A negative electrode composite material, a method for preparing the same, and a battery

Abstract

This invention relates to the field of new energy batteries, specifically to a negative electrode composite material, its preparation method, and a battery. The negative electrode composite material of this invention comprises a porous graphite framework, silicon nanowires and metal nanoparticles deposited in the pores of the porous graphite framework, a first coating layer covering the surface of the porous graphite framework, and a second coating layer covering the surface of the first coating layer; wherein the metal nanoparticles include gold nanoparticles; the first coating layer is an amorphous carbon coating layer; and the second coating layer is a fast ion conductor coating layer. The negative electrode composite material of this invention maintains high energy density while also exhibiting excellent cycle life and rate performance, thereby achieving a balance between structural stability and interfacial dynamics.

Description

Technical Field

[0001] This invention relates to the field of new energy batteries, specifically to a negative electrode composite material, its preparation method, and a battery. Background Technology

[0002] Lithium-ion batteries, as important electrochemical energy storage devices, are widely used in electric vehicles, portable electronic devices, and other fields. Traditional graphite anode materials, due to their relatively low theoretical capacity (approximately 372 mAh / g), limit further improvements in battery energy density. Silicon-based materials, with a theoretical specific capacity as high as 4200 mAh / g, are considered ideal anode materials for next-generation high-energy-density lithium-ion batteries. However, silicon materials exhibit a volume expansion effect of approximately 300% during charge and discharge, leading to electrode material structure damage, active material pulverization and shedding, and repeated rupture and reconstruction of the solid electrolyte interface film, resulting in rapid capacity decay and shortened cycle life.

[0003] In existing technologies, silicon nanofiberization or carbon coating strategies are commonly used to alleviate the aforementioned problems. For example, silicon nanoparticles are mechanically mixed with graphite, or a single carbon layer is used to coat silicon. However, mechanical mixing results in weak interfacial bonding between silicon and the carbon matrix, leading to silicon agglomeration and detachment during long-term cycling. While a single carbon coating can partially improve conductivity, it is difficult to effectively suppress lithium-ion transport impedance, resulting in poor rate performance, and the carbon layer is prone to cracking and failure during silicon volume changes. Furthermore, existing technologies for loading silicon into porous carbon frameworks often employ physical impregnation or chemical vapor deposition to directly grow silicon, lacking precise confinement control and interfacial strengthening, leading to uneven silicon distribution and weak bonding with the matrix. Simultaneously, catalysts are prone to agglomeration in unconfined environments, affecting the controllable growth of silicon nanowires. Moreover, existing technologies often focus on single coatings, making it difficult to simultaneously address multiple technical challenges such as volume expansion, poor conductivity, and slow ion transport. Summary of the Invention

[0004] In view of this, the present invention aims to provide a negative electrode composite material, its preparation method and battery, to solve the problems of silicon-based negative electrode materials in the prior art, such as short cycle life due to volume expansion, low rate performance limited by poor conductivity, rapid capacity decay due to interface instability and slow lithium-ion transport affecting fast charging capability.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: A first aspect of the present invention provides a negative electrode composite material, the negative electrode composite material comprising a porous graphite skeleton, silicon nanowires and metal nanoparticles deposited in the pores of the porous graphite skeleton, a first coating layer covering the surface of the porous graphite skeleton, and a second coating layer covering the surface of the first coating layer. The metal nanoparticles include gold nanoparticles; The first coating layer is an amorphous carbon coating layer; The second coating layer is a fast ion conductor coating layer.

[0006] Optionally, the porous graphite framework has a pore size of 2-50 nm; and / or, the porous graphite framework has a porosity of 30-50%; and / or, the silicon nanowire has a diameter of 5-20 nm; and / or, the metal nanoparticles have a Dn50 of 2-10 nm.

[0007] Optionally, the thickness of the amorphous carbon coating layer is 5~20 nm; and / or, the thickness of the fast ion conductor coating layer is 20~100 nm.

[0008] Optionally, based on the total mass of the negative electrode composite material, the content of the silicon nanowires is 10~40wt%; and / or, based on the total mass of the negative electrode composite material, the content of the gold nanoparticles is 0.5~1.5wt%.

[0009] Optionally, the fast ion conductor coating layer is at least one of the following: aluminum-doped lithium titanium phosphate coating layer, aluminum-doped lithium germanium phosphate coating layer, aluminum-doped lithium zirconium phosphate coating layer, aluminum-doped lithium tin phosphate coating layer, and aluminum-doped lithium lanthanum zirconium oxide coating layer.

[0010] A second aspect of the present invention provides a method for preparing a negative electrode composite material, the method comprising the following steps: S1. Biomass material is subjected to hydrothermal treatment to obtain a carbon precursor. The carbon precursor is placed in a first inert atmosphere for activation treatment to obtain porous carbon. The porous carbon is subjected to a first calcination treatment in a second inert atmosphere to obtain a first material. The first material is ground and sieved to obtain porous graphite particles. S2. Disperse gold nanoparticles in a first solvent to obtain a suspension; immerse the porous graphite particles in the suspension and perform ultrasonic treatment to obtain a second material; perform a first drying treatment on the second material to obtain porous graphite particles loaded with gold nanoparticles. S3. Disperse the porous graphite particles loaded with gold nanoparticles in liquid silane to obtain a dispersion; subject the dispersion to a first vacuum treatment and a high-temperature treatment to obtain a third material; centrifuge and wash the third material and then perform a second drying treatment to obtain a porous graphite-silicon nanowire composite material. S4. The porous graphite-silicon nanowire composite material is subjected to a second vacuum treatment and then subjected to a second calcination treatment in a first composite atmosphere to obtain a composite material coated with a first coating layer; the composite material coated with the first coating layer is dispersed in a fast ion conductor precursor solution and spray-dried to obtain a fourth material; the fourth material is subjected to a third calcination treatment in a third inert atmosphere. The first composite atmosphere contains at least one of methane, acetylene, ethane, propane, and ethylene.

[0011] Optionally, the biomass material includes at least one of cellulose, lignin, and starch; and / or, the liquid-phase silane is at least one of tetramethylsilane, dimethylsilane, methylsilane, phenylsilane, and diphenylsilane; and / or, the first solvent includes at least one of hexane and isooctane; and / or, the mass ratio of the porous graphite particles to the suspension is 1:(10~15), and the solid content in the suspension is 5~10%; and / or, the mass ratio of the composite material coated with the first coating layer to the fast ion conductor precursor solution is 1:(2~3).

[0012] Optionally, in step S1, the hydrothermal treatment conditions include: a temperature of 180~220℃ and a time of 4~8h; and / or, the activation treatment conditions include: a temperature of 700~900℃ and a time of 1~3h; and / or, the first calcination treatment conditions include: a temperature of 2600~3200℃ and a time of 1~3h; and / or, in step S2, the ultrasonic treatment conditions include: a temperature of 15~35℃ and a time of 20~40min, with a frequency of 0.2~0.8MHz; and / or, the first drying treatment conditions include: a temperature of 50~70℃ and a time of 3~5h; and / or, in step S3, the pressure of the first vacuum treatment is 0.05... ~0.15 Pa; and / or, the conditions for the high-temperature treatment include: a temperature of 300~500℃ and a time of 1~3h; and / or, the conditions for the second drying treatment include: a temperature of 60~90℃ and a time of 8~12h; and / or, in step S4, the pressure of the second vacuum treatment is 0.05~0.15 Pa; and / or, the conditions for the second calcination treatment include: a temperature of 500~800℃ and a time of 0.5~2h; and / or, the conditions for the spray drying treatment include: an inlet air temperature of 150~200℃ and an outlet air temperature of 60~100℃; and / or, the conditions for the third calcination treatment include: a temperature of 700~800℃ and a time of 2~4h.

[0013] Optionally, the method for preparing the gold nanoparticles includes: mixing an aqueous solution of chloroauric acid and a tetraoctylammonium bromide toluene solution and then stirring to obtain a mixed solution; mixing the mixed solution with an aqueous solution of sodium borohydride and then performing an ice bath reduction treatment; The chloroauric acid aqueous solution has a molar mass of 0.05~0.15 mol / L; the tetraoctylammonium bromide toluene solution has a molar mass of 0.03~0.08 mol / L; and the sodium borohydride aqueous solution has a molar mass of 0.1~0.3 mol / L.

[0014] A third aspect of the present invention provides a battery comprising a negative electrode material, the negative electrode material comprising the above-described negative electrode composite material and / or a negative electrode composite material prepared according to the above-described preparation method.

[0015] The beneficial technical effects of the present invention through the above technical solution are as follows: (1) The negative electrode composite material of the present invention comprises a porous graphite framework, silicon nanowires, gold nanoparticles, an amorphous carbon coating layer, and a fast ion conductor coating layer. The present invention effectively buffers the volume expansion of silicon nanowires during charge and discharge by confining the growth of silicon nanowires within the porous graphite framework, thereby improving cycle stability; the amorphous carbon coating layer promotes the formation of a more uniform and stable SEI film on the surface of the silicon nanowires, further enhancing cycle stability; and the fast ion conductor coating layer constructs a fast lithium-ion migration channel, improving ionic conductivity and significantly enhancing rate performance. The synergistic effect of the above technical features enables the negative electrode composite material of the present invention to maintain high energy density while possessing excellent cycle life and rate performance, thereby achieving a unity of structural stability and interfacial dynamics.

[0016] (2) In the preparation method of the negative electrode composite material of the present invention, the silicon nanowires are grown in situ within the pores of the porous graphite framework by catalysis of gold nanoparticles; the amorphous carbon coating layer is coated on the surface of the porous graphite framework and the silicon nanowires; the fast ion conductor coating layer is coated on the outer surface of the amorphous carbon coating layer. The porous graphite framework is formed by high-temperature graphitization of biomass-derived porous carbon, providing growth space and volume buffer for the silicon nanowires; the gold nanoparticles are prepared and deposited in the pores by phase transfer reduction, realizing the confined and controllable growth of silicon nanowires; the amorphous carbon coating layer is formed by chemical vapor deposition, improving the stability of the SEI film; the fast ion conductor coating layer is formed by spray drying and high-temperature sintering, which can construct a fast lithium-ion migration channel.

[0017] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0018] This invention discloses a negative electrode composite material, its preparation method, and a battery. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0019] In the description of this invention, the list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0022] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0023] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0024] To address the shortcomings of existing silicon-based anode materials, such as short cycle life due to volume expansion, low rate performance limited by poor conductivity, rapid capacity decay due to interface instability, and slow lithium-ion transport affecting fast charging capability, this invention adopts the following technical solution: A first aspect of the present invention provides a negative electrode composite material, the negative electrode composite material comprising a porous graphite skeleton, silicon nanowires and metal nanoparticles deposited in the pores of the porous graphite skeleton, a first coating layer covering the surface of the porous graphite skeleton, and a second coating layer covering the surface of the first coating layer. The metal nanoparticles include gold nanoparticles; The first coating layer is an amorphous carbon coating layer; The second coating layer is a fast ion conductor coating layer.

[0025] The anode composite material of this invention comprises a porous graphite framework, silicon nanowires, gold nanoparticles, an amorphous carbon coating layer, and a fast ion conductor coating layer. This invention effectively buffers the volume expansion of silicon nanowires during charge and discharge by confining their growth within the porous graphite framework, thereby improving cycle stability. The amorphous carbon coating layer promotes the formation of a more uniform and stable SEI film on the surface of the silicon nanowires, further enhancing cycle stability. The fast ion conductor coating layer constructs a fast lithium-ion migration channel, improving ionic conductivity and significantly enhancing rate performance. The synergistic effect of these technical features enables the anode composite material of this invention to maintain high energy density while possessing excellent cycle life and rate performance, thus achieving a balance between structural stability and interfacial dynamics.

[0026] According to the present invention, the appropriate pore size of the porous graphite framework has the technical effect of limiting the volume expansion of silicon nanowires. If the pore size of the porous graphite framework is too large, it may lead to significant volume expansion of the silicon nanowires, thereby affecting the cycle performance of the battery; if the pore size of the porous graphite framework is too small, it may make it difficult to deposit metal catalyst particles. In the present invention, the pore size of the porous graphite framework can be 2~50 nm. Exemplarily, the pore size of the porous graphite framework can be any value selected from 2 nm, 10 nm, 20 nm, 30 nm, 40 nm, and 50 nm, or any value within the range formed by any two of the above values.

[0027] According to the present invention, a suitable porosity of the porous graphite framework can provide suitable growth space for silicon nanowires. If the porosity of the porous graphite framework is too large, it may lead to insufficient mechanical strength of the anode composite material; if the porosity of the porous graphite framework is too small, it may lead to a low final silicon content. In the present invention, the porosity of the porous graphite framework can be 30-50%. Exemplarily, the porosity of the porous graphite framework is any value selected from 30%, 35%, 40%, 45%, and 50%, or any value within the range formed by any pair of the above values.

[0028] According to the present invention, a suitable diameter of silicon nanowires can further improve the cycle performance of the battery. If the diameter of the silicon nanowires is too large, it may lead to significant volume expansion and poor cycle performance; if the diameter of the silicon nanowires is too small, it may lead to a high specific surface area and the formation of a thicker SEI film. In the present invention, the diameter of the silicon nanowires can be 5~20 nm. Exemplarily, the diameter of the silicon nanowires can be any value selected from 5 nm, 8 nm, 10 nm, 15 nm, 18 nm, and 20 nm, or any value within the range formed by any pair of the above values.

[0029] According to the present invention, the Dn50 of suitable metal nanoparticles can control the diameter of silicon nanowires. If the Dn50 of the metal nanoparticles is too large, it may result in an excessively large diameter of the silicon nanowires; if the Dn50 of the metal nanoparticles is too small, it may result in an excessively small diameter of the silicon nanowires. In the present invention, the Dn50 of the metal nanoparticles can be 2~10 nm. Exemplarily, the Dn50 of the metal nanoparticles can be any value selected from 2 nm, 3 nm, 4 nm, 5 nm, 8 nm, and 10 nm, or any value within the range formed by any pair of the above values.

[0030] In this invention, an appropriate thickness of the amorphous carbon coating layer has the technical effect of improving the stability of the SEI film. If the thickness of the amorphous carbon coating layer is too thick, it may lead to a decrease in specific capacity; if the thickness of the amorphous carbon coating layer is too thin, it may lead to an incomplete carbon coating layer. In some embodiments of this invention, the thickness of the amorphous carbon coating layer can be 5~20 nm. Exemplarily, the thickness of the amorphous carbon coating layer can be any value selected from 5 nm, 8 nm, 10 nm, 15 nm, 18 nm, and 20 nm, or any value within the range formed by any pair of the above values.

[0031] In this invention, an appropriate thickness of the fast ion conductor coating layer has the technical effect of improving ionic conductivity and enhancing rate performance. If the thickness of the fast ion conductor coating layer is too thick, it may lead to an elongated lithium-ion migration path and a decrease in rate performance; if the thickness of the fast ion conductor coating layer is too thin, it may lead to an incomplete fast ion conductor coating layer. In some embodiments of this invention, the thickness of the fast ion conductor coating layer can be 20~100 nm. Exemplarily, the thickness of the fast ion conductor coating layer can be any value selected from 20 nm, 40 nm, 60 nm, 80 nm, and 100 nm, or any value within the range formed by any two of the above values.

[0032] In this invention, a suitable content of silicon nanowires achieves the technical effect of balancing high specific capacity and high cycle stability. In some embodiments of this invention, the content of silicon nanowires can be 10-40 wt%, based on the total mass of the negative electrode composite material. For example, based on the total mass of the negative electrode composite material, the content of silicon nanowires can be any value from 10 wt%, 15 wt%, 20 wt%, 30 wt%, and 40 wt%, or any value within the range formed by any pair of the above values.

[0033] In this invention, the appropriate content of gold nanoparticles can control the content and diameter of silicon nanowires within a suitable range. In some embodiments of this invention, the content of gold nanoparticles can be 0.5~1.5 wt%, based on the total mass of the negative electrode composite material. Exemplarily, based on the total mass of the negative electrode composite material, the content of gold nanoparticles can be any value from 10 wt%, 15 wt%, 20 wt%, 30 wt%, and 40 wt%, or any value within the range formed by any pair of the above values.

[0034] In some embodiments of the present invention, the fast ion conductor coating layer can be at least one selected from aluminum-doped lithium titanium phosphate coating layer, aluminum-doped lithium germanium phosphate coating layer, aluminum-doped lithium zirconium phosphate coating layer, aluminum-doped lithium tin phosphate coating layer, and aluminum-doped lithium lanthanum zirconium oxide coating layer. Preferably, the fast ion conductor coating layer of the present invention is an aluminum-doped lithium titanium phosphate coating layer. More preferably, the aluminum doping amount in the fast ion conductor coating layer of the present invention is 0.5~2.5 wt%. A second aspect of the present invention provides a method for preparing a negative electrode composite material, the method comprising the following steps: S1. Biomass material is subjected to hydrothermal treatment to obtain a carbon precursor. The carbon precursor is placed in a first inert atmosphere for activation treatment to obtain porous carbon. The porous carbon is subjected to a first calcination treatment in a second inert atmosphere to obtain a first material. The first material is ground and sieved to obtain porous graphite particles. S2. Disperse gold nanoparticles in a first solvent to obtain a suspension; immerse the porous graphite particles in the suspension and perform ultrasonic treatment to obtain a second material; perform a first drying treatment on the second material to obtain porous graphite particles loaded with gold nanoparticles. S3. Disperse the porous graphite particles loaded with gold nanoparticles in liquid silane to obtain a dispersion; subject the dispersion to a first vacuum treatment and a high-temperature treatment to obtain a third material; centrifuge and wash the third material and then perform a second drying treatment to obtain a porous graphite-silicon nanowire composite material. S4. The porous graphite-silicon nanowire composite material is subjected to a second vacuum treatment and then subjected to a second calcination treatment in a first composite atmosphere to obtain a composite material coated with a first coating layer; the composite material coated with the first coating layer is dispersed in a fast ion conductor precursor solution and spray-dried to obtain a fourth material; the fourth material is subjected to a third calcination treatment in a third inert atmosphere. The first composite atmosphere contains at least one of methane, acetylene, ethane, propane, and ethylene.

[0035] In the preparation method of the negative electrode composite material of the present invention, the silicon nanowires are grown in situ within the pores of the porous graphite framework by catalysis of gold nanoparticles; the amorphous carbon coating layer is coated on the surface of the porous graphite framework and the silicon nanowires; the fast ion conductor coating layer is coated on the outer surface of the amorphous carbon coating layer. The porous graphite framework is formed by high-temperature graphitization of biomass-derived porous carbon, providing growth space and volume buffer for the silicon nanowires; the gold nanoparticles are prepared and deposited within the pores by phase transfer reduction, achieving confined and controllable growth of the silicon nanowires; the amorphous carbon coating layer is formed by chemical vapor deposition, improving the stability of the SEI film; the fast ion conductor coating layer is formed by spray drying and high-temperature sintering, constructing a fast lithium-ion migration channel.

[0036] For example, the biomass material may include at least one of cellulose, lignin and starch.

[0037] For example, the liquid-phase silane may be at least one of tetramethylsilane, dimethylsilane, methylsilane, phenylsilane, and diphenylsilane.

[0038] For example, the first solvent may include at least one of hexane and isooctane.

[0039] In some embodiments of the present invention, the mass ratio of the porous graphite particles to the suspension can be 1:(10~15), and the solid content in the suspension can be 5~10%.

[0040] In some embodiments of the present invention, the mass ratio of the composite material coated with the first coating layer to the fast ion conductor precursor solution can be 1:(2~3).

[0041] In some embodiments of the present invention, in step S1, the conditions for the hydrothermal treatment may include: a temperature of 180~220℃ and a time of 4~8h; and / or, the conditions for the activation treatment may include: a temperature of 700~900℃ and a time of 1~3h; and / or, the conditions for the first calcination treatment may include: a temperature of 2600~3200℃ and a time of 1~3h.

[0042] In some embodiments of the present invention, in step S2, the conditions for ultrasonic treatment may include: a temperature of 15~35℃, a time of 20~40min, and a frequency of 0.2~0.8MHz; and / or, the conditions for the first drying treatment may include: a temperature of 50~70℃ and a time of 3~5h.

[0043] In some embodiments of the present invention, in step S3, the pressure of the first vacuum treatment can be 0.05~0.15 Pa; and / or, the conditions of the high-temperature treatment can include: a temperature of 300~500℃ and a time of 1~3h; and / or, the conditions of the second drying treatment can include: a temperature of 60~90℃ and a time of 8~12h.

[0044] In some embodiments of the present invention, in step S4, the pressure of the second vacuum treatment can be 0.05~0.15 Pa; and / or, the conditions of the second calcination treatment can include: a temperature of 500~800℃ and a time of 0.5~2h; and / or, the conditions of the spray drying treatment can include: an inlet air temperature of 150~200℃ and an outlet air temperature of 60~100℃; and / or, the conditions of the third calcination treatment can include: a temperature of 700~800℃ and a time of 2~4h.

[0045] This invention uses gold nanoparticles as a catalyst to achieve controllable growth of silicon nanowires within a confined space, ensuring a strong interfacial bond between the silicon nanowires and the graphite substrate. In some embodiments of this invention, the preparation method of the gold nanoparticles may include: mixing an aqueous solution of chloroauric acid and a tetraoctylammonium bromide toluene solution and then stirring to obtain a mixed solution; mixing the mixed solution with an aqueous solution of sodium borohydride and then performing an ice bath reduction treatment; The molar mass of the chloroauric acid aqueous solution can be 0.05~0.15 mol / L; the molar mass of the tetraoctylammonium bromide toluene solution can be 0.03~0.08 mol / L; and the molar mass of the sodium borohydride aqueous solution can be 0.1~0.3 mol / L.

[0046] A third aspect of the present invention provides a battery comprising a negative electrode material, the negative electrode material comprising the above-described negative electrode composite material and / or a negative electrode composite material prepared according to the above-described preparation method.

[0047] In some embodiments of the present invention, the battery further includes an electrolyte and a separator. That is, the battery includes a positive electrode, a negative electrode, an electrolyte, and a separator.

[0048] In this embodiment, the specific material or type of the separator is not limited, and any separator known in the art that can be used in secondary batteries can be selected.

[0049] It should also be noted that the battery of the present invention does not limit the specific material or type of electrolyte, and can use any components and types known in the art that can be used in secondary batteries, as long as the purpose of this application can be achieved.

[0050] Since the battery provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0051] The present invention will be further described in detail below through examples. All raw materials used in the examples are commercially available.

[0052] Example 1 The method for preparing the negative electrode composite material in this embodiment includes the following steps: (1) Preparation of porous graphite particles Cellulose was used as a raw material and hydrothermally treated at 200℃ for 6 hours to obtain a carbon precursor, which was then activated at 800℃ under a nitrogen atmosphere for 2 hours to form porous carbon. The porous carbon was placed in a high-temperature furnace and heated to 3000℃ at a rate of 5℃ / min under argon protection, and held at that temperature for 4 hours to form a porous graphite framework with a pore size distribution of 5-40 nm. After grinding and sieving, porous graphite particles with a particle size D50 of 6 μm were obtained.

[0053] (2) Porous graphite particles loaded with gold nanoparticles A 0.1 mol / L aqueous solution of chloroauric acid and a 0.05 mol / L solution of tetraoctylammonium bromide in toluene were mixed at a volume ratio of 1:1 and stirred for 30 minutes. Then, a 0.2 mol / L aqueous solution of sodium borohydride was slowly added, followed by rapid reduction in an ice bath to obtain gold nanoparticles with a D50 of 2 nm. The gold nanoparticles were dispersed in a mixed solvent of hexane and isooctane (volume ratio 10:1), and porous graphite was immersed in this suspension. The suspension was ultrasonicated for 30 minutes, followed by vacuum drying at 65°C for 3 hours to allow the gold nanoparticles to be uniformly deposited within the pores, resulting in porous graphite particles loaded with gold nanoparticles. The mass ratio of porous graphite to gold nanoparticle suspension was 1:12.

[0054] (3) Porous graphite-silicon nanowire composite materials Porous graphite loaded with gold nanoparticles was dispersed in tetramethylsilane at a mass ratio of 1:12. The dispersion was transferred to a stainless steel pressure reactor, evacuated to 0.1 Pa, and then sealed. The reactor was placed in a high-temperature furnace, heated to 400°C at a rate of 5°C / min, and held for 2 hours to grow silicon nanowires in situ within the porous graphite channels. After the reaction was completed, the product was collected by centrifugation, washed several times with anhydrous ethanol, and dried at 80°C to obtain a porous graphite-silicon nanowire composite material.

[0055] (4) Preparation of the coating layer A porous graphite-silicon nanowire composite material was placed in a tube furnace, evacuated to 0.1 Pa, and heated to 600°C at a rate of 5°C / min. An acetylene / argon mixture (volume ratio 1:1) was then introduced, and the reaction was allowed to proceed for 1 hour, forming an amorphous carbon coating layer on the surface of the porous graphite-silicon nanowire composite material. Lithium acetate, aluminum nitrate, tetrabutyl titanate, and ammonium dihydrogen phosphate were dissolved in equal volumes of anhydrous ethanol, with concentrations of 1 mol / L, 0.3 mol / L, 1 mol / L, and 2 mol / L, respectively. The lithium ion solution, aluminum ion solution, and phosphate ion solution were then added dropwise to the titanium ion solution in that order, and the mixture was stirred for 4 hours to obtain a fast ion conductor precursor solution. Amorphous carbon-coated porous graphite-silicon nanowire composite material was dispersed in a fast-ion conductor precursor solution, followed by spray drying at an inlet air temperature of 180°C and an outlet air temperature of 80°C, resulting in a porous graphite-silicon nanowire composite material with a double layer of amorphous carbon-fast-ion conductor precursor coating. The mass ratio of the amorphous carbon-coated porous graphite-silicon nanowire composite material to the fast-ion conductor precursor solution was 1:2.5. This composite material was then heated at 750°C under a nitrogen atmosphere for 3 hours to form a uniform aluminum-doped lithium titanium phosphate coating layer, yielding the anode composite material of this embodiment.

[0056] In the negative electrode composite material of this embodiment, the silicon content is 23 wt%, the silicon nanowire diameter is 8 nm, the thickness of the amorphous carbon coating layer is 12 nm, and the thickness of the aluminum-doped lithium titanium phosphate coating layer is 55 nm.

[0057] Example 2 The preparation method of the negative electrode composite material in this embodiment is the same as that in Embodiment 1, except that the growth temperature of silicon nanowires is adjusted to 500℃ in the preparation of porous graphite-silicon nanowire composite material.

[0058] In the negative electrode composite material prepared in this embodiment, the silicon content is 34 wt%, the silicon nanowire diameter is 16 nm, the thickness of the amorphous carbon coating layer is 12 nm, and the thickness of the aluminum-doped lithium titanium phosphate coating layer is 55 nm.

[0059] Example 3 The preparation method of the negative electrode composite material in this embodiment is the same as that in Embodiment 1, except that the reaction time of carbon coating is adjusted to 0.5 hours during the preparation of the coating layer.

[0060] In the negative electrode composite material prepared in this embodiment, the silicon content is 23 wt%, the silicon nanowire diameter is 8 nm, the thickness of the amorphous carbon coating layer is 6 nm, and the thickness of the aluminum-doped lithium titanium phosphate coating layer is 55 nm.

[0061] Example 4 The preparation method of the negative electrode composite material in this embodiment is the same as that in Example 1, except that lithium acetate, tetrabutyl titanate, and ammonium dihydrogen phosphate are replaced with lithium nitrate, n-butyl titanate, and phosphoric acid, respectively.

[0062] In the negative electrode composite material prepared in this embodiment, the silicon content is 23 wt%, the silicon nanowire diameter is 8 nm, the thickness of the amorphous carbon coating layer is 12 nm, and the thickness of the aluminum-doped lithium titanium phosphate coating layer is 62 nm.

[0063] Comparative Example 1 The preparation method of the negative electrode composite material in this comparative example is the same as that in Example 1, except that porous graphite is replaced with conventional artificial graphite.

[0064] In the negative electrode composite material prepared in this comparative example, the silicon content is 13 wt%, the silicon nanowire diameter is 8 nm, the thickness of the amorphous carbon coating layer is 12 nm, and the thickness of the aluminum-doped lithium titanium phosphate coating layer is 55 nm.

[0065] Comparative Example 2 The preparation method of the negative electrode composite material in this comparative example is the same as that in Example 1, except that fast ion conductor coating is not performed, and the final result is a porous graphite-silicon nanowire composite material coated with amorphous carbon.

[0066] In the negative electrode composite material prepared in this comparative example, the silicon content is 23 wt%, the diameter of the silicon nanowires is 8 nm, and the thickness of the amorphous carbon coating layer is 12 nm.

[0067] Test Example 1 Batteries were prepared using the negative electrode materials obtained in Examples 1-4 and Comparative Examples 1-2, respectively. The specific methods included: A negative electrode material, sodium carboxymethyl cellulose, binder, carbon black, and deionized water were placed in a 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 current collector foil, 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 as the separator, and a 1 mol / L lithium hexafluorophosphate solution (where the solvent was a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1) was used as the electrolyte. CR2032 coin cells were assembled in an argon-filled glove box and their electrochemical performance was tested. The electrochemical performance test results of the battery are shown in Table 1.

[0068] Methods for testing electrochemical performance include: First-week charging specific capacity: voltage range 0.01-1.5V, current density 0.5A / g, the charging specific capacity of the first week was tested.

[0069] Capacity retention after 500 charge-discharge cycles: The voltage range is 0.05-1.2V, the current density is 2A / g, and the capacity retention is tested after 500 cycles.

[0070] Charging specific capacity: The voltage range is 0.05-1.2V, and the current density is 10A / g. The charging specific capacity is tested.

[0071] Table 1 As shown in Table 1, the batteries prepared using the negative electrode composite materials in the application examples exhibit significantly improved charge specific capacity and capacity retention. Specifically, compared to the above examples, Comparative Example 1 has a lower charge specific capacity and poorer cycle stability because conventional artificial graphite cannot provide growth space for silicon nanowires within the graphite particles and thus cannot confine the growth of silicon nanowires or buffer the volume expansion of silicon nanowires. Compared to the above examples, Comparative Example 2 has a lower charge specific capacity at a current density of 10 A / g because it lacks coating for fast ion conductors, resulting in a slower lithium-ion migration rate and poorer rate performance.

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A negative electrode composite material, characterized in that, The negative electrode composite material includes a porous graphite skeleton, silicon nanowires and metal nanoparticles deposited in the pores of the porous graphite skeleton, a first coating layer covering the surface of the porous graphite skeleton, and a second coating layer covering the surface of the first coating layer. The metal nanoparticles include gold nanoparticles; The first coating layer is an amorphous carbon coating layer; The second coating layer is a fast ion conductor coating layer.

2. The negative electrode composite material according to claim 1, characterized in that, The porous graphite framework has a pore size of 2~50 nm; and / or, The porosity of the porous graphite framework is 30-50%; and / or, The diameter of the silicon nanowires is 5~20 nm; and / or, The Dn50 of the metal nanoparticles is 2~10nm.

3. The negative electrode composite material according to claim 1, characterized in that, The thickness of the amorphous carbon coating layer is 5~20 nm; and / or, The thickness of the fast ion conductor coating layer is 20~100nm.

4. The negative electrode composite material according to claim 1, characterized in that, Based on the total mass of the negative electrode composite material, the content of the silicon nanowires is 10~40 wt%; and / or, Based on the total mass of the negative electrode composite material, the content of the gold nanoparticles is 0.5~1.5wt%.

5. The negative electrode composite material according to claim 1, characterized in that, The fast ion conductor coating is at least one of the following: aluminum-doped lithium titanium phosphate coating, aluminum-doped lithium germanium phosphate coating, aluminum-doped lithium zirconium phosphate coating, aluminum-doped lithium tin phosphate coating, and aluminum-doped lithium lanthanum zirconium oxide coating.

6. A method for preparing a negative electrode composite material, characterized in that, The preparation method includes the following steps: S1. Biomass material is subjected to hydrothermal treatment to obtain a carbon precursor. The carbon precursor is placed in a first inert atmosphere for activation treatment to obtain porous carbon. The porous carbon is subjected to a first calcination treatment in a second inert atmosphere to obtain a first material. The first material is ground and sieved to obtain porous graphite particles. S2. Disperse gold nanoparticles in a first solvent to obtain a suspension; immerse the porous graphite particles in the suspension and perform ultrasonic treatment to obtain a second material; perform a first drying treatment on the second material to obtain porous graphite particles loaded with gold nanoparticles. S3. Disperse the porous graphite particles loaded with gold nanoparticles in liquid silane to obtain a dispersion; subject the dispersion to a first vacuum treatment and a high-temperature treatment to obtain a third material; centrifuge and wash the third material and then perform a second drying treatment to obtain a porous graphite-silicon nanowire composite material. S4. The porous graphite-silicon nanowire composite material is subjected to a second vacuum treatment and then subjected to a second calcination treatment in a first composite atmosphere to obtain a composite material coated with a first coating layer; the composite material coated with the first coating layer is dispersed in a fast ion conductor precursor solution and spray-dried to obtain a fourth material; the fourth material is subjected to a third calcination treatment in a third inert atmosphere. The first composite atmosphere contains at least one of methane, acetylene, ethane, propane, and ethylene.

7. The preparation method according to claim 6, characterized in that, The biomass material includes at least one of cellulose, lignin, and starch; and / or, The liquid-phase silane is at least one selected from tetramethylsilane, dimethylsilane, methylsilane, phenylsilane, and diphenylsilane; and / or, The first solvent includes at least one of hexane and isooctane; and / or, The mass ratio of the porous graphite particles to the suspension is 1:(10~15), and the solid content in the suspension is 5~10%; and / or The mass ratio of the composite material coated with the first coating layer to the fast ion conductor precursor solution is 1:(2~3).

8. The preparation method according to claim 6, characterized in that, In step S1, the conditions for the hydrothermal treatment include: a temperature of 180~220℃ and a time of 4~8h; and / or, the conditions for the activation treatment include: a temperature of 700~900℃ and a time of 1~3h; and / or, the conditions for the first calcination treatment include: a temperature of 2600~3200℃ and a time of 1~3h; and / or, In step S2, the conditions for ultrasonic treatment include: a temperature of 15~35℃, a time of 20~40 min, and a frequency of 0.2~0.8 MHz; and / or, the conditions for the first drying treatment include: a temperature of 50~70℃ and a time of 3~5 h; and / or, In step S3, the pressure of the first vacuum treatment is 0.05~0.15 Pa; and / or, the conditions for the high-temperature treatment include: a temperature of 300~500℃ and a time of 1~3 h; and / or, the conditions for the second drying treatment include: a temperature of 60~90℃ and a time of 8~12 h; and / or, In step S4, the pressure of the second vacuum treatment is 0.05~0.15 Pa; and / or, the conditions of the second calcination treatment include: a temperature of 500~800℃ and a time of 0.5~2h; and / or, the conditions of the spray drying treatment include: an inlet air temperature of 150~200℃ and an outlet air temperature of 60~100℃; and / or, the conditions of the third calcination treatment include: a temperature of 700~800℃ and a time of 2~4h.

9. The preparation method according to claim 6, characterized in that, The method for preparing the gold nanoparticles includes: mixing an aqueous solution of chloroauric acid and a tetraoctylammonium bromide toluene solution and stirring to obtain a mixed solution; mixing the mixed solution with an aqueous solution of sodium borohydride and then performing an ice bath reduction treatment; The chloroauric acid aqueous solution has a molar mass of 0.05~0.15 mol / L; the tetraoctylammonium bromide toluene solution has a molar mass of 0.03~0.08 mol / L; and the sodium borohydride aqueous solution has a molar mass of 0.1~0.3 mol / L.

10. A battery, characterized in that, The battery includes a negative electrode material, which includes the negative electrode composite material according to any one of claims 1 to 5 and / or the negative electrode composite material prepared by the preparation method according to any one of claims 6 to 9.

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