Coal-based hard carbon material, preparation method thereof and application of the coal-based hard carbon material as negative electrode material of sodium ion battery

Abstract

The application discloses a coal-based hard carbon material, a preparation method thereof and application of the coal-based hard carbon material as a negative electrode material of a sodium ion battery, and belongs to the technical field of sodium ion battery materials. Coal powder is subjected to one-stage wet ball milling with an activator solution, the one-stage ball milling mixture is filtered and dried to obtain pre-activated material; the pre-activated material is subjected to one-stage carbonization treatment, the carbonization product is subjected to acid pickling and drying to obtain pre-carbonized material; the pre-carbonized material is subjected to two-stage wet ball milling with a modifier solution, the two-stage ball milling mixture is filtered and dried to obtain activated material; the activated material is subjected to two-stage carbonization treatment to obtain a coal-based hard carbon material with a high sodium storage capacity and a pore structure of short-range order and long-range disorder; the coal-based hard carbon material is applied as a negative electrode material of a sodium ion battery, and the obtained sodium ion battery exhibits high reversible specific capacity, a first coulomb efficiency and excellent charge-discharge cycle stability.

Description

Technical Field

[0001] This invention relates to a hard carbon material, particularly a modified coal-based hard carbon material, and also to a method for improving the performance of coal-based hard carbon materials based on mechanical activation and chemical modification, as well as the application of coal-based hard carbon materials as anode materials for sodium-ion batteries, belonging to the field of battery technology. Background Technology

[0002] Lithium-ion batteries possess advantages such as excellent stability, high energy density, and low self-discharge rate, and have entered commercial applications. However, the high price and limited resources of lithium restrict their development. Sodium-ion batteries, due to their lower cost, abundant storage capacity, safety, environmental friendliness, and outstanding low-temperature performance, are gradually becoming a strong competitor to lithium-ion batteries. The working principle of sodium-ion batteries is similar to that of lithium-ion batteries; however, due to the unique properties of sodium... + Because it is difficult to form stable intercalation compounds with graphite, sodium-ion batteries cannot directly use commercially available graphite from lithium-ion batteries as the anode material. Therefore, the development of high-capacity sodium-ion battery anode materials is urgently needed.

[0003] Hard carbon materials, as a type of carbon that is difficult to graphitize, tend to have shorter processing ranges during high-temperature carbonization and possess high sodium-ion storage capacity, making them the most promising anode material for commercial applications in sodium-ion batteries. Currently, the mainstream precursor raw materials for hard carbon materials include biomass, resins, and pitch; however, due to issues such as unstable raw material supply, high prices, and complex preparation processes, large-scale industrialization is difficult. Coal, as an abundant, inexpensive, and high-carbon source, is a highly promising precursor raw material for the preparation of hard carbon materials.

[0004] However, coal has a relatively stable structure, and direct carbonization easily produces an ordered graphite-like structure, which is not conducive to increasing the sodium ion storage capacity. Summary of the Invention

[0005] In view of the technical problems in the existing technology, such as the stable structure of coal and the tendency for direct carbonization to generate ordered graphite-like structures, which is not conducive to improving the sodium ion storage capacity, the first objective of this invention is to provide a coal-based hard carbon material with a short-range ordered and long-range disordered pore structure, which endows it with a high sodium storage capacity and meets the requirements of hard carbon anode materials for sodium-ion batteries.

[0006] The second objective of this invention is to provide a method for preparing coal-based hard carbon materials, which uses coal powder as raw material, has low cost, simple process, and is conducive to industrial production.

[0007] The third objective of this invention is to provide an application of a coal-based hard carbon material as a negative electrode material for sodium-ion batteries, resulting in sodium-ion batteries exhibiting high reversible specific capacity, initial coulombic efficiency, and excellent charge-discharge cycle stability.

[0008] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing a coal-based hard carbon material, the method comprising the following steps:

[0009] S1: Coal powder and activator solution are subjected to a first-stage wet ball milling process. The ball-milled mixture is then filtered and dried to obtain a pre-activated material. The activator solution includes at least one of sodium hypochlorite solution, potassium dichromate solution, potassium hydroxide solution, and potassium permanganate solution.

[0010] S2: The pre-activated material is subjected to a carbonization process, and the carbonization product is acid washed and dried to obtain the pre-carbonized material;

[0011] S3: The pre-carbonized material and the modifier solution are subjected to two-stage wet ball milling. The mixture from the two-stage ball milling is filtered and dried to obtain the activated material. The modifier solution is a kerosene solution of organic peroxide.

[0012] S4: The activated material is subjected to a two-stage carbonization process to obtain coal-based hard carbon material.

[0013] Based on the relatively stable structure of pulverized coal, direct carbonization easily generates an ordered graphite-like structure. The key to this invention lies in employing a two-stage ball milling process, combined with activators and modifiers, to activate and modify the pulverized coal, enabling it to easily form a short-range ordered, long-range disordered pore structure during high-temperature carbonization. In the first stage of mechanical ball milling and activator action, the pulverized coal particle size is refined, and it undergoes an oxidation reaction with the activator, destroying its macromolecular structure and introducing more oxygen-containing functional groups. The low-temperature pre-carbonization process promotes the volatilization of small molecules, disrupting the complexation of impurity elements with the pulverized coal, thus achieving better deep deashing during acid washing. In the second stage of ball milling, organic peroxides are used to further activate and modify the pre-carbonized material. Under high-temperature carbonization, the abundant oxygen-containing functional groups inhibit the excessive formation of graphitized structures, promoting the formation of a short-range ordered, long-range disordered pore structure, thereby obtaining a hard carbon material with higher sodium storage capacity.

[0014] As a preferred embodiment, the pulverized coal is pre-treated by acid washing and deashing to reduce the ash content to below 1%. This deashing treatment improves the sodium storage capacity of the hard carbon material.

[0015] As a preferred embodiment, the concentration of the activator solution is 0.1–1 mol / L.

[0016] As a preferred embodiment, the conditions for the first-stage wet ball milling are: a liquid-to-solid ratio of 5–10 mL:1 g, a ball-to-material mass ratio of 1:0.5–0.1, a rotation speed of 200–500 r / min, and a time of 1–5 h. Under the mechanical force of the ball mill, the coal powder and activator are fully mixed, resulting in numerous defects on the surface of the coal powder, which enhances its reactivity and reduces the activation energy required for the reaction between the coal powder and the activator. If the ball milling speed is too low or the time is too short, the activation purpose will not be achieved, while if the ball milling speed is too high or the time is too long, energy consumption will increase.

[0017] As a preferred embodiment, the conditions for the first-stage carbonization treatment are: under a protective atmosphere, at a temperature of 300–800°C, for a time of 1–3 hours. The first-stage carbonization treatment is mainly carried out at a relatively low temperature, and low-temperature pre-carbonization can promote the volatilization of small organic molecules, while breaking the complexation of impurity elements with coal powder, thereby enabling the pickling process to achieve better deep deashing.

[0018] As a preferred embodiment, the mass percentage concentration of organic peroxide in the modifier solution is 5-10%. Kerosene is used as the solvent in the modifier solution. Firstly, kerosene has good wetting properties for the pre-carbonized material, which facilitates the full action of the organic peroxide on the pre-carbonized material. Secondly, it provides a reaction medium for the activation and modification reaction between the pre-carbonized material and the modifier. Thirdly, kerosene itself can react with the pre-carbonized material and remain in the pre-carbonized material in a branched form, playing a pore-forming role during the high-temperature carbonization process through vaporization and fracture.

[0019] As a preferred embodiment, the organic peroxide includes at least one of hydrogen peroxide, peracetic acid, and cycloacetone peroxide.

[0020] As a preferred embodiment, the conditions for the two-stage wet ball milling are: a liquid-to-solid ratio of 2–6 mL:1 g, a ball-to-material mass ratio of 1:0.5–0.1, a rotation speed of 100–300 r / min, and a time of 30–60 min. Under the mechanical force of the ball mill, the pre-carbonized material and the modifier are thoroughly mixed, allowing the modifier to fully penetrate the interior of the pre-carbonized material. Simultaneously, the mechanical ball milling enhances the reactivity of the pre-carbonized material, reducing the activation energy required for the reaction between the coal powder and the modifier. If the ball milling speed is too low or the time is too short, the modification objective will not be achieved, while if the ball milling speed is too high or the time is too long, energy consumption will increase.

[0021] As a preferred embodiment, the conditions for the two-stage carbonization treatment are: under an inert atmosphere, at a temperature of 1200–1600°C, for a time of 1–3 hours. The two-stage carbonization treatment is carried out at a relatively high temperature, which is beneficial for improving the degree of carbonization of the pre-carbonized material.

[0022] This invention also provides a coal-based hard carbon material obtained by the aforementioned preparation method. The coal-based hard carbon material provided by this invention has a short-range ordered, long-range disordered microporous structure, which differs from hard carbon materials formed by conventional carbonization of coal powder.

[0023] This invention also provides an application of a coal-based hard carbon material as a negative electrode material for sodium-ion batteries.

[0024] The resulting sodium-ion battery exhibits high reversible specific capacity, initial coulombic efficiency, and excellent charge-discharge cycle stability.

[0025] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects:

[0026] The coal-based hard carbon material provided by this invention has a short-range ordered and long-range disordered pore structure, exhibiting high sodium storage capacity. When used as an anode material for sodium-ion batteries, the resulting sodium-ion batteries demonstrate high reversible specific capacity, initial coulombic efficiency, and excellent charge-discharge cycle stability. For example, the reversible specific capacity is greater than 300 mAh / g, the initial coulombic efficiency is higher than 78%, and the capacity retention rate is over 95% after 100 charge-discharge cycles.

[0027] The method for preparing coal-based hard carbon materials provided by this invention has simple operation, low cost, stable raw material supply, and broad prospects for commercial application. Attached Figure Description

[0028] Figure 1 The first charge-discharge specific capacity curves of the hard carbon materials prepared in Example 1 and Comparative Examples 1-4 are shown.

[0029] Figure 2 Charge-discharge cycle performance curves of the hard carbon materials prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0030] The following examples are intended to further illustrate the present invention, but not to limit the scope of protection of the claims of the present invention.

[0031] The performance testing methods for the hard carbon materials involved in the following specific embodiments and comparative embodiments are uniformly described as follows: The prepared hard carbon material was mixed with Super P and PVDF in a ratio of 8:1:1 to form a slurry, which was then coated onto copper foil and dried in a vacuum oven for 12 hours. After cutting, hard carbon electrode sheets were obtained. Then, button half-cells were assembled in an argon-filled glove box. Sodium sheets were used as the negative electrode, glass fiber was used as the separator, and 1M NaClO4 (solvent: EC:EDC = 1:1, Vol%) was used as the electrolyte. The assembled battery underwent electrochemical performance testing using a Blue Battery Tester, with a charge / discharge voltage range of 0-2V and a current density of 20mA / g.

[0032] In the following specific examples, the pulverized coal is pre-treated by acid washing and deashing until the ash content is less than 1%.

[0033] Example 1

[0034] 30g of coal powder and 300mL of 0.1mol / L sodium hypochlorite solution were added to a ball mill and ball-milled for 3 hours, with a ball-to-material ratio of 1:0.2 and a ball milling speed of 300r / min. After ball milling, the material was filtered and dried. The dried material was carbonized at 600℃ under an inert atmosphere for 2 hours, and then washed with 3mol / L hydrochloric acid for 1 hour to remove introduced impurities. After filtration and drying, an intermediate material was obtained. 10g of the intermediate material and 30ml of a mixture of kerosene and hydrogen peroxide were added to a ball mill and ball-milled for 30 minutes, with a kerosene to hydrogen peroxide mass ratio of 1:0.1 and a ball-to-material ratio of 1:0.1. The ball milling speed was 200r / min. After ball milling, the material was filtered and dried. The material dried by ball milling was carbonized at 1400℃ under an inert atmosphere for 2 hours, cooled to room temperature with the furnace, and then thoroughly ground to obtain a hard carbon material. The prepared material was tested and found to have a reversible specific capacity of 319.8 mAh / g, a coulombic efficiency of 80.4% in the first week, and a capacity retention of 95.3% after 100 charge-discharge cycles.

[0035] Example 2

[0036] 30g of coal powder and 150mL of 1mol / L potassium hydroxide solution were added to a ball mill and ball-milled for 5 hours, with a ball-to-material ratio of 1:0.5 and a ball milling speed of 200r / min. After ball milling, the material was filtered and dried. The dried material was carbonized at 300℃ under an inert atmosphere for 3 hours, and then washed with 3mol / L hydrochloric acid for 1 hour to remove introduced impurities. After filtration and drying, an intermediate material was obtained. 10g of the intermediate material and 60ml of a mixture of kerosene and peracetic acid were added to a ball mill and ball-milled for 60 minutes, with a kerosene to peracetic acid mass ratio of 1:0.05 and a ball-to-material ratio of 1:0.5. The ball milling speed was 100r / min. After ball milling, the material was filtered and dried. The material after the second ball milling and drying was carbonized at 1500℃ under an inert atmosphere for 1 hour, cooled to room temperature with the furnace, and thoroughly ground to obtain a hard carbon material. The prepared material was tested and found to have a reversible specific capacity of 307.6 mAh / g, a coulombic efficiency of 77.8% in the first week, and a capacity retention of 95.8% after 100 charge-discharge cycles.

[0037] Example 3

[0038] 30g of coal powder and 200mL of 0.1mol / L potassium permanganate solution were added to a ball mill and ball-milled for 1 hour, with a ball-to-material ratio of 1:0.1 and a ball milling speed of 500r / min. After ball milling, the material was filtered and dried. The dried material was carbonized at 800℃ under an inert atmosphere for 1 hour, and then washed with 3mol / L hydrochloric acid for 1 hour to remove introduced impurities. After filtration and drying, an intermediate material was obtained. 10g of the intermediate material and 20ml of a mixture of kerosene and cyclopropanone peroxide were added to a ball mill and ball-milled for 40 minutes, with a kerosene to cyclopropanone peroxide mass ratio of 1:0.08 and a ball-to-material ratio of 1:0.3. The ball milling speed was 300r / min. After ball milling, the material was filtered and dried. The material after the second ball milling and drying was carbonized at 1200℃ under an inert atmosphere for 3 hours, cooled to room temperature with the furnace, and then thoroughly ground to obtain a hard carbon material. The prepared material was tested and found to have a reversible specific capacity of 320.3 mAh / g, a coulombic efficiency of 84.4% in the first week, and a capacity retention of 96.4% after 100 charge-discharge cycles.

[0039] Example 4

[0040] 30g of coal powder and 300mL of 0.1mol / L potassium dichromate solution were added to a ball mill and ball-milled for 2 hours, with a ball-to-material ratio of 1:0.2 and a ball milling speed of 300r / min. After ball milling, the material was filtered and dried. The dried material was carbonized at 500℃ under an inert atmosphere for 2 hours, and then washed with 3mol / L hydrochloric acid for 1 hour to remove introduced impurities. After filtration and drying, an intermediate material was obtained. 10g of the intermediate material and 40ml of a mixture of kerosene and hydrogen peroxide were added to a ball mill and ball-milled for 40min, with a kerosene to hydrogen peroxide mass ratio of 1:0.1 and a ball-to-material ratio of 1:0.1. The ball milling speed was 300r / min. After ball milling, the material was filtered and dried. The material after the second ball milling and drying was carbonized at 1300℃ under an inert atmosphere for 2 hours, cooled to room temperature with the furnace, and then thoroughly ground to obtain a hard carbon material. The prepared material was tested and found to have a reversible specific capacity of 311.2 mAh / g, a coulombic efficiency of 85.7% in the first week, and a capacity retention of 94.8% after 100 charge-discharge cycles.

[0041] Comparative Example 1

[0042] The pulverized coal is directly carbonized without ball milling activation, and other conditions are the same as in Example 1, including the following steps:

[0043] 30g of coal powder was carbonized at 500℃ in an inert atmosphere for 2 hours, then heated to 1300℃ and carbonized for another 2 hours. The mixture was then cooled to room temperature in the furnace and thoroughly ground to obtain a hard carbon material. Testing showed that the prepared material had a reversible specific capacity of 210.3mAh / g, a coulombic efficiency of 68.4% in the first week, and a capacity retention of 91.4% after 100 charge-discharge cycles.

[0044] Comparative Example 2

[0045] The ball milling process is carried out without the addition of an activator, and other conditions are the same as in Example 1, including the following steps:

[0046] 30g of coal powder and 300mL of water were added to a ball mill and ball-milled for 2 hours, controlling the ball-to-material ratio at 1:0.2 and the milling speed at 300r / min. After ball milling, the material was filtered and dried. The dried material was then carbonized at 500℃ under an inert atmosphere for 2 hours to obtain an intermediate material. 10g of the intermediate material and 40ml of a mixture of kerosene and hydrogen peroxide were added to a ball mill and ball-milled for 40 minutes, with the kerosene to hydrogen peroxide mass ratio in the mixture being 1:0.1 and the ball-to-material ratio being 1:0.1. The milling speed was 300r / min. After ball milling, the material was filtered and dried. The material after the second ball milling and drying was carbonized at 1300℃ under an inert atmosphere for 2 hours, cooled to room temperature with the furnace, and thoroughly ground to obtain a hard carbon material. The prepared material was tested and found to have a reversible specific capacity of 267.9mAh / g, a first-cycle coulombic efficiency of 69.1%, and a capacity retention of 92.7% after 100 charge-discharge cycles.

[0047] Comparative Example 3

[0048] Only one stage of high-temperature carbonization is used, with other conditions the same as in Example 1, including the following steps:

[0049] 30g of coal powder and 300mL of 0.1mol / L potassium dichromate solution were added to a ball mill and ball-milled for 2 hours, with a ball-to-material ratio of 1:0.2 and a ball milling speed of 300r / min. After ball milling, the material was filtered and dried. The dried material was washed with 3mol / L hydrochloric acid for 1 hour to remove introduced impurities, and then filtered and dried to obtain an intermediate material. 10g of the intermediate material and 40ml of a mixture of kerosene and hydrogen peroxide were added to a ball mill and ball-milled for 40 minutes, with a kerosene to hydrogen peroxide mass ratio of 1:0.1 and a ball-to-material ratio of 1:0.1. The ball milling speed was 300r / min. After ball milling, the material was filtered and dried. The material after the second ball milling and drying was carbonized at 1300℃ in an inert atmosphere for 2 hours, cooled to room temperature with the furnace, and then thoroughly ground to obtain a hard carbon material. The prepared material was tested and found to have a reversible specific capacity of 262.8 mAh / g, a coulombic efficiency of 70.1% in the first week, and a capacity retention of 89.6% after 100 charge-discharge cycles.

[0050] Comparative Example 4

[0051] The second-stage ball milling process does not involve the addition of any modifiers, and all other conditions are the same as in Example 1, including the following steps:

[0052] 30g of pulverized coal and 300mL of 0.1mol / L potassium dichromate solution were added to a ball mill and ball-milled for 2 hours, controlling the ball-to-material ratio at 1:0.2 and the milling speed at 300r / min. After ball milling, the material was filtered and dried. The ball-milled and dried material was carbonized at 500℃ under an inert atmosphere for 2 hours, and then washed with 3mol / L hydrochloric acid for 1 hour to remove introduced impurities. After filtration and drying, an intermediate material was obtained. 10g of the intermediate material and 40ml of kerosene were placed in a ball mill and ball-milled for 40 minutes at a milling speed of 300r / min. After ball milling, the material was filtered and dried. The material after the second ball milling and drying was carbonized at 1300℃ under an inert atmosphere for 2 hours, cooled to room temperature with the furnace, and thoroughly ground to obtain a hard carbon material. The prepared material was tested and found to have a reversible specific capacity of 259.4mAh / g, a first-cycle coulombic efficiency of 72.5%, and a capacity retention of 93.8% after 100 charge-discharge cycles.

Claims

1. A method for preparing a coal-based hard carbon material, characterized in that: Includes the following steps: S1: Coal powder and activator solution are subjected to a first-stage wet ball milling process. The ball-milled mixture is then filtered and dried to obtain a pre-activated material. The activator solution includes at least one of sodium hypochlorite solution, potassium dichromate solution, potassium hydroxide solution, and potassium permanganate solution. S2: The pre-activated material is subjected to a carbonization process, and the carbonization product is acid washed and dried to obtain the pre-carbonized material; S3: The pre-carbonized material and the modifier solution are subjected to two-stage wet ball milling. The mixture from the two-stage ball milling is filtered and dried to obtain the activated material. The modifier solution is a kerosene solution of organic peroxide. S4: The activated material is subjected to a two-stage carbonization process to obtain coal-based hard carbon material.

2. The method for preparing a coal-based hard carbon material according to claim 1, characterized in that: The pulverized coal is pre-treated by acid washing and deashing until the ash content is less than 1%.

3. The method for preparing a coal-based hard carbon material according to claim 1, characterized in that: The concentration of the activator solution is 0.1~1 mol / L.

4. A method for preparing a coal-based hard carbon material according to any one of claims 1 to 3, characterized in that: The conditions for the first stage of wet ball milling are: liquid-to-solid ratio of 5-10 mL:1 g, ball-to-material mass ratio of 1:0.5-0.1, rotation speed of 200-500 r / min, and time of 1-5 h.

5. The method for preparing a coal-based hard carbon material according to claim 1, characterized in that: The conditions for the carbonization process are: under a protective atmosphere, at a temperature of 300~800℃, for a time of 1~3h.

6. The method for preparing a coal-based hard carbon material according to claim 1, characterized in that: The organic peroxide concentration in the modifier solution is 5-10% by mass; the organic peroxide includes at least one of peracetic acid and cycloacetone peroxide.

7. The method for preparing a coal-based hard carbon material according to claim 1, characterized in that: The conditions for the two-stage wet ball milling are as follows: liquid-to-solid ratio of 2-6 mL:1 g, ball-to-material mass ratio of 1:0.5-0.1, rotation speed of 100-300 r / min, and time of 30-60 min.

8. The method for preparing a coal-based hard carbon material according to claim 1, characterized in that: The conditions for the two-stage carbonization process are: under an inert atmosphere, at a temperature of 1200~1600℃, for a time of 1~3h.

9. A coal-based hard carbon material, characterized in that: It is obtained by the preparation method described in any one of claims 1 to 8.

10. The application of the coal-based hard carbon material according to claim 9, characterized in that: Applications as a negative electrode material for sodium-ion batteries.

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