A composite silicon-based negative electrode active material and its preparation method and application

Abstract

The present invention discloses a composite silicon-based negative electrode active material, its preparation method, and application. The preparation method of the composite silicon-based negative electrode active material comprises: S1, dispersing aluminum-silicon alloy powder in anhydrous ethanol, adding tetrabutyl titanate, ultrasonically treating under alkaline conditions, and vacuum drying to obtain a TiO2-coated aluminum-silicon alloy precursor; S2, selectively etching to remove the aluminum phase, washing to neutrality, and vacuum drying to obtain a TiO2@porous silicon intermediate with through-pores; S3, high-temperature calcination; S4, dispersing a sulfide electrolyte and the calcined product in an organic solvent, ball milling, and vacuum drying to remove the solvent. Also disclosed are a composite silicon-based negative electrode active material prepared using the above preparation method, a composite silicon-based negative electrode including the composite silicon-based negative electrode active material, and a sulfide all-solid-state lithium-ion battery. The present invention solves key problems such as large volume expansion and poor interface stability of silicon-based materials in sulfide all-solid-state batteries.

Description

Technical Field

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

[0002] With the growing demand for high-energy-density batteries in electric vehicles and energy storage systems, silicon-based anode materials have attracted significant attention due to their theoretical specific capacity of up to 4200 mAh / g. However, silicon materials experience a volume change of approximately 300% during charge and discharge, leading to structural damage and a sharp decline in cycling performance. Existing modification techniques, such as nanosizing (reducing silicon particle size to below 150 nm), can alleviate some of these issues but still fall short of meeting practical requirements. Furthermore, conventional carbon coatings (such as graphene and carbon nanotubes) are prone to structural collapse after long-term cycling and fail to effectively constrain silicon particle expansion. Meanwhile, sulfide solid electrolytes, while offering excellent ionic conductivity, exhibit poor interfacial compatibility with silicon anodes. Silicon volume expansion can cause microcracks in the electrolyte layer, disrupting ion transport pathways. Furthermore, chemical side reactions occur at the interface between silicon and sulfide electrolytes, forming insulating phases such as Li-Si-PS. Traditional solutions, such as polymer buffer layers or single oxide coatings (such as SiO2), suffer from low ionic conductivity and insufficient mechanical strength. Furthermore, while existing porous silicon structures fabricated by etching aluminum-silicon alloys can provide expansion space, they still face the following challenges in sulfide battery systems: the porous structure is prone to collapse during cycling, lacks rigid protection, and lacks an effective ion transport network. These technical bottlenecks severely restrict the practical application of silicon-based anodes in sulfide all-solid-state batteries. Therefore, developing silicon-based composite anodes that combine volume expansion buffering, high ion conductivity, and interfacial stability has become key to promoting the commercial application of sulfide all-solid-state batteries. Summary of the Invention

[0003] In order to solve the above technical problems, the purpose of the present invention is to provide a composite silicon-based negative electrode active material and its preparation method and application, which is prepared by titanium dioxide coating and porosification and sulfide electrolyte synergistic modification. The present invention uses aluminum silicon alloy as raw material, and generates a titanium dioxide coating layer in situ on the surface by hydrolysis of tetrabutyl titanate; then selectively etches with hydrochloric acid to remove the aluminum phase, forming a porous silicon structure with through-holes, while retaining a complete titanium dioxide shell; then calcining heat treatment at high temperature under an inert atmosphere to optimize the crystallinity of titanium dioxide and the silicon-titanium dioxide interface bonding; 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-holes provide a buffer space for expansion, and the three-dimensional ion network formed by the sulfide electrolyte filling improves the interface conductivity. This material has good compatibility with sulfide solid electrolytes, and its preparation process is simple and low-cost, making it suitable for large-scale production. It provides an innovative solution for the development of high-energy-density all-solid-state lithium batteries.

[0004] The object of the present invention is achieved through the following technical solutions:

[0005] In a first aspect, the present invention provides a method for preparing a composite silicon-based negative electrode active material, comprising the following steps:

[0006] S1. Dispersing aluminum-silicon alloy powder in anhydrous ethanol, adding tetrabutyl titanate, ultrasonically treating under alkaline conditions, and vacuum drying to obtain a TiO2-coated aluminum-silicon alloy precursor;

[0007] S2, placing the TiO2-coated aluminum-silicon alloy precursor in an acid solution for selective etching to remove the aluminum phase, washing it to neutrality, and vacuum drying it to obtain a TiO2@porous silicon intermediate with through-pores;

[0008] S3, calcining the TiO2@porous silicon intermediate;

[0009] S4, dispersing the sulfide electrolyte and the TiO2@porous silicon intermediate calcined in step S3 into an organic solvent, performing ball milling, and vacuum drying to remove the solvent.

[0010] As some specific embodiments of the present invention, in step S1, the mass ratio of aluminum to silicon in the aluminum-silicon alloy powder is 6-8:4-2, preferably 7:3.

[0011] As some specific embodiments of the present invention, the mass ratio of tetrabutyl titanate to aluminum silicon alloy powder is 0.05-0.15:1.

[0012] 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% to 30%, preferably 25%; the pH value of the alkaline condition is 8 to 10.

[0013] As 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.

[0014] As 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% to 12%, preferably 10%;

[0015] And / or, the etching reaction time is 4 to 10 h, and the etching reaction temperature is 35 to 45° C., preferably 40° C.;

[0016] And / or, the washing comprises washing with deionized water 3 to 5 times.

[0017] In some specific embodiments of the present invention, in step S3, the calcination is performed in a tube furnace under an inert gas atmosphere, wherein the inert gas includes argon. The calcination temperature is 600-800°C, the holding time is 2-5 hours, and the heating rate is 2-5°C / min. The high-temperature calcination crystallizes the TiO2 coating and strengthens the interfacial bonding between the TiO2 and the silicon substrate.

[0018] As some specific embodiments of the present invention, in step S4, the sulfide electrolyte includes at least one of Li3PS4, Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0019] As 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.

[0020] As 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.

[0021] In some specific embodiments of the present invention, in step S4, the ball milling speed is 200-300 rpm and the time is 2-4 hours. Through wet ball milling, the sulfide electrolyte is fully filled into the porous structure of the TiO2@porous silicon intermediate and covers the surface of the particles.

[0022] As some specific embodiments of the present invention, the vacuum drying is carried out in a vacuum oven, the vacuum drying temperature is 60-100°C, the time is 6-15 h, and the vacuum degree is 0.03-0.08 MPa.

[0023] In a second aspect, the present invention provides a composite silicon-based negative electrode active material prepared by any of the preparation methods described above.

[0024] In a third aspect, the present invention provides a composite silicon-based negative electrode, comprising the composite silicon-based negative electrode active material described above, and also comprising a sulfide electrolyte, a conductive agent, and a binder.

[0025] As some specific embodiments of the present invention, the sulfide electrolyte is selected from one or more of Li3PS4, Li6PS5Cl, Li6PS5Br, and Li6PS5I;

[0026] The conductive agent is selected from at least one of vapor grown carbon fiber (VGCF), carbon black, super carbon, carbon nanotubes, and activated carbon;

[0027] The binder is selected from at least one of polyisobutylene, styrene-butadiene rubber, polyacrylic acid, and polymethyl methacrylate;

[0028] The mass ratio of the composite silicon-based negative electrode active material, sulfide electrolyte, conductive agent and binder is 6-8:3-1: 0.7-0.9:0.3-0.1, preferably 7:2:0.8:0.2.

[0029] 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, sulfide electrolyte, conductive agent, and binder in a toluene solvent, stirring evenly to form a slurry, and evenly coating the slurry on a copper foil current collector with a scraper to form a wet film, and vacuum drying to obtain the result.

[0030] In some specific embodiments of the present invention, the vacuum drying temperature 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.

[0031] As some specific embodiments of the present invention, the thickness of the wet film is 80-120 μm, preferably 100 μm.

[0032] In a fourth aspect, the present invention provides a sulfide all-solid-state lithium-ion battery, comprising the composite silicon-based negative electrode described in any one of the above items, and also comprising a composite positive electrode and a sulfide electrolyte.

[0033] As some specific embodiments of the present invention, the composite positive electrode includes NCM811, Li6PS5Cl sulfide solid electrolyte, and conductive agent VGCF.

[0034] When preparing the composite silicon-based negative electrode active material, the present invention first coats titanium dioxide on the outer layer of the silicon-aluminum alloy to maintain the spherical structure of the particles. During the subsequent etching process, the pore structure will not collapse or the pores will be blocked, and the internal porous structure will be maintained, leaving sufficient space for the volume expansion of silicon during the charge and discharge process. Subsequently, a high-temperature calcination treatment at 600-800°C is performed to further optimize the crystallinity of titanium dioxide and the silicon-titanium dioxide interface bonding, thereby 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, thereby optimizing the ion conduction path and enhancing ion transport.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1) The modified silicon-based composite anode material provided by this invention significantly reduces the volume expansion rate of the silicon anode while maintaining the high specific capacity of silicon itself through the synergistic effect of the rigid titanium dioxide coating and the internal porous silicon structure. The unique coral-like porous structure, when filled with a sulfide electrolyte, forms a three-dimensional ion transport network, significantly improving interfacial ionic conductivity. The composite anode is in close contact with the sulfide electrolyte, maintaining the integrity of the electrode structure. This fundamentally solves the key issues of silicon-based materials in sulfide all-solid-state batteries, such as large volume expansion and poor interfacial stability, and provides a practical technical solution for achieving high-energy-density all-solid-state lithium batteries.

[0037] 2) The aluminum-silicon alloy etching method and liquid electrolyte infiltration technology used in the preparation process have the advantages of low cost and easy scalability, and are suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0039] Figure 1 This is a flow chart of the preparation method of the titanium dioxide-coated porous silicon / sulfide electrolyte composite material of the present invention;

[0040] Figure 2 This is the SEM image of the calcined TiO2@porous silicon intermediate prepared in Example 1;

[0041] Figure 3This is the EDS spectrum of the calcined TiO2@porous silicon intermediate prepared in Example 1;

[0042] Figure 4 This is the EDS spectrum of the TiO2@porous silicon@Li6PS5Cl composite material prepared in Example 1;

[0043] Figure 5 This is the SEM image of the product prepared in Comparative Example 1;

[0044] Figure 6 This is the SEM image of the product prepared in Comparative Example 2;

[0045] Figure 7 This is the SEM image of the product prepared in Comparative Example 5. DETAILED DESCRIPTION

[0046] 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 are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0047] The present invention provides a method for preparing a composite silicon-based negative electrode active material (i.e., titanium dioxide-coated porous silicon / sulfide electrolyte composite material). The preparation process is as follows: Figure 1 As shown:

[0048] (1) Al-Si alloy powder was dispersed in anhydrous ethanol, tetrabutyl titanate was added, ultrasonic treatment was performed under alkaline conditions, and then vacuum drying was performed to obtain a TiO2-coated Al-Si alloy precursor;

[0049] (2) placing the product of step (1) in a hydrochloric acid solution for selective etching to remove the aluminum phase, and then washing with deionized water until neutral to obtain a TiO2@porous silicon intermediate with through pores;

[0050] (3) The etched sample is placed in a tube furnace and calcined at high temperature under argon protection to crystallize the TiO2 coating layer and enhance the interface bonding between TiO2 and the silicon substrate;

[0051] (4) The sulfide electrolyte and the product of step (3) are dispersed in anisole solvent and ball-milled, and then vacuum-dried to remove the solvent, so that the electrolyte fully fills the porous structure and covers the surface of the particles, thereby obtaining a composite material of TiO2@porous silicon@sulfide electrolyte.

[0052] Example 1

[0053] 1. Preparation of composite silicon-based negative electrode active materials

[0054] A method for preparing a titanium dioxide-coated porous silicon / sulfide electrolyte composite material, comprising the following steps:

[0055] (1) Preparation of TiO2-coated aluminum-silicon alloy precursor: 10.0 g aluminum-silicon alloy powder (mass ratio of aluminum to silicon is 7:3) was dispersed in 200 mL of anhydrous ethanol and magnetically stirred for 30 minutes. Then, 1.2 g of tetrabutyl titanate (accounting for 12% of the mass of the aluminum-silicon alloy) was added and magnetically stirred for 30 minutes to make it uniformly dispersed. Then, 25% ammonia water was added dropwise to adjust the pH to 9.0±0.2. The mixture was ultrasonically treated at a frequency of 40 kHz for 3 hours and then vacuum-dried at 60°C for 12 hours with a vacuum degree of 0.06 MPa to obtain a TiO2-coated aluminum-silicon alloy precursor.

[0056] (2) Preparation of porous structure by selective etching: 8.0 g of the TiO2-coated aluminum-silicon alloy precursor product was placed in 150 mL of 10 wt% hydrochloric acid solution and etched for 8 h in a 40 °C water bath with mechanical stirring (300 rpm). The product was then washed with deionized water five times until neutral (pH = 7.0 ± 0.2), and then dried in a vacuum oven at 80 °C for 6 h with a vacuum degree of 0.06 MPa to obtain a TiO2@porous silicon intermediate.

[0057] (3) High-temperature calcination treatment: 5.0 g of the etched TiO2@porous silicon intermediate sample was placed in a tube furnace and heated to 700°C at a rate of 3°C / min under an argon atmosphere for heat treatment. The temperature was kept at this temperature for 3 hours and then naturally cooled to room temperature to obtain the calcined TiO2@porous silicon intermediate.

[0058] (4) Sulfide electrolyte composite: In an argon-filled glove box, 4.0 g of the calcined sample and 4.0 g of Li6PS5Cl sulfide electrolyte were added to 40 mL of anisole solvent and ball-milled at 250 rpm for 4 h. The mixture was then vacuum-dried at 80 °C and 0.08 MPa for 12 h to obtain a TiO2@porous silicon@Li6PS5Cl composite material.

[0059] like Figure 2 As shown in FIG, this is an SEM image (magnification of 10,000 times) of the calcined TiO2@porous silicon intermediate prepared in step (3) of Example 1, in which a regular spherical porous structure can be observed; Figure 3 As shown, this is the EDS 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.

[0060] like Figure 4As shown in FIG, this is the EDS 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 is mainly concentrated in the center of the spherical particles. The S element comes from the sulfide electrolyte and is mainly concentrated on the periphery of the particles. There is also a small amount distributed inside the particles. This shows that the sulfide electrolyte is filled in the pores of the porous silicon and coated on the outer layer of TiO2.

[0061] 2. Preparation of composite silicon-based negative electrode sheet

[0062] The TiO2@porous silicon@Li6PS5Cl composite material is prepared into a negative electrode sheet by wet film formation. The specific steps are as follows:

[0063] Working in an argon-filled glove box, 7.0 g of the prepared TiO2@porous silicon@Li6PS5Cl composite, 2.0 g of the Li6PS5Cl sulfide electrolyte, 0.8 g of the conductive carbon (VGCF), and 0.2 g of the polyisobutylene binder were mixed in 50 mL of toluene solvent and magnetically stirred for 2 hours to form a uniform slurry. The slurry was evenly coated onto a 10 μm thick copper foil current collector using a doctor blade, with a wet film thickness of 100 μm. The slurry was then dried in a vacuum oven at 100°C and 0.05 MPa for 10 hours to remove any residual solvent, resulting in the negative electrode sheet. The resulting sheet was then cut into 10 mm diameter discs for later use.

[0064] 3. Preparation of sulfide all-solid-state lithium-ion batteries

[0065] 1. Preparation of composite cathode system:

[0066] 80 mg of NCM811 powder, 15 mg of Li6PS5Cl sulfide solid electrolyte, and 5 mg of conductive agent VGCF powder were placed in a mortar and ground for 30 min to prepare a composite positive electrode system.

[0067] 2. Assemble the pressure cell:

[0068] (1) In an argon-filled glove box, 30 mg of sulfide electrolyte Li6PS5Cl powder was placed in a pressure battery mold with a diameter of 10 mm and pressed into tablets on a tablet press. A pressure of 1 ton was applied and the pressure was maintained for 1 min.

[0069] (2) Then spread 30 mg of composite cathode system powder on the surface of the electrolyte sheet, apply 1 ton of pressure, and maintain the pressure for 1 minute;

[0070] (3) Then lay the composite silicon-based negative electrode sheet flat on the other side of the electrolyte sheet, apply 1 ton of pressure, and maintain the pressure for 1 minute;

[0071] (4) A 10 mm diameter aluminum foil is placed on the surface of the composite positive electrode sheet as the positive electrode current collector. After assembly, a pressure of 1 ton is applied and maintained for 1 minute to obtain a sulfide all-solid-state lithium-ion battery for testing and standby use.

[0072] Example 2

[0073] A method for preparing a titanium dioxide-coated porous silicon / sulfide electrolyte composite material, comprising the following steps:

[0074] (1) Preparation of TiO2-coated aluminum-silicon alloy precursor: 15.0 g aluminum-silicon alloy powder (mass ratio of aluminum to silicon is 7:3) was dispersed in 300 mL of anhydrous ethanol and magnetically stirred for 40 minutes. Then, 2.25 g of tetrabutyl titanate (accounting for 15% of the mass of the aluminum-silicon alloy) was added and stirred for 40 minutes until uniform dispersion. Then, 25% ammonia water was added dropwise to adjust the pH to 9.5±0.2. The mixture was ultrasonically treated at a frequency of 45 kHz for 4 hours. Finally, the mixture was vacuum dried at 70°C for 10 hours with a vacuum degree of 0.08 MPa to obtain a TiO2-coated aluminum-silicon alloy precursor.

[0075] (2) Preparation of porous structure by selective etching: 12.0 g of the precursor product was placed in 200 mL of 12 wt% hydrochloric acid solution and etched with mechanical stirring (350 rpm) in a 50 °C water bath for 6 h. Then, it was washed with deionized water 5 times until neutral (pH = 7.0 ± 0.2). Finally, it was vacuum dried at 90 °C for 8 h with a vacuum degree of 0.08 MPa to obtain TiO2@porous silicon intermediate.

[0076] (3) High-temperature calcination treatment: 6.0 g of the etched sample was placed in a tubular furnace, protected by an argon atmosphere, and heated to 750 °C at a rate of 5 °C / min, kept at this temperature for 4 hours, and then naturally cooled to room temperature to obtain a crystallized TiO2@porous silicon intermediate.

[0077] (4) Sulfide electrolyte composite: The operation was carried out in an argon-filled glove box. 5.0 g of the calcined sample and 5.0 g of Li6PS5Cl sulfide electrolyte were added to 50 mL of anisole solvent and ball milled at 300 rpm for 3 h. Then, the mixture was vacuum dried at 85 °C and 0.05 MPa for 15 h to obtain TiO2@porous silicon@Li6PS5Cl composite material.

[0078] The same method as in Example 1 was used to prepare a composite silicon-based negative electrode plate and assembled into a sulfide all-solid-state lithium-ion battery.

[0079] Comparative Example 1

[0080] Step (1) in Example 1 was eliminated, and the TiO2-coated aluminum-silicon alloy precursor was not prepared. The untreated aluminum-silicon alloy was directly used for etching, and the remaining steps were carried out with reference to Example 1.

[0081] The SEM images of the samples prepared in Comparative Example 1 are as follows: Figure 5 As shown, it can be observed that the spherical morphology cannot be maintained after etching, and there is no obvious porous structure. The structure collapses after etching.

[0082] Comparative Example 2

[0083] Step (2) in Example 1 is eliminated, and the TiO2-coated aluminum-silicon alloy precursor is not etched with hydrochloric acid. The remaining steps are carried out according to Example 1.

[0084] The SEM images of the samples prepared in Comparative Example 2 are as follows: Figure 6 As shown, it can be observed that the sample without hydrochloric acid etching does not have a porous structure, which does not inhibit the volume expansion of silicon during the charge and discharge process.

[0085] Comparative Example 3

[0086] Step (3) in Example 1 was eliminated, and high-temperature calcination treatment was not performed. The remaining steps were carried out according to Example 1.

[0087] Not calcining has little effect on the morphology of the product, but it will mainly lead to insufficient strength of the TiO2 shell, which cannot better limit the volume expansion of silicon, resulting in rapid capacity decay during the cycle.

[0088] Comparative Example 4

[0089] Step (4) in Example 1 was eliminated, and no composite treatment with the sulfide electrolyte was performed. The remaining steps were carried out in accordance with Example 1.

[0090] In Example 1 Figure 2 That is the SEM image of the TiO2@porous silicon intermediate sample. Without the composite sulfide electrolyte, the ion conduction will be significantly reduced, and the solid-solid interface between the active material and the sulfide electrolyte cannot be improved, which makes the battery rate performance and capacity much worse.

[0091] Comparative Example 5

[0092] The preparation was carried out with reference to the paper "Surface Modification and Electrochemical Performance Study of Titanium Dioxide-Coated Porous Silicon Composite Materials": Based on Example 1, the silicon-aluminum alloy powder was first etched in hydrochloric acid and then coated with titanium dioxide, without high-temperature calcination and without compounding with a sulfide solid electrolyte.

[0093] The SEM images of the prepared samples are as follows Figure 7As 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, and the spherical morphology cannot be maintained, and the volume expansion cannot be inhibited; when titanium dioxide is then coated by the sol-gel method, it will fill in the formed porous structure, causing blockage, and the reserved space for volume expansion is reduced; and the strength of titanium dioxide is insufficient; the ionic conductivity of the composite material is low.

[0094] Effect Example 1

[0095] The batteries prepared in the above embodiments and comparative examples were tested as follows:

[0096] The all-solid-state battery was tested using a Xinwei battery test system, model CT-4000, with a charge and discharge rate of 0.2C-0.5C, a voltage range of 4.3-2.5V, and a temperature of 28°C. The discharge capacity of the sulfide all-solid-state battery was tested. The results are shown in Table 1 below:

[0097] Table 1 Sulfide all-solid-state lithium-ion battery charge and discharge test

[0098]

[0099] As can be seen from the above table, the discharge capacity at 0.2C and 0.5C, coulombic efficiency and capacity retention rate after 30 cycles in Examples 1 and 2 are significantly higher than those in Comparative Examples 1-5. This is mainly because the synergistic effect of the rigid titanium dioxide coating and the internal porous silicon structure effectively suppresses the volume expansion of the silicon negative electrode, while maintaining the high specific capacity of silicon, and solves the problem of structural collapse of the silicon material during the charge and discharge process; and after the porous structure is filled with sulfide electrolyte, a three-dimensional continuous ion transport network is formed, the solid-solid interface ion conductivity is improved, showing excellent interface stability and structural integrity, and the cycle stability is significantly improved.

[0100] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a composite silicon-based negative electrode active material, characterized in that: The steps include: S1. Dispersing aluminum-silicon alloy powder in anhydrous ethanol, adding tetrabutyl titanate, ultrasonically treating under alkaline conditions, and vacuum drying to obtain a TiO2-coated aluminum-silicon alloy precursor; In the aluminum-silicon alloy powder, the mass ratio of aluminum to silicon is 6-8:4-2; S2, placing the TiO2-coated aluminum-silicon alloy precursor in an acid solution for selective etching to remove the aluminum phase, washing it to neutrality, and vacuum drying it to obtain a TiO2@porous silicon intermediate with through-pores; S3, calcining the TiO2@porous silicon intermediate; S4, dispersing the sulfide electrolyte and the TiO2@porous silicon intermediate calcined in step S3 into an organic solvent, ball milling the mixture, and vacuum drying to remove the solvent; The sulfide electrolyte includes Li6PS5Cl.

2. The preparation method according to claim 1, characterized in that In step S1, at least one of the following technical features is included: (1) The mass ratio of tetrabutyl titanate to aluminum silicon alloy powder is 0.05-0.15:1; (2) The alkaline condition is adjusted by an ammonium hydroxide aqueous solution, the mass fraction of the ammonium hydroxide aqueous solution is 20% to 30%, and the pH value of the alkaline condition is 8 to 10; (3) 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, characterized in that In step S2, the acid solution includes a hydrochloric acid solution, and the mass fraction of the hydrochloric acid solution is 8% to 12%; And / or, the etching reaction time is 4 to 10 h, and the etching reaction temperature is 35 to 45° C.; And / or, the washing comprises washing with deionized water 3 to 5 times.

4. The preparation method according to claim 1, characterized in that In step S3, the calcination is carried out under inert gas protection; 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, characterized in that In step S4, at least one of the following technical features is included: (1) The mass ratio of the sulfide electrolyte to the calcined TiO2@porous silicon intermediate is 1:1-4; (2) The organic solvent is at least one selected from anisole, toluene, xylene, and butyl ether; (3) The ball milling speed is 200-300 rpm and the time is 2-4 h.

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

7. A composite silicon-based negative electrode active material, characterized in that: The method is prepared according to any one of claims 1 to 6.

8. A composite silicon-based negative electrode, characterized in that: The composite silicon-based negative electrode active material according to claim 7 further comprises a sulfide electrolyte, a conductive agent and a binder.

9. The composite silicon-based negative electrode according to claim 8, characterized in that: 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 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.

10. A sulfide all-solid-state lithium-ion battery, characterized in that: It comprises the composite silicon-based negative electrode as described in claim 8 or 9, and also comprises a composite positive electrode and a sulfide electrolyte.

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