aluminum film-modified silicon substrate is placed in a 6wt% phosphoric acid solution using ethylene glycol and deionized water as solvents. A constant voltage of 6V is maintained, and pores are created on the polished aluminum film using anodizing, forming a porous alumina film-modified silicon substrate with a pore size of 100nm. This porous alumina film serves as a template for the subsequent fabrication of nanowires; that is, a porous oxide template is prepared using anodizing. The porous alumina template is relatively easy to remove later. Since the intrinsic expansion of silicon anode materials can lead to particle breakage, the reserved pore size of the porous alumina template can buffer the particle breakage caused by expansion during the silicon lithium intercalation process, thereby inhibiting SEI formation and reducing electrolyte consumption. If the pore size is too small, the reserved buffer pore size will be insufficient and unable to effectively alleviate expansion.

[0052] S15. After cleaning the porous alumina film-modified silicon substrate with HF aqueous solution, electron-free deposition is performed to deposit an Au layer on the porous alumina film surface of the porous alumina film-modified silicon substrate to obtain a gold layer porous alumina film-modified silicon substrate. The gold layer porous alumina film-modified silicon substrate is then immersed in an etching solution containing H2O2 and HF for etching to obtain silicon nanowires.

[0053] The mechanism of Au deposition is as follows: after the exposed silicon wafer surface at the pores of the porous alumina film is treated with HF, a large number of Si-H bonds are formed. Si-H bonds have strong reducing properties, while Au+ has strong oxidizing properties. The two undergo a redox reaction, and Au+ gains electrons and is reduced to Au atoms, which are deposited on the Si surface in the form of nanoparticles to form a discontinuous Au particle film.

[0054] Furthermore, the etching mechanism involves Au particles acting as a catalyst. The Si beneath the Au particles is oxidized to SiO2 by H2O2 in the etching solution and dissolved by HF, causing the Au particles to sink. Therefore, in the areas covered by Au particles, Si is gradually etched downwards, forming "tunnels." Since the Au particle film is discontinuous, the gaps between adjacent Au particles are not etched, resulting in the formation of silicon nanowires between adjacent "tunnels."

[0055] The reaction formula is as follows:

[0056] Si + 2H₂O₂ + 6F - +4H + →[SiF6] 2- +4H2O.

[0057] S16. The gold-coated porous alumina film-modified silicon substrate is transferred to the PECVD preparation chamber. The furnace chamber is evacuated. Silane, borane and hydrogen are used as reaction gases to carry out primary and secondary reactions for deposition. During the deposition process, the silane flow rate is 6 sccm, the borane flow rate is 0.7 sccm and the hydrogen flow rate is 160 sccm. After deposition, a certain amount of boron is deposited between the silicon nanowires. After cooling, boron-coated silicon nanowires are obtained.

[0058] The deposition process involves primary and secondary reactions. The primary reaction involves electron bombardment of silane and borane to generate ionic groups (silicon ions, boron ions, and hydrogen ions) and neutral groups (hydrogen). The secondary reaction involves collisions between the generated ionic groups and neutral groups to form new groups (silicon, boron, and hydrogen). These groups serve as the raw materials for the deposition of silicon nanoparticles. Silicon nanowires are then deposited within the pores of a porous alumina template using these new groups, altering the atomic arrangement within the silicon nanowires. Simultaneously, the surface of the silicon nanowires is modified with boron, resulting in a porous alumina film-modified silicon nanowire array template with deposited silicon nanowires.

[0059] S17. The silicon nanowire array template modified with a porous alumina film of deposited silicon nanowires is acid-washed with 5wt% dilute hydrochloric acid to remove the surface-modified porous alumina film, and then washed with deionized water to obtain a boron-doped silicon nanowire array.

[0060] S2, Preparation of multilayer MXene

[0061] Prepare a 5% hydrofluoric acid etching solution, place the MXene precursor pure silicon material in the etching solution and etch at 45°C for 54 hours, collect the MXene, adjust the pH of the collected MXene to neutral, then filter and collect again to obtain multilayer MXene.

[0062] S3, Preparation of boron-doped silicon nanowires / multilayer MXene composite anode materials

[0063] Boron-doped silicon nanowires and multilayer MXene materials were mixed at a mass ratio of 5:0.5 and dispersed in ethanol under ultrasonication. The total mass ratio of boron-doped silicon nanowires and multilayer MXene materials to the mass-volume ratio of ethanol was 1:3. The resulting solution was then subjected to ultra-low temperature freeze-drying and pulverization at -100℃ to obtain a boron-doped silicon nanowire / multilayer MXene composite anode material.

[0064] According to the ratio of boron-doped silicon nanowires / multilayer MXene composite anode material: binder: conductive agent = 8:1:1, a boron-doped modified silicon composite anode slurry was prepared. The prepared anode slurry was coated and sheeted, dried and sliced ​​into 14mm diameter discs. The discs were then placed in a glove box with water and oxygen concentrations of less than 0.1ppm. A half-cell with a lithium foil counter electrode was prepared using a CR2032 battery case. The prepared half-cells were left to stand for more than 10 hours to ensure full immersion of the electrolyte. The half-cells were then subjected to charge-discharge tests, and the test results are shown in Table 1.

[0065] Example 2

[0066] This embodiment provides a method for preparing a boron-doped modified silicon composite anode material, including the following steps:

[0067] S1, Preparation of boron-doped silicon nanowires

[0068] S11. The silicon wafer was ultrasonically cleaned sequentially with acetone, anhydrous ethanol, hydrofluoric acid, and deionized water for 20 minutes to remove organic and inorganic impurities from the surface. The cleaned silicon wafer was then dried in a forced-air drying oven at 60°C. Using an aluminum block as the deposition source, a 10 μm thick aluminum film was deposited on the silicon wafer surface via electron beam evaporation to prepare an aluminum-modified silicon substrate. The deposition time was 5 hours.

[0069] S12. Place the obtained aluminum film-modified silicon substrate into a 2wt% sodium hydroxide solution and clean it at 60°C for 2 minutes to remove the aluminum oxide impurity layer on the surface.

[0070] S13. Electrochemically polish the aluminum-film-modified silicon substrate with the surface oxide layer removed using an electrolyte composed of phosphoric acid, chromium trioxide, and water at 120 mA·cm⁻¹. -2Constant current electrochemical polishing was performed at a specific current density to achieve a bright mirror finish on the aluminum foil surface, resulting in a polished aluminum film that modifies the silicon substrate. Since the aluminum film undergoes alkaline cleaning in S12, surface defects may remain; polishing removes these defects, leading to more uniform subsequent reactions. The polished aluminum film is then washed with deionized water and dried for later use. The mass ratio of phosphoric acid, chromium trioxide, and water is 80:12:8, and the polishing time is 70 seconds.

[0071] S14. The polished aluminum film-modified silicon substrate is placed in a 6wt% phosphoric acid solution using ethylene glycol and deionized water as solvents. A constant voltage of 6V is maintained, and pores are created on the polished aluminum film using anodizing, forming a porous alumina film-modified silicon substrate with a pore size of 100nm. This porous alumina film serves as a template for the subsequent fabrication of nanowires; that is, a porous oxide template is prepared using anodizing. The porous alumina template is relatively easy to remove later. Since the intrinsic expansion of silicon anode materials can lead to particle breakage, the reserved pore size of the porous alumina template can buffer the particle breakage caused by expansion during the silicon lithium intercalation process, thereby inhibiting SEI formation and reducing electrolyte consumption. If the pore size is too small, the reserved buffer pore size will be insufficient and unable to effectively alleviate expansion.

[0072] S15. After cleaning the porous alumina film-modified silicon substrate with HF aqueous solution, electron-free deposition is performed to deposit an Au layer on the porous alumina film surface of the porous alumina film-modified silicon substrate to obtain a gold layer porous alumina film-modified silicon substrate. The gold layer porous alumina film-modified silicon substrate is then immersed in an etching solution containing H2O2 and HF for etching to obtain silicon nanowires.

[0073] The mechanism of Au deposition is as follows: after the exposed silicon wafer surface at the pores of the porous alumina film is treated with HF, a large number of Si-H bonds are formed. Si-H bonds have strong reducing properties, while Au+ has strong oxidizing properties. The two undergo a redox reaction, and Au+ gains electrons and is reduced to Au atoms, which are deposited on the Si surface in the form of nanoparticles to form a discontinuous Au particle thin film.

[0074] Furthermore, the etching mechanism involves Au particles acting as a catalyst. The Si beneath the Au particles is oxidized to SiO2 by H2O2 in the etching solution and dissolved by HF, causing the Au particles to sink. Therefore, in the areas covered by Au particles, Si is gradually etched downwards, forming "tunnels." Since the Au particle film is discontinuous, the gaps between adjacent Au particles are not etched, resulting in the formation of silicon nanowires between adjacent "tunnels."

[0075] S16. The gold-coated porous alumina film-modified silicon substrate is transferred to the PECVD preparation chamber. The furnace chamber is evacuated. Silane, borane and hydrogen are used as reaction gases to carry out primary and secondary reactions for deposition. During the deposition process, the silane flow rate is 6 sccm, the borane flow rate is 0.7 sccm and the hydrogen flow rate is 160 sccm. After deposition, a certain amount of boron is deposited between the silicon nanowires. After cooling, boron-coated silicon nanowires are obtained.

[0076] The deposition process involves primary and secondary reactions. The primary reaction involves electron bombardment of silane and borane to generate ionic groups (silicon ions, boron ions, and hydrogen ions) and neutral groups (hydrogen). The secondary reaction involves collisions between the generated ionic groups and neutral groups to form new groups (silicon, boron, and hydrogen). These groups serve as the raw materials for the deposition of silicon nanoparticles. Silicon nanowires are then deposited within the pores of a porous alumina template using these new groups, altering the atomic arrangement within the silicon nanowires. Simultaneously, the surface of the silicon nanowires is modified with boron, resulting in a porous alumina film-modified silicon nanowire array template with deposited silicon nanowires.

[0077] S17. The silicon nanowire array template modified with a porous alumina film of deposited silicon nanowires is acid-washed with 5wt% dilute hydrochloric acid to remove the surface-modified porous alumina film, and then washed with deionized water to obtain a boron-doped silicon nanowire array.

[0078] S2, Preparation of multilayer MXene

[0079] Prepare a 5% hydrofluoric acid etching solution, place the MXene precursor pure silicon material in the etching solution and etch at 45°C for 54 hours, collect the MXene, adjust the pH of the collected MXene to neutral, then filter and collect again to obtain multilayer MXene.

[0080] S3, Preparation of boron-doped silicon nanowires / multilayer MXene composite anode materials

[0081] Boron-doped silicon nanowires and multilayer MXene materials were mixed at a mass ratio of 5:1 and dispersed in ethylene glycol under ultrasonication. The mass-volume ratio of the total mass of the boron-doped silicon nanowires and multilayer MXene materials to that of ethylene glycol was 1:6. The resulting solution was then subjected to cryogenic freeze-drying and pulverization at -70°C to obtain a boron-doped silicon nanowire / multilayer MXene composite anode material.

[0082] According to the ratio of boron-doped silicon nanowires / multilayer MXene composite anode material: binder: conductive agent = 8:1:1, a boron-doped modified silicon composite anode slurry was prepared. The prepared anode slurry was coated and sheeted, dried and sliced ​​into 14mm diameter discs. The discs were then placed in a glove box with water and oxygen concentrations of less than 0.1ppm. A half-cell with a lithium foil counter electrode was prepared using a CR2032 battery case. The prepared half-cells were left to stand for more than 10 hours to ensure full immersion of the electrolyte. The half-cells were then subjected to charge-discharge tests, and the test results are shown in Table 1.

[0083] Example 3

[0084] This embodiment provides a method for preparing a boron-doped modified silicon composite anode material, including the following steps:

[0085] S1, Preparation of boron-doped silicon nanowires

[0086] S11. The silicon wafer was ultrasonically cleaned sequentially with acetone, anhydrous ethanol, hydrofluoric acid, and deionized water for 20 minutes to remove organic and inorganic impurities from the surface. The cleaned silicon wafer was then dried in a forced-air drying oven at 60°C. Using an aluminum block as the deposition source, a 10 μm thick aluminum film was deposited on the silicon wafer surface via electron beam evaporation to prepare an aluminum-modified silicon substrate. The deposition time was 5 hours.

[0087] S12. Place the obtained aluminum film-modified silicon substrate into a 2wt% sodium hydroxide solution and clean it at 60°C for 2 minutes to remove the aluminum oxide impurity layer on the surface.

[0088] S13. Electrochemically polish the aluminum-film-modified silicon substrate with the surface oxide layer removed using an electrolyte composed of phosphoric acid, chromium trioxide, and water at 120 mA·cm⁻¹. -2 Constant current electrochemical polishing was performed at a specific current density to achieve a bright mirror finish on the aluminum foil surface, resulting in a polished aluminum film that modifies the silicon substrate. Since the aluminum film undergoes alkaline cleaning in S12, surface defects may remain; polishing removes these defects, leading to more uniform subsequent reactions. The polished aluminum film is then washed with deionized water and dried for later use. The mass ratio of phosphoric acid, chromium trioxide, and water is 80:12:8, and the polishing time is 100 seconds.

[0089] S14. The polished aluminum film-modified silicon substrate is placed in a 6wt% phosphoric acid solution using ethylene glycol and deionized water as solvents. A constant voltage of 6V is maintained, and pores are created on the polished aluminum film using anodizing, forming a porous alumina film-modified silicon substrate with a pore size of 100nm. This porous alumina film serves as a template for the subsequent fabrication of nanowires; that is, a porous oxide template is prepared using anodizing. The porous alumina template is relatively easy to remove later. Since the intrinsic expansion of silicon anode materials can lead to particle breakage, the reserved pore size of the porous alumina template can buffer the particle breakage caused by expansion during the silicon lithium intercalation process, thereby inhibiting SEI formation and reducing electrolyte consumption. If the pore size is too small, the reserved buffer pore size will be insufficient and unable to effectively alleviate expansion.

[0090] S15. After cleaning the porous alumina film-modified silicon substrate with HF aqueous solution, electron-free deposition is performed to deposit an Au layer on the porous alumina film surface of the porous alumina film-modified silicon substrate to obtain a gold layer porous alumina film-modified silicon substrate. The gold layer porous alumina film-modified silicon substrate is then immersed in an etching solution containing H2O2 and HF for etching to obtain silicon nanowires.

[0091] The mechanism of Au deposition is as follows: after the exposed silicon wafer surface at the pores of the porous alumina film is treated with HF, a large number of Si-H bonds are formed. Si-H bonds have strong reducing properties, while Au+ has strong oxidizing properties. The two undergo a redox reaction, and Au+ gains electrons and is reduced to Au atoms, which are deposited on the Si surface in the form of nanoparticles to form a discontinuous Au particle thin film.

[0092] Furthermore, the etching mechanism involves Au particles acting as a catalyst. The Si beneath the Au particles is oxidized to SiO2 by H2O2 in the etching solution and dissolved by HF, causing the Au particles to sink. Therefore, in the areas covered by Au particles, Si is gradually etched downwards, forming "tunnels." Since the Au particle film is discontinuous, the gaps between adjacent Au particles are not etched, resulting in the formation of silicon nanowires between adjacent "tunnels."

[0093] S16. The gold-coated porous alumina film-modified silicon substrate is transferred to the PECVD preparation chamber. The furnace chamber is evacuated. Silane, borane and hydrogen are used as reaction gases to carry out primary and secondary reactions for deposition. During the deposition process, the silane flow rate is 6 sccm, the borane flow rate is 0.7 sccm and the hydrogen flow rate is 160 sccm. After deposition, a certain amount of boron is deposited between the silicon nanowires. After cooling, boron-coated silicon nanowires are obtained.

[0094] The deposition process involves primary and secondary reactions. The primary reaction involves electron bombardment of silane and borane to generate ionic groups (silicon ions, boron ions, and hydrogen ions) and neutral groups (hydrogen). The secondary reaction involves collisions between the generated ionic groups and neutral groups to form new groups (silicon, boron, and hydrogen). These groups serve as the raw materials for the deposition of silicon nanoparticles. Silicon nanowires are then deposited within the pores of a porous alumina template using these new groups, altering the atomic arrangement within the silicon nanowires. Simultaneously, the surface of the silicon nanowires is modified with boron, resulting in a porous alumina film-modified silicon nanowire array template with deposited silicon nanowires.

[0095] S17. The silicon nanowire array template modified with a porous alumina film of deposited silicon nanowires is acid-washed with 5wt% dilute hydrochloric acid to remove the surface-modified porous alumina film, and then washed with deionized water to obtain a boron-doped silicon nanowire array.

[0096] S2, Preparation of multilayer MXene

[0097] Prepare a 5% hydrofluoric acid etching solution, place the MXene precursor pure silicon material in the etching solution and etch at 45°C for 54 hours, collect the MXene, adjust the pH of the collected MXene to neutral, then filter and collect again to obtain multilayer MXene.

[0098] S3, Preparation of boron-doped silicon nanowires / multilayer MXene composite anode materials

[0099] Boron-doped silicon nanowires and multilayer MXene materials were mixed at a mass ratio of 5:2 and dispersed in propanol under ultrasonication. The mass-volume ratio of the total mass of the boron-doped silicon nanowires and multilayer MXene materials to the propanol was 1:10. The resulting solution was freeze-dried and pulverized at -50°C to obtain a boron-doped silicon nanowire / multilayer MXene composite anode material.

[0100] According to the ratio of boron-doped silicon nanowires / multilayer MXene composite anode material: binder: conductive agent = 8:1:1, a boron-doped modified silicon composite anode slurry was prepared. The prepared anode slurry was coated and sheeted, dried and sliced ​​into 14mm diameter discs. The discs were then placed in a glove box with water and oxygen concentrations of less than 0.1ppm. A half-cell with a lithium foil counter electrode was prepared using a CR2032 battery case. The prepared half-cells were left to stand for more than 10 hours to ensure full immersion of the electrolyte. The half-cells were then subjected to charge-discharge tests, and the test results are shown in Table 1.

[0101] Comparative Example 1

[0102] The difference between this comparative example and Example 1 is that the reaction gas in step S16 does not include borane, but only silane and hydrogen are used as the reaction gas, while the rest is the same as in Example 1.

[0103] Comparative Example 2

[0104] The difference between this comparative example and Example 1 is that step S14 uses 3 wt% phosphoric acid instead of 6 wt% phosphoric acid, while the rest is the same as in Example 1. As shown in Table 1, the phosphoric acid concentration affects the pore size of the porous alumina membrane. A decrease in concentration will correspondingly reduce the pore size of the porous alumina membrane, thus affecting the performance of the prepared half-cell.

[0105] Comparative Example 3

[0106] The difference between this comparative example and Example 1 is that S2 and S3 are not included. Boron-doped silicon nanowires are used instead of boron-doped silicon nanowire / multilayer MXene composite anode material to prepare the anode slurry. Otherwise, it is the same as Example 1. As shown in Table 1, multilayer MXene can effectively alleviate the expansion effect caused by silicon nanowire particles during charging and discharging, and avoid the degradation of cycle performance caused by the active material in the cell electrode sheet falling off from the current collector due to expansion.

[0107] Comparative Example 4

[0108] The difference between Comparative Example 4 and Example 1 is that in S14, a constant voltage of 9V is used instead of 6V; otherwise, they are the same as in Example 1. As shown in Table 1, increasing the voltage increases the pore size of the material, leading to an increase in the diameter of the silicon nanowires, which in turn affects the performance of the prepared half-cell.

[0109] Table 1. Performance test results of the half-cells prepared in Examples 1-3 and Comparative Examples 1-4

[0110]

[0111] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0112] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0113] The present invention has been illustrated with the above embodiments to describe the detailed process flow of the present invention. However, the present invention is not limited to the above detailed process flow, that is, it does not mean that the present invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a boron-doped modified silicon composite anode material, characterized in that, Includes the following steps: A silicon substrate is provided, and an aluminum film with a thickness of 5-20 μm is formed on the surface of the silicon substrate. Porous alumina film is then created to modify the silicon substrate. A gold layer is deposited on the surface of the porous alumina film-modified silicon substrate, and then co-deposited using silicon, boron, and hydrogen as reactants. The substrate is then acid-washed to obtain a boron-doped silicon nanowire array. Multilayer MXene material and the boron-doped silicon nanowire array are dispersed in a solvent and subjected to ultra-low temperature freeze-drying at -100℃ to -50℃ to obtain a boron-doped silicon nanowire / multilayer MXene composite anode material. The pore-forming process includes the following steps: after cleaning the silicon substrate, aluminum is used as the plating source to form an aluminum film with a thickness of 5-20 μm on the surface of the silicon substrate to obtain an aluminum film-modified silicon substrate. The aluminum film-modified silicon substrate is placed in an electrolyte, and a constant voltage of 1-20V and a constant current of 0.3-2.5A are controlled to form pores on the aluminum film-modified silicon substrate by anodizing, thereby forming a porous alumina film-modified silicon substrate with a pore size of 100-300 nm. The electrolyte is a 6wt% phosphoric acid solution using ethylene glycol and deionized water as solvents.

2. The preparation method according to claim 1, characterized in that, The process prior to creating the aperture also includes polishing the aluminum film-modified silicon substrate, specifically including the following steps: removing the oxide layer on the surface of the aluminum film-modified silicon substrate, and then polishing it at a current density of 50–200 mA·cm. −2 The aluminum film-modified silicon substrate is electrochemically polished under a polishing time of 50-100s to obtain a polished aluminum film-modified silicon substrate. The electrolyte for electrochemical polishing includes phosphoric acid, chromium trioxide, and water, and the mass ratio of phosphoric acid, chromium trioxide, and water is 80:5-12:8-15.

3. The preparation method according to claim 2, characterized in that, The aluminum film-modified silicon substrate is placed in a sodium hydroxide solution to remove the surface oxide layer. The concentration of the sodium hydroxide solution is 0.02wt% to 10wt%, and the temperature is 50 to 80℃.

4. The preparation method according to claim 1, characterized in that, The co-deposition includes the following steps: co-depositing the boron source, silicon source, and hydrogen at a gas flow ratio of 0.5–5:60:1–5 under a protective atmosphere, wherein the deposition temperature is 500℃–1000℃ and the deposition time is 1–5 hours; and / or, The protective atmosphere is selected from nitrogen, argon, or an argon-hydrogen mixture; and / or, The silicon source is silane, and the boron source is borane.

5. The preparation method according to claim 1, characterized in that, The acid used for pickling is selected from one or two of dilute hydrochloric acid, dilute sulfuric acid, and dilute nitric acid.

6. The preparation method according to claim 1, characterized in that, The preparation method of the multilayer MXene material is as follows: the multilayer MXene material is prepared by hydrofluoric acid etching, the etching temperature is 45℃~80℃, the hydrofluoric acid concentration is 10%~20%, the etching time is 36h~72h, and the size of the multilayer MXene is 5μm~10μm.

7. The preparation method according to claim 1, characterized in that, The solvent is selected from any one of ethanol, ethylene glycol, and propanol.

8. The preparation method according to claim 1, characterized in that, The mass ratio of the boron-doped silicon nanowire material to the multilayer MXene material is 5:0.5 to 2; The total mass ratio of the boron-doped silicon nanowire material and the multilayer MXene material to the solvent is 1:3 to 10.

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