CN114497476A - Expanded graphite nano-silicon composite negative electrode material for lithium ion battery and preparation method thereof - Google Patents
Expanded graphite nano-silicon composite negative electrode 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 cathode material for a lithium ion battery and a preparation method thereof, wherein high-purity crystalline flake graphite is prepared into expandable graphite; then preparing the expandable graphite into expanded graphite in a reaction system; meanwhile, under the protection of inert gas, silane is thermally decomposed to generate nano-silicon, the nano-silicon is deposited in the expanded graphite sheet layer and on the surface of the expanded graphite sheet layer, acetylene gas is introduced, reaction products enter a carbon coating section along with gas flow, and the composite cathode material which takes the expanded graphite as a framework and is formed by coating a layer of carbon material on the outer surface of the expanded graphite sheet layer and the surface of the expanded graphite sheet layer is coated with the nano-silicon. Compared with the prior art, the invention skillfully utilizes the expanded graphite as the framework of the whole composite material, utilizes the excellent conductivity of the graphite sheet layer in the expanded graphite, and reserves sufficient expansion space for the expansion in the process of lithium intercalation and deintercalation of nano silicon by the holes and the gaps of the expanded graphite, thereby inhibiting the volume expansion of the composite material in the process of lithium intercalation and ensuring the stability of the whole 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 the 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 popularization of lithium batteries, the demand for high energy density lithium ion batteries is increasing. The practical application capacity of the graphite negative electrode is very close to the theoretical specific capacity (372mAh/g) at present. It is difficult to meet the increasing demand of the market for energy density of lithium batteries.
Silicon is expected to become a new-generation cathode material of a lithium ion battery due to the fact that the silicon is ten times of the theoretical specific capacity (4200mAh/g) of graphite, the silicon is rich in reserve, low in price and low in charging and discharging voltage, and attention of researchers is attracted, but the silicon material serving as the cathode material of the lithium ion battery is accompanied by huge volume expansion (more than 300%) in the processes of lithium removal and lithium insertion, cracking and pulverization of an electrode material can be caused, capacity is rapidly attenuated, and in addition, the problems that the conductivity of the silicon material is poor, rapid transportation of lithium ions and electrons is difficult to achieve and the like are caused, and the cycle stability and the rate performance of the silicon material are poor. The popularization and the application of the method are limited. How to design a novel material structure aiming at the defects of the silicon material becomes a problem to be solved urgently at present.
Disclosure of Invention
The invention aims to solve the problems that the larger volume effect and poor conductivity of a silicon material in the electrochemical lithium deintercalation process affect the cycle performance and the rate performance of an electrode material, designs and realizes a composite cathode material which takes expanded graphite as a framework, deposits nano silicon particles in and on the surface of an expanded graphite sheet layer and is modified by coating a layer of acetylene antipyretic carbon material outside, and provides an expanded graphite nano silicon cathode composite material with good cycle stability and excellent rate performance and a preparation method thereof.
The purpose of the invention can be realized by the following technical scheme:
a preparation method of an expanded graphite nano-silicon composite negative electrode material for a lithium ion battery comprises the following steps:
s1, stirring and mixing the flake graphite with an oxidant and an intercalation agent aqueous solution at a certain temperature, washing with water, filtering and drying to obtain expandable graphite A;
in the process, because the flake graphite is a crystal with a layered structure, the layers are combined with each other by weak van der Waals force, and a graphite interlayer compound can be formed under the action of a strong oxidant and an intercalator;
s2, feeding the A prepared in the step S1 into a reaction system, and instantly decomposing and gasifying a graphite intercalation compound at high temperature to push away graphite sheets so as to generate expansion macroscopically and form intermediate expanded graphite B;
s3, mixing high-purity silane and inert gas according to a certain proportion while carrying out 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 the nano silicon is deposited in and on the graphite sheet layer of the expanded graphite B to obtain an intermediate product C;
in the process, silane can diffuse due to concentration gradient, part of silane enters the expanded graphite sheet layer to be pyrolyzed to generate nano silicon particles, the nano silicon particles are deposited in the expanded graphite sheet layer, part of silane does not enter the expanded graphite sheet layer to be pyrolyzed 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, enabling the intermediate product C to enter a carbon coating section of a reaction system along with airflow, conveying high-purity acetylene to the reaction system, controlling the flow rate of the acetylene, controlling the concentration of the acetylene in an acetylene deposition section of the reaction system, the 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, introducing the high-purity acetylene into a deposition device, and depositing the high-purity acetylene on the surface of the intermediate product C due to pyrolysis reaction to obtain an intermediate D;
in step S4, the intermediate C is originally formed by expanding the oxidant and the intercalating agent, and the prepared expanded graphite has some surface defects, and after coating with acetylene pyrolytic carbon at high temperature, the surface defects are repaired to some extent, and the expanded volume is reduced, so that the graphite sheet shrinks, and the silicon nano-particles in the graphite sheet are tightly coated;
s5, cooling, grading and screening the intermediate D to obtain the expanded graphite nano-silicon composite anode material;
preferably, the purity of the flake graphite in the step S1 is more than or equal to 99.5%, and the particle size is 0.1-45 μm; the oxidant is one or more of potassium permanganate, potassium dichromate, potassium trioxide, potassium chlorate and hydrogen peroxide which do not contain sulfur and nitrogen elements; the intercalation agent is one or more of phosphoric acid, perchloric acid and glacial acetic acid which do not contain sulfur and nitrogen elements;
preferably, in step S1, the ratio of flake graphite: oxidizing agent: the dosage ratio of the intercalation agent is 0.1-10 kg: 0.1-10L: 0.26-2.07L; the heating temperature is 25-85 ℃, and the reaction time is 0.01-5 h;
preferably, the control range of the expanded volume quality of the expanded graphite B in the step S2 is 50-400 mL/g; the high-temperature reaction temperature is 600-1200 ℃; the pressure is 0.01-100 KPa; the reaction time is 0.05-2 h;
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; in the step S3, the inert gas is one or more of nitrogen, argon or helium;
preferably, the acetylene flow rate in the step S4 is less than 200L/min, and the acetylene concentration in the acetylene deposition section is 0.01-100 g/L; the method is characterized in that the coating thickness of a pyrolytic carbon layer is controlled by controlling the flow rate of acetylene and the concentration of acetylene at an acetylene deposition section, so that the expanded graphite nano-silicon composite anode material with certain specific capacity is prepared;
preferably, the steps S2, S3 and S4 are performed in a connected reaction system, and the expanded graphite is uniformly dispersed in the reaction system all the time; due to the characteristic of low volume density of the expanded graphite B, the expanded graphite B is uniformly distributed in the reaction system under the action of the flow of the airflow in the reaction system and the turbulent device of the reaction system;
the invention provides an expanded graphite nano-silicon composite negative electrode material for a lithium ion battery;
the invention also provides an application of the expanded graphite nano-silicon composite negative electrode material for the lithium ion battery, and 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.
Compared with the prior art, the invention has the following advantages:
1. the expanded graphite silicon cathode composite material for the lithium ion battery takes expanded graphite as a framework, nano silicon particles are deposited in a graphite sheet layer and on the surface of the graphite sheet layer, and the nano silicon particles are coated by pyrolytic carbon of acetylene after being deposited so as to modify the surface of the expanded graphite; after the expandable graphite is expanded, the layer-to-layer distance of the graphite sheets is obviously enlarged, a plurality of open gaps exist among the sheets, so that the specific surface area is overlarge, and the SEI film is not favorably formed. Meanwhile, in the process of preparing the composite material, the silicon content of a final product and the size of the grain size of the nano silicon crystal 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 small, the absolute expansion of silicon is small, and the cycle performance of the composite material is better; the expanded graphite coated by pyrolytic carbon also reduces the direct exposure of silicon nanoparticles on the surface of the material; because graphite flake layers in the expanded graphite are mutually connected to form a three-dimensional conductive network, 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 rate capability and the cycle performance are facilitated, and the partial inactivation of the material and the reduction of the material capacity and the cycle performance caused by the overlow migration speed of electrons and ions in the cycle process of the battery are avoided. Further, the nano-silicon particles are deposited in the graphite sheet layer, and at the moment, the volume change of the nano-silicon in the lithium releasing and embedding 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 sheet layer of the expanded graphite is utilized to be beneficial to the exertion of the multiplying power and the cycle performance of the material; the holes and the gaps of the expanded graphite reserve sufficient expansion space for the lithium desorption process of the nano silicon, so that the volume expansion of the composite material in the lithium desorption process is inhibited, the stability of the whole material in the circulation process is ensured, and finally, the defects of the expanded graphite are repaired by coating the carbon material, so that the electrochemical properties such as the conductivity, the circulation stability, the charge and discharge efficiency, the rate capability and the like of the silicon cathode are better improved.
3. The invention creatively combines the preparation of the expanded graphite, the preparation of the nano silicon particles by the silane and the coating of the pyrolytic carbon of the acetylene in the same reaction system, and 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 negative electrode material for a lithium ion battery according to the present invention;
FIG. 2 is an SEM topography 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 present application;
fig. 4 is a graph showing cycle performance of the expanded graphite nano-silicon composite anode materials prepared in examples 1 to 5 of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described, and it is obvious that the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1:
a preparation method of an expanded graphite nano-silicon composite negative electrode material for a lithium ion battery is implemented according to a preparation flow chart shown in figure 1:
(1) the particle size range of 3kg is Dmin: 0.25 μm, D10: 2.5 μm, D50: 5.4 μm, Dmax: 18.65 μm; stirring and mixing flake graphite with the purity of 99.92 percent, potassium permanganate and glacial acetic acid in a container, wherein the content of the flake graphite: potassium permanganate: the ratio of glacial acetic acid was 3 kg: 0.3L: 0.26L, the temperature is controlled to be 45 ℃, the reaction time is 0.5h, and the expandable graphite A is obtained after water washing, solid-liquid separation and drying.
(2) Conveying the A into a reaction system, controlling the reaction temperature to be 650 ℃, the pressure to be 25KPa, and 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 rate of the high-purity silane is 60L/min, and an intermediate product C is obtained.
(3) And (3) allowing the intermediate product C to enter an acetylene deposition section of the reactor along with the airflow, controlling the temperature at 650 ℃, controlling the pressure at 25KPa, controlling the reaction residence time of the material in the section to be 3h, introducing high-purity acetylene into the acetylene deposition section, wherein the flow rate is 125L/min, and the high-purity acetylene generates pyrolytic carbon due to pyrolysis reaction and is deposited on the surface of the intermediate product C to obtain an intermediate product D.
(4) And cooling, grading and screening the intermediate D to obtain the finished product of the expanded graphite nano-silicon composite negative electrode material.
The button cell composed of the obtained expanded graphite nano-silicon composite negative electrode material and metallic lithium is tested for electrochemical performance, the assembled button cell is placed on a Xinwei test cabinet for testing, the current of 0.1C is discharged to 0.005V, and the button cell is placed for 30min and then discharged to 0.005V at the current of 0.02C; the charge capacity and first effect were recorded with a 0.1C current charged to 2.0V. The specific discharge capacity of the negative pole piece can reach 1347mAh/g, the first efficiency is 90.8%, and the capacity of 83.4% can be still maintained after 200 cycles.
Example 2:
a preparation method of an expanded graphite nano-silicon composite negative electrode material for a lithium ion battery is implemented according to a preparation flow chart shown in figure 1:
(1) 2.2kg particle size range Dmin: 0.67 μm, D10: 4.8 μm, D50: 10.7 μm, Dmax: 27.66 μm; flake graphite with the purity of 99.93 percent, potassium permanganate and glacial acetic acid are stirred and mixed in a container, wherein the flake graphite: potassium permanganate: the ratio of glacial acetic acid was 2.2 kg: 0.35L: 0.26L, the temperature is controlled to be 55 ℃, the reaction time is 0.5h, and the expandable graphite A is obtained after water washing, solid-liquid separation and drying.
(2) Conveying the A into a reaction system, controlling the reaction temperature to be 850 ℃, the pressure to be 45KPa, 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 rate of the high-purity silane is 140L/min, and an intermediate product C is obtained.
(3) And (3) allowing the intermediate product C to enter an acetylene deposition section of the reactor along with the airflow, controlling the temperature to be 850 ℃, controlling the pressure to be 45KPa, controlling the reaction residence time of the material in the section to be 4h, introducing high-purity acetylene into the acetylene deposition section, wherein the flow rate is 85L/min, and the high-purity acetylene generates pyrolytic carbon due to pyrolysis reaction and is deposited on the surface of the intermediate product C to obtain an intermediate product D.
(4) And cooling, grading and screening the intermediate D to obtain the finished product of the expanded graphite nano-silicon composite negative electrode material.
The button cell composed of the obtained expanded graphite nano-silicon composite negative electrode material and metallic lithium is tested for electrochemical performance, the assembled button cell is placed on a Xinwei test cabinet for testing, the current of 0.1C is discharged to 0.005V, and the button cell is placed for 30min and then discharged to 0.005V at the current of 0.02C; the charge capacity and first effect were recorded with a 0.1C current charged to 2.0V. The specific discharge capacity of the negative pole piece can reach 1368mAh/g, the first efficiency is 89.5%, and 82.9% of capacity can be still maintained after 200 cycles.
Example 3:
a preparation method of an expanded graphite nano-silicon composite negative electrode material for a lithium ion battery is implemented according to a preparation flow chart shown in figure 1:
(1) the particle size range of 4.0kg was Dmin: 0.21 μm, D10: 5.2 μm, D50: 11.4 μm, Dmax: 34.54 μm; stirring and mixing flake graphite with the purity of 99.91 percent, potassium permanganate and glacial acetic acid in a container, wherein the content of the flake graphite is as follows: potassium permanganate: the ratio of glacial acetic acid was 4.0 kg: 1.24L: 0.65L, the temperature is controlled to be 70 ℃, the reaction time is 0.1h, and the expandable graphite A is obtained after water washing, solid-liquid separation and drying.
(2) Conveying the A into a reaction system, controlling the reaction temperature to be 950 ℃, the pressure to be 10KPa, 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 rate of the high-purity silane is 120L/min, and an intermediate product C is obtained.
(3) And (3) allowing the intermediate product C to enter an acetylene deposition section of the reactor along with the airflow, controlling the temperature to be 950 ℃, controlling the pressure to be 10KPa, controlling the reaction residence time of the material in the section to be 4h, introducing high-purity acetylene into the acetylene deposition section, wherein the flow rate is 36L/min, and the high-purity acetylene generates pyrolytic carbon due to pyrolysis reaction and is deposited on the surface of the intermediate product C to obtain an intermediate product D.
(4) And cooling, grading and screening the intermediate D to obtain the finished product of the expanded graphite nano-silicon composite negative electrode material.
The button cell composed of the obtained expanded graphite nano-silicon composite negative electrode material and metallic lithium is tested for electrochemical performance, the assembled button cell is placed on a Xinwei test cabinet for testing, the current of 0.1C is discharged to 0.005V, and the button cell is placed for 30min and then discharged to 0.005V at the current of 0.02C; the charge capacity and first effect were recorded with a 0.1C current charged to 2.0V. The specific discharge capacity of the negative pole piece can reach 1236mAh/g, the first efficiency is 88.6%, and the capacity of 81.8% can be still maintained after 200 cycles.
Example 4:
a preparation method of an expanded graphite nano-silicon composite negative electrode material for a lithium ion battery is implemented according to a preparation flow chart shown in figure 1:
(1) the particle size range of 5.0kg was Dmin: 0.39 μm, D10: 7.81 μm, D50: 16.32 μm, Dmax: 41.26 μm; stirring and mixing flake graphite with the purity of 99.90 percent, potassium permanganate and glacial acetic acid in a container, wherein the content of the flake graphite: potassium permanganate: the ratio of glacial acetic acid was 5.0 kg: 1.74L: 0.86L, the temperature is controlled to be 55 ℃, the reaction time is 0.6h, and the expandable graphite A is obtained after water washing, solid-liquid separation and drying.
(2) Conveying the A into a reaction system, controlling the reaction temperature to be 880 ℃, the pressure to be 5KPa, 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 rate of the high-purity silane is 220L/min, and an intermediate product C is obtained.
(3) And (3) allowing the intermediate product C to enter an acetylene deposition section of the reactor along with the airflow, controlling the temperature at 880 ℃, controlling the pressure at 5KPa, controlling the reaction residence time of the material in the section at 2.5h, introducing high-purity acetylene into the acetylene deposition section at a flow rate of 45L/min, and depositing the high-purity acetylene on the surface of the intermediate product C to obtain an intermediate product D, wherein the high-purity acetylene generates pyrolytic carbon due to a pyrolysis reaction.
(4) And cooling, grading and screening the intermediate D to obtain the finished product of the expanded graphite nano-silicon composite negative electrode material.
The button cell composed of the obtained expanded graphite nano-silicon composite negative electrode material and metallic lithium is tested for electrochemical performance, the assembled button cell is placed on a Xinwei test cabinet for testing, the current of 0.1C is discharged to 0.005V, and the button cell is placed for 30min and then discharged to 0.005V at the current of 0.02C; the charge capacity and first effect were recorded with a 0.1C current charged to 2.0V. The specific discharge capacity of the negative pole piece can reach 1367mAh/g, the first efficiency is 85.7%, and the capacity of 81.9% can be still maintained after 200 cycles.
Example 5:
a preparation method of an expanded graphite nano-silicon composite negative electrode material for a lithium ion battery is implemented according to a preparation flow chart shown in figure 1:
(1) the particle size range of 3.6kg was Dmin: 0.12 μm, D10: 2.21 μm, D50: 6.35 μm, Dmax: 37.26 μm; stirring and mixing the flake graphite with the purity of 99.870 percent, potassium permanganate and glacial acetic acid in a container, wherein the weight percentage of the flake graphite is as follows: potassium permanganate: the ratio of glacial acetic acid was 3.6 kg: 2.04L: 2.07L, controlling the temperature at 25 ℃, reacting for 3.5h, washing with water, separating solid and liquid, and drying to obtain the expandable graphite A.
(2) Conveying the A into a reaction system, controlling the reaction temperature to be 1050 ℃, the pressure to be 2KPa, 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 rate of the high-purity silane is 250L/min, and an intermediate product C is obtained.
(3) And (3) allowing the intermediate product C to enter an acetylene deposition section of the reactor along with the airflow, controlling the temperature at 1050 ℃, controlling the pressure at 2KPa, controlling the reaction residence time of the material in the section to be 4.5h, introducing high-purity acetylene into the acetylene deposition section, wherein the flow rate is 85L/min, and the high-purity acetylene generates pyrolytic carbon due to pyrolysis reaction and is deposited on the surface of the intermediate product C to obtain an intermediate D.
(4) And cooling, grading and screening the intermediate D to obtain the finished product of the expanded graphite nano-silicon composite negative electrode material.
Taking the obtained expanded graphite nano-silicon composite negative electrode material and artificial graphite together as a negative electrode material and forming a button cell with metal lithium according to the mass ratio of 1:9 to carry out electrochemical performance test, placing the assembled button cell on a Xinwei test cabinet to carry out test, discharging the current at 0.1 ℃ to 0.005V, standing for 30min, and then discharging the current at 0.02 ℃ to 0.005V; the charge capacity and first effect were recorded with a 0.1C current charged to 2.0V. The specific discharge capacity of the negative pole piece can reach 450mAh/g, the first efficiency is 93.6%, and the capacity of 88.6% can be still maintained after 200 cycles.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present 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 solutions described in the foregoing embodiments can still be modified, or some technical features of the foregoing embodiments can be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A preparation method of an expanded graphite nano-silicon composite negative electrode material for a lithium ion battery is characterized by comprising the following steps:
s1, stirring and mixing the flake graphite with an oxidant and an intercalation agent 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 an oxide and an intercalation agent between layers of expandable graphite A at high temperature to push away expandable graphite sheets to prepare expanded graphite B;
s3, mixing high-purity silane and inert gas according to a certain proportion while the step S2 is carried out, sending the mixture into a silicon deposition section of a reaction system, carrying out thermal decomposition on the silane to generate nano silicon particles, and depositing the nano silicon in and on the graphite sheet layer of the expanded graphite B to obtain an intermediate product C;
s4, enabling the intermediate product C to enter a carbon coating section of a reaction system along with airflow, conveying high-purity acetylene to the reaction system, controlling the flow rate of the acetylene and the concentration of the acetylene at 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 the materials at 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 product D;
and S5, cooling, grading and screening the intermediate D to obtain the expanded graphite nano-silicon composite anode material.
2. The preparation method of the expanded graphite nano-silicon composite negative electrode material for the lithium ion battery according to claim 1, wherein the purity of the flake graphite in S1 is more than or equal to 99.5%, and the particle size is 0.1-45 μm; the oxidant is one or more of potassium permanganate, potassium dichromate, potassium trioxide, potassium chlorate and hydrogen peroxide which do not contain sulfur and nitrogen elements; the intercalation agent is one or more of phosphoric acid, perchloric acid and glacial acetic acid which do not contain sulfur and nitrogen elements.
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 in S1, the ratio of flake graphite: oxidizing agent: the dosage ratio of the intercalation agent is 0.1-10 kg: 0.1-10L: 0.26-2.07L; the heating temperature is 25-85 ℃, and the reaction time is 0.01-5 h.
4. 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 expanded volume quality control range of the expanded graphite B in S2 is 50-400 mL/g; the high-temperature reaction temperature is 600-1200 ℃; the pressure is 0.01-100 KPa; the reaction time is 0.05-2 h.
5. The preparation method of the expanded graphite nano-silicon composite anode material for the lithium ion battery as claimed in claim 1 or 2, wherein the molar concentration ratio of the high-purity silane to the inert gas in S3 is 1-10: 5; the flow rate of the high-purity silane is less than or equal to 300L/min.
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 inert gas in the S3 is one or more of nitrogen, argon or helium.
7. 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 acetylene flow in S4 is less than 200L/min, and the acetylene concentration in an acetylene deposition section is 0.01-100 g/L.
8. 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 performed in a communicated reaction system, and the expanded graphite is uniformly dispersed in the reaction system all the time.
9. An expanded graphite nano-silicon composite negative electrode material for a lithium ion battery, which is characterized by being prepared by the preparation method of any one of claims 1 to 8.
10. The application of the expanded graphite nano-silicon composite negative electrode material for the lithium ion battery as claimed in claim 9, 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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