Hard carbon composite material with double-shell structure and preparation method thereof

Abstract

The application provides a hard carbon composite material with a double-shell structure and a preparation method thereof. The method comprises the following steps: mixing a hard carbon precursor raw material with a metal salt solution, performing spray drying, and performing high-temperature carbonization to obtain a hard carbon precursor; performing chemical deposition of the hard carbon precursor and a metal salt, and performing high-temperature sintering to obtain porous metal oxide coated hard carbon; and performing gas phase deposition of halogen and carbon source gas to coat the porous metal oxide coated hard carbon with halogen-containing amorphous carbon, thereby obtaining the hard carbon composite material with the double-shell structure. The hard carbon composite material utilizes the porous structure of the intermediate layer and the abundant oxygen-containing groups to store more lithium ions, thereby improving the capacity and kinetic performance and reducing the expansion. The halogen-containing amorphous carbon of the outer layer forms halogenated carbon to improve the electron transport rate of the material, and a part of the carbon is coated on the shell to insulate the electrolyte, thereby reducing the side reaction, improving the high-temperature storage and cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery material preparation technology, specifically providing a hard carbon composite material with a double-layer shell structure and its preparation method. Background Technology

[0002] Lithium-ion batteries are internationally recognized as an ideal chemical energy source, with advantages such as small size, large capacity, and high voltage. They are widely used in electronic products such as mobile phones and laptops, and the ever-expanding electric vehicle sector will bring even greater development opportunities for lithium-ion batteries.

[0003] The performance of lithium-ion batteries primarily depends on the structure and properties of the internal materials used. These materials include positive electrode materials, negative electrode materials, electrolytes, and separators. The selection and quality of the positive and negative electrode materials directly determine the performance and price of the lithium-ion battery. Therefore, research into inexpensive, high-performance positive and negative electrode materials has always been a key focus of the lithium-ion battery industry.

[0004] Carbon materials are typically used as anode materials. Hard carbon materials are used in 48V, HEV, and long-cycle lithium-ion batteries and sodium-ion batteries due to their advantages such as fast charging, good low-temperature performance, and low expansion. However, due to the numerous defects on the surface of hard carbon materials and their large specific surface area, their initial efficiency and compaction density are relatively low. Coating modification is the most effective way to improve the initial efficiency of materials. Currently, commercially available hard carbon materials mainly improve initial efficiency by coating their surface with soft carbon, which improves the initial efficiency but reduces the rate performance. For example, patent application number 202010634584.3 discloses a method for preparing a nitrogen-doped hard carbon-coated artificial graphite composite material. The composite material has a core-shell structure, with an artificial graphite core and a nitrogen-doped hard carbon coating layer on the outer shell. Although this hard carbon composite material can improve the cycle performance at low rates, it does not significantly improve the power performance and high-rate cycle performance of the material. Summary of the Invention

[0005] To improve the initial efficiency and high-rate cycling performance of hard carbon materials, this invention improves kinetic performance, high-temperature storage, and cycling performance by coating the surface of hard carbon with a porous metal oxide and amorphous carbon bilayer structure.

[0006] To achieve the above-mentioned objectives, this invention provides a hard carbon composite material with a double-layer shell structure and a method for preparing the same.

[0007] On the one hand, the present invention provides the following technical solution:

[0008] A method for preparing a hard carbon composite material with a double-layer shell structure, the method comprising:

[0009] Hard carbon precursor raw material is mixed with metal salt solution, spray dried and carbonized at high temperature to obtain hard carbon precursor.

[0010] The hard carbon precursor and metal salt were chemically deposited and sintered at high temperature to obtain porous metal oxide-coated hard carbon.

[0011] By vapor-phase deposition of halogen and carbon source gas, amorphous carbon containing halogen is coated onto the surface of the porous metal oxide-coated hard carbon, thereby obtaining the hard carbon composite material with the double-layer shell structure.

[0012] The hard carbon composite material utilizes the porous structure and abundant oxygen-containing groups in the middle layer to store more lithium ions, thereby improving capacity and kinetic performance and reducing expansion. The outer layer contains halogen-containing amorphous carbon, some of which forms halogenated carbon to improve the electron transport rate of the material, while some carbon coats the outer shell to isolate the electrolyte, reduce its side reactions, and improve high-temperature storage and cycle performance.

[0013] Furthermore, the hard carbon precursor material is a hydrocarbon;

[0014] The preparation process of the hard carbon precursor includes:

[0015] The hydrocarbon was dissolved in deionized water, a metal salt compound was added, the mixture was dispersed evenly, spray-dried, and then carbonized at 600-900°C for 1-6 hours under an inert atmosphere to obtain the hard carbon precursor.

[0016] Furthermore, the preparation process of the porous metal oxide-coated hard carbon includes:

[0017] The hard carbon precursor was dispersed in deionized water to prepare solution A with a mass concentration of 1-10 wt%.

[0018] The metal salt is dissolved in deionized water to prepare solution B with a mass concentration of 1-10 wt%.

[0019] Solution B is added to solution A, and then an alkaline solution is added to adjust the pH value to 8-11. The mixture is then reacted at 50-150℃ for 1-6 hours to form a gel. After filtration and vacuum drying, the resulting material is sintered at 600-1000℃ for 1-6 hours under an inert atmosphere. After natural cooling, the material is pulverized to obtain the porous metal oxide-coated hard carbon material.

[0020] Furthermore, the mass ratio of the hard carbon precursor, the metal salt compound, and the alkaline solution is 100:1 to 10:10 to 50.

[0021] Furthermore, the implementation of the method also includes:

[0022] The porous metal oxide is coated onto the hard carbon material. First, an inert gas is introduced to purge the air from the pipe. Then, a carbon source mixture is introduced, and carbonization is carried out at a temperature of 700–1000°C for 1–6 hours.

[0023] After carbonization, the material is cooled to room temperature under an inert atmosphere, then pulverized and graded to obtain the hard carbon composite material with the double-layer shell structure.

[0024] Furthermore, the hydrocarbon is one or more of phenolic resin, glucose, sucrose, starch, and lignin;

[0025] The metal salt compound is one or more of nickel chloride, cobalt chloride, ferric chloride, copper chloride, and silver chloride.

[0026] Furthermore, the mass ratio of the hydrocarbon to the metal salt compound is 100:1 to 10.

[0027] Furthermore, the metal salt is one or more of the following: silver nitrate, silver acetate, silver oxalate, silver sulfate, silver n-butoxide, copper nitrate, copper acetate, copper oxalate, copper sulfate, and copper n-butoxide.

[0028] The alkaline solution is one or more of the following: ammonia, urea, formamide, sodium hydroxide, potassium hydroxide, sodium bicarbonate, and potassium bicarbonate.

[0029] Furthermore, the carbon source mixed gas is composed of a carbon source and a halogen gas, wherein the volume ratio of the carbon source to the halogen gas is 10:1 to 5; and the flow rate is 10 to 100 ml / min.

[0030] The carbon source is one or more of methane, ethane, ethylene, and acetylene;

[0031] The halogen gas is one or more of chlorine, bromine, and fluorine.

[0032] In another aspect, the present invention provides the following technical solution:

[0033] A hard carbon composite material with a double-shell structure, wherein the hard carbon composite material with a double-shell structure is prepared based on any of the above methods;

[0034] The composite material has a core-shell structure, with a core of hard carbon, a middle layer of porous metal oxide, and an outer shell of amorphous carbon.

[0035] The thickness ratio of the core, intermediate layer and outer shell is 100:1 to 10:1 to 10.

[0036] Compared with the prior art, the hard carbon composite material with a double-layer shell structure and its preparation method of the present invention have the following outstanding advantages:

[0037] (1) The composite material of the present invention utilizes the porous structure of the intermediate layer and its rich oxygen-containing groups to store more lithium ions, improve capacity and kinetic performance, and reduce expansion; at the same time, the porous metal oxide deposited on the surface of hard carbon material by acid-base chemical reaction has the characteristics of uniform coating and stable structure.

[0038] (2) In the outer layer of halogen-containing amorphous carbon, some carbon forms halogenated carbon to improve the electron transport rate of the material, and some carbon is coated on the shell to isolate the electrolyte, reduce its side reactions, and improve high-temperature storage and its cycling performance. Attached Figure Description

[0039] Figure 1 This is a SEM image of the hard carbon composite material with a double-layer shell structure according to the present invention. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Example 1

[0041] Step S1:

[0042] 100g of phenolic resin was dissolved in 1000g of deionized water, then 5g of nickel chloride was added, dispersed evenly, spray dried, and then carbonized at 750℃ for 3h under an inert argon atmosphere to obtain a hard carbon precursor.

[0043] Step S2:

[0044] 100g of hard carbon precursor was dispersed in 2000g of deionized water to prepare a 5wt% solution A; 5g of silver nitrate was dissolved in 100g of deionized water to prepare a 5wt% solution B; under mechanical stirring, solution B was added to solution A, and then 30g of ammonia solution was added to adjust the pH to 9. The mixture was then reacted at 100℃ for 3h to form a gel, filtered, and vacuum dried at 80℃ for 24h. The resulting material was then sintered at 800℃ for 3h under an argon inert atmosphere, allowed to cool naturally to room temperature, and pulverized to obtain a porous metal oxide-coated hard carbon material.

[0045] Step S3:

[0046] The porous metal oxide-coated hard carbon material was transferred to a tube furnace. First, argon inert gas was introduced to purge the air from the tube. Then, a methane mixture (volume ratio: methane: chlorine = 10:3; flow rate: 50 ml / min) was introduced and carbonized at 800℃ for 3 hours. After that, the methane mixture was stopped, and the furnace was cooled to room temperature under an argon inert atmosphere. The material was then pulverized and graded to obtain a hard carbon composite material with a double-layer shell structure. Example 2

[0047] Step S1:

[0048] 100g of glucose was dissolved in 1000g of deionized water, then 1g of cobalt chloride was added, the mixture was dispersed evenly, spray-dried, and then carbonized at 600℃ for 6h under an inert argon atmosphere to obtain a hard carbon precursor.

[0049] Step S2:

[0050] 100g of hard carbon precursor was dispersed in 10000g of deionized water to prepare solution A with a mass concentration of 1wt%; 1g of silver acetate was dissolved in 100g of deionized water to prepare solution B with a mass concentration of 1wt%; solution B was added to solution A under mechanical stirring, and then 100g of 10wt% sodium hydroxide solution was added to adjust pH=8. The mixture was then reacted at 50℃ for 6h to form a gel, filtered, and vacuum dried at 80℃ for 24h. The resulting material was then sintered at 600℃ for 6h under an argon inert atmosphere, allowed to cool naturally to room temperature, and pulverized to obtain porous metal oxide-coated hard carbon material.

[0051] Step S3:

[0052] The porous metal oxide-coated hard carbon material was transferred to a tube furnace. First, argon inert gas was introduced to purge the air from the tube. Then, an acetylene mixture (volume ratio: acetylene:fluorine = 10:1; flow rate: 10 ml / min) was introduced, and carbonization was carried out at 700℃ for 6 hours. After that, the acetylene mixture was stopped, and the furnace was cooled to room temperature under an argon inert atmosphere. The material was then crushed and graded to obtain a hard carbon composite material with a double-layer shell structure. Example 3

[0053] Step S1:

[0054] 100g of sucrose was dissolved in 500g of deionized water, then 10g of ferric chloride was added, the mixture was dispersed evenly, spray-dried, and then carbonized at 900℃ for 1h under an inert argon atmosphere to obtain a hard carbon precursor.

[0055] Step S2:

[0056] 100g of hard carbon precursor was dispersed in 1000g of deionized water to prepare solution A with a mass concentration of 10wt%; 10g of silver oxalate was dissolved in 100g of deionized water to prepare solution B with a mass concentration of 10wt%; solution B was added to solution A under mechanical stirring, and then 50g of formamide was added to adjust pH=11. The mixture was then reacted at 150℃ for 1h to form a gel, filtered, and vacuum dried at 80℃ for 24h. The resulting material was then sintered at 1000℃ for 1h under an argon inert atmosphere, allowed to cool naturally to room temperature, and pulverized to obtain porous metal oxide-coated hard carbon material.

[0057] Step S3:

[0058] The porous metal oxide-coated hard carbon material was transferred to a tube furnace. First, argon inert gas was introduced to purge the air inside the tube. Then, an ethylene mixed gas (volume ratio: ethylene: bromine = 10:5; flow rate: 100 ml / min) was introduced, and carbonization was carried out at 1000℃ for 1 hour. After that, the ethylene mixed gas was stopped, and the furnace was cooled to room temperature under an argon inert atmosphere. The material was then crushed and graded to obtain a hard carbon composite material with a double-layer shell structure.

[0059] Comparative Example 1:

[0060] The hard carbon precursor from step S1 in the embodiment is transferred to a tube furnace. First, argon inert gas is introduced to purge the air from the tube. Then, a methane mixture (volume ratio: methane: chlorine = 10:3; flow rate: 50 ml / min) is introduced and carbonized at 800°C for 3 hours. After that, the methane mixture is stopped, and argon inert atmosphere is introduced and the temperature is lowered to room temperature. The mixture is then pulverized and graded to obtain the hard carbon composite material.

[0061] Comparative Example 2:

[0062] The porous metal oxide prepared in step S2 of Example 1 was used to coat the hard carbon material, which was then transferred to a tube furnace and carbonized at 800°C for 3 hours. After cooling to room temperature, the material was crushed and graded to obtain the hard carbon composite material.

[0063] Performance testing of the materials prepared in the above embodiments and comparative examples:

[0064] (1) SEM test

[0065] The hard carbon composite material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown.

[0066] Depend on Figure 1 As can be seen from the results, the composite material prepared in Example 1 exhibits a spherical structure with a uniform size distribution and a particle size between 3 and 6 µm.

[0067] (2) Physical and chemical performance testing

[0068] The particle size, tap density, specific surface area, powder conductivity, and powder OI value of the composite materials prepared in the examples and comparative examples were tested. The tests were conducted according to the methods specified in the national standard GB / T-24533-2019, "Graphite Anode Materials for Lithium-ion Batteries". The test results are shown in Table 1.

[0069] Table 1

[0070] serial number Powder conductivity (S / cm) Powder OI value <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Tap density (g / cm 3 )]]> Particle size (D50, µm) Example 1 103 3.5 7.76 0.89 6.5 Example 2 101 3.6 7.34 0.87 5.8 Example 3 94 3.7 7.12 0.84 5.4 Comparative Example 1 34 4.5 4.52 0.93 7.4 Comparative Example 2 78 4.0 5.67 0.80 6.8

[0071] As can be seen from Table 1, the hard carbon composite materials obtained in "Example 1", "Example 2" and "Example 3" are superior to the comparative examples in terms of powder conductivity and specific surface area. The reason is that the conductivity of the composite material is improved by coating the material surface with metal oxides, which rely on the high electronic conductivity of the metal oxides, and the specific surface area of ​​the material is improved by surface modification with mixed gas.

[0072] (3) Button cell battery test

[0073] The hard carbon composite material used in the examples and comparative examples was assembled into a coin cell as the negative electrode material for lithium-ion batteries. The specific preparation method of the negative electrode material was as follows: a binder, conductive agent, and solvent were added to the composite material, stirred to form a slurry, coated onto copper foil, and then dried and rolled. The conductive agent SP and the solvent was double-distilled water, prepared as a negative electrode sheet according to the composite material ratio of CMC:SBR:SP:H2O = 95:2.5:1.5:1:150mL; a lithium metal sheet was used as the counter electrode; the electrolyte was LiPF6 / EC+DEC, where LiPF6 was the electrolyte, and a 1:1 volume ratio mixture of EC and DEC was used as the solvent, with an electrolyte concentration of 1.3 mol / L; a polyethylene (PE) membrane was used as the separator. The coin cell assembly was carried out in an argon-filled glove box. Electrochemical performance was performed using a Wuhan Landian CT2001A battery tester. The charge / discharge voltage range was 0.00V to 1.5V, and the charge / discharge rate was 0.5C / 0.5C. The initial discharge specific capacity and initial charge / discharge efficiency of the coin cells were tested. Rate performance (2C / 0.1C), cycle performance (0.5C / 0.5C, 100 cycles), and DCR (DC resistance) were also tested. The test results are shown in Table 2.

[0074] Table 2

[0075] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 First discharge specific capacity (mAh / g) 418.3 416.4 412.5 332.2 395.5 First charge / discharge efficiency (%) 87.3 86.4 85.8 83.1 82.3 Cycling performance (0.5C / 0.5C, 100 cycles) 94.5% 94.2% 93.9% 91.1% 91.0% DCR (Ω) 23.5 26.9 28.7 43.5 32.5 Multiplier (2C / 0.1C) 92.2% 91.7% 91.0% 84.5% 84.0%

[0076] As can be seen from Table 2, the coin cells made with the hard carbon composite materials of "Example 1", "Example 2" and "Example 3" have significantly higher cycle life and rate performance than the comparative examples. This is because the hard carbon composite material prepared by the present invention through chemical reaction can uniformly and densely dope metal compounds in hard carbon, reduce impedance, improve kinetic performance and rate performance, and improve high-rate cycle performance.

[0077] (4) Soft-pack battery test:

[0078] The composite materials used in the examples and comparative examples were slurried and coated to prepare negative electrode sheets, using ternary materials (LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3A 5Ah pouch cell was prepared using O2 as the positive electrode, LiPF6 (solvent EC:DEC:PC = 1:1:1 volume ratio 1:1:1, electrolyte concentration 1.3mol / L) as the electrolyte, and Celgard 2400 membrane as the separator.

[0079] To test the electrolyte absorption capacity of the electrode: Use a pipette to draw 10 mL of electrolyte and then drop it onto the surface of the electrode. Observe the absorption time of the electrolyte on the surface of the electrode until it is completely absorbed. Record the time (S), which is the electrolyte absorption capacity of the electrode.

[0080] Electrode liquid retention rate: By testing the porosity of the electrode, the theoretical liquid retention capacity of the electrode is calculated as m1. Then, the electrode is immersed in the electrolyte, and the mass of electrolyte absorbed by the electrode is measured as m2. The liquid retention rate of the electrode is then calculated as m2 / m1*100%. The results are shown in Table 3.

[0081] Table 3

[0082] serial number Liquid aspiration rate (S) Liquid retention rate Example 1 17 93.1% Example 2 19 92.3% Example 3 23 91.2% Comparative Example 1 43 80.1% Comparative Example 2 36 84.9%

[0083] As can be seen from Table 3, the liquid absorption and retention capacity of the negative electrode prepared by the hard carbon composite material obtained in "Example 1", "Example 2" and "Example 3" is significantly better than that of the comparative example. The reason is that the hard carbon material in the examples has a high specific surface area, which improves the liquid absorption and retention performance of the electrode.

[0084] The rate performance of the pouch battery was then tested. The charge / discharge voltage range was 2.75–4.2V, and the temperature was 25±3.0℃. The batteries were charged at 1.0C, 3.0C, 5.0C, 10.0C, and 20.0C, and discharged at 1.0C. The charging capacity and constant current ratio were calculated. The results are shown in Table 4.

[0085] Table 4

[0086]

[0087] As shown in Table 4, the rate charging performance of the soft-pack batteries in "Example 1", "Example 2" and "Example 3" is significantly better than that of the comparative example, that is, the charging time is shorter. The reason for this is that the porous metal and amorphous carbon coated hard carbon materials deposited by chemical method and vapor deposition method have the advantages of high density and low impedance, thereby reducing the electronic impedance of the material and improving the rate performance.

[0088] High-temperature storage test: The battery capacity under full charge was tested at 60℃ and recorded as X1. After being placed at 60℃ for 30 days, the battery capacity was tested again and recorded as X2. The charge retention rate was calculated as X2 / X1*100%. The battery was then fully charged to 100% SOC and the battery capacity was tested as X3. The recovery capacity was calculated as X3 / X1*100%. The results are shown in Table 5.

[0089] Table 5

[0090] Example number Charge retention rate / % Capacity recovery rate / % Example 1 96.4% 98.5% Example 2 96.8% 98.4% Example 3 97.3% 98.9% Comparative Example 1 94.7% 96.1% Comparative Example 2 95.5% 97.3%

[0091] As can be seen from Table 5, the hard carbon composite materials prepared by “Example 1”, “Example 2” and “Example 3” have excellent high-temperature storage performance. The reason is that the hard carbon material is coated with a double-layer porous metal oxide and amorphous carbon to reduce the contact between its core hard carbon and the electrolyte, reduce its side reactions, and improve its high-temperature storage performance.

[0092] The hard carbon composite material is similar to that prepared by replacing the metal salt with one or more combinations of silver nitrate, silver acetate, silver oxalate, silver sulfate, silver n-butoxide, copper nitrate, copper acetate, copper oxalate, copper sulfate, and copper n-butoxide.

[0093] Replacing the alkaline solution with one or more of ammonia, urea, formamide, sodium hydroxide, potassium hydroxide, sodium bicarbonate, or potassium bicarbonate, the resulting hard carbon composite material is similar.

[0094] By replacing the metal salt compound with one or more combinations of nickel chloride, cobalt chloride, ferric chloride, copper chloride, and silver chloride, the resulting hard carbon composite material has similar properties.

[0095] By replacing hydrocarbons with one or more combinations of phenolic resin, glucose, sucrose, starch, and lignin, hard carbon composite materials with similar properties can be obtained.

[0096] The embodiments described above are merely preferred embodiments of the present invention. Ordinary variations and substitutions made by those skilled in the art within the scope of the technical solutions of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a hard carbon composite material with a double-layer shell structure, characterized in that, The implementation of the method includes: Hard carbon precursor raw material is mixed with metal salt A solution, spray dried and carbonized at high temperature to obtain hard carbon precursor. The hard carbon precursor and metal salt B are chemically deposited and sintered at high temperature to obtain porous metal oxide-coated hard carbon. By vapor-depositing halogen and carbon source gas, amorphous carbon containing halogen is coated onto the surface of the porous metal oxide-coated hard carbon to obtain the hard carbon composite material with the double-layer shell structure. The metal salt compound A is one or more of nickel chloride, cobalt chloride, ferric chloride, copper chloride, and silver chloride; The metal salt B is one or more of the following: silver nitrate, silver acetate, silver oxalate, silver sulfate, silver n-butoxide, copper nitrate, copper acetate, copper oxalate, copper sulfate, and copper n-butoxide. The preparation process of the porous metal oxide-coated hard carbon includes: The hard carbon precursor was dispersed in deionized water to prepare solution A with a mass concentration of 1-10 wt%. The metal salt B is dissolved in deionized water to prepare a solution B with a mass concentration of 1-10 wt%. Solution B is added to solution A, and then an alkaline solution is added to adjust the pH value to 8-11. The mixture is then reacted at 50-150℃ for 1-6 hours to form a gel. After filtration and vacuum drying, the resulting material is sintered at 600-1000℃ for 1-6 hours under an inert atmosphere. After natural cooling and pulverization, the porous metal oxide-coated hard carbon material is obtained.

2. The method for preparing a hard carbon composite material with a double-layer shell structure according to claim 1, characterized in that, The hard carbon precursor raw material is a hydrocarbon; The preparation process of the hard carbon precursor includes: The hydrocarbon was dissolved in deionized water, metal salt A was added, the mixture was dispersed evenly, spray-dried, and then carbonized at 600-900°C for 1-6 hours under an inert atmosphere to obtain the hard carbon precursor.

3. The method for preparing a hard carbon composite material with a double-layer shell structure according to claim 2, characterized in that, The mass ratio of the hard carbon precursor, metal salt A compound, and alkaline solution is 100:1 to 10:10 to 50.

4. The method for preparing a hard carbon composite material with a double-layer shell structure according to claim 3, characterized in that, The implementation of the method also includes: The porous metal oxide is coated onto the hard carbon material. First, an inert gas is introduced to purge the air from the pipe. Then, a carbon source mixture is introduced, and carbonization is carried out at a temperature of 700–1000°C for 1–6 hours. After carbonization, the material is cooled and crushed under an inert atmosphere to obtain the hard carbon composite material with the double-layer shell structure.

5. The method for preparing a hard carbon composite material with a double-layer shell structure according to claim 2, characterized in that, The hydrocarbon is one or more of phenolic resin, glucose, sucrose, starch, and lignin.

6. The method for preparing a hard carbon composite material with a double-layer shell structure according to claim 5, characterized in that, The mass ratio of the hydrocarbon compound to metal salt A is 100:1 to 10.

7. The method for preparing a hard carbon composite material with a double-layer shell structure according to claim 2, characterized in that, The alkaline solution is one or more of the following: ammonia, urea, formamide, sodium hydroxide, potassium hydroxide, sodium bicarbonate, and potassium bicarbonate.

8. The method for preparing a hard carbon composite material with a double-layer shell structure according to claim 4, characterized in that, The carbon source mixed gas is composed of a carbon source and a halogen gas, and the volume ratio of the carbon source to the halogen gas is 10:1 to 5; the flow rate is 10 to 100 ml / min. The carbon source is one or more of methane, ethane, ethylene, and acetylene; The halogen gas is one or more of chlorine, bromine, and fluorine.

9. A hard carbon composite material with a double-layer shell structure, characterized in that, The hard carbon composite material with the double-layer shell structure is prepared based on the method according to any one of claims 1-8; The composite material has a core-shell structure, with a core of hard carbon, a middle layer of porous metal oxide, and an outer shell of amorphous carbon. The thickness ratio of the core, intermediate layer and outer shell is 100:1 to 10:1 to 10.

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