Hierarchical channel silicon-carbon negative electrode material, preparation method thereof, negative electrode plate and solid-state battery

Abstract

The invention relates to the technical field of solid-state battery negative electrode materials, in particular to a hierarchical porous silicon-carbon negative electrode material, a preparation method thereof, a negative electrode piece and a solid-state battery. Comprising the following steps: (a) mixing nano silicon powder, a carbon source, a surfactant, a boron source, a phosphorus source and a solvent to obtain a sol solution; (b) freezing the sol obtained in the step (a), and then drying to obtain an aerogel precursor; and (c) carbonizing the aerogel precursor obtained in the step (b) to obtain the hierarchical porous silicon-carbon negative electrode material. According to the method, vertical macropores (5-50 [mu] m) created by an ice template method are used for directionally releasing expansion stress, mesopores (2-50 nm) formed by a surfactant are used for promoting permeation of sulfide electrolyte, micropores (1t, 2 nm) formed by carbon pyrolysis are used for limiting migration of silicon particles, and the volume expansion rate of the silicon-carbon negative electrode material is reduced from 300% to 1t through arrangement of multistage pore channels; 75%.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery anode material technology, and more specifically, to a multi-level porous silicon-carbon anode material, its preparation method, anode sheet, and solid-state battery. Background Technology

[0002] With the rapid development of new energy vehicles and the energy storage industry, higher requirements have been placed on the energy density, safety, and cycle life of lithium-ion batteries. All-solid-state batteries, especially those using high-ionic-conductivity sulfide solid electrolytes, are considered an important development direction for next-generation power batteries. However, their commercial application still faces severe challenges, with the compatibility of anode materials being one of the key bottlenecks.

[0003] Silicon-based anodes have attracted much attention due to their extremely high theoretical specific capacity (approximately 4200 mAh / g), making them an ideal choice to break through the energy density limit of existing graphite anodes. However, when silicon-based anodes are combined with sulfide solid electrolytes for use in all-solid-state batteries, their inherent defects are further amplified, mainly presenting the following three levels of technical challenges: 1. Massive volume expansion leads to structural failure. Silicon materials undergo intense alloying / dealloying reactions during charging and discharging, resulting in a volume expansion rate exceeding 300%. This repeated and massive volume change generates extreme mechanical stress within the electrode, causing silicon particle pulverization, electrode structure collapse, and failure of the solid-solid contact points with the solid electrolyte, thus leading to rapid capacity decay.

[0004] 2. A single pore structure cannot synergistically optimize stress buffering and ion transport. Existing silicon-carbon composite materials typically feature single micropores or disordered mesopores. This simple pore design has inherent limitations: firstly, it cannot achieve graded stress buffering, making it difficult to effectively cope with the large volume expansion of silicon; secondly, the lack of directional, interconnected ion transport channels results in slow lithium-ion transport kinetics within the solid-state electrode, limiting the battery's rate performance.

[0005] 3. Unstable solid-solid interfaces lead to a surge in interfacial impedance. Sulfide solid electrolytes are typically sensitive to air and have narrow electrochemical windows. The significant volume changes of the silicon anode easily create cracks and gaps at the interface, which not only increases interfacial impedance but also exposes new, active silicon surfaces and electrolytes, inducing continuous interfacial side reactions. This unstable interface causes repeated rupture and reconstruction of the solid electrolyte interphase (SEI) film, continuously consuming active lithium ions and electrolytes, resulting in a sustained increase in the battery's interfacial impedance and a significant decrease in cycle stability.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The primary objective of this invention is to provide a method for preparing a multi-level porous silicon-carbon anode material. This method utilizes an ice-templating method to create vertical macropores (5-50 μm) that directionally release expansion stress. Mesopores (2-50 nm) formed by surfactants promote the permeation of sulfide electrolytes. Micropores (<2 nm) formed by carbon pyrolysis restrict silicon particle migration. Through this multi-level pore structure, the volume expansion rate of the silicon-carbon anode material is reduced from 300% to <75%. Boron doping enhances electronic conductivity, while phosphorus doping forms a stable solid electrolyte interphase (SEI) film, reducing interfacial impedance. A continuous carbon network provides mechanical support and a conductive path for the material.

[0008] The second objective of this invention is to provide a method for preparing a hierarchical porous silicon-carbon anode material. This hierarchical pore structure significantly increases the solid-solid contact area, but also exacerbates the risk of side reactions. The material also incorporates synergistic doping of boron and phosphorus. Phosphorus doping preferentially reacts, promoting the formation of a dense and stable SEI film rich in Li3PO4, effectively preventing direct contact between silicon and the sulfide electrolyte, thus minimizing side reactions. Boron doping enhances the electronic conductivity of the carbon framework, constructing a highly efficient electron transport channel.

[0009] The third objective of this invention is to provide a negative electrode sheet.

[0010] The fourth objective of this invention is to provide a solid-state battery in which, when the negative electrode is applied to a sulfide all-solid-state battery, due to the synergistic effect of the structure, interface and skeleton, the capacity retention rate is >90% after 500 cycles at a charge-discharge rate of 0.5 C.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a method for preparing a multi-level porous silicon-carbon anode material, comprising the following steps: (a) Mix nano-silicon powder, carbon source, surfactant, boron source, phosphorus source and solvent to obtain sol solution; (b) The sol obtained in step (a) is subjected to freeze treatment and then dried to obtain an aerogel precursor; (c) The aerogel precursor obtained in step (b) is subjected to carbonization treatment to obtain the multi-level porous silicon-carbon anode material.

[0012] Preferably, in step (a), the particle size of the nano-silicon powder is 50~100 nm.

[0013] Preferably, the carbon source includes at least one of graphene oxide, sucrose, glucose, fructose, maltose, lactose, starch, cellulose, chitosan, lignin, phenolic resin, epoxy resin, polyimide, polyacrylonitrile, polyvinyl chloride, or polyvinyl alcohol.

[0014] Preferably, the surfactant includes a cationic surfactant; more preferably, the cationic surfactant includes a quaternary ammonium salt surfactant; even more preferably, the quaternary ammonium salt surfactant includes at least one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

[0015] Preferably, the boron source includes at least one of boric acid, ammonium tetraborate, triethyl borate, or ammonia borane.

[0016] Preferably, the phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium hypophosphite, or phytic acid.

[0017] Preferably, in step (a), the mass ratio of the nano-silicon powder, the carbon source, the surfactant, the boron source and the phosphorus source is 10:15~25:1~3:0.3~0.8:0.8~1.5.

[0018] Preferably, the solid content of the sol solution is 12wt%~18wt%.

[0019] Preferably, in step (a), the mixture is further subjected to ultrasonic treatment, the power of which is 600~1000W and the duration of which is 1~3h.

[0020] Preferably, during the ultrasonic treatment, the temperature of the solution system is 20~30℃.

[0021] Preferably, in step (b), the freezing process includes: (1) First stage: Cool to -5 to -15℃ at a rate of 0.5~2℃ / min and hold for 20~40 min; (2) Second stage: rapidly cool to -30~-50℃ at a rate of 3~8℃ / min and keep warm for 10~14 h.

[0022] Preferably, in step (b), the drying process includes: cooling to -70~-90℃, vacuum degree 10~15Pa, and drying for 20~28 h.

[0023] Preferably, in step (c), the carbonization process includes: (1) First carbonization: In an inert atmosphere, the temperature is increased to 350-450℃ at a heating rate of 1-3℃ / min and held for 1-3 h; (2) Second carbonization: In an inert atmosphere, the temperature is raised to 700-900℃ at a heating rate of 2-5℃ / min and held for 2-4 hours.

[0024] Preferably, the inert atmosphere includes argon and / or nitrogen; more preferably, the gas flow rate of the inert atmosphere is 40-60 ml / min.

[0025] Secondly, the present invention also provides a multi-level porous silicon-carbon anode material, which is mainly prepared by the preparation method of the multi-level porous silicon-carbon anode material.

[0026] Preferably, the multi-level porous silicon-carbon anode material comprises: a first mesopore with a pore size of 5~50μm, a second mesopore with a pore size of 2~50nm, and a third mesopore with a pore size of less than 2nm.

[0027] Thirdly, the present invention also provides a negative electrode sheet, which is mainly made of the aforementioned multi-level porous silicon-carbon negative electrode material.

[0028] Fourthly, the present invention also provides a solid-state battery, including the aforementioned negative electrode sheet.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention provides a method for preparing a multi-level porous silicon-carbon anode material, which uses the ice template method to create vertical macropores (5~50μm) to release expansion stress in a directional manner, and the surfactant-formed mesopores (2~50nm) to promote the permeation of sulfide electrolyte, and the micropores (<2nm) formed by carbon pyrolysis to restrict the migration of silicon particles. Through the multi-level pore arrangement, the volume expansion rate of the silicon-carbon anode material is reduced from 300% to <75%.

[0030] (2) The method for preparing a multi-level porous silicon-carbon anode material provided by the present invention is that boron doping can improve electronic conductivity, phosphorus doping can form a stable solid electrolyte interphase (SEI) film and reduce interfacial impedance; the continuous carbon network provides mechanical support and conductive path for the material.

[0031] (3) The multi-level porous silicon-carbon anode material provided by this invention greatly increases the solid-solid contact area due to the multi-level pores, but also exacerbates the risk of side reactions. The material also incorporates synergistic doping of boron and phosphorus. Phosphorus doping preferentially reacts, promoting the formation of a dense and stable SEI film rich in Li3PO4, which effectively avoids direct contact between silicon and sulfide electrolyte, thereby minimizing side reactions; while boron doping enhances the electronic conductivity of the carbon skeleton, constructing an efficient electron transport channel.

[0032] (4) The solid-state battery prepared by the multi-level porous silicon-carbon anode material provided by the present invention has a capacity retention rate of >90% after 500 cycles at a charge-discharge rate of 0.5 C. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0034] In a first aspect, embodiments of the present invention provide a method for preparing a multi-level porous silicon-carbon anode material, specifically: (a) First, the raw materials are prepared and a uniform sol is prepared by mixing nano-silicon powder, carbon source, surfactant, boron source, phosphorus source and solvent to obtain a sol solution; (b) The sol obtained in step (a) is subjected to freeze treatment and then dried to obtain an aerogel precursor; (c) The aerogel precursor obtained in step (b) is subjected to carbonization treatment to obtain the multi-level porous silicon-carbon anode material.

[0035] The method provided in this invention utilizes vertical macropores (5-50 μm) created by the ice template method to directionally accommodate the enormous expansion stress of silicon particles, preventing them from damaging the overall structure. Mesopores (2-50 nm) formed by surfactant self-assembly promote the permeation of sulfide electrolytes, while micropores (<2 nm) formed by carbon pyrolysis restrict silicon particle migration. This structural design ensures the structural integrity of the electrode during cycling and provides the prerequisite for efficient ion transport, reducing the material's volume expansion rate from 300% to <75%.

[0036] In one specific implementation, in step (a), the particle size of the nano-silicon powder is 50~100 nm, for example, any one value or any two values ​​from 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, and 100 nm.

[0037] In one specific embodiment, the carbon source includes at least one of graphene oxide, sucrose, glucose, fructose, maltose, lactose, starch, cellulose, chitosan, lignin, phenolic resin, epoxy resin, polyimide, polyacrylonitrile, polyvinyl chloride, or polyvinyl alcohol. Whether it's a porous structure or a stable interface, a robust framework is needed as a carrier to improve the material's cycling stability. Firstly, it acts as a mechanical framework, preventing the collapse of hierarchical channels during long-term cycling; secondly, it acts as an electronic conductor, connecting each encapsulated silicon particle to ensure rapid electron flow; and thirdly, it acts as a carrier for dopant elements, with boron and phosphorus atoms firmly anchored within the carbon mesh. Further, this carbon framework is formed through the pyrolysis of the carbon source. In a preferred embodiment, the carbon source includes graphene oxide and a second carbon source, the second carbon source including at least one of sucrose, glucose, fructose, maltose, lactose, starch, cellulose, chitosan, lignin, phenolic resin, epoxy resin, polyimide, polyacrylonitrile, polyvinyl chloride, or polyvinyl alcohol.

[0038] In one specific embodiment, the surfactant includes a cationic surfactant, which carries a positive charge and can be effectively adsorbed onto the surface of negatively charged graphene oxide or silicon particles, providing a stable template effect. More preferably, the cationic surfactant includes a quaternary ammonium salt surfactant; even more preferably, the quaternary ammonium salt surfactant includes at least one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

[0039] In one specific embodiment, the boron source includes at least one of boric acid, ammonium tetraborate, triethyl borate, or ammoniaborane.

[0040] In one specific embodiment, the phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium hypophosphite, or phytic acid.

[0041] In one specific implementation, in step (a), the mass ratio of nano-silicon powder, carbon source, surfactant, boron source, and phosphorus source is 10:15~25:1~3:0.3~0.8:0.8~1.5, for example, any ratio or any two ratios within the range of 10:15:1:0.3:0.8, 10:25:3:0.8:1.5, 10:20:2:0.5:1.0, 10:18:3:0.8:1.2, and 10:22:1:0.3:1.0.

[0042] In one specific embodiment, the solvent is preferably deionized water, and the solid content of the sol solution is adjusted to 12wt%~18wt% by the solvent, for example, any one value or a range of any two values ​​among 12wt%, 13wt%, 15wt%, 16wt%, and 18wt%.

[0043] In one specific implementation, in step (a), after mixing, ultrasonic treatment is also performed. Ultrasonic treatment helps to disperse the mixture evenly. The power of ultrasonic treatment is 600~1000W, for example, any one value or any two values ​​from 600W, 700W, 800W, 900W, and 1000W. The ultrasonic treatment time is 1~3h, for example, any one value or any two values ​​from 1h, 1.5h, 2h, 2.5h, and 3h.

[0044] In one specific implementation, during the ultrasonic treatment, the temperature of the solution system is 20~30℃, preferably room temperature, such as any one value or a range of any two values ​​among 20℃, 24℃, 25℃, 26℃, 28℃, and 30℃.

[0045] In one specific implementation, for step (b), the freezing process includes a two-step freezing technique. The first step (slow cooling) determines the "direction" and "skeleton" of the channels—creating large vertical pores. The second step (rapid cooling) determines the "stability" and "fineness" of the structure—locking in the large pores and creating mesopores. (1) First stage: Cool to -5 to -15°C (e.g., any one value or any two values ​​among 0.5°C / min, 0.8°C / min, 1°C / min, 1.5°C / min, 2°C / min) at a rate of 0.5 to 2°C / min, and hold at that temperature for 20 to 40 minutes (e.g., any one value or any two values ​​among 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes). (2) Second stage: rapidly cool to -30~-50℃ (e.g., any one value or any two values ​​of 3℃ / min, 5℃ / min, 7℃ / min, 8℃ / min) at a rate of 3~8℃ / min, and hold at that temperature for 10~14 h (e.g., any one value or any two values ​​of 10h, 11h, 12h, 13h, 14h).

[0046] In one specific implementation, in step (b), the drying process is carried out at a lower temperature, including: cooling to -70~-90℃ (e.g., any one value or a range of any two values ​​among -70℃, -75℃, -80℃, -85℃, and -90℃), vacuum degree of 10~15Pa (e.g., any one value or a range of any two values ​​among 10Pa, 11Pa, 12Pa, 13Pa, 14Pa, and 15Pa), and drying for 20~28 h (e.g., any one value or a range of any two values ​​among 20 h, 23 h, 24 h, 26 h, and 28 h).

[0047] In one specific implementation, step (c) involves a two-step carbonization process, which is a key inventive point in this invention for ensuring the performance of both "conductivity" and "interface" in the "structure-interface-conductivity" triple synergistic design. This includes: (1) First carbonization: In an inert atmosphere, the temperature is increased to 350~450℃ (e.g., any one value or any two values ​​of 350℃, 380℃, 400℃, 420℃, 440℃, 450℃) at a heating rate of 1~3℃ / min (e.g., any one value or any two values ​​of 1℃ / min, 1.5℃ / min, 3℃ / min, 2.5℃ / min, 3℃ / min) and held for 1~3 h (e.g., any one value or any two values ​​of 1h, 1.5h, 2h, 2.5h, 3h). (2) Second carbonization: In an inert atmosphere, the temperature is increased to 700-900℃ (e.g., any one value or a range of any two values ​​among 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min) at a heating rate of 2-5℃ / min, and held at that temperature for 2-4 h (e.g., any one value or a range of any two values ​​among 2h, 2.5h, 3h, 3.5h, 4h).

[0048] In one specific embodiment, the inert atmosphere includes argon and / or nitrogen; in a more specific embodiment, the gas flow rate of the inert atmosphere is 40 to 60 ml / min (e.g., any one value or a range of any two values ​​among 40 ml / min, 45 ml / min, 50 ml / min, 55 ml / min, and 60 ml / min).

[0049] Secondly, the present invention also provides a multi-level porous silicon-carbon anode material, which is mainly prepared by a method for preparing multi-level porous silicon-carbon anode materials.

[0050] In one specific embodiment, the multi-level porous silicon-carbon anode material includes: a first mesopore with a pore size of 5~50μm, a second mesopore with a pore size of 2~50 nm, and a third mesopore with a pore size of less than 2nm.

[0051] Thirdly, the present invention also provides a negative electrode sheet, which is mainly made of multi-level porous silicon-carbon negative electrode material.

[0052] Fourthly, the present invention also provides a solid-state battery, including a negative electrode sheet. Due to the synergistic effect of the three major designs of the multi-level porous silicon-carbon negative electrode material structure, interface and skeleton, the prepared test battery retains a capacity of >90% after 500 cycles at a charge-discharge rate of 0.5 C.

[0053] Example 1 The method for preparing the multi-level porous silicon-carbon anode material provided in this embodiment includes: (1) Weigh 10 g of mixed nano-silica powder with a particle size of 50-100 nm, 20 g of sucrose, 2 g of cetyltrimethylammonium bromide, 0.5 g of boric acid, and 1.2 g of ammonium dihydrogen phosphate. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0054] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. First, it was cooled from room temperature to -10℃ at a rate of 1℃ / min and kept at that temperature for 30 min. Then, it was cooled to -40℃ at a rate of 5℃ / min and kept at that temperature for 12 h to complete the directional growth of ice crystals.

[0055] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0056] (4) The aerogel precursor was heated to 400℃ at 2℃ / min and kept for 2h under the protection of argon flow rate of 50 ml / min, and then heated to 800℃ at 3℃ / min and kept for 3h to obtain the multi-level porous silicon-carbon anode material.

[0057] Example 2 The method for preparing the multi-level porous silicon-carbon anode material provided in this embodiment includes: (1) Weigh 10 g of mixed nano-silica powder with a particle size of 50-100 nm, 20 g of glucose, 2 g of cetyltrimethylammonium bromide, 0.5 g of boric acid, and 1.2 g of ammonium dihydrogen phosphate. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0058] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. First, it was cooled from room temperature to -10℃ at a rate of 1℃ / min and held for 30 min. Then, it was cooled to -40℃ at a rate of 5℃ / min and held for 12 h to complete the directional growth of ice crystals.

[0059] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0060] (4) The aerogel precursor was heated to 400℃ at 2℃ / min and kept for 2h under the protection of argon flow rate of 50 ml / min, and then heated to 800℃ at 3℃ / min and kept for 3h to obtain the multi-level porous silicon-carbon anode material.

[0061] Example 3 The method for preparing the multi-level porous silicon-carbon anode material provided in this embodiment includes: (1) Weigh 10 g of mixed nano-silica powder with a particle size of 50-100 nm, 20 g of phenolic resin, 2 g of cetyltrimethylammonium bromide, 0.5 g of boric acid, and 1.2 g of ammonium dihydrogen phosphate. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0062] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. First, it was cooled from room temperature to -10℃ at a rate of 1℃ / min and held for 30 min. Then, it was cooled to -40℃ at a rate of 5℃ / min and held for 12 h to complete the directional growth of ice crystals.

[0063] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0064] (4) The aerogel precursor was heated to 400℃ at 2℃ / min and kept for 2h under the protection of argon flow rate of 50 ml / min, and then heated to 800℃ at 3℃ / min and kept for 3h.

[0065] Example 4 The method for preparing the multi-level porous silicon-carbon anode material provided in this embodiment includes: (1) Weigh 10 g of mixed nano-silica powder with a particle size of 50-100 nm, 20 g of sucrose, 1 g of hexadecyltrimethylammonium bromide, 0.5 g of boric acid, and 1.2 g of ammonium dihydrogen phosphate. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0066] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. First, it was cooled from room temperature to -10℃ at a rate of 1℃ / min and held for 30 min. Then, it was cooled to -40℃ at a rate of 5℃ / min and held for 12 h to complete the directional growth of ice crystals.

[0067] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0068] (4) The aerogel precursor was heated to 400℃ at 2℃ / min and kept for 2h under the protection of argon flow rate of 50 ml / min, and then heated to 800℃ at 3℃ / min and kept for 3h.

[0069] Example 5 The method for preparing the multi-level porous silicon-carbon anode material provided in this embodiment includes: (1) Weigh 10 g of mixed nano-silica powder with a particle size of 50-100 nm, 20 g of sucrose, 3 g of cetyltrimethylammonium bromide, 0.5 g of boric acid, and 1.2 g of ammonium dihydrogen phosphate. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0070] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. First, it was cooled from room temperature to -10℃ at a rate of 1℃ / min and held for 30 min. Then, it was cooled to -40℃ at a rate of 5℃ / min and held for 12 h to complete the directional growth of ice crystals.

[0071] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0072] (4) The aerogel precursor was heated to 400℃ at 2℃ / min and kept for 2h under the protection of argon flow rate of 50 ml / min, and then heated to 800℃ at 3℃ / min and kept for 3h.

[0073] Example 6 The method for preparing the multi-level porous silicon-carbon anode material provided in this embodiment includes: (1) Weigh 10 g of mixed nano-silica powder with a particle size of 50-100 nm, 20 g of sucrose, 2 g of cetyltrimethylammonium bromide, 0.3 g of boric acid, and 1.2 g of ammonium dihydrogen phosphate. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0074] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. First, it was cooled from room temperature to -10℃ at a rate of 1℃ / min and held for 30 min. Then, it was cooled to -40℃ at a rate of 5℃ / min and held for 12 h to complete the directional growth of ice crystals.

[0075] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0076] (4) The aerogel precursor was heated to 400℃ at 2℃ / min and kept for 2h under the protection of argon flow rate of 50 ml / min, and then heated to 800℃ at 3℃ / min and kept for 3h.

[0077] Example 7 The method for preparing the multi-level porous silicon-carbon anode material provided in this embodiment includes: (1) Weigh 10 g of mixed nano-silica powder with a particle size of 50-100 nm, 20 g of sucrose, 2 g of cetyltrimethylammonium bromide, 0.8 g of boric acid, and 1.2 g of ammonium dihydrogen phosphate. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0078] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. First, it was cooled from room temperature to -10℃ at a rate of 1℃ / min and held for 30 min. Then, it was cooled to -40℃ at a rate of 5℃ / min and held for 12 h to complete the directional growth of ice crystals.

[0079] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0080] (4) The aerogel precursor was heated to 400℃ at 2℃ / min and kept for 2h under the protection of argon flow rate of 50 ml / min, and then heated to 800℃ at 3℃ / min and kept for 3h.

[0081] Example 8 The method for preparing the multi-level porous silicon-carbon anode material provided in this embodiment includes: (1) Weigh 10 g of mixed nano-silica powder with a particle size of 50-100 nm, 20 g of sucrose, 2 g of cetyltrimethylammonium bromide, 0.5 g of boric acid, and 1.2 g of ammonium dihydrogen phosphate. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0082] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. First, it was cooled from room temperature to -10℃ at a rate of 0.5℃ / min and kept at that temperature for 30 min. Then, it was cooled to -40℃ at a rate of 3℃ / min and kept at that temperature for 12 h to complete the directional growth of ice crystals.

[0083] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0084] (4) The aerogel precursor was heated to 400℃ at 2℃ / min and kept for 2h under the protection of argon flow rate of 50 ml / min, and then heated to 800℃ at 3℃ / min and kept for 3h.

[0085] Example 9 The method for preparing the multi-level porous silicon-carbon anode material provided in this embodiment includes: (1) Weigh 10 g of mixed nano-silica powder with a particle size of 50-100 nm, 20 g of sucrose, 2 g of cetyltrimethylammonium bromide, 0.5 g of boric acid, and 1.2 g of ammonium dihydrogen phosphate. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0086] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. First, it was cooled from room temperature to -10℃ at a rate of 2℃ / min and kept at that temperature for 30 min. Then, it was cooled to -40℃ at a rate of 8℃ / min and kept at that temperature for 12 h to complete the directional growth of ice crystals.

[0087] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0088] (4) The aerogel precursor was heated to 400℃ at 2℃ / min and kept for 2h under the protection of argon flow rate of 50 ml / min, and then heated to 800℃ at 3℃ / min and kept for 3h.

[0089] Example 10 The method for preparing the multi-level porous silicon-carbon anode material provided in this embodiment includes: (1) Weigh 10 g of mixed nano-silicon powder with a particle size of 50-100 nm, 10 g of sucrose, 10 g of graphene oxide, 2 g of hexadecyltrimethylammonium bromide, 0.5 g of boric acid, and 1.2 g of ammonium dihydrogen phosphate. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0090] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. First, it was cooled from room temperature to -10℃ at a rate of 1℃ / min and kept at that temperature for 30 min. Then, it was cooled to -40℃ at a rate of 5℃ / min and kept at that temperature for 12 h to complete the directional growth of ice crystals.

[0091] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0092] (4) The aerogel precursor was heated to 400℃ at 2℃ / min and kept for 2h under the protection of argon flow rate of 50 ml / min, and then heated to 800℃ at 3℃ / min and kept for 3h to obtain the multi-level porous silicon-carbon anode material.

[0093] Comparative Example 1 The method for preparing the silicon-carbon anode material provided in Comparative Example 1 includes: (1) Weigh 10 g of mixed nano-silicon powder with a particle size of 50-100 nm, 20 g of sucrose, and 2 g of cetyltrimethylammonium bromide, without adding boron or phosphorus sources. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0094] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. First, it was cooled from room temperature to -10℃ at a rate of 1℃ / min and held for 30 min. Then, it was cooled to -40℃ at a rate of 5℃ / min and held for 12 h to complete the directional growth of ice crystals.

[0095] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0096] (4) The aerogel precursor was heated to 400℃ at 2℃ / min and kept for 2h under the protection of argon flow rate of 50 ml / min, and then heated to 800℃ at 3℃ / min and kept for 3h.

[0097] Comparative Example 2 The method for preparing the silicon-carbon anode material provided in Comparative Example 2 includes: (1) Weigh 10 g of mixed nano-silicon powder with a particle size of 50-100 nm, 20 g of sucrose, 0.5 g of boric acid, and 1.2 g of ammonium dihydrogen phosphate, without adding any surfactant. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0098] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. Direct freezing method was adopted: the temperature was directly cooled from room temperature to -40℃ at a rate of 2℃ / min and kept at the temperature for 12 h.

[0099] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0100] (4) The aerogel precursor was heated to 400℃ at 2℃ / min and kept for 2h under the protection of argon flow rate of 50 ml / min, and then heated to 800℃ at 3℃ / min and kept for 3h.

[0101] Comparative Example 3 The method for preparing the silicon-carbon anode material provided in Comparative Example 3 includes: (1) Weigh 10 g of mixed nano-silica powder with a particle size of 50-100 nm, 20 g of sucrose, 2 g of cetyltrimethylammonium bromide, 0.5 g of boric acid, and 1.2 g of ammonium dihydrogen phosphate. Mix the above raw materials with 200 ml of deionized water, with a solid content of 15%. Sonicate the mixed solution at 800 W power and 25 °C for 2 h to obtain a uniform sol.

[0102] (2) The obtained sol was injected into a polytetrafluoroethylene mold with a filling degree of 80%. First, it was cooled from room temperature to -10℃ at a rate of 1℃ / min and held for 30 min. Then, it was cooled to -40℃ at a rate of 5℃ / min and held for 12 h to complete the directional growth of ice crystals.

[0103] (3) Freeze-dry the frozen sample at -80℃ cold trap temperature and 10 Pa vacuum for 24 h to obtain the aerogel precursor.

[0104] (4) The aerogel precursor was heated to 400℃ at 2℃ / min for 2h under the protection of argon flow rate of 50 ml / min, and then directly cooled to 600℃ at 3℃ / min without heat preservation treatment.

[0105] Test case The silicon-carbon anode materials obtained in Examples 1-10 and Comparative Examples 1-3 were used to prepare electrode sheets.

[0106] The preparation method of the electrode includes: using silicon-carbon anode material obtained in Examples 1-10 and Comparative Examples 1-3 in a ratio of 95:5 to PAA binder, weighing 342 mg of silicon-carbon anode material and 18 mg of PAA binder and adding them to 2 mL of DMF, and obtaining a uniformly mixed anode slurry by magnetic stirring. Take a clean copper foil, clean the surface with anhydrous ethanol, and after the surface is air-dried, apply the above slurry to the surface of the copper foil using a scraping method (silicon-carbon loading ≈ 0.2 mg / cm³). 2 Then, the copper foil coated with the negative electrode slurry was placed in an 80°C vacuum drying oven and dried for 4 hours to remove the DMF. After drying, the electrode sheet was removed and then punched into a composite silicon-carbon negative electrode sheet with a diameter of 10 mm using a punching machine.

[0107] The all-solid-state battery assembly was completed in an argon glove box and a specially designed battery casing was used, which was equipped with a 10 mm diameter ceramic sleeve and two stainless steel pressure plates to seal the battery.

[0108] The assembly process mainly includes four steps: electrolyte layer preparation, electrode layer composite, counter electrode preparation, and battery encapsulation. First, 100 mg of Li6PS5Cl solid electrolyte powder is transferred to a mold sleeve, and a pressure of 100 MPa is applied and held for 5 min on a tablet press to form a dense electrolyte sheet. Then, the side of the electrode sheet carrying the active material is placed on the electrolyte layer, and a pressure of 380 MPa is applied and held for 10 min to ensure a tight bond between the electrode and electrolyte layers. Next, a Li-In alloy counter electrode is assembled on the other side of the electrolyte layer, and a pressure of 100 MPa is applied and held for 1 min to ensure good metal-electrolyte interface contact. Finally, the assembled mold sleeve is placed into a specially designed battery casing, a pressure sensor is installed, and an initial axial pressure of 100 MPa is applied.

[0109] Battery testing methods The voltage range is 2.5~4.25 V. The circuit is first cycled once at a charge-discharge rate of 0.1 C, and then cycled 500 times at a charge-discharge rate of 0.5 C. Table 1 records the capacity retention rate, volume expansion rate and interface impedance after 500 cycles.

[0110] Table 1. Battery capacity retention, volume expansion rate, and interfacial impedance after 500 cycles.

[0111] As can be seen from Examples 1-10, within the preferred process parameters described in this invention, the prepared materials all exhibit excellent cycle stability (capacity retention >85% after 500 cycles) and low volume expansion (<75%). Among them, Examples 1, 5, 7, and 10 show the best overall performance.

[0112] Comparative Example 1, lacking boron and phosphorus doping, had a high initial discharge capacity but poor interface stability and a sharp decline in cycle performance. Comparative Example 2, lacking a multi-level channel structure, experienced severe volume expansion and poor cycle performance. Comparative Example 3, due to incomplete carbonization, had poor material structure stability and unsatisfactory performance indicators.

[0113] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a multi-level porous silicon-carbon anode material, characterized in that, Includes the following steps: (a) Mix nano-silicon powder, carbon source, surfactant, boron source, phosphorus source and solvent to obtain sol solution; (b) The sol obtained in step (a) is subjected to freeze treatment and then dried to obtain an aerogel precursor; (c) The aerogel precursor obtained in step (b) is subjected to carbonization treatment to obtain the multi-level porous silicon-carbon anode material.

2. The method for preparing the multi-level porous silicon-carbon anode material according to claim 1, characterized in that, In step (a), the particle size of the nano-silicon powder is 50~100 nm; Preferably, the carbon source includes at least one of graphene oxide, sucrose, glucose, fructose, maltose, lactose, starch, cellulose, chitosan, lignin, phenolic resin, epoxy resin, polyimide, polyacrylonitrile, polyvinyl chloride, or polyvinyl alcohol. Preferably, the surfactant comprises a cationic surfactant; more preferably, the cationic surfactant comprises a quaternary ammonium salt surfactant; even more preferably, the quaternary ammonium salt surfactant comprises at least one selected from hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide. Preferably, the boron source includes at least one selected from boric acid, ammonium tetraborate, triethyl borate, or ammoniaborane; Preferably, the phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium hypophosphite, or phytic acid.

3. The method for preparing the multi-level porous silicon-carbon anode material according to claim 1 or 2, characterized in that, In step (a), the mass ratio of the nano-silicon powder, the carbon source, the surfactant, the boron source, and the phosphorus source is 10:15~25:1~3:0.3~0.8:0.8~1.5; Preferably, the solid content of the sol solution is 12wt%~18wt%.

4. The method for preparing the multi-level porous silicon-carbon anode material according to claim 1, characterized in that, In step (a), the mixture is further subjected to ultrasonic treatment, the power of which is 600~1000W and the duration of which is 1~3h. Preferably, during the ultrasonic treatment, the temperature of the solution system is 20~30℃.

5. The method for preparing the multi-level porous silicon-carbon anode material according to claim 1, characterized in that, In step (b), the freezing process includes: (1) First stage: Cool to -5 to -15℃ at a rate of 0.5~2℃ / min and hold for 20~40 min; (2) Second stage: rapidly cool to -30~-50℃ at a rate of 3~8℃ / min and keep warm for 10~14 h.

6. The method for preparing the multi-level porous silicon-carbon anode material according to claim 1, characterized in that, In step (b), the drying process includes: cooling to -70~-90℃, vacuum degree 10~15Pa, and drying for 20~28 h.

7. The method for preparing the multi-level porous silicon-carbon anode material according to claim 1, characterized in that, In step (c), the carbonization process includes: (1) First carbonization: In an inert atmosphere, the temperature is increased to 350-450℃ at a heating rate of 1-3℃ / min and held for 1-3h; (2) Second carbonization: In an inert atmosphere, the temperature is raised to 700-900℃ at a heating rate of 2-5℃ / min and held for 2-4 h; Preferably, the inert atmosphere includes argon and / or nitrogen; more preferably, the gas flow rate of the inert atmosphere is 40-60 ml / min.

8. A multi-level porous silicon-carbon anode material, mainly prepared by the preparation method of the multi-level porous silicon-carbon anode material as described in any one of claims 1-7; Preferably, the multi-level porous silicon-carbon anode material comprises: The first mesopore has a pore size of 5~50μm, the second mesopore has a pore size of 2~50 nm, and the third mesopore has a pore size of less than 2nm.

9. A negative electrode sheet, mainly made of the multi-level porous silicon-carbon negative electrode material as described in claim 8.

10. A solid-state battery, comprising the negative electrode sheet as described in claim 9.

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