Method for preparing hard carbon material using humic acid, hard carbon material and application

Abstract

The application discloses a method for preparing hard carbon material by using humic acid, and the hard carbon material and application, and belongs to the technical field of sodium ion batteries. Humic acid is mixed with lye and a nitrogen-containing modifier, and after reaction, insoluble substances are removed, and the remaining solution is dried to obtain modified humic acid. The modified humic acid is sequentially subjected to low-temperature pre-carbonization treatment and high-temperature carbonization treatment to obtain hard carbon material. The hard carbon material has a short-range ordered and long-range disordered structure, is rich in sodium storage defect sites, and shows good sodium deintercalation behavior. When the hard carbon material is used as a negative electrode material of a sodium ion battery, the sodium ion battery has high sodium storage specific capacity, rate performance and cycle stability.

Description

Technical Field

[0001] This invention relates to a hard carbon material, a method for preparing hard carbon material using phytic acid, and the application of hard carbon material in sodium-ion batteries, belonging to the field of battery technology. Background Technology

[0002] In recent years, the cost of lithium-ion batteries has remained high due to resource scarcity. Against this backdrop, sodium-ion batteries have gradually developed due to their advantages such as abundant resources, low cost, safety, and environmental friendliness. Commercial lithium-ion batteries use graphite as the anode material, with a theoretical specific capacity of 372 mA·h / g. However, because sodium ions are difficult to form stable intercalation compounds with graphite, sodium-ion batteries cannot directly use graphite as the anode material.

[0003] Hard carbon, as an amorphous carbon material with a high degree of disorder, possesses a high sodium storage capacity and is currently the most commercially promising anode material for sodium-ion batteries. Hard carbon materials are typically prepared by pyrolysis and carbonization of precursors such as biomass, resin, pitch, and coal. Biomass and resin precursors suffer from drawbacks such as high cost, low yield, and unstable raw material supply. Coal and pitch are inexpensive and have a stable supply; however, due to their high impurity content and the tendency for carbonization to form ordered graphite structures, the performance of the prepared products is generally mediocre.

[0004] Humic acid, a low-rank coal extract, possesses advantages such as suitable chemical activity, easily tunable molecular structure, wide availability, and low cost, making it a potential high-quality precursor for hard carbon materials. Compared to coal, humic acid has a smaller relative molecular weight and a richer structure of active functional groups, easily forming disordered hard carbon structures during carbonization. Furthermore, the carbon content in humic acid is higher than that of precursor raw materials such as biomass and resins, implying higher yields. Chinese patent CN114516627A uses humic acid and pitch as hard and soft carbon sources to prepare soft and hard carbon composite nanomaterials, but the sodium storage capacity of the resulting soft and hard carbon composite materials is relatively low. Summary of the Invention

[0005] To address the technical problems of existing hard carbon materials used as anode materials for sodium-ion batteries, the first objective of this invention is to provide a hard carbon material with a short-range ordered and long-range disordered structure, rich in sodium storage defect sites, exhibiting good sodium insertion / extraction behavior, and thus suitable for use as anode material for sodium-ion batteries.

[0006] The second objective of this invention is to provide a method for preparing hard carbon materials, which uses humic acid as a raw material, is low in cost, simple in process, and conducive to large-scale production.

[0007] The third objective of this invention is to provide a hard carbon material for use as a negative electrode material in sodium-ion batteries, resulting in sodium-ion batteries with high sodium storage capacity, rate performance, and cycle stability.

[0008] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing hard carbon materials using humic acid. The method involves mixing and reacting humic acid with an alkaline solution and a nitrogen-containing modifier to remove insoluble substances, drying the remaining solution to obtain modified humic acid, and then subjecting the modified humic acid to a low-temperature pre-carbonization treatment and a high-temperature carbonization treatment to obtain the hard carbon material.

[0009] This invention uses humic acid as a raw material to prepare hard carbon materials that meet the requirements of sodium-ion battery anode applications. First, humic acid is modified by reacting it with an alkaline solution and a nitrogen-containing modifier. On the one hand, the alkaline solution effectively reduces the ash content of the humic acid by dissolving it; on the other hand, the nitrogen-containing modifier reacts chemically with the active groups in the humic acid to introduce nitrogen-containing groups. The modified humic acid is further activated at low temperature, undergoing pre-oxidation and doping with an active gas. This introduces a large number of oxygen-containing and nitrogen-containing functional groups into the humic acid. The introduction of these functional groups effectively inhibits graphitization during the subsequent high-temperature carbonization process and promotes the formation of numerous microporous structures, particularly beneficial for the short-range ordered and long-range disordered structures of sodium insertion / extraction, significantly improving the electrochemical performance of the coal-based hard carbon material.

[0010] As a preferred embodiment, the alkaline solution is at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, and ammonia water. These alkaline solutions are conventional alkaline solutions, and their use is primarily for purifying humic acid, which is more conducive to improving the sodium storage performance of hard carbon materials.

[0011] As a preferred embodiment, the nitrogen-containing modifier is at least one selected from urea, melamine, polypyrrole, and ammonium carbonate. These nitrogen-containing modifiers can chemically react with the active groups in humic acid to form covalent or ionic bonds, thereby chemically modifying the humic acid. After modification, these nitrogen-containing modifiers effectively inhibit the graphitization of humic acid during subsequent high-temperature carbonization processes, while simultaneously promoting the formation of numerous short-range ordered and long-range disordered microporous structures.

[0012] As a preferred embodiment, the mass ratio of humic acid to nitrogen-containing modifier is 100:1 to 10. Components such as urea or melamine in the nitrogen-containing modifier can chemically react with humic acid under hydrothermal reaction conditions, thereby introducing nitrogen atom doping. This promotes the formation of a porous structure with short-range order and long-range disorder in the carbon material during the high-temperature carbonization process, increasing the interlayer spacing and improving the reversible sodium storage capacity of the material. The humic acid includes at least one of coal humic acid, soil humic acid, and aquatic humic acid.

[0013] As a preferred embodiment, the alkaline solution is used to adjust the pH of the system to 9–12. Preferred pH conditions facilitate humic acid extraction and simultaneously provide a favorable pH environment for the modification of nitrogen-containing modifiers.

[0014] As a preferred embodiment, the reaction conditions are: a liquid-to-solid ratio of 3–10 mL:1 g, a temperature of 30–80 °C, and a time of 1–6 h. Maintaining a suitable liquid-to-solid ratio during the reaction helps to fully dissolve the humic acid, while an excessively high liquid-to-solid ratio will increase the load on the subsequent evaporation process. Appropriately increasing the reaction temperature during the reaction helps to promote the reaction between humic acid and the modifier, but if the temperature is too high, it will cause the humic acid to denature.

[0015] As a preferred embodiment, the conditions for the low-temperature pre-carbonization treatment are: carbonization at 300–800°C for 1–5 hours under a controlled atmosphere; the controlled atmosphere contains 1–10% by volume of an active gas, which is at least one of ammonia, carbon dioxide, and oxygen. The controlled atmosphere also contains an inert gas, such as nitrogen or argon. During the low-temperature pre-carbonization process, on the one hand, humic acid itself has a relatively small molecular weight and contains many active functional groups, such as carboxyl groups, phenolic hydroxyl groups, and carbonyl groups. These active functional groups are easily oxidized and pyrolyzed by the active gas during pre-carbonization to form cross-linked structures or to be doped with nitrogen, which helps increase the storage sites of sodium ions in the hard carbon material. On the other hand, during the low-temperature pre-carbonization process, a small number of aromatic ring structures in the humic acid macromolecule are destroyed under a weakly oxidizing atmosphere, further promoting the formation of disordered structures in the hard carbon material. Appropriately increasing the temperature during the low-temperature pre-carbonization process helps to promote the destruction of aromatic ring structures, but excessively high temperatures will lead to a significant decrease in carbon yield, which is detrimental to production.

[0016] As a preferred embodiment, the high-temperature carbonization conditions are: carbonization at 1100–1600°C for 1–5 hours under an inert atmosphere. During the high-temperature carbonization process, active functional groups and doped nitrogen-containing groups in humic acid are removed, generating a large number of defect sites. This promotes the formation of short-range ordered and long-range disordered structures in hard carbon materials, significantly improving their electrochemical performance. If the carbonization temperature is too high or the time is too long, graphitization of the hard carbon is likely to occur. If the carbonization temperature is too low or the time is too short, it is not conducive to the removal of active groups and the formation of disordered structures.

[0017] This invention also provides a hard carbon material obtained by the aforementioned preparation method. The hard carbon material of this invention possesses a short-range ordered, long-range disordered structure and is rich in sodium-storage defect sites, exhibiting good sodium insertion / extraction behavior, and can be used as a negative electrode material for sodium-ion batteries.

[0018] This invention also provides an application of hard carbon material as a negative electrode material for sodium-ion batteries.

[0019] The hard carbon material of this invention is used as a negative electrode material for sodium-ion batteries, and the resulting sodium-ion batteries have high sodium storage capacity, rate performance and cycle stability.

[0020] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:

[0021] 1) This invention uses humic acid as a raw material for hard carbon materials. As a low-rank coal extract, humic acid has the advantages of suitable chemical activity, easily controllable molecular structure, wide availability, and low cost, which is conducive to large-scale production. Compared with existing precursor raw materials such as biomass and resins, humic acid hard carbon has a higher carbon yield, higher product consistency, stable performance, and the raw materials are widely available, have a stable supply, are inexpensive, and have broad prospects for commercial application.

[0022] 2) The preparation process of the hard carbon material of the present invention uses humic acid as the main raw material and obtains a hard carbon material with short-range ordered and long-range disordered structure, rich in sodium storage defect sites and excellent electrochemical performance through a process path combining wet modification, pre-carbonization and high-temperature carbonization.

[0023] 3) In the preparation process of the hard carbon material of the present invention, the ash that may exist in humic acid is removed by alkaline dissolution treatment. Under the action of nitrogen-containing modifier, humic acid is further activated. Nitrogen-containing groups react with humic acid, and nitrogen atoms are introduced into the active sites of humic acid. The introduction of nitrogen atoms makes humic acid more inclined to generate a porous and disordered hard carbon structure in the subsequent carbonization process.

[0024] 4) The preparation process of the hard carbon material of the present invention adopts a two-stage carbonization process. In the first stage of low-temperature pre-carbonization, a small amount of aromatic ring structure in the humic acid macromolecule is destroyed under a weak oxidizing atmosphere, which further promotes the generation of disordered structure of hard carbon material. In the second stage of high-temperature carbonization, the active functional groups in humic acid are thermally desorbed, generating a large number of defect sites, which promotes the formation of short-range ordered and long-range disordered structure of hard carbon material and significantly improves the electrochemical performance of hard carbon material.

[0025] 5) The hard carbon material of the present invention is applied to the negative electrode of sodium-ion batteries, resulting in higher sodium storage capacity, rate performance and cycle stability. Attached Figure Description

[0026] Figure 1 The graphs show the initial charge-discharge specific capacity curves of the hard carbon material products in Example 1 and the comparative examples. Detailed Implementation

[0027] 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.

[0028] Example 1

[0029] Material preparation: 20g of humic acid and 1g of melamine were mixed and then added to 100mL of sodium hydroxide solution. The mixture was stirred and heated at 80℃ for 2h, and the pH value of the reaction was controlled at 12. After the reaction was completed, the insoluble matter was removed and the remaining liquid was dried to obtain modified humic acid. The modified humic acid was pre-carbonized at low temperature for 4h at 800℃ under a CO2 atmosphere of 5 vol.% (CO2 / CO2+Ar). After the pre-carbonization was completed, 100 vol.% Ar was introduced and carbonized at 1300℃ for 2h. The mixture was then cooled to room temperature in the furnace and ground to obtain hard carbon material.

[0030] Performance Testing: The prepared hard carbon anode material was mixed with Super P and PVDF at a mass ratio of 8:1:1 and ground for 30 min. NMP was added and stirred for 6 h to form a slurry, which was then coated onto copper foil and dried in a vacuum oven at 70℃ for 12 h. 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 anode, glass fiber as the separator, and 1M NaClO4 (solvent: EC:EDC = 1:1, Vol%) as the electrolyte. The assembled battery was tested using a Blue Battery Tester with a charge / discharge voltage range of 0-2V and a current density of 0.1C (1C = 200mA / g). The test results showed that the reversible specific capacity of the button cell was 318.3 mAh / g, and the first-cycle charge / discharge coulombic efficiency was 84.2%.

[0031] Example 2

[0032] Material preparation: 20g of humic acid and 2g of urea were mixed and then added to 100mL of ammonia water. The mixture was stirred and heated at 50℃ for 3h, and the pH value of the reaction was controlled at 10. After the reaction was completed, the insoluble matter was removed and the remaining liquid was dried to obtain modified humic acid. The modified humic acid was pre-carbonized at low temperature for 2h at 300℃ under an O2 atmosphere of 21 vol.% (O2 / O2+Ar). After the pre-carbonization was completed, 100 vol.% Ar was introduced and carbonized at 1100℃ for 2h. The mixture was then cooled to room temperature in the furnace and ground to obtain hard carbon material.

[0033] Performance Testing: The battery assembly and performance testing procedures were the same as in Example 1. The button cell's reversible specific capacity was tested to be 320.4 mAh / g, and its first-week charge-discharge coulombic efficiency was 82.2%.

[0034] Example 3

[0035] Material preparation: 20g of humic acid and 0.5g of polypyridine were mixed and then added to 100mL of sodium carbonate solution. The mixture was stirred and heated at 30℃ for 6h, and the pH value of the reaction was controlled at 11. After the reaction was completed, the insoluble matter was removed and the remaining liquid was dried to obtain modified humic acid. The modified humic acid was pre-carbonized at low temperature for 1h at 500℃ under an O2 atmosphere of 10 vol.% (NH3 / NH3+Ar). After the pre-carbonization was completed, 100 vol.% Ar was introduced and carbonized at 1400℃ for 2h. The mixture was then cooled to room temperature in the furnace and ground to obtain hard carbon material.

[0036] Performance Testing: The battery assembly and performance testing procedures were the same as in Example 1. The button cell's reversible specific capacity was tested to be 309.7 mAh / g, and its first-week charge-discharge coulombic efficiency was 79.8%.

[0037] Example 4

[0038] Material preparation: 20g of humic acid and 1g of ammonium carbonate were mixed and then added to 100mL of ammonia solution. The mixture was stirred and heated at 60℃ for 4h, and the pH value of the reaction was controlled at 10. After the reaction was completed, the insoluble matter was removed and the remaining liquid was dried to obtain modified humic acid. The modified humic acid was pre-carbonized at low temperature for 3h at 500℃ under a CO2 atmosphere of 20 vol.% (CO2 / CO2+Ar). After the pre-carbonization was completed, 100 vol.% Ar was introduced and carbonized at 1200℃ for 2h. The mixture was cooled to room temperature in the furnace and then ground to obtain hard carbon material.

[0039] Performance Testing: The battery assembly and performance testing procedures were the same as in Example 1. The button cell's reversible specific capacity was tested to be 303.3 mAh / g, and its first-week charge-discharge coulombic efficiency was 76.2%.

[0040] Comparative Example 1

[0041] Hard carbon anode materials were prepared directly by carbonization with humic acid without any modification treatment, and other conditions were the same as in Example 1.

[0042] Material preparation: Humic acid was pre-carbonized at low temperature for 4 hours at 800℃ in a CO2 atmosphere of 5 vol.% (CO2 / CO2+Ar); after pre-carbonization, 100 vol.% Ar was introduced and carbonized at 1300℃ for 2 hours. The material was then cooled to room temperature in the furnace and ground to obtain hard carbon material.

[0043] Performance Testing: The battery assembly and performance testing procedures were the same as in Example 1. The button cell's reversible specific capacity was tested to be 213.8 mAh / g, and its first-week charge-discharge coulombic efficiency was 68.7%.

[0044] Comparative Example 2

[0045] The humic acid modification process involves a pH value greater than 14, with other conditions the same as in Example 1, and includes the following steps:

[0046] Material preparation: 20g of humic acid and 1g of melamine were mixed and then added to 100mL of sodium hydroxide solution. The mixture was stirred and heated at 80℃ for 2h, and the pH value of the reaction was controlled to be greater than 14. After the reaction was completed, the insoluble matter was removed and the remaining liquid was dried to obtain modified humic acid. The modified humic acid was pre-carbonized at low temperature for 4h at 800℃ under a CO2 atmosphere of 5 vol.% (CO2 / CO2+Ar). After the pre-carbonization was completed, 100 vol.% Ar was introduced and carbonized at 1300℃ for 2h. The mixture was cooled to room temperature in the furnace and then ground to obtain hard carbon material.

[0047] Performance Testing: The battery assembly and performance testing procedures were the same as in Example 1. The button cell's reversible specific capacity was tested to be 255.3 mAh / g, and its first-week charge-discharge coulombic efficiency was 70.2%.

[0048] Comparative Example 3

[0049] The low-temperature pre-carbonization process uses an inert atmosphere, and other conditions are the same as in Example 1, including the following steps:

[0050] Material preparation: 20g of humic acid and 1g of melamine were mixed and then added to 100mL of sodium hydroxide solution. The mixture was stirred and heated at 80℃ for 2h, and the pH value of the reaction was controlled at 12. After the reaction was completed, the insoluble matter was removed and the remaining liquid was dried to obtain modified humic acid. The modified humic acid was pre-carbonized at low temperature at 800℃ and 100vol.%Ar atmosphere for 4h. After the pre-carbonization was completed, the temperature was raised to 1300℃ and carbonized for 2h. The mixture was then cooled to room temperature in the furnace and ground to obtain hard carbon material.

[0051] Performance Testing: The battery assembly and performance testing procedures were the same as in Example 1. The button cell's reversible specific capacity was tested to be 235.9 mAh / g, and its first-week charge-discharge coulombic efficiency was 68.9%.

[0052] Comparative Example 4

[0053] Without low-temperature pre-carbonization treatment, other conditions are the same as in Example 1, including the following steps:

[0054] Material preparation: 20g of humic acid and 1g of melamine were mixed and then added to 100mL of sodium hydroxide solution. The mixture was stirred and heated at 80℃ for 2h, and the pH value of the reaction was controlled at 12. After the reaction was completed, the insoluble matter was removed and the remaining liquid was dried to obtain modified humic acid. The modified humic acid was carbonized at 1300℃ in 100vol.% Ar atmosphere for 2h, cooled to room temperature in the furnace, and ground to obtain hard carbon material.

[0055] Performance Testing: The battery assembly and performance testing procedures were the same as in Example 1. The button cell's reversible specific capacity was tested to be 260.0 mAh / g, and its first-week charge-discharge coulombic efficiency was 71.5%.

Claims

1. A method for preparing hard carbon materials using humic acid, characterized in that: After mixing and reacting humic acid with alkaline solution and nitrogen-containing modifier, insoluble matter is removed, and the remaining solution is dried to obtain modified humic acid. The modified humic acid is then subjected to low-temperature pre-carbonization treatment and high-temperature carbonization treatment in sequence to obtain hard carbon material. The nitrogen-containing modifier is at least one of urea, melamine, polypyrrole, and ammonium carbonate; The mass ratio of humic acid to nitrogen-containing modifier is 100:1~10; The alkaline solution is used to adjust the pH of the system to 9-12; The reaction conditions are: liquid-to-solid ratio of 3-10 mL:1 g, temperature of 30-80 °C, and time of 1-6 h. The conditions for the low-temperature pre-carbonization treatment are as follows: carbonization for 1 to 5 hours at a temperature of 300 to 800°C under a controlled atmosphere; the controlled atmosphere contains 1 to 10% by volume of an active gas, which is at least one of carbon dioxide and oxygen.

2. The method for preparing hard carbon materials using humic acid according to claim 1, characterized in that: The alkaline solution is at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, and ammonia water.

3. The method for preparing hard carbon materials using humic acid according to claim 1, characterized in that: The conditions for high-temperature carbonization are: carbonization at 1100~1600℃ for 1~5 hours under an inert atmosphere.

4. A hard carbon material, characterized in that: It is obtained by the preparation method described in any one of claims 1 to 3.

5. The application of the hard carbon material according to claim 4, characterized in that: Applications as a negative electrode material for sodium-ion batteries.

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