A high-performance silicon-carbon negative electrode material for lithium batteries and its preparation method

Abstract

The present invention provides a high-performance silicon-carbon negative electrode material for lithium batteries and a preparation method thereof. The preparation method comprises the following steps: (1) crushing and drying industrial silicon slag to obtain waste silicon powder, calcining the waste silicon powder at high temperature in an inert gas atmosphere to remove impurities, and obtaining silicon powder with higher purity; (2) acid-washing and water-washing the silicon powder, and then drying it to obtain high-purity silicon powder; (3) adding the high-purity silicon powder, an organic compound monomer, and ammonium persulfate to a solvent in a certain proportion, and then reacting the mixture by high-speed vacuum wet ball milling and ice bath stirring to obtain a polymer-coated nano-silicon composite material; (5) stirring the nano-silicon composite material, perfluorobutylsulfonamide, and graphite to obtain a mixed slurry, and then spray drying and calcining it to obtain a silicon-carbon negative electrode material. The silicon-carbon negative electrode material prepared by this method has high initial efficiency and good stability, and the preparation process is low in cost, simple to operate, and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and in particular to a high-performance silicon-carbon negative electrode material for lithium batteries and a preparation method thereof.

[0002] With the rapid development of mobile electronics and the new energy vehicle industry, market demands for the energy density of lithium-ion batteries are increasing. Anode materials, as key components of lithium-ion batteries, play a decisive role in battery energy performance. The theoretical specific capacity of graphite, a traditional anode material, is only 372 mAh / g, which is insufficient for high-energy-density lithium-ion batteries. Silicon, on the other hand, boasts a theoretical capacity of 4200 mAh / g, more than ten times that of graphite. To achieve higher energy density, the industry consensus is that silicon-based anodes should be developed for use in lithium-ion battery systems.

[0003] While silicon-based anode materials hold broad application prospects, practical silicon applications still face technical challenges. The most significant challenges are: 1) Volume expansion reaches 320% after lithium insertion, which further leads to material pulverization, changes in electrode structure, and the continuous formation of a solid electrolyte (SEI) film; and 2) Silicon is an intrinsically semiconductor material with poor conductivity. Due to these bottlenecks, silicon cannot yet be used solely as an anode material. Currently, battery material companies primarily combine silicon with graphite, conductive agents, and other carbon materials. The introduction of carbon materials can improve the conductivity of silicon-carbon anodes. Nanoscaling is an effective solution to silicon's volume expansion problem. Research has shown that reducing silicon to less than 150 nm in at least one dimension effectively mitigates this volume expansion problem and prevents material pulverization and breakage.

[0004] Chinese patent CN104112850A provides a silicon-carbon negative electrode material based on photovoltaic waste silicon and its preparation method, which simply mixes purified and modified micron and submicron silicon with graphite and applies it to lithium-ion battery negative electrode materials. This composite material uses waste silicon mud from the photovoltaic industry as raw material, adopts step-by-step refinement, controls the particle size of silicon powder within a reasonable range, balances the particle size and specific surface area, and alleviates the volume expansion of silicon to a certain extent, so that nano-silicon can exert better performance. Organic matter is pyrolyzed to form amorphous carbon coating on the surface of flaky nano-silicon. After high-temperature calcination, a stable and uniform amorphous carbon coating can be formed on the surface of the silicon material, thereby improving the coulombic efficiency and cycle stability of the material. However, this process is relatively expensive and cannot be industrialized. The polymer cracking single-layer coating can only alleviate the volume expansion of silicon to a certain extent. The structure of silicon is still unstable and cannot improve the initial charge and discharge efficiency of the material.

[0005] Chinese patent CN 110931744 A provides a method for preparing silicon-carbon materials, which involves adding polymer monomers to a silicon source and using heat polymerization to obtain a polymer nanobelt-coated silicon material. This process forms a silicon-carbon negative electrode material with a high-porosity network-like coating structure, which can not only effectively buffer the volume expansion of silicon during the lithium insertion and extraction process, but also extend the cycle life of lithium-ion batteries. However, this process has high reaction conditions and limited cost control. In addition, heating may cause the nanosilicon to be oxidized, which is prone to side reactions. This process also does not control the particle size of silicon, and is even more unable to improve the initial efficiency of silicon. Summary of the Invention

[0006] In response to the above technical problems, the present invention provides a high-performance silicon-carbon negative electrode material for lithium batteries and a preparation method. Using industrial waste silicon slag as raw material, organic monomers are introduced during the ball milling process to initiate in-situ polymerization of the monomers and construct a carbon coating, which not only reduces production costs but also provides a buffer layer for silicon volume expansion. A small amount of silicon-oxygen bonds on the surface of the nano-silicon form hydrogen bonds with the organic monomers, thereby guiding the directional and regular growth of the polymer. The uniform and regular polymer coating facilitates rapid electrolyte infiltration and provides a large amount of pseudocapacitance through redox reactions, enabling the nano-silicon to exert better performance. In addition, by spray drying and introducing nitrogen and fluorine sources, nitrogen-fluorine co-doped carbon-coated nano-silicon particles are obtained. These particles are then mixed with a certain amount of graphite to form a graphite structure skeleton that coats the nano-silicon, significantly improving the initial charge and discharge efficiency and cycle stability of the silicon-carbon.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A high-performance silicon-carbon negative electrode material for lithium batteries comprises a two-layer coating structure doped with nano-silicon and fluorine and nitrogen ions, which is coated on the outside of the nano-silicon. The two-layer coating structure comprises an inner coating layer and an outer coating layer. The inner coating layer is amorphous carbon generated by polymer decomposition, and the outer coating layer is a coating layer formed by a structural skeleton provided by graphite. The inner coating layer of the nano-silicon is generated by polymer decomposition. In the process of controlling the particle size of the nano-silicon, organic monomers are directly synthesized into polymers through an oxidation-reduction method, and nitrogen ions and fluoride ions are incorporated into the coating layer through a mixing reaction and spray drying.

[0009] Furthermore, the particle size of the silicon-carbon negative electrode material is 50-300 nm.

[0010] The present invention also provides a method for preparing the high-performance silicon-carbon negative electrode material for lithium batteries, comprising the following steps:

[0011] (1) Grinding and drying industrial waste silicon slag to obtain waste silicon powder, and sintering the waste silicon powder at high temperature to remove impurities;

[0012] (2) The silicon powder after high-temperature sintering and impurity removal is acid-washed and washed with pure water to obtain high-purity silicon powder;

[0013] (3) High-purity silicon powder and organic monomer are added to a solvent and ultrasonically dispersed to obtain a slurry. The slurry and zirconium oxide balls are then added to a ball mill, the ball mill is vacuum-treated, and then ball milling is performed. An initiator is added during the ball milling process.

[0014] (4) placing the ball-milled slurry in an ice bath for reaction, and filtering to obtain a polymer-coated nano-silicon composite material after the reaction is completed;

[0015] (5) The polymer-coated nano-silicon composite material, perfluorobutylsulfonamide and graphite are added to a dispersant, mixed and stirred to obtain a mixed slurry, which is then spray-dried and calcined at high temperature to obtain a fluorine-nitrogen co-doped high-performance silicon-carbon negative electrode material for lithium batteries.

[0016] Furthermore, in step (1), the purity of the industrial waste silicon slag used is ≥80%, and most of the organic matter is removed by high-temperature sintering. The high-temperature sintering is carried out in an inert gas, and the inert gas is high-purity nitrogen or high-purity argon. The heating rate is 5°C / min, and the temperature is controlled at 200°C for 2h, and at 700-800°C for 2h, and then naturally cooled to room temperature.

[0017] Furthermore, in step (2), the acid used for pickling is one or more of hydrochloric acid, nitric acid, and sulfuric acid, the acid concentration is 1-3 mol / L, the pickling temperature is 25-50°C, the pickling time is 1-8 hours, and the pure water washing temperature is 15-40°C, the time is 1-4 hours, and the purity of the obtained high-purity silicon powder is ≥99%.

[0018] Furthermore, in step (3), the solvent is dilute hydrochloric acid with a concentration of 1-2 M, the solid content of the slurry is 5-50%, the organic monomer is aniline, pyrrole, thiophene or acrylamide, and the mass ratio of high-purity silicon powder to the organic monomer is 10:(1-5).

[0019] Furthermore, in step (3), the mass ratio of the total mass of high-purity silicon powder and organic monomer to the mass of zirconia balls is 10:(5~30), the particle size of the zirconia balls is 0.1~2 mm, the ball milling speed is 200~800 rpm, the ball milling time is 0.5~3h, and the vacuum degree of the ball milling jar is ≤-90Kpa.

[0020] Furthermore, in step (3), the initiator is ammonium persulfate, the mass ratio of ammonium persulfate to organic monomer is 1:(2-4), and the initiator is added to the ball mill in 3-5 times.

[0021] Furthermore, in step (4), the ice bath reaction temperature is -10~5°C, the ice bath reaction time is 1~5h, and the particle size of the polymer-coated nano-silicon composite material is 50~120nm.

[0022] Furthermore, in step (5), the mass ratio of the polymer-coated nano-silicon composite material to graphite is 1:(1-3), the mass fraction of perfluorobutylsulfonamide in the polymer-coated nano-silicon composite material is 2-10%, the dispersant is one of ethanol, methanol, and acetone, the stirring time is 2-10 h, the temperature is 0-60° C., the feed rate is 5 mL / min, the spray pressure is 2 MPa, and the high-temperature sintering conditions are the same as those in step (1).

[0023] Beneficial effects of the present invention: The silicon-carbon negative electrode material of the present invention mainly comprises three parts: the first part is the internal base nano-silicon material, the second part is the indeterminate carbon coating layer formed by decomposition of organic matter, and the third part is the graphite skeleton layer.

[0024] The present invention is simple and easy to implement. Nano-silicon and organic monomers are simultaneously vacuum ball-milled to induce a redox reaction in the monomers to generate a polymer coating layer, which provides a buffer layer for the volume expansion of silicon. This process is simple, low-cost, and reduces side reactions. A small amount of silicon-oxygen bonds on the surface of the nano-silicon form hydrogen bonds with the organic monomers, thereby guiding the directional and regular growth of the polymer. The uniform and regular polymer nano-coating layer is conducive to the rapid infiltration of the electrolyte, provides a large amount of pseudocapacitance through the redox reaction, and enables the nano-silicon to exert better performance.

[0025] The present invention uses perfluorobutylsulfonamide to dope the coating with fluorine and nitrogen ions, improving the material's conductivity and ion mobility, and boosting the initial charge and discharge efficiency of nanosilicon. Spray drying is used for granulation and secondary coating of the nanosilicon. Graphite provides a spatial structural framework for the nanosilicon, further reducing its volume expansion. The addition of graphite also creates space for ion doping. Fluorine and nitrogen co-doping and graphite coating significantly enhance the electrochemical performance of the nanosilicon. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the SEM image of the silicon-carbon negative electrode material prepared in Example 1. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to specific examples. It should be understood that the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention, and that those skilled in the art may make non-essential improvements and adjustments based on the contents of the above invention.

[0028] Example 1

[0029] The preparation method of the high-performance silicon-carbon negative electrode material for lithium batteries of this embodiment comprises the following steps:

[0030] (1) Use a crusher to crush the waste silicon slag to an average particle size of ≤2mm, and then dry it in a blast drying oven to a moisture content of ≤2%. Place the dried waste silicon powder in a horizontal tube furnace and heat it to 800℃ at a rate of 5℃ / min under a nitrogen atmosphere for 2 hours to perform high-temperature impurity removal.

[0031] (2) The silicon powder after high-temperature impurity removal is placed in 1M dilute hydrochloric acid and stirred at 40°C for 2 hours. It is then washed with pure water until neutral, and then filtered and dried in a vacuum to obtain high-purity silicon powder with a purity greater than 99.8%.

[0032] (3) Weigh 50 g of high-purity silicon powder and 5 g of aniline monomer and add them to 1 M dilute hydrochloric acid. Ultrasonicate for 15 min. Put the solution and 150 g of zirconium oxide beads into a ball mill. Vacuum the ball mill and ball mill at 400 rpm for 1.5 h. During this period, ammonium persulfate was added three times. The total mass of persulfate was 15 g. Finally, a nano-silicon mixed slurry was obtained.

[0033] (4) The nano-silicon mixed slurry was stirred in an ice bath for 4 h, and vacuum filtered to obtain a polymer-coated nano-silicon composite material.

[0034] (5) Weigh 10 g of nano-silicon composite material, 1 g of perfluorobutylsulfonamide and 20 g of graphite and add them together in 250 mL of ethanol. Stir for 4 h to obtain a mixed slurry. Then spray dry the slurry. After drying, calcine it under an argon atmosphere, heat it to 200 °C at a rate of 5 °C / min and keep it for 2 h. Continue to heat it to 800 °C and keep it for 2 h. Cool it naturally to room temperature. Finally, obtain a silicon-carbon negative electrode material for lithium batteries with excellent performance.

[0035] Example 2

[0036] The preparation method of the high-performance silicon-carbon negative electrode material for lithium batteries of this embodiment comprises the following steps:

[0037] (1) Use a crusher to crush the waste silicon slag to an average particle size of ≤2mm, and then dry it in a blast drying oven to a moisture content of ≤2%. Place the dried waste silicon powder in a horizontal tube furnace and heat it to 200℃ at a rate of 5℃ / min under a nitrogen atmosphere for 2 hours. Then continue to heat it to 800℃ and keep it for 2 hours to perform high-temperature impurity removal.

[0038] (2) The silicon powder after high-temperature impurity removal is placed in 1M dilute hydrochloric acid, stirred at 40°C for 2 hours, washed with pure water until neutral, and then filtered and vacuum dried to obtain high-purity silicon powder with a purity greater than 99.8%.

[0039] (3) Weigh 50 g of high-purity silicon powder and 5 g of pyrrole monomer and add them to 1 M dilute hydrochloric acid. Ultrasonicate for 15 min, then put them into a ball mill together with 150 g of zirconium oxide beads. Vacuum the ball mill and ball mill at 400 rpm for 1.5 h. During this period, ammonium persulfate was added three times. The total mass of persulfate was 15 g. Finally, a nano-silicon mixed slurry was obtained.

[0040] (4) The nano-silicon mixed slurry was stirred and reacted in an ice bath for 4 h, and a polymer-coated nano-silicon composite material was obtained by vacuum filtration and vacuum drying.

[0041] (5) Weigh 10 g of nano-silicon composite material, 1 g of perfluoro-n-butylsulfonamide, and 20 g of graphite and add them to 250 mL of ethanol. Stir for 4 h to obtain a mixed slurry. The slurry is then spray-dried and calcined under an argon atmosphere. The temperature is raised to 200 °C at a rate of 5 °C / min and kept at this temperature for 2 h. The temperature is then raised to 800 °C and kept at this temperature for 2 h. The mixture is then naturally cooled to room temperature to obtain a silicon-carbon negative electrode material for lithium batteries with excellent performance.

[0042] Example 3

[0043] The preparation method of the high-performance silicon-carbon negative electrode material for lithium batteries of this embodiment comprises the following steps:

[0044] (1) Use a crusher to crush the waste silicon slag to an average particle size of ≤2 mm, and then dry it in a blast drying oven to a moisture content of ≤2%. Place the dried waste silicon powder in a horizontal tube furnace and heat it to 200℃ at a rate of 5℃ / min under a nitrogen atmosphere for 2 hours. Then continue to heat it to 800℃ and keep it for 2 hours to perform high-temperature impurity removal.

[0045] (2) The silicon powder after high-temperature impurity removal is placed in 1M dilute hydrochloric acid, stirred at 40°C for 2 hours, washed with pure water until neutral, and then filtered and vacuum dried to obtain high-purity silicon powder with a purity greater than 99.8%.

[0046] (3) Weigh 50 g of high-purity silicon powder and 5 g of thiophene monomer and add them to 1 M dilute hydrochloric acid. Ultrasonicate for 15 min, then put them into a ball mill together with 150 g of zirconium oxide beads. Vacuum the ball mill and ball mill at 400 rpm for 1.5 h. During this period, ammonium persulfate was added three times. The total mass of persulfate was 15 g. Finally, a nano-silicon mixed slurry was obtained.

[0047] (4) The nano-silicon mixed slurry was stirred and reacted in an ice bath for 4 h, and a polymer-coated nano-silicon composite material was obtained by vacuum filtration and vacuum drying.

[0048] (5) Weigh 10 g of nano-silicon composite material, 2 g of perfluorobutylsulfonamide, and 20 g of graphite and add them to 250 mL of ethanol. Stir for 4 h to obtain a mixed slurry. The slurry is then spray-dried and calcined under an argon atmosphere. The temperature is raised to 200 °C at a rate of 5 °C / min and kept at this temperature for 2 h. The temperature is then raised to 800 °C and kept at this temperature for 2 h. The mixture is then naturally cooled to room temperature to obtain a silicon-carbon negative electrode material for lithium batteries with excellent performance.

[0049] Example 4

[0050] The preparation method of the high-performance silicon-carbon negative electrode material for lithium batteries of this embodiment comprises the following steps:

[0051] (1) Use a crusher to crush the waste silicon slag to an average particle size of ≤2 mm, and then dry it in a blast drying oven to a moisture content of ≤2%. Place the dried waste silicon powder in a horizontal tube furnace and heat it to 200℃ at a rate of 5℃ / min under a nitrogen atmosphere for 2 hours. Then continue to heat it to 800℃ and keep it for 2 hours to perform high-temperature impurity removal.

[0052] (2) The silicon powder after high-temperature impurity removal is placed in 1M dilute hydrochloric acid, stirred at 40°C for 2 hours, washed with pure water until neutral, and then filtered and vacuum dried to obtain high-purity silicon powder with a purity greater than 99.8%.

[0053] (3) Weigh 50 g of high-purity silicon powder and 5 g of acrylamide monomer and add them to 1 M dilute hydrochloric acid. Ultrasonicate for 15 min and then place them together with 150 g of zirconium oxide beads in a ball mill. Vacuum the ball mill and ball mill at 400 rpm for 1.5 h. During this period, ammonium persulfate was added three times. The total mass of persulfate was 15 g. Finally, a nano-silicon mixed slurry was obtained.

[0054] (4) The nano-silicon mixed slurry was stirred and reacted in an ice bath for 4 h, and a polymer-coated nano-silicon composite material was obtained by vacuum filtration and vacuum drying.

[0055] (5) Weigh 10 g of nano-silicon composite material, 2 g of perfluorobutanesulfonamide and 10 g of graphite and add them together into 250 mL of ethanol, stir for 8 h to obtain a mixed slurry, then spray dry the slurry, and calcine it under an argon atmosphere after drying. Heat it to 800 °C at a rate of 5 °C / min and keep it for 2 h, continue to heat it to 800 °C and keep it for 2 h, and naturally cool it to room temperature to obtain a silicon-carbon negative electrode material for lithium batteries with excellent performance.

[0056] Comparative Example 1

[0057] (1) Use a crusher to crush the waste silicon slag to an average particle size of ≤2mm, and then dry it in a blast drying oven to a moisture content of ≤2%. Place the dried waste silicon powder in a horizontal tube furnace and heat it to 200℃ at a rate of 5℃ / min under a nitrogen atmosphere. Keep it at this temperature for 2h, then continue to heat it to 800℃ and keep it at this temperature for 2h to remove impurities at high temperature.

[0058] (2) Place the silicon powder after high-temperature impurity removal in 1M dilute hydrochloric acid. Stir at 40°C for 2 hours, filter, and wash with pure water until neutral. Then, dry the washed silicon powder in a vacuum to obtain high-purity silicon powder with a purity greater than 99.8%.

[0059] Comparative Example 2

[0060] (1) Use a crusher to crush the waste silicon slag to an average particle size of ≤2mm, and then dry it in a blast drying oven to a moisture content of ≤2%. Place the dried waste silicon powder in a horizontal tube furnace and heat it to 200℃ at a rate of 5℃ / min under a nitrogen atmosphere. Keep it at this temperature for 2h, then continue to heat it to 800℃ and keep it at this temperature for 2h to remove impurities at high temperature.

[0061] (2) Place the silicon powder after high-temperature impurity removal in 1M dilute hydrochloric acid. Stir at 40°C for 2 hours, filter, and wash with pure water until neutral. Then, dry the washed silicon powder in a vacuum to obtain high-purity silicon powder with a purity greater than 99.8%.

[0062] (3) Weigh 50 g of high-purity silicon powder and add it to an appropriate amount of dilute hydrochloric acid. Ultrasonicate for 15 min, then put it into a ball mill together with 150 g of zirconium oxide beads. Vacuum the ball mill and ball mill at 400 rpm for 1.5 h to obtain nano-silicon slurry. Add 2 g of aniline monomer to the nano-silicon slurry, stir and react in an ice bath for 4 h, and obtain a polymer-coated nano-silicon composite material by vacuum filtration and vacuum drying.

[0063] (4) Weigh 10 g of nano-silicon composite material and 10 g of graphite and add them to ethanol, stir for 8 h to obtain a mixed slurry, then spray dry the slurry, calcine it under argon atmosphere after drying, heat it to 800 °C at a rate of 5 °C / min and keep it for 2 h, and cool it naturally to room temperature to obtain a silicon-carbon negative electrode material for lithium batteries with excellent performance.

[0064] The prepared silicon-carbon anode material was assembled into a half-cell and electrochemical performance tested. The silicon-carbon anode material, Super P, and binder were homogenized and smeared at a mass ratio of 8:1:1. The binder consisted of a solution of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA) at a mass ratio of 1:1:1. The electrolyte was a conventional LiPF6 electrolyte. A lithium sheet served as the counter electrode and the cells were assembled into a CR2025 button cell. Charge and discharge tests were conducted at room temperature using a LANHE CT2001A blue-electrode test system at a current density of 100 mA / g over a voltage range of 0.005–2.0 V.

[0065] Table 1 Electrochemical performance test of Examples 1-4 and Comparative Examples 1-2

[0066]

[0067] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-performance silicon-carbon negative electrode material for lithium batteries, characterized by: The high-performance silicon-carbon negative electrode material for lithium batteries comprises a two-layer coating structure of nano-silicon doped with fluorine and nitrogen ions, which is coated on the outside of the nano-silicon. The two-layer coating structure comprises an inner coating layer and an outer coating layer. The inner coating layer is amorphous carbon generated by polymer decomposition, and the outer coating layer is a coating layer formed by a structural skeleton provided by graphite. The inner coating layer of the nano-silicon is generated by polymer decomposition. In the process of controlling the particle size of the nano-silicon, organic monomers are directly synthesized into polymers through an oxidation-reduction method, and nitrogen ions and fluoride ions are incorporated into the coating layer through a mixing reaction and spray drying. The preparation method of high-performance silicon-carbon negative electrode material for lithium batteries comprises the following steps: (1) Grinding and drying industrial waste silicon slag to obtain waste silicon powder, and sintering the waste silicon powder at high temperature to remove impurities; (2) The silicon powder after high-temperature sintering and impurity removal is acid-washed and washed with pure water to obtain high-purity silicon powder; (3) High-purity silicon powder and organic monomer are added to a solvent and ultrasonically dispersed to obtain a slurry. The slurry and zirconium oxide balls are then added to a ball mill, the ball mill is vacuum-treated, and then ball milling is performed. An initiator is added during the ball milling process. (4) placing the ball-milled slurry in an ice bath for reaction, and filtering to obtain a polymer-coated nano-silicon composite material after the reaction is completed; (5) The polymer-coated nano-silicon composite material, perfluorobutylsulfonamide and graphite are added to a dispersant, mixed and stirred to obtain a mixed slurry, which is then spray-dried and calcined at high temperature to obtain a fluorine-nitrogen co-doped high-performance silicon-carbon negative electrode material for lithium batteries.

2. The high-performance silicon-carbon negative electrode material for lithium batteries according to claim 1, characterized in that: The particle size of the silicon-carbon negative electrode material is 50-300 nm.

3. The method for preparing a high-performance silicon-carbon negative electrode material for a lithium battery according to claim 1, characterized in that The following steps are involved: (1) Grinding and drying industrial waste silicon slag to obtain waste silicon powder, and sintering the waste silicon powder at high temperature to remove impurities; (2) The silicon powder after high-temperature sintering and impurity removal is acid-washed and washed with pure water to obtain high-purity silicon powder; (3) High-purity silicon powder and organic monomer are added to a solvent and ultrasonically dispersed to obtain a slurry. The slurry and zirconium oxide balls are then added to a ball mill, the ball mill is vacuum-treated, and then ball milling is performed. An initiator is added during the ball milling process. (4) placing the ball-milled slurry in an ice bath for reaction, and filtering to obtain a polymer-coated nano-silicon composite material after the reaction is completed; (5) The polymer-coated nano-silicon composite material, perfluorobutylsulfonamide and graphite are added to a dispersant, mixed and stirred to obtain a mixed slurry, which is then spray-dried and calcined at high temperature to obtain a fluorine-nitrogen co-doped high-performance silicon-carbon negative electrode material for lithium batteries.

4. The method for preparing a high-performance silicon-carbon negative electrode material for a lithium battery according to claim 3, wherein: In the step (1), the purity of the industrial waste silicon slag used is ≥80%, and most of the organic matter is removed by high-temperature sintering. The high-temperature sintering is carried out in an inert gas, and the inert gas is high-purity nitrogen or high-purity argon. The heating rate is 5°C / min, and the temperature is controlled at 200°C for 2h, and at 700-800°C for 2h, and then naturally cooled to room temperature.

5. The method for preparing a high-performance silicon-carbon negative electrode material for a lithium battery according to claim 3, wherein: In step (2), the acid used for pickling is one or more of hydrochloric acid, nitric acid, and sulfuric acid, the acid concentration is 1-3 mol / L, the pickling temperature is 25-50°C, the pickling time is 1-8 hours, and the pure water washing temperature is 15-40°C, and the time is 1-4 hours.

6. The high-performance silicon-carbon negative electrode material for lithium batteries and the preparation method thereof according to claim 3, characterized in that: In step (3), the solvent is dilute hydrochloric acid with a concentration of 1-2M, the solid content of the slurry is 5-50%, the organic monomer is aniline, pyrrole, thiophene or acrylamide, and the mass ratio of high-purity silicon powder to the organic monomer is 10:(1-5).

7. The high-performance silicon-carbon negative electrode material for lithium batteries and the preparation method thereof according to claim 3, characterized in that: In the step (3), the mass ratio of the total mass of high-purity silicon powder and organic monomer to the mass of zirconia balls is 10:(5-30), the particle size of the zirconia balls is 0.1-2 mm, the ball milling speed is 200-800 rpm, the ball milling time is 0.5-3 h, and the vacuum degree of the ball milling jar is ≤-90 KPa.

8. The high-performance silicon-carbon negative electrode material for lithium batteries and the preparation method thereof according to claim 3, characterized in that: In step (3), the initiator is ammonium persulfate, the mass ratio of ammonium persulfate to organic monomer is 1:(2-4), and the initiator is added to the ball mill in 3-5 times.

9. The high-performance silicon-carbon negative electrode material for lithium batteries and the preparation method thereof according to claim 3, characterized in that: In the step (4), the ice bath reaction time is 1 to 5 hours, and the particle size of the polymer-coated nano-silicon composite material is 50 to 120 nm.

10. The high-performance silicon-carbon negative electrode material for lithium batteries and the preparation method thereof according to claim 3, characterized in that: In the step (5), the mass ratio of the polymer-coated nano-silicon composite material to graphite is 1:(1-3), the mass fraction of perfluorobutylsulfonamide in the polymer-coated nano-silicon composite material is 2-10%, the dispersant is one of ethanol, methanol, and acetone, the stirring time is 2-10 h, the feed rate is 5 mL / min, the spray pressure is 2 MPa, and the high-temperature sintering conditions are the same as those in step (1).

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