CN113078297B

CN113078297B - Silicon-carbon negative electrode material and preparation method thereof

Info

Publication number: CN113078297B
Application number: CN202010007396.8A
Authority: CN
Inventors: 邱彦星; 张海林; 计结胜; 王卡
Original assignee: Evergrande New Energy Technology Shenzhen Co Ltd
Current assignee: Evergrande New Energy Technology Shenzhen Co Ltd
Priority date: 2020-01-04
Filing date: 2020-01-04
Publication date: 2022-07-22
Anticipated expiration: 2040-01-04
Also published as: CN113078297A

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a silicon-carbon negative electrode material and a preparation method thereof. The preparation method of the silicon-carbon negative electrode material comprises the steps of mixing diatomite and an organic acid solution to obtain a precursor material; mixing the precursor material and a reducing agent for reaction to obtain a silica precursor; dispersing the silica precursor material and the carbon nano tube in an organic solvent, and calcining to obtain a silicon-carbon anode material; wherein the reducing agent is ascorbic acid and/or ascorbate. According to the invention, the diatomite with low price is used as a raw material, the silicon-carbon negative electrode material is obtained by reducing with a reducing agent and coating with the carbon nano tube, and the silicon-carbon negative electrode material has the advantages of wide raw material source, low cost, mild reaction conditions and easiness in process control, and has the advantages of high porosity, large specific surface area, high specific capacity, good cycle performance and safety performance and good application prospect.

Description

Silicon-carbon negative electrode material and preparation method thereof

Technical Field

The invention belongs to the technical field of batteries, and particularly relates to a silicon-carbon negative electrode material and a preparation method thereof.

Background

The lithium ion battery as a new generation secondary battery has the advantages of high energy density, long cycle service life, low self-discharge rate, no memory effect and the like. The negative electrode material used by the lithium ion battery mainly adopts graphite materials, but the specific capacity of the negative electrode material is low (the theoretical specific capacity is only 372mAh/g), and the application requirement of the current high-energy density storage device cannot be met. The silicon material is considered as one of the most potential cathode materials with high storage capacity, is a new generation cathode material which is possible to replace graphite, and has the advantages of the theoretical specific capacity value reaching 4200mAh/g, a low-insertion-and-extraction lithium voltage platform and the like. However, in the process of charging and discharging silicon as the negative electrode material of the lithium ion battery, the silicon negative electrode material is accompanied with huge volume change (300%), so that the silicon material is crushed and pulverized on an electrode sheet, the electrode coating is dropped off and the like, and finally the capacity is rapidly attenuated,severely hampering its practical application in lithium ion batteries. Meanwhile, since silicon is a semiconductor material, the conductivity is poor (6.7 × 10)^-4Scm^-1) Resulting in poor rate capability of the silicon material. Therefore, in order to solve the problems of expansion and poor conductivity of the silicon material, it is necessary to modify the material by coating.

The invention patent with application number 201711350301.7 discloses a silicon-carbon composite negative electrode material and a preparation method thereof, and a lithium ion battery, wherein the silicon-carbon negative electrode material is prepared mainly through a solid phase method, the material is of a core-shell structure, the inner core is porous silicon, the shell is a carbon nano tube/graphene/amorphous carbon composite body, and the solid phase method has the defects of poor consistency, high cost, high energy consumption and the like, so that the cost of the silicon-carbon material is high. The invention patent with application number 201810489255.7 discloses a hierarchical porous silicon-carbon composite structure with diatomite as a raw material and a preparation method thereof, wherein magnesium powder is added into the diatomite raw material, the exothermic temperature of magnesium thermal reaction is utilized, the temperature and time are controlled, acid is firstly produced into a porous silicon material through an intermediate product, and finally the porous silicon material is compounded with a carbon material to obtain the hierarchical porous silicon-carbon composite material.

Disclosure of Invention

The invention aims to provide a preparation method of a silicon-carbon negative electrode material, and aims to solve the technical problems of high cost, low specific capacity, difficult control of a reaction process and the like in the conventional silicon material coating modification.

Another object of the present invention is to provide a silicon carbon negative electrode material.

It is a further object of the present invention to provide a lithium ion battery.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:

a preparation method of a silicon-carbon negative electrode material comprises the following steps:

mixing diatomite with an acid solution to obtain a precursor material;

mixing the precursor material with a reducing agent for reaction to obtain a silica precursor material;

dispersing the silica precursor material and the carbon nano tube in an organic solvent, and calcining to obtain a silicon-carbon negative electrode material;

wherein the reducing agent is ascorbic acid and/or ascorbate.

In a preferable technical scheme of the invention, in a mixture formed by mixing the precursor material and the reducing agent, the mass ratio of the precursor material to the reducing agent is 100 (1-20).

In a preferred embodiment of the present invention, the concentration of the reducing agent is 0.01mol/L to 0.1 mol/L.

In a preferable embodiment of the present invention, the step of mixing diatomaceous earth with an acid solution is performed, wherein the mass ratio of the diatomaceous earth to the acid solution is 1 (10-100).

As a preferred technical solution of the present invention, the acid solution is an organic acid solution.

In a further preferred embodiment of the present invention, the organic acid in the organic acid solution is at least one selected from the group consisting of formic acid, acetic acid, propionic acid, butyric acid, caprylic acid, adipic acid, oxalic acid, malonic acid, succinic acid, maleic acid, tartaric acid, benzoic acid, phenylacetic acid, phthalic acid, and terephthalic acid.

As a preferable technical scheme of the invention, the mass concentration of the acid solution is 1-10%.

As a preferred technical scheme of the invention, the step of dispersing the silicon-oxygen precursor material and the carbon nano-tubes in an organic solvent is carried out, wherein the mass ratio of the silicon-oxygen precursor material to the carbon nano-tubes to the organic solvent is 100 (1-5): 100-500).

In a preferred embodiment of the present invention, the step of dispersing the silica precursor material and the carbon nanotubes in an organic solvent is performed, and the organic solvent is at least one selected from N-methylpyrrolidone, carbon tetrachloride and tetrahydrofuran.

As a preferable technical scheme of the invention, the step of mixing the diatomite and the acid solution is carried out at the temperature of 60-150 ℃.

In a preferred embodiment of the present invention, the diatomaceous earth is mixed with an acid solution for a time period of 1 to 12 hours.

As a preferred technical scheme of the invention, the temperature of the mixing reaction of the precursor material and the reducing agent is 120-180 ℃.

As a preferable technical scheme of the invention, the time for mixing and reacting the precursor material and the reducing agent is 1-6 h.

As a preferred technical scheme of the invention, the calcination is to heat up to 500-900 ℃ at a heating rate of 1-10 ℃/min and keep the temperature for 1-6 h under an inert atmosphere.

The silicon-carbon negative electrode material has porosity of 40-58% and specific surface area of 10m²/g-11m²/g。

As a preferable technical scheme of the invention, in the silicon-carbon negative electrode material, the mass ratio of silicon to carbon is (40-45) to (55-60).

A lithium ion battery comprises a positive electrode, a negative electrode, electrolyte and a diaphragm positioned between the positive electrode and the negative electrode, wherein the negative electrode comprises the silicon-carbon negative electrode material.

In the preparation method of the silicon-carbon cathode material, metal is not used as a reducing agent, but ascorbic acid and/or ascorbate is used as an organic reducing agent, so that the reduction reaction condition is mild and easy to control, the reduction effect is complete, other metal impurities are not introduced, and potential safety hazards caused by the introduction of the metal impurities to subsequent reactions and lithium ion batteries are avoided; secondly, after the ascorbic acid and/or ascorbate are/is reduced, nano holes are left in the silicon material, the nano holes can help to reduce the expansion volume of the silicon in the charging and discharging process, provide buffer for the silicon, avoid the damage of an electrode structure, have large specific surface area, have better liquid absorption and retention capacity, reduce the rebound rate of a pole piece, and are beneficial to improving the primary efficiency and keep the performance stable in the charging and discharging circulating process; thirdly, the carbon nano tubes are coated on the surface of the silicon-oxygen material to form a coating layer, so that the structural integrity can be maintained, the mechanical strength of the obtained silicon-carbon negative electrode material is enhanced, the volume expansion of silicon can be buffered, and the continuous generation of an SEI film is avoided; the carbon nano tube with the net structure also has a faster bulk phase lithium ion diffusion rate, and can further improve the electrochemical performance of the obtained silicon-carbon negative electrode material in the circulation process; finally, in the preparation method of the silicon-carbon cathode material, the diatomite is used as the silicon raw material, and the diatomite has a unique pore channel structure, so that the silicon material with a porous structure can be obtained after the diatomite is reduced by the reducing agent, the specific surface area of the material can be further increased, the expansion volume of the silicon is reduced, and the diatomite also has the advantages of wide raw material source and low cost, and is beneficial to the development of lithium ion batteries.

The silicon-carbon negative electrode material prepared by the preparation method of the silicon-carbon negative electrode material has the porosity of 40-58 percent and the specific surface area of 10m²/g-11m²The method has the advantages of high specific capacity of the silicon material, high specific capacity, good cycle performance and good safety performance.

Drawings

Fig. 1 is an SEM image (5000 ×) of a silicon carbon anode material provided in example 1 of the present invention.

Detailed Description

In order to make the objects, technical solutions and technical effects of the embodiments of the present invention clearer and more completely describe the technical solutions in the embodiments of the present invention, the embodiments described below are a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art without making any creative effort in combination with the embodiments of the present invention belong to the protection scope of the present invention. Those whose specific conditions are not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer; the reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

In the description of the present invention, it should be understood that the weight of the related components mentioned in the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight between each component, and therefore, it is within the scope of the disclosure that the content of the related components is scaled up or down according to the embodiments of the present invention. Specifically, the weight in the embodiment of the present invention may be μ g, mg, g, kg, etc. in units of mass known in the chemical field.

In addition, unless the context clearly uses otherwise, an expression of a word in the singular is to be understood as encompassing the plural of the word. The terms "comprises" or "comprising" are intended to specify the presence of stated features, quantities, steps, operations, elements, portions, or combinations thereof, but are not intended to preclude the presence or addition of one or more other features, quantities, steps, operations, elements, portions, or combinations thereof.

The embodiment of the invention provides a preparation method of a silicon-carbon anode material, which comprises the following steps:

s1, mixing diatomite with an acid solution to obtain a precursor material;

s2, mixing the precursor material and a reducing agent for reaction to obtain a silica precursor;

s3, dispersing the silica precursor material and the carbon nano tubes in an organic solvent, and calcining to obtain a silicon-carbon negative electrode material;

wherein the reducing agent comprises ascorbic acid and/or ascorbate.

In the preparation method of the silicon-carbon cathode material, metal is not used as a reducing agent, but the ascorbic acid and/or ascorbate is used as an organic reducing agent, so that the reduction reaction condition is mild and easy to control, the reduction effect is complete, other metal impurities cannot be introduced, and potential safety hazards to subsequent reaction and a lithium ion battery caused by the introduction of the metal impurities are avoided; secondly, after the ascorbic acid and/or ascorbate are/is reduced, nano holes are left in the silicon material, the nano holes can help to reduce the expansion volume of the silicon in the charging and discharging process, provide buffer for the silicon, avoid the damage of an electrode structure, have large specific surface area, have better liquid absorption and retention capacity, reduce the rebound rate of a pole piece, and are beneficial to improving the primary efficiency and keep the performance stable in the charging and discharging circulating process; thirdly, the carbon nano tube is coated on the surface of the silicon-oxygen material to form a coating layer, so that the structural integrity can be maintained, the mechanical strength of the obtained silicon-carbon anode material is enhanced, the volume expansion of silicon can be buffered, and the continuous generation of an SEI (solid electrolyte interphase) film is avoided; the carbon nano tube with the net structure also has a faster bulk phase lithium ion diffusion rate, and can further improve the electrochemical performance of the obtained silicon-carbon negative electrode material in the circulation process; finally, in the preparation method of the silicon-carbon cathode material, the diatomite is used as the silicon raw material, and the diatomite has a unique pore channel structure, so that the silicon material with a porous structure can be obtained after the diatomite is reduced by the reducing agent, the specific surface area of the material can be further increased, the expansion volume of the silicon is reduced, and the diatomite also has the advantages of wide raw material source and low cost.

In S1, the diatomaceous earth is mixed with an acid solution, and the diatomaceous earth is immersed in the acid solution, and the diatomaceous earth is corroded by the acid solution, so that the number of pores in the diatomaceous earth can be increased, the specific surface area can be increased, and impurities such as alumina, iron oxide, calcium oxide, magnesium oxide and the like in the diatomaceous earth can be removed. In some embodiments, the mass ratio of diatomaceous earth to acid solution is 1 (10-100). By optimizing the mass ratio of the diatomite to the acid solution, the acid solution can fully exert the corrosion effect and the impurity removal effect to obtain the silicon material with large specific surface area and high purity, the production cost can be reduced, and the waste and acid residue are avoided. In particular, typical but non-limiting mass ratios of the diatomaceous earth of the present invention to the acid solution may be 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1: 100.

In some embodiments, the acid solution is preferably an organic acid solution. This is because the reaction conditions of the organic acid are milder than those of the inorganic acid, the reaction is more complete, and the corrosion to the equipment is lighter when the organic acid solution is mixed with diatomaceous earth.

Preferably, the organic acid in the organic acid solution is selected from at least one of formic acid, acetic acid, propionic acid, butyric acid, caprylic acid, adipic acid, oxalic acid, malonic acid, succinic acid, maleic acid, tartaric acid, benzoic acid, phenylacetic acid, phthalic acid, and terephthalic acid.

In some embodiments, the acid solution has a mass concentration of 1% to 10%. The concentration of the acid solution has close relation with the effect of removing impurities and the corrosion effect. If the concentration of the acid solution is too low, the impurity removal rate is obviously reduced, and the purposes of corroding the diatomite material and increasing the number of holes cannot be achieved; if the concentration of the acid solution is too high, although the impurity removal effect and the corrosion effect are good, the high-concentration acid will affect the subsequent treatment steps, and the production cost is also increased. In particular, typical but non-limiting mass concentrations of the acid solutions of the invention may be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.

In the mixing treatment process of the diatomite and the acid solution, the temperature and the time of the mixing treatment are also related to the effect of the organic acid on removing impurities in the diatomite and the corrosion effect of the diatomite. Through optimizing the temperature and the time of mixing treatment, both can promote the speed of getting rid of impurity, reach corresponding corrosion effect sooner, can also reduction in production cost, avoid extravagant. In some embodiments, the temperature of the mixing treatment of the diatomite and the acid solution is 60-150 ℃, and the time of the mixing treatment is 1-12 h. Specifically, typical but non-limiting temperatures in the mixing process may be 60 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃; typical but non-limiting times in the mixing process may be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12 h.

Preferably, the diatomite can be soaked in deionized water and centrifugally separated before being mixed with the acid solution, so that a part of impurities are removed, and the efficiency of removing the impurities is further improved.

In S2, the precursor material obtained in S1 is mixed with a reducing agent (ascorbic acid and/or ascorbate) to react, thereby obtaining a silica precursor. In some embodiments, the mass ratio of precursor material to reducing agent is 100 (1-20). By optimizing the mass ratio of the precursor material to the reducing agent, the reducing agent can fully reduce silicon oxide in the precursor material, and the sufficient reducing agent can also ensure that the obtained silicon oxide precursor particles have uniform size and better dispersion degree. In particular, typical but non-limiting mass ratios between the precursor material and the reducing agent may be 100:1, 100:5, 100:10, 100:15, 100: 20.

In some embodiments, the reducing agent is added at a concentration of 0.01mol/L to 0.1mol/L when the precursor material is mixed with the reducing agent. The ascorbic acid and/or ascorbate, as a reducing agent, plays an important role in the preparation process of the silicon-carbon negative electrode material of the invention. The reducing agent is added into the precursor material to carry out reduction reaction, so that nano holes can be left on the precursor material, and the material has the advantages of high porosity and large specific surface area. Specifically, typical, but non-limiting, concentrations of the reducing agent are 0.01mol/L, 0.025mol/L, 0.05mol/L, 0.075mol/L, 0.1 mol/L.

The mixed reaction condition of the precursor material and the reducing agent has close relation with the completion degree of the reduction reaction, the optimization of the reaction condition of the precursor material and the reducing agent is favorable for the full reaction completion of the reduction reaction, and the improvement of the porosity and the specific surface area of the precursor material is also favorable. In some embodiments, the temperature for mixing and reacting the precursor material and the reducing agent is 120 ℃ to 180 ℃, and the temperature can accelerate the reduction reaction rate and promote the reducing agent to generate nano holes on the precursor material. Specifically, typical but non-limiting temperatures for the mixing reaction of the precursor material and the reducing agent may be 120 ℃, 130 ℃, 140 ℃, 150 ℃, 160 ℃, 170 ℃, 180 ℃. In some embodiments, the precursor material is mixed with the reducing agent for a reaction time of 1h to 6h to ensure completion of the reaction. It is mentioned that typical, but not limiting, times in the mixing reaction of the precursor material and the reducing agent may be 1h, 2h, 3h, 4h, 5h, 6 h.

Preferably, the mixing reaction of the precursor material and the reducing agent is carried out by a hydrothermal method. The hydrothermal method is helpful for improving the integrity of the particles of the obtained silica precursor material, and the particles of the silica precursor material are uniformly distributed, are not easy to agglomerate and can avoid introducing impurities. Specifically, the mixing reaction of the precursor material and the reducing agent can be completed in a high-pressure reaction kettle.

And S3, dispersing the silica precursor material obtained in the step S2 and carbon nanotubes in an organic solvent, and calcining to coat the carbon nanotubes on the surface of the silica precursor material, thereby obtaining the silicon-carbon negative electrode material. In some embodiments, the mass ratio of the silicon oxide precursor material to the carbon nanotubes and the organic solvent is 100 (1-5): 100-500). By optimizing the mass ratio of the silicon-oxygen precursor material, the carbon nano tubes and the organic solvent, the sufficient organic solvent can prevent the silicon-oxygen precursor material from self-agglomerating, and the sufficient carbon nano tubes can ensure that the surface of the silicon-oxygen precursor material is completely coated, so that the mechanical strength and the electrochemical performance of the obtained silicon-carbon cathode material are improved.

Preferably, when the silicon-oxygen precursor material and the carbon nanotubes are dispersed in the organic solvent, the silicon-oxygen precursor material and the carbon nanotubes are fully mixed and then dispersed in the organic solvent. The reason is that the silicon-oxygen precursor has a small particle size and is easy to agglomerate, and if the silicon-oxygen precursor is directly added into an organic solvent, the carbon nanotubes cannot be uniformly coated on the surface of the silicon-oxygen precursor due to the agglomeration of the silicon-oxygen precursor, so that the coating effect is influenced, and the mechanical strength and the electrochemical performance of the obtained silicon-carbon anode material are negatively influenced.

When the silica precursor material and the carbon nano tube are dispersed in the organic solvent, the organic solvent is at least one selected from N-methyl pyrrolidone, carbon tetrachloride and tetrahydrofuran.

After dispersing the silica precursor material and the carbon nanotubes in an organic solvent, calcining the silica precursor material to enable the carbon nanotubes to generate a carbonization reaction, and finishing coating the silica precursor material to form the silicon-carbon negative electrode material with the carbon nanotube coating layer. By optimizing the calcining conditions, the carbon nano tube is facilitated to completely coat the silica precursor material, the coating layer is more uniform, and the thermal stability and the cycle life of the obtained silicon-carbon material can be improved. In some embodiments, the calcination is carried out under an inert atmosphere, the temperature is increased to 500-900 ℃ at a heating rate of 1-10 ℃/min, and the temperature is maintained for 1-6 h.

The invention provides a silicon-carbon negative electrode material which is prepared by the preparation method, and the silicon-carbon negative electrode material has the porosity of 40-58% and the specific surface area of 10m²/g-11m²/g。

Furthermore, in the silicon-carbon negative electrode material, the mass ratio of silicon to carbon is (40-45) to (55-60).

The silicon-carbon negative electrode material has high porosity and large specific surface area, can fully exert the advantage of high theoretical specific capacity of the silicon material, and has the advantages of high specific capacity, good cycle performance and good safety performance.

Correspondingly, the lithium ion battery comprises a positive electrode, a negative electrode, an electrolyte and a diaphragm positioned between the positive electrode and the negative electrode, wherein the negative electrode comprises the silicon-carbon negative electrode material.

In some embodiments, the anode further comprises an anode conductive agent, an anode binder, and/or an anode additive. The negative electrode conductive agent, the negative electrode binder and/or the negative electrode additive in the embodiment of the invention are not particularly limited, and may be selected conventionally in the art. Preferably, the mass of the silicon-carbon negative electrode material accounts for 80-99% of the total mass of the negative electrode.

In some embodiments, the lithium ion battery may also include a casing or overwrap for packaging. The embodiment of the present invention is not particularly limited to the exterior package as long as it is stable to the electrolyte and has sufficient sealing performance. The packaging form of the lithium ion battery of the invention includes but is not limited to button cell batteries, cylindrical batteries and soft package batteries.

In order to make the above implementation details and operations of the present invention clearly understood by those skilled in the art and to make the progress of the silicon carbon anode material and the preparation method thereof obviously apparent, the above technical solution is illustrated by the following examples.

Example 1

A preparation method of the silicon-carbon negative electrode material comprises the following steps:

(1) adding 1g of diatomite into 100ml of deionized water for soaking, performing centrifugal separation, then adding the diatomite into 10ml of 10% formic acid solution, soaking for 2 hours at the temperature of 150 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the deionized water into a high-pressure reaction kettle, adding 2g of ascorbic acid reducing agent with the concentration of 0.1mol/L, reacting at the temperature of 180 ℃ for 1 hour, and then filtering, washing and vacuum-drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 100ml of oily carbon nanotube conducting liquid with the concentration of 5%, ball-milling uniformly, adding into 300ml of N-methylpyrrolidone organic solvent, performing ultrasonic dispersion uniformly, spray-drying, transferring into a tube furnace, heating to 750 ℃ at the heating rate of 5 ℃/min under the inert atmosphere of argon, keeping the temperature for 3 hours, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 2

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into 10ml of 10% acetic acid solution for soaking for 5 hours at the temperature of 120 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the mixture into a high-pressure reaction kettle, adding 2g of sodium ascorbate with the concentration of 0.1mol/L, reacting for 3 hours at the temperature of 160 ℃, and then filtering, washing and vacuum drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 80ml of oily carbon nanotube conductive liquid with the concentration of 5%, ball-milling uniformly, adding into 300ml of N-methylpyrrolidone organic solvent, performing ultrasonic dispersion uniformly, spray-drying, transferring into a tube furnace, heating to 900 ℃ at the heating rate of 1 ℃/min under the inert atmosphere of argon, keeping the temperature for 1h, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 3

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into 10ml of 10% propionic acid solution for soaking for 8 hours at the temperature of 100 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the mixture into a high-pressure reaction kettle, adding 2g of potassium ascorbate with the concentration of 0.1mol/L, reacting at the temperature of 150 ℃ for 3 hours, and filtering, washing and vacuum drying to obtain a silica precursor material;

(3) adding 100g of silicon-oxygen precursor material into 60ml of oily carbon nanotube conducting liquid with the concentration of 5%, ball-milling uniformly, adding into 300ml of N-methylpyrrolidone organic solvent, ultrasonically dispersing uniformly, spray-drying, transferring into a tube furnace, heating to 500 ℃ at the heating rate of 10 ℃/min under the inert atmosphere of argon, keeping the temperature for 6 hours, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 4

(1) Adding 1g of diatomite into 100ml of deionized water, soaking, performing centrifugal separation, then adding the diatomite into a 10ml of 10% butyric acid solution, soaking for 10 hours at the temperature of 80 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the deionized water into a high-pressure reaction kettle, adding 5g of ascorbic acid with the concentration of 0.05mol/L, reacting for 6 hours at the temperature of 120 ℃, and then filtering, washing and vacuum-drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 40ml of oily carbon nanotube conductive liquid with the concentration of 5%, ball-milling uniformly, adding into 300ml of N-methylpyrrolidone organic solvent, performing ultrasonic dispersion uniformly, spray-drying, transferring into a tube furnace, heating to 750 ℃ at the heating rate of 5 ℃/min under the inert atmosphere of argon, keeping the temperature for 3 hours, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 5

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into 10ml of 10% oxalic acid solution, soaking for 12 hours at the temperature of 60 ℃, filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the mixture into a high-pressure reaction kettle, adding 5g of sodium ascorbate with the concentration of 0.05mol/L, reacting at the temperature of 180 ℃ for 1h, and then filtering, washing and vacuum drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 20ml of oily carbon nanotube conductive liquid with the concentration of 5%, ball-milling uniformly, adding into 300ml of N-methylpyrrolidone organic solvent, performing ultrasonic dispersion uniformly, spray-drying, transferring into a tube furnace, heating to 900 ℃ at the heating rate of 1 ℃/min under the inert atmosphere of argon, keeping the temperature for 1h, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 6

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into 10ml of 10% maleic acid solution, soaking for 2 hours at the temperature of 150 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the mixture into a high-pressure reaction kettle, adding 5g of potassium ascorbate with the concentration of 0.05mol/L, reacting at the temperature of 160 ℃ for 3 hours, and filtering, washing and vacuum-drying to obtain a silica precursor material;

(3) adding 100g of silicon-oxygen precursor material into 100ml of oily carbon nanotube conducting liquid with the concentration of 5%, ball-milling uniformly, adding into 300ml of N-methylpyrrolidone organic solvent, ultrasonically dispersing uniformly, spray-drying, transferring into a tube furnace, heating to 500 ℃ at the heating rate of 10 ℃/min under the inert atmosphere of argon, keeping the temperature for 6 hours, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 7

(1) Adding 1g of diatomite into 100ml of deionized water, soaking, performing centrifugal separation, then adding the diatomite into 100ml of 10% benzoic acid solution with the concentration, soaking for 5 hours at the temperature of 120 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the deionized water into a high-pressure reaction kettle, adding 10g of ascorbic acid with the concentration of 0.05mol/L, reacting for 3 hours at the temperature of 150 ℃, and then filtering, washing and vacuum-drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 80ml of oily carbon nanotube conductive liquid with the concentration of 5%, ball-milling uniformly, adding into 300ml of N-methylpyrrolidone organic solvent, performing ultrasonic dispersion uniformly, spray-drying, transferring into a tube furnace, heating to 750 ℃ at the heating rate of 5 ℃/min under the inert atmosphere of argon, keeping the temperature for 3 hours, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 8

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into 100ml of 10% tartaric acid solution with the concentration of 100 ℃ for soaking for 8 hours at the temperature of 100 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the mixture into a high-pressure reaction kettle, adding 10g of sodium ascorbate with the concentration of 0.05mol/L, reacting for 6 hours at the temperature of 120 ℃, and then filtering, washing and vacuum drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 60ml of oily carbon nanotube conductive liquid with the concentration of 5%, ball-milling uniformly, adding into 300ml of N-methylpyrrolidone organic solvent, performing ultrasonic dispersion uniformly, spray-drying, transferring into a tube furnace, heating to 900 ℃ at the heating rate of 1 ℃/min under the inert atmosphere of argon, keeping the temperature for 1h, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 9

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into 50ml of 5% formic acid solution for soaking for 10 hours at the temperature of 80 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the mixture into a high-pressure reaction kettle, adding 10g of potassium ascorbate with the concentration of 0.05mol/L, reacting at the temperature of 180 ℃ for 1h, and then filtering, washing and vacuum drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 40ml of oily carbon nanotube conducting liquid with the concentration of 5% for ball milling uniformly, adding into 500ml of carbon tetrachloride organic solvent, performing ultrasonic dispersion uniformly, performing spray drying, transferring into a tube furnace, heating to 500 ℃ at the heating rate of 10 ℃/min under the inert atmosphere of argon, performing heat preservation for 6 hours, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 10

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into 50ml of 5% acetic acid solution for soaking for 12 hours at the temperature of 60 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the deionized water into a high-pressure reaction kettle, adding 20g of ascorbic acid with the concentration of 0.01mol/L, reacting for 3 hours at the temperature of 160 ℃, and then filtering, washing and vacuum-drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 20ml of oily carbon nanotube conductive liquid with the concentration of 5%, ball-milling uniformly, adding into 500ml of carbon tetrachloride organic solvent, ultrasonically dispersing uniformly, spray-drying, transferring into a tube furnace, heating to 750 ℃ at the heating rate of 5 ℃/min under the inert atmosphere of argon, keeping the temperature for 3 hours, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 11

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into a propionic acid solution with the concentration of 50ml and the concentration of 5% for soaking for 2 hours at the temperature of 150 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the deionized water into a high-pressure reaction kettle, adding 20g of sodium ascorbate with the concentration of 0.01mol/L, reacting at the temperature of 150 ℃ for 3h, and then filtering, washing and vacuum-drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 100ml of oily carbon nanotube conducting liquid with the concentration of 5% for uniform ball milling, adding into 500ml of carbon tetrachloride organic solvent, performing ultrasonic dispersion uniformly, performing spray drying, transferring into a tube furnace, heating to 900 ℃ at the heating rate of 1 ℃/min under the inert atmosphere of argon, keeping the temperature for 1h, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 12

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into a butyric acid solution with the concentration of 50ml and the concentration of 5% for soaking for 5 hours at the temperature of 120 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the deionized water into a high-pressure reaction kettle, adding 20g of potassium ascorbate with the concentration of 0.01mol/L, reacting at the temperature of 120 ℃ for 6 hours, and then filtering, washing and vacuum-drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 80ml of oily carbon nanotube conductive liquid with the concentration of 5%, ball-milling uniformly, adding into 500ml of carbon tetrachloride organic solvent, ultrasonically dispersing uniformly, spray-drying, transferring into a tube furnace, heating to 500 ℃ at the heating rate of 10 ℃/min under the inert atmosphere of argon, keeping the temperature for 6 hours, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 13

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into oxalic acid solution with the concentration of 50ml and the concentration of 5% and soaking for 8 hours at the temperature of 100 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the deionized water into a high-pressure reaction kettle, adding 5g of mixed solution of ascorbic acid and sodium ascorbate (the mass ratio of the ascorbic acid to the sodium ascorbate is 1:1) with the concentration of 0.05mol/L, reacting for 1 hour at the temperature of 180 ℃, and then filtering, washing and vacuum drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 60ml of oily carbon nanotube conducting liquid with the concentration of 5% for ball milling uniformly, adding into 500ml of carbon tetrachloride organic solvent, performing ultrasonic dispersion uniformly, performing spray drying, transferring into a tube furnace, heating to 750 ℃ at the heating rate of 5 ℃/min under the inert atmosphere of argon, performing heat preservation for 3h, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 14

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into a maleic acid solution with the concentration of 50ml and the concentration of 5% for soaking for 10 hours at the temperature of 80 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the mixture into a high-pressure reaction kettle, adding 5g of mixed solution of ascorbic acid and sodium ascorbate (the mass ratio of the ascorbic acid to the sodium ascorbate is 1:1) with the concentration of 0.05mol/L, reacting for 3 hours at the temperature of 160 ℃, and then filtering, washing and vacuum drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 40ml of oily carbon nanotube conducting liquid with the concentration of 5% for uniform ball milling, adding into 500ml of carbon tetrachloride organic solvent, performing ultrasonic dispersion uniformly, performing spray drying, transferring into a tube furnace, heating to 900 ℃ at the heating rate of 1 ℃/min under the inert atmosphere of argon, keeping the temperature for 1h, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 15

(1) Adding 1g of diatomite into 100ml of deionized water, soaking, performing centrifugal separation, then adding the diatomite into a benzoic acid solution with the concentration of 500ml and the concentration of 5% and soaking for 12 hours at the temperature of 60 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the deionized water into a high-pressure reaction kettle, adding 5g of mixed solution of ascorbic acid and sodium ascorbate (the mass ratio of the ascorbic acid to the sodium ascorbate is 1:1) with the concentration of 0.05mol/L, reacting for 3 hours at the temperature of 150 ℃, and then filtering, washing and vacuum drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 20ml of oily carbon nanotube conductive liquid with the concentration of 5%, ball-milling uniformly, adding into 500ml of carbon tetrachloride organic solvent, ultrasonically dispersing uniformly, spray-drying, transferring into a tube furnace, heating to 500 ℃ at the heating rate of 10 ℃/min under the inert atmosphere of argon, keeping the temperature for 6 hours, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 16

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into a tartaric acid solution with the concentration of 500ml and the concentration of 5% for soaking for 2 hours at the temperature of 150 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the deionized water into a high-pressure reaction kettle, adding 5g of mixed solution of ascorbic acid and sodium ascorbate (the mass ratio of the ascorbic acid to the sodium ascorbate is 1:1) with the concentration of 0.05mol/L, reacting for 6 hours at the temperature of 120 ℃, and then filtering, washing and vacuum drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 100ml of oily carbon nanotube conducting liquid with the concentration of 5% for uniform ball milling, adding into 500ml of carbon tetrachloride organic solvent, performing ultrasonic dispersion uniformly, performing spray drying, transferring into a tube furnace, heating to 750 ℃ at the heating rate of 5 ℃/min under the inert atmosphere of argon, performing heat preservation for 3h, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 17

(1) Adding 1g of diatomite into 100ml of deionized water, soaking, performing centrifugal separation, then adding the diatomite into 100ml of 1% formic acid solution with the concentration, soaking for 5 hours at the temperature of 120 ℃, and then filtering and drying to obtain a precursor material;

(3) adding 100g of silica precursor material into 80ml of oily carbon nanotube conducting liquid with the concentration of 5% for uniform ball milling, adding into 500ml of carbon tetrachloride organic solvent, performing ultrasonic dispersion uniformly, performing spray drying, transferring into a tube furnace, heating to 900 ℃ at the heating rate of 1 ℃/min under the inert atmosphere of argon, keeping the temperature for 1h, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 18

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into 100ml of 1% acetic acid solution with the concentration of 100 ℃ for soaking for 8 hours at the temperature of 100 ℃, and then filtering and drying to obtain a precursor material;

(2) adding 100g of precursor material into 1000ml of deionized water, transferring the deionized water into a high-pressure reaction kettle, adding 5g of mixed solution of ascorbic acid and sodium ascorbate (the mass ratio of the ascorbic acid to the sodium ascorbate is 1:1) with the concentration of 0.05mol/L, reacting for 3 hours at the temperature of 160 ℃, and then filtering, washing and vacuum drying to obtain a silica precursor material;

(3) adding 100g of silica precursor material into 60ml of oily carbon nanotube conducting liquid with the concentration of 5% for ball milling uniformly, adding into 500ml of carbon tetrachloride organic solvent, performing ultrasonic dispersion uniformly, performing spray drying, transferring into a tube furnace, heating to 500 ℃ at the heating rate of 10 ℃/min under the inert atmosphere of argon, performing heat preservation for 6 hours, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Example 19

(1) Adding 1g of diatomite into 100ml of deionized water for soaking and centrifugal separation, then adding the diatomite into a 1% propionic acid solution with the concentration of 100ml and the temperature of 80 ℃ for soaking for 10 hours, and then filtering and drying to obtain a precursor material;

Example 20

(1) Adding 1g of diatomite into 100ml of deionized water, soaking, performing centrifugal separation, then adding the diatomite into a butyric acid solution with the concentration of 100ml and the concentration of 1%, soaking for 12 hours at the temperature of 60 ℃, and then filtering and drying to obtain a precursor material;

Comparative example 1

Adding 1g of diatomite into 100ml of deionized water for soaking, performing centrifugal separation, then adding the diatomite into a hydrochloric acid solution with the concentration of 100ml and the concentration of 1% and the temperature of 60 ℃ for soaking for 12 hours, and then filtering, washing and drying to obtain the purified diatomite. Uniformly mixing purified diatomite and magnesium powder according to the mass ratio of 1:5, heating to 1000 ℃ at the speed of 10 ℃/min under a vacuum environment, reducing for 5h, naturally cooling to room temperature, then soaking in a hydrochloric acid solution with the concentration of 1% and the temperature of 60 ℃ for 12h to remove impurities, filtering, washing, drying and the like to obtain the porous silicon material. And (2) adding 100g of the porous silicon material into 100ml of oily carbon nanotube conducting liquid with the concentration of 5%, ball-milling uniformly, adding into 500ml of carbon tetrachloride organic solvent, ultrasonically dispersing uniformly, spray-drying, transferring into a tubular furnace, heating to 500 ℃ at the heating rate of 10 ℃/min under the inert atmosphere of argon, keeping the temperature for 6 hours, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon negative electrode material.

Comparative example 2

Adding 100g of silicon monoxide (manufacturer: Ky Yongsho photoelectricity technology Limited company, manufactured by Dongguan city, model: KY-SI/01) into 100ml of oily carbon nanotube conducting liquid with the concentration of 5%, adding the mixture into 500ml of carbon tetrachloride organic solvent, performing ultrasonic dispersion, performing spray drying, transferring the mixture into a tube furnace, heating to 500 ℃ at the heating rate of 10 ℃/min under the inert atmosphere of argon, performing heat preservation for 6 hours, cooling to room temperature under the inert atmosphere of argon, crushing, and grading to obtain the silicon-carbon cathode material.

And (3) performance testing:

(1) and (4) SEM test:

the SEM image of the silicon-carbon negative electrode material prepared in example 1 is shown in fig. 1, and it can be seen that the silicon-carbon negative electrode material obtained in the present invention is granular, has a particle size of (1-5) μm, and has a uniform size distribution.

(2) And (3) testing the performance of the button cell:

the silicon-carbon negative electrode materials prepared in examples 1-20, comparative example 1 and comparative example 2 are used as negative electrode materials of lithium ion batteries to assemble button batteries, and are respectively marked as A1, A2, A3 … … A20, B1 and B2.

The preparation method comprises the following steps: adding a binder, a conductive agent and a solvent into a lithium ion battery negative electrode material, stirring and pulping, coating the mixture on copper foil, and drying and rolling to prepare a negative electrode plate; the used binder is LA132, the conductive agent is SP, the solvent is NMP, and the proportion of the used negative electrode material, SP, PVDF and NMP is 95 g: 1 g: 4 g: 220 mL; in the electrolyte, LiPF6 is used as electrolyte, and a mixture of EC and DEC with the volume ratio of 1:1 is used as a solvent; the metal lithium sheet is a counter electrode, and the diaphragm is a polypropylene (PP) film. The button cell assembly was performed in a hydrogen-filled glove box. The electrochemical performance is carried out on a battery tester of Wuhan blue electricity CT2001A type, the charging and discharging voltage range is 0.005V to 2.0V, and the charging and discharging speed is 0.1C.

The test results are shown in table 1.

Table 1 physical properties of silicon carbon negative electrode materials of examples 1 to 20 and comparative examples 1 to 2 and performance test results of button cell prepared therefrom

As can be seen from the data in table 1, the porosity and the specific surface area of the silicon carbon negative electrode materials obtained in examples 1 to 20 of the present invention, and the specific capacity and the first efficiency of the prepared lithium ion battery are significantly better than those of comparative example 1 and comparative example 2. The reason for this may be: according to the invention, the porosity and specific surface area of the material can be improved and the first efficiency and specific capacity of the material are improved by organic acid corrosion and using ascorbic acid and/or ascorbate as an organic reducing agent; the silicon-carbon negative electrode material obtained by taking magnesium powder as a reducing agent is difficult to completely remove due to the introduction of different impurities, so that the specific capacity and the first efficiency are low. In addition, the coating of the carbon nano tube can improve the electron conduction rate of the material, and the first efficiency is also improved.

(3) Soft package battery performance test

The materials obtained in example 1 and example 2 … …, example 20, comparative example 1 and comparative example 2 are respectively used as negative electrode materials to prepare negative electrode plates, NCM811 is used as a positive electrode material, LiPF6/EC + DEC (volume ratio 1:1) is used as electrolyte, Celgard 2400 membrane is used as a diaphragm, 5Ah soft package batteries C1, C2, C3 … … C20, D1 and D2 are prepared, and the liquid absorption capacity, the electrode plate rebound and the cycle performance (1C/1C,2.5-4.2V, 300 times) of the negative electrode plates are tested.

TABLE 2 comparison of liquid-absorbing and liquid-retaining capacities of negative electrode sheets prepared from silicon-carbon negative electrode materials of examples 1 to 20 and comparative examples 1 to 2

As can be seen from Table 2, the liquid absorbing and retaining ability of the silicon carbon anode materials obtained in examples 1-20 is significantly higher than that of comparative example 1 and comparative example 2. Experimental results show that the silicon-carbon negative electrode material has high liquid absorption and retention capacity. The reason is that: the prepared silicon-carbon negative electrode material has rich porous structure and large specific surface area, thereby improving the liquid absorption and retention capacity of the silicon-carbon negative electrode material and reducing the rebound of a pole piece.

TABLE 3 CYCLIC COMPARATIONS OF BUCKET BATTERIES PREPARED FROM SILICON-CARBON ANODE MATERIALS OF EXAMPLES 1-20 AND COMPARATIVE EXAMPLES 1-2

As can be seen from table 3, the cycle performance of the pouch batteries prepared from the silicon-carbon negative electrode materials obtained in examples 1 to 20 is significantly better than that of comparative examples 1 and 2, because the porous silicon-carbon material prepared by the hydrothermal method has the characteristic of low expansion rate, and the cycle performance of the material is improved.

In conclusion, the silicon-carbon negative electrode material provided by the invention takes diatomite as a raw material, the silicon-oxygen precursor is obtained by soaking the diatomite in organic acid and reducing the diatomite by using a specific reducing agent, and then the carbon nano tube is coated on the surface of the silicon-oxygen precursor, so that the porosity and the specific surface area of the silicon-carbon negative electrode material can be increased, the liquid absorption and retention capacity of the silicon-carbon negative electrode material are improved, the rebound rate of a pole piece is reduced, and the primary efficiency, the specific capacity and the cycle performance of an obtained lithium ion battery can be improved.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is specific and detailed, but not to be understood as limiting the scope of the present invention. It should be noted that various changes and modifications can be made by those skilled in the art without departing from the spirit of the invention, and these changes and modifications are all within the scope of the invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The preparation method of the silicon-carbon anode material is characterized by comprising the following steps of:

mixing diatomite with an acid solution to obtain a precursor material; the acid solution is an organic acid solution;

dispersing the silica precursor material and the carbon nano tube in an organic solvent, and calcining to obtain a silicon-carbon negative electrode material; when the silicon-oxygen precursor material and the carbon nano tubes are dispersed in an organic solvent, the silicon-oxygen precursor material and the carbon nano tubes are fully mixed and then dispersed in the organic solvent;

wherein the reducing agent is ascorbic acid and/or ascorbate.

2. The preparation method of the silicon-carbon anode material is characterized in that in a mixture formed by mixing the precursor material and a reducing agent, the mass ratio of the precursor material to the reducing agent is 100 (1-20); and/or the presence of a gas in the atmosphere,

the concentration of the reducing agent is 0.01mol/L-0.1 mol/L.

3. The preparation method of the silicon-carbon negative electrode material is characterized by comprising the step of mixing diatomite and an acid solution, wherein the mass ratio of the diatomite to the acid solution is 1 (10-100); and/or the presence of a gas in the atmosphere,

the organic acid is selected from at least one of formic acid, acetic acid, propionic acid, butyric acid, caprylic acid, adipic acid, oxalic acid, malonic acid, succinic acid, maleic acid, tartaric acid, benzoic acid, phenylacetic acid, phthalic acid and terephthalic acid; and/or the presence of a gas in the atmosphere,

the mass concentration of the acid solution is 1-10%.

4. The method for preparing silicon-carbon anode material according to claim 1, wherein the step of dispersing the silicon-oxygen precursor material and the carbon nanotubes in an organic solvent comprises the steps of (1-5) mixing the silicon-oxygen precursor material, the carbon nanotubes and the organic solvent by a mass ratio of (100-) - (500); and/or the presence of a gas in the atmosphere,

the organic solvent is at least one of N-methyl pyrrolidone, carbon tetrachloride and tetrahydrofuran.

5. The method for preparing a silicon-carbon anode material according to any one of claims 1 to 4, wherein the step of mixing the diatomaceous earth with the acid solution is performed at a temperature of 60 ℃ to 150 ℃; and/or the presence of a gas in the gas,

the time of the mixing treatment is 1-12 h.

6. The method for preparing the silicon-carbon anode material according to any one of claims 1 to 4, wherein the temperature for mixing and reacting the precursor material and the reducing agent is 120 ℃ to 180 ℃; and/or the presence of a gas in the gas,

the time for mixing and reacting the precursor material and the reducing agent is 1-6 h.

7. The method for preparing the silicon-carbon anode material according to any one of claims 1 to 4, wherein the calcination is carried out by heating to 500-900 ℃ at a heating rate of 1-10 ℃/min and keeping the temperature for 1-6 h under an inert atmosphere.

8. The silicon-carbon negative electrode material is prepared by the preparation method of any one of claims 1 to 7, and is characterized in that the porosity of the silicon-carbon negative electrode material is 40-58%, and the specific surface area of the silicon-carbon negative electrode material is 10m²/g-11m²/g。

9. The silicon-carbon anode material of claim 8, wherein the silicon-carbon anode material has a silicon-to-carbon mass ratio of (40-45) to (55-60).

10. A lithium ion battery comprises a positive electrode, a negative electrode, an electrolyte and a diaphragm positioned between the positive electrode and the negative electrode, wherein the negative electrode comprises the silicon-carbon negative electrode material prepared by the preparation method of any one of claims 1 to 7 or the silicon-carbon negative electrode material of claim 8 or 9.