Hard carbon negative electrode material and preparation method and application thereof
By using fluorine-doped porous hard carbon nanospheres doped with manganese acetate and pre-lithiated with a lithium source, the problem of low initial coulombic efficiency of hard carbon anode materials was solved, achieving higher electrochemical performance and stability.
Patent Information
- Application Number
- CN202511157051.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-19
- Publication Date
- 2025-11-28
AI Technical Summary
The hard carbon anode material has lattice defects during the preparation process, which leads to a low initial coulombic efficiency.
Fluorine-doped porous hard carbon nanospheres doped with manganese acetate were used. MnF2 and MnO crystals were inserted into the porous structure in situ, and combined with lithium source pre-lithiation treatment to construct a highly stable SEI film and improve the first coulombic efficiency of the material.
It significantly improves the first coulombic efficiency of hard carbon anode materials, compensates for the capacity loss caused by the decrease in specific surface area, and enhances the stability of the materials.
Abstract
Description
Technical Field
[0001] This application relates to the technical field of hard carbon anode materials, and more specifically, to a hard carbon anode material, its preparation method, and its application. Background Technology
[0002] Hard carbon anode materials are carbon materials that are difficult to graphitize. They are actually pyrolytic carbon obtained through the pyrolysis of polymers, petrochemical products, or biomass. Hard carbon materials have an interlaced layered structure with large interlayer spacing, allowing lithium ions to insert and extract from different angles, thereby increasing the diffusion rate of lithium ions and enabling rapid charge and discharge. At the same time, hard carbon materials have a stable structure and minimal volume expansion during charge and discharge, resulting in excellent long-cycle performance.
[0003] However, the structure of hard carbon materials also has certain defects. Specifically, during the preparation of hard carbon materials, a large number of lattice defects are generated in the internal structure of hard carbon materials. As a result, during the lithium intercalation process, lithium ions are not only intercalated between carbon atom layers, but also intercalated into lattice defects, which leads to a low initial coulombic efficiency of hard carbon anode materials. Summary of the Invention
[0004] To improve the shortcomings of conventional hard carbon anode materials with low initial coulombic efficiency, this application provides a hard carbon anode material, its preparation method, and its application.
[0005] In a first aspect, this application provides a hard carbon anode material, which adopts the following technical solution: A hard carbon anode material is obtained by carbonizing fluorine-doped porous hard carbon nanospheres adsorbed by acetic acid; the fluorine-doped porous hard carbon nanospheres are obtained by carbonizing a precursor constructed from double-bonded siloxane, fluorinated acrylic acid monomer and methacryloxypropyl heptaisobutyl POSS.
[0006] Reducing the specific surface area of hard carbon anode materials is one of the effective ways to improve their first coulombic efficiency. In this application, by utilizing the high fluorine content and porous structure of fluorine-doped porous hard carbon nanospheres and the adsorption effect of manganese acetate, MnF2 and MnO crystals are introduced into the fluorine-doped porous hard carbon nanospheres in situ to reduce the specific surface area and thus improve the first coulombic efficiency of the hard carbon anode material. At the same time, MnF2 and MnO crystals can also provide reverse electrochemical reactions to effectively compensate for the capacity loss caused by the decrease in specific surface area.
[0007] Preferably, the preparation method of the fluorine-doped porous hard carbon nanospheres includes the following steps: Precursor construction: Under a nitrogen atmosphere, double-bonded siloxane, fluorinated acrylic acid monomer and methacryloxypropyl heptaisobutyl POSS were added to an aqueous emulsifier solution. The temperature was then raised to 60-80℃ and a free radical initiator was added. The reaction was maintained at this temperature for 12-16 hours and then cooled to room temperature. The mixture was then washed with water and dried to obtain the precursor. Primary carbonization: The precursor is carbonized in a nitrogen atmosphere at a temperature of 600-650℃ for 1-3 hours to obtain the primary carbonization product. Secondary carbonization: The primary carbonization product is immersed in hydrofluoric acid solution for 10-20 min, then washed until neutral, and then subjected to secondary carbonization again under nitrogen atmosphere. The secondary carbonization temperature is 1100-1300℃ and the secondary carbonization time is 1-3 h to obtain fluorine-doped porous hard carbon nanospheres.
[0008] The introduction of porous structures can significantly improve the electrochemical performance of hard carbon anode materials. The channels can store a large amount of electrolyte, forming an ion buffer. The porous structure can shorten the distance of lithium ion diffusion and electron conduction, thereby increasing the diffusion rate. Fluorine doping can enhance the lithium ion transport capacity.
[0009] Preferably, in the secondary carbonization, the primary carbonization product, washed to neutral, is mixed with a lithium source, and then secondary carbonization is performed.
[0010] In the application, the primary carbonization products are pre-lithiated using a lithium source, which allows elemental lithium to be introduced into the fluorine-doped porous hard carbon nanospheres in advance. This compensates for the irreversible lithium-ion loss caused by lattice defects in the hard carbon anode material and the lithium-ion consumed in the SEI, thus indirectly improving the first coulombic efficiency of the hard carbon anode material. In addition, the lithium source can also form a highly stable SEI film rich in LiF in situ with fluorine ions, thereby further improving the stability and coulombic efficiency of the hard carbon anode material.
[0011] Preferably, the lithium source is one of lithium powder, lithium nitride, lithium fluoride, lithium hydride, lithium acetate, and lithium stearate.
[0012] Preferably, the lithium source is lithium powder, and the mass ratio of the primary carbonization product to the lithium powder is (18-20):1.
[0013] Compared to other lithium source components, lithium powder has fewer impurity elements, and when the primary carbonization product and lithium powder are in the above mass ratio, the pre-lithiation effect will be better, thus enabling the hard carbon anode material to have a better first coulombic efficiency.
[0014] Preferably, the double-bonded siloxane is one of methacryloyloxypropyltrimethoxysilane and methacryloyloxypropyltriethoxysilane.
[0015] Preferably, the fluorinated acrylate monomer is one of fluorinated acrylic acid, fluorinated methacrylic acid, fluorinated methyl acrylate, fluorinated methyl methacrylate, fluorinated ethyl acrylate, fluorinated ethyl methacrylate, and fluorinated n-butyl acrylate.
[0016] Preferably, the mass ratio of the double-bonded siloxane, the fluorinated acrylate monomer, and the methacryloxypropyl heptaisobutyl POSS is (10-14):1:(0.2-0.4).
[0017] When the double-bonded siloxane, fluorinated acrylate monomer, and methacryloxypropylheptaisobutyl POSS are used in the above mass ratio, the prepared fluorine-doped porous hard carbon nanospheres will have more abundant fluorine doping and the pores will be more uniform and stable.
[0018] Secondly, this application provides a method for preparing a hard carbon anode material, employing the following technical solution: A method for preparing a hard carbon anode material includes the following steps: S1. Dissolve acetic acid in ethanol solvent, then add fluorine-doped porous hard carbon nanospheres and mix and stir for 1-3 hours. Then heat until the ethanol evaporates and finally vacuum dry to obtain the precursor of the negative electrode material. S2. Under a nitrogen atmosphere, the precursor of the anode material is first heated to 300-400℃ at a heating rate of 5℃ / min and held at that temperature for 2-3 hours. Then, it is heated to 500-600℃ at a heating rate of 10℃ / min and held at that temperature for 4-6 hours. Finally, it is cooled to room temperature to obtain the hard carbon anode material.
[0019] Thirdly, this application provides an application of a hard carbon anode material, employing the following technical solution: An application of a hard carbon anode material, said hard carbon anode material being used to prepare battery anode sheets.
[0020] In summary, this application has the following beneficial effects: 1. Reducing the specific surface area of hard carbon anode materials is one of the effective ways to improve their first coulombic efficiency. In this application, by utilizing the high fluorine content and porous structure of fluorine-doped porous hard carbon nanospheres and the adsorption effect of manganese acetate, MnF2 and MnO crystals are introduced into the fluorine-doped porous hard carbon nanospheres in situ to reduce the specific surface area and thus improve the first coulombic efficiency of the hard carbon anode material. At the same time, MnF2 and MnO crystals can also provide reverse electrochemical reactions to effectively compensate for the capacity loss caused by the decrease in specific surface area.
[0021] 2. In this application, the primary carbonization product is pre-lithiated by a lithium source, which allows elemental lithium to be introduced into the fluorine-doped porous hard carbon nanospheres in advance. This compensates for the irreversible lithium ion loss caused by lattice defects in the hard carbon anode material and the lithium ions consumed in the SEI, thereby indirectly improving the first coulombic efficiency of the hard carbon anode material. In addition, the lithium source can also form a highly stable SEI film rich in LiF in situ with fluorine ions, thereby further improving the stability and coulombic efficiency of the hard carbon anode material. Detailed Implementation
[0022] The present application will be further described in detail below with reference to Examples 1-7 and Comparative Example 1.
[0023] raw material Manganese acetate CAS: 15243-27-3; Lithium powder CAS: 7439-93-2; Methacryloxypropyltrimethoxysilane CAS: 2530-85-0; Trifluoroethyl methacrylate CAS: 352-87-4; Methacryloxypropylheptaisobutyl POSS (Hubei Maidehao); Ethanol CAS: 64-17-5.
[0024] Example 1 A hard carbon anode material, the preparation method of which includes the following steps: S1. Dissolve 1.5g of manganese acetic acid in 30ml of ethanol solvent, then add 1g of fluorine-doped porous hard carbon nanospheres and mix and stir for 2h. Then heat until the ethanol evaporates and finally vacuum dry to obtain the precursor of the negative electrode material. S2. Under a nitrogen atmosphere, the precursor of the anode material is first heated to 350°C at a heating rate of 5°C / min and held at that temperature for 3 hours. Then, it is heated to 600°C at a heating rate of 10°C / min and held at that temperature for 5 hours. Finally, it is cooled to room temperature to obtain the hard carbon anode material.
[0025] The preparation method of fluorine-doped porous hard carbon nanospheres includes the following steps: Precursor construction: Under a nitrogen atmosphere, 12g of methacryloxypropyltrimethoxysilane, 1g of trifluoroethyl methacrylate and 0.3g of methacryloxypropylheptaisobutyl POSS were added to 250ml of 4wt% SDS emulsifier aqueous solution. Then, the temperature was raised to 70℃ and 0.15g of free radical initiator AIBN was added. The reaction was maintained at this temperature for 12h and then cooled to room temperature. After washing with water and drying, the precursor was obtained. Primary carbonization: The precursor is carbonized in a nitrogen atmosphere at a temperature of 600℃ for 2 hours to obtain the primary carbonization product. Secondary carbonization: The primary carbonization product was immersed in hydrofluoric acid solution for 15 min, then washed until neutral, and then subjected to secondary carbonization again under nitrogen atmosphere. The secondary carbonization temperature was 1200℃ and the secondary carbonization time was 2 h to obtain fluorine-doped porous hard carbon nanospheres.
[0026] Example 2 The difference from Example 1 is that the amount of each raw material added in the precursor construction is different, as detailed below.
[0027] The preparation method of fluorine-doped porous hard carbon nanospheres includes the following steps: Precursor construction: Under a nitrogen atmosphere, 10 g of methacryloyloxypropyltrimethoxysilane, 1 g of trifluoroethyl methacrylate and 0.4 g of methacryloyloxypropylheptaisobutyl POSS were added to 300 ml of 4 wt% SDS emulsifier aqueous solution. The temperature was then raised to 70 °C and 0.10 g of free radical initiator AIBN was added. The reaction was maintained at this temperature for 12 h and then cooled to room temperature. The product was then washed with water and dried to obtain the precursor.
[0028] Primary carbonization: The precursor is carbonized in a nitrogen atmosphere at a temperature of 600℃ for 2 hours to obtain the primary carbonization product. Secondary carbonization: The primary carbonization product was immersed in hydrofluoric acid solution for 15 min, then washed until neutral, and then subjected to secondary carbonization again under nitrogen atmosphere. The secondary carbonization temperature was 1200℃ and the secondary carbonization time was 2 h to obtain fluorine-doped porous hard carbon nanospheres.
[0029] Example 3 The difference from Example 1 is that the amount of each raw material added in the precursor construction is different, as detailed below.
[0030] The preparation method of fluorine-doped porous hard carbon nanospheres includes the following steps: Precursor construction: Under a nitrogen atmosphere, 14 g of methacryloyloxypropyltrimethoxysilane, 1 g of trifluoroethyl methacrylate and 0.2 g of methacryloyloxypropylheptaisobutyl POSS were added to 200 ml of 4 wt% SDS emulsifier aqueous solution. The temperature was then raised to 70 °C and 0.18 g of free radical initiator AIBN was added. The reaction was maintained at this temperature for 12 h and then cooled to room temperature. The product was then washed with water and dried to obtain the precursor.
[0031] Primary carbonization: The precursor is carbonized in a nitrogen atmosphere at a temperature of 600℃ for 2 hours to obtain the primary carbonization product. Secondary carbonization: The primary carbonization product was immersed in hydrofluoric acid solution for 15 min, then washed until neutral, and then subjected to secondary carbonization again under nitrogen atmosphere. The secondary carbonization temperature was 1200℃ and the secondary carbonization time was 2 h to obtain fluorine-doped porous hard carbon nanospheres.
[0032] Example 4 The difference from Example 1 is that in the secondary carbonization, the primary carbonization product, which has been washed to neutral, is mixed with a lithium source, and then secondary carbonization is carried out. The specific steps are as follows.
[0033] The preparation method of fluorine-doped porous hard carbon nanospheres includes the following steps: Precursor construction: Under a nitrogen atmosphere, 10 g of methacryloyloxypropyltrimethoxysilane, 1 g of trifluoroethyl methacrylate and 0.4 g of methacryloyloxypropylheptaisobutyl POSS were added to 300 ml of 4 wt% SDS emulsifier aqueous solution. The temperature was then raised to 70 °C and 0.10 g of free radical initiator AIBN was added. The reaction was maintained at this temperature for 12 h and then cooled to room temperature. The product was then washed with water and dried to obtain the precursor.
[0034] Primary carbonization: The precursor is carbonized in a nitrogen atmosphere at a temperature of 600℃ for 2 hours to obtain the primary carbonization product. Secondary carbonization: The primary carbonization product was immersed in hydrofluoric acid solution for 15 min, then washed until neutral and mixed with lithium powder at a mass ratio of 19:1. The mixture of primary carbonization product and lithium powder was then subjected to secondary carbonization under a nitrogen atmosphere at a temperature of 1200℃ for 2 h to obtain fluorine-doped porous hard carbon nanospheres.
[0035] Example 5 The difference from Example 4 is that lithium powder is replaced with lithium stearate, as detailed below.
[0036] The preparation method of fluorine-doped porous hard carbon nanospheres includes the following steps: Precursor construction: Under a nitrogen atmosphere, 10 g of methacryloyloxypropyltrimethoxysilane, 1 g of trifluoroethyl methacrylate and 0.4 g of methacryloyloxypropylheptaisobutyl POSS were added to 300 ml of 4 wt% SDS emulsifier aqueous solution. The temperature was then raised to 70 °C and 0.10 g of free radical initiator AIBN was added. The reaction was maintained at this temperature for 12 h and then cooled to room temperature. The product was then washed with water and dried to obtain the precursor.
[0037] Primary carbonization: The precursor is carbonized in a nitrogen atmosphere at a temperature of 600℃ for 2 hours to obtain the primary carbonization product. Secondary carbonization: The primary carbonization product was immersed in hydrofluoric acid solution for 15 min, then washed until neutral and mixed with lithium stearate at a mass ratio of 19:1. The mixture of primary carbonization product and lithium powder was then subjected to secondary carbonization under a nitrogen atmosphere at a temperature of 1200℃ for 2 h to obtain fluorine-doped porous hard carbon nanospheres.
[0038] Example 6 The difference from Example 4 is that the mass ratio of the primary carbonization product to lithium powder is different, as detailed below.
[0039] Precursor construction: Under a nitrogen atmosphere, 10 g of methacryloyloxypropyltrimethoxysilane, 1 g of trifluoroethyl methacrylate and 0.4 g of methacryloyloxypropylheptaisobutyl POSS were added to 300 ml of 4 wt% SDS emulsifier aqueous solution. The temperature was then raised to 70 °C and 0.10 g of free radical initiator AIBN was added. The reaction was maintained at this temperature for 12 h and then cooled to room temperature. The product was then washed with water and dried to obtain the precursor.
[0040] Primary carbonization: The precursor is carbonized in a nitrogen atmosphere at a temperature of 600℃ for 2 hours to obtain the primary carbonization product. Secondary carbonization: The primary carbonization product was immersed in hydrofluoric acid solution for 15 min, then washed until neutral and mixed with lithium powder at a mass ratio of 18:1. The mixture of primary carbonization product and lithium powder was then subjected to secondary carbonization under a nitrogen atmosphere at a temperature of 1200℃ for 2 h to obtain fluorine-doped porous hard carbon nanospheres.
[0041] Example 7 The difference from Example 4 is that the mass ratio of the primary carbonization product to lithium powder is different, as detailed below.
[0042] Precursor construction: Under a nitrogen atmosphere, 10 g of methacryloyloxypropyltrimethoxysilane, 1 g of trifluoroethyl methacrylate and 0.4 g of methacryloyloxypropylheptaisobutyl POSS were added to 300 ml of 4 wt% SDS emulsifier aqueous solution. The temperature was then raised to 70 °C and 0.10 g of free radical initiator AIBN was added. The reaction was maintained at this temperature for 12 h and then cooled to room temperature. The product was then washed with water and dried to obtain the precursor.
[0043] Primary carbonization: The precursor is carbonized in a nitrogen atmosphere at a temperature of 600℃ for 2 hours to obtain the primary carbonization product. Secondary carbonization: The primary carbonization product was immersed in hydrofluoric acid solution for 15 min, then washed until neutral and mixed with lithium powder at a mass ratio of 20:1. The mixture of primary carbonization product and lithium powder was then subjected to secondary carbonization under a nitrogen atmosphere at a temperature of 1200℃ for 2 h to obtain fluorine-doped porous hard carbon nanospheres.
[0044] Comparative Example 1 A hard carbon anode material, composed solely of fluorine-doped porous hard carbon nanospheres, is prepared by the following steps: Includes the following steps: Precursor construction: Under a nitrogen atmosphere, 12g of methacryloxypropyltrimethoxysilane, 1g of trifluoroethyl methacrylate and 0.3g of methacryloxypropylheptaisobutyl POSS were added to 250ml of 4wt% SDS emulsifier aqueous solution. Then, the temperature was raised to 70℃ and 0.15g of free radical initiator AIBN was added. The reaction was maintained at this temperature for 12h and then cooled to room temperature. After washing with water and drying, the precursor was obtained. Primary carbonization: The precursor is carbonized in a nitrogen atmosphere at a temperature of 600℃ for 2 hours to obtain the primary carbonization product. Secondary carbonization: The primary carbonization product was immersed in hydrofluoric acid solution for 15 min, then washed until neutral, and then subjected to secondary carbonization again under nitrogen atmosphere at a temperature of 1200℃ for 2 h. After that, the temperature was increased to 350℃ at a rate of 5℃ / min and held for 3 h. Then, the temperature was increased to 600℃ at a rate of 10℃ / min and held for 5 h. Finally, the temperature was cooled to room temperature to obtain hard carbon anode material.
[0045] Performance testing The hard carbon anode materials of Examples 1-7 and Comparative Example 1 were used as samples for the first coulombic efficiency test.
[0046] The coin cell preparation method is as follows: The sample, binder (PVDF) and conductive carbon black (Super P) are mixed evenly in a mass ratio of 8:1:1, and NMP is added to adjust the solid content of the slurry to 50%. Then, the prepared slurry is coated onto copper foil to form electrodes. The coated electrodes are dried in a vacuum oven at 120 °C for 12 h. Then, a dual-electrode coin cell is formed with the counter electrode lithium metal sheet. The electrolyte is a 1 mol / L LiPF6 / EC / DEC (v / v=1:1:1) solution. The battery assembly is completed in a glove box filled with high-purity argon.
[0047] The initial coulombic efficiency of the prepared coin cell was tested under the following conditions: first, 0.1C discharge with a cutoff voltage of 1mV, followed by 0.1C charging with a cutoff voltage of 1.5V. The test data are shown in Table 1.
[0048] Table 1. Initial Coulomb Efficiency Test Results of Examples 1-7 and Comparative Example 1 First Coulomb efficiency / % First Coulomb efficiency / % Example 1 91.2 Example 5 91.4 Example 2 90.9 Example 6 91.6 Example 3 90.7 Example 7 91.7 Example 4 91.9 Comparative Example 1 72.0 Referring to Examples 1-3 and Comparative Example 1 and in conjunction with Table 1, it can be seen that the initial coulombic efficiency of Examples 1-3 is significantly improved compared to Comparative Example 1. This indicates that the adsorption and blending carbonization of manganese acetate and fluorine-doped porous hard carbon nanospheres can effectively improve the initial coulombic efficiency of hard carbon anode materials.
[0049] The reason for this is that reducing the specific surface area of hard carbon anode materials is one of the effective ways to improve their first coulombic efficiency. Examples 1-3 utilize the high fluorine content and porous structure of fluorine-doped porous hard carbon nanospheres and the adsorption effect of manganese acetate to introduce MnF2 and MnO crystals into the fluorine-doped porous hard carbon nanospheres in situ, thereby reducing the specific surface area and improving the first coulombic efficiency of the hard carbon anode materials. At the same time, MnF2 and MnO crystals can also provide reverse electrochemical reactions, effectively compensating for the capacity loss caused by the decrease in specific surface area.
[0050] Compared to Examples 2 and 3, Example 1 has a higher first coulombic efficiency, which indicates that when the raw materials are added in the same proportion as in Example 1 during the precursor construction, the prepared hard carbon anode material will have a better first coulombic efficiency.
[0051] The reason for this may be that when the double-bonded siloxane, fluorinated acrylate monomer, and methacryloxypropyl heptaisobutyl POSS are used in the above mass ratio, the prepared fluorine-doped porous hard carbon nanospheres will have more abundant fluorine doping and the pores will be more uniform and stable.
[0052] Referring to Examples 1 and 4 and in conjunction with Table 1, it can be seen that the first coulombic efficiency of Example 4 is significantly improved compared to Example 1. This indicates that the pre-embedding of the lithium source can significantly improve the first coulombic efficiency of the hard carbon anode material.
[0053] The reason for this is that by pre-lithiating the primary carbonization products with a lithium source, elemental lithium is introduced into the fluorine-doped porous hard carbon nanospheres in advance. This compensates for the irreversible lithium-ion loss caused by lattice defects in the hard carbon anode material and the lithium-ion consumed in the SEI, thus indirectly improving the first coulombic efficiency of the hard carbon anode material. In addition, the lithium source can also form a highly stable SEI film rich in LiF in situ with fluorine ions, thereby further improving the stability and coulombic efficiency of the hard carbon anode material.
[0054] Referring to Examples 4-5 and Table 1, it can be seen that the initial coulombic efficiency of Example 5 is slightly lower than that of Example 4. This indicates that the choice of lithium source also affects the initial coulombic efficiency of hard carbon anode material. Specifically, compared with lithium stearate, using lithium powder as lithium source can make the hard carbon anode material have a better initial coulombic efficiency.
[0055] The reason for this may be that lithium powder contains fewer impurity elements compared to other lithium source components, which indirectly improves the first coulombic efficiency of hard carbon anode materials.
[0056] Referring to Examples 4, 6, and 7 and in conjunction with Table 1, it can be seen that the initial coulombic efficiency of Examples 6-7 is slightly lower than that of Example 1. This indicates that when the mass ratio of primary carbonization product to lithium powder is used as in Example 4, pre-lithiation will have a better effect, thereby promoting the hard carbon anode material to have a better initial coulombic efficiency.
[0057] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.
Claims
1. A hard carbon anode material, characterized in that: The fluorine-doped porous hard carbon nanospheres were obtained by carbonization of fluorine-doped porous hard carbon nanospheres adsorbed by acetic acid; the fluorine-doped porous hard carbon nanospheres were obtained by carbonization of a precursor constructed from double-bonded siloxane, fluorinated acrylic acid monomer and methacryloxypropyl heptaisobutyl POSS.
2. The hard carbon anode material according to claim 1, characterized in that, The preparation method of the fluorine-doped porous hard carbon nanospheres includes the following steps: Precursor construction: Under a nitrogen atmosphere, double-bonded siloxane, fluorinated acrylic acid monomer and methacryloxypropyl heptaisobutyl POSS were added to an aqueous emulsifier solution. The temperature was then raised to 60-80℃ and a free radical initiator was added. The reaction was maintained at this temperature for 12-16 hours and then cooled to room temperature. The mixture was then washed with water and dried to obtain the precursor. Primary carbonization: The precursor is carbonized in a nitrogen atmosphere at a temperature of 600-650℃ for 1-3 hours to obtain the primary carbonization product. Secondary carbonization: The primary carbonization product is immersed in hydrofluoric acid solution for 10-20 min, then washed until neutral, and then subjected to secondary carbonization again under nitrogen atmosphere. The secondary carbonization temperature is 1100-1300℃ and the secondary carbonization time is 1-3 h to obtain fluorine-doped porous hard carbon nanospheres.
3. The hard carbon anode material according to claim 2, characterized in that: In the secondary carbonization process, the primary carbonization product, washed to neutral, is mixed with a lithium source, and then subjected to secondary carbonization.
4. The hard carbon anode material according to claim 3, characterized in that: The lithium source is one of lithium powder, lithium nitride, lithium fluoride, lithium hydride, lithium acetate, and lithium stearate.
5. The hard carbon anode material according to claim 4, characterized in that: The lithium source is lithium powder, and the mass ratio of the primary carbonization product to the lithium powder is (18-20):
1.
6. The hard carbon anode material according to claim 1, characterized in that: The double-bonded siloxane is one of methacryloyloxypropyltrimethoxysilane and methacryloyloxypropyltriethoxysilane.
7. The hard carbon anode material according to claim 1, characterized in that: The fluorinated acrylate monomer is one of fluorinated acrylic acid, fluorinated methacrylic acid, fluorinated methyl acrylate, fluorinated methyl methacrylate, fluorinated ethyl acrylate, fluorinated ethyl methacrylate, and fluorinated n-butyl acrylate.
8. The hard carbon anode material according to claim 1, characterized in that: The mass ratio of the double-bonded siloxane, the fluorinated acrylate monomer, and the methacryloyloxypropyl heptaisobutyl POSS is (10-14):1:(0.2-0.4).
9. A method for preparing the hard carbon anode material according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Dissolve acetic acid in ethanol solvent, then add fluorine-doped porous hard carbon nanospheres and mix and stir for 1-3 hours. Then heat until the ethanol evaporates and finally vacuum dry to obtain the precursor of the negative electrode material. S2. Under a nitrogen atmosphere, the precursor of the anode material is first heated to 300-400℃ at a heating rate of 5℃ / min and held at that temperature for 2-3 hours. Then, it is heated to 500-600℃ at a heating rate of 10℃ / min and held at that temperature for 4-6 hours. Finally, it is cooled to room temperature to obtain the hard carbon anode material.
10. The application of the hard carbon anode material according to any one of claims 1-8, characterized in that: The hard carbon anode material is used to prepare battery anode sheets.