CN103400970B - A kind of nano-silicon/graphene lithium-ion battery negative electrode material and preparation method thereof - Google Patents

Abstract

The invention relates to a nanometer silicon/graphene lithium ion battery cathode material and a preparation method thereof. The cathode material comprises nanometer silicon and graphene, wherein the granularity of nanometer silicon granules is 10-100nm, and the mass ratio of nanometer silicon to graphene is 1:(5-10). The preparation method of the nanometer silicon/graphene lithium ion battery cathode material comprises the following steps of: preparing an electron solution; reducing a silicon tetrachloride liquid phase into nanometer silicon; preparing a graphene oxide glue sample solution; loading the graphene oxide glue sample solution on nanometer silicon; and drying and sintering the semi-finished product of the composite electrode material. According to the preparation method, after the nanometer silicon granules the granularity of which can be controlled are obtained through a liquid phase reducing method; in a mode that a glue body is separated out through replacing a solvent graphene is reduced and a glue layer is formed at the same time, and moreover the glue layer is adsorbed on an existing nanometer silicon glue nucleus; the obtained nanometer silicon has a better size and a better structure, can combine graphene and nanometer silicon efficiently in the term of molecule size; the obtained silicon carbon material has stable circulation performance and excellent electric conducting performance.

Description

A kind of nano-silicon/graphene lithium-ion battery negative electrode material and preparation method thereof

technical field

The invention belongs to the field of electrochemistry and new energy materials, and in particular relates to a nano-silicon/graphene lithium-ion battery negative electrode material and a preparation method thereof.

Background technique

Since the first commercialized lithium-ion battery products were launched by Sony Corporation of Japan in 1991, lithium-ion batteries have been developed for more than 20 years. Lithium-ion batteries have a unique charging and discharging mechanism of inserting/extracting lithium ions, so compared with similar battery products, it has the advantages of large specific capacity, high working voltage, high safety, and low environmental pollution. The development of negative electrode materials as the main body of lithium-ion battery storage has become a key point to improve the total specific capacity, charge-discharge and cycle performance of lithium-ion batteries.

In the early days, the anode materials of lithium-ion batteries were mainly lithium alloys. The main problems were poor cycle performance and large initial irreversible capacity. The fundamental reason is that there is a reorganization of the crystal structure of the negative electrode material during the charge and discharge process, resulting in a large volume expansion; in addition, there is also a volume change between phases that causes the loss of lithium intercalation substances. Therefore, in commercial batteries after industrialization, alloy materials with high theoretical specific capacity are abandoned and graphite-like carbon materials that form intercalation compounds with lithium ions are used instead. Since graphitic carbon materials can accommodate lithium ions through their graphite interstitials, the problem of volume expansion is solved. And this kind of graphite-like carbon material with excellent electrochemical performance has become the most common negative electrode material in commercial lithium-ion batteries.

However, the low theoretical capacity of graphite-like carbon materials for lithium storage has always been a fundamental problem. The theoretical specific capacity of general graphite-based carbon materials is only 372mAh/g, but it has reached 370mAh/g in practical applications, which is basically close to the theoretical level. Even modified graphite-like carbon materials have a capacity of only 450mAh/g. Therefore, although graphite ensures the cycle performance of lithium-ion batteries, it also greatly limits its total specific capacity, which is far behind the current functional requirements for lithium-ion batteries. Therefore, the development of lithium-ion battery anode materials other than graphite-based carbon materials with high capacity has become a top priority.

In comparison, silicon-based anode materials have more advantages in performance among non-carbon anode materials. It has the highest theoretical capacity ratio (forming Li4.4Si, the theoretical capacity is as high as 4200mAh/g) and relatively low lithium intercalation potential. Compared with other metal materials, it also has better stability and safety, and the source of raw materials is also more abundant. Therefore, the research on silicon-based anode materials is always going on. However, it also has a volume effect (volume expansion rate > 300%) in the process of charging and discharging, which leads to structural collapse of the material itself, gradual pulverization, loss of electrical contact between the active material and the current collector, and electrical conductivity during the charging and discharging process. loss, which eventually leads to the loss of reversible capacity.

However, at present, there are certain solutions to the technical problems existing in silicon-based materials. By treating silicon to the nanometer scale, the absolute volume change can be greatly reduced, or surface modification, doping, compounding and other methods can be used to form a coated or highly dispersed system, thereby improving the mechanical properties of the material to ease the release of lithium. The internal stress generated by the volume expansion during the process destroys the material structure, which can eliminate the influence of the volume effect, thereby achieving the purpose of improving its electrochemical cycle stability. But on the other hand, pure nano-silicon is easy to agglomerate, and the silicon-based material modified by the existing surface modification and doping technology has new problems of high cost, poor doping level, and uneven product. Therefore, lithium-ion batteries using pure nano-silicon or modified silicon-based materials as negative electrode materials can only lie in the laboratory and cannot be successfully industrialized.

In addition, breakthroughs have been made in the research and development of carbon materials with better electrochemical performance. After switching to single-layer graphene as the negative electrode material of lithium-ion batteries, its theoretical capacity ratio can reach 744mAh/g, while the reported graphene negative electrode material, its first discharge capacity can reach 650mAh/g, after 100 cycles, its The capacity remains at the level of 460mAh/g. Therefore, although the theoretical capacity of graphene is weaker than that of some metals and silicon-based materials, if it can be closely combined with the high capacity of silicon-based materials, the cycle performance of silicon-based materials can be improved. In the research report, silicon powder (~40nm) and graphene were mechanically mixed and ground according to the mass ratio of 1:1. The first discharge specific capacity was 2158mAh/g, and the discharge specific capacity after 30 cycles could reach 1168mAh/g. , which is still three times the specific capacity of existing carbon materials.

Therefore, the combination of nano-silicon and graphene with a high theoretical capacity ratio is the focus of current research on non-carbon anode materials. At present, the main combination method is always on the mechanical scale, mainly using the ball milling method to combine graphene and nano-silicon. Although it can achieve a certain effect, due to the uneven mixing of the mechanical scale, the performance of graphene cannot be improved. fully use. However, the heat treatment method that can achieve molecular scale combination has high energy consumption, and the COD chemical vapor deposition method is expensive, which is not suitable for industrial development. Therefore, it is very necessary and far-reaching to develop an effective combination technology of graphene and nano-silicon. The higher the level of this bonding, the better the performance of the new silicon-carbon based pole piece material. The cheaper the raw materials and preparation methods, the easier it is to carry out industrialization.

Contents of the invention

In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a nano-silicon/graphene lithium-ion battery negative electrode material with excellent electrical conductivity and stable cycle performance.

Another object of the present invention is to provide a preparation method of nano-silicon/graphene lithium-ion battery negative electrode material.

In order to solve the above problems, the technical scheme adopted in the present invention is as follows:

A nano-silicon/graphene lithium-ion battery negative electrode material, which includes nano-silicon and graphene, wherein the particle size of the nano-silicon particle is 10-100 nm, and the mass ratio of the nano-silicon to the graphene is 1:5-10.

Since the theoretical specific capacity of graphene (~700mAh/g) is smaller than that of nano-silicon, excessive graphene will lead to a decrease in the average specific capacity of the material as a whole. Therefore, when the ratio of nano-silicon to graphene is greater than 1:10 , the overall specific capacity of the material begins to decay. In addition, if the content of nano-silicon and graphene is less than 1:5, graphene will not be able to completely cover nano-silicon, so that there is still the possibility of agglomeration among nano-silicon particles and loss of electrical contact, which will further affect the cycle performance of the material.

A preparation method of nano-silicon/graphene lithium-ion battery negative electrode material, comprising the following steps:

(1) Preparation of electronic solution: Under the protection of argon, dissolve metal lithium and co-solvent in the dehydrated first-class solvent, and magnetically stir to dissolve. When using electrons, store them in an argon environment for later use;

(2) Liquid-phase reduction of silicon tetrachloride into nano-silicon: under the protection of argon, in the reactor equipped with the electronic solution prepared in step (1), dropwise add 5% to 20% of the total weight of the electronic solution. % of silicon tetrachloride, accompanied by magnetic stirring or electric stirring, after the silicon tetrachloride is added dropwise, the suspension of nano-silicon particles with a particle size of 10 to 100nm in the electronic solution is obtained, preferably, stirring The speed of the machine is maintained at 100-300 rpm;

(3) Preparation of graphene oxide colloidal solution: use water as a dispersant, configure graphite oxide aqueous solution or graphene suspension, then add nitric acid, mix graphite oxide aqueous solution or graphene suspension with nitric acid, and sonicate the solution Finally, repeated centrifugation and washing, the system was washed until the pH was close to neutral, then vacuum-dried, and then the obtained dried product was ultrasonically treated with the second type of solvent to form a colloidal solution;

(4) Graphene oxide colloidal solution loaded on nano-silicon: Stir the nano-silicon suspension in the electronic solution in step (2) at high speed until uniform, and add electronic solution as a reducing agent to dilute, and then start slowly Add dropwise the graphene oxide colloidal solution that step (3) makes, determine the addition amount of graphene solution according to the mass ratio of nano-silicon and graphene, stir, and gradually precipitate graphite along with the mixing of the first type solvent and the second type solvent ene, after the graphene solution is added dropwise, then undergo ultrasonic treatment to disperse nano-silicon and graphene, preferably, the stirring speed is 150 to 300 rpm;

(5) Drying and sintering of semi-finished composite electrode materials: the mixed solution obtained in step (4) is subjected to differential centrifugation, vacuum filtration and drying, then placed in a quartz boat and placed in an argon-protected tube furnace. The gas flow rate is controlled, calcined, and the obtained product is crushed and sieved to obtain a composite electrode material.

As a further technical solution of the present invention, the cosolvent described in step (1) is an organic compound of polycyclic aromatic hydrocarbons, the first type of solvent is an organic compound of ethers or amines, and the first solvent described in step (3) is an organic compound of polycyclic aromatic hydrocarbons. The second type of solvents are amine or alcohol solvents.

As a co-solvent, polycyclic aromatic hydrocarbons can make the lithium ions formed after the dissolution of metallic lithium be embedded in the aromatic layer, thereby shifting the dissolution equilibrium and further promoting the formation of solvated electrons in the solvent. Since there is no active hydrogen in amines and ethers, the solvated electrons have a longer lifetime, which is sufficient to complete the reduction process, so amines and ethers are selected as the first type of solvent. Since amines or alcohols can form π-hydrogen bonds with graphite and graphene, and can also form traditional hydrogen bonds with partially oxidized sites on graphite and graphene, which can effectively assist the dissolution of graphite and graphene, alcohols are selected Class 2 solvents or amines.

Preferably, the cosolvent described in step (1) is biphenyl, 4,4'-diaminobiphenyl, 4,4'-dimethoxybiphenyl and the like, and among anthracene, naphthalene, phenanthrene and graphene one or more of two.

Preferably, the first type of solvent is one or more of ethylenediamine, tripropylamine, morpholine, dicyclohexyl ether, ethylene glycol dimethyl ether and diethyl ether.

Preferably, the second type of solvent described in step (3) is one or more than two of ethanol, ethylenediamine, tripropylamine, cyclohexanol and ethylene glycol.

As a further technical solution of the present invention, the amount of lithium metal used in step (1) is 1% to 5% of the total weight of the electronic solution, and the amount of co-solvent used is 0% to 5% of the total weight of the electronic solution. The absence of a co-solvent also leads to the formation of solvated electrons, but the reaction proceeds more slowly.

As a further technical scheme of the present invention, the mass fraction of graphite oxide aqueous solution or graphene suspension described in step (3) is 0.5～1.5g/L, the mass concentration of described nitric acid is 60%～70%, graphite oxide The volume ratio of aqueous solution or graphene suspension to nitric acid is 1:2-10.

As a further technical solution of the present invention, the mass fraction of the glue-like solution in step (3) is 0.1-5 g/L.

As a further technical solution of the present invention, the mass ratio of nano-silicon to graphene oxide in step (4) is 1:5-10.

As a further technical solution of the present invention, the mass percentage of the electronic solution added in step (4) is 0%-5%, and the frequency of ultrasonic treatment is 40-80 Hz.

As a further technical solution of the present invention, the gas flow rate in step (5) is 20-100 mL/min, the sintering temperature is 500° C.-800° C., and the calcination is 2-5 hours.

Compared with the prior art, the beneficial effects of the present invention are:

1) For the silicon-carbon composite electrode material prepared in the present invention, after obtaining nano-silicon particles with a more controllable particle size by means of liquid phase reduction, the graphene is reduced and a glue layer is formed at the same time by changing the solvent to precipitate colloids, and adsorbed on The existing nano-silica gel core, so that the combination of silicon and carbon at the molecular level is achieved. The silicon-carbon composite material obtained by this method has stable cycle performance. Compared with traditional graphite and pure graphene materials, it has twice the The above specific capacity, and the reaction is completed in the same phase, the operation is simple, and it can be completed without special equipment.

2) The present invention reduces silicon tetrachloride into nano-silicon in a liquid phase, then loads part of the graphene oxide on the nano-silicon in situ in the liquid phase, and further reduces the part of the graphene oxide to graphene in a reducing environment, which can Efficiently combine graphene and nano-silicon at the molecular scale to provide a graphene-nano-silicon anode material with better performance.

3) The liquid-phase reduction technology adopted in the present invention reduces silicon tetrachloride into nano-silicon in liquid phase, and the obtained nano-silicon has better scale and structure.

4) The present invention uses nano-silicon to have the highest theoretical specific capacity among comparable materials, and uses graphene as a carrier to load at the molecular level, which can effectively reduce the volume effect of the material and further improve the overall cycle performance.

5) Graphene in the composite material of the present invention can effectively suppress the volume expansion of the silicon negative electrode, so the prepared nano-silicon/graphene lithium-ion battery negative electrode material has excellent electrical conductivity, and the corresponding lithium-ion battery has a large specific capacity and long cycle life. Good performance.

Detailed ways

Example 1:

Under the protection of argon, 1% by mass of lithium metal and 1% of biphenyl were dissolved in 1 kg of ethylene glycol dimethyl ether, and magnetically stirred to dissolve, and the dissolved solution was dark green. Then, silicon tetrachloride with a mass ratio of 5% was added dropwise to the solution, and the dropwise addition was completed within 1 hour. At the same time, magnetic stirring was added to maintain 100 rpm, and the stirring was stopped after 1 hour.

Using water as a dispersant, configure a 0.5 g/L graphene suspension, add 60% nitric acid with a volume ratio of 1:2, and then ultrasonicate for 0.5 h. After the treatment, the obtained solution was repeatedly centrifuged and washed until pH=7. After vacuum drying, ultrasonic treatment was performed for 0.5 h again to dissolve it in cyclohexanol to form a 0.1 g/L graphene oxide gel-like solution.

Stir the nano-silicon suspension at a speed of 200 rpm, and during the stirring process, add the above-mentioned 0.1g/L graphene oxide solution dropwise according to the mass ratio of nano-silicon: graphene = 1:8, drop within 1h Finished adding. After 1 hour, use 40 Hz ultrasonic to disperse for 0.5 hour. After the dispersion is completed, centrifuge at 16,000 rpm for 0.5 hour. After the centrifugation is completed, vacuum filter, dry, then place in a quartz boat, place in a tube furnace protected by argon, maintain a gas flow rate of 20mL/min, calcinate at 500°C for 2h, crush the obtained product and sieve , to obtain the composite electrode material of Example 1.

Example 2:

Under the protection of argon, 3% by mass of lithium metal and 5% of 4,4'-dimethoxybiphenyl were dissolved in 1kg of tripropylamine, and magnetically stirred to dissolve. After dissolution, the solution was close to dark blue. Then, silicon tetrachloride with a mass ratio of 20% was added dropwise to the solution, and the dropwise addition was completed within 3 hours. At the same time, magnetic stirring was added, and the temperature was maintained at 150 rpm, and the stirring was stopped after 1 hour.

Using water as a dispersant, configure a 0.5g/L graphite oxide aqueous solution, add 60% nitric acid with a volume ratio of 1:5, and use ultrasonic treatment for 0.5h. After the treatment, the obtained solution was repeatedly centrifuged and washed until pH=7. After vacuum drying, ultrasonic treatment was performed for 3 h again, and it was dissolved in ethanol to form a 5 g/L graphene oxide colloidal solution.

Stir the nano-silicon suspension at a speed of 150 rpm, and during the stirring process, add the above-mentioned 5g/L graphene oxide solution dropwise at a mass ratio of nano-silicon:graphene=1:5, and add dropwise within 2h complete. After 2 hours, 40 Hz ultrasonic was used to disperse for 1 hour. After the dispersion was completed, the centrifugal speed was 16000 revolutions per minute, and the centrifugation was performed for 0.5 hours. After the centrifugation is completed, vacuum filter, dry, then place in a quartz boat, place in a tube furnace protected by argon, maintain a gas flow rate of 30mL/min, calcinate at 600°C for 5h, crush the obtained product and sieve , to obtain the composite electrode material of Example 2.

Example 3:

Under the protection of argon, 5% lithium metal and 5% anthracene were dissolved in 1 kg of morpholine by mass percentage, and magnetic stirring was used to dissolve, and the dissolved solution was close to metallic black. Then, silicon tetrachloride with a mass ratio of 20% was added dropwise to the solution, and the dropwise addition was completed within 3 hours. At the same time, magnetic stirring was added, and the temperature was maintained at 150 rpm, and the stirring was stopped after 1 hour.

Using water as a dispersant, configure a 0.5 g/L graphene suspension, add 60% nitric acid with a volume ratio of 1:10, and then use 60 Hz ultrasonic treatment for 0.5 h. After the treatment, the obtained solution was repeatedly centrifuged and washed until pH=7. After vacuum drying, ultrasonic treatment was performed for 3 h again to dissolve it in ethylene glycol and configure a 1 g/L graphene oxide colloidal solution.

Stir the nano-silicon suspension at a speed of 200 rpm, and during the stirring process, add the above-mentioned 1g/L graphene oxide solution dropwise at a mass ratio of nano-silicon: graphene = 1:10, and add dropwise within 2 hours complete. After 2 hours, ultrasonic dispersion was used for another 1 hour. After the dispersion was completed, the centrifugal speed was 16,000 revolutions per minute, and centrifuged for 0.5 hours. After the centrifugation is completed, vacuum filter, dry, then place in a quartz boat, place in an argon-protected tube furnace, maintain a gas flow rate of 50mL/min, calcinate at 800°C for 3h, crush the obtained product and sieve , to obtain the composite electrode material of Example 3.

Example 4:

Under the protection of argon, metal lithium with a mass percentage of 5% was directly dissolved in 1 kg of ethylenediamine without adding a co-solvent, and magnetically stirred to dissolve. The dissolved solution was dark blue. Then, silicon tetrachloride with a mass ratio of 15% was added dropwise to the solution, and the dropwise addition was completed within 2 hours. At the same time, magnetic stirring was added, and the temperature was maintained at 200 rpm, and the stirring was stopped after 1 hour.

Using water as a dispersant, configure a 0.5g/L graphite oxide aqueous solution, add 60% nitric acid with a volume ratio of 1:2, and then use ultrasonic treatment for 0.5h. After the treatment, the obtained solution was repeatedly centrifuged and washed until pH=7. After vacuum drying, ultrasonic treatment was performed for 1 h again, and it was dissolved in ethanol to form a 2 g/L graphene oxide colloidal solution.

Stir the nano-silicon suspension at a speed of 300 rpm, and during the stirring process, add the above-mentioned 2g/L graphene oxide solution dropwise at a mass ratio of nano-silicon: graphene = 1:9, and add dropwise within 2 hours complete. After 2 hours, use 60Hz ultrasonic to disperse for 1 hour. After the dispersion is completed, centrifuge at 30,000 rpm for 1 hour. After the centrifugation is completed, vacuum filter, dry, then place in a quartz boat, place in an argon-protected tube furnace, maintain a gas flow rate of 70mL/min, calcinate at 800°C for 2 hours, crush the obtained product and sieve , to obtain the composite electrode material of Example 4.

Example 5:

Under the protection of argon, metal lithium with a mass percentage of 5% was directly dissolved in 1 kg of tripropylamine without adding a co-solvent, and magnetically stirred to dissolve. After dissolution, the solution was metallic black. Then, silicon tetrachloride with a mass ratio of 20% was added dropwise to the solution, and the dropwise addition was completed within 1 hour. At the same time, magnetic stirring was added, and the temperature was maintained at 300 rpm, and the stirring was stopped after 1 hour.

Using water as a dispersant, configure a 0.5 g/L graphene suspension, add 60% nitric acid with a volume ratio of 1:2, and then ultrasonically treat it for 0.5 h. After the treatment, the obtained solution was repeatedly centrifuged and washed until pH=7. After vacuum drying, ultrasonic treatment was performed for 1 h again to dissolve it in cyclohexanol to form a 5 g/L graphene oxide colloidal solution.

Stir the nano-silicon suspension at a speed of 300 rpm, and during the stirring process, add the above-mentioned 5g/L graphene oxide solution dropwise at a mass ratio of nano-silicon: graphene = 1:9, and add dropwise within 2 hours over. After 2 hours, use 80Hz ultrasonic to disperse for 1 hour. After the dispersion is completed, centrifuge at 30,000 rpm for 1 hour. After the centrifugation is completed, vacuum filter, dry, then place in a quartz boat, place in a tube furnace protected by argon, maintain a gas flow rate of 100mL/min, calcinate at 500°C for 5h, crush the obtained product and sieve , to obtain the composite electrode material of Example 5.

Comparative example:

Using water as a dispersant, configure a 0.4 g/L graphene suspension, add 60% nitric acid with a volume ratio of 1:2, and then ultrasonicate for 0.5 h. After the treatment, the obtained solution was repeatedly centrifuged and washed until pH=7. After vacuum drying, ultrasonic treatment was performed for 1 h again to dissolve it in water to form a 0.4 g/L graphene oxide colloidal solution.

Take a certain amount of commercially available nano-silicon with a particle size of 20-50nm, expose it to the air for 16 hours, then add the above-mentioned nano-silicon to water, and ultrasonically disperse it for 1 hour. The mass ratio is nano-silicon:graphene=1:2 drops Add the above-mentioned 0.4g/L graphene oxide solution, and complete the dropwise addition within 2 hours. After 2 hours, use 40Hz ultrasonic dispersion for 1.5 hours. After the dispersion is completed, vacuum filter, dry, and then place it in a quartz boat, and place it in a tube furnace protected by a mixed gas of hydrogen and argon (hydrogen: argon = 6%: 94%) , maintaining a gas flow rate of 70 mL/min, calcining at 800° C. for 1 h, crushing the obtained product and sieving to obtain the composite electrode material of the comparative example.

The electrical performance test method of the above-mentioned Examples 1 to 5 and Comparative Examples is as follows: the obtained electrode material is placed on a copper foil to make a negative pole piece, and assembled with a lithium metal sheet to form a 2016 button battery, and the electrolyte solution is 1mol/L The LiPF ₆ is dissolved in DMC, in the voltage range of 0.02-1.5V, at room temperature, the charge-discharge cycle test is carried out with a current of 100mAh/g, and the cycle is 100 times.

The result list of the electrical property test of above-mentioned embodiment 1～5 and comparative example is as follows:

It can be seen from the above table that the preparation method of the present invention has a significant difference compared with the comparative example, and the negative electrode material of the present invention can effectively retain capacity. However, the first discharge specific capacity of the existing graphite carbon negative electrode material is 350mAh/g, and the retention capacity is 320～340mAh/g. Therefore, the specific capacity of the negative electrode material of the present invention is far better than the existing graphite carbon negative electrode material and Similar to the performance of silicon carbon anode materials. This is due to the fact that both the new loading method and reduction method can effectively control the tight combination between nano-silicon and graphene, and graphene acts as a buffer substance to prevent the volume change caused by structural damage, thereby eliminating the problem of poor cycle performance.

The above-mentioned embodiment is only a preferred embodiment of the present invention, and cannot be used to limit the protection scope of the present invention. Any insubstantial changes and substitutions made by those skilled in the art on the basis of the present invention belong to the scope of the present invention. Scope of protection claimed.

Claims (9)

1. A negative electrode material for a nano-silicon/graphene lithium-ion battery, characterized in that it includes nano-silicon and graphene, wherein the particle size of the nano-silicon particle is 10-100 nm, and the mass ratio of nano-silicon to graphene is 1:5- 10; The preparation method of described nano-silicon/graphene lithium-ion battery negative electrode material comprises the following steps: (1) Preparation of electronic solution: Under the protection of argon, dissolve metal lithium and organic compounds of polycyclic aromatic hydrocarbons in dehydrated first-class solvents, and magnetically stir to dissolve. After the dissolution is completed, the solution contains For electrons with the same stoichiometric ratio as lithium, store them in an argon environment for later use; The first type of solvent is an ether or amine organic compound; (2) Liquid-phase reduction of silicon tetrachloride into nano-silicon: under the protection of argon, add 5% to 20% of the total weight of the electronic solution dropwise to the reactor equipped with the electronic solution prepared in step (1). Silicon tetrachloride, accompanied by magnetic stirring or electric stirring, after the silicon tetrachloride is added dropwise, a suspension of nano-silicon particles with a particle size of 10-100nm in the electronic solution is obtained; (3) Preparation of graphene oxide colloidal solution: use water as a dispersant, configure graphite oxide aqueous solution or graphene suspension, then add nitric acid, mix graphite oxide aqueous solution or graphene suspension with nitric acid, and sonicate the solution Afterwards, repeated centrifugation and washing, washing the system to pH = 7, then vacuum-drying, and then ultrasonically treating the obtained dried product with a second-type solvent to form a glue-like solution; The second type of solvent is an amine or alcohol solvent; (4) Graphene oxide colloidal solution loaded on nano-silicon: Stir the nano-silicon suspension in the electronic solution in step (2) at high speed until uniform, and add electronic solution as a reducing agent to dilute, and then start slowly Add dropwise the graphene oxide colloidal solution that step (3) makes, determine the addition amount of graphene oxide colloidal solution by the mass ratio of nano-silicon and graphene, stir, accompany the mixing of the first class solvent and the second class solvent Graphene is gradually precipitated, and after the graphene oxide colloidal solution is added dropwise, it is then subjected to ultrasonic treatment to disperse nano-silicon and graphene; (5) Drying and sintering of semi-finished composite electrode materials: the mixed solution obtained in step (4) is centrifuged, vacuum filtered and dried, then placed in a quartz boat, placed in a tube furnace protected by argon, and controlled gas Flow rate, calcining, crushing the obtained product and sieving to obtain a composite electrode material. 2. a preparation method of nano-silicon/graphene lithium-ion battery negative electrode material as claimed in claim 1, is characterized in that comprising the following steps: (1) Preparation of electronic solution: Under the protection of argon, dissolve metal lithium and organic compounds of polycyclic aromatic hydrocarbons in dehydrated first-class solvents, and magnetically stir to dissolve. After the dissolution is completed, the solution contains For electrons with the same stoichiometric ratio as lithium, store them in an argon environment for later use; The first type of solvent is an ether or amine organic compound; (2) Liquid-phase reduction of silicon tetrachloride into nano-silicon: under the protection of argon, add 5% to 20% of the total weight of the electronic solution dropwise to the reactor equipped with the electronic solution prepared in step (1). Silicon tetrachloride, accompanied by magnetic stirring or electric stirring, after the silicon tetrachloride is added dropwise, a suspension of nano-silicon particles with a particle size of 10-100nm in the electronic solution is obtained; (3) Preparation of graphene oxide colloidal solution: use water as a dispersant, configure graphite oxide aqueous solution or graphene suspension, then add nitric acid, mix graphite oxide aqueous solution or graphene suspension with nitric acid, and sonicate the solution Afterwards, repeated centrifugation and washing, washing the system to pH = 7, then vacuum-drying, and then ultrasonically treating the obtained dried product with the second type of solvent to form a glue-like solution; The second type of solvent is an amine or alcohol solvent; (4) Graphene oxide colloidal solution loaded on nano-silicon: Stir the nano-silicon suspension in the electronic solution in step (2) at high speed until uniform, and add electronic solution as a reducing agent to dilute, and then start slowly Add dropwise the graphene oxide colloidal solution prepared in step (3), determine the addition amount of the graphene oxide colloidal solution according to the mass ratio of nano-silicon and graphene, stir, and accompany the mixing of the first type solvent and the second type solvent Graphene is gradually precipitated, and after the graphene oxide colloidal solution is added dropwise, ultrasonic treatment is performed to disperse nano-silicon and graphene; (5) Drying and sintering of semi-finished composite electrode materials: the mixed solution obtained in step (4) is centrifuged, vacuum filtered and dried, then placed in a quartz boat, placed in a tube furnace protected by argon, and controlled gas Flow rate, calcining, crushing the obtained product and sieving to obtain a composite electrode material. 3. the preparation method of nano-silicon/graphene lithium-ion battery negative electrode material according to claim 2, is characterized in that: the organic compound of polycyclic aromatic hydrocarbons described in step (1) is biphenyl, 4,4 '- One or more of diaminobiphenyl, 4,4'-dimethoxybiphenyl, anthracene, naphthalene, phenanthrene and graphene, and the ether organic compound described in step (1) is dicyclohexyl ether One or more of ethylene glycol dimethyl ether and ether, the amine organic compound described in step (1) is ethylenediamine, tripropylamine, morpholine, and the amine solvent described in step (3) is One or two of ethylenediamine and tripropylamine, and the alcohol solvent in step (3) is one or more of ethanol, cyclohexanol and ethylene glycol. 4. the preparation method of nano-silicon/graphene lithium-ion battery negative electrode material according to claim 2, is characterized in that: the consumption of metal lithium described in step (1) is 1%～5% of electronic solution gross weight, The amount of polycyclic aromatic hydrocarbon organic compounds is 0%-5% of the total weight of the electronic solution. 5. The preparation method of nano-silicon/graphene lithium-ion battery negative electrode material according to claim 2, characterized in that: the mass fraction of graphite oxide aqueous solution or graphene suspension described in step (3) is 0.5～1.5 g/L, the mass concentration of the nitric acid is 60%-70%, and the volume ratio of graphite oxide aqueous solution or graphene suspension to nitric acid is 1:2-10. 6. The preparation method of nano-silicon/graphene lithium-ion battery negative electrode material according to claim 2, characterized in that: the mass fraction of graphene oxide in the glue-like solution described in step (3) is 0.1～5g/L . 7. The preparation method of nano-silicon/graphene lithium-ion battery negative electrode material according to claim 2, characterized in that the mass ratio of nano-silicon to graphene in step (4) is 1:5-10. 8. The preparation method of nano-silicon/graphene lithium-ion battery negative electrode material according to claim 2, characterized in that: the mass percentage of the electronic solution added in step (4) is 0% to 5%, and the frequency of ultrasonic treatment 40-80Hz. 9. The preparation method of nano-silicon/graphene lithium-ion battery negative electrode material according to claim 2, characterized in that: the gas flow rate in step (5) is 20-100mL/min, and the sintering temperature is 500°C-800°C, Calcination 2 ~ 5h.