CN114583148B - A method for preparing silicon oxide-based graphite composite negative electrode material for lithium ion battery - Google Patents

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a preparation method of a silicon oxide-based graphite composite negative electrode material for a lithium ion battery, which comprises the steps of adding aluminum trifluoride into a mixed solvent, stirring until the aluminum trifluoride is uniformly dispersed, adding SiO _x powder, spray-drying to obtain pre-coated SiO _x powder, adding the pre-coated SiO _x powder into water, performing ultrasonic dispersion for 10-20min to obtain solution C, adding polyethylene glycol into water, mixing and stirring until clarification to obtain solution D, adding the solution D into the solution C, stirring, adding graphite gel powder, continuously stirring, centrifuging, washing the solid, drying the solid, and roasting under nitrogen protection.

Description

A method for preparing silicon oxide-based graphite composite negative electrode material for lithium ion battery

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a method for preparing a silicon oxide-based graphite composite negative electrode material for lithium ion batteries.

Background technique

In recent years, lithium-ion battery technology has developed rapidly and has been widely used in portable electronic devices, new energy vehicles, and power storage. Breaking through the bottleneck of existing electrode materials is the key to developing high-capacity and long-life lithium-ion batteries. The negative electrode material is a carrier of lithium ions and electrons, plays a role in energy storage and release, and is an important component of the battery. Therefore, the electrochemical properties of the negative electrode material also determine the performance of the battery to some extent.

Silicon has attracted widespread attention due to its high theoretical capacity, low working potential, and abundant reserves. However, silicon as a negative electrode material still has many defects such as poor conductivity and huge volume changes during lithium insertion and delithiation.

Summary of the invention

Purpose of the invention: In view of the above technical problems, the present invention proposes a method for preparing a silicon oxide-based graphite composite negative electrode material for lithium-ion batteries.

The technical solutions adopted are as follows:

A method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium ion battery comprises the following steps:

S1: Mix and stir the resorcinol and formaldehyde solutions until they are clear, then add sodium carbonate and continue stirring to obtain solution A; add melamine and boric acid into water, keep the mixture at 75-85°C for 30-50 minutes, and then cool to obtain solution B; add solution A into solution B, stir for 20-40 minutes, and then add graphite; keep the mixture at 75-85°C for 30-50 minutes, and then heat to 90-95°C for 36-48 hours to obtain graphite wet gel; dry and grind the mixture to obtain graphite gel powder;

S2: Under argon protection, SiO is heated to 1000-1050°C for disproportionation treatment for 3-5 hours and then cooled in the furnace to obtain SiO _x powder;

S3: adding aluminum trifluoride to a mixed solvent consisting of isopropanol and water, stirring until uniformly dispersed, then adding the SiO _x powder, continuing to stir and spray drying to obtain a pre-coated SiO _x powder;

S4: Add the pre-coated SiO _x powder into water and ultrasonically disperse for 10-20 minutes to obtain solution C, add polyethylene glycol into water, mix and stir until clear, obtain solution D, add solution D into solution C, stir the mixed solution at 60-70° C. for 2-3 hours, add the graphite gel powder, continue stirring for 2-3 hours, centrifuge, wash the obtained solid with water and then dry it, and finally calcine it at 800-900° C. for 2-4 hours under nitrogen protection.

Furthermore, the mass ratio of melamine to boric acid in S1 is 2.4-2.6:1.

Furthermore, the amount of graphite added to S1 is 5-10% of the sum of the mass of solution A and solution B.

Furthermore, the heating rate during the SiO disproportionation treatment in S2 is 10-15°C/min.

Furthermore, the volume ratio of isopropanol to water in S3 is 1:10-15.

Furthermore, the mass ratio of aluminum trifluoride to SiO _x powder in S3 is 1:50-100.

Furthermore, during spray drying in S3, the air inlet temperature is 180-200°C, and the discharge port temperature is 60-80°C.

Furthermore, the mass ratio of pre-coated SiO _x powder and graphite gel powder in S4 is 1:4-6.

Furthermore, the sintered product is pre-fired before the roasting in S4, the pre-fired temperature is 300-350°C, and the pre-fired time is 1-2h.

Furthermore, the heating rate during pre-firing is 10-15°C/min, and the heating rate during sintering is 2-5°C/min.

Beneficial effects of the present invention:

As Li ⁺ insertion/extraction behavior is repeated, the volume change of SiO2 material after complete lithiation cannot be ignored. The continuous "breathing phenomenon" of SiO2 will cause the electrode material to crack, powderize or even fall off, resulting in rapid attenuation of the reversible capacity of the battery. In addition, SiO2 has low conductivity, which will seriously affect the actual rate characteristics of the battery under high current charge and discharge. In view of these drawbacks, converting it into _SiO2x through disproportionation reaction to increase the content of inactive substances and construct suitable electrode components has become a feasible method. Graphite has better conductivity and mechanical properties and is the best second phase for composite with _SiO2 material. In the present invention, resorcinol-formaldehyde is used as the carbon source, melamine is used as the nitrogen source, and boric acid is used as the boron source. The prepared graphite gel has a stable cross-linked network, high mechanical strength and thermal stability, high residual carbon content after carbonization, and good surface wettability. _AlF3 pre-coating reduces the electrochemical impedance of _SiO2x , so that the electrochemical performance at high rates is improved. In addition, it is easy to combine with ^F- in the electrolyte during the cycle to form a good ion conductor _AlF4- ^, so that Li ⁺ rapid insertion and removal becomes possible, and the multilayer coating structure formed after calcining AlF ₃ and polyethylene glycol advantageously reduces the contact area between SiO _x particles and the electrolyte, forming a stable solid-phase electrolyte interface film, and the addition of graphite gel plays a role in bridging and coating each SiO _x particle, thereby improving the conductivity of the entire electrode and inhibiting the volume change during the lithium insertion and removal process. The lithium ion battery prepared by the silicon oxide-based graphite composite negative electrode material of the present invention has excellent electrochemical performance, the first charging specific capacity reaches more than 1300 mAh/g, the first charging and discharging efficiency is about 90%, and the capacity retention rate can reach more than 81% after 100 cycles.

Detailed ways

If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased from the market.

Embodiment 1:

A method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium-ion battery:

16 g of resorcinol and 40 mL of 30 wt% formaldehyde solution were mixed and stirred until clarified, then 0.08 g of sodium carbonate was added and stirred continuously to obtain solution A. 4.8 g of melamine and 2 g of boric acid were added to 50 mL of water, kept at 85° C. for 50 min, and then cooled to obtain solution B. Solution A was added to solution B, stirred for 40 min, and then 10 g of graphite was added. The mixture was kept at 85° C. for 50 min, and then heated to 95° C. for 48 h to obtain graphite wet gel, which was dried and ground to obtain graphite gel powder. Under argon protection, 100 g of SiO was heated to 1050° C. at a rate of 15° C./min for disproportionation treatment for 5 h, and then cooled with the furnace to obtain SiO _x powder. 1 g of aluminum trifluoride was added to a mixed solvent consisting of isopropanol (20 mL) and water (280 mL), stirred until uniformly dispersed, and then 60 g of SiO _x powder was added, and the mixture was stirred continuously and then spray-dried. During the spray drying, the air inlet temperature was 200°C and the discharge port temperature was 80°C to obtain pre-coated SiO _x powder. 2 g of pre-coated SiO _x powder was added to 200 mL of water and ultrasonically dispersed for 20 min to obtain solution C. 40 g of polyethylene glycol was added to 300 mL of water, and the mixture was mixed and stirred until clarified to obtain solution D. Solution D was added to solution C, and the mixed solution was stirred at 70°C for 3 h. 10 g of graphite gel powder was added, and stirring was continued for 3 h. The solid was washed with water and then dried. Under nitrogen protection, the temperature was first increased to 350°C at a rate of 15°C/min for pre-calcination for 2 h, and then the temperature was increased to 900°C at a rate of 5°C/min for calcination for 4 h.

Embodiment 2:

A method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium-ion battery:

16 g of resorcinol and 40 mL of 30 wt% formaldehyde solution were mixed and stirred until clarified, then 0.08 g of sodium carbonate was added and stirred continuously to obtain solution A. 4.8 g of melamine and 2 g of boric acid were added to 50 mL of water, kept at 75° C. for 30 min, and then cooled to obtain solution B. Solution A was added to solution B, stirred for 20 min, and then 10 g of graphite was added. The mixture was kept at 75° C. for 30 min, and then heated to 90° C. for reaction for 36-48 h to obtain graphite wet gel, which was dried and ground to obtain graphite gel powder. Under argon protection, 100 g of SiO was heated to 1000° C. at a rate of 10° C./min, treated for 3 h, and then cooled with the furnace to obtain SiO _x powder. 1 g of aluminum trifluoride was added to a mixed solvent consisting of isopropanol (20 mL) and water (280 mL), stirred until uniformly dispersed, and then 60 g of SiO _x powder was added, and the mixture was stirred continuously and then spray-dried. During the spray drying, the air inlet temperature was 180°C and the discharge port temperature was 60°C to obtain pre-coated SiO _x powder. 2 g of pre-coated SiO _x powder was added to 200 mL of water and ultrasonically dispersed for 10 min to obtain solution C. 40 g of polyethylene glycol was added to 300 mL of water, and the mixture was mixed and stirred until clarified to obtain solution D. Solution D was added to solution C, and the mixed solution was stirred at 60°C for 2 h. 10 g of graphite gel powder was added, and stirring was continued for 2 h. The solid was washed with water and then dried. Under nitrogen protection, the temperature was first increased to 300°C at a rate of 10°C/min and pre-calcined for 1 h. The temperature was then increased to 800°C at a rate of 2°C/min and calcined for 2 h.

Embodiment 3:

A method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium-ion battery:

16 g of resorcinol and 40 mL of 30 wt% formaldehyde solution were mixed and stirred until clear, then 0.08 g of sodium carbonate was added and stirred continuously to obtain solution A. 4.8 g of melamine and 2 g of boric acid were added to 50 mL of water, kept at 75°C for 50 min, and then cooled to obtain solution B. Solution A was added to solution B, stirred for 20 min, and then 10 g of graphite was added. The mixture was kept at 85°C for 30 min, and then heated to 95°C for reaction for 36 h to obtain graphite wet gel, which was dried and ground to obtain graphite gel powder. Under argon protection, 100 g of SiO was heated to 1000°C at a rate of 15°C/min, treated for 5 h, and then cooled with the furnace to obtain SiO _x powder. 1 g of aluminum trifluoride was added to a mixed solvent consisting of isopropanol (20 mL) and water (280 mL), stirred until uniformly dispersed, and then 60 g of SiO _x powder was added, and the mixture was continued to be stirred and then spray-dried. During the spray drying, the air inlet temperature was 180°C and the discharge port temperature was 80°C to obtain pre-coated SiO _x powder. 2 g of pre-coated SiO _x powder was added to 200 mL of water and ultrasonically dispersed for 10 min to obtain solution C. 40 g of polyethylene glycol was added to 300 mL of water, and the mixture was mixed and stirred until clarified to obtain solution D. Solution D was added to solution C, and the mixed solution was stirred at 70°C for 2 h. 10 g of graphite gel powder was added, and the mixture was continued to be stirred for 3 h. The mixture was centrifuged, and the obtained solid was washed with water and then dried. Under nitrogen protection, the temperature was first increased to 350°C at a rate of 10°C/min for pre-calcination for 1 h, and then the temperature was increased to 850°C at a rate of 5°C/min for calcination for 4 h.

Embodiment 4:

A method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium-ion battery:

16 g of resorcinol and 40 mL of 30 wt% formaldehyde solution were mixed and stirred until clear, then 0.08 g of sodium carbonate was added and stirred continuously to obtain solution A. 4.8 g of melamine and 2 g of boric acid were added to 50 mL of water, kept at 85° C. for 30 min, and then cooled to obtain solution B. Solution A was added to solution B, stirred for 40 min, and then 10 g of graphite was added. The mixture was kept at 75° C. for 50 min, and then heated to 90° C. for 48 h to obtain graphite wet gel, which was dried and ground to obtain graphite gel powder. Under argon protection, 100 g of SiO was heated to 1050° C. at a rate of 10° C./min for disproportionation treatment for 3 h, and then cooled with the furnace to obtain SiO _x powder. 1 g of aluminum trifluoride was added to a mixed solvent consisting of isopropanol (20 mL) and water (280 mL), stirred until uniformly dispersed, and then 60 g of SiO _x powder was added, and the mixture was stirred continuously and then spray-dried. During the spray drying, the air inlet temperature was 200°C and the discharge port temperature was 60°C to obtain pre-coated SiO _x powder. 2 g of pre-coated SiO _x powder was added to 200 mL of water and ultrasonically dispersed for 20 min to obtain solution C. 40 g of polyethylene glycol was added to 300 mL of water, and the mixture was mixed and stirred until clarified to obtain solution D. Solution D was added to solution C, and the mixed solution was stirred at 60°C for 3 h. 10 g of graphite gel powder was added, and the mixture was stirred continuously for 2 h. The mixture was centrifuged, and the obtained solid was washed with water and then dried. Under nitrogen protection, the temperature was first increased to 300°C at a rate of 15°C/min and pre-calcined for 2 h, and then the temperature was increased to 900°C at a rate of 2°C/min and calcined for 2 h.

Embodiment 5:

A method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium-ion battery:

16 g of resorcinol and 40 mL of 30 wt% formaldehyde solution were mixed and stirred until clarified, then 0.08 g of sodium carbonate was added and stirred continuously to obtain solution A. 4.8 g of melamine and 2 g of boric acid were added to 50 mL of water, kept at 85° C. for 50 min, and then cooled to obtain solution B. Solution A was added to solution B, stirred for 40 min, and then 10 g of graphite was added. The mixture was kept at 85° C. for 50 min, and then heated to 95° C. for 48 h to obtain graphite wet gel, which was dried and ground to obtain graphite gel powder. Under argon protection, 100 g of SiO was heated to 1050° C. at a rate of 15° C./min for disproportionation treatment for 5 h, and then cooled with the furnace to obtain SiO _x powder. 1 g of aluminum trifluoride was added to a mixed solvent consisting of isopropanol (20 mL) and water (280 mL), stirred until uniformly dispersed, and then 60 g of SiO _x powder was added, and the mixture was stirred continuously and then spray-dried. During the spray drying, the air inlet temperature was 200°C and the discharge port temperature was 80°C to obtain pre-coated SiO _x powder. 2 g of pre-coated SiO _x powder was added to 200 mL of water and ultrasonically dispersed for 20 min to obtain solution C. 40 g of polyethylene glycol was added to 300 mL of water, and the mixture was mixed and stirred until clarified to obtain solution D. Solution D was added to solution C, and the mixed solution was stirred at 70°C for 3 h. 10 g of graphite gel powder was added, and stirring was continued for 3 h. The solid was washed with water and then dried. The solid was heated to 900°C at a rate of 5°C/min under nitrogen protection and calcined for 4 h.

Comparative Example 1

Comparative Example 1 is substantially the same as Example 1, except that graphite powder with the same particle size is used instead of the graphite gel powder.

A method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium-ion battery:

Under argon protection, 100 g SiO was heated to 1050 °C at a rate of 15 °C/min for disproportionation treatment for 5 h and then cooled in the furnace to obtain SiO _x powder. 1 g aluminum trifluoride was added to a mixed solvent consisting of isopropanol (20 mL) and water (280 mL), stirred until uniformly dispersed, and then 60 g SiO _x powder was added. After continued stirring, it was spray-dried. During the spray drying, the air inlet temperature was 200 °C and the outlet temperature was 80 °C to obtain pre-coated SiO _x powder. 2 g pre-coated SiO _x powder was added into 200 mL of water and ultrasonically dispersed for 20 min to obtain solution C. 40 g of polyethylene glycol was added into 300 mL of water and mixed and stirred until clarified to obtain solution D. Solution D was added into solution C and the mixed solution was stirred at 70 °C for 3 h. 10 g of graphite powder was added and stirring was continued for 3 h. The solid was washed with water and then dried. Under nitrogen protection, the temperature was first increased to 350 °C at a rate of 15 °C/min for pre-calcination for 2 h, and then the temperature was increased to 900 °C at a rate of 5 °C/min for calcination for 4 h.

Comparative Example 2

Comparative Example 2 is substantially the same as Example 1, except that SiO _powder is replaced by SiO with the same particle size.

A method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium-ion battery:

16 g of resorcinol and 40 mL of 30 wt% formaldehyde solution were mixed and stirred until clarified, then 0.08 g of sodium carbonate was added and stirred continuously to obtain solution A. 4.8 g of melamine and 2 g of boric acid were added to 50 mL of water, kept warm at 85° C. for 50 min, and then cooled to obtain solution B. Solution A was added to solution B, stirred for 40 min, and then 10 g of graphite was added. The mixture was kept warm at 85° C. for 50 min, and then heated to 95° C. for 48 h to obtain a wet graphite gel, which was dried and ground to obtain a graphite gel powder. 1 g of aluminum trifluoride was added to a mixed solvent consisting of isopropanol (20 mL) and water (280 mL), stirred until uniformly dispersed, and then 60 g of SiO powder was added, and the mixture was stirred continuously and then spray-dried. During the spray drying, the air inlet temperature was 200°C and the discharge port temperature was 80°C to obtain pre-coated SiO powder. 2 g of pre-coated SiO powder was added to 200 mL of water and ultrasonically dispersed for 20 min to obtain solution C. 40 g of polyethylene glycol was added to 300 mL of water, and the mixture was stirred until clarified to obtain solution D. Solution D was added to solution C, and the mixed solution was stirred at 70°C for 3 h. 10 g of graphite gel powder was added, and the mixture was stirred continuously for 3 h. The mixture was centrifuged, and the obtained solid was washed with water and then dried. Under nitrogen protection, the temperature was first raised to 350°C at a rate of 15°C/min for pre-calcination for 2 h, and then the temperature was raised to 900°C at a rate of 5°C/min for calcination for 4 h.

Comparative Example 3

Comparative Example 3 is substantially the same as Example 1, except that no pre-coating treatment is performed.

A method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium-ion battery:

16 g of resorcinol and 40 mL of 30 wt% formaldehyde solution were mixed and stirred until clear, then 0.08 g of sodium carbonate was added and stirred continuously to obtain solution A. 4.8 g of melamine and 2 g of boric acid were added to 50 mL of water, kept at 85°C for 50 min, and then cooled to obtain solution B. Solution A was added to solution B, stirred for 40 min, and then 10 g of graphite was added. The mixture was kept at 85°C for 50 min, and then heated to 95°C for 48 h to obtain graphite wet gel, which was dried and ground to obtain graphite gel powder. Under argon protection, 100 g of SiO was heated to 1050°C at a rate of 15°C/min for disproportionation treatment for 5 h, and then cooled with the furnace to obtain SiO _x powder. 2 g of SiO _x powder was added into 200 mL of water and ultrasonically dispersed for 20 min to obtain solution C. 40 g of polyethylene glycol was added into 300 mL of water and mixed and stirred until clarified to obtain solution D. Solution D was added into solution C and the mixed solution was stirred at 70 °C for 3 h. 10 g of graphite gel powder was added and continued to be stirred for 3 h. The solid was washed with water and then dried. Under nitrogen protection, the temperature was first increased to 350 °C at a rate of 15 °C/min for pre-calcination for 2 h, and then the temperature was increased to 900 °C at a rate of 5 °C/min for calcination for 4 h.

Comparative Example 4

Comparative Example 4 is substantially the same as Example 1, except that it is not treated with polyethylene glycol.

A method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium-ion battery:

16 g of resorcinol and 40 mL of 30 wt% formaldehyde solution were mixed and stirred until clarified, then 0.08 g of sodium carbonate was added and stirred continuously to obtain solution A. 4.8 g of melamine and 2 g of boric acid were added to 50 mL of water, kept at 85° C. for 50 min, and then cooled to obtain solution B. Solution A was added to solution B, stirred for 40 min, and then 10 g of graphite was added. The mixture was kept at 85° C. for 50 min, and then heated to 95° C. for 48 h to obtain graphite wet gel, which was dried and ground to obtain graphite gel powder. Under argon protection, 100 g of SiO was heated to 1050° C. at a rate of 15° C./min for disproportionation treatment for 5 h, and then cooled with the furnace to obtain SiO _x powder. 1 g of aluminum trifluoride was added to a mixed solvent consisting of isopropanol (20 mL) and water (280 mL), stirred until uniformly dispersed, and then 60 g of SiO _x powder is added, and the mixture is stirred continuously and then spray-dried. During spray drying, the air inlet temperature is 200°C and the discharge port temperature is 80°C to obtain pre-coated SiO _x powder. 2 g of pre-coated SiO _x powder is added to 200 mL of water and ultrasonically dispersed for 20 min to obtain solution C. 10 g of graphite gel powder is added to solution C, and the mixture is stirred continuously for 3 h and centrifuged. The obtained solid is washed with water and then dried. Under nitrogen protection, the temperature is first increased to 350°C at a rate of 15°C/min for pre-calcination for 2 h, and then the temperature is increased to 900°C at a rate of 5°C/min for calcination for 4 h.

Performance Testing:

The silicon oxide-based graphite composite negative electrode materials prepared in Examples 1-5 of the present invention and Comparative Examples 1-4 are respectively weighed and mixed with superconducting carbon and polyacrylic acid in a mass ratio of 8:1:1, wherein the polyacrylic acid is mixed in the form of a solution with a mass content of 10%. After the mixture is stirred into a slurry, it is coated on a copper foil, dried, and cut into pieces to obtain a pole piece, which is placed in a glove box, with a metal lithium sheet as a counter electrode, a polypropylene diaphragm, and a 1 mol/L LiPF ₆ /EC+DEC+EMC solution as an electrolyte, wherein EC is ethylene carbonate, DEC is diethyl carbonate, and EMC is ethyl methyl carbonate, and the volume ratio of the three is 1:1:1, and a CR2032 button battery is assembled in a glove box filled with dry argon.

The battery performance test was carried out at 25±2℃, the steps are as follows:

(1) 0.1C discharge to 0.005V; (2) stand for 1 min; (3) 0.05C discharge to 0.005V; (4) stand for 1 min; (5) 0.02C discharge to 0.005V; (6) stand for 1 min; (7) 0.1C charge to 3.0V; (8) stand for 1 min. The above steps were cycled 100 times. The battery performance test results prepared by the silicon oxide-based graphite composite negative electrode materials in Examples 1-5 and Comparative Examples 1-4 are shown in Table 1:

Table 1:

As can be seen from Table 1 above, the lithium-ion battery prepared by the silicon oxide-based graphite composite negative electrode material of the present invention has excellent electrochemical properties, the first charge specific capacity reaches more than 1300 mAh/g, the first charge and discharge efficiency is about 90%, and the capacity retention rate can reach more than 81% after 100 cycles.

The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. The preparation method of the silicon oxide-based graphite composite anode material for the lithium ion battery is characterized by comprising the following steps of:

S1: mixing resorcinol and formaldehyde solution, stirring until the mixture is clear, adding sodium carbonate, continuously stirring to obtain solution A, adding melamine and boric acid into water, preserving heat at 75-85 ℃ for 30-50min, cooling to obtain solution B, adding solution A into solution B, stirring for 20-40min, adding graphite, preserving heat at 75-85 ℃ for 30-50min, heating to 90-95 ℃ for reacting for 36-48h to obtain graphite wet gel, drying and grinding to obtain graphite gel powder;

s2: under the protection of argon, heating the SiO to 1000-1050 ℃ for disproportionation treatment for 3-5 hours, and then cooling along with a furnace to obtain SiO _x powder;

s3: adding aluminum trifluoride into a mixed solvent composed of isopropanol and water, stirring until the mixture is uniformly dispersed, adding SiO _x powder, continuously stirring, and then spray-drying to obtain pre-coated SiO _x powder;

s4: adding pre-coated SiO _x powder into water, performing ultrasonic dispersion for 10-20min to obtain a solution C, adding polyethylene glycol into water, mixing and stirring until the mixture is clarified to obtain a solution D, adding the solution D into the solution C, stirring the mixed solution at 60-70 ℃ for 2-3h, adding graphite gel powder, continuously stirring for 2-3h, centrifuging, washing the obtained solid, drying, and roasting at 800-900 ℃ for 2-4h under the protection of nitrogen.

2. The method for preparing the silicon oxide-based graphite composite anode material for the lithium ion battery according to claim 1, wherein the mass ratio of melamine to boric acid in S1 is 2.4-2.6:1.

3. The method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium ion battery according to claim 1, wherein the addition amount of graphite in S1 is 5-10% of the sum of the mass of the solution A and the mass of the solution B.

4. The method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium ion battery according to claim 1, wherein the heating rate in the disproportionation treatment of SiO in S2 is 10-15 ℃/min.

5. The method for preparing a silicon oxide-based graphite composite anode material for a lithium ion battery according to claim 1, wherein the volume ratio of isopropanol to water in S3 is 1:10-15.

6. The method for preparing a silicon oxide-based graphite composite anode material for a lithium ion battery according to claim 1, wherein the mass ratio of aluminum trifluoride to SiO _x powder in S3 is 1:50-100.

7. The method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium ion battery according to claim 1, wherein the temperature of an air inlet is 180-200 ℃ and the temperature of a discharge outlet is 60-80 ℃ during spray drying in the step S3.

8. The preparation method of the silicon oxide-based graphite composite anode material for the lithium ion battery as claimed in claim 1, wherein the mass ratio of the pre-coated SiO _x powder to the graphite gel powder in S4 is 1:4-6.

9. The method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium ion battery according to claim 1, wherein the pre-sintering is performed before the calcination in the step S4, the pre-sintering temperature is 300-350 ℃, and the pre-sintering time is 1-2h.

10. The method for preparing a silicon oxide-based graphite composite negative electrode material for a lithium ion battery according to claim 9, wherein the temperature rising speed during pre-sintering is 10-15 ℃/min, and the temperature rising speed during sintering is 2-5 ℃/min.