Battery negative electrode coal-based hard carbon material and preparation method and application thereof

Abstract

The application relates to the technical field of sodium ion batteries, in particular to a battery negative electrode coal-based hard carbon material and a preparation method and application thereof. Through one-step oxidation molten salt method, Na2O2 is used as an oxidant, Na2CO3 generated by the reaction of Na2O2 and CO2 in the pre-oxidation process can be used as a cosolvent of the molten salt method, and the utilization rate of raw materials is improved. Moreover, the reaction of Na2O2 and CO2 generates O2, which is more conducive to forming C-O-C bridging bonds, controlling the yield of O2, and forming microporous channels; the obtained hard carbon material has a wider interlayer spacing of microcrystals and a larger sodium storage capacity, the reversible specific capacity is greater than 300 mAh / g, the first charge-discharge coulombic efficiency is high, and excellent sodium storage performance is exhibited; and a sodium ion battery with high energy density, long cycle life, excellent rate performance and lower cost can be obtained.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a coal-based hard carbon material for battery anodes, its preparation method, and its application. Technical Background

[0002] Today, the traditional energy structure is transforming at an unprecedented pace. As a representative of electrochemical energy storage technology, lithium-ion batteries have begun commercialization and large-scale application, developing particularly rapidly. While lithium-ion batteries boast advantages such as high energy density and long cycle life, the scarcity and uneven distribution of lithium resources limit their development. Sodium-ion batteries, due to their low cost and abundant natural resources, have become a promising direction for large-scale energy storage technology. The successful application of sodium-ion batteries largely depends on the innovation of low-cost, high-performance active electrode materials. For example, using graphite as the anode material in lithium-ion batteries significantly reduces costs while ensuring electrochemical performance. As the lowest-cost and highest-carbon natural carbon source, the conversion technology of coal into high-value carbon materials is of great significance to the development of anode materials for sodium-ion batteries. Coal, as a traditional energy source with abundant reserves and diverse types, possesses a molecular structure with moderate molecular weight and easy control, making it a potential precursor for hard carbon anodes used in sodium storage. The thermal conversion process of anthracite is also accompanied by intense microcrystalline rearrangement; how to suppress its graphitization trend is key to controlling the microstructure. Anthracite has a high degree of crystallinity, which makes it easy to form soft carbon materials with a high degree of graphitization during the carbonization process. Sodium-ion batteries require carbon materials with low graphitization (large interlayer spacing) and loose structure (pore structure <0.5nm). Therefore, widening the interlayer spacing of carbon materials is one of the important means to improve the sodium storage performance of coal-based carbon anodes.

[0003] Current research rarely focuses on the effective control of the microstructure of coal-based carbon materials. During high-temperature conversion, anthracite exhibits a trend of vertical stacking, lateral growth, and tight interlayer spacing in its microcrystalline structure, which is significantly inhibited after modification. To achieve effective control of the microcrystalline structure, current research widely employs gas-phase and liquid-phase pre-oxidation methods, successfully preparing a series of hard carbon materials with different crystallite sizes. Results show that gas-phase and liquid-phase oxidation introduces oxygen-containing functional groups, primarily carbonyl groups, promoting the formation of cross-linked structures and thus inhibiting the graphitization process of bituminous coal. Compared to raw anthracite, heating with a mixed pre-oxidant yields hard carbon materials with wider interlayer spacing. Furthermore, the molten salt method can form ideal microcrystalline structures. The salt, in its molten state, shuttles within the carbon material framework, inhibiting microcrystalline growth and forming ultrapores (size <0.5 nm), which are beneficial for sodium ion storage. However, the molten salt process introduces impurities of alkali metal elements, which reduces the specific capacity of the negative electrode material. This is something we need to overcome in the process. Using sodium salt as a co-solvent can effectively solve this problem and also play a role in pre-intercalation of sodium, thereby improving the initial coulombic efficiency.

[0004] Both the pre-oxidation and molten salt methods mentioned above can effectively widen the spacing of the carbon layers. However, due to the selection of pre-oxidants and co-solvents, as well as the lack of synergy in heat treatment, they become two different process steps. The complex process increases the cost of industrial production, and the process route needs to be optimized. Summary of the Invention

[0005] To address the problems associated with using coal-based carbon materials as anode materials in sodium-ion batteries, and to shorten the process and reduce costs, this invention provides a coal-based hard carbon material for battery anodes. This hard carbon material is prepared via a one-step molten salt oxidation method, exhibiting a wider interlayer spacing, greater sodium storage capacity, a reversible specific capacity greater than 300 mAh / g, and high initial charge-discharge coulombic efficiency, demonstrating excellent sodium storage performance. This results in a sodium-ion battery with high energy density, long cycle life, excellent rate performance, and lower cost.

[0006] The technical solution of the present invention is as follows:

[0007] A coal-based hard carbon material for battery negative electrode is obtained by uniformly mixing pulverized coal powder with an oxidation promoter and a co-solvent, carbonizing it at high temperature, and then coating it with pyrolytic carbon.

[0008] The oxidation accelerator is sodium peroxide powder; the co-solvent is sodium chloride.

[0009] The method for preparing the above-mentioned coal-based hard carbon material for battery anode is characterized by comprising the following steps:

[0010] (1) One-step oxidation molten salt method: The pretreated coal powder is mixed evenly with the oxidation promoter and the co-solvent, heated under an oxidizing atmosphere, and then heated to a high temperature under a protective atmosphere for molten salt treatment;

[0011] (2) High-temperature heat treatment: After the material treated in step (1) is washed with water to remove the molten salt, it is heated at high temperature under a protective atmosphere;

[0012] (3) Pyrolytic carbon coating: The material obtained in step (2) is heated under a protective atmosphere and then a gaseous carbon source is introduced. The carbon is coated by chemical vapor deposition to obtain the hard carbon anode material for sodium-ion batteries.

[0013] Preferably, in step (1), the mass ratio of coal powder to oxidation promoter and co-solvent is 10:(0.5~4):(0.5~4).

[0014] Preferably, the oxidation atmosphere in step (1) is CO2, and the flow rate is 0.1-5 L / min for 1 kg of carbon source; the oxidation temperature is 200-500 ºC and the holding time is 0.5-5 h; then the temperature is raised to 500-1000ºC under a protective atmosphere and the holding time is 0.5-5 h.

[0015] Preferably, the carbonization temperature in step (2) is 1000~1600ºC, the holding time is 0.5~5h, and the protective atmosphere is N2 or Ar.

[0016] Preferably, the gaseous carbon source in step (3) is one or more of methane, acetylene, propylene or propane, and the gas flow rate is 0.5~3L / min; the conditions for the vapor deposition method are: temperature of 500-900ºC and time of 60~200min.

[0017] Preferably, the pretreatment process of the coal powder in step (1) is deashing treatment to remove impurities inside the coal powder and improve its purity.

[0018] Application of the coal-based hard carbon material for battery anodes prepared by the above method in sodium-ion batteries.

[0019] Coal powder is heat-treated together with an oxidation accelerator and a co-solvent. Both the oxidation accelerator and the co-solvent are sodium-based compounds, which can pre-intercalate sodium into the carbon layer, improving the initial coulombic efficiency. Na2O2 is used as the oxidant, and the Na2CO3 generated during the pre-oxidation process can serve as a co-solvent in the molten salt method, improving the utilization rate of raw materials. Moreover, the reaction of Na2O2 and CO2 to generate O2 is more conducive to the formation of COC bridging bonds. Controlling the O2 yield also facilitates the formation of micropores.

[0020] The beneficial effects of this invention are:

[0021] The present invention provides a method for preparing coal-based hard carbon materials for sodium-ion batteries that ingeniously combines pre-oxidation and molten salt methods. By using a one-step process that combines oxidation and molten salt treatment, the microstructure of the carbon material is adjusted to facilitate sodium ion storage. The anode material prepared by this method has a wider interlayer spacing, a larger sodium storage capacity, a reversible specific capacity greater than 300 mAh / g, and high initial charge-discharge coulombic efficiency, exhibiting excellent sodium storage performance. This results in a sodium-ion battery with high energy density, long cycle life, excellent rate performance, and lower cost. The preparation process of the sodium-ion battery hard carbon anode material provided by this invention is simple and continuous, has low production costs, and the raw materials can be recycled, which can well meet industrial needs. Attached Figure Description

[0022] Figure 1 SEM image of the coal-based hard carbon material prepared in Example 1;

[0023] Figure 2 TEM image of the coal-based hard carbon material prepared in Example 1;

[0024] Figure 3 The constant current charge-discharge curve of the coal-based hard carbon material prepared in Example 1 is shown. Detailed Implementation

[0025] Example 1

[0026] A method for preparing a coal-based hard carbon material for battery anodes, comprising the following steps:

[0027] (1) Put the smokeless coal powder into a grinder and grind it to 150 mesh, sieve it, and then grind the sieved material into 200 mesh in a ball mill;

[0028] (2) Take 50 g of sieved coal powder, add 200 mL of deashing solution (volume ratio, distilled water: 37% HCl: 40% HF = 50: 30: 20), heat in a 90ºC water bath for 4 h, filter, and rinse with hot water until neutral;

[0029] (3) Mix the treated coal powder with the oxidation promoter sodium peroxide and the co-solvent sodium chloride at a mass ratio of 100:5:5, place it in a high-temperature furnace, heat it to 300ºC under a carbon dioxide atmosphere, keep it at that temperature for 1 h, and then heat it to 1000ºC under nitrogen protection and keep it at that temperature for 1 h.

[0030] (4) The treated coal powder is washed with water to remove molten salt, and then put back into the high-temperature furnace and carbonized at 1100ºC for 0.5 h under a nitrogen atmosphere;

[0031] (5) Add the carbon material from step (4) into the rotary kiln, heat it to 800ºC, and introduce acetylene (C2H2) gas at a flow rate of 1.5 L / min.-1 The acetylene gas was introduced for 10 minutes, then the acetylene gas was turned off, and N2 was introduced. The mixture was kept at this temperature for 120 minutes to obtain the carbon material for the negative electrode of a sodium-ion battery.

[0032] Example 2

[0033] A method for preparing a coal-based hard carbon material for battery anodes, comprising the following steps:

[0034] (1) Put the smokeless coal powder into a grinder and grind it to 100 mesh, sieve it, and then grind the sieved material into 150 mesh in a ball mill;

[0035] (2) Take 50 g of sieved coal powder, add 150 mL of deashing solution (volume ratio: distilled water: 37% HCl: 40% HF = 40: 30: 30), heat in an 80ºC water bath for 6 h, filter, and rinse with hot water until neutral;

[0036] (3) The treated coal powder is mixed evenly with the oxidation promoter sodium peroxide and the co-solvent sodium chloride at a mass ratio of 100:20:20, placed in a high-temperature furnace, heated to 400ºC under a carbon dioxide atmosphere, kept at the temperature for 3 h, and then heated to 1100ºC under nitrogen protection and kept at the temperature for 0.5 h.

[0037] (4) The treated coal powder is washed with water to remove molten salt, and then put back into the high-temperature furnace and heated to 1400ºC for 2 h under a nitrogen atmosphere.

[0038] (5) Add the carbon material from step (4) into the rotary kiln, heat it to 900 °C, and introduce methane gas at a flow rate of 1.5 L / min. -1 The methane gas is introduced for 10 minutes, then the methane gas is turned off and N2 is introduced. The mixture is kept at this temperature for 60 minutes to obtain the carbon material for the negative electrode of sodium-ion batteries.

[0039] Example 3

[0040] A method for preparing a coal-based hard carbon material for battery anodes, comprising the following steps:

[0041] (1) Put the anthracite into a grinder and grind it to 200 mesh, sieve it, and then grind the sieved material into 250 mesh in a ball mill;

[0042] (2) Take 50 g of sieved coal powder, add 300 mL of deashing solution (volume ratio, distilled water: 37% HCl: 40% HF = 30: 40: 30), heat in a 70 ºC water bath for 10 h, filter, and rinse with hot water until neutral;

[0043] (3) Mix the treated coal powder with the oxidation promoter sodium peroxide and the co-solvent sodium chloride at a mass ratio of 100:40:40, place it in a high-temperature furnace, heat it to 500 ºC under a carbon dioxide atmosphere, keep it at the temperature for 4 h, and then heat it to 700 ºC under nitrogen protection and keep it at the temperature for 5 h.

[0044] (4) The treated coal powder is washed with water to remove molten salt, and then put back into the high-temperature furnace and heated to 1500 ºC for 3 h under a nitrogen atmosphere;

[0045] (5) Add the carbon material from step (4) into the rotary kiln, heat it to 500 °C, and introduce acetylene (C2H2) gas at a flow rate of 1.5 L / min. -1 The acetylene gas was introduced for 20 minutes, then the acetylene gas was turned off, and N2 was introduced. The mixture was kept at this temperature for 200 minutes to obtain the carbon material for the negative electrode of a sodium-ion battery.

[0046] Example 4

[0047] A method for preparing a coal-based hard carbon material for battery anodes, comprising the following steps:

[0048] (1) Put lignite powder into a grinder and grind it to 100 mesh, sieve it, and then grind the sieved material into 150 mesh in a ball mill;

[0049] (2) Take 50 g of sieved coal powder, add 400 mL of deashing solution (volume ratio, distilled water: 37% HCl: 40% HF = 40: 30: 30), heat in a 90 ºC water bath for 4 h, filter, and rinse with hot water until neutral;

[0050] (3) Mix the treated coal powder with the oxidation promoter sodium peroxide and the co-solvent sodium chloride at a mass ratio of 100:30:30, place it in a high-temperature furnace, heat it to 300ºC under a carbon dioxide atmosphere, keep it at that temperature for 2 h; then heat it to 500ºC under nitrogen protection and keep it at that temperature for 5 h.

[0051] (4) The treated coal powder is washed with water to remove molten salt, and then put back into the high-temperature furnace and heated to 1600 ºC for 2 h under an argon atmosphere;

[0052] (5) Add the carbon material from step (4) into the rotary kiln, heat it to 900 °C, and introduce methane gas at a flow rate of 1.5 L / min. -1 The methane gas is introduced for 15 minutes, then the methane gas is turned off and N2 is introduced. The mixture is kept at this temperature for 60 minutes to obtain the carbon material for the negative electrode of sodium-ion batteries.

[0053] Example 5

[0054] A method for preparing a coal-based hard carbon material for battery anodes, comprising the following steps:

[0055] (1) Put the bituminous coal powder into a grinder and grind it to 100 mesh, sieve it, and then grind the sieved material into 150 mesh in a ball mill;

[0056] (2) Take 50 g of sieved coal powder, add 200 mL of deashing solution (volume ratio, distilled water: 37% HCl: 40% HF = 40: 30: 30), heat in a 90ºC water bath for 4 h, filter, and rinse with hot water until neutral;

[0057] (3) Mix the treated coal powder with the oxidation promoter sodium peroxide and the co-solvent sodium chloride at a mass ratio of 100:30:30, place it in a high-temperature furnace, heat it to 300ºC under a carbon dioxide atmosphere, keep it at that temperature for 5 h, and then heat it to 800ºC under nitrogen protection and keep it at that temperature for 4 h.

[0058] (4) The treated coal powder is washed with water to remove molten salt, and then put back into the high-temperature furnace and heated to 1400ºC for 2 h under a nitrogen atmosphere.

[0059] (5) Add the carbon material from step (4) into the rotary kiln, heat it to 900 °C, and introduce methane gas at a flow rate of 1.5 L / min. -1 The methane gas is introduced for 15 minutes, then the methane gas is turned off and N2 is introduced. The mixture is kept at this temperature for 60 minutes to obtain the carbon material for the negative electrode of sodium-ion batteries.

[0060] Comparative Example 1

[0061] A method for preparing a coal-based hard carbon material for battery anodes, comprising the following steps:

[0062] (1) Put the smokeless coal powder into a grinder and grind it to 150 mesh, sieve it, and then grind the sieved material into 200 mesh in a ball mill;

[0063] (2) Take 50 g of sieved coal powder, add 200 mL of deashing solution (volume ratio, distilled water: 37% HCl: 40% HF = 40: 30: 30), heat in a 90ºC water bath for 4 h, filter, and rinse with hot water until neutral;

[0064] (3) Mix the treated coal powder with the oxidation accelerator sodium peroxide at a mass ratio of 100:15, place it in a high-temperature furnace, heat it to 300ºC under a carbon dioxide atmosphere, and keep it at that temperature for 4 hours; then take out the material and mix it with the co-solvent sodium chloride at a mass ratio of 100:15, place it in a high-temperature furnace again, and heat it to 900ºC under nitrogen protection for 4 hours.

[0065] (4) The treated coal powder is washed with water to remove molten salt, and then put back into the high-temperature furnace and carbonized at 1100ºC for 2 hours under a nitrogen atmosphere.

[0066] (5) Add the carbon material from step (4) into the rotary kiln, heat it to 800ºC, and introduce acetylene C2H2 gas at a flow rate of 1.5 L / min. -1 The acetylene gas was introduced for 10 minutes, then N2 was introduced and kept at that temperature for 120 minutes; thus, carbon material for the negative electrode of sodium-ion batteries was obtained.

[0067] Comparative Example 2

[0068] A method for preparing a coal-based hard carbon material for battery anodes, comprising the following steps:

[0069] (1) Put the smokeless coal powder into a grinder and grind it to 100 mesh, sieve it, and then grind the sieved material into 150 mesh in a ball mill;

[0070] (2) Take 50 g of sieved coal powder, add 200 mL of deashing solution (volume ratio, distilled water: 37% HCl: 40% HF = 40: 30: 30), heat in a 90ºC water bath for 4 h, filter, and rinse with hot water until neutral;

[0071] (3) Mix the treated coal powder with 30% potassium nitrate solution as an oxidation promoter and sodium chloride as a co-solvent at a mass ratio of 100:30:30. Place the mixture in a high-temperature furnace and heat it to 300ºC under a nitrogen atmosphere. After holding the temperature for 1 h, raise the temperature to 800ºC and hold it for 5 h.

[0072] (4) The treated coal powder is washed with water to remove molten salt, and then put back into the high-temperature furnace and heated to 1100 ºC for 2 h under a nitrogen atmosphere;

[0073] (5) Add the carbon material from step (4) into the rotary kiln, heat it to 900 °C, and introduce methane gas at a flow rate of 1.5 L / min. -1 The methane gas is introduced for 10 minutes, then the methane gas is turned off and N2 is introduced. The mixture is kept at this temperature for 60 minutes to obtain the carbon material for the negative electrode of sodium-ion batteries.

[0074] Comparative Example 3

[0075] A method for preparing a coal-based hard carbon material for battery anodes, comprising the following steps:

[0076] (1) Put the smokeless coal powder into a grinder and grind it to 100 mesh, sieve it, and then grind the sieved material into 150 mesh in a ball mill;

[0077] (2) Take 50 g of sieved coal powder, add 200 mL of deashing solution (volume ratio, distilled water: 37% HCl: 40% HF = 40: 30: 30), heat in a 90 ºC water bath for 4 h, filter, and rinse with hot water until neutral;

[0078] (3) Mix the treated coal powder with the oxidation promoter sodium peroxide at a mass ratio of 100:30, place it in a high-temperature furnace, heat it to 300 ºC under a carbon dioxide atmosphere, keep it at that temperature for 5 h, then switch to a nitrogen atmosphere, raise the temperature to 800 ºC, and keep it at that temperature for 5 h.

[0079] (4) The treated coal powder is washed with water to remove molten salt, and then put back into the high-temperature furnace and heated to 1100 ºC for 2 h under a nitrogen atmosphere;

[0080] (5) Add the carbon material from step (4) into the rotary kiln, heat it to 900 °C, and introduce methane gas at a flow rate of 1.5 L / min. -1 The methane gas is introduced for 10 minutes, then the methane gas is turned off and N2 is introduced. The mixture is kept at this temperature for 60 minutes to obtain the carbon material for the negative electrode of sodium-ion batteries.

[0081] Except that sodium chloride is no longer added as a co-solvent in step (3) of Example 2, and only sodium carbonate Na2CO3 generated by the reaction of oxidant Na2O2 and CO2 is used as a co-solvent, the conditions such as molten salt temperature and holding time remain unchanged; the subsequent processing repeats the steps in Example 2, and thus the carbon material for sodium-ion battery negative electrode is obtained.

[0082] Simulated battery assembly and testing

[0083] The carbon material used for the sodium-ion battery negative electrode prepared above was ground and mixed with a conductive agent and sodium alginate binder at a mass ratio of 90:5:5 until homogeneous. An appropriate amount of pure water was added, and the mixture was ground again to form a uniformly dispersed slurry. This slurry was then coated onto a current collector aluminum foil (with an areal density controlled at 6 mg / cm²). 2 After drying at 70 ºC, the electrode sheets were punched into 12 mm diameter sheets and dried at 120 ºC for 5 hours under vacuum. They were then transferred to an argon-filled glove box for later use. The simulated battery assembly was performed in an Ar atmosphere glove box, using metallic sodium as the counter electrode and a 1 mol / L NaPF6 solution as the electrolyte. The NaPF6 solution consisted of ethylene carbonate and diethyl carbonate in a 1:1 volume ratio. Glass fiber filter paper was used as the separator. The electrode sheets from the examples and comparative examples were assembled into CR2032 coin cells. Constant current charge-discharge tests were performed using a Blue Electric charge-discharge tester at a C / 10 current density, with a discharge cutoff voltage of 0V and a charging cutoff voltage of 2V. The assembled simulated batteries underwent charge-discharge tests, and the results are shown in Table 1.

[0084]

[0085] Finally, the method of the present invention is merely a preferred embodiment and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made without departing from the principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A coal-based hard carbon material for battery anodes, characterized in that, The pulverized coal powder is mixed evenly with an oxidation accelerator and a co-solvent, heated under an oxidizing atmosphere, and then heated to a high temperature under a protective atmosphere for molten salt treatment; after high-temperature carbonization, it is coated with pyrolytic carbon to obtain the final product; the pyrolytic carbon coating is carbon coating by chemical vapor deposition under a protective atmosphere. The oxidation accelerator is sodium peroxide powder; the co-solvent is sodium chloride. The oxidizing atmosphere is CO2, the oxidizing heating temperature is 200~500℃, and the molten salt temperature is 500℃~1100℃.

2. A method for preparing the coal-based hard carbon material for the battery negative electrode as described in claim 1, characterized in that, Includes the following steps: (1) One-step oxidation molten salt method: The pretreated coal powder is mixed evenly with the oxidation promoter and the co-solvent, heated under an oxidizing atmosphere, and then heated to a high temperature under a protective atmosphere for molten salt treatment; (2) High-temperature heat treatment: After the material treated in step (1) is washed with water to remove the molten salt, it is heated at high temperature under a protective atmosphere; (3) Pyrolytic carbon coating: The material obtained in step (2) is heated under a protective atmosphere and then a gaseous carbon source is introduced. The carbon is coated by chemical vapor deposition to obtain the hard carbon anode material for the battery.

3. The preparation method according to claim 2, characterized in that, In step (1), the mass ratio of coal powder to oxidation promoter and co-solvent is 10:0.5~4:0.5~4.

4. The preparation method according to claim 2, characterized in that, In step (1), the flow rate of the oxidizing atmosphere is 0.1-5 L / (min·1kg coal powder); the holding time for oxidizing heating is 0.5-4 h; and the holding time for molten salt is 0.5-5 h.

5. The preparation method according to claim 2, characterized in that, The high-temperature heating treatment in step (2) is 1000~1400℃, the holding time is 0.5~5h, and the protective atmosphere is N2.

6. The preparation method according to claim 2, characterized in that, The gaseous carbon source in step (3) is one or more of methane, acetylene, propylene or propane, and the gas flow rate is 0.5~3L / min; the conditions for the vapor deposition method are: temperature of 500-900℃ and time of 10~200min.

7. The preparation method according to claim 2, characterized in that, The pretreatment process for pulverized coal in step (1) is: ash removal.

8. The application of the coal-based hard carbon material for battery anodes obtained by the preparation method according to any one of claims 2-7 in sodium-ion batteries.

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