A modified porous silicon composite negative electrode material and its preparation method and application

Abstract

The present invention discloses a modified porous silicon composite negative electrode material, a preparation method thereof, and an application thereof, relating to the technical field of all-solid-state batteries. A composite conductive polymer is prepared by mixing a PEDOT:PSS aqueous solution, a lithium polyvinyl sulfonate aqueous solution, and dimethyl sulfoxide. The porous silicon prepared by reaction under ice-water bath conditions is coated and modified to obtain a modified porous silicon material. The modified porous silicon material is then ultrasonically mixed with a sulfide electrolyte in a toluene solvent to extract the target material. The obtained material alleviates the volume expansion of the silicon-based negative electrode during charge and discharge through a porous structure, improves the electron conduction efficiency by coating with a composite conductive polymer, optimizes the ion conduction path by combining with a sulfide electrolyte, and forms a stable interface buffer layer to inhibit side reactions. The material can be used to prepare a negative electrode sheet, and is combined with an NCM811 positive electrode sheet and a sulfide solid electrolyte sheet to form an all-solid-state battery. The material significantly improves the negative electrode interface stability, enhances the battery cycle life and rate performance, and has important application value in the field of high energy density energy storage.

Description

Technical Field

[0001] The present invention relates to the technical field of all-solid-state batteries, and in particular to a modified porous silicon composite negative electrode material and a preparation method and application thereof. Background Art

[0002] Sulfide all-solid-state lithium batteries are a key development direction for next-generation batteries due to their high safety and potential for high energy density. Conventional lithium-ion batteries use graphite anodes, but their low theoretical specific capacity makes them inadequate for meeting future high-energy storage needs. Silicon, with its extremely high theoretical specific capacity and low delithiation potential, is considered a promising anode material. However, silicon experiences severe volume expansion (~300%) during charge and discharge, leading to structural damage, pulverization of active materials, and repeated cracking and regeneration of the solid electrolyte interface film, ultimately significantly degrading battery cycle performance. To mitigate silicon's volume expansion, researchers have proposed various strategies, including nanostructuring, porous design, carbon coating, and alloying. Among them, porous silicon has attracted considerable attention because its internal pores can effectively buffer volume changes. Typically, porous silicon can be prepared by chemical etching, but a simple pore structure cannot address silicon's low intrinsic electronic conductivity and poor interface with the solid electrolyte. The application of silicon negative electrodes in sulfide solid-state batteries still faces the following challenges: the interface stability between silicon and sulfide electrolyte is poor, and side reactions are prone to occur; the electronic / ionic conductivity of silicon is low, resulting in severe polarization and poor rate performance; the volume expansion of silicon during charging and discharging will destroy the close contact between the solid electrolyte and the electrode, increasing the interface impedance. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a modified porous silicon composite negative electrode material, its preparation method, and application. A porous silicon skeleton is prepared by etching an aluminum-silicon alloy with hydrochloric acid to suppress the volume expansion of silicon. The modified porous silicon is then coated with a composite conductive polymer of poly (3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS) and lithium polyvinyl sulfonate in a mixed solvent of dimethyl sulfoxide and water to enhance electronic conductivity. Finally, a sulfide electrolyte is wet-deposited to fill the pores of the modified porous silicon, optimizing the ion conduction path and enhancing ion transport.

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

[0005] <First Aspect>

[0006] The present invention provides a method for preparing a modified porous silicon composite negative electrode material, comprising the following steps:

[0007] S1. Modifying porous silicon with a composite conductive polymer, extracting a reaction product and drying it to obtain a modified porous silicon material, wherein the composite conductive polymer is obtained by mixing a PEDOT:PSS aqueous solution, a lithium polyvinyl sulfonate aqueous solution, and dimethyl sulfoxide;

[0008] S2. Mixing the modified porous silicon material, sulfide electrolyte, and organic solvent under sealed conditions for reaction, extracting the reaction product, and drying it to obtain the modified porous silicon composite negative electrode material.

[0009] As an embodiment, the mass ratio of the PEDOT:PSS aqueous solution to the lithium polyvinyl sulfonate aqueous solution is (1-3):1.

[0010] As an embodiment, the mass ratio of the dimethyl sulfoxide and the PEDOT:PSS aqueous solution is (3-6):50.

[0011] In some embodiments, the mass ratio of the dimethyl sulfoxide to the PEDOT:PSS aqueous solution is (3.5~5.3):50.

[0012] As an embodiment, the concentration of the PEDOT:PSS aqueous solution is 0.8-2 wt.%.

[0013] In some embodiments, the concentration of the PEDOT:PSS aqueous solution is 1.5 wt.%.

[0014] As an embodiment, the mass ratio of PEDOT to PSS in the PEDOT:PSS aqueous solution is 1:(2~8).

[0015] In some embodiments, the mass ratio of PEDOT to PSS in the PEDOT:PSS aqueous solution is 1:6.

[0016] As an embodiment, the concentration of the lithium polyvinyl sulfonate aqueous solution is 3.5-10.5 wt.%.

[0017] In some embodiments, the concentration of the lithium polyvinyl sulfonate aqueous solution is 7 wt.%.

[0018] As an embodiment, the preparation method of the lithium polyvinyl sulfonate aqueous solution is: obtaining the lithium polyvinyl sulfonate aqueous solution by neutralizing the lithium-containing alkaline solution.

[0019] As an embodiment, the concentration of the polyethylene sulfonic acid aqueous solution is 4-13 wt.%.

[0020] In some embodiments, the concentration of the polyethylene sulfonic acid aqueous solution is 8.3 wt.%.

[0021] As an embodiment, the lithium-containing alkaline solution is a lithium hydroxide aqueous solution.

[0022] As an embodiment, the concentration of the lithium-containing alkaline solution is 4-10 wt.%.

[0023] As an embodiment, the preparation method of the polyvinyl sulfonic acid aqueous solution is: exchanging sodium ions in the sodium polyvinyl sulfonate aqueous solution with hydrogen ions using a hydrogen-type strongly acidic cation exchange resin.

[0024] As an embodiment, the concentration of the sodium polyethylene sulfonate aqueous solution is 5-15 wt.%.

[0025] In some embodiments, the concentration of the sodium polyethylene sulfonate aqueous solution is 10 wt.%.

[0026] As an embodiment, the preparation method of the lithium polyethylene sulfonate aqueous solution is: the sodium ions in the sodium polyethylene sulfonate aqueous solution are exchanged for hydrogen ions by a hydrogen-type strongly acidic cation exchange resin to obtain an intermediate containing a sulfonic acid group, and then the hydrogen ions of the sulfonic acid group are neutralized by a lithium hydroxide aqueous solution to obtain the lithium polyethylene sulfonate aqueous solution.

[0027] In some embodiments, 10 g of sodium polyethylene sulfonate is dissolved in 90 g of deionized water, and the solution is passed through a column of hydrogen-type strong acidic cation exchange resin. The cations react with the H on the resin. + An exchange occurs, exchanging the terminal group of the monomer from -SO3Na to -SO3H, and then neutralizing with a 7wt.% lithium hydroxide aqueous solution to pH=7 to obtain a lithium polyvinyl sulfonate aqueous solution.

[0028] As an embodiment, the mass ratio of the composite conductive polymer to the porous silicon is (5-15):1.

[0029] In some embodiments, the mass ratio of the composite conductive polymer to porous silicon is 10:1.

[0030] As an embodiment, the reaction time during the preparation of the composite conductive polymer is 2 to 4 hours.

[0031] As an embodiment, the reaction time of the modification treatment is 2 to 4 hours.

[0032] As an embodiment, the porous silicon is obtained by adding aluminum-silicon alloy powder to a hydrochloric acid aqueous solution at 0° C. for a reaction of 4 to 10 hours, washing, extracting and drying the reaction product.

[0033] As an embodiment, the mass ratio of aluminum to silicon in the aluminum-silicon alloy powder is (5~7):4.

[0034] In some embodiments, the mass ratio of aluminum to silicon in the aluminum-silicon alloy powder is 6:4.

[0035] As an embodiment, the concentration of the hydrochloric acid aqueous solution is 8-12 wt.%.

[0036] In some embodiments, the concentration of the hydrochloric acid aqueous solution is 10 wt.%.

[0037] As an embodiment, the porous silicon is washed with deionized water after the reaction is completed.

[0038] As an embodiment, the mass ratio of the modified porous silicon to the sulfide electrolyte is (3~5):1.

[0039] In some embodiments, the mass ratio of the modified porous silicon to the sulfide electrolyte is 4:1.

[0040] As an embodiment, the sulfide electrolyte is Li6PS5Cl.

[0041] As an embodiment, the organic solvent is toluene.

[0042] As an embodiment, the usage ratio of the modified porous silicon and the organic solvent is (0.8~1.2)g:10mL.

[0043] In some embodiments, the modified porous silicon and the organic solvent are used in a ratio of 1 g: 10 mL.

[0044] As an embodiment, in step S1, the modification treatment is carried out by magnetic stirring.

[0045] As an embodiment, the composite conductive polymer is stirred and mixed by magnetic stirring.

[0046] As an embodiment, the porous silicon is prepared by stirring and mixing in a magnetic stirring manner.

[0047] In some embodiments, the magnetic stirring speed is 800 rpm.

[0048] As an embodiment, in step S2, the modified porous silicon composite negative electrode material is prepared by performing a mixing reaction through ultrasonic treatment.

[0049] In some embodiments, the ultrasonic treatment has an oscillation frequency of 20 kHz.

[0050] As an embodiment, the extraction of the reaction product in step S1 and / or step S2 is performed by solid-liquid separation by centrifugation.

[0051] In some embodiments, the centrifugation speed is 5000 rpm and the time is 20 min.

[0052] As an embodiment, the drying in step S1 and / or step S2 is performed by vacuum drying.

[0053] In some embodiments, the drying parameters are: vacuum degree 0.08 MPa, temperature 80°C.

[0054] <Second Aspect>

[0055] The present invention provides a modified porous silicon composite negative electrode material, which is prepared by the above method.

[0056] <Third Aspect>

[0057] The present invention provides an application of a modified porous silicon composite negative electrode material in an all-solid-state lithium-ion battery.

[0058] As an embodiment, the negative electrode sheet in the battery is obtained by pressing the modified porous silicon composite negative electrode material.

[0059] As an embodiment, the positive electrode sheet in the battery is formed by mixing and pressing a ternary positive electrode material, a sulfide solid electrolyte and a conductive agent.

[0060] As an embodiment, the ternary positive electrode material is a nickel-cobalt-manganese-lithium ternary material.

[0061] As an embodiment, the nickel-cobalt-manganese-lithium ternary material is one or more of NCM811, NCM622, and NCM523.

[0062] In some embodiments, the conductive agent is VGCF.

[0063] In some embodiments, the mass ratio of the NCM811, sulfide solid electrolyte, and conductive agent is 80:15:5.

[0064] As an embodiment, the electrolyte sheet in the battery is formed by pressing a sulfide electrolyte material.

[0065] In some embodiments, the sulfide electrolyte is Li6PS5Cl.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] The modified porous silicon composite negative electrode material preparation method provided by the present invention, through a multi-scale synergistic modification strategy, simultaneously solves key problems such as volume expansion, interfacial impedance, and ion conduction of silicon-based negative electrodes in solid-state batteries, and constructs an efficient and stable electron / ion dual-conducting network. It has significant technical advantages in improving the cycle stability and rate performance of silicon-based negative electrodes in all-solid-state batteries, specifically:

[0068] (1) Alleviate volume expansion and improve structural stability

[0069] A silicon-based material with a uniform porous structure is prepared by reacting aluminum-silicon alloy powder with hydrochloric acid in an ice-water bath. This material is then vacuum-dried to form a stable pore structure. This porous structure provides ample buffer space for silicon expansion during charge and discharge, effectively suppressing particle breakage and structural pulverization, ensuring the integrity of the electrode structure during cycling and improving electrochemical performance.

[0070] (2) Conductive coating layer to enhance electron transfer efficiency

[0071] PEDOT:PSS is used to form a continuous conductive network, and lithium polyethylene sulfonate introduces lithium-affinity groups to enhance the chemical bonding between the polymer and the silicon surface. After coating, the material is vacuum dried to form an elastic conductive layer, which has the dual functions of electronic conduction and mechanical buffering.

[0072] (3) Optimize the ion conduction path and build an electron / ion dual conduction network

[0073] The lithium sulfonate groups on the surface of the modified porous silicon form a lithium ion conduction interface layer with the sulfide electrolyte. This structure constructs a continuous dual conduction network of porous silicon skeleton electronic conduction / sulfide electrolyte ion conduction, significantly improving the electrochemical performance of the negative electrode.

[0074] (4) Interface buffer layer to inhibit side reactions

[0075] The composite conductive polymer coating works synergistically with the sulfide electrolyte to form a three-layer interface protection structure:

[0076] In the inner layer, the porous silicon pore walls provide physical support to resist volume expansion stress;

[0077] The middle layer, a conductive polymer elastic layer, absorbs mechanical stress while blocking direct contact between silicon and the electrolyte, inhibiting the side reaction of lithium ion reduction to form the SEI film;

[0078] On the outside, the sulfide electrolyte forms a stable interface with the lithium-affinity groups of the polymer layer, reducing the risk of lithium ion enrichment and dendrite growth at the interface.

[0079] (4) The process is highly controllable and suitable for large-scale production

[0080] The preparation method adopts industrial mature technology, is easy to scale up and control, and provides a reliable process basis for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] 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:

[0082] Figure 1 This is a flow chart of the preparation method of the modified porous silicon composite negative electrode material provided by the present invention;

[0083] Figure 2 This is a SEM image of the porous silicon material prepared in Example 1 of the present invention, with a magnification of ×2000;

[0084] Figure 3 This is a SEM image of the porous silicon material prepared in Example 1 of the present invention, with a magnification of ×10000. DETAILED DESCRIPTION

[0085] The present invention will be described in detail below with reference to the examples. The following examples 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 those skilled in the art may make several adjustments and improvements without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0086] For ease of understanding, the abbreviations or nouns mentioned below are first explained:

[0087] PEDOT:PSS aqueous solution: CAS number: 155090-83-8, product number: P191136, 1.5 wt.% aqueous solution, PEDOT:PSS = 1:6, purchased from Aladdin Chemical Reagent Platform;

[0088] Hydrogen form strong acidic cation exchange resin: model IR-120(H), CAS number: 9002-23-7, purchased from Aladdin Chemical Reagent Platform;

[0089] Aluminum-silicon alloy powder: composed of 60% aluminum and 40% silicon by mass, with a particle size of 6-8um;

[0090] VGCF: carbon nanofiber conductive agent, VGCF-H, purchased from Kejing Zhida Technology Co., Ltd.

[0091] This specific embodiment provides a method for preparing a modified porous silicon composite negative electrode material, the steps are as follows: Figure 1 shown.

[0092] (1) Prepare porous silicon materials and composite conductive polymers separately, specifically:

[0093] Preparation of porous silicon material: silicon-aluminum alloy powder is etched in a hydrochloric acid aqueous solution, then washed with deionized water, and centrifugally dried to obtain a porous silicon material.

[0094] Preparation of composite conductive polymers:

[0095] Passing an aqueous solution of sodium polyvinyl sulfonate through a cation exchange resin to obtain polyvinyl sulfonic acid, which is then lithiated to obtain lithium polyvinyl sulfonate;

[0096] A PEDOT:PSS aqueous solution, a lithium polyvinyl sulfonate aqueous solution, and dimethyl sulfoxide are mixed and stirred to prepare a composite conductive polymer.

[0097] (2) Modification of porous silicon using composite conductive polymers, specifically:

[0098] The modified porous silicon is coated with a composite conductive polymer and then centrifugally dried to obtain the modified porous silicon material.

[0099] (3) The sulfide solid electrolyte is deposited in the pores of the modified porous silicon by ultrasonic treatment, and then centrifugally dried to obtain a modified porous silicon composite negative electrode material.

[0100] The method is specifically described below through examples.

[0101] Example 1

[0102] This embodiment provides a method for preparing a modified porous silicon composite negative electrode material, the steps of which are as follows:

[0103] S1. Modifying porous silicon using a composite conductive polymer to obtain a modified porous silicon material;

[0104] S11, mixing 5 g of a PEDOT:PSS aqueous solution, 5 g of a lithium polyvinyl sulfonate aqueous solution, and 0.526 g of dimethyl sulfoxide, and magnetically stirring for 2 h to obtain a composite conductive polymer;

[0105] S12. Add 1 g of porous silicon material to 10 g of composite conductive polymer, stir magnetically for 2 h, then separate the solid and liquid by centrifugation, and then dry in a constant temperature vacuum at 80° C. for 10 h to obtain a modified porous silicon material.

[0106] The preparation method of lithium polyvinyl sulfonate aqueous solution is as follows: dissolve 10g of sodium polyvinyl sulfonate in 90g of deionized water, pass the solution through a column of hydrogen-type strong acid cation exchange resin, and the cations react with the H on the resin. + An exchange occurs, exchanging the terminal group of the monomer from -SO3Na to -SO3H, and then neutralizing it with a 7wt.% lithium hydroxide aqueous solution to pH=7 to obtain an aqueous solution of lithium polyvinyl sulfonate with a terminal group of -SO3Li.

[0107] It should be noted that, according to calculation, the concentration of polyvinyl sulfonic acid is about 8.3 wt.%, and the concentration of lithium polyvinyl sulfonate is about 7 wt.%.

[0108] The preparation method of porous silicon material is as follows:

[0109] 3 g of aluminum-silicon alloy powder was added to 15 mL of a 10 wt.% hydrochloric acid aqueous solution. The reaction system was placed in an ice-water bath and stirred continuously with a magnetic stirrer. After etching for 10 h, the reaction product was washed three times with deionized water, centrifuged, and then dried in a vacuum at 80 ° C for 10 h to obtain a porous silicon material. Figure 2 and Figure 3 shown.

[0110] In order to ensure the smooth progress of the reaction, in this embodiment, the aluminum-silicon alloy powder is added to the hydrochloric acid in batches to avoid short-term heat accumulation caused by the exothermic reaction and to maintain the relative temperature of the system.

[0111] S2. Preparation of modified porous silicon composite negative electrode material

[0112] In an argon glove box, 0.25 g of sulfide electrolyte (Li6PS5Cl) with D50 = 5 μm, 1 g of modified porous silicon, and 10 mL of toluene were added to a sealed reaction bottle, and then ultrasonically treated for 3 h (the frequency of ultrasonic oscillation was 20 kHz). The reaction product was then extracted by solid-liquid separation by centrifugation, and finally dried in a constant temperature vacuum at 80 ° C for 10 h to obtain a modified porous silicon composite negative electrode material.

[0113] In this embodiment, the magnetic stirring speed used is 800 rpm; the centrifugal parameters are: speed 5000 rpm, time 20 min; vacuum drying: vacuum degree 0.08 MPa, temperature 80°C.

[0114] Example 2

[0115] This embodiment provides a method for preparing a modified porous silicon composite negative electrode material, the steps of which are as follows:

[0116] S1. Modifying porous silicon using a composite conductive polymer to obtain a modified porous silicon material;

[0117] S11, mixing 15 g of a PEDOT:PSS aqueous solution, 5 g of a lithium polyvinyl sulfonate aqueous solution, and 1.05 g of dimethyl sulfoxide, and magnetically stirring for 2 h to obtain a composite conductive polymer;

[0118] S12. Add 1 g of porous silicon material to 10 g of composite conductive polymer, stir magnetically for 2 h, then separate the solid and liquid by centrifugation, and then dry in a constant temperature vacuum at 80° C. for 10 h to obtain a modified porous silicon material.

[0119] The preparation method of lithium polyvinyl sulfonate aqueous solution is as follows: dissolve 10g of sodium polyvinyl sulfonate in 90g of deionized water, pass the solution through a column of hydrogen-type strong acid cation exchange resin, and the cations react with the H on the resin. + An exchange occurs, exchanging the terminal group of the monomer from -SO3Na to -SO3H, and then neutralizing it with a 7wt.% lithium hydroxide aqueous solution to pH=7 to obtain lithium polyvinyl sulfonate with the terminal group being -SO3Li.

[0120] The preparation method of porous silicon material is as follows:

[0121] 3 g of aluminum-silicon alloy powder was added to 15 mL of a 10 wt.% hydrochloric acid aqueous solution. The reaction system was placed in an ice-water bath and stirred continuously with a magnetic stirrer. After reacting for 5 h, the reaction product was washed three times with deionized water, centrifuged, and then dried in a constant temperature vacuum at 80 ° C for 10 h to obtain a porous silicon material.

[0122] In order to ensure the smooth progress of the reaction, in this embodiment, the aluminum-silicon alloy powder is added to the hydrochloric acid in batches to avoid short-term heat accumulation caused by the exothermic reaction and to maintain the relative temperature of the system.

[0123] S2. Preparation of modified porous silicon composite negative electrode material

[0124] In an argon glove box, 0.25 g of sulfide electrolyte (Li6PS5Cl), 1 g of modified porous silicon, and 10 mL of toluene were added to a sealed reaction bottle, and then ultrasonically treated for 3 h (the frequency of ultrasonic oscillation was 20 kHz). The reaction product was then extracted by solid-liquid separation by centrifugation, and finally dried in a constant temperature vacuum at 80 ° C for 10 h to obtain a modified porous silicon composite negative electrode material.

[0125] In this embodiment, the magnetic stirring speed used is 800 rpm; the centrifugal parameters are: speed 5000 rpm, time 20 min; vacuum drying: vacuum degree 0.08 MPa, temperature 80°C.

[0126] Comparative Example 1

[0127] This comparative example provides a method for preparing a composite negative electrode material. The steps are basically the same as those in Example 1, except that:

[0128] Instead of using porous silicon material, aluminum-silicon alloy powder is directly used for coating modification, that is, the porous silicon material in step S12 is replaced by aluminum-silicon alloy powder to prepare a modified silicon material.

[0129] Comparative Example 2

[0130] This comparative example provides a method for preparing a composite negative electrode material. The steps are basically the same as those in Example 1, except that:

[0131] The modified porous silicon material is not wrapped with a composite conductive polymer, and the modified porous silicon is directly replaced with the porous silicon material in step S2.

[0132] Comparative Example 3

[0133] This comparative example provides a method for preparing a composite negative electrode material. The steps are basically the same as those in Example 1, except that:

[0134] The modified porous silicon material is directly used as the negative electrode material without performing step S2.

[0135] Comparative Example 4

[0136] This comparative example provides a method for preparing a composite negative electrode material. The steps are basically the same as those in Example 1, except that:

[0137] The porous silicon was not modified by using a composite conductive polymer, but only by using a PEDOT:PSS aqueous solution.

[0138] Detection and Analysis

[0139] (1) Pressure battery assembly

[0140] The composite negative electrode materials prepared in the above examples and comparative examples were assembled into pressure batteries for testing, and the steps were as follows:

[0141] In an argon 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 a tablet on a tablet press. A pressure of 1 ton was applied and the pressure was maintained for 1 minute to obtain an electrolyte tablet.

[0142] 30 mg of the composite cathode material was spread flat on the surface of the electrolyte sheet, and 1 ton of pressure was applied again and the pressure was maintained for 1 minute to press into a sheet;

[0143] Spread 10 mg of the composite negative electrode material on the other side of the electrolyte sheet and press it into a tablet by applying a pressure of 1 ton and maintaining the pressure for 1 minute.

[0144] A 15um thick, 10mm diameter aluminum foil was placed on the surface of the composite positive electrode sheet as the positive electrode current collector, and a 15um thick copper foil was placed on the other side as the negative electrode current collector. After the assembly was completed, a pressure of 1 ton was applied and maintained for 1 minute to obtain a sulfide all-solid-state lithium-ion battery.

[0145] The preparation steps of the composite positive electrode are as follows: 80 mg of NCM811 powder, 15 mg of Li6PS5Cl sulfide solid electrolyte, and 5 mg of conductive agent VGCF powder are placed in a mortar and ground for 30 minutes to obtain a composite positive electrode material.

[0146] (2) Performance testing

[0147] The Xinwei battery testing system (model CT-4000) was used to test the all-solid-state battery for charge and discharge. A 0.2C-0.5C rate charge and discharge process was used. The specific charge and discharge method was: first 0.2C charge and discharge cycles for 3 rounds, then jump to 0.5C cycle. The voltage range was 4.3-2.5V, and the temperature was 28°C. The discharge capacity of the sulfide all-solid-state battery was tested. The test results are shown in Table 1.

[0148] Table 1. Battery performance data of sulfide all-solid-state lithium batteries

[0149]

[0150] As can be seen from Table 1, the discharge capacity, coulombic efficiency, and cycling stability after 30 cycles of the batteries of Examples 1 and 2 at 0.2C and 0.5C are significantly higher than those of Comparative Examples 1 to 4. The composite anode system provided by the present invention constructs a continuous electron / ion dual-conducting network, improves the anode interface stability, and significantly enhances the electrochemical performance of silicon anodes in sulfide all-solid-state batteries. This is mainly reflected in the following aspects:

[0151] (1) Porous structure buffers volume expansion:

[0152] The porous silicon structure formed by hydrochloric acid etching of the aluminum-silicon alloy reserves space for silicon's volume expansion at the mesoscopic scale. During the battery's charge and discharge processes, silicon undergoes significant volume changes. This porous structure accommodates this expansion, preventing silicon particle fracture and electrode structural damage caused by excessive volume expansion, thereby ensuring the integrity and stability of the electrode.

[0153] (2) Interface interaction optimization performance:

[0154] Lithium polyethylene sulfonate is a lithium-containing polyelectrolyte. The flexible polymer chain can wrap porous silicon and inhibit the structural damage caused by volume expansion. The Li in the sulfonic acid group + Providing an ion transport path and improving interfacial ion conductivity. After the composite conductive polymer is coated on porous silicon, the conductive polymer can better adhere to the porous silicon surface at the interface between the two, further enhancing electron transport. Subsequent wet ultrasonic treatment with a sulfide electrolyte establishes an ion exchange path between the electrolyte and the modified porous silicon, promoting ion transport and improving the electrochemical performance of the entire system.

[0155] 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 modified porous silicon composite negative electrode material, characterized in that: The following steps are involved: S1. Modifying porous silicon with a composite conductive polymer, extracting a reaction product and drying it to obtain a modified porous silicon material, wherein the composite conductive polymer is obtained by mixing a PEDOT:PSS aqueous solution, a lithium polyvinyl sulfonate aqueous solution, and dimethyl sulfoxide, and the mass ratio of the composite conductive polymer to the porous silicon is (5-15):1; S2. Mixing the modified porous silicon material, sulfide electrolyte, and organic solvent under sealed conditions for reaction, extracting the reaction product, and drying it to obtain the modified porous silicon composite negative electrode material.

2. The method according to claim 1, characterized in that It also includes one or more of the following technical features: A1, the mass ratio of the PEDOT:PSS aqueous solution to the lithium polyvinyl sulfonate aqueous solution is (1-3): 1; B1, the mass ratio of the dimethyl sulfoxide and the PEDOT:PSS aqueous solution is (3-6): 50; C1, the mass ratio of PEDOT to PSS in the PEDOT:PSS aqueous solution is 1: (2-8); D1, the concentration of the PEDOT:PSS aqueous solution is 0.8-2 wt.%; E1. The concentration of the lithium polyvinyl sulfonate aqueous solution is 3.5-10.5 wt.%.

3. The method according to claim 1, characterized in that The porous silicon is obtained by adding aluminum-silicon alloy powder to a hydrochloric acid aqueous solution at 0° C. to react for 4 to 10 hours, washing, extracting and drying the reaction product.

4. The method according to claim 3, characterized in that It also includes one or more of the following technical features: A2. The mass ratio of aluminum to silicon in the aluminum-silicon alloy powder is (5-7):4; B2. The concentration of the hydrochloric acid aqueous solution is 8-12 wt.%.

5. The method according to claim 1, wherein It also includes one or more of the following technical features: A3, the mass ratio of the modified porous silicon material and the sulfide electrolyte is (3-5): 1; B3. The usage ratio of the modified porous silicon material and the organic solvent is (0.8~1.2)g:10mL.

6. The method according to claim 1, characterized in that It also includes one or more of the following technical features: A4, the sulfide electrolyte is Li6PS5Cl; B4. The organic solvent is toluene.

7. The method according to claim 1, characterized in that It also includes one or more of the following technical features: In steps A5 and S1, the modification treatment is performed by magnetic stirring; B5. The composite conductive polymer is stirred and mixed by magnetic stirring; C5. The porous silicon is prepared by stirring and mixing by magnetic stirring; In steps D5 and S2, the modified porous silicon composite negative electrode material is prepared by performing a mixing reaction through ultrasonic treatment.

8. A modified porous silicon composite negative electrode material, characterized in that: It is prepared according to the method according to any one of claims 1 to 7.

9. Use of the modified porous silicon composite negative electrode material according to claim 8 in an all-solid-state battery.

10. The use according to claim 9, characterized in that It also includes one or more of the following technical features: A6. The negative electrode sheet in the battery is obtained by pressing the modified porous silicon composite negative electrode material; B6. The positive electrode sheet in the battery is formed by mixing and pressing a ternary positive electrode material, a sulfide solid electrolyte and a conductive agent; C6. The electrolyte sheet in the battery is formed by pressing a sulfide electrolyte material.

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