Composite silicon-based negative electrode active material as well as preparation method and application thereof

Abstract

The invention discloses a composite silicon-based negative electrode active material as well as a preparation method and application thereof. The preparation method of the composite silicon-based negative electrode active material comprises the following steps: S1, dispersing aluminum-silicon alloy powder in absolute ethyl alcohol, adding tetrabutyl titanate, performing ultrasonic treatment under an alkaline condition, and performing vacuum drying to obtain a TiO2-coated aluminum-silicon alloy precursor; s2, performing selective etching, removing an aluminum phase, washing to be neutral, and performing vacuum drying to obtain a TiO2-at-porous silicon intermediate with through pore channels; s3, performing high-temperature calcination treatment; and S4, dispersing the sulfide electrolyte and the calcined product into an organic solvent, carrying out ball milling treatment, and carrying out vacuum drying to remove the solvent. The invention also discloses the composite silicon-based negative electrode active material prepared by the preparation method, a composite silicon-based negative electrode comprising the composite silicon-based negative electrode active material, and a sulfide all-solid-state lithium ion battery. The key problems of large volume expansion, poor interface stability and the like of a silicon-based material in a sulfide all-solid-state battery are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of all-solid-state lithium batteries, and in particular to a composite silicon-based negative electrode active material and a preparation method and application thereof. The composite silicon-based negative electrode active material has a synergistic structure of "rigid shell-porous buffer" and is prepared by titanium dioxide coating and porous synergistic sulfide electrolyte modification. Background Art

[0002] With the growing demand for high-energy-density batteries in electric vehicles and energy storage systems, silicon-based negative electrode materials have attracted much attention due to their theoretical specific capacity of up to 4200 mAh / g. However, silicon materials undergo a volume change of about 300% during the charge and discharge process, resulting in electrode structural damage and a sharp decline in cycle performance. Existing modification technologies such as nano-sizing (reducing the size of silicon particles to less than 150 nm) can alleviate some of the problems, but they are still difficult to meet the needs under practical application conditions; in addition, conventional carbon coatings (such as graphene, carbon nanotubes, etc.) are prone to structural collapse after long-term cycling and cannot effectively constrain the expansion behavior of silicon particles. On the other hand, although sulfide solid electrolytes have excellent ionic conductivity, they have poor interfacial compatibility with silicon negative electrodes. The volume expansion of silicon can cause microcracks in the electrolyte layer and destroy the ion transport channel; and silicon and sulfide electrolytes will undergo chemical side reactions at the interface to generate insulating phases such as Li-Si-PS. Traditional solutions such as polymer buffer layers or single oxide coatings (such as SiO2) have defects such as low ionic conductivity or insufficient mechanical strength. In addition, although the existing porous silicon structure prepared by etching aluminum-silicon alloy can provide expansion space, it still faces the following problems in the sulfide battery system: the porous structure is easy to collapse during the cycle, lacks rigid protection and effective ion transport network. These technical bottlenecks seriously restrict the practical application of silicon-based anodes in sulfide all-solid-state batteries. Therefore, the development of silicon-based composite anodes that combine volume expansion buffering, high ion conductivity and interface stability has become the key to promoting the commercial application of sulfide all-solid-state batteries. Summary of the invention

[0003] To solve the above technical problems, the object of the present invention is to provide a composite silicon-based anode active material, its preparation method and application, which are prepared by the synergistic modification of titanium dioxide coating, porousization and sulfide electrolyte. The present invention uses an aluminum-silicon alloy as a raw material, and in-situ generates a titanium dioxide coating layer on the surface through the hydrolysis of tetrabutyl titanate; then hydrochloric acid is used for selective etching to remove the aluminum phase to form a porous silicon structure with through channels, while retaining a complete titanium dioxide outer shell; then heat treatment is carried out by high-temperature calcination in an inert atmosphere to optimize the crystallinity of titanium dioxide and the interfacial bonding between silicon and titanium dioxide; finally, the sulfide electrolyte is filled into the porous structure and coated on the surface by wet infiltration to achieve close solid-solid contact, so as to optimize the ion conduction path and enhance ion transport. The titanium dioxide coating layer in the present invention can effectively inhibit the volume expansion of silicon, the internal through channels provide a buffer space for expansion, and the three-dimensional ion network formed by the filling of the sulfide electrolyte improves the interfacial conductivity. This material has good compatibility with sulfide solid electrolytes, and the preparation process is simple and the cost is low, which is suitable for large-scale production, providing an innovative solution for the development of high-energy-density all-solid-state lithium batteries.

[0004] The object of the present invention is achieved by the following technical solutions: In the first aspect, the present invention provides a preparation method of a composite silicon-based anode active material, including the following steps: S1. Disperse the aluminum-silicon alloy powder in absolute ethanol, add tetrabutyl titanate, and perform ultrasonic treatment under alkaline conditions, and obtain a TiO2-coated aluminum-silicon alloy precursor after vacuum drying; S2. Place the TiO2-coated aluminum-silicon alloy precursor in an acid solution for selective etching, remove the aluminum phase, wash to neutrality, and vacuum dry to obtain a TiO2@porous silicon intermediate with through channels; S3. Carry out calcination treatment on the TiO2@porous silicon intermediate; S4. Disperse the sulfide electrolyte and the TiO2@porous silicon intermediate calcined in step S3 into an organic solvent for ball milling treatment, and obtain the product after vacuum drying to remove the solvent.

[0005] As some specific embodiments of the present invention, in step S1, in the aluminum-silicon alloy powder, the mass ratio of aluminum to silicon is 6-8:4-2, preferably 7:3.

[0006] As some specific embodiments of the present invention, the mass ratio of tetrabutyl titanate to the aluminum-silicon alloy powder is 0.05-0.15:1.

[0007] As some specific embodiments of the present invention, in step S1, the alkaline condition is adjusted by an aqueous ammonium hydroxide solution, the mass fraction of the aqueous ammonium hydroxide solution is 20%-30%, preferably 25%; the pH value of the alkaline condition is 8-10.

[0008] In some specific embodiments of the present invention, in step S1, the frequency of the ultrasonic treatment is 30 - 50 kHz, preferably 40 kHz; and the time is 2 - 4 h.

[0009] In some specific embodiments of the present invention, in step S2, the acid solution includes a hydrochloric acid solution, and the mass fraction of the hydrochloric acid solution is 8% - 12%, preferably 10%; and / or, the reaction time of the etching is 4 - 10 h, the reaction temperature of the etching is 35 - 45 °C, preferably 40 °C; and / or, the washing includes washing 3 - 5 times with deionized water.

[0010] In some specific embodiments of the present invention, in step S3, the calcination is carried out in a tube furnace; the calcination is carried out under the protection of an inert gas, and the inert gas includes argon; the temperature of the calcination is 600 - 800 °C, the heat preservation time is 2 - 5 h, and the heating rate is 2 - 5 °C / min. Through high-temperature calcination, the TiO2 coating layer is crystallized, and at the same time, the interfacial bonding between TiO2 and the silicon matrix is enhanced.

[0011] In some specific embodiments of the present invention, in step S4, the sulfide electrolyte includes at least one of Li3PS4, Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0012] In some specific embodiments of the present invention, in step S4, the mass ratio of the sulfide electrolyte to the calcined TiO2@porous silicon intermediate is 1:1 - 4.

[0013] In some specific embodiments of the present invention, in step S4, the organic solvent is selected from at least one of anisole, toluene, xylene, and butyl ether.

[0014] In some specific embodiments of the present invention, in step S4, the rotation speed of the ball milling is 200 - 300 rpm; and the time is 2 - 4 h. Through wet ball milling, the sulfide electrolyte is fully filled into the porous structure of the TiO2@porous silicon intermediate and coats the surface of its particles.

[0015] In some specific embodiments of the present invention, the vacuum drying is carried out using a vacuum oven, the temperature of the vacuum drying is 60 - 100 °C, the time is 6 - 15 h; and the vacuum degree is 0.03 - 0.08 MPa.

[0016] In a second aspect, the present invention provides a composite silicon-based anode active material prepared by using the preparation method described in any one of the above.

[0017] In a third aspect, the present invention provides a composite silicon-based negative electrode, which includes the composite silicon-based negative electrode active material described above, and also includes a sulfide electrolyte, a conductive agent, and a binder.

[0018] As some specific embodiments of the present invention, the sulfide electrolyte is selected from one or more of Li3PS4, Li6PS5Cl, Li6PS5Br, and Li6PS5I; The conductive agent is selected from at least one of vapor-grown carbon fiber (VGCF), carbon black, super carbon, carbon nanotubes, and activated carbon; The binder is selected from at least one of polyisobutylene, styrene-butadiene rubber, polyacrylic acid, and polymethyl methacrylate; The mass ratio of the composite silicon-based negative electrode active material, the sulfide electrolyte, the conductive agent, and the binder is 6-8:3-1: 0.7-0.9:0.3-0.1, preferably 7:2:0.8:0.2.

[0019] As some specific embodiments of the present invention, the preparation method of the composite silicon-based negative electrode includes: in a glove box filled with argon, mixing the composite silicon-based negative electrode active material, the sulfide electrolyte, the conductive agent, and the binder in a toluene solvent, stirring evenly to form a slurry, and uniformly coating the slurry on a copper foil current collector with a scraper to form a wet film, and then obtaining the product after vacuum drying.

[0020] As some specific embodiments of the present invention, the temperature of the vacuum drying is 80-120 °C, the vacuum degree is 0.04-0.06 MPa, and the time is 8-12 h; preferably 100 °C, 0.05 MPa, and 10 h.

[0021] As some specific embodiments of the present invention, the thickness of the wet film is 80-120 μm, preferably 100 μm.

[0022] In a fourth aspect, the present invention provides a sulfide all-solid-state lithium-ion battery, which includes the composite silicon-based negative electrode described in any one of the above, and also includes a composite positive electrode and a sulfide electrolyte.

[0023] As some specific embodiments of the present invention, the composite positive electrode includes NCM811, Li6PS5Cl sulfide solid electrolyte, and a conductive agent VGCF.

[0024] When preparing the composite silicon-based anode active material of the present invention, titanium dioxide is first coated on the outer layer of the silicon-aluminum alloy to maintain the spherical structure of the particles. During the subsequent etching process, it will not cause the collapse of the pore structure and the blockage of the pores, and maintain the internal porous structure, reserving enough space for the volume expansion of silicon during charge and discharge; then, high-temperature calcination treatment at 600-800 °C is carried out, which can further optimize the crystallinity of titanium dioxide and the interface combination of silicon-titanium dioxide, enhancing the strength and hardness of titanium dioxide. On the one hand, it can perfectly limit the volume expansion of the internal silicon, and on the other hand, it can resist the external stacking pressure required by the solid-state battery, so that the spherical particles will not be crushed; finally, the sulfide electrolyte is filled into the porous structure and coated on the surface by wet infiltration to achieve close solid-solid contact, optimize the ion conduction path, and enhance ion transport.

[0025] Compared with the prior art, the present invention has the following beneficial effects: 1) The modified silicon-based composite anode material provided by the present invention, through the synergistic effect of the rigid titanium dioxide coating layer and the internal porous silicon structure, while significantly reducing the volume expansion rate of the silicon anode, still maintains the high specific capacity of silicon itself; the unique coral-like porous structure forms a three-dimensional ion transport network after being filled with the sulfide electrolyte, significantly improving the interfacial ionic conductivity; the composite anode is in close contact with the sulfide electrolyte, maintaining the integrity of the electrode structure. Fundamentally solving the key problems such as large volume expansion and poor interfacial stability of silicon-based materials in sulfide all-solid-state batteries, providing a practical technical solution for realizing high-energy-density all-solid-state lithium batteries.

[0026] 2) The aluminum-silicon alloy etching method and the liquid-phase electrolyte infiltration technology adopted in the preparation process have the advantages of low cost and easy amplification, and are suitable for large-scale production. Description of the Drawings

[0027] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, purposes and advantages of the present invention will become more obvious: Figure 1 It is the process flow chart of the preparation method of the titanium dioxide-coated porous silicon / sulfide electrolyte composite material of the present invention; Figure 2 It is the SEM image of the calcined TiO2@porous silicon intermediate prepared in Example 1; Figure 3 It is the EDS energy spectrum of the calcined TiO2@porous silicon intermediate prepared in Example 1; Figure 4 It is the EDS energy spectrum of the TiO2@porous silicon@Li6PS5Cl composite material prepared in Example 1; Figure 5 It is the SEM image of the product prepared in Comparative Example 1; Figure 6 SEM image of the product prepared in Comparative Example 2; Figure 7 SEM image of the product prepared in Comparative Example 5. Specific Embodiments

[0028] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made. These all fall within the protection scope of the present invention.

[0029] The present invention provides a method for preparing a composite silicon-based anode active material (i.e., a titanium dioxide-coated porous silicon / sulfide electrolyte composite material), and the preparation process is as Figure 1 shown: (1) Disperse aluminum-silicon alloy powder in absolute ethanol, add tetrabutyl titanate, perform ultrasonic treatment under alkaline conditions, and then perform vacuum drying treatment to obtain a TiO2-coated aluminum-silicon alloy precursor; (2) Place the product of step (1) in a hydrochloric acid solution for selective etching. After removing the aluminum phase, wash it with deionized water until neutral to obtain a TiO2@porous silicon intermediate with through pores; (3) Place the etched sample in a tube furnace and perform high-temperature calcination treatment under argon protection to crystallize the TiO2 coating layer and simultaneously enhance the interfacial bonding between TiO2 and the silicon matrix; (4) Disperse the sulfide electrolyte and the product of step (3) into anisole solvent for ball milling treatment, and then vacuum dry to remove the solvent, so that the electrolyte fully fills the porous structure and coats the particle surface to obtain a TiO2@porous silicon@ sulfide electrolyte composite material.

[0030] Example 1 I. Preparation of Composite Silicon-Based Anode Active Material A method for preparing a titanium dioxide-coated porous silicon / sulfide electrolyte composite material, the steps are as follows: (1) Preparation of TiO2-coated aluminum-silicon alloy precursor: Disperse 10.0 g of aluminum-silicon alloy powder (the mass ratio of aluminum to silicon is 7:3) in 200 mL of absolute ethanol, magnetically stir for 30 minutes, then add 1.2 g of tetrabutyl titanate (12% of the mass of the aluminum-silicon alloy), magnetically stir for 30 minutes to disperse it evenly, then dropwise add 25% ammonia water to adjust the pH to 9.0 ± 0.2, perform ultrasonic treatment at a frequency of 40 kHz for 3 hours, and then vacuum dry at 60 °C for 12 hours, with a vacuum degree of 0.06 MPa, to obtain a TiO2-coated aluminum-silicon alloy precursor; (2)Preparation of porous structure by selective etching: Take 8.0 g of the precursor product of aluminum-silicon alloy coated with TiO2 and place it in 150 mL of 10 wt% hydrochloric acid solution. Under the condition of a water bath at 40 °C, mechanically stir (300 rpm) and etch for 8 hours. Then wash it 5 times with deionized water until neutral (pH = 7.0 ± 0.2), and then dry it in vacuum at 80 °C for 6 hours with a vacuum degree of 0.06 MPa to obtain the TiO2@porous silicon intermediate; (3)High-temperature calcination treatment: Place 5.0 g of the etched TiO2@porous silicon intermediate sample in a tube furnace. Under an argon atmosphere, heat it to 700 °C at a rate of 3 °C / min for heat treatment, hold for 3 hours, and then naturally cool to room temperature to obtain the calcined TiO2@porous silicon intermediate; (4)Sulfide electrolyte composite: Operate in a glove box filled with argon. Add 4.0 g of the calcined sample and 4.0 g of Li6PS5Cl sulfide electrolyte to 40 mL of anisole solvent, and ball-mill for 4 hours at a rotation speed of 250 rpm. Then dry it in vacuum at 80 °C and 0.08 MPa for 12 hours to obtain the TiO2@porous silicon@Li6PS5Cl composite material.

[0031] As Figure 2 shown, it is the SEM image (magnification: 10,000 times) of the calcined TiO2@porous silicon intermediate prepared in step (3) of Example 1, and a regular spherical porous structure can be observed; as Figure 3 shown, it is the EDS energy spectrum of the calcined TiO2@porous silicon intermediate prepared in step (3) of Example 1. It can be observed that the sample contains Ti and Si elements, indicating that TiO2 is successfully coated on the porous silicon.

[0032] As Figure 4 shown, it is the EDS energy spectrum of the TiO2@porous silicon@Li6PS5Cl composite material prepared in step (4) of Example 1. It can be observed that the sample contains S and Si elements. The Si element comes from the porous silicon, and the Si element is mainly concentrated in the center of the spherical particles. The S element comes from the sulfide electrolyte, and the S element is mainly concentrated on the periphery of the particles, and there is also a small amount distributed inside the particles. This indicates that the sulfide electrolyte fills the pores of the porous silicon and coats the outer layer of TiO2.

[0033] II. Preparation of composite silicon-based negative electrode sheet The above TiO2@porous silicon@Li6PS5Cl composite material is prepared into a negative electrode sheet by wet film formation. The specific steps are as follows: The operations are carried out in a glove box filled with argon. Take 7.0 g of the prepared TiO2@porous silicon@Li6PS5Cl composite material, 2.0 g of Li6PS5Cl sulfide electrolyte, 0.8 g of conductive carbon VGCF, and 0.2 g of polyisobutene binder, mix them in 50 mL of toluene solvent, and stir magnetically for 2 hours to form a uniform slurry. Coating the slurry evenly on a copper foil current collector (with a thickness of 10 μm) by a doctor blade method, and controlling the wet film thickness to be 100 μm; then place it in a vacuum drying oven and dry it at 100 °C and 0.05 MPa for 10 hours to remove the residual solvent, obtaining a negative electrode sheet, and then cut it into small round pieces with a diameter of 10 mm for standby.

[0034] III. Preparation of Sulfide All-Solid-State Lithium-Ion Batteries 1. Preparation of a composite positive electrode system: Put 80 mg of NCM811 powder, 15 mg of Li6PS5Cl sulfide solid electrolyte, and 5 mg of conductive agent VGCF powder into a mortar and grind for 30 min to prepare a composite positive electrode system.

[0035] 2. Assembly of a pressure battery: (1) The operations are carried out in a glove box filled with argon. Put 30 mg of Li6PS5Cl powder of sulfide electrolyte into a pressure battery mold with a diameter of 10 mm, press it into a sheet on a tablet press, apply a pressure of 1 ton, and keep the pressure for 1 min; (2) Then spread 30 mg of the composite positive electrode system powder evenly on the surface of the electrolyte sheet, apply a pressure of 1 ton, and keep the pressure for 1 min; (3) Then spread the composite silicon-based negative electrode sheet evenly on the other side of the electrolyte sheet, apply a pressure of 1 ton, and keep the pressure for 1 min; (4) Place an aluminum foil with a diameter of 10 mm on the surface of the composite positive electrode sheet as the positive electrode current collector. After assembly, apply a pressure of 1 ton and keep the pressure for 1 min to obtain a sulfide all-solid-state lithium-ion battery for standby testing.

[0036] Example 2 A preparation method of a titanium dioxide-coated porous silicon / sulfide electrolyte composite material, the steps are as follows: (1) Preparation of a TiO2-coated aluminum-silicon alloy precursor: Take 15.0 g of aluminum-silicon alloy powder (the mass ratio of aluminum to silicon is 7:3), disperse it in 300 mL of absolute ethanol, stir magnetically for 40 minutes, then add 2.25 g of tetrabutyl titanate (accounting for 15% of the mass of the aluminum-silicon alloy), stir for 40 minutes until evenly dispersed, then dropwise add 25% ammonia water to adjust the pH to 9.5 ± 0.2, perform ultrasonic treatment at a frequency of 45 kHz for 4 hours, and finally vacuum dry at 70 °C for 10 hours, with a vacuum degree of 0.08 MPa, to obtain a TiO2-coated aluminum-silicon alloy precursor; (2)Preparation of porous structure by selective etching: Take 12.0 g of the precursor product and place it in 200 mL of 12 wt% hydrochloric acid solution. Under the condition of a 50 °C water bath, mechanically stir (350 rpm) for etching for 6 hours. Then wash it 5 times with deionized water until neutral (pH = 7.0 ± 0.2). Finally, vacuum dry it at 90 °C for 8 hours, with a vacuum degree of 0.08 MPa, to obtain the TiO2@porous silicon intermediate; (3)High-temperature calcination treatment: Place 6.0 g of the etched sample in a tube furnace, protect it under an argon atmosphere, heat it to 750 °C at a rate of 5 °C / min, hold for 4 hours, and then naturally cool to room temperature to obtain the crystallized TiO2@porous silicon intermediate.

[0037] (4)Sulfide electrolyte composite: Operate in a glove box filled with argon. Add 5.0 g of the calcined sample and 5.0 g of the Li6PS5Cl sulfide electrolyte to 50 mL of anisole solvent, and ball mill for 3 hours at a rotation speed of 300 rpm. Then vacuum dry at 85 °C and 0.05 MPa for 15 hours to obtain the TiO2@porous silicon@Li6PS5Cl composite material.

[0038] Prepare a composite silicon-based negative electrode sheet by the same method as in Example 1, and assemble it into a sulfide all-solid-state lithium-ion battery.

[0039] Comparative Example 1 Cancel step (1) in Example 1, do not prepare the TiO2-coated aluminum-silicon alloy precursor, and directly etch the untreated aluminum-silicon alloy. The remaining steps are all carried out with reference to Example 1.

[0040] The SEM image of the sample prepared in Comparative Example 1 is as Figure 5 shown. It can be observed that after etching, the spherical morphology cannot be maintained, there is no obvious porous structure, and the structure collapses after etching.

[0041] Comparative Example 2 Cancel step (2) in Example 1, do not etch the TiO2-coated aluminum-silicon alloy precursor with hydrochloric acid, and the remaining steps are all carried out according to Example 1.

[0042] The SEM image of the sample prepared in Comparative Example 2 is as Figure 6 shown. It can be observed that the sample without etching with hydrochloric acid will not show a porous structure, which will not play an inhibitory role in the volume expansion of silicon during charge and discharge.

[0043] Comparative Example 3 Cancel step (3) in Example 1, do not perform high-temperature calcination treatment, and the remaining steps are all carried out according to Example 1.

[0044] Non-calcination has little effect on the morphology of the product, mainly resulting in insufficient strength of the TiO2 shell, which cannot better restrict the volume expansion of silicon, leading to rapid capacity decay during cycling.

[0045] Comparative Example 4 Cancel step (4) in Example 1 and do not perform composite treatment with the sulfide electrolyte. The remaining steps are carried out according to Example 1.

[0046] In Example 1 Figure 2 That is, the SEM image of the TiO2@porous silicon intermediate sample. Without composite sulfide electrolyte, it will significantly reduce ion conduction, and the solid-solid interface between the active material and the sulfide electrolyte cannot be improved, resulting in much worse rate performance and capacity utilization of the battery.

[0047] Comparative Example 5 Preparation was carried out with reference to the paper "Surface Modification and Electrochemical Properties of Titanium Dioxide Coated Porous Silicon Composites": On the basis of Example 1, first etch the silicon-aluminum alloy powder in hydrochloric acid, then carry out titanium dioxide coating treatment, and do not perform high-temperature calcination treatment, nor composite sulfide solid electrolyte.

[0048] The SEM image of the prepared sample is as Figure 7 shown. It can be observed that etching the silicon-aluminum alloy first is prone to over-etching, which will cause the particle structure to collapse, unable to maintain the spherical morphology and unable to play a role in inhibiting volume expansion; when titanium dioxide is coated by the sol-gel method later, it will fill the formed porous structure, causing blockage and reducing the reserved space for volume expansion; and the strength of titanium dioxide is insufficient; the ionic conductivity of the composite material is relatively low.

[0049] Effect Example 1 Test the batteries prepared in the above examples and comparative examples as follows: Use a Neware battery test system with the equipment model CT-4000 to perform charge and discharge tests on the all-solid-state battery. Use a charge and discharge step of 0.2C - 0.5C, the voltage range is 4.3 - 2.5V, the temperature is 28°C, and test the discharge capacity of the sulfide all-solid-state battery. The results are shown in Table 1 below: Table 1 Charge and Discharge Test of Sulfide All-Solid-State Lithium-Ion Batteries

[0050] As can be seen from the above table, the discharge capacities, Coulombic efficiencies, and capacity retention rates after 30 cycles at 0.2C and 0.5C in Examples 1 and 2 are significantly higher than those in Comparative Examples 1-5. This is mainly because through the synergistic effect of the titanium dioxide rigid coating layer and the internal porous silicon structure, the volume expansion of the silicon anode is effectively inhibited, while the high specific capacity of silicon can be maintained, solving the problem of structural collapse of silicon materials during charge and discharge; and after the porous structure is filled with a sulfide electrolyte, a three-dimensional continuous ion transport network is formed, improving the solid-solid interface ion conduction performance, showing excellent interface stability and structural integrity, and significantly improving the cycle stability.

[0051] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A preparation method of a composite silicon-based anode active material, characterized in that, It includes the following steps: S1. Disperse the aluminum-silicon alloy powder in absolute ethanol, add tetrabutyl titanate, and perform ultrasonic treatment under alkaline conditions. After vacuum drying, a TiO2-coated aluminum-silicon alloy precursor is obtained. S2. Place the TiO2-coated aluminum-silicon alloy precursor in an acid solution for selective etching. After removing the aluminum phase, wash it to neutrality and vacuum dry to obtain a TiO2@porous silicon intermediate with through pores. S3. Calcinate the TiO2@porous silicon intermediate. S4. Disperse the sulfide electrolyte and the calcined TiO2@porous silicon intermediate in step S3 into an organic solvent for ball milling. After vacuum drying to remove the solvent, it is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, it includes at least one of the following technical features: (1) In the aluminum-silicon alloy powder, the mass ratio of aluminum to silicon is 6-8:4-2. (2) The mass ratio of tetrabutyl titanate to the aluminum-silicon alloy powder is 0.05-0.15:

1. (3) The alkaline condition is adjusted by an aqueous ammonium hydroxide solution. The mass fraction of the aqueous ammonium hydroxide solution is 20%-30%, and the pH value of the alkaline condition is 8-10. (4) The frequency of the ultrasonic treatment is 30-50 kHz, and the time is 2-4 h.

3. The preparation method according to claim 1, wherein In step S2, the acid solution includes a hydrochloric acid solution, and the mass fraction of the hydrochloric acid solution is 8%-12%. And / or, the reaction time of the etching is 4-10 h, and the reaction temperature of the etching is 35-45 °C. And / or, the washing includes washing 3-5 times with deionized water.

4. The preparation method according to claim 1, characterized in that, In step S3, the calcination is carried out under the protection of an inert gas; the calcination temperature is 600-800 °C, the holding time is 2-5 h, and the heating rate is 2-5 °C / min.

5. The preparation method according to claim 1, wherein In step S4, it includes at least one of the following technical features: (1) The sulfide electrolyte includes at least one of Li3PS4, Li6PS5Cl, Li6PS5Br, and Li6PS5I. (2) The mass ratio of the sulfide electrolyte to the calcined TiO2@porous silicon intermediate is 1:1-4. (3) The organic solvent is selected from at least one of anisole, toluene, xylene, and butyl ether. (4) The rotation speed of the ball milling is 200-300 rpm; the time is 2-4 h.

6. The preparation method according to claim 1, characterized in that, The temperature of the vacuum drying is 60-100 °C, the time is 6-15 h; the vacuum degree is 0.03-0.08 MPa.

7. A composite silicon-based anode active material, characterized in that, It is prepared by using the preparation method described in any one of claims 1-6.

8. A composite silicon-based negative electrode, characterized in that, It includes the composite silicon-based anode active material described in claim 7, and also includes a sulfide electrolyte, a conductive agent, and a binder.

9. The composite silicon-based negative electrode according to claim 8, wherein The sulfide electrolyte is selected from one or more of Li3PS4, Li6PS5Cl, Li6PS5Br, and Li6PS5I. The conductive agent is selected from at least one of vapor-grown carbon fiber, carbon black, super carbon, carbon nanotube, and activated carbon. The binder is selected from at least one of polyisobutylene, styrene-butadiene rubber, polyacrylic acid, and polymethyl methacrylate. The mass ratio of the composite silicon-based anode active material, sulfide electrolyte, conductive agent and binder is 6 to 8:3 to 1:0.7 to 0.9:0.3 to 0.

1.

10. A sulfide all-solid-state lithium-ion battery, characterized in that, Comprising the composite silicon-based anode as described in claim 8 or 9, further comprising a composite cathode and a sulfide electrolyte.

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