CN114497476B - Expanded graphite nano-silicon composite anode material for lithium ion battery and preparation method thereof - Google Patents
Expanded graphite nano-silicon composite anode material for lithium ion battery and preparation method thereof Download PDFInfo
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Abstract
The invention provides an expanded graphite nano-silicon composite anode material for a lithium ion battery and a preparation method thereof, wherein high-purity flake graphite is firstly prepared into expandable graphite; then preparing the expandable graphite into expanded graphite in a reaction system; and meanwhile, under the protection of inert gas, silane is thermally decomposed to generate nano silicon, the nano silicon is deposited in and on the surface of the expanded graphite sheet, acetylene gas is introduced, and a reaction product enters a carbon coating section along with the gas flow to form a composite anode material which takes expanded graphite as a framework and is formed by depositing nano silicon on the expanded graphite sheet and the surface and then coating a layer of carbon material outside. Compared with the prior art, the invention skillfully utilizes the expanded graphite as the skeleton of the whole composite material, and utilizes the excellent conductivity of the graphite sheet layer in the expanded graphite, and the holes and the gaps of the expanded graphite reserve sufficient expansion space for the expansion in the process of removing and embedding the lithium from the nano silicon, thereby inhibiting the volume expansion of the composite material in the process of removing and embedding the lithium and ensuring the stability of the whole composite material in the circulating process.
Description
Technical Field
The invention relates to a silicon negative electrode material for a lithium ion battery, in particular to an expanded graphite nano silicon composite negative electrode material for a lithium ion battery and a preparation method thereof.
Background
The lithium ion battery has the advantages of high energy density, long cycle life, small self-discharge, no memory effect and the like, and is widely applied to the fields of consumer electronics, electric automobiles and energy storage power stations; with the popularity of lithium battery applications, there is an increasing demand for high energy density lithium ion batteries. The actual application capacity of the graphite cathode is very close to the theoretical specific capacity (372 mAh/g) at present. It is difficult to meet the increasing demand of the market for lithium battery energy density.
Silicon is ten times as large as the theoretical specific capacity (4200 mAh/g) of graphite, and has rich silicon reserves, low price and lower charge-discharge voltage, so that the silicon is expected to become a new generation negative electrode material of a lithium ion battery, attention of a large number of researchers is drawn, however, the silicon material is used as the negative electrode material of the lithium ion battery, and is accompanied by huge volume expansion (more than 300 percent) in the lithium removal and intercalation processes, so that cracking and pulverization of the electrode material are caused, capacity is quickly attenuated, and in addition, the problems of poor conductivity of the silicon material, difficulty in realizing quick transportation of lithium ions and electrons and the like are caused, so that the cycling stability and the multiplying power performance are poor. Limiting the popularization and application. How to design a novel material structure aiming at the defects of a silicon material becomes a problem to be solved at present.
Disclosure of Invention
Aiming at the problems that the silicon material has larger volume effect and poor conductivity in the electrochemical lithium intercalation and deintercalation process and affects the cycle performance and the multiplying power performance of the electrode material, the invention designs and realizes a composite negative electrode material which takes expanded graphite as a framework, nano silicon particles are deposited in and on the surface of an expanded graphite sheet layer, and a layer of acetylene antipyretic carbon material is coated outside for modification, and provides an expanded graphite nano silicon negative electrode composite material with good cycle stability and excellent multiplying power performance and a preparation method thereof.
The aim of the invention can be achieved by the following technical scheme:
the preparation method of the expanded graphite nano-silicon composite anode material for the lithium ion battery comprises the following steps:
s1, stirring and mixing flake graphite, an oxidant and an intercalator aqueous solution at a certain temperature, and washing, filtering and drying to obtain expandable graphite A;
in the process, since the flake graphite is a crystal with a layered structure, the layers are combined by weak van der Waals force, and a graphite interlayer compound is formed under the action of a strong oxidant and an intercalating agent;
s2, sending the A prepared in the step S1 into a reaction system, and pushing away graphite sheets by instant decomposition and gasification of a graphite interlayer compound at high temperature to macroscopically expand to form an intermediate product expanded graphite B;
s3, mixing high-purity silane and inert gas according to a certain proportion while performing the step S2, and then sending the mixture into a silicon deposition section of a reaction system, wherein the silane is thermally decomposed at high temperature to generate nano silicon particles, and nano silicon is deposited in and on the surface of a graphite sheet of the expanded graphite B to obtain an intermediate product C;
in the process, silane diffuses due to concentration gradient, part of the silane enters the expanded graphite sheet layer to generate nano silicon particles through pyrolysis, the nano silicon particles are deposited in the expanded graphite sheet layer, and part of the silane does not enter the expanded graphite sheet layer and is thermally decomposed to generate nano silicon particles, and the nano silicon particles are adsorbed on the surface of the expanded graphite B under the strong adsorption action of the expanded graphite;
s4, conveying the high-purity acetylene to a reaction system along with the air flow, controlling the flow of the acetylene, controlling the acetylene concentration of an acetylene deposition section of the reaction system, controlling the temperature to 600-1200 ℃, controlling the pressure to 0.01-100KPa, controlling the reaction residence time of materials in the section to 0.5-5h, and introducing the high-purity acetylene into a deposition device, wherein the high-purity acetylene is deposited on the surface of the intermediate product C due to pyrolysis reaction, so as to obtain an intermediate D;
in the step S4, the intermediate C is originally expanded by an oxidant and an intercalation agent, the prepared expanded graphite has some surface defects, after being coated by acetylene pyrolytic carbon at high temperature, the surface defects are repaired to a certain extent, the expansion volume is reduced, and the graphite sheet layer is contracted to tightly wrap the silicon nano-particles in the graphite sheet layer;
s5, cooling, grading and screening the intermediate D to obtain the expanded graphite nano-silicon composite anode material;
preferably, the purity of the crystalline flake graphite in the step S1 is more than or equal to 99.5%, and the granularity is 0.1-45 mu m; the oxidant is one or more of potassium permanganate, potassium dichromate, trioxymethylene, potassium chlorate and hydrogen peroxide which are not sulfur and nitrogen elements; the intercalation agent is one or more of phosphoric acid, perchloric acid and glacial acetic acid which are not sulfur-containing and nitrogen-containing elements;
preferably, in step S1, the crystalline flake graphite: oxidizing agent: the dosage ratio of the intercalation agent is 0.1-10kg:0.1-10L:0.26-2.07L; the heating temperature is 25-85 ℃ and the reaction time is 0.01-5h;
preferably, the control range of the volume quality of the expanded graphite B in the step S2 is 50-400mL/g; the high-temperature reaction temperature is 600-1200 ℃; the pressure is 0.01-100KPa; the reaction time is 0.05-2h;
preferably, the molar concentration ratio of the high-purity silane to the inert gas in the step S3 is 1-10:5; the flow rate of the high-purity silane is less than or equal to 300L/min; the inert gas in the step S3 is one or more of nitrogen, argon or helium;
preferably, in the step S4, the acetylene flow rate is less than 200L/min, and the acetylene concentration of the acetylene deposition section is 0.01-100g/L; the preparation method aims at controlling the coating thickness of the pyrolytic carbon layer by controlling the flow of acetylene and the acetylene concentration of the acetylene deposition section, so as to prepare the expanded graphite nano-silicon composite anode material with a certain specific capacity;
preferably, the steps S2, S3 and S4 are in a communicated reaction system, and the expanded graphite is uniformly dispersed in the reaction system all the time; due to the low volume density of the expanded graphite B and the action of the flow of the air flow in the reaction system and the turbulence device of the reaction system, the expanded graphite B is uniformly distributed in the reaction system;
the invention provides an expanded graphite nano-silicon composite anode material for a lithium ion battery;
the invention also provides application of the expanded graphite nano-silicon composite anode material for the lithium ion battery, and the expanded graphite nano-silicon composite anode material is matched with other anode materials to be used as the anode material of the lithium ion battery.
Compared with the prior art, the invention has the following advantages:
1. the expanded graphite silicon negative electrode composite material for the lithium ion battery takes expanded graphite as a framework, nano silicon particles are deposited in and on the surface of a graphite sheet layer, and after the nano silicon particles are deposited, pyrolytic carbon of acetylene is used for wrapping the nano silicon particles, so that the surface of the expanded graphite is modified; after the expandable graphite is expanded, the layer-by-layer spacing of the graphite sheets is obviously enlarged, a plurality of open gaps exist between the sheets to cause overlarge specific surface area, which is unfavorable for the formation of SEI films, and the coating of the carbon material wraps and modifies the surface of the expandable graphite, so that the surface pores are filled, the specific surface area of the material is reduced, and the stability of the material is enhanced. Meanwhile, in the process of preparing the composite material, the silicon content of the final product and the size of the grain size of the nano silicon are controlled by controlling the flow rate of silane in a reaction system, the molar concentration ratio of silane to inert gas and the reaction condition of the reaction system; the crystal grains are smaller, the absolute expansion of silicon is smaller, and the cycle performance of the composite material is better; the expanded graphite coated by pyrolytic carbon also reduces the direct exposure of silicon nano particles on the surface of the material; the graphite sheets in the expanded graphite are connected with each other to form a three-dimensional conductive network, so that the electronic conductivity of the material is improved, the improvement of the overall dynamic performance of the material, the exertion of the material capacity and the improvement of the multiplying power performance and the cycle performance are facilitated, and the problems of partial inactivation of the material and the reduction of the material capacity and the cycle performance caused by the too low migration speed of electrons and ions in the battery cycle process are avoided. Further, nano silicon particles are deposited in the graphite sheet, at this time, the volume change of nano silicon in the lithium removal and intercalation process can be effectively buffered due to the pores of the expanded graphite, so that the rapid transmission of ions and electrons is facilitated, and the circulation stability of the material is improved.
2. In the invention, the excellent conductivity of the graphite flake of the expanded graphite is beneficial to the exertion of material multiplying power and cycle performance; the holes and the gaps of the expanded graphite reserve sufficient expansion space for the lithium removing and inserting process of the nano silicon, so that the volume expansion of the composite material in the lithium removing and inserting process is restrained, the stability of the whole material in the circulating process is ensured, and finally, the defects of the expanded graphite are repaired by adopting the coating of the carbon material, so that the electrochemical performances such as the conductivity, the circulating stability, the charge-discharge efficiency, the multiplying power performance and the like of the silicon cathode are better improved.
3. The preparation of the expanded graphite, the preparation of the nano silicon particles by the silane and the pyrolytic carbon coating of the acetylene are creatively combined and implemented in the same reaction system, so that the preparation method is beneficial to energy conservation and industrial production.
Drawings
FIG. 1 is a flow chart of the preparation of an expanded graphite nano-silicon composite anode material for a lithium ion battery;
FIG. 2 is an SEM morphology of the expanded graphite nano-silicon composite anode material prepared in example 2;
FIG. 3 is a schematic structural diagram of an expanded graphite nano-silicon composite anode material prepared by the method;
fig. 4 is a cycle performance chart of the expanded graphite nano-silicon composite anode material prepared in examples 1-5 of the present application.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1:
the preparation method of the expanded graphite nano-silicon composite anode material for the lithium ion battery is implemented according to the preparation flow chart shown in fig. 1:
(1) 3kg particle size range Dmin:0.25 μm, D10:2.5 μm, D50:5.4 μm, dmax:18.65 μm; stirring and mixing the crystalline flake graphite with the purity of 99.92 percent with potassium permanganate and glacial acetic acid in a container, wherein the crystalline flake graphite is prepared by the following steps: potassium permanganate: the glacial acetic acid ratio was 3kg:0.3L:0.26L, controlling the temperature to 45 ℃ and the reaction time to 0.5h, and obtaining the expandable graphite A through water washing, solid-liquid separation and drying.
(2) Conveying the A into a reaction system, controlling the reaction temperature to be 650 ℃, controlling the pressure to be 25KPa, enabling the material reaction time to be 1h, simultaneously opening a high-purity silane and high-purity argon conveying pipeline, and controlling the molar concentration ratio of the high-purity silane to the high-purity argon to be 1:2.5, the flow of the high-purity silane is 60L/min, and the intermediate product C is obtained.
(3) The intermediate product C enters an acetylene deposition section of the reactor along with air flow, the temperature is controlled to 650 ℃, the pressure is controlled to 25KPa, the reaction residence time of materials in the section is controlled to 3h, high-purity acetylene is introduced into the acetylene deposition section, the flow is 125L/min, the high-purity acetylene generates pyrolytic carbon due to pyrolysis reaction, and the pyrolytic carbon is deposited on the surface of the intermediate product C, so that an intermediate D is obtained.
(4) And cooling, grading and screening the intermediate D to obtain the finished product of the expanded graphite nano-silicon composite anode material.
Performing electrochemical performance test on the button cell composed of the obtained expanded graphite nano silicon composite anode material and metallic lithium, placing the assembled button cell on a new-wire test cabinet for test, discharging the current of 0.1C to 0.005V, and discharging the current of 0.02C to 0.005V after the button cell is placed for 30 min; the 0.1C current was charged to 2.0V, recording the charge capacity and first effect. The specific discharge capacity of the negative electrode plate can reach 1347mAh/g, the first efficiency is 90.8%, and the capacity of 83.4% can be maintained after 200 cycles.
Example 2:
the preparation method of the expanded graphite nano-silicon composite anode material for the lithium ion battery is implemented according to the preparation flow chart shown in fig. 1:
(1) 2.2kg of particles were taken as Dmin:0.67 μm, D10:4.8 μm, D50:10.7 μm, dmax:27.66 μm; stirring and mixing crystalline flake graphite with purity of 99.93 percent with potassium permanganate and glacial acetic acid in a container, wherein the crystalline flake graphite: potassium permanganate: the ratio of glacial acetic acid was 2.2kg:0.35L:0.26L, controlling the temperature to 55 ℃ and the reaction time to 0.5h, and obtaining the expandable graphite A through water washing, solid-liquid separation and drying.
(2) Conveying the A into a reaction system, controlling the reaction temperature to 850 ℃, controlling the pressure to 45KPa, enabling the material reaction time to be 1.5h, simultaneously opening a high-purity silane and high-purity argon conveying pipeline, and controlling the molar concentration ratio of the high-purity silane to the high-purity argon to be 1:2.0, the flow of the high-purity silane is 140L/min, and the intermediate product C is obtained.
(3) The intermediate product C enters an acetylene deposition section of the reactor along with air flow, the temperature is controlled to 850 ℃, the pressure is controlled to be 45KPa, the reaction residence time of materials in the section is controlled to be 4h, high-purity acetylene is introduced into the acetylene deposition section, the flow is 85L/min, the high-purity acetylene generates pyrolytic carbon due to pyrolysis reaction, and the pyrolytic carbon is deposited on the surface of the intermediate product C, so that an intermediate D is obtained.
(4) And cooling, grading and screening the intermediate D to obtain the finished product of the expanded graphite nano-silicon composite anode material.
Performing electrochemical performance test on the button cell composed of the obtained expanded graphite nano silicon composite anode material and metallic lithium, placing the assembled button cell on a new-wire test cabinet for test, discharging the current of 0.1C to 0.005V, and discharging the current of 0.02C to 0.005V after the button cell is placed for 30 min; the 0.1C current was charged to 2.0V, recording the charge capacity and first effect. The specific discharge capacity of the negative electrode plate can reach 1368mAh/g, the first efficiency is 89.5%, and the capacity of 82.9% can be still maintained after 200 cycles.
Example 3:
the preparation method of the expanded graphite nano-silicon composite anode material for the lithium ion battery is implemented according to the preparation flow chart shown in fig. 1:
(1) 4.0kg of particles were taken as Dmin:0.21 μm, D10:5.2 μm, D50:11.4 μm, dmax:34.54 μm; stirring and mixing the crystalline flake graphite with the purity of 99.91 percent with potassium permanganate and glacial acetic acid in a container, wherein the crystalline flake graphite is prepared by the following steps: potassium permanganate: the glacial acetic acid ratio was 4.0kg:1.24L:0.65L, controlling the temperature to 70 ℃ and the reaction time to 0.1h, and obtaining the expandable graphite A through water washing, solid-liquid separation and drying.
(2) Conveying the A into a reaction system, controlling the reaction temperature to 950 ℃, controlling the pressure to 10KPa, enabling the material reaction time to be 0.5h, simultaneously opening a high-purity silane and high-purity argon conveying pipeline, and controlling the molar concentration ratio of the high-purity silane to the high-purity argon to be 1:1.6, the flow of the high-purity silane is 120L/min, and an intermediate product C is obtained.
(3) The intermediate product C enters an acetylene deposition section of the reactor along with air flow, the temperature is controlled to 950 ℃, the pressure is controlled to 10KPa, the reaction residence time of materials in the section is controlled to 4h, high-purity acetylene is introduced into the acetylene deposition section, the flow is 36L/min, the high-purity acetylene generates pyrolytic carbon due to pyrolysis reaction, and the pyrolytic carbon is deposited on the surface of the intermediate product C, so that an intermediate D is obtained.
(4) And cooling, grading and screening the intermediate D to obtain the finished product of the expanded graphite nano-silicon composite anode material.
Performing electrochemical performance test on the button cell composed of the obtained expanded graphite nano silicon composite anode material and metallic lithium, placing the assembled button cell on a new-wire test cabinet for test, discharging the current of 0.1C to 0.005V, and discharging the current of 0.02C to 0.005V after the button cell is placed for 30 min; the 0.1C current was charged to 2.0V, recording the charge capacity and first effect. The specific discharge capacity of the negative electrode plate can reach 1236mAh/g, the first efficiency is 88.6%, and the capacity of 81.8% can be maintained after 200 cycles.
Example 4:
the preparation method of the expanded graphite nano-silicon composite anode material for the lithium ion battery is implemented according to the preparation flow chart shown in fig. 1:
(1) 5.0kg of the particle size range Dmin:0.39 μm, D10:7.81 μm, D50:16.32 μm, dmax:41.26 μm; stirring and mixing the crystalline flake graphite with the purity of 99.90 percent with potassium permanganate and glacial acetic acid in a container, wherein the crystalline flake graphite is prepared by the following steps: potassium permanganate: the glacial acetic acid ratio was 5.0kg:1.74L:0.86L, controlling the temperature to 55 ℃ and the reaction time to 0.6h, and obtaining the expandable graphite A through water washing, solid-liquid separation and drying.
(2) Conveying the A into a reaction system, controlling the reaction temperature to 880 ℃, controlling the pressure to 5KPa, enabling the material reaction time to be 1.5h, simultaneously opening a high-purity silane and high-purity argon conveying pipeline, and controlling the molar concentration ratio of the high-purity silane to the high-purity argon to be 1:4.2, the flow of the high-purity silane is 220L/min, and an intermediate product C is obtained.
(3) The intermediate product C enters an acetylene deposition section of the reactor along with air flow, the temperature is controlled to 880 ℃, the pressure is controlled to 5KPa, the reaction residence time of materials in the section is controlled to 2.5h, high-purity acetylene is introduced into the acetylene deposition section, the flow is 45L/min, the high-purity acetylene generates pyrolytic carbon due to pyrolysis reaction, and the pyrolytic carbon is deposited on the surface of the intermediate product C, so that an intermediate D is obtained.
(4) And cooling, grading and screening the intermediate D to obtain the finished product of the expanded graphite nano-silicon composite anode material.
Performing electrochemical performance test on the button cell composed of the obtained expanded graphite nano silicon composite anode material and metallic lithium, placing the assembled button cell on a new-wire test cabinet for test, discharging the current of 0.1C to 0.005V, and discharging the current of 0.02C to 0.005V after the button cell is placed for 30 min; the 0.1C current was charged to 2.0V, recording the charge capacity and first effect. The specific discharge capacity of the negative electrode plate can reach 1367mAh/g, the first efficiency is 85.7%, and the capacity of 81.9% can be maintained after 200 cycles.
Example 5:
the preparation method of the expanded graphite nano-silicon composite anode material for the lithium ion battery is implemented according to the preparation flow chart shown in fig. 1:
(1) 3.6kg of particles were taken in the range Dmin:0.12 μm, D10:2.21 μm, D50:6.35 μm, dmax:37.26 μm; stirring and mixing the crystalline flake graphite with the purity of 99.870% with potassium permanganate and glacial acetic acid in a container, wherein the crystalline flake graphite is prepared by the following steps: potassium permanganate: the glacial acetic acid ratio was 3.6kg:2.04L:2.07L, controlling the temperature to 25 ℃ and the reaction time to 3.5h, and obtaining the expandable graphite A through water washing, solid-liquid separation and drying.
(2) Conveying the A into a reaction system, controlling the reaction temperature to 1050 ℃, controlling the pressure to 2KPa, enabling the material reaction time to be 0.5h, simultaneously opening a high-purity silane and high-purity argon conveying pipeline, and controlling the molar concentration ratio of the high-purity silane to the high-purity argon to be 1:4.8, the flow of the high-purity silane is 250L/min, and the intermediate product C is obtained.
(3) The intermediate product C enters an acetylene deposition section of the reactor along with air flow, the temperature is controlled to 1050 ℃, the pressure is controlled to be 2KPa, the reaction residence time of materials in the section is controlled to be 4.5h, high-purity acetylene is introduced into the acetylene deposition section, the flow is 85L/min, the high-purity acetylene generates pyrolytic carbon due to pyrolysis reaction, and the pyrolytic carbon is deposited on the surface of the intermediate product C, so that an intermediate D is obtained.
(4) And cooling, grading and screening the intermediate D to obtain the finished product of the expanded graphite nano-silicon composite anode material.
The obtained expanded graphite nano silicon composite anode material and artificial graphite are taken as anode materials and metal lithium together according to the mass ratio of 1:9 to form a button cell for electrochemical performance test, the assembled button cell is placed on a Xinwei test cabinet for test, the current of 0.1C is discharged to 0.005V, and the current of 0.02C is discharged to 0.005V after the mixture is placed for 30 min; the 0.1C current was charged to 2.0V, recording the charge capacity and first effect. The specific discharge capacity of the negative electrode plate can reach 450mAh/g, the first efficiency is 93.6%, and the capacity of 88.6% can be maintained after 200 cycles.
The above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (8)
1. The preparation method of the expanded graphite nano-silicon composite anode material for the lithium ion battery is characterized by comprising the following steps of:
s1, stirring and mixing flake graphite, an oxidant and an intercalator aqueous solution under the heating condition, and washing, filtering and drying to obtain expandable graphite A;
s2, sending the A prepared in the step S1 into a silicon deposition section of a reaction system, and instantly decomposing and gasifying oxide and intercalation agent among the expandable graphite A layers to push away the expandable graphite sheets at high temperature so as to prepare expanded graphite B;
s3, mixing high-purity silane and protective gas according to a certain proportion while performing the step S2, and then sending the mixture into a silicon deposition section of a reaction system, wherein the silane is thermally decomposed to generate nano silicon particles, and nano silicon is deposited in and on the surface of a graphite sheet layer of the expanded graphite B to obtain an intermediate product C, wherein the protective gas is nitrogen or inert gas;
s4, conveying high-purity acetylene to a reaction system along with the air flow entering a carbon coating section of the reaction system, controlling the flow rate of the acetylene and the concentration of the acetylene in an acetylene deposition section of the reaction system, controlling the reaction temperature to be 600-1200 ℃, the pressure to be 0.01-100KPa, controlling the reaction residence time of materials in the section to be 0.5-5h, carrying out pyrolysis reaction on the high-purity acetylene, and depositing carbon on the surface of the intermediate product C to obtain an intermediate D;
s5, cooling, grading and screening the intermediate D to obtain the expanded graphite nano-silicon composite anode material;
wherein, the purity of the crystalline flake graphite in S1 is more than or equal to 99.5 percent, and the granularity is 0.1 mu m-45 mu m; the oxidant is one or more of potassium permanganate, potassium chlorate and hydrogen peroxide which are not sulfur and nitrogen elements; the intercalation agent is one or more of phosphoric acid, perchloric acid and glacial acetic acid which are not sulfur-containing and nitrogen-containing elements;
flake graphite: oxidizing agent: the dosage ratio of the intercalation agent is 0.1-10kg:0.1-10L:0.26-2.07L; the heating temperature is 25-85 ℃ and the reaction time is 0.01-5h.
2. The preparation method of the expanded graphite nano-silicon composite anode material for the lithium ion battery, which is characterized in that the control range of the expanded volume and the quality of the expanded graphite B in S2 is 50-400mL/g; the high-temperature reaction temperature is 600-1200 ℃; the pressure is 0.01-100KPa; the reaction time is 0.05-2h.
3. The method for preparing the expanded graphite nano-silicon composite anode material for the lithium ion battery according to claim 1 or 2, wherein the molar concentration ratio of the high-purity silane to the inert gas in the S3 is 1-10:5; the flow rate of the high-purity silane is less than or equal to 300L/min.
4. The method for preparing an expanded graphite nano-silicon composite anode material for a lithium ion battery according to claim 1 or 2, wherein the inert gas in S3 is one or more of argon or helium.
5. The preparation method of the expanded graphite nano-silicon composite anode material for the lithium ion battery according to claim 1 or 2, wherein the flow rate of acetylene in S4 is less than 200L/min, and the concentration of acetylene in an acetylene deposition section is 0.01-100g/L.
6. The method for preparing the expanded graphite nano-silicon composite anode material for the lithium ion battery according to claim 1 or 2, wherein the steps S2, S3 and S4 are in a communicated reaction system, and the expanded graphite is uniformly dispersed in the reaction system all the time.
7. An expanded graphite nano-silicon composite anode material for lithium ion batteries, which is characterized by being prepared by the preparation method of any one of claims 1-6.
8. The use of the expanded graphite nano-silicon composite negative electrode material for a lithium ion battery according to claim 7, wherein the expanded graphite nano-silicon composite negative electrode material is matched with other negative electrode materials to be used as the negative electrode material of the lithium ion battery.
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