Silicon-carbon negative electrode material applied to sulfide solid-state battery and modification method of silicon-carbon negative electrode material

Abstract

The invention relates to a silicon-carbon negative electrode material applied to a sulfide solid-state battery, a modification method of the silicon-carbon negative electrode material, the sulfide solid-state battery and a preparation method of the sulfide solid-state battery. The modification method comprises the following steps: providing a porous silicon carbon material, and dispersing the porous silicon carbon material in pure water or absolute ethyl alcohol to obtain a solution A; adding a metal source into pure water, dropwise adding oxalic acid or an alkaline solution, and uniformly stirring to obtain a solution B; transferring the solution A into a water bath kettle for stirring, slowly dropwise adding the solution B until water is evaporated to dryness, and uniformly coating the surface of the silicon carbon material with the precursor material to obtain a coated material; and drying the coated material, heating and preserving heat in a nitrogen atmosphere, and converting the metal oxide precursor on the surface into a metal oxide to obtain the silicon-carbon negative electrode material. The lithium ion transport layer constructed in situ on the porous silicon carbon material avoids the addition of a solid electrolyte, improves the first discharge capacity and cycle stability of the battery, and has high capacity retention rate.

Description

Technical Field

[0001] The present invention relates to the technical field of sulfide solid-state battery materials, and particularly relates to a silicon-carbon negative electrode material for sulfide solid-state batteries and a modification method thereof. Background Art

[0002] In the preparation process of solid-state lithium batteries, silicon-carbon negative electrodes have broad application prospects due to their high theoretical specific capacity and high cycle stability compared to pure silicon. However, there are pores reserved for the volume expansion and contraction of silicon particles inside the silicon-carbon negative electrode material, resulting in poor internal ionic conductivity. When applied to all-solid-state batteries, since the solid electrolyte can only wrap around the outside of the silicon-carbon material, it will be more prominent in the solid-solid contact with the solid electrolyte, ultimately leading to the inability to exert the high-capacity advantage of the silicon-carbon negative electrode and poor cycle stability, severely restricting its practical application in solid-state batteries.

[0003] Prior Art 1 (Patent Application No.: 202110826580.X), a silicon-carbon solid-state battery and its preparation method. The present invention discloses a silicon-carbon solid-state battery, including a negative electrode sheet, a positive electrode sheet, and a sheet-shaped solid electrolyte between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet includes a silicon-carbon material and a solid electrolyte uniformly mixed with the silicon-carbon material; the positive electrode sheet includes a positive electrode material and a solid electrolyte uniformly mixed with the positive electrode material; wherein, the solid electrolytes distributed in the positive electrode sheet and the negative electrode sheet bond the positive electrode material and the silicon-carbon material into a whole respectively; the solid electrolyte is a gel solid electrolyte of the PVDF system; the present invention distributes the gel electrolyte in the active substances of the positive electrode sheet and the negative electrode sheet, and the gel electrolyte sheet is between the positive electrode sheet and the negative electrode sheet, effectively binding the silicon-carbon material and alleviating the deformation during the cycle.

[0004] Prior Art 2 (Patent Application No.: 202410691412.8) discloses a silicon-carbon negative electrode material, its preparation method, and an all-solid-state lithium-ion battery. The present invention provides a silicon-carbon negative electrode material, its preparation method, and an all-solid-state lithium battery, including a porous carbon skeleton and a plurality of composite silicon-based materials dispersed on the porous carbon skeleton. The composite silicon-based materials include silicon-based particles and a sulfide solid electrolyte layer coated on the surface of the silicon-based particles. By setting a sulfide solid electrolyte layer on the surface of the silicon particles inside the silicon-carbon material, the present invention can provide an ion conduction network for the silicon-based particles in the core, greatly improving the ionic conductivity of the obtained silicon-carbon negative electrode material, thereby enhancing its rate performance.

[0005] However, in the prior art 1, adding a solid electrolyte to the electrode reduces the proportion of the active material, making it difficult to exert the advantage of the high specific capacity of the silicon anode. The full text does not mention the specific capacity. In the case of low capacity, a high retention rate has little practical significance. In the prior art 2, the solid electrolyte is coated on the surface of the silicon-carbon material, and the ionic conductivity of the sulfide solid electrolyte used as the coating material often drops significantly.

[0006] Therefore, the prior art needs to be improved. Summary of the Invention

[0007] In the prior art, the high-capacity advantage of the silicon-carbon anode in solid-state batteries cannot be exerted, and the cycle stability is poor, seriously restricting its practical application in solid-state batteries. Therefore, the present application provides a silicon-carbon anode material for sulfide solid-state batteries and its modification method to solve the above problems.

[0008] To achieve the above object, in the first aspect, the present invention provides a modification method for a silicon-carbon anode material for sulfide solid-state batteries, which includes the following steps: S11. Provide a porous silicon-carbon material, disperse it in pure water or absolute ethanol to obtain solution A; S12. Add a metal source to pure water, dropwise add oxalic acid or an alkaline solution and stir evenly to obtain solution B; S13. Transfer the solution A to a water bath and stir, slowly dropwise add the solution B until the water is evaporated, and uniformly coat the precursor material on the surface of the silicon-carbon material to obtain the coated material; S14. After drying the coated material, heat and keep it warm in a nitrogen atmosphere to convert the metal oxide precursor on the surface into a metal oxide to obtain the silicon-carbon anode material; Wherein, in S12, the metal source is any one or a combination of aluminum nitrate, aluminum isopropoxide, aluminum sulfate, aluminum acetate, titanium tetrachloride, tetrabutyl titanate, isopropyl titanate, titanium isopropoxide, titanium sulfate, titanium oxysulfate, titanium trichloride, magnesium nitrate, magnesium chloride, magnesium sulfate, magnesium acetate, magnesium phosphate, zinc nitrate, zinc chloride, zinc sulfate, zinc acetate, zinc phosphate, ammonium vanadate, sodium vanadate, potassium vanadate, and the mass fraction of the metal source is 0.5-5 wt.% of the porous silicon-carbon material.

[0009] In one implementation, in S11, the mass fraction of the metal oxide in the silicon-carbon anode material after coating is 1%-20%.

[0010] In one implementation, in S11, a dispersant can also be added, and the dispersant is sodium dodecylbenzenesulfonate or polyvinylpyrrolidone.

[0011] In one implementation, in S12, the alkaline solution includes any one of sodium hydroxide, potassium hydroxide, aqueous lithium hydride solution, and ammonia water, and its concentration ranges from 0.1 to 5 g / ml.

[0012] In one implementation, in S13, the temperature of the water bath is 50 to 100 °C.

[0013] In one implementation, in S14, the heating temperature is 300 to 600 °C, and the heat preservation time is 2 to 5 h.

[0014] In a second aspect, the present invention also provides a silicon-carbon anode material for a sulfide solid-state battery, which is made by the modification method of the silicon-carbon anode material for a sulfide solid-state battery described in any one of the above.

[0015] In a third aspect, the present invention also provides a sulfide solid-state battery, which includes a negative electrode, and the negative electrode includes the above-mentioned silicon-carbon anode material for a sulfide solid-state battery.

[0016] In one implementation, the negative electrode further includes conductive carbon black, a binder, a sulfide solid-state electrolyte, a lithium sheet, and an indium sheet. Among them, the mass fraction ratio of the silicon-carbon anode material, conductive carbon black, and binder is (50% - 80%):(10% - 20%):(5% - 10%).

[0017] In a fourth aspect, the present invention also provides a preparation method for a sulfide solid-state battery, which is characterized in that it is used to prepare the sulfide solid-state battery described in any one of claims 1 to 9, and specifically includes: S21. Weigh the anode material, conductive carbon black, and binder in proportion, and add deionized water to mix them into a uniform slurry; S22. Use a homogenizer to fully mix the materials evenly; after passing the slurry through a sieve, coat it evenly on a copper foil and dry it in a vacuum drying oven at 90 °C; S23. After the dried electrode sheet is roll-pressed, it is cut into electrode pieces; S24. Cold-press the sulfide solid-state electrolyte into a mold; S25. Attach the electrode sheet to one side of the sulfide solid-state electrolyte, and cold-press to make the electrode sheet and the sulfide solid-state electrolyte closely combined; S26. Attach the lithium sheet and the indium sheet to the other side of the sulfide solid-state electrolyte respectively, add a current collector, and cold-press to make the lithium sheet and the indium sheet closely combined and in close contact with the sulfide solid-state electrolyte to obtain a negative electrode; S27. Provide a sulfide solid-state electrolyte and a positive electrode, and assemble them with the negative electrode to obtain the sulfide solid-state battery; Wherein the positive electrode is lithium iron phosphate (LiFePO4) or nickel cobalt manganese oxide (NCM).

[0018] Beneficial effects: In this application, by coating the surface of the porous silicon-carbon material with an oxide, the coating is carried out using a solution method and under a water bath condition, and finally converted into a metal oxide through heat treatment. Among them, the carbon skeleton in the porous silicon-carbon material can enhance the conductivity of the material and accommodate the volume expansion of silicon, and the nano-silicon particles have good cycle stability; coating the porous silicon-carbon material with an electron-insulating and ion-conductive metal oxide can reduce the formation of dendrites, and at the same time reduce the direct contact between the electrolyte and silicon, restricting the expansion of silicon during charging. The present invention avoids the addition of a solid electrolyte by in-situ constructing a lithium-ion transport layer on the porous silicon-carbon material, improves the initial discharge capacity and cycle stability of the battery, and has a high capacity retention rate. Description of the Drawings

[0019] Figure 1 is a flowchart of the steps of a method for modifying a silicon-carbon negative electrode material applied to a sulfide solid-state battery provided by the present invention; Figure 2 is a flowchart of the steps of a method for preparing a sulfide solid-state battery provided by the present invention; Figure 3 is a 0.33C cycle performance comparison chart of a sulfide solid-state battery provided by some embodiments of the present invention; Figure 4 is a rate performance chart of a sulfide solid-state battery provided by some embodiments of the present invention; Figure 5 is a transmission electron microscope (TEM) image of a sulfide solid-state battery provided by some embodiments of the present invention.

[0020] The realization, functional features, and advantages of the object of the present invention will be further described with reference to the embodiments and the accompanying drawings. Detailed Embodiments

[0021] In order to make the object, technical solution, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention. In addition, the descriptions of the above terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms are not necessarily directed to the same embodiment or example. Moreover, the technical features involved in various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0022] Specifically refer to Figure 1 , Figure 1It is a process flow diagram of a modification method for a silicon-carbon anode material applied to a sulfide solid-state battery provided by the present invention. The present invention provides a modification method for a silicon-carbon anode material applied to a sulfide solid-state battery, which includes the following steps: S11. Provide a porous silicon-carbon material, disperse it in pure water or absolute ethanol to obtain solution A; S12. Add a metal source to pure water, dropwise add oxalic acid or an alkaline solution and stir evenly to obtain solution B; S13. Transfer the solution A to a water bath for stirring, slowly dropwise add the solution B until the water is evaporated, and uniformly coat the precursor material on the surface of the silicon-carbon material to obtain the coated material; S14. After drying the coated material, heat and keep it warm in a nitrogen atmosphere to convert the metal oxide precursor on the surface into a metal oxide to obtain the silicon-carbon anode material; Among them, in S12, the metal source is any one or a combination of aluminum nitrate, aluminum isopropoxide, aluminum sulfate, aluminum acetate, titanium tetrachloride, tetrabutyl titanate, isopropyl titanate, titanium isopropoxide, titanium sulfate, titanium oxysulfate, titanium trichloride, magnesium nitrate, magnesium chloride, magnesium sulfate, magnesium acetate, magnesium phosphate, zinc nitrate, zinc chloride, zinc sulfate, zinc acetate, zinc phosphate, ammonium vanadate, sodium vanadate, potassium vanadate, and the mass fraction of the metal source is 0.5-5 wt.% of the porous silicon-carbon material.

[0023] In this application, by providing a porous silicon-carbon material, the specific surface area of the material can be increased, thereby improving the energy density and cycle stability of the battery. By adding a metal source to form a metal oxide on the surface, the conductivity, stability of the electrode material and the interfacial compatibility with the sulfide solid electrolyte can be improved. By uniformly coating the metal oxide on the surface of the silicon-carbon material, it helps to improve the electrochemical performance of the battery, reduce the swelling problem of silicon, and improve the cycle life.

[0024] Specifically, in S11, the mass fraction of the metal oxide in the silicon-carbon anode material after coating is 1%-20%. In S11, a dispersant can also be added, and the dispersant is sodium dodecylbenzenesulfonate or polyvinylpyrrolidone. By adding the dispersant, the dispersibility of the silicon-carbon material in the solution can be improved, ensuring that the metal source is evenly attached to the surface of the silicon-carbon material, avoiding agglomeration or precipitation, and helping the subsequent coating treatment and uniform coating of the electrode material, further improving the battery performance.

[0025] Specifically, in S12, the alkaline solution includes any one of sodium hydroxide, potassium hydroxide, aqueous lithium hydride solution, and ammonia water, and its concentration ranges from 0.1 to 5 g / ml. As a solvent, the alkaline solution can adjust the reaction conditions, promote the reaction between the metal source and the silicon-carbon material, and help form a metal oxide coating layer. When using alkaline solutions such as sodium hydroxide and potassium hydroxide, it can help adjust the reaction rate and reaction pathway, thereby controlling the structure and thickness of the metal oxide coating layer. Oxalic acid has a strong chelating effect and can form stable chelates or complexes with metal ions, which helps keep the metal ions stable in the solution, thus avoiding premature precipitation of metal ions or unwanted reactions with other components. Oxalic acid can optimize the deposition conditions of the metal precursor and promote the uniform coating of the metal oxide on the surface of the silicon-carbon material.

[0026] Specifically, in S13, the temperature of the water bath is 50 to 100 °C. By setting the temperature of the water bath at 50 to 100 °C, the evaporation rate of the solution can be effectively controlled, avoiding damage to the material or non-uniform formation of metal oxides at too high temperatures. In addition, it also helps with the uniform coating of the precursor material, ensuring that the metal oxide adheres uniformly to the silicon-carbon surface.

[0027] Specifically, in S14, the heating temperature is 300 to 600 °C, and the heat preservation time is 2 to 5 h. Through high-temperature treatment, not only can the formation of metal oxides be promoted, but also the mechanical stability of the silicon-carbon material can be enhanced, thereby improving the durability and cycling performance of the battery.

[0028] In the modification method of the silicon-carbon negative electrode material applied to the sulfide solid-state battery provided by the present invention, the process flow can be simplified, which is suitable for large-scale production and cost reduction. The direct metal oxide coating layer provides good chemical stability and mechanical strength, and optimizes the ion conduction path. In addition, it can also adapt to a specific electrolyte environment and reduce unnecessary side reactions.

[0029] Specifically refer to Figure 2 , Figure 2 which is the step flow chart of the preparation method of the sulfide solid-state battery provided by the present invention. The present invention also provides a sulfide solid-state battery, which includes a negative electrode, and the negative electrode includes the silicon-carbon negative electrode material applied to the sulfide solid-state battery provided by the present invention. The negative electrode also includes conductive carbon black, binder, sulfide solid electrolyte, lithium sheet, and indium sheet. Among them, the mass fraction ratio of the silicon-carbon negative electrode material, conductive carbon black, and binder is (50% - 80%):(10% - 20%):(5% - 10%). By adding materials such as conductive carbon black and binder to the negative electrode, the conductivity and adhesiveness of the negative electrode can be improved, ensuring the high-efficiency performance of the battery.

[0030] The preparation method of the sulfide solid-state battery provided by the present invention specifically includes: S21. Weigh the anode material, conductive carbon black, and binder proportionally, add deionized water, and mix them into a homogeneous slurry. S22. Use a homogenizer to fully mix the materials evenly; after passing the slurry through a sieve, coat it evenly on the copper foil and dry it in a vacuum drying oven at 90 °C. S23. After rolling the dried electrode sheet, cut it into electrode pieces. S24. Cold-press the sulfide solid electrolyte into a mold. S25. Attach the electrode piece to one side of the sulfide solid electrolyte and cold-press to tightly bond the electrode piece and the sulfide solid electrolyte. S26. Attach a lithium sheet and an indium sheet to the other side of the sulfide solid electrolyte respectively, add a current collector, and cold-press to tightly bond the lithium sheet and the indium sheet and make them in close contact with the sulfide solid electrolyte to obtain the anode. S27. Provide a sulfide solid electrolyte and a cathode, and assemble them with the anode to obtain the sulfide solid-state battery. Wherein the cathode is lithium iron phosphate (LiFePO4) or nickel cobalt manganese oxide (NCM).

[0031] Preferably, the sulfide solid electrolyte includes any one of Li6PS5Cl, Li6PS5I (lithium thiophosphate electrolyte), and Li 10 GeP2S 12 among them.

[0032] Example 1 S11. Disperse 10 g of porous silicon carbon in 300 ml of ultrapure water, then add 0.1 g of sodium dodecylbenzenesulfonate, and continue stirring for 2 h to prepare solution A. S12. Add 0.1 g of aluminum nitrate and 2 g of oxalic acid to 50 ml of ultrapure water and stir for 15 min to obtain a well-mixed solution B. S13. Transfer solution A to a water bath at 80 °C and stir, and gradually add solution B drop by drop using a separatory funnel. Let the two react fully until the water is evaporated, and then perform a drying treatment. S14. Heat the dried material to 500 °C in a nitrogen atmosphere and hold for 3 h to convert the metal oxide precursor on the surface into alumina, obtaining an alumina-coated silicon carbon anode material.

[0033] Example 2 S11. Disperse 10 g of porous silicon carbon in 300 ml of absolute ethanol to prepare solution A. S12. Provide 10 ml of 3 wt.% tetrabutyl titanate as solution B, and the tetrabutyl titanate accounts for 3% of the mass of the silicon carbon material. S13. Transfer solution A to a water bath at 80 °C and stir, then dropwise add solution B using a separatory funnel. Let the two react fully until the water is completely evaporated, and then conduct a drying treatment. S14. Heat the coated material to 700 °C in a nitrogen atmosphere and hold for 3 h to convert the metal oxide precursor on the surface into titanium dioxide, obtaining a silicon-carbon anode material coated with titanium dioxide.

[0034] Example 3 S11. Add 10 g of porous silicon-carbon to 300 ml of absolute ethanol for dispersion to prepare solution A. S12. Provide 10 ml of 3 wt.% magnesium nitrate as solution B, and dropwise add 3 ml of 3% sodium hydroxide aqueous solution (0.1 g / ml). Here, the concentration of the sodium hydroxide aqueous solution is 0.1 g / ml, and the magnesium nitrate accounts for 3% of the mass of the silicon-carbon material. S13. Transfer solution A to a water bath at 80 °C and stir, then dropwise add solution B using a separatory funnel. Let the two react fully until the water is completely evaporated, and then conduct a drying treatment. S14. Heat the coated material to 500 °C in a nitrogen atmosphere and hold for 3 h to convert the metal oxide precursor on the surface into magnesium oxide, obtaining a silicon-carbon anode material coated with magnesium oxide.

[0035] Example 4 S11. Add 10 g of porous silicon-carbon to 300 ml of absolute ethanol for dispersion to prepare solution A. S12. Provide 10 ml of 3 wt.% zinc nitrate as solution B, and dropwise add 3 ml of 3% sodium hydroxide aqueous solution (0.1 g / ml). Here, the concentration of the sodium hydroxide aqueous solution is 0.1 g / ml, and the zinc nitrate accounts for 3% of the mass of the silicon-carbon material. S13. Transfer solution A to a water bath at 80 °C and stir, then dropwise add solution B using a separatory funnel. Let the two react fully until the water is completely evaporated, and then conduct a drying treatment. S14. Heat the coated material to 500 °C in a nitrogen atmosphere and hold for 3 h to convert the metal oxide precursor on the surface into zinc oxide, obtaining a silicon-carbon anode material coated with zinc oxide.

[0036] Example 5 S11. Add 10 g of porous silicon-carbon to 300 ml of absolute ethanol for dispersion to prepare solution A. S12. Provide 10 ml of 3 wt.% ammonium vanadate as solution B, and dropwise add 3 ml of 3% sodium hydroxide aqueous solution (0.1 g / ml). Here, the concentration of the sodium hydroxide aqueous solution is 0.1 g / ml, and the ammonium vanadate accounts for 3% of the mass of the silicon-carbon material. S13. Transfer solution A to a water bath at 80 °C and stir. Then, dropwise add solution B using a separatory funnel. Let the two react fully until the water is completely evaporated, and then conduct a drying treatment. S14. Heat the coated material to 500 °C in a nitrogen atmosphere and hold for 3 h to convert the metal oxide precursor on the surface into lithium vanadate, obtaining a silicon-carbon negative electrode material coated with lithium vanadate.

[0037] Example 6 S11. Add 10 g of porous silicon-carbon to 300 ml of absolute ethanol for dispersion to prepare solution A. S12. Provide 10 ml of 3 wt.% tin sulfate as solution B, and dropwise add 3 ml of 3% sodium hydroxide aqueous solution (0.1 g / ml). Here, the concentration of the sodium hydroxide aqueous solution is 0.1 g / ml, and the ammonium vanadate accounts for 3% of the mass of the silicon-carbon material. S13. Transfer solution A to a water bath at 80 °C and stir. Then, dropwise add solution B using a separatory funnel. Let the two react fully until the water is completely evaporated, and then conduct a drying treatment. S14. Heat the coated material to 500 °C in a nitrogen atmosphere and hold for 3 h to convert the metal oxide precursor on the surface into tin oxide, obtaining a silicon-carbon negative electrode material coated with tin oxide.

[0038] Comparative Example 1 The uncoated porous silicon-carbon material in the above examples.

[0039] Prepare a sulfide solid-state battery using the provided silicon-carbon negative electrode material and conduct an electrochemical performance test: The preparation of the sulfide solid-state battery specifically includes: S21. Provide 70 g of silicon-carbon negative electrode material, 15 g of conductive carbon black, and 8 g of binder CMC, and add deionized water to mix into a uniform slurry. S22. Use a homogenizer to fully mix the materials evenly; after passing the slurry through a sieve, uniformly coat it on a copper foil and dry it in a vacuum drying oven at 90 °C. S23. After rolling the dried electrode sheet, cut it into electrode pieces. S24. Cold-press the sulfide solid-state electrolyte into a mold. S25. Attach the electrode piece to one side of the sulfide solid-state electrolyte and cold-press to tightly bond the electrode piece and the sulfide solid-state electrolyte. S26. Attach a lithium sheet and an indium sheet to the other side of the sulfide solid-state electrolyte respectively, add a current collector, and cold-press to tightly bond the lithium sheet, indium sheet and make them in close contact with the sulfide solid-state electrolyte to obtain a negative electrode. S27. Provide a sulfide solid electrolyte and a positive electrode lithium iron phosphate, assemble them with the negative electrode to obtain the sulfide solid-state battery, and tighten the screws to ensure the external pressure for the operation of the solid-state battery.

[0040] Among them, the electrolyte in step S24 is a Li2S-P2S5 electrolyte, which has a high ionic conductivity and can be formed into a sheet at low temperature. The electrolyte in step S27 is a Li7P3S11 electrolyte, which has a high conductivity and better chemical stability near the lithium metal negative electrode, and is suitable for improving the safety of the battery during long-term use.

[0041] Test parameters: The cyclic test uses a current density of 0.33C, and the rate test uses 0.1, 0.2, 0.5, 0.8, 1, 0.1C.

[0042] The test results are shown in Table 1 and Table 2.

[0043] Table 1: Cyclic performance test results of Examples 1-2 and Comparative Example 1.

[0044] Table 2: Rate performance test results of Examples 1-2 and Comparative Example 1.

[0045] According to Table 1 and Figure 3 , where Figure 3 is a 0.33C cyclic performance comparison chart of the sulfide solid-state battery provided by some embodiments of the present invention. It can be seen that for the silicon-carbon negative electrode material coated with titanium dioxide provided in Example 2, the initial reversible capacity is 1460 mAh / g, the first Coulombic efficiency is 80.45%, and after 100 cycles, the capacity retention rate is 74.5%, showing relatively excellent cyclic performance.

[0046] According to Table 2 and Figure 4 , where Figure 4 is a rate performance chart of the sulfide solid-state battery provided by some embodiments of the present invention. It can be seen that for the silicon-carbon negative electrode material coated with titanium dioxide provided in Example 2, the initial reversible capacity at 0.1C is 1446 mAh / g, at a current density of 1C, the reversible capacity is 919 mAh / g, and the capacity retention rate is 63.57%, which is about 20% higher than that of the comparative example, showing relatively excellent 1C retention rate.

[0047] Through Figure 5 the transmission electron microscope (TEM) image of the sulfide solid-state battery provided by some embodiments of the present invention, it can be seen that the oxide is successfully coated on the surface of the silicon-carbon negative electrode, and the thickness of the coating layer is about 2 nm.

[0048] In summary, in the present application, by coating an oxide on the surface of the porous silicon-carbon material, the coating is carried out using a solution method and under water bath conditions, and finally converted into a metal oxide through heat treatment. Among them, the carbon skeleton in the porous silicon-carbon material can enhance the conductivity of the material and accommodate the volume expansion of silicon, and the nano-silicon particles have good cycle stability; coating the porous silicon-carbon material with a metal oxide that is electronically insulating and ion-conductive can reduce the formation of dendrites, while reducing the direct contact between the electrolyte and silicon and restricting the expansion of silicon during charging. The present invention avoids the addition of a solid electrolyte by in-situ constructing a lithium-ion transport layer on the porous silicon-carbon material, improves the initial discharge capacity and cycle stability of the battery, and has a high capacity retention rate.

[0049] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. A method for modifying a silicon-carbon negative electrode material for a sulfide solid-state battery, characterized in that: The following steps are involved: S11, providing a porous silicon-carbon material, and dispersing the material in pure water or anhydrous ethanol to obtain a solution A; S12, adding a metal source into pure water, adding dropwise oxalic acid or an alkaline solution and stirring evenly to obtain a solution B; S13, transferring the solution A to a water bath for stirring, slowly adding the solution B dropwise until the water is evaporated to dryness, and uniformly coating the precursor material on the surface of the silicon-carbon material to obtain a coated material; S14, drying the coated material, heating and keeping warm in a nitrogen atmosphere to convert the metal oxide precursor on the surface into metal oxide, thereby obtaining the silicon-carbon negative electrode material; Among them, in S12, the metal source is any one of aluminum nitrate, aluminum isopropoxide, aluminum sulfate, aluminum acetate, titanium tetrachloride, tetrabutyl titanate, isopropyl titanate, titanium isopropoxide, titanium sulfate, titanium oxysulfate, titanium trichloride, magnesium nitrate, magnesium chloride, magnesium sulfate, magnesium acetate, magnesium phosphate, zinc nitrate, zinc chloride, zinc sulfate, zinc acetate, zinc phosphate, ammonium vanadate, sodium vanadate, and potassium vanadate, or a combination thereof, and the mass fraction of the metal source is 0.5~5wt.% of the porous silicon-carbon material.

2. The method for modifying the silicon-carbon negative electrode material for sulfide solid-state batteries according to claim 1, characterized in that: In S11, the mass fraction of the metal oxide in the silicon-carbon negative electrode material after coating is 1% to 20%.

3. The method for modifying the silicon-carbon negative electrode material for sulfide solid-state batteries according to claim 1, characterized in that: In S11, a dispersant may be added, and the dispersant may be sodium dodecylbenzenesulfonate or polyvinyl pyrrolidone.

4. The method for modifying the silicon-carbon negative electrode material for sulfide solid-state batteries according to claim 1, characterized in that: In S12, the alkaline solution includes any one of sodium hydroxide, potassium hydroxide, lithium hydride aqueous solution and ammonia water, and the concentration range of the alkaline solution is 0.1-5 g / ml.

5. The method for modifying the silicon-carbon negative electrode material for sulfide solid-state batteries according to claim 1, characterized in that: In S13, the temperature of the water bath is 50-100°C.

6. The method for modifying the silicon-carbon negative electrode material for sulfide solid-state batteries according to claim 1, characterized in that: In S14, the heating temperature is 300-600°C and the insulation time is 2-5h.

7. A silicon-carbon negative electrode material for sulfide solid-state batteries, characterized in that: It is made by the modification method of the silicon-carbon negative electrode material used in sulfide solid-state batteries according to any one of claims 1 to 6.

8. A sulfide solid-state battery, characterized in that: It comprises a negative electrode, wherein the negative electrode comprises the silicon-carbon negative electrode material for sulfide solid-state batteries as claimed in claim 7.

9. The sulfide solid-state battery according to claim 8, characterized in that: The negative electrode also includes conductive carbon black, a binder, a sulfide solid electrolyte, a lithium sheet and an indium sheet, wherein the mass fraction ratio of the silicon-carbon negative electrode material, the conductive carbon black and the binder is (50%~80%): (10%~20%): (5%~10%).

10. A method for preparing a sulfide solid-state battery, characterized in that: Used to prepare the sulfide solid-state battery according to any one of claims 1 to 9, specifically comprising: S21, weighing the negative electrode material, conductive carbon black and binder in proportion, adding deionized water and mixing into a uniform slurry; S22, using a homogenizer to fully mix the materials; after sieving the slurry, evenly apply it on the copper foil, and dry it in a vacuum drying oven at 90°C; S23, the dried electrode sheet is rolled and cut into electrode sheets; S24, cold-pressing the sulfide solid electrolyte into a mold; S25, attaching the electrode sheet to one side of the sulfide solid electrolyte, and cold pressing to tightly combine the electrode sheet and the sulfide solid electrolyte; S26, attaching a lithium sheet and an indium sheet to the other side of the sulfide solid electrolyte respectively, adding a current collector, and cold pressing to make the lithium sheet and the indium sheet tightly combined and in close contact with the sulfide solid electrolyte to obtain a negative electrode; S27, providing a sulfide solid electrolyte and a positive electrode, and assembling them with the negative electrode to obtain the sulfide solid-state battery; The positive electrode is lithium iron phosphate or nickel cobalt manganese oxide.

Images