Composite hard carbon material, preparation method thereof, application and battery

Abstract

The application discloses a kind of composite hard carbon materials and preparation method, application, battery thereof.The composite hard carbon material of the application includes the core of hard carbon particle, and the alumina layer and amorphous carbon layer are sequentially coated on the core from inside to outside;The mass ratio of the alumina layer and the hard carbon particle is 0.5-5%, and the thickness of the amorphous carbon layer is 5-20 μm.The lithium ion battery or sodium ion battery made of the composite hard carbon material of the application has higher initial efficiency and platform discharge capacity ratio, and has excellent lithium storage and sodium storage performance, and the discharge capacity of lithium ion battery and sodium ion battery is high.

Description

Technical Field

[0001] This invention relates to a composite hard carbon material, its preparation method, applications, and batteries. Background Technology

[0002] In recent years, with the rise of the new energy industry, secondary batteries such as lithium-ion batteries and sodium-ion batteries have gradually entered social production and daily life. However, with people's increasing demand for high-quality, low-cost products, the secondary battery industry has also placed higher demands on the negative electrode materials of batteries. Researching and developing high-capacity, low-cost negative electrode materials has become the key to solving this problem.

[0003] Currently, commercially available anode materials used in rechargeable batteries are mainly graphite materials, which exhibit high structural stability and excellent electrochemical performance. Graphite has become the primary anode material for lithium-ion batteries due to its small volume change, structural stability, and stable cycle performance. However, commercially available graphite anodes have essentially reached the theoretical capacity of 372 mAh / g for lithium-ion batteries. Simultaneously, due to the small interlayer spacing of graphite, it exhibits very low sodium storage capacity in sodium-ion batteries. Therefore, developing novel anode materials is crucial to solving this problem.

[0004] Hard carbon is a carbon material with large interlayer spacing, which is beneficial for sodium ion insertion and extraction. Furthermore, hard carbon exhibits superior lithium storage performance compared to graphite, thus significantly improving the performance of lithium-ion and sodium-ion batteries. However, hard carbon also presents some challenges in its use. Its large specific surface area leads to the formation of a significant amount of SEI film during the first cycle, resulting in a substantial reduction in the battery's initial efficiency. Simultaneously, the high specific surface area results in a higher proportion of capacity in the ramp zone during battery cycling, thereby limiting the battery's usability.

[0005] Therefore, there is an urgent need to develop an anode material that has excellent lithium and sodium storage performance, high initial efficiency, and a high proportion of platform capacity during charge and discharge. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the shortcomings of existing hard carbon anode materials, such as low initial efficiency and high capacity ratio in the ramp region due to their high specific surface area. This invention provides a composite hard carbon material, its preparation method, applications, and batteries. Lithium-ion or sodium-ion batteries made from the composite hard carbon material of this invention exhibit high initial efficiency and high plateau discharge capacity ratio, while also possessing excellent lithium and sodium storage performance, resulting in high discharge capacity for both lithium-ion and sodium-ion batteries.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The present invention provides a composite hard carbon material comprising a core of hard carbon particles, and an alumina layer and an amorphous carbon layer sequentially coated on the core from the inside out; the mass ratio of the alumina layer to the hard carbon particles is 0.5 to 5%, and the thickness of the amorphous carbon layer is 5 to 20 μm.

[0009] In this invention, the specific surface area of ​​the composite hard carbon material is preferably 2–13 m². 2 / g, for example 2.1m 2 / g, 2.3m 2 / g, 2.7m 2 / g, 2.8m 2 / g, 3.1m 2 / g, 3.2m 2 / g, 3.7m 2 / g, 4.3m 2 / g, 4.7m 2 / g, 5.8m 2 / g, 8.7m 2 / g, 10.7m 2 / g or 12.3m 2 / g.

[0010] In this invention, the specific surface area of ​​the composite hard carbon material is preferably 2.5–11 m². 2 / g, more preferably 2.7–10.7m 2 / g, more preferably 2.7–5.8m 2 / g, for example 3.2m 2 / g.

[0011] In this invention, the hard carbon particles can be carbon that is conventionally difficult to graphitize in the art, preferably one or more of resin-based hard carbon, pitch-based hard carbon and biomass-based hard carbon, and more preferably resin-based hard carbon.

[0012] In this invention, the sodium charge capacity of the hard carbon particles can be conventional in the art, generally ranging from 67 to 200 mAh / g.

[0013] In this invention, the initial efficiency of sodium-ion batteries using the hard carbon particles as the negative electrode material is generally between 37.4% and 75%.

[0014] In this invention, the lithium battery capacity of the hard carbon particles can be conventional in the art, generally between 350 and 450 mAh / g.

[0015] In this invention, the initial efficiency of sodium-ion batteries using the hard carbon particles as the negative electrode material is generally between 32% and 75%.

[0016] In this invention, the particle size D50 of the hard carbon particles can be conventional in the art, preferably 3 to 20 μm, and more preferably 8 μm.

[0017] In this invention, the mass ratio of the alumina layer to the hard carbon particles is preferably 0.6% to 4%, for example, 0.68%, 0.82%, 1.36%, 2.17%, or 3.40%.

[0018] In this invention, the mass ratio of the alumina layer to the hard carbon particles is preferably 1.2-2.5%, more preferably 1.36-2.17%.

[0019] In this invention, the thickness of the alumina layer is preferably 0.10 to 15 μm.

[0020] In this invention, the alumina layer is preferably achieved by the following method: in the mixture of hard carbon particles and aluminum salt, the aluminum salt is hydrolyzed to form an alumina precursor, which is dried, deposited on the surface of the hard carbon particles, and then calcined to remove the water of crystallization.

[0021] The hydrolysis is preferably achieved by adding a pH adjuster to the solution of the aluminum salt to adjust the solution to alkalinity.

[0022] The pH adjuster is preferably a weak base that does not contain metal cations, and more preferably ammonia.

[0023] The pH adjuster can be added in a manner conventional in the art, but preferably by dripping.

[0024] In some preferred embodiments of the present invention, the pH adjuster is ammonia water, the concentration of the ammonia water is 25%, and the mass ratio of the ammonia water to the aluminum salt is 0.1 to 10, more preferably 1:1.

[0025] The aluminum salt can be a conventional compound in the art that can be hydrolyzed to form aluminum oxide, preferably aluminum nitrate.

[0026] In the mixture, the mass ratio of the hard carbon particles to the solvent can be conventional in the art, preferably 0.1 to 1, and more preferably 0.5.

[0027] The solvent can be conventional in the art, and is generally water.

[0028] The amount of aluminum salt used should satisfy the mass ratio of the alumina layer to the hard carbon particles as described above.

[0029] Preferably, the mixture also includes a surfactant.

[0030] The surfactant is used to make the hard carbon particles more evenly dispersed in the mixed solution.

[0031] The surfactant may be conventional in the art, and preferably is hexadecylammonium bromide.

[0032] The amount of surfactant added can be as conventional as that to disperse the hard carbon particles evenly, and preferably the mass ratio of surfactant to solvent in the mixture is 0.01 to 0.1.

[0033] The mixture can be prepared by conventional methods in the art, preferably by adding the aluminum salt to a suspension containing the hard carbon particles and stirring until homogeneous.

[0034] The drying temperature can be conventional in the art, preferably 80-120°C, and more preferably 100°C.

[0035] The calcination temperature is preferably 300–800°C, more preferably 400–700°C, and even more preferably 450–550°C, for example 500°C.

[0036] The calcination time can be conventional in the art, preferably 0.5 to 3 hours, more preferably 0.5 to 1.5 hours, and even more preferably 1 hour.

[0037] The calcination step is preferably carried out in a rotary kiln, and more preferably in a CVD rotary kiln.

[0038] In this invention, the thickness of the amorphous carbon layer is preferably 5 to 19 μm, for example 5 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 15 μm or 19 μm.

[0039] In this invention, the thickness of the amorphous carbon layer is preferably 9-15, more preferably 11-13, and even more preferably 12.

[0040] In this invention, the amorphous carbon layer is preferably obtained by vapor deposition.

[0041] The carbon source in the vapor deposition is preferably acetylene.

[0042] More preferably, the gas phase in the vapor deposition includes the carbon source and the inert gas.

[0043] The inert gas is a gas that conventionally does not participate in the reaction, preferably nitrogen.

[0044] The volume ratio of the carbon source gas to the inert gas can be conventional in the art, preferably (0.1-2):1, and more preferably 1:1.

[0045] The temperature for vapor-phase carbon deposition can be conventional in the art, preferably 900–1800°C, more preferably 900–1100°C, and even more preferably 1000°C.

[0046] The time for vapor-phase carbon deposition is preferably 1 to 3 hours, more preferably 1 to 2.5 hours, and even more preferably 2 hours.

[0047] The present invention also provides a method for preparing the composite hard carbon material as described above, which includes the following steps: sequentially coating the surface of the hard carbon particles with the alumina layer and the amorphous carbon layer to obtain the composite hard carbon material.

[0048] The present invention also provides the application of the composite hard carbon material as described above as a negative electrode material in a negative electrode sheet or battery.

[0049] Preferably, the battery is a lithium-ion battery or a sodium-ion battery.

[0050] The present invention also provides a battery comprising the composite hard carbon material as described above.

[0051] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0052] The reagents and raw materials used in this invention are all commercially available.

[0053] The positive and progressive effects of this invention are as follows: the composite hard carbon material prepared by this invention has good application effects in both lithium-ion batteries and sodium-ion batteries. The lithium-ion batteries and sodium-ion batteries made from this invention have excellent electrochemical performance, especially in terms of discharge capacity, initial efficiency, and plateau percentage. The discharge capacity of lithium-ion batteries is higher than 480 mAh / g, and can even reach more than 600 mAh / g; the initial efficiency is higher than 82%, and can even reach as high as 93.3%; and the plateau percentage is higher than 60%, and can even reach as high as 89.2%. The discharge capacity of sodium-ion batteries is higher than 220 mAh / g, and can even reach as high as 330 mAh / g; the initial efficiency is higher than 79%, and can even reach as high as 91.2%; and the plateau percentage is higher than 54%, and can even reach as high as 85.4%. Detailed Implementation

[0054] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0055] The main raw materials used in the following embodiments and comparative examples of the present invention are as follows:

[0056] Hard carbon particles, resin-based hard carbon, purchased from Shanghai Shanshan Technology Co., Ltd., with a particle size D50 of 8μm.

[0057] All other raw materials are standard commercially available products.

[0058] Example 1

[0059] A. Disperse 500g of hard carbon particles and 10g of hexadecyl ammonium bromide in 1000g of deionized water and stir with a paddle stirrer until a uniform suspension is formed.

[0060] B. Add 50g of aluminum nitrate powder to the suspension in A and stir until it is evenly dispersed. Then add 50g of ammonia water and stir until it is a uniform suspension.

[0061] C. Place the suspension obtained in B into a forced-air drying oven to evaporate the water in the suspension. Set the temperature to 100℃ until a dry powder is obtained.

[0062] D. Place the powder obtained in C into a CVD rotary furnace, heat it to 500℃ under nitrogen protection, and hold it at that temperature for 1 hour to form an Al2O3 coating layer.

[0063] E. Continuing the reaction conditions from D, the temperature is further increased to 1000℃, and a mixture of nitrogen and acetylene gas with a volume ratio of 1:1 is introduced. The mixture is held at this temperature for 2 hours to deposit the carbon coating layer. The final product is a composite hard carbon material with both Al2O3 and amorphous carbon double coating layers. After ion beam cutting, it is characterized by SEM, and the thickness of the amorphous carbon layer is measured to be 12 μm.

[0064] Example 2

[0065] In step A, the amount of hard carbon added was changed to 1000g, and the other steps and conditions were the same as in Example 1. A composite hard carbon material with Al2O3 and amorphous carbon double coating was obtained. After ion beam cutting, it was characterized by SEM, and the thickness of its amorphous carbon layer was measured to be 5μm.

[0066] Example 3

[0067] In step A, the amount of hard carbon added was 200g, and the other steps and conditions were the same as in Example 1. A composite hard carbon material with Al2O3 and amorphous carbon double coating was obtained. After ion beam cutting, it was characterized by SEM, and the thickness of its amorphous carbon layer was measured to be 19μm.

[0068] Example 4

[0069] In step B, the amount of aluminum nitrate added was 30g, and the other steps and conditions were the same as in Example 1. A composite hard carbon material with Al2O3 and amorphous carbon double coating was obtained. After ion beam cutting, it was characterized by SEM, and the thickness of its amorphous carbon layer was measured to be 13μm.

[0070] Example 5

[0071] In step B, the amount of aluminum nitrate added was 80g, and the other steps and conditions were the same as in Example 1. A composite hard carbon material with Al2O3 and amorphous carbon double coating was obtained. After ion beam cutting, it was characterized by SEM, and the thickness of its amorphous carbon layer was measured to be 11μm.

[0072] Example 6

[0073] In step D, the heat preservation time was 0.5 h, and the other steps and conditions were the same as in Example 1. The resulting composite hard carbon material with Al2O3 and amorphous carbon double coating was characterized by SEM after ion beam cutting, and the thickness of its amorphous carbon layer was measured to be 12 μm.

[0074] Example 7

[0075] In step D, the heat preservation time was 1.5 h, and the other steps and conditions were the same as in Example 1. A composite hard carbon material with Al2O3 and amorphous carbon double coating was obtained. After ion beam cutting, it was characterized by SEM, and the thickness of its amorphous carbon layer was measured to be 13 μm.

[0076] Example 8

[0077] In step D, the heat preservation temperature was 400℃, and the other steps and conditions were the same as in Example 1. A composite hard carbon material with Al2O3 and amorphous carbon double coating was obtained. After ion beam cutting, it was characterized by SEM, and the thickness of its amorphous carbon layer was measured to be 11μm.

[0078] Example 9

[0079] In step D, the heat preservation temperature was 700℃, and the other steps and conditions were the same as in Example 1. A composite hard carbon material with Al2O3 and amorphous carbon double coating was obtained. After ion beam cutting, it was characterized by SEM, and the thickness of its amorphous carbon layer was measured to be 12μm.

[0080] Example 10

[0081] In step E, the heat preservation time is 1 hour, and the other steps and conditions are the same as in Example 1. A composite hard carbon material with Al2O3 and amorphous carbon double coating is obtained. After ion beam cutting, it is characterized by SEM, and the thickness of its amorphous carbon layer is measured to be 10 μm.

[0082] Example 11

[0083] In step E, the carbonization time was 2.5 h, and the other steps and conditions were the same as in Example 1. A composite hard carbon material with Al2O3 and amorphous carbon double coating was obtained. After ion beam cutting, it was characterized by SEM, and the thickness of its amorphous carbon layer was measured to be 15 μm.

[0084] Example 12

[0085] In step E, the heat preservation carbonization temperature was 900℃, and the other steps and conditions were the same as in Example 1. A composite hard carbon material with Al2O3 and amorphous carbon double coating was obtained. After ion beam cutting, it was characterized by SEM, and the thickness of its amorphous carbon layer was measured to be 10μm.

[0086] Example 13

[0087] In step E, the carbonization temperature was 1100℃, and the other steps and conditions were the same as in Example 1. A composite hard carbon material with Al2O3 and amorphous carbon double coating was obtained. After ion beam cutting, it was characterized by SEM, and the thickness of its amorphous carbon layer was measured to be 9μm.

[0088] Comparative Example 1

[0089] Hard carbon particles.

[0090] Comparative Example 2

[0091] Perform only step AD of Example 1, without performing step E, to obtain a hard carbon material with an alumina coating.

[0092] Comparative Example 3

[0093] The hard carbon material particles from Example 1 were placed in a CVD rotary furnace and heated to 1000°C under nitrogen protection. A mixture of nitrogen and acetylene was introduced at a ratio of 1:1, and the mixture was held for 2 hours to deposit a carbon coating layer. The resulting hard carbon material with a carbon coating layer was then obtained. After ion beam cutting, the material was characterized by SEM, and the thickness of its amorphous carbon layer was measured to be 11 μm.

[0094] Comparative Example 4

[0095] 500g of hard carbon particles were first placed in a CVD rotary furnace, and a mixture of nitrogen and acetylene gas with a volume ratio of 1:1 was introduced. The mixture was held at this temperature for 2 hours to deposit a carbon coating layer. After cooling, the steps of Example 1 (AD) were performed sequentially to obtain a composite hard carbon material first coated with an amorphous carbon layer and then coated with an alumina layer. After ion beam cutting, the material was characterized by SEM, and the thickness of the amorphous carbon layer was measured to be 12μm.

[0096] Effect Example

[0097] 1. Specific surface area determination

[0098] Testing instrument: 3020 fully automatic surface area and pore size analyzer from Mic Corporation, USA.

[0099] Test conditions: CO2 purity 99.9%, tested under liquid nitrogen (77.3K).

[0100] Pre-test treatment: The sample to be tested was degassed under vacuum in a heating furnace at 100℃ for 12 hours.

[0101] The specific surface area of ​​the negative electrode materials obtained in Examples 1-13 and Comparative Examples 1-4 was tested using the above test method, and the results are shown in Table 1.

[0102] 2. Electrochemical performance testing of lithium-ion batteries

[0103] The hard carbon materials obtained in Examples 1-13 and Comparative Examples 1-4 were weighed and mixed according to a mass ratio of hard carbon material: conductive agent (conductive carbon black): binder (CMC) of 90:5:5. An appropriate amount of deionized water was added to form a slurry, which was then coated onto copper foil and dried in a vacuum drying oven for 12 hours to form a negative electrode. The electrolyte was a 1M LiPF6 solution with a solvent ratio of EC:DEC:DMC = 1:1:1 (volume ratio). A polypropylene microporous membrane (Celgard 2400) was used as the separator, and a lithium sheet was used as the counter electrode. The batteries were assembled. Constant current charge-discharge experiments were conducted using a LAND battery testing system with a charge-discharge voltage window of 0.01–2.0V and a charge-discharge rate of 0.1C. The lithium battery capacity, initial efficiency, and plateau percentage are shown in Table 1.

[0104] 3. Sodium-ion battery test

[0105] The negative electrode materials obtained in Examples 1-11 and Comparative Examples 1-4 were weighed and mixed according to a mass ratio of negative electrode material: conductive agent (conductive carbon black): binder (CMC) of 90:5:5. The mixture was then thoroughly ground to obtain a viscous slurry. This slurry was then coated onto copper foil using a scraping method and allowed to air dry at room temperature. The coated film was then placed in a vacuum oven at 80°C and dried for 12 hours. The dried electrode film was removed and pressed into a circular electrode sheet with a diameter of approximately 1 cm. All tested batteries were CR2016 coin cells. The electrolyte was a 1M NaClO4 solution with a solvent ratio of EC:DEC = 1:1 (volume ratio). The prepared circular electrode sheet was used as the positive electrode, metallic sodium as the negative electrode, and a polypropylene microporous membrane (Celgard 2400) as the separator. The CR2016 coin cells were assembled in an argon-filled glove box. Constant current charge-discharge experiments were conducted using the LAND battery testing system. The charge-discharge voltage window was 0.01–2.0V, and the charge-discharge rate was 0.1C. The sodium battery capacity, initial efficiency, and plateau percentage were obtained, as shown in Table 1.

[0106] Table 1. Data table of characterization results for examples and comparative examples.

[0107]

[0108]

[0109] In Table 1, the alumina layer ratio refers to the mass ratio of the alumina layer to the hard carbon particles.

[0110] As shown in Table 1 above, the lithium-ion and sodium-ion batteries made from the composite hard carbon materials obtained in the embodiments of the present invention exhibit excellent electrochemical performance, especially in terms of discharge capacity, initial efficiency, and plateau ratio. The lithium-ion batteries obtained by the present invention all have lithium-ion capacities exceeding 480 mAh / g, initial efficiencies exceeding 80%, and plateau ratios exceeding 60%; the sodium-ion batteries obtained by the present invention all have discharge capacities exceeding 220 mAh / g, initial efficiencies exceeding 79%, and plateau ratios exceeding 60%. Their overall performance is significantly superior to that of the comparative hard carbon materials.

[0111] Comparative Example 2, which only has an alumina layer, Comparative Example 3, which only has an amorphous carbon layer, and Comparative Example 4, which has a different coating order for alumina and amorphous carbon layers than the present invention, all resulted in composite hard carbon materials with significantly worse electrochemical performance than the present invention.

[0112] The comparison of Examples 1-5 shows that the proportion of the alumina layer and the thickness of the carbon layer have a significant impact on the electrochemical performance of the hard carbon material. In Example 2, both the proportion of the alumina layer and the thickness of the carbon layer are relatively small. Although the discharge capacity is high, the initial efficiency and plateau percentage are significantly lower than in Example 1. In Example 3, both the proportion of the alumina layer and the thickness of the carbon layer are relatively large, resulting in a significant decrease in discharge capacity, and the initial efficiency is also slightly lower than in Example 1.

[0113] A comparison of Examples 6-9 with Example 1 shows that, with the proportion of the alumina layer and the thickness of the carbon layer being basically the same as in Example 1, the temperature and time during the calcination and dehydration process in step D to form the alumina coating layer also affect the specific surface area of ​​the obtained hard carbon material, ultimately affecting the electrochemical performance of the hard carbon material. When the calcination time in step D is shorter or longer, or the calcination temperature is higher or lower, the electrochemical performance of the obtained hard carbon material decreases to a certain extent compared with Example 1.

[0114] A comparison of Examples 10, 11 and Example 1 shows that the time for gas phase carbon deposition in step E mainly affects the thickness of the deposited carbon layer. When the deposition time is shortened or extended, i.e. when the thickness of the deposited carbon layer is smaller or larger, the electrochemical performance of the obtained negative electrode material decreases to a certain extent compared with Example 1.

[0115] Compared with Example 1, Example 1, Example 2, Example 3, and Example 4, the only difference is the temperature of gas phase carbon deposition, which results in a different thickness of the deposited carbon layer. The electrochemical performance of the final composite hard carbon material is somewhat lower than that of Example 1.

Claims

1. A composite hard carbon material, characterized in that, It comprises a core of hard carbon particles, and an alumina layer and an amorphous carbon layer sequentially coating the core from the inside out; the mass ratio of the alumina layer to the hard carbon particles is 1.2~1.36%, and the thickness of the amorphous carbon layer is 9~15μm; the specific surface area of ​​the composite hard carbon material is 2~5.8m². 2 / g; The amorphous carbon layer is obtained by vapor phase carbon deposition; the temperature of the vapor phase carbon deposition is 1000~1800℃; the time of the vapor phase carbon deposition is 2~3h; The preparation method of the composite hard carbon material includes the following steps: sequentially coating the surface of the hard carbon particles with the alumina layer and the amorphous carbon layer to obtain the composite hard carbon material; The alumina layer is achieved by the following method: in the mixture of hard carbon particles and aluminum salt, the aluminum salt is hydrolyzed to form an alumina precursor, which is dried and deposited on the surface of the hard carbon particles, and then calcined to remove the water of crystallization, thereby obtaining the alumina layer.

2. The composite hard carbon material as described in claim 1, characterized in that, The specific surface area of ​​the composite hard carbon material is 2.7~5.8 m². 2 / g.

3. The composite hard carbon material as described in claim 1, characterized in that, The specific surface area of ​​the composite hard carbon material is 2.1 m². 2 / g, 2.3m 2 / g, 2.7m 2 / g, 2.8m 2 / g, 3.1m 2 / g, 3.2m 2 / g, 3.7m 2 / g, 4.3m 2 / g, 4.7m 2 / g or 5.8m 2 / g.

4. The composite hard carbon material as described in claim 1, characterized in that, The hard carbon particles are one or more of resin-based hard carbon, organic polymer pyrolytic carbon, and carbon black. And / or, the particle size D50 of the hard carbon particles is 1~16μm.

5. The composite hard carbon material as described in claim 4, characterized in that, The hard carbon particles are resin-based hard carbon. And / or, the particle size D50 of the hard carbon particles is 8 μm.

6. The composite hard carbon material as described in claim 1, characterized in that, The mass ratio of the alumina layer to the hard carbon particles is 1.36%. And / or, the thickness of the alumina layer is 0.10~15μm.

7. The composite hard carbon material as described in claim 1, characterized in that, The thickness of the amorphous carbon layer is 11~13 μm.

8. The composite hard carbon material as described in claim 1, characterized in that, The thickness of the amorphous carbon layer is 9 μm, 10 μm, 11 μm, 12 μm, 13 μm or 15 μm.

9. A method for preparing a composite hard carbon material as described in any one of claims 1 to 8, characterized in that, It includes the following steps: sequentially coating the surface of the hard carbon particles with the alumina layer and the amorphous carbon layer to obtain the composite hard carbon material.

10. The method for preparing the composite hard carbon material as described in claim 9, characterized in that, The alumina layer is achieved by the following method: in the mixture of hard carbon particles and aluminum salt, the aluminum salt is hydrolyzed to form an alumina precursor, which is dried and deposited on the surface of the hard carbon particles, and then calcined to remove the water of crystallization, thereby obtaining the alumina layer.

11. The method for preparing the composite hard carbon material as described in claim 10, characterized in that, The hydrolysis is achieved by adding a pH adjuster to the solution of the aluminum salt to adjust the solution to alkalinity.

12. The method for preparing the composite hard carbon material as described in claim 11, characterized in that, The pH adjuster is a weak base that does not contain metal cations.

13. The method for preparing the composite hard carbon material as described in claim 12, characterized in that, The pH adjuster is ammonia.

14. The method for preparing the composite hard carbon material as described in claim 12, characterized in that, The pH adjuster is added dropwise.

15. The method for preparing the composite hard carbon material as described in claim 11, characterized in that, The pH adjuster is ammonia water, the concentration of the ammonia water is 25%, and the mass ratio of the ammonia water to the aluminum salt is 1:

1.

16. The method for preparing the composite hard carbon material as described in claim 10, characterized in that, The aluminum salt is aluminum nitrate.

17. The method for preparing the composite hard carbon material as described in claim 10, characterized in that, In the mixture, the mass ratio of the hard carbon particles to the solvent is 0.1 to 1.

18. The method for preparing the composite hard carbon material as described in claim 17, characterized in that, In the mixture, the mass ratio of the hard carbon particles to the solvent is 0.

5.

19. The method for preparing the composite hard carbon material as described in claim 17, characterized in that, The solvent is water.

20. The method for preparing the composite hard carbon material as described in claim 10, characterized in that, The mixture also includes surfactants.

21. The method for preparing the composite hard carbon material as described in claim 20, characterized in that, The surfactant is hexadecylammonium bromide.

22. The method for preparing the composite hard carbon material as described in claim 20, characterized in that, The mass ratio of the surfactant to the solvent in the mixture is 0.01 to 0.

1.

23. The method for preparing the composite hard carbon material as described in claim 10, characterized in that, The drying temperature is 80~120℃.

24. The method for preparing the composite hard carbon material as described in claim 23, characterized in that, The drying temperature is 100°C.

25. The method for preparing the composite hard carbon material as described in claim 10, characterized in that, The calcination temperature is 300~800℃.

26. The method for preparing the composite hard carbon material as described in claim 25, characterized in that, The calcination temperature is 400~700℃.

27. The method for preparing the composite hard carbon material as described in claim 26, characterized in that, The calcination temperature is 450~550℃.

28. The method for preparing the composite hard carbon material as described in claim 27, characterized in that, The calcination temperature is 500℃.

29. The method for preparing the composite hard carbon material as described in claim 10, characterized in that, The calcination time is 0.5 to 3 hours.

30. The method for preparing the composite hard carbon material as described in claim 29, characterized in that, The calcination time is 0.5~1.5h.

31. The method for preparing the composite hard carbon material as described in claim 30, characterized in that, The calcination time is 1 hour.

32. The method for preparing the composite hard carbon material as described in claim 10, characterized in that, The calcination step is carried out in a rotary kiln.

33. The method for preparing the composite hard carbon material as described in claim 32, characterized in that, The calcination step is carried out in a CVD rotary furnace.

34. The method for preparing the composite hard carbon material as described in claim 9, characterized in that, The amorphous carbon layer is obtained by vapor-phase carbon deposition.

35. The method for preparing the composite hard carbon material as described in claim 34, characterized in that, The carbon source in the gaseous carbon deposition is acetylene.

36. The method for preparing the composite hard carbon material as described in claim 35, characterized in that, The gas phase in the gas phase carbon deposition includes acetylene and nitrogen.

37. The method for preparing the composite hard carbon material as described in claim 36, characterized in that, The volume ratio of the acetylene to the nitrogen is (0.1~2):

1.

38. The method for preparing the composite hard carbon material as described in claim 37, characterized in that, The volume ratio of acetylene to nitrogen is 1:

1.

39. The method for preparing the composite hard carbon material as described in claim 34, characterized in that, The temperature for vapor-phase carbon deposition is 1000~1800℃.

40. The method for preparing the composite hard carbon material as described in claim 39, characterized in that, The temperature for the vapor-phase carbon deposition is 1000℃.

41. The method for preparing the composite hard carbon material as described in claim 34, characterized in that, The time for gas phase carbon deposition is 2-3 hours.

42. The method for preparing the composite hard carbon material as described in claim 41, characterized in that, The time for gas phase carbon deposition was 2 hours.

43. The application of a composite hard carbon material as described in any one of claims 1 to 8 as a negative electrode material in a negative electrode sheet or battery.

44. The application as described in claim 43, characterized in that, The battery is a lithium-ion battery or a sodium-ion battery.

45. A battery, characterized in that, It includes the composite hard carbon material as described in any one of claims 1 to 8.

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