Negative electrode material, preparation method thereof and battery

Abstract

The invention relates to the technical field of batteries, in particular to a negative electrode material, a preparation method thereof and a battery. The negative electrode material comprises a silicon nano material; the metal silicide layer at least partially coats the surface of the silicon nano material; the nitrogen and sulfur doped carbon layer at least partially coats the surface of the metal silicide; and the thickness of the metal silicide layer is greater than that of the nitrogen and sulfur doped carbon layer. According to the negative electrode material, the preparation method thereof and the battery provided by the invention, the coating structure of the negative electrode material is optimized, and the metal silicide / heteroatom doped carbon double-layer coated silicon nano material can be prepared by adopting a synthesis method which is low in energy consumption and capable of constructing a functional multi-layer coating structure, so that the long cycle life and the high-rate fast charging performance can be considered at the same time.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to negative electrode materials, their preparation methods, and batteries. Background Technology

[0002] Silicon-based materials are considered an important development direction for lithium-ion battery anode materials due to their high theoretical specific capacity (4200 mAh / g). However, their practical application is limited by problems such as volume expansion (expansion rate >300% during cycling), poor conductivity, and instability of the SEI film. To address these issues, in existing technologies, the introduction of metal silicides is believed to improve rate performance and cycle life by enhancing electronic conductivity and mitigating the volume expansion of silicon.

[0003] Currently, metal silicides are typically synthesized using a high-temperature solid-state reaction method, which involves mixing silicon powder and metal powder in a certain proportion and then subjecting them to high-temperature heat treatment. The reaction temperature can reach as high as 1200℃~1600℃, resulting in high energy consumption during production. Furthermore, while metal silicides have good electronic conductivity, they have poor ionic conductivity. In addition, there is room for further improvement in the compatibility of metal silicides with electrolytes.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] To address the issues of high energy consumption, difficulty in achieving both electronic and ionic conductivity, and poor compatibility with electrolytes in the production of metal silicide-silicon anode materials, this invention provides an anode material, its preparation method, and a battery, thereby obtaining a silicon-based anode material with low energy consumption and excellent cycle and fast-charging performance.

[0006] Based on this, the present invention has the following technical solution: In a first aspect, the present invention provides an anode material comprising: a silicon nanomaterial; a metal silicide layer at least partially coated on the surface of the silicon nanomaterial; and a nitrogen-sulfur-doped carbon layer at least partially coated on the surface of the metal silicide layer; wherein the thickness of the metal silicide layer is greater than the thickness of the nitrogen-sulfur-doped carbon layer.

[0007] This invention discovers that by at least partially coating the surface of a metal silicide layer with a nitrogen-sulfur-doped carbon layer of the aforementioned thickness, the synergistic effect of the metal silicide layer and the nitrogen-sulfur-doped carbon layer can be achieved, simultaneously enhancing the electronic and ionic conductivity of the material. This allows the battery to maintain high capacity and efficiency during high-rate charge-discharge (such as fast charging). Simultaneously, the metal silicide layer can suppress the expansion of silicon nanomaterials during charge-discharge, while the nitrogen-sulfur-doped carbon layer helps improve the compatibility of the material with the electrolyte, forming a more stable SEI film.

[0008] In this invention, "at least partially covered" can be understood as: partial or complete coverage. Whether it is partial or complete coverage, the thickness of the metal silicide layer and the thickness of the nitrogen-sulfur-doped carbon layer are calculated by independently measuring the thickness of multiple points on the corresponding layer structure, thereby calculating the average thickness of the layer. The thickness ratio of the metal silicide layer to the nitrogen-sulfur-doped carbon layer is the ratio of their average thicknesses.

[0009] Preferably, in the negative electrode material provided by the present invention, the thickness of the nitrogen-sulfur-doped carbon layer is 10 nm to 30 nm, for example, it can be any value among 10 nm, 15 nm, 20 nm, 25 nm, and 30 nm, or a range of values ​​with any two values ​​as endpoints. When the thickness of the nitrogen-sulfur-doped carbon layer is too large, its electron transport resistance increases, leading to a decrease in the specific capacity of the negative electrode material, thereby reducing the energy density of the battery. When the thickness of the nitrogen-sulfur-doped carbon layer is too small, it cannot adequately isolate the contact between the electrolyte and the metal silicide layer, resulting in uneven growth of the SEI film, increased interfacial impedance, decreased cycle stability of the negative electrode material, and thus reduced cycle performance of the battery.

[0010] More preferably, the thickness ratio of the metal silicide layer to the nitrogen-sulfur-doped carbon layer is (1.5~5):1, for example, it can be any value among 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0, 4.5:1, and 5.0:1, or a range of values ​​with any two values ​​as endpoints. If the thickness of the metal silicide layer is too large, it will lose elasticity due to increased rigidity and will not be able to effectively buffer the mechanical stress during cycling, leading to the pulverization of the active material. If the thickness of the metal silicide layer is too small, it will also not be able to effectively buffer the volume changes during lithium ion insertion / extraction, causing the active material to pulverize and the electrode structure to be damaged.

[0011] According to the negative electrode material provided by the present invention, the nitrogen content in the nitrogen-sulfur-doped carbon layer is 3.5% to 12%, for example, it can be any value from 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.5%, 12.0%, or a range of values ​​with any two values ​​as endpoints. If the nitrogen content in the nitrogen-sulfur-doped carbon layer is too high, it will lead to a decrease in the structural stability of the carbon layer, resulting in damage during cycling. If the nitrogen content in the nitrogen-sulfur-doped carbon layer is too low, it will not be able to effectively improve the electronic conductivity of the carbon layer.

[0012] According to the negative electrode material provided by the present invention, the sulfur content in the nitrogen-sulfur-doped carbon layer is 2% to 8.5%, for example, it can be any value from 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, or a range of values ​​with any two values ​​as endpoints. If the sulfur content in the nitrogen-sulfur-doped carbon layer is too high, it will lead to a decrease in the structural stability of the carbon layer, resulting in damage during cycling. If the sulfur content in the nitrogen-sulfur-doped carbon layer is too low, it will not be able to effectively improve the lithium-ion diffusion rate of the carbon layer.

[0013] According to the present invention, the silicon nanomaterial can be a structure such as silicon particles, porous silicon material, silicon nanowire, or silicon thin film. Preferably, the silicon nanomaterial is made of silicon particles.

[0014] According to the present invention, the silicon nanomaterial has a particle size D50 of 200nm to 800nm. The particle size D50 can be any value among 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, and 800nm, or a range of values ​​where any two values ​​are endpoints.

[0015] According to the present invention, the thickness of the metal silicide layer is 20nm to 80nm, for example, it can be any value among 20nm, 30nm, 40nm, 50nm, 60nm, 70nm and 80nm, or any two of the values ​​are the endpoints of the range.

[0016] According to the present invention, the metal silicide layer is made of one or more of the following materials: Cu3Si, Cu5Si, FeSi2, FeSi, Fe3Si2, Ni2Si, and CoSi2.

[0017] According to the present invention, the nitrogen-sulfur doped carbon layer is formed by high-temperature carbonization of a mixture of nitrogen-containing carbon source and sulfur source at 400℃~600℃. High-temperature carbonization is carried out at 400℃~600℃, where the temperature can be any value among 400℃, 450℃, 500℃, 550℃ or 600℃, or a range of values ​​with any two values ​​as endpoints.

[0018] According to the present invention, the nitrogen-containing carbon source comprises one or more combinations of polyvinylpyrrolidone, polyacrylonitrile, and polypyrrole. When the selected nitrogen-containing carbon source is used to form the nitrogen-sulfur-doped carbon layer, it is more conducive to the formation of a relatively ordered and uniform carbon layer structure in the anode material compared with other substances, thereby obtaining a better lithium-ion migration path.

[0019] According to the present invention, the sulfur source comprises one or more combinations of thiourea, p-toluene disulfide, and sodium thiosulfate. When the selected sulfur source is used to form the nitrogen-sulfur-doped carbon layer, it exhibits better reaction controllability compared to other substances.

[0020] According to the method for preparing the negative electrode material provided by the present invention, the mass ratio of the nitrogen-containing carbon source to the sulfur source is (3~5):(1~2); for example, it can be any ratio among 3:1, 3:1.5, 4:1, 4:2, 5:1, or 5:2, or a range with any two of these ratios as endpoints. If the proportion of the nitrogen-containing carbon source is too high, it is detrimental to the rate performance of the negative electrode material; if the proportion is too low, it is detrimental to the cycle stability of the negative electrode material.

[0021] Secondly, the present invention provides a method for preparing a negative electrode material, comprising coating the surface of the silicon nanomaterial with a metal silicide layer using a solvothermal method.

[0022] According to the method for preparing the negative electrode material provided by the present invention, the solvothermal method includes: mixing silicon nanomaterials, metal halide and a first solvent to obtain a suspension; and then heating the suspension at 5×10⁻⁶ ℃. -6 MPa ~2×10 -5 The reaction was carried out at MPa and 400℃~600℃ and kept at this temperature for 0.5h~3h to obtain the first precursor.

[0023] The pressure and temperature during the preparation of the first precursor are related to the quality and thickness of the metal silicide layer of the first precursor. Within the above-mentioned preferred range, it is more conducive to obtaining a negative electrode material with good cycle stability.

[0024] The suspension is at 5×10 -6 MPa ~2×10 -5 The reaction is carried out at MPa and 400℃~600℃, and held at this temperature for 0.5h~3h, wherein the pressure can be, for example, 5×10 MPa. -6 MPa, 6×10 -6 MPa, 7×10 -6 MPa, 8×10 -6 MPa, 9×10 -6 MPa, 10×10 -6MPa, 1.1×10 -5 MPa, 1.2×10 -5 MPa, 1.3×10 -5 MPa, 1.4×10 -5 MPa, 1.5×10 -5 MPa, 1.6×10 - 5 MPa, 1.7×10 -5 MPa, 1.8×10 -5 MPa, 1.9×10 -5 MPa, 2×10 -5 The temperature can be any value in MPa, or a range of values ​​with any two values ​​as endpoints. The temperature can be any value in 400℃, 450℃, 500℃, 550℃, and 600℃, or a range of values ​​with any two values ​​as endpoints. The time can be any value in 0.5h, 1h, 1.5h, 2h, 2.5h, and 3h, or a range of values ​​with any two values ​​as endpoints.

[0025] According to the method for preparing the negative electrode material provided by the present invention, the mass ratio of the metal halide to the silicon nanomaterial is 1:(1.2~2.2), for example, it can be any ratio among 1:1.2, 1:1.5, 1:1.8, 1:2.0 or 1:2.2, or a range with any two of these ratios as endpoints. A mass ratio of the metal halide to the silicon nanomaterial within the above range is more conducive to the formation of a suitable metal silicide layer in the negative electrode material.

[0026] According to the method for preparing the negative electrode material provided by the present invention, the metal halide is selected from one or a combination of two or more of cupric chloride, cuprous chloride, ferric chloride, ferrous chloride, nickel chloride, and cobalt chloride. When the selected metal halide is used to form the first precursor, it is more beneficial to improve the cycle stability of the negative electrode material compared with other substances.

[0027] The method for preparing the negative electrode material according to the present invention further includes: mixing the first precursor, a nitrogen-containing carbon source, a sulfur source, and a second solvent, coating an organic material at 45°C to 65°C, and drying to obtain a second precursor; and carbonizing the second precursor at 400°C to 600°C under an inert atmosphere.

[0028] The process involves coating organic matter at a temperature between 45°C and 65°C, where the temperature can be any value among 45°C, 50°C, 55°C, 60°C, or 65°C, or a range of values ​​with any two values ​​as endpoints. If the temperature is too low, it is detrimental to improving the coating efficiency; if the temperature is too high, it is detrimental to improving the uniformity of the coating.

[0029] The second precursor undergoes high-temperature carbonization at 400℃~600℃, where the temperature can be any value among 400℃, 450℃, 500℃, 550℃, or 600℃, or a range of values ​​with any two values ​​as endpoints. If the temperature is too low, it is not conducive to the carbonization of the organic layer; if the temperature is too high, it is not conducive to obtaining a suitable nitrogen and sulfur content in the carbon layer.

[0030] According to the method for preparing the negative electrode material provided by the present invention, the mass ratio of the mixture of nitrogen-containing carbon source and sulfur source to the first precursor is (4~7):(4.5~10), for example, it can be any ratio among 4:4.5, 4:6, 5:7, 6:8, 7:9 or 7:10, or a range with any two of these ratios as endpoints. If the mass proportion of the first precursor is too high, the first precursor cannot be uniformly coated; if the mass proportion of the first precursor is too low, the coating layer will be too thick.

[0031] According to the method for preparing the negative electrode material provided by the present invention, the preparation method includes the following steps: S1: Dissolve the metal halide in a first solvent to obtain a metal halide solution; then disperse the silicon nanomaterial in the metal halide solution to obtain a suspension; The suspension was subjected to 5×10 -6 MPa ~2×10 -5 The reaction was carried out at 400℃~600℃ under MPa, with the temperature increased by 5~10℃ / min, and held at the temperature for 0.5h~3h; after the reaction was completed, the product was centrifuged, washed and dried to obtain the first precursor. S2: Dissolve a nitrogen-containing carbon source and a sulfur source in a second solvent to obtain a nitrogen-containing carbon source / sulfur source solution; then disperse the first precursor in the nitrogen-containing carbon source / sulfur source solution, and stir to coat the organic matter at 45℃~65℃, and dry to obtain the second precursor; Under an inert atmosphere, the second precursor is heated to 400℃~600℃ at a rate of 5~10℃ / min for high-temperature carbonization and held at that temperature for 2h~4h. The mass ratio of the nitrogen-containing carbon source, sulfur source and the first precursor is (3~5):(1~2):(4.5~10).

[0032] The reaction is carried out by heating to 400℃~600℃ at a rate of 5~10℃ / min, wherein the heating rate can be any value among 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, or a range of values ​​with any two of these values ​​as endpoints.

[0033] The high-temperature carbonization is carried out by heating to 400℃~600℃ at a rate of 5~10℃ / min, wherein the heating rate can be any value among 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, or a range of values ​​with any two of these values ​​as endpoints.

[0034] According to the method for preparing the negative electrode material provided by the present invention, the first solvent and the second solvent are each independently selected from one or more combinations of ethanol, acetone and methanol.

[0035] According to the method for preparing the negative electrode material provided by the present invention, the concentration of the nitrogen-containing carbon source in the nitrogen-containing carbon source / sulfur source solution is 3.0 wt%~5.0 wt%.

[0036] According to the method for preparing the negative electrode material provided by the present invention, the concentration of sulfur source in the nitrogen-containing carbon source / sulfur source solution is 1.0 wt%~2.0 wt%.

[0037] Controlling the concentrations of the nitrogen-containing carbon source and sulfur source in the nitrogen-containing carbon source / sulfur source solution within the aforementioned range is more conducive to obtaining a negative electrode material that balances rate performance and cycle stability.

[0038] According to the method for preparing the negative electrode material provided by the present invention, the concentration of the metal halide solution is 5wt% to 20wt%, for example, it can be any value among 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, or 20wt%, or a range of values ​​with any two values ​​as endpoints. If the concentration of the metal halide solution is too high, it is detrimental to the controllability of the reaction; if the concentration of the metal halide solution is too low, it is detrimental to the formation of a metal silicide layer.

[0039] In this invention, the inert gas can be argon, nitrogen, etc., and is not specifically limited thereto.

[0040] Thirdly, the present invention provides a battery containing the aforementioned negative electrode material.

[0041] Based on this, the technical solution of the present invention has the following beneficial effects: The negative electrode material, its preparation method, and battery provided by this invention optimize the coating structure of the negative electrode material and adopt a low-energy-consumption synthesis method that can construct functional multilayer coating structures. This method can produce metal silicide / heteroatom-doped carbon bilayer coated silicon nanomaterials, which can simultaneously achieve long cycle life and high-rate fast charging performance. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0043] Unless otherwise specified, all raw materials used in the examples and comparative examples are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.

[0044] The weight-average molecular weight of polyvinylpyrrolidone is 40,000 to 58,000, and the weight-average molecular weight of polyacrylonitrile is 25,000 to 80,000.

[0045] Example 1 This embodiment provides a negative electrode material, the preparation method of which includes the following steps: (1) Prepare an ethanol solution of copper chloride with a concentration of 12 wt%, and then ultrasonically disperse silicon particles with a particle size D50 of 500 nm in the solution to obtain a suspension, wherein the mass ratio of copper chloride to nano-silicon particles is 1:1.6. (2) The suspension obtained in step (1) is encapsulated in a stainless steel pressure reactor, vacuumed and placed in a high-temperature furnace, heated to 550°C and kept at that temperature for 1 hour. The heating rate is 10°C / min. After the reaction is completed, the product is centrifuged, washed several times with ethanol, and then dried at 80°C to obtain the first precursor. (3) Prepare an ethanol solution of polyvinylpyrrolidone / thiourea, wherein the concentration of polyvinylpyrrolidone is 4.5 wt% and the concentration of thiourea is 1.0 wt%. Then, the first precursor is ultrasonically dispersed in the solution and stirred at 55°C for 4 h. The mass ratio of polyvinylpyrrolidone, thiourea and the first precursor is 4.5:1.0:7.0. Then, the second precursor is dried at 80°C. (4) The second precursor is placed in a tube furnace and heated to 450°C and held for 2 hours under an argon atmosphere. The heating rate is 5°C / min. Cu3Si / heteroatom-doped carbon bilayer coated silicon nanomaterials can be obtained. The Cu3Si layer is 46 nm thick and the carbon layer is 17 nm thick. Nitrogen and sulfur elements are doped in the carbon layer. The nitrogen content in the carbon layer is 8.6% and the sulfur content is 4.2%.

[0046] Example 2 This embodiment provides a negative electrode material, the preparation method of which includes the following steps: (1) Prepare an ethanol solution of ferrous chloride with a concentration of 12 wt%, and then ultrasonically disperse silicon particles with a particle size D50 of 500 nm in the solution to obtain a suspension, wherein the mass ratio of ferrous chloride to nano-silicon particles is 1:1.3. (2) The suspension obtained in step (1) is encapsulated in a stainless steel pressure reactor, vacuumed and placed in a high-temperature furnace, heated to 600°C and kept at that temperature for 1 hour. The heating rate is 10°C / min. After the reaction is completed, the product is centrifuged, washed several times with ethanol, and then dried at 80°C to obtain the first precursor. (3) Prepare an ethanol solution of polyvinylpyrrolidone / thiourea, wherein the concentration of polyvinylpyrrolidone is 4.5 wt% and the concentration of thiourea is 1.0 wt%. Then, the first precursor is ultrasonically dispersed in the solution and stirred at 55°C for 4 h. The mass ratio of polyvinylpyrrolidone, thiourea and the first precursor is 4.5:1.0:7.0. Then, the second precursor is dried at 80°C. (4) The second precursor is placed in a tube furnace and heated to 450°C and held for 2 hours under an argon atmosphere. The heating rate is 5°C / min. Fe3Si2 / heteroatom-doped carbon bilayer coated silicon nanomaterial is obtained. The Fe3Si2 layer is 62 nm thick and the carbon layer is 21 nm thick. Nitrogen and sulfur elements are doped in the carbon layer. The nitrogen content in the carbon layer is 8.8% and the sulfur content is 4.3%.

[0047] Example 3 This embodiment provides a negative electrode material, the preparation method of which includes the following steps: (1) Prepare an ethanol solution of nickel chloride with a concentration of 12 wt%, and then ultrasonically disperse silicon particles with a particle size D50 of 200 nm in the solution to obtain a suspension, wherein the mass ratio of nickel chloride to nano-silicon particles is 1:1.6. (2) The suspension obtained in step (1) is encapsulated in a stainless steel pressure reactor, vacuumed and placed in a high-temperature furnace, heated to 550°C and kept at that temperature for 0.5 h. The heating rate is 10°C / min. After the reaction is completed, the product is centrifuged, washed several times with ethanol, and then dried at 80°C to obtain the first precursor. (3) Prepare an ethanol solution of polyvinylpyrrolidone / thiourea, wherein the concentration of polyvinylpyrrolidone is 4.5 wt% and the concentration of thiourea is 1.0 wt%. Then, the first precursor is ultrasonically dispersed in the solution and stirred at 55°C for 4 h. The mass ratio of polyvinylpyrrolidone, thiourea and the first precursor is 4.5:1.0:7.0. Then, the second precursor is dried at 80°C. (4) The second precursor is placed in a tube furnace and heated to 450°C and held for 2 hours under an argon atmosphere. The heating rate is 5°C / min. Ni2Si / heteroatom-doped carbon bilayer coated silicon nanomaterial is obtained. The Ni2Si layer is 27 nm thick and the carbon layer is 16 nm thick. The carbon layer is doped with nitrogen and sulfur elements. The nitrogen content in the carbon layer is 8.4% and the sulfur content is 3.9%.

[0048] Example 4 This embodiment provides a negative electrode material, the preparation method of which includes the following steps: (1) Prepare an ethanol solution of copper chloride with a concentration of 12 wt%, and then ultrasonically disperse silicon particles with a particle size D50 of 500 nm in the solution to obtain a suspension, wherein the mass ratio of copper chloride to nano-silicon particles is 1:1.6. (2) The suspension obtained in step (1) is encapsulated in a stainless steel pressure reactor, vacuumed and placed in a high-temperature furnace, heated to 500°C and kept at that temperature for 1 hour. The heating rate is 10°C / min. After the reaction is completed, the product is centrifuged, washed several times with ethanol, and then dried at 80°C to obtain the first precursor. (3) Prepare an ethanol solution of polyacrylonitrile / thiourea, wherein the concentration of polyacrylonitrile is 4.5 wt% and the concentration of thiourea is 1.0 wt%. Then, the first precursor is ultrasonically dispersed in the solution and stirred at 55°C for 4 h. The mass ratio of polyacrylonitrile, thiourea and the first precursor is 4.5:1.0:6.5. Then, the second precursor is dried at 80°C. (4) The second precursor is placed in a tube furnace and heated to 450°C and held for 2 hours under an argon atmosphere. The heating rate is 5°C / min. Cu3Si / heteroatom-doped carbon bilayer coated silicon nanomaterial is obtained. The Cu3Si layer is 38 nm thick and the carbon layer is 15 nm thick. The carbon layer is doped with nitrogen and sulfur elements. The nitrogen content in the carbon layer is 10.7% and the sulfur content is 4.6%.

[0049] Example 5 This embodiment provides a negative electrode material, the preparation method of which includes the following steps: (1) Prepare an ethanol solution of copper chloride with a concentration of 12 wt%, and then ultrasonically disperse silicon particles with a particle size D50 of 500 nm in the solution to obtain a suspension, wherein the mass ratio of copper chloride to nano-silicon particles is 1:1.6. (2) The suspension obtained in step (1) is encapsulated in a stainless steel pressure reactor, vacuumed and placed in a high-temperature furnace, heated to 550°C and kept at that temperature for 2 hours. The heating rate is 10°C / min. After the reaction is completed, the product is centrifuged, washed several times with ethanol, and then dried at 80°C to obtain the first precursor. (3) Prepare an ethanol solution of polyvinylpyrrolidone / p-toluene disulfide, wherein the concentration of polyvinylpyrrolidone is 4.5 wt% and the concentration of p-toluene disulfide is 1.0 wt%. Then, the first precursor is ultrasonically dispersed in the solution and stirred at 55°C for 4 h. The mass ratio of polyvinylpyrrolidone, p-toluene disulfide and the first precursor is 4.5:1.0:7.0. Then, the second precursor is dried at 80°C. (4) The second precursor is placed in a tube furnace and heated to 450°C and held for 2 hours under an argon atmosphere. The heating rate is 5°C / min. Cu3Si / heteroatom-doped carbon bilayer coated silicon nanomaterials can be obtained. The Cu3Si layer is 74 nm thick and the carbon layer is 18 nm thick. The carbon layer is doped with nitrogen and sulfur elements. The nitrogen content in the carbon layer is 8.3% and the sulfur content is 3.2%.

[0050] Comparative Example 1 This comparative example provides a negative electrode material whose preparation method differs from that of Example 1 in that: in step (3), thiourea is replaced with an equal mass of polyvinylpyrrolidone. Finally, a Cu3Si / nitrogen-doped carbon bilayer coated silicon nanomaterial is obtained, wherein the Cu3Si layer thickness is 47 nm, the carbon layer thickness is 18 nm, the nitrogen content in the carbon layer is 9.2%, and the sulfur content is 0.

[0051] Comparative Example 2 This comparative example provides a negative electrode material whose preparation method differs from that of Example 1 in that: in step (3), thiourea is replaced with an equal mass of tin tetrachloride. Finally, a Cu3Si / nitrogen- and tin-doped carbon bilayer coated silicon nanomaterial is obtained, wherein the Cu3Si layer thickness is 46 nm, the carbon layer thickness is 16 nm, the nitrogen content in the carbon layer is 8.5%, and the tin content is 3.4%.

[0052] Comparative Example 3 This comparative example provides a negative electrode material whose preparation method differs from that of Example 1 in that: in step (3), thiourea is replaced with an equal mass of phytic acid. Finally, Cu3Si / nitrogen and phosphorus-doped carbon bilayer coated silicon nanomaterials are obtained, wherein the Cu3Si layer thickness is 47 nm, the carbon layer thickness is 17 nm, the nitrogen content in the carbon layer is 8.6%, and the phosphorus content is 2.6%.

[0053] Test Case Performance Testing Batteries were prepared using the negative electrode materials obtained in each embodiment and comparative example. Specific methods included: The negative electrode material, sodium carboxymethyl cellulose, binder, carbon black, and deionized water were placed in the stirring tank of a stirrer at a mass ratio of 95:2:2:1:100 and stirred to obtain a negative electrode slurry. The slurry was coated onto a copper foil current collector, dried at 80°C, and rolled to obtain a negative electrode sheet. A lithium metal sheet was used as the counter electrode, a polypropylene membrane was used as the separator, and a 1 mol / L lithium hexafluorophosphate solution (in which the solvent was a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1) was used as the electrolyte. The CR2032 coin cell was assembled in an argon-filled glove box and its electrochemical performance was tested.

[0054] The electrochemical performance test results of the battery are shown in Table 1.

[0055] Table 1. Electrochemical performance test results of the battery

[0056] As shown in Table 1, the metal silicide / heteroatom-doped carbon bilayer coated silicon nanomaterials obtained by the methods of the various embodiments of the present invention exhibit excellent electrochemical performance. The resulting batteries have a first-cycle charge specific capacity of over 1690 mAh / g at 0.5 A / g; a capacity retention of over 90% after 500 cycles at a rate of 2 A / g; and a charge specific capacity of over 480 mAh / g at a rate of 10 A / g. The batteries obtained from the negative electrode materials of Comparative Examples 1-3 show relatively poor electrochemical performance.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode material, characterized in that, include: Silicon nanomaterials; At least partially coated with a metal silicide layer on the surface of the silicon nanomaterial; A nitrogen-sulfur-doped carbon layer that at least partially coats the surface of the metal silicide layer; The thickness of the metal silicide layer is greater than the thickness of the nitrogen-sulfur-doped carbon layer.

2. The negative electrode material according to claim 1, characterized in that, The thickness of the nitrogen-sulfur-doped carbon layer is 10 nm to 30 nm; Preferably, the thickness ratio of the metal silicide layer to the nitrogen-sulfur-doped carbon layer is (1.5~5):

1.

3. The negative electrode material according to claim 1 or 2, characterized in that, The nitrogen content in the nitrogen-sulfur-doped carbon layer is 3.5% to 12%; and / or, the sulfur content in the nitrogen-sulfur-doped carbon layer is 2% to 8.5%.

4. The negative electrode material according to any one of claims 1 to 3, characterized in that, The particle size D50 of the silicon nanomaterial is 200nm~800nm.

5. The negative electrode material according to any one of claims 1 to 4, characterized in that, The material of the metal silicide layer is selected from one or more combinations of Cu3Si, Cu5Si, FeSi2, FeSi, Fe3Si2, Ni2Si, and CoSi2.

6. The negative electrode material according to any one of claims 1 to 5, characterized in that, The nitrogen-sulfur doped carbon layer is formed by high-temperature carbonization of a mixture of nitrogen-containing carbon source and sulfur source at 400℃~600℃. Preferably, the nitrogen-containing carbon source includes one or more of polyvinylpyrrolidone, polyacrylonitrile, and polypyrrole; and / or, the sulfur source includes one or more of thiourea, p-toluene disulfide, and sodium thiosulfate. More preferably, the mass ratio of the nitrogen-containing carbon source to the sulfur source is (3~5):(1~2).

7. The method for preparing the negative electrode material according to any one of claims 1 to 6, characterized in that, The metal silicide layer is coated onto the surface of the silicon nanomaterial using a solvothermal method.

8. The method for preparing the negative electrode material according to claim 7, characterized in that, The solvothermal method includes: mixing silicon nanomaterials, metal halides, and a first solvent to obtain a suspension; and then subjecting the suspension to a 5×10⁻⁶ ℃ high-temperature, high-temperature, and low-temperature (LTT) process. -6 MPa ~2×10 -5 The reaction was carried out at MPa and 400℃~600℃ and held for 0.5h~3h to obtain the first precursor; Preferably, the metal halide is selected from one or more combinations of copper chloride, cuprous chloride, ferric chloride, ferrous chloride, nickel chloride, and cobalt chloride; More preferably, the mass ratio of the metal halide to the silicon nanomaterial is 1:(1.2~2.2).

9. The method for preparing the negative electrode material according to claim 8, characterized in that, Also includes: The first precursor, nitrogen-containing carbon source, sulfur source and second solvent are mixed, and the organic matter is coated at 45℃~65℃. After drying, the second precursor is obtained. The second precursor was subjected to high-temperature carbonization at 400℃~600℃ under an inert atmosphere; Preferably, the mass ratio of the mixture of nitrogen-containing carbon source and sulfur source to the first precursor is (4~7):(4.5~10).

10. A battery, characterized in that, The negative electrode material comprising any one of claims 1 to 6 or the negative electrode material prepared by any one of claims 7 to 9.

Images