Wide-temperature lithium battery negative electrode material based on hard carbon / graphite compounding and preparation method thereof

Abstract

The invention belongs to the technical field of lithium battery negative electrode materials, and particularly relates to a hard carbon / graphite composite-based wide-temperature lithium battery negative electrode material and a preparation method thereof. According to the invention, graphite is subjected to modification treatment and is matched with a composite carbon source composed of high amylose and cane sugar for common use, and the compound metal powder is added, so that the first discharge capacity of the lithium battery negative electrode material is effectively improved, and excellent first coulombic efficiency is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery negative electrode materials, and specifically relates to a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are new high-energy batteries that use lithium-intercalated compounds as their positive and negative electrode materials. They have gained widespread popularity due to their advantages, including high specific capacity, high operating voltage, low self-discharge, excellent safety, and long charge-discharge cycle life. They are now used in large-scale energy storage, power tools, and portable electronic devices. The rapid development of lithium-ion batteries is primarily due to the contributions of electrode materials, particularly research on carbon anode materials. There are many types of carbon anode materials, and graphite, with its low charge-discharge voltage platform, high cycle stability, and low cost, is currently considered an ideal anode material for lithium-ion battery applications. Hard carbon materials, due to their random arrangement, offer high capacity, low cost, and excellent cycle performance, making them a hot topic in lithium battery anode material research.

[0003] A Chinese patent (publication number CN107732245B) discloses a method for preparing a hard carbon / graphene composite negative electrode material for lithium batteries. The method comprises stabilizing an organic polymer, mixing it with lamellar graphene in an organic solvent, ultrasonicating it, and then heating it to react, thereby obtaining a composite precursor of hard carbon / graphene. The precursor is then mixed with nano-spherical metal powder, and subjected to high-temperature thermal decomposition under gas protection to form spherical hard carbon coated on the surface of the nano-spherical metal powder and sandwiched between the lamellar graphene, thereby obtaining a hard carbon / graphene composite negative electrode material. However, the negative electrode material prepared by this patented technology has problems such as insufficient first discharge capacity and the need to improve the first coulomb efficiency, which affects its further expansion and use.

[0004] Therefore, there is an urgent need for a wide-temperature lithium battery negative electrode material based on hard carbon-graphite composite. By screening suitable component materials, the first discharge capacity of the lithium battery negative electrode material can be effectively improved and a good first coulombic efficiency can be obtained. Summary of the Invention

[0005] The purpose of the present invention is to provide a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite and a preparation method thereof. By modifying the graphite, using it in conjunction with a composite carbon source composed of high-amylose starch and sucrose, and adding a compound metal powder, the first discharge capacity of the lithium battery negative electrode material is effectively improved, and an excellent first coulombic efficiency is obtained.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The first aspect of the present invention provides a method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite, comprising the following steps:

[0008] S1: Pre-treating 20 to 24 parts of a carbon source by weight, then uniformly mixing with 8 to 12 parts of modified graphite and 40 to 44 parts of methanol, and then adding 10 to 14 parts of a mixture of sodium metaaluminate and sodium hydroxide and heating the mixture to obtain a precursor;

[0009] S2: 10 to 14 parts of the precursor and 0.8 to 1.2 parts of metal powder are mixed to perform a carbonization reaction to obtain a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite.

[0010] As a preferred solution, the weight proportion of the carbon source in the present invention can be 20 parts, 21 parts, 22 parts, 23 parts or 24 parts.

[0011] As a preferred solution, the weight proportion of the modified graphite in the present invention can be 8 parts, 9 parts, 10 parts, 11 parts or 12 parts.

[0012] As a preferred solution, the weight parts of methanol in the present invention can be 40 parts, 41 parts, 42 parts, 43 parts or 44 parts.

[0013] As a preferred solution, the weight proportion of the metal powder in the present invention can be 0.8 parts, 0.9 parts, 1.0 parts, 1.1 parts or 1.2 parts.

[0014] As a preferred solution, the preparation method of the modified graphite includes: first surface-treating commercially available graphite powder with potassium hydroxide to obtain surface-treated graphite; and then modifying the surface-treated graphite with magnesium nitrate to obtain modified graphite.

[0015] As a preferred solution, the particle size of the commercially available graphite powder is 200 to 800 nm.

[0016] As a preferred solution, the surface treatment step includes: adding 8 to 12 parts of potassium hydroxide to 160 to 200 parts of deionized water by weight and mixing evenly, then adding 8 to 12 parts of commercially available graphite powder and stirring for 2 to 4 hours, drying the water at 80 to 90° C., transferring to a tube furnace for high-temperature calcination, cooling to room temperature, washing with water until the pH is neutral, and drying.

[0017] As a preferred solution, the high-temperature calcination conditions include: under argon protection, heating to 800-900° C. at a rate of 3-5° C. / min, and keeping the temperature for 100-120 minutes.

[0018] As a preferred solution, the modification treatment step includes: dissolving 0.16 to 0.22 parts of magnesium nitrate hexahydrate in 90 to 100 parts of deionized water, then adding 8 to 12 parts of surface-treated graphite and stirring for 30 to 40 minutes, transferring to a reactor for hydrothermal reaction, and vacuum drying.

[0019] As a preferred solution, the conditions of the hydrothermal reaction are: temperature of 160-180° C. and time of 16-20 h.

[0020] The present invention first uses potassium hydroxide to perform surface treatment on commercially available graphite powder. Potassium hydroxide, as a strong alkaline substance, can react with defect sites on the graphite surface and selectively etch to form pores. At the same time, potassium hydroxide and graphite form volatile substances such as carbon dioxide at high temperature, and the residual pore structure forms a porous network, thereby obtaining surface-treated graphite. Magnesium nitrate is then loaded on the surface-treated graphite through a hydrothermal reaction to obtain modified graphite. During a subsequent carbonization reaction, the magnesium compound in the modified graphite is thermally decomposed to generate magnesium oxide nanoparticles and release gas, thereby etching the graphite to form micropores.

[0021] As a preferred solution, the carbon source is high-amylose starch and sucrose; the mass ratio of high-amylose starch to sucrose in the carbon source is (1-2):1.

[0022] As a preferred solution, the high-amylose starch has an amylose content of 70-80%.

[0023] The high-amylose starch of the present invention tends to form partially graphitized ordered carbon layers when pyrolyzed, thereby enhancing electronic conductivity and reducing polarization, and providing a stable carbon skeleton containing abundant lithium storage sites. Sucrose easily generates abundant micropores and mesopores when pyrolyzed, thereby increasing lithium ion storage sites and improving capacity. Sucrose, as a small molecule carbon source, can fill the macroporous gaps of amylose carbon, forming a hierarchical pore structure, optimizing the ion transmission path, and thus improving the first discharge capacity and the first coulombic efficiency.

[0024] As a preferred solution, the mixed solution contains sodium metaaluminate with a mass concentration of 0.8 to 1.2% and sodium hydroxide with a mass concentration of 1.6 to 2.4%.

[0025] As a preferred solution, the metal powder is iron-nickel powder and dendritic silver-coated copper powder; the mass ratio of the iron-nickel powder to the dendritic silver-coated copper powder in the metal powder is (1-2):1.

[0026] As a preferred solution, the particle size of the iron-nickel powder in the metal powder is 300-700 nm, and the particle size of the dendritic silver-coated copper powder is 800-1000 nm.

[0027] The high conductivity of the iron-nickel powder of the present invention can form an efficient electron transmission path, reduce electrode polarization, and improve the first discharge capacity. At the same time, its high strength can inhibit the volume expansion of the carbon material and reduce irreversible capacity loss. The porous dendritic structure of the dendritic silver-coated copper powder provides abundant lithium ion diffusion channels, accelerating the kinetic process. The dendritic silver-coated copper powder and the iron-nickel powder jointly construct a three-dimensional conductive network. The dendrites of the dendritic silver-coated copper powder provide fast electron channels, and the iron-nickel powder provides high-capacity lithium storage sites. The synergistic effect improves the first discharge capacity and the first coulombic efficiency.

[0028] As a preferred solution, the pretreatment step in step S1 includes: placing under nitrogen atmosphere protection, heating to 220-240° C. and keeping warm for 10-20 minutes.

[0029] As a preferred solution, the temperature treatment step in step S1 includes: aging for 100 to 120 minutes, then transferring to a high-temperature reactor, heating to 180 to 200° C. and keeping warm for 5 to 7 hours, cooling to room temperature, filtering, washing with methanol, and drying.

[0030] As a preferred solution, the carbonization reaction step in step S2 includes: placing it under the protection of a nitrogen atmosphere and carbonizing it at 900-940° C. for 3-4 hours.

[0031] The second aspect of the present invention provides a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite prepared by the preparation method described in the first aspect.

[0032] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0033] 1. The present invention uses high-amylose starch and sucrose for compounding and controls the mass ratio of the two to achieve good results. The ordered layers of amylose carbon expand the interlayer spacing, and the sucrose-derived micropores provide additional lithium storage sites, synergistically increasing the amount of lithium ion embedding, thereby improving the first discharge capacity and the first coulombic efficiency.

[0034] 2. The present invention optimizes the pore structure of the graphite surface through surface treatment, which can increase the diffusion channels of lithium ions, reduce the diffusion resistance of lithium ions, increase active lithium storage sites, and thus improve the first discharge capacity; the pore structure can promote the uniform infiltration of the electrolyte into the graphite surface, reduce the aggregation of local high-concentration lithium ions, reduce the first irreversible capacity loss and improve the coulombic efficiency. The surface-treated graphite of the present invention will form uniform pores after modification reaction and carbonization reaction, provide additional lithium storage sites and accelerate the diffusion of lithium ions, thereby increasing the first discharge capacity; magnesium doping can regulate the graphite interlayer spacing, provide a shorter diffusion path for lithium ions, and improve the conductivity between graphite particles, reduce polarization loss, and thus improve the first coulombic efficiency.

[0035] 3. The high conductivity of the iron-nickel powder of the present invention can form an efficient electron transmission path, reduce electrode polarization, and improve the first discharge capacity. At the same time, its high strength can inhibit the volume expansion of the carbon material and reduce the irreversible capacity loss; the porous dendritic structure of the dendritic silver-coated copper powder provides abundant lithium ion diffusion channels, accelerating the kinetic process; the dendritic silver-coated copper powder and the iron-nickel powder jointly construct a three-dimensional conductive network, the dendrites of the dendritic silver-coated copper powder provide fast electron channels, and the iron-nickel powder provides high-capacity lithium storage sites, which synergistically improve the first discharge capacity and the first coulombic efficiency. DETAILED DESCRIPTION

[0036] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0037] The sources of some components in the Examples and Comparative Examples are as follows:

[0038] High-amylose starch, model HI-70, with an amylose content of 72%, was purchased from Anhui Quanyin High-Tech Seed Co., Ltd.;

[0039] Commercially available starch, CAS number 9005-25-8, was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0040] Sucrose, CAS No. 57-50-1, was purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0041] Commercially available graphite powder I, product number G810364, particle size 300 nm, was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.;

[0042] Commercially available graphite powder II, product number G434784, particle size 15 μm, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0043] Magnesium nitrate hexahydrate, CAS No. 13446-18-9, was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0044] Methanol, CAS number 67-56-1, was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0045] Sodium metaaluminate, CAS No. 11138-49-1, was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0046] Iron-nickel powder, product number I384532, particle size 400 nm, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0047] Dendritic silver-coated copper powder, with a particle size of 1000 nm, was purchased from Suzhou Fudi New Material Technology Co., Ltd.

[0048] Commercially available silver-coated copper powder, product number S776874, with a particle size of 3.5 μm, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0049] Example 1

[0050] This embodiment provides a method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite, comprising the following steps:

[0051] S1: In parts by weight, 24 parts of carbon source (16 parts of high-amylose starch and 8 parts of sucrose) were pretreated (placed under nitrogen atmosphere, heated to 240°C and kept warm for 10 minutes), then mixed with 12 parts of modified graphite and 44 parts of methanol, and then 14 parts of a mixed solution (containing 1.2% by mass concentration of sodium metaaluminate and 2.4% by mass concentration of sodium hydroxide) were added and aged for 120 minutes. Then, the mixture was transferred to a high-temperature reactor, heated to 200°C and kept warm for 5 hours. After cooling to room temperature, it was filtered, washed with methanol, and dried to obtain a precursor;

[0052] S2: 14 parts of the precursor and 1.2 parts of metal powder (0.8 parts of iron-nickel powder and 0.4 parts of dendritic silver-coated copper powder) were mixed, placed under nitrogen atmosphere protection, and carbonized at 940°C for 3h to obtain a wide-temperature lithium battery negative electrode material based on hard carbon / graphite composite.

[0053] Preparation of the modified graphite: In parts by weight, 12 parts of potassium hydroxide are added to 200 parts of deionized water and mixed evenly, then 12 parts of commercially available graphite powder I (article number G810364) are added and stirred for 4 hours, the moisture is dried at 90°C, and the mixture is transferred to a tubular furnace for high-temperature calcination (under argon protection, the temperature is raised to 900°C at a rate of 5°C / min and kept warm for 100 minutes). After cooling to room temperature, the mixture is washed with water until the pH is neutral and dried to obtain surface-treated graphite; 0.22 parts of magnesium nitrate hexahydrate are dissolved in 100 parts of deionized water, and then 12 parts of the surface-treated graphite are added and stirred for 40 minutes, and the mixture is transferred to a reactor for hydrothermal reaction (temperature is 180°C, time is 16 hours), and vacuum drying is performed.

[0054] Example 2

[0055] This embodiment provides a method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite, comprising the following steps:

[0056] S1: In parts by weight, 20 parts of carbon source (10 parts of high-amylose starch and 10 parts of sucrose) were pretreated (placed under nitrogen atmosphere, heated to 220°C and kept warm for 20 minutes), then mixed with 8 parts of modified graphite and 40 parts of methanol, and then 10 parts of a mixed solution (containing 0.8% by mass concentration of sodium metaaluminate and 1.6% by mass concentration of sodium hydroxide) were added and aged for 100 minutes. The mixture was then transferred to a high-temperature reactor, heated to 180°C and kept warm for 7 hours. After cooling to room temperature, it was filtered, washed with methanol, and dried to obtain a precursor;

[0057] S2: 10 parts of the precursor and 0.8 parts of metal powder (0.4 parts of iron-nickel powder and 0.4 parts of dendritic silver-coated copper powder) were mixed, placed under nitrogen atmosphere, and carbonized at 900°C for 4 hours to obtain a wide-temperature lithium battery negative electrode material based on hard carbon / graphite composite.

[0058] Preparation of the modified graphite: In parts by weight, 8 parts of potassium hydroxide are added to 160 parts of deionized water and mixed evenly, then 8 parts of commercially available graphite powder I (article number G810364) are added and stirred for 2 hours, the moisture is dried at 80°C, and the mixture is transferred to a tube furnace for high-temperature calcination (under argon protection, the temperature is raised to 800°C at a rate of 3°C / min and kept warm for 120 minutes), cooled to room temperature, washed with water until the pH is neutral, and dried to obtain surface-treated graphite; 0.16 parts of magnesium nitrate hexahydrate are dissolved in 90 parts of deionized water, and then 8 parts of the surface-treated graphite are added and stirred for 30 minutes, transferred to a reactor for hydrothermal reaction (temperature is 160°C, time is 20 hours), and vacuum dried.

[0059] Example 3

[0060] This embodiment provides a method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite, comprising the following steps:

[0061] S1: In parts by weight, 22 parts of carbon source (14 parts of high-amylose starch and 8 parts of sucrose) were pretreated (placed under nitrogen atmosphere, heated to 230°C and kept warm for 15 minutes), then stirred evenly with 10 parts of modified graphite and 42 parts of methanol, and then 12 parts of a mixed solution (containing 1.0% by mass concentration of sodium metaaluminate and 2.0% by mass concentration of sodium hydroxide) were added and aged for 110 minutes, then transferred to a high-temperature reactor, heated to 190°C and kept warm for 6 hours, cooled to room temperature, filtered, washed with methanol, and dried to obtain a precursor;

[0062] S2: 12 parts of the precursor and 1.1 parts of metal powder (0.7 parts of iron-nickel powder and 0.4 parts of dendritic silver-coated copper powder) were mixed, placed under nitrogen atmosphere, and carbonized at 920°C for 3.5 hours to obtain a wide-temperature lithium battery negative electrode material based on hard carbon / graphite composite.

[0063] Preparation of the modified graphite: In parts by weight, 10 parts of potassium hydroxide are added to 180 parts of deionized water and mixed evenly, then 10 parts of commercially available graphite powder I (Article No. G810364) are added and stirred for 3 hours, the moisture is dried at 85°C, and the mixture is transferred to a tubular furnace for high-temperature calcination (under argon protection, the temperature is raised to 850°C at a rate of 4°C / min and kept warm for 110 minutes), cooled to room temperature, washed with water until the pH is neutral, and dried to obtain surface-treated graphite; 0.18 parts of magnesium nitrate hexahydrate are dissolved in 95 parts of deionized water, and then 10 parts of the surface-treated graphite are added and stirred for 35 minutes, transferred to a reactor for hydrothermal reaction (temperature is 170°C, time is 18 hours), and vacuum dried.

[0064] Comparative Example 1

[0065] The difference between this comparative example and Example 1 is that commercially available starch (CAS No. 9005-25-8) is used instead of high-amylose starch (model HI-70).

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 1 is that the amount of high-amylose starch is changed to 22 parts and the amount of sucrose is changed to 2 parts.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 1 is that the amount of high-amylose starch is changed to 4 parts and the amount of sucrose is changed to 20 parts.

[0070] Comparative Example 4

[0071] The difference between this comparative example and Example 1 is that commercially available graphite powder I (article number G810364) is used instead of modified graphite.

[0072] Comparative Example 5

[0073] The difference between this comparative example and Example 1 is that commercially available graphite powder II (article number G434784) is used instead of commercially available graphite powder I (article number G810364) to prepare the modified graphite.

[0074] Comparative Example 6

[0075] The difference between this comparative example and Example 1 is that commercially available silver-coated copper powder (item number S776874) is used instead of the dendritic silver-coated copper powder.

[0076] Comparative Example 7

[0077] The difference between this comparative example and Example 1 is that the amount of iron-nickel powder is changed to 1.1 parts and the amount of dendritic silver-coated copper powder is changed to 0.1 parts.

[0078] Comparative Example 8

[0079] The difference between this comparative example and Example 1 is that the amount of iron-nickel powder is changed to 0.4 parts and the amount of dendritic silver-coated copper powder is changed to 0.8 parts.

[0080] Performance Testing

[0081] The negative electrode material is made into a paste with styrene-butadiene rubber and a water-based adhesive, evenly coated on both sides of the copper foil, rolled and cut into negative electrode sheets; used for lithium battery assembly, the first discharge capacity and first coulombic efficiency are tested with reference to "GB / T24533-2019 Graphite Anode Materials for Lithium-ion Batteries".

[0082] Table 1 Performance test results

[0083] First discharge capacity (mAh / g) First coulombic efficiency (%) Example 1 357.2 94.8 Example 2 355.6 94.3 Example 3 356.5 94.6 Comparative Example 1 317.8 91.3 Comparative Example 2 334.7 92.8 Comparative Example 3 342.4 93.2 Comparative Example 4 292.9 89.8 Comparative Example 5 332.5 92.4 Comparative Example 6 321.2 91.9 Comparative Example 7 345.7 93.1 Comparative Example 8 346.3 93.5

[0084] From the above performance test results, it can be seen that Examples 1-3 have the best comprehensive performance, with an initial discharge capacity of 355.6 to 357.2 mAh / g and an initial coulombic efficiency of 94.3 to 94.8; this is mainly because the graphite is modified and used in conjunction with a composite carbon source consisting of high-amylose starch and sucrose, and a compound metal powder is added to effectively improve the initial discharge capacity of the lithium battery negative electrode material and obtain an excellent initial coulombic efficiency.

[0085] Compared with Example 1, Comparative Example 1 uses commercially available starch (CAS No. 9005-25-8) instead of high-amylose starch (model HI-70). Due to the lack of the effect of high-amylose starch, the first discharge capacity is reduced and the first coulombic efficiency deteriorates. Compared with Example 1, the amount of high-amylose starch in Comparative Example 2 is changed to 22 parts and the amount of sucrose is changed to 2 parts. Since the amount of sucrose is too small, the compounding effect is not good, the first discharge capacity is reduced and the first coulombic efficiency deteriorates. Compared with Example 1, the amount of high-amylose starch in Comparative Example 3 is changed to 4 parts and the amount of sucrose is changed to 20 parts. Since the amount of high-amylose starch is too small, the compounding effect is not good, the first discharge capacity is reduced and the first coulombic efficiency deteriorates. Compared with Example 1, Comparative Example 4 uses commercially available graphite powder I (article number G810364) instead of modified graphite, the first discharge capacity is reduced and the first coulombic efficiency deteriorates. Compared with Example 1, Comparative Example 5 uses commercially available graphite powder II (article number G4 34784) was used to replace the commercially available graphite powder I (Article No. G810364) for the preparation of modified graphite. Since the particle size of the commercially available graphite powder II was too large, the modification effect was not good, the first discharge capacity was reduced, and the first coulomb efficiency deteriorated. Compared with Example 1, Comparative Example 6 used commercially available silver-coated copper powder (Article No. S776874) to replace the dendritic silver-coated copper powder. The dendritic silver-coated copper powder lacked the effect of dendrites, so the first discharge capacity was reduced and the first coulomb efficiency deteriorated. Compared with Example 1 In comparison, in Comparative Example 7, the amount of iron-nickel powder was changed to 1.1 parts and the amount of dendritic silver-coated copper powder was changed to 0.1 parts. Since the amount of dendritic silver-coated copper powder was too small, the compounding effect was poor, the first discharge capacity decreased, and the first coulombic efficiency deteriorated. Compared with Example 1, the amount of iron-nickel powder in Comparative Example 8 was changed to 0.4 parts and the amount of dendritic silver-coated copper powder was changed to 0.8 parts. Since the amount of iron-nickel powder was too small, the compounding effect was poor, the first discharge capacity decreased, and the first coulombic efficiency deteriorated.

Claims

1. A method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite, characterized in that: include Follow these steps: S1: Pre-treating 20 to 24 parts of a carbon source by weight, then uniformly mixing with 8 to 12 parts of modified graphite and 40 to 44 parts of methanol, and then adding 10 to 14 parts of a mixture of sodium metaaluminate and sodium hydroxide and heating the mixture to obtain a precursor; S2: mixing 10 to 14 parts of the precursor and 0.8 to 1.2 parts of metal powder to perform a carbonization reaction to obtain a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite; The preparation method of the modified graphite comprises: firstly performing surface treatment on commercially available graphite powder with potassium hydroxide to obtain surface-treated graphite; and then performing modification treatment on the surface-treated graphite with magnesium nitrate to obtain modified graphite.

2. The method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite according to claim 1, characterized in that: The particle size of the commercially available graphite powder is 200 to 800 nm.

3. The method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite according to claim 1, characterized in that: The surface treatment step includes: adding 8 to 12 parts of potassium hydroxide to 160 to 200 parts of deionized water by weight and mixing them evenly, then adding 8 to 12 parts of commercially available graphite powder and stirring for 2 to 4 hours, drying the water at 80 to 90° C., transferring the graphite powder to a tube furnace for high-temperature calcination, cooling it to room temperature, washing it with water until the pH is neutral, and drying it.

4. The method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite according to claim 1, characterized in that: The modification treatment step includes: dissolving 0.16-0.22 parts of magnesium nitrate hexahydrate in 90-100 parts of deionized water, adding 8-12 parts of surface-treated graphite and stirring for 30-40 minutes, transferring to a reactor for hydrothermal reaction, and vacuum drying.

5. The method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite according to claim 1, characterized in that: The carbon source is high-amylose starch and sucrose; the mass ratio of high-amylose starch to sucrose in the carbon source is (1-2):

1.

6. The method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite according to claim 5, characterized in that: The high-amylose starch has an amylose content of 70-80%.

7. The method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite according to claim 1, characterized in that: The metal powder is iron-nickel powder and dendritic silver-coated copper powder; The mass ratio of the iron-nickel powder to the dendritic silver-coated copper powder in the metal powder is (1-2):

1.

8. The method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite according to claim 1, characterized in that: The particle size of the iron-nickel powder in the metal powder is 300-700 nm, and the particle size of the dendritic silver-coated copper powder is 800-1000 nm.

9. The method for preparing a wide-temperature lithium battery negative electrode material based on a hard carbon / graphite composite according to claim 1, characterized in that: The pretreatment steps in step S1 include: placing under nitrogen atmosphere, heating to 220-240° C. and keeping warm for 10-20 minutes; The temperature treatment step in step S1 includes: aging for 100 to 120 minutes, then transferring to a high-temperature reactor, heating to 180 to 200° C. and keeping the temperature for 5 to 7 hours, cooling to room temperature, filtering, washing with methanol, and drying.

10. A wide-temperature lithium battery negative electrode material based on hard carbon / graphite composite, characterized in that: Prepared according to the method according to any one of claims 1 to 9.