Preparation method of lithium battery anode material with carbon-coated nano-silicon, iron oxide and graphite as raw materials, using red mud / diabase.

Abstract

This invention relates to a method for preparing carbon-coated nano-silicon, iron oxide, and graphite anode materials for lithium batteries using red mud / diabase as raw materials. The method involves processing industrial solid waste red mud, adding petroleum coke, and reducing it at high temperature to obtain Si. Then, iron-rich diabase is added, and the mixture is ground, magnetically separated, and acid-treated to obtain Fe3O4 magnetic powder. This powder is then mixed and ground to prepare a nano-silicon / iron oxide composite material, which is then coated with a nano-carbon layer (carbon nanotubes + graphene). After high-temperature carbonization of the above product, it is mixed with artificial graphite, then coated with asphalt and carbonized again. Finally, a lithium supplement is added. The resulting composite lithium battery anode product possesses advantages such as high initial coulombic efficiency, high specific capacity, and good cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for preparing a lithium-ion battery anode material. Background Technology

[0002] The energy density of a lithium battery depends on its specific capacity and operating voltage. Specific capacity is determined by both the positive and negative electrode specific capacities, while the operating voltage is determined by the difference between the positive and negative electrode voltages. Generally, a higher specific capacity and a lower operating voltage are better for the negative electrode. Various materials can be used as negative electrodes in lithium batteries, primarily carbon-based and non-carbon-based. Carbon-based materials include graphite, hard carbon, and soft carbon, while non-carbon-based materials mainly include alloys (silicon-based and tin-based negative electrodes), lithium metal, lithium titanate, and nitrides. Among these, graphite (natural / artificial) is the mainstream negative electrode material due to its low and stable lithium intercalation potential (0.01–0.2V), high theoretical specific capacity (372 mA·h / g), low cost, environmental friendliness, and relatively superior cycle performance and safety.

[0003] Currently, mainstream manufacturers have achieved specific capacities of 360-365 mAh / g for high-end graphite anodes, approaching the theoretical upper limit of 372 mAh / g. As the demand for higher energy density in lithium-ion batteries continues to grow, the search for new anode materials with even higher specific capacities is urgently needed. Among known anode materials, silicon boasts a theoretical specific capacity of up to 4200 mAh / g, more than 10 times that of graphite. Furthermore, it provides channels for lithium-ion insertion and extraction from various directions, exhibiting excellent fast-charging performance, making it the future trend for anode materials.

[0004] In recent years, a lithium storage mechanism involving transition metal oxides has been confirmed, known as a "conversion reaction." Iron oxides are representative of this type of electrode material, with iron(III) oxide (Fe3O4) attracting particular attention due to its high theoretical specific capacity (924 mAh / g, with each Fe3O4 nanoparticle corresponding to 8 lithium ions), low cost, environmental friendliness, ease of preparation, and relatively high conductivity. It has become a promising class of anode materials and is therefore a current research hotspot.

[0005] Both silicon and iron(III) oxide have theoretically higher specific capacities than graphite, yet they are not widely used, undoubtedly due to their inherent drawbacks. Silicon's biggest drawbacks are poor conductivity and volume expansion. During charge and discharge, the lithium insertion / extraction reaction in silicon is accompanied by large volume changes (>300%), causing structural damage and mechanical pulverization, leading to rapid capacity decay and poor cycle performance. The main reason hindering the application of iron(III) oxide anode materials is their poor conductivity, resulting in low energy efficiency; the significant volume expansion during lithium-ion insertion / extraction also causes electrode material breakage and pulverization, easily leading to loss of good electrical and mechanical contact between active particles and the solid electrolyte interphase (SEI) film on the electrode surface, resulting in loss of electrode protection and rapid capacity decay.

[0006] Red mud, also known as red clay, is an industrial solid waste discharged after refining alumina from bauxite. It is an insoluble residue and can be classified into sintering red mud, Bayer process red mud, and combined process red mud, with its main components being SiO2, Al2O3, CaO, and Fe2O3. Due to the difficulty in removing the high content of chemical alkalis bound to red mud, as well as the presence of fluorine, aluminum, and other impurities, experts worldwide have conducted extensive scientific research on the comprehensive utilization of red mud, but progress has been limited. Therefore, the treatment and comprehensive utilization of red mud waste has become a major global challenge.

[0007] Diabase is a metamorphic ore rich in iron and copper, and it is dark green, greenish-black, or grayish-green. One type is called ferruginous diabase. The ferruginous diabase sample used in this invention is mainly composed of magnetite (Fe3O4), with small amounts of hematite and iron silicate.

[0008] Multi-element analysis results of diabase samples (%)

[0009] Summary of the Invention

[0010] The purpose of this invention is to propose a lithium battery anode material with a specific capacity exceeding that of graphite anodes, thereby solving the problem of the difficulty in improving the specific capacity of existing lithium batteries.

[0011] The technical solution of the present invention is as follows: a method for preparing a lithium battery anode material with carbon coating of nano-silicon, iron oxide and graphite using red mud / diabase as raw materials, comprising the following steps: step 1) obtaining silicon from red mud; step 2) obtaining iron oxide from diabase; step 3) preparing a coupled anode precursor of nano-silicon / iron oxide; step 4) carbon coating of the coupled anode precursor; step 5) secondary carbon coating of the silicon / iron oxide composite material coated with nano-carbon layer; and step 6) setting a lithium supplement electrode in the battery.

[0012] Silicon is produced by smelting and reducing a large amount of silicon dioxide in red mud in a muffle furnace using a non-metallic thermal reduction method. One or more of petroleum coke, semi-coke, and charcoal are selected as the carbon source for the reducing agent, with petroleum coke being preferred. The main considerations are fixed carbon, ash content, volatile matter, and moisture content. Generally, a high fixed carbon content and low ash content are required to reduce the total amount of reducing agent needed, reduce impurities introduced by ash, and relatively reduce the amount of slag, thus lowering the impurity content in the silicon. The selected carbon source contains 90-95% fixed carbon, 0.17-0.6% ash, and no more than 3.5%-13% volatile matter. At room temperature, silicon has one more atomic layer than carbon and easily loses electrons, resulting in stronger reducing properties. However, at a high temperature of 1700 degrees Celsius, carbon has stronger reducing properties than silicon. The chemical reaction equation is: SiO₂ + 2C → Si + 2CO↑. Silicon produced by this method has a high purity, with a mass fraction reaching 97.00%-99.00%.

[0013] Diabase was added to a planetary ball mill for coarse grinding and magnetic separation to obtain an iron concentrate with an iron grade of 65.84%. Then, it was subjected to a fine grinding and magnetic separation process. The test ore sample was finely ground to 90%-325 mesh and then subjected to a first-stage magnetic separation under a magnetic field strength of 600 Gauss. The iron concentrate produced was subjected to two magnetic separations under magnetic field strengths of 400 Gauss and 350 Gauss, respectively. The separated iron concentrate was then acid-treated. The acid was one or more of hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, citric acid, and malic acid, with hydrochloric acid being preferred. The acid treatment produced ferric oxide that met the requirements, with a Fe3O4 purity of over 97% and an iron grade of ≥71%.

[0014] Silicon and iron(III) oxide (mass ratio of silicon to iron(III) oxide 6-7:3-4) are mixed and placed in a high-speed stirred disperser with a certain amount of solvent. The solvent is selected from one or more of methanol, ethanol, propanol, isopropanol, and butanol, preferably ethanol. The solid content in the solid-solvent mixture is 30%. The mixture is stirred until homogeneous using mechanical or magnetic stirring, followed by ultrasonic oscillation to obtain a suspension. The suspension is then ground in a high-speed sand mill with a linear speed of 15-18 m / s, preferably 15 m / s. Coarse grinding is performed for 120-200 minutes, preferably 180 minutes; followed by fine grinding for 120-200 minutes, preferably 180 minutes. After grinding, the mixture is spray-dried to obtain a composite of nano-silicon and nano-iron(III) oxide, i.e., a coupled negative electrode precursor of nano-silicon / iron(III) oxide.

[0015] A nano-carbon layer is coated onto the surface of a coupled silicon / ferric oxide precursor. The carbon source is one or more selected from citric acid, malic acid, graphene, artificial graphite, natural graphite, glucose, carbon nanotubes, and pitch, preferably carbon nanotubes + graphene. The coupled silicon / ferric oxide precursor is mixed with the carbon source at a mass ratio of 1.5:1. The mixture is placed in a high-temperature tube furnace under inert gas protection, with the inert gas being one of nitrogen, argon, neon, helium, and carbon dioxide, preferably nitrogen. The temperature is increased to 600-650℃ at a rate of 1.5-2.5℃ / min and held for 4 hours, followed by natural cooling to obtain a silicon / ferric oxide composite material coated with a nano-carbon layer. The composite material not only effectively improves the conductivity of silicon / ferric oxide composite material as a negative electrode material and effectively buffers the volume expansion of silicon / ferric oxide composite material during charge-discharge cycles, but also helps silicon / ferric oxide composite material to self-assemble into uniform submicron particles. At the same time, Fe3O4 particles can effectively separate graphene sheets, prevent sheet accumulation, and increase the contact area of ​​composite material, thereby improving the electrochemical performance of composite negative electrode material.

[0016] By embedding graphite powder (either artificial or natural graphite) into a silicon / ferric oxide composite material coated with a nano-carbon layer, the high charge / discharge capacity of the silicon / ferric oxide composite material is ensured, while also giving the material itself high-rate charge / discharge capability and good high and low temperature performance. This significantly improves the cycle life of the silicon / ferric oxide composite anode material. The encapsulation forms a "core-shell" structure, which has good compatibility with the electrolyte, avoiding the delamination of the graphite layer caused by the co-intercalation of solvated lithium ions. It also buffers the volume expansion of artificial graphite particles during charge and discharge, greatly improving the cycle performance and high-current charge / discharge performance of the artificial graphite.

[0017] When silicon / iron oxide composite material coated with nano-carbon layer is mixed with artificial graphite, the interlayer spacing of the graphite layer is smaller than the interlayer spacing of the layered lithium compound. During charging and discharging, the interlayer spacing of the graphite layer changes due to the insertion and extraction of lithium ions, which can easily cause the graphite layer to peel off and pulverize. Organic solvents may also co-intercalate into the graphite layer or decompose, affecting the battery cycle performance.

[0018] To overcome the above problems, a secondary carbon coating method is used. The carbon source for secondary coating is one or more selected from citric acid, malic acid, glucose, and asphalt, with asphalt being preferred. Asphalt is a glossy brown / black carbon material obtained by processing coal or petroleum.

[0019] Asphalt is dissolved in a solvent selected from one or more of tetrahydrofuran, dichloromethane, xylene, and carbon disulfide, with tetrahydrofuran being preferred. The mixture is stirred mechanically, magnetically, or ultrasonically. After dissolving the asphalt, a mixture of silicon / ferric oxide composite material coated with a nano-carbon layer and artificial graphite is added, and the mixture is magnetically stirred for 2 hours. The mixture is then dried and carbonized: placed in a high-temperature tube furnace under inert gas protection (nitrogen, argon, neon, helium, and carbon dioxide, preferably nitrogen), the temperature is increased to 800-1050℃ at a rate of 1.5-2.5℃ / min, held for 8-12 hours, and then naturally cooled to obtain a secondary carbon-coated silicon / ferric oxide and graphite composite anode material.

[0020] By coating the graphite surface with pitch with a high softening point, the compatibility between the negative electrode material and the electrolyte can be improved. Modifying graphite materials with coating materials (such as pitch) can prevent direct contact between graphite and electrolyte, prevent the destruction of graphite structure caused by the co-intercalation of solvent molecules, and improve the cycle performance of graphite materials.

[0021] The formation of the SEI film on the surface of the secondary carbon-coated silicon / iron tetroxide and graphite composite anode material requires a large amount of lithium source. An additional lithium replenishment electrode is added to the battery, and by utilizing the phase transition properties of the phase transition layer in the lithium replenishment electrode at a predetermined temperature, lithium replenishment can be performed only when needed. The lithium material contained in the lithium replenishment electrode includes at least one of Li₂S, Li₂MoO₃, LiFeBO₃, Li₂FeSiO₄, Li₅FeO₄, Li₂NiO₂, and Li₂CuO₂.

[0022] The beneficial effects of this invention are as follows: Silicon and iron oxide (Fe3O4) act as active materials in the composite material, providing capacity, while graphene, carbon nanotubes, and artificial graphite act as carriers, buffering volume expansion. The synergistic effect between the various materials and components achieves complementary advantages. The discharge specific capacity and charge specific capacity are close to 500 mAh / g, significantly higher than the theoretical specific capacity of 372 mA•h / g for pure graphite anode materials, breaking through current limits and demonstrating promising application prospects. The resulting composite lithium-ion battery anode product simultaneously possesses advantages such as high initial coulombic efficiency, high specific capacity, and good cycle performance. Attached Figure Description

[0023] Figure 1 Example 1: Specific Capacity & Coulomb Efficiency Diagram;

[0024] Figure 2 Example 1: X1000 SEM scan of the secondary carbon-coated silicon / ferric oxide and graphite composite anode material;

[0025] Figure 3Example 1: X2000 SEM scan of a silicon / iron tetroxide / graphite composite anode material with secondary carbon coating;

[0026] Figure 4 X5000 SEM scan of the silicon / iron tetroxide and graphite composite anode material with secondary carbon coating in Example 1. Detailed Implementation

[0027] Example 1

[0028] A method for preparing carbon-coated nano-silicon, iron oxide, and graphite anode materials for lithium batteries using red mud / diabase as raw materials includes the following steps:

[0029] Step S1: Silicon is obtained by reducing silicon dioxide in red mud using carbon heating. Red mud, a solid waste from alumina tailings, is produced using a sintering method, with a SiO2 content of 23.56%. Low-sulfur, low-ash petroleum coke is chosen as the reducing agent, containing 0.18% ash, 99.13% fixed carbon, 0.36% volatile matter, and 0.33% sulfur. The red mud is smelted in a muffle furnace at 1700 degrees Celsius for 6 hours. The chemical reaction equation is: SiO2 + 2C → Si + 2CO↑. The silicon obtained by this method has a purity of 97.86%. In addition to silicon, it also contains some calcium and iron, and the impurity content meets the requirements for subsequent use.

[0030] Step S2: The diabase was crushed to 1mm and added to a planetary ball mill for grinding. After 4 hours of coarse grinding to 200 mesh, magnetic separation was performed to obtain a rough iron concentrate with an iron content of 65.84%. The grinding balls were then replaced and the concentrate was finely ground for 4 hours to 90%-325 mesh. After that, a first-stage magnetic separation was performed under a magnetic field strength of 600 Gauss. The iron concentrate produced was then subjected to two magnetic separations under magnetic field strengths of 400 Gauss and 350 Gauss, respectively. The separated iron concentrate was then treated with hydrochloric acid to produce iron(III) oxide (iron content ≥71%, Fe3O4 purity 97%).

[0031] Step S3: Preparation of the coupled anode precursor of nano-silicon / ferric oxide. Silicon and ferric oxide (mass ratio 7:3) were mixed and placed in a high-speed stirrer with a certain amount of ethanol as a solvent. The solid content of the silicon, ferric oxide, and ethanol mixture was 30%. The mixture was stirred until homogeneous and ultrasonically vibrated for 30 minutes to obtain a suspension. The suspension was then ground in a high-speed sand mill at a linear speed of 15 m / s for 180 minutes of coarse grinding followed by 180 minutes of fine grinding, for a total of 6 hours. The material was then removed and its particle size was measured using a Malvern laser particle size analyzer, showing a D50 of 0.139 µm and a D90 of 0.328 µm. After spray drying, the coupled anode precursor of nano-silicon / ferric oxide was obtained.

[0032] Table 1 Grinding index of suspension in step S3

[0033]

[0034] Step S4: Coat the surface of the coupled anode precursor of nano-silicon and nano-ferric oxide with a layer of nano-carbon. The carbon source selected for coating is carbon nanotubes + graphene. The mass ratio of the coupled anode precursor of nano-silicon / ferric oxide to the carbon source is 1.5:1. The mixture is placed in a high-temperature tube furnace and heated to 650℃ at a heating rate of 2.5℃ / min under nitrogen protection, held at this temperature for 4 hours, and then naturally cooled to obtain the silicon / ferric oxide composite material coated with the nano-carbon layer.

[0035] Step S5: Add artificial graphite to the silicon / iron oxide composite material coated with nano-carbon layer, with a wt% ratio of 30 parts composite material to 70 parts artificial graphite.

[0036] Step S6: Secondary Coating and Carbonization. Asphalt is dissolved in tetrahydrofuran solvent, and a mixture of silicon / ferric oxide composite material coated with a nano-carbon layer and artificial graphite is added, with a wt% ratio of 80% composite material to 20% asphalt. The mixture is magnetically stirred for 2 hours, followed by drying and carbonization: the mixture is placed in a high-temperature tube furnace and heated to 1050℃ at a rate of 2.5℃ / min under nitrogen protection, held at that temperature for 8 hours, and then allowed to cool naturally to obtain a secondary carbon-coated silicon / ferric oxide and graphite composite anode material.

[0037] Step S6: When assembling the battery, an additional lithium replenishment electrode is set. The lithium replenishment electrode contains one of Li2S, Li2MoO3, LiFeBO3, Li2FeSiO4, Li5FeO4, Li2NiO2 and Li2CuO2, which serves to replenish lithium.

[0038] Example 2

[0039] A method for preparing carbon-coated nano-silicon, iron oxide, and graphite anode materials for lithium batteries using red mud / diabase as raw materials includes the following steps:

[0040] Steps S1 and S2 are the same as in Example 1.

[0041] Step S3: Preparation of nano-silicon / ferric oxide coupled anode precursor. Silicon and ferric oxide (mass ratio 6.5:3.5) were mixed and placed in a high-speed stirrer with a certain amount of deionized water as a solvent. The solid content in the silicon, ferric oxide, and deionized water mixture was controlled at 30%. After grinding for 4 hours, the mixture was removed, and the particle size distribution was measured using a Malvern laser particle size analyzer. The particle size range was D50 of 0.532 µm and D90 of 1.281 µm. After spray drying, the nano-silicon / ferric oxide coupled anode precursor was obtained.

[0042] Step S4: Coat the surface of the coupled silicon and iron oxide nano-coated anode precursor with a layer of carbon nanotubes. The carbon source selected for coating is carbon nanotubes + graphene, and the mass ratio of the coupled silicon / iron oxide nano-coated anode precursor to the carbon source is 1.8:1. Place the mixture in a high-temperature tube furnace, and under nitrogen protection, heat it to 600℃ at a heating rate of 2.5℃ / min, hold it at that temperature for 4 hours, and then allow it to cool naturally to obtain the silicon / iron oxide composite material coated with the carbon nanotube layer.

[0043] Step S5: Add artificial graphite to the silicon / iron oxide composite material coated with nano-carbon layer, with a wt% ratio of 48 parts composite material to 52 parts artificial graphite.

[0044] Step S6: Secondary Coating and Carbonization. Asphalt is dissolved in tetrahydrofuran solvent, and a composite material consisting of a silicon / ferric oxide composite coated with a nano-carbon layer and artificial graphite is added, with a wt% ratio of 85% composite material to 15% asphalt. The mixture is magnetically stirred for 2 hours, followed by drying and carbonization: the mixture is placed in a high-temperature tube furnace and heated to 950℃ at a rate of 2.5℃ / min under nitrogen protection, held at that temperature for 8 hours, and then allowed to cool naturally to obtain a secondary carbon-coated silicon / ferric oxide and graphite composite anode material.

[0045] Step S6 is the same as in Example 1.

[0046] Example 3

[0047] A method for preparing carbon-coated nano-silicon, iron oxide, and graphite anode materials for lithium batteries using red mud / diabase as raw materials includes the following steps:

[0048] Steps S1 and S2 are the same as in Example 1.

[0049] Step S3: Preparation of the coupled anode precursor of nano-silicon / ferric oxide. Silicon and ferric oxide (mass ratio 6:4) were mixed and placed in a high-speed stirred disperser with a certain amount of deionized water as a solvent. The solid content of the silicon, ferric oxide, and deionized water mixture was 30%. After grinding for 2 hours, the mixture was removed, and the particle size range (D50) was measured to be 0.854 µm and D90 to be 1.688 µm using a Malvern laser particle size analyzer. After spray drying, the coupled anode precursor of nano-silicon / ferric oxide was obtained.

[0050] Step S4: Coat the surface of the coupled anode precursor of nano-silicon and nano-ferric oxide with a layer of nano-carbon. The carbon source selected for coating is carbon nanotubes + graphene, and the mass ratio of the coupled anode precursor of nano-silicon / ferric oxide to the carbon source is 2:1. Place the mixture in a high-temperature tube furnace, and under argon protection, heat it to 650℃ at a heating rate of 2.5℃ / min, hold it at that temperature for 4 hours, and then allow it to cool naturally to obtain the silicon / ferric oxide composite material coated with the nano-carbon layer.

[0051] Step S5: Add artificial graphite to the silicon / iron oxide composite material coated with nano-carbon layer, with a wt% ratio of 10 parts composite material to 90 parts artificial graphite.

[0052] Step S6: Secondary Coating and Carbonization. Asphalt is dissolved in tetrahydrofuran solvent, and a composite material consisting of a silicon / ferric oxide composite material coated with a nano-carbon layer and artificial graphite is added, with a wt% ratio of composite material 90:asphalt 10. The mixture is magnetically stirred for 2 hours, followed by drying and carbonization: the mixture is placed in a high-temperature tube furnace and heated to 900℃ at a rate of 2.5℃ / min under nitrogen protection, held at that temperature for 8 hours, and then naturally cooled to obtain a secondary carbon-coated silicon / ferric oxide and graphite composite anode material.

[0053] Step S6 is the same as in Example 1.

[0054] Table 2. Tap density and specific surface area of ​​Examples 1, 2, and 3

[0055] Example <![CDATA[Tap density (g / cm 3 ).]]> <![CDATA[Specific surface area (m 2 / g)]]> 1 1.202 33.09 2 1.193 29.87　 3 1.071　 20.66

[0056] Table 3. Cycle count, discharge specific capacity, charge specific capacity, and coulombic efficiency data for Example 1

[0057]

[0058] From Table 3 and Figure 1 As can be seen, the lithium battery anode material prepared by Example 1, consisting of carbon-coated nano-silicon, iron oxide, and graphite, has a higher specific capacity than traditional graphite anodes by 340-360 mAh / g. It exhibits excellent cycle performance and rate capability, with an initial discharge specific capacity of 536.6 mAh / g at 0.05-3.0V and 200 mA / g current density. After 20 discharge cycles, the specific capacity remains at 472.2 mAh / g, demonstrating good electrochemical performance. The initial coulombic efficiency is 64.4%. Table 2 also shows excellent tap density and specific surface area measurements.

Claims

1. A method for preparing lithium battery anode materials using red mud / diabase as raw materials, comprising carbon-coated nano-silicon, iron oxide, and graphite, characterized by: Step 1) Silicon extraction from red mud: Red mud is mixed with a reducing agent and carbon source and placed in a reactor. At a high temperature of 1700 degrees Celsius, silicon dioxide is reduced to silicon by carbon, with a silicon mass fraction of 97.00%-99.00%. Step 2) Obtaining Fe3O4 from diabase: The diabase is coarsely ground and magnetically separated to obtain a rough iron concentrate. The rough iron concentrate is then finely ground and magnetically separated. After fine grinding to a particle size of -325 mesh and a content of 90%, it is subjected to a first-stage magnetic separation under a magnetic field strength of 600 Gauss. The produced iron concentrate is then subjected to two magnetic separations under magnetic field strengths of 400 Gauss and 350 Gauss, respectively. The magnetically separated iron concentrate is then acid-treated to obtain Fe3O4 with a purity of over 97% and an iron grade of ≥71%. Step 3) Preparation of nano-silicon / ferric oxide coupled anode precursor: The silicon obtained in step 1) and the ferric oxide obtained in step 2) are mixed at a mass ratio of 6-7:3-4, placed in a high-speed stirrer, and then a solvent is added. The solid content in the solid-solvent mixture is 30%. The mixture is stirred until uniform, and then subjected to ultrasonic oscillation to obtain a suspension. The suspension is then placed in a high-speed sand mill for grinding. The linear speed of the sand mill is 15m-18m / s. The mixture is first coarsely ground for 120-200 minutes, and then finely ground for 120-200 minutes. After fine grinding, it is spray-dried to obtain a composite of nano-silicon and nano-ferric oxide, namely the nano-silicon / ferric oxide coupled anode precursor. Step 4) Carbon Coating of Coupled Anode Precursor: The coupled anode precursor from Step 3) is mixed with a carbon source at a mass ratio of 1.5:

1. The mixture is placed in a high-temperature tube furnace and heated to 600-650℃ at a rate of 1.5-2.5℃ / min under inert gas protection. The temperature is held for 4 hours and then allowed to cool naturally to obtain a silicon / iron oxide composite material coated with a nano-carbon layer. The carbon source used in this step is one or more of citric acid, malic acid, graphene, glucose, carbon nanotubes, and pitch. Step 5) Secondary carbon coating of silicon / ferric oxide composite material with nano-carbon layer: The product obtained in step 4) is mixed with artificial graphite to obtain mixture A. The mass ratio of mixture A to artificial graphite is 3:

7. A carbon source is selected and dispersed in a solvent, and ultrasonically vibrated to obtain dispersion B. Mixture A is added to dispersion B at a mass ratio of mixture A to dispersion B of 8:

2. The mixture is magnetically stirred for 2 hours, and then transferred to a high-temperature tube furnace. Under inert gas protection, the temperature is raised to 800-1050℃ at a heating rate of 1.5-2.5℃ / min and held for 8-12 hours. Then it is naturally cooled to obtain a secondary carbon-coated silicon / ferric oxide and graphite composite anode material. The carbon source used in this step is one or more of citric acid, malic acid, glucose, and asphalt. Step 6) When using the secondary carbon-coated silicon / iron tetroxide and graphite composite negative electrode material from step 5) to make a battery, a lithium-filling electrode is set in the battery.

2. The method for preparing lithium battery anode material using red mud / diabase as raw material, comprising carbon-coated nano-silicon, iron oxide, and graphite, as described in claim 1, is characterized in that: Step 1) The carbon source of the reducing agent used is one or more of petroleum coke, semi-coke, and charcoal.

3. The method for preparing lithium battery anode material using red mud / diabase as raw material, comprising carbon-coated nano-silicon, iron oxide, and graphite, as described in claim 1, is characterized in that: Step 2) The acid used for acid treatment is one or more of the following: hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, citric acid, and malic acid.

4. The method for preparing lithium battery anode material using red mud / diabase as raw material, comprising carbon-coated nano-silicon, iron oxide, and graphite, as described in claim 1, is characterized in that: Step 3) The solvent used is one or more of methanol, ethanol, propanol, isopropanol, and butanol.

5. The method for preparing lithium battery anode material using red mud / diabase as raw material, comprising carbon-coated nano-silicon, iron oxide, and graphite, as described in claim 1, is characterized in that: Step 5) The inert gas is one of nitrogen, argon, neon, helium, or carbon dioxide.

6. The method for preparing lithium battery anode material using red mud / diabase as raw material, comprising carbon-coated nano-silicon, iron oxide, and graphite, as described in claim 1, is characterized in that: Step 5) uses one of the following solvents: tetrahydrofuran, dichloromethane, xylene, and carbon disulfide.

7. The method for preparing lithium battery anode material using red mud / diabase as raw material, comprising carbon-coated nano-silicon, iron oxide, and graphite, as described in claim 1, is characterized in that: Step 5) The inert gas is one of nitrogen, argon, neon, helium, or carbon dioxide.

8. The method for preparing lithium battery anode material using red mud / diabase as raw material, comprising carbon-coated nano-silicon, iron oxide, and graphite, as described in claim 1, is characterized in that: Step 6) The lithium material contained in the lithium electrode includes at least one of Li2S, Li2MoO3, LiFeBO3, Li2FeSiO4, Li5FeO4, Li2NiO2 and Li2CuO2.

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