Preparation method of sodium ion battery hard carbon negative electrode material

Abstract

The invention discloses a preparation method of a sodium-ion battery hard carbon negative electrode material, and belongs to the field of sodium-ion batteries. Inorganic strong acid ferric salt, a chain type carbon source and a stabilizer are dispersed in N, N-dimethylformamide, heating and stirring are performed to obtain a precursor solution, and the precursor solution is subjected to spray drying to obtain a precursor; dissolving the precursor, a sodium salt organic matter, inorganic strong acid zinc salt and dimethylimidazole in methanol, and sequentially performing centrifugation, washing and vacuum drying to obtain a precursor coating; and carrying out two-step high-temperature calcination on the precursor coating in an argon atmosphere, carrying out suction filtration and water washing, and carrying out vacuum drying to obtain the sodium-ion battery hard carbon negative electrode material. According to the invention, the hard carbon negative electrode material with a rich closed-pore structure, a stable solid electrolyte interface and sufficient active sites can be generated. Under the combined action of the characteristics, the sodium storage capacity and the structural stability of the negative electrode of the sodium-ion battery are greatly improved, so that the initial coulombic efficiency and the specific capacity of the sodium-ion battery are improved.

Description

Technical Field

[0001] The present invention belongs to the field of sodium-ion batteries, and particularly relates to a method for preparing a hard carbon negative electrode material for a sodium-ion battery. Background Art

[0002] The uncontrolled combustion of fossil fuels is the main factor exacerbating the greenhouse effect and driving global warming. This process not only raises global temperatures but also has a profound impact on the balance of ecosystems, agricultural production, the availability of fresh water resources, and climate patterns. In the face of these challenges, electrochemical energy storage systems, due to their advantages in solving the problems of uneven temporal and spatial distribution of renewable energy, exhibit great application potential and broad prospects for large-scale energy storage. Through efficient energy storage and intelligent release, electrochemical energy storage systems help balance the intermittent supply of renewable energy such as wind energy and solar energy, providing strong technical support for the stable utilization of clean energy and the reliability of the power grid. Lithium-ion batteries, due to their excellent high energy density and outstanding cycle stability, have become the mainstream rechargeable battery technology in the market and are widely used in fields such as electric vehicles and portable electronic devices. However, the relatively low abundance of lithium resources in the earth's crust and their significant geographical inhomogeneity limit the feasibility and sustainability of lithium-ion batteries in more extensive large-scale energy storage applications.

[0003] Sodium-ion batteries, due to their low cost, abundant sodium resources, and wide geographical distribution, are gradually regarded as a highly potential candidate technology for electrochemical energy storage systems. In addition, sodium and lithium, as elements in the same main group of the periodic table, share similar chemical properties and electrochemical behaviors, which makes sodium-ion batteries theoretically an effective alternative to lithium-ion batteries. With the acceleration of the commercialization process of sodium-ion batteries, the demand for high-performance hard carbon negative electrode materials is increasing day by day, which also brings a series of technical and scientific research challenges. Currently, there is still a need for further breakthroughs in optimizing the electrochemical performance of hard carbon negative electrodes and improving the initial Coulomb efficiency (ICE).

[0004] Chinese patent document with the publication number CN116544386A discloses a starch-based hard carbon sodium-ion battery negative electrode material, its preparation method and application. This material has a wide range of closed pore structures, significantly enhancing its sodium deintercalation and sodium intercalation capabilities and further improving the specific capacity of the material. However, some oxygen-containing functional groups and defects will appear in this material, which will capture Na +And cause irreversible capacity loss. The Chinese patent document with the publication number CN117735521A discloses a hard carbon negative electrode material, its preparation method, application, and sodium-ion battery. This hard carbon negative electrode material has an appropriate pore size distribution and specific surface area, and has excellent electrochemical performance when applied to a battery. However, the solid electrolyte interface (SEI) generated at the interface between the hard carbon and the electrolyte will consume irreversible sodium ions, resulting in a low initial Coulomb efficiency (ICE). Summary of the Invention

[0005] The object of the present invention is to provide a preparation method of a hard carbon negative electrode material for a sodium-ion battery. The present invention can produce a hard carbon negative electrode material with a rich pore structure, a stable solid electrolyte interface, and sufficient active sites. The combined action of these characteristics can greatly improve the sodium storage capacity and structural stability of the negative electrode of the sodium-ion battery, and further improve the initial Coulomb efficiency and specific capacity of the sodium-ion battery.

[0006] To achieve the above-mentioned invention object, the present invention provides a preparation method of a hard carbon negative electrode material for a sodium-ion battery, including the following steps: (1) Disperse an inorganic strong acid iron salt, a chain carbon source, and a stabilizer in N,N-dimethylformamide, heat and stir to obtain a precursor solution, and spray-dry the precursor solution to obtain a precursor; (2) Dissolve the precursor, a sodium salt organic compound, an inorganic strong acid zinc salt, and dimethylimidazole in methanol, and successively perform centrifugation, washing, and vacuum drying to obtain a precursor coating; (3) Perform a first high-temperature calcination on the precursor coating in an argon atmosphere, then introduce carbon dioxide gas, and then perform a second high-temperature calcination. After cooling, wash it in 2M dilute hydrochloric acid, and then wash it with water until neutral. After vacuum drying, obtain the hard carbon negative electrode material for the sodium-ion battery.

[0007] Preferably, in step (1), the inorganic strong acid iron salt is one of ferric chloride, ferric sulfate, and ferric nitrate; the chain carbon source is one of polyacrylonitrile, phenolic resin, epoxy resin, and polyaniline; the stabilizer is one of cetyltrimethylammonium bromide, polyethylene glycol, and citric acid; the molar concentration of the inorganic strong acid iron salt in the precursor solution is 0.01 - 0.5 mol / L, and the mass ratio of the inorganic strong acid iron salt, the stabilizer, and the chain carbon source is 1:1 - 1.7:2 - 3, and the heating and stirring temperature is 80 - 90 °C, and the time is 6 - 10 h.

[0008] Preferably, in step (2), the sodium salt organic compound is one of disodium phthalate, disodium ethylenediaminetetraacetate, trisodium citrate, and sodium tartrate; the inorganic strong acid zinc salt is one of zinc chloride, zinc sulfate, and zinc nitrate; the mass ratio of the precursor, the sodium salt organic compound, the inorganic strong acid zinc salt, and dimethylimidazole is 1:0.1 - 0.6:1 - 5:2 - 10.

[0009] Preferably, in step (3), the conditions for the first high-temperature calcination are as follows: heating up to 600 - 800 °C, with a heating rate of 2 - 5 °C / min and a holding time of 1 - 4 h; the conditions for the second high-temperature calcination are as follows: heating up to 1000 - 1500 °C, with a heating rate of 5 - 10 °C / min and a time of 1 - 2 h; the concentration of dilute hydrochloric acid is 2 M; the conditions for vacuum drying are: temperature of 70 - 90 °C and time of 8 - 12 h.

[0010] The beneficial effects of the present invention are as follows: 1. The technical solution provided by the present invention combines an inorganic strong acid iron salt with a chain carbon source, conducts high-temperature calcination and carbon dioxide gas etching to generate iron carbide and a hard carbon composite material. Iron carbide itself has high reaction activity, so it has excellent sodium storage capacity. Combining it with hard carbon can further increase the sodium storage capacity of the overall negative electrode material; the addition of iron carbide effectively improves the conductivity of the hard carbon negative electrode, which enhances the utilization efficiency of the material and promotes the rapid diffusion of sodium ions, thereby improving the charge and discharge efficiency of the battery; at the same time, iron carbide helps to maintain the structural integrity of hard carbon during the charge and discharge process, reducing the expansion and contraction of the material caused by volume changes, which helps to enhance the cycle life of the battery; in addition, iron carbide has high surface wettability to the electrolyte, which helps to improve the sodium storage and penetration ability, further enhancing the battery performance.

[0011] 2. The technical solution provided by the present invention can react with the surface of hard carbon by adding a sodium salt organic matter to form a stable SEI layer, which helps to reduce the irreversible sodium ion loss during the first charge and discharge process, thereby significantly improving the initial Coulomb efficiency of the battery; this stable SEI layer reduces the repeated formation of SEI during the battery cycle, avoiding excessive consumption of sodium ions and the electrolyte, which affects the battery performance; this stable SEI layer can prevent direct contact between the hard carbon negative electrode and the electrolyte, reducing the occurrence of side reactions, thereby improving the safety of the battery; due to the protection of the SEI layer, the structural integrity of the hard carbon negative electrode is maintained, reducing the volume expansion and contraction during the charge and discharge process, thereby improving the cycle stability of the battery.

[0012] 3. In the technical solution provided by the present invention, a two-step calcination method is adopted during the carbonization process. The precursor coating is pyrolyzed in an initial argon environment, and iron inorganic strong acid salt and chain carbon source will form iron carbide particles. Then, carbon dioxide gas is further introduced to assist in increasing the number and volume of closed pores at a higher temperature. The closed pore environment provides more storage sites for sodium ions, and these sites can effectively embed and extract sodium ions during the charge and discharge process of the battery. At the same time, zinc metal formed by zinc inorganic strong acid salt at high temperature will vaporize to form some micropores, and these pore environments can significantly improve the sodium storage capacity of the hard carbon negative electrode; the existence of closed pores helps to form a stable sodium ion embedding platform at a lower voltage. Due to the increase in the number and volume of closed pores, the initial Coulomb efficiency of the hard carbon negative electrode in the sodium ion battery is improved, which means that the irreversible capacity loss during the first charge and discharge process of the battery is reduced, and the efficiency and energy utilization rate of the battery are improved; the assistance of carbon dioxide not only increases the number and volume of closed pores, but also maintains the original morphology of the hard carbon negative electrode during this process, which helps to maintain the structural integrity of the electrode and reduce the structural degradation during the charge and discharge cycle.

[0013] 4. The hard carbon negative electrode material for sodium ion battery prepared by the technical solution provided by the present invention has outstanding effects in the negative electrode of the sodium ion battery. The specific capacities at current densities of 0.1, 0.2, 0.5, 1, 2, and 5 A / g are 459.3 - 468.1, 430.0 - 436.9, 370.6 - 373.2, 291.3 - 295.5, 261.2 - 271.0, and 219.5 - 226.9 mAh / g respectively. At the same time, under the cycle of 0.1 A / g, the ICE can be maintained at a retention rate of 92.0 - 96.5%. Description of the Drawings

[0014] Figure 1 Scanning electron microscope (SEM) image of the hard carbon negative electrode material for sodium ion battery prepared in Example 1; Figure 2 X-ray diffraction (XRD) pattern of the hard carbon negative electrode material for sodium ion battery prepared in Example 1; Figure 3 Rate performance graph of the hard carbon negative electrode material for sodium ion battery prepared in Example 1. Detailed Description of the Invention

[0015] The present invention will be described in detail below in conjunction with examples and comparative examples, but the present invention is not limited thereto. Example 1

[0016] (1) Disperse ferric chloride, epoxy resin, and cetyltrimethylammonium bromide in 50 ml of N,N-dimethylformamide, and then heat and stir at 90 °C for 8 h to obtain a precursor solution. Among them, the molar concentration of ferric chloride in the precursor solution is 0.01 mol / L, and the mass ratio of ferric chloride, cetyltrimethylammonium bromide, and epoxy resin is 1:1.3:2. Spray-dry the precursor solution to obtain a precursor; (2) Dissolve the precursor, disodium phthalate, zinc chloride, and dimethylimidazole in methanol and stir overnight, then centrifuge, wash, and dry to obtain a precursor coating. Among them, the mass ratio of the precursor, disodium phthalate, zinc chloride, and dimethylimidazole is 1:0.6:1:10; (3) Place the precursor coating in a tube furnace, and under an argon atmosphere, raise the temperature to 650 °C at a heating rate of 2 °C / min, with a calcination time of 3 h to obtain a carbonized product. Then, introduce carbon dioxide gas, raise the temperature to 1500 °C at a heating rate of 10 °C / min, with a calcination time of 1 h. After cooling, wash in 2 M dilute hydrochloric acid, further filter with water by suction, and vacuum dry at 90 °C for 12 h to finally obtain a hard carbon anode material for sodium-ion batteries. Example 2

[0017] (1) Disperse ferric nitrate, polyacrylonitrile, and polyethylene glycol in 50 ml of N,N-dimethylformamide, and then heat and stir at 80 °C for 10 h to obtain a precursor solution. Among them, the molar concentration of ferric nitrate in the precursor solution is 0.1 mol / L, and the mass ratio of ferric nitrate, polyethylene glycol, and polyacrylonitrile is 1:1:2. Spray-dry the precursor solution to obtain a precursor; (2) Dissolve the precursor, disodium ethylenediaminetetraacetate, zinc nitrate, and dimethylimidazole in methanol and stir overnight, then centrifuge, wash, and dry to obtain a precursor coating. Among them, the mass ratio of the precursor, disodium ethylenediaminetetraacetate, zinc nitrate, and dimethylimidazole is 1:0.1:5:2; (3) Place the precursor coating in a tube furnace, and under an argon atmosphere, raise the temperature to 800 °C at a heating rate of 5 °C / min, with a calcination time of 1 h to obtain a carbonized product. Then, introduce carbon dioxide gas, raise the temperature to 1200 °C at a heating rate of 5 °C / min, with a calcination time of 2 h. After cooling, wash in 2 M dilute hydrochloric acid, further filter with water by suction, and vacuum dry at 80 °C for 10 h to finally obtain a hard carbon anode material for sodium-ion batteries. Example 3

[0018] (1) Disperse ferric sulfate, polyaniline, and citric acid in 50 ml of N,N-dimethylformamide, and then heat and stir at 85 °C for 6 h to obtain a precursor solution. Among them, the molar concentration of ferric sulfate in the precursor solution is 0.5 mol / L, and the mass ratio of ferric sulfate, citric acid, and polyaniline is 1:1.7:3. Spray-dry the precursor solution to obtain a precursor; (2) Dissolve the precursor, trisodium citrate, zinc sulfate, and dimethylimidazole in methanol and stir overnight, then centrifuge, wash, and dry to obtain a precursor coating. Among them, the mass ratio of the precursor, disodium ethylenediaminetetraacetate, zinc sulfate, and dimethylimidazole is 1:0.6:5:2; (3) Place the precursor coating in a tubular furnace, and under an argon atmosphere, raise the temperature to 600 °C at a heating rate of 3 °C / min, with a calcination time of 4 h to obtain a carbonized product. Then, introduce carbon dioxide gas, raise the temperature to 1000 °C at a heating rate of 5 °C / min, with a calcination time of 1 h. After cooling, wash in 2 M dilute hydrochloric acid, then further filter with water by suction and wash with water, and dry in vacuum at 70 °C for 9 h to finally obtain a hard carbon anode material for sodium-ion batteries. Example 4

[0019] (1) Disperse ferric nitrate, phenolic resin, and polyethylene glycol in 50 ml of N,N-dimethylformamide, and then heat and stir at 90 °C for 7 h to obtain a precursor solution. Among them, the molar concentration of ferric nitrate in the precursor solution is 0.2 mol / L, and the mass ratio of ferric nitrate, polyethylene glycol, and phenolic resin is 1:1:3. Spray-dry the precursor solution to obtain a precursor; (2) Dissolve the precursor, sodium tartrate, zinc chloride, and dimethylimidazole in methanol and stir overnight, then centrifuge, wash, and dry to obtain a precursor coating. Among them, the mass ratio of the precursor, disodium phthalate, zinc chloride, and dimethylimidazole is 1:0.1:1:10; (3) Place the precursor coating in a tubular furnace, and under an argon atmosphere, raise the temperature to 800 °C at a heating rate of 4 °C / min, with a calcination time of 2 h to obtain a carbonized product. Then, introduce carbon dioxide gas, raise the temperature to 1500 °C at a heating rate of 10 °C / min, with a calcination time of 2 h. After cooling, wash in 2 M dilute hydrochloric acid, then further filter with water by suction and wash with water, and dry in vacuum at 80 °C for 8 h to finally obtain a hard carbon anode material for sodium-ion batteries. Comparative Example 1

[0020] In this comparative example, inorganic strong acid iron salt is not added, and the other processes are the same as those in Example 1. Comparative Example 2

[0021] In this comparative example, sodium salt organic matter is not added, and the other processes are the same as those in Example 1. Comparative Example 3

[0022] In this comparative example, carbon dioxide was not introduced, and the other procedures were the same as those in Example 1.

[0023] Performance test: The negative electrode materials obtained according to the examples and comparative examples were directly used as negative electrode sheets. A sodium metal sheet was used as the counter electrode, and a 1 mol / L NaPF 6 EC / DMC (1:1 Vol%) solution was used as the electrolyte, and a binder-free glass fiber filter paper of whatman was used as the separator. A 2032-type button battery was assembled in a glove box under an argon atmosphere. The test results are shown in Table 1:

[0024] The sodium-ion battery hard carbon negative electrode material obtained in Example 1 was subjected to scanning electron microscopy test, and the obtained SEM image is as Figure 1 shown. It can be seen from the figure that the microscopic morphology of the sodium-ion battery hard carbon negative electrode material described in the present invention is a block structure, and the surface feature is porous. The formation of this porous structure is attributed to the carbon dioxide etching technology, which creates abundant closed pores in the hard carbon material, providing more active sites for the storage of sodium ions. These sites can effectively embed and extract sodium ions during the charge and discharge process of the battery, thus significantly improving the sodium storage capacity of the hard carbon negative electrode; in the technical solution of the present invention, a two-step calcination method is adopted during the carbonization process. The precursor coating is cracked in an argon environment at a relatively low initial temperature. The inorganic strong acid iron salt and the chain carbon source will form iron carbide particles. At a higher temperature, carbon will further crack, and the microcrystal lattice will further curl to form a closed pore environment. The carbon dioxide gas helps to increase the number and volume of closed pores. The closed pore environment provides more storage sites for sodium ions, and these sites can effectively embed and extract sodium ions during the charge and discharge process of the battery. If a one-step calcination method is adopted, the formed iron carbide particles may be too large, resulting in a reduction in active sites. In addition, the zinc metal formed by the inorganic strong acid zinc salt at high temperature will vaporize to form some micropores, and these pore environments can significantly improve the sodium storage capacity of the hard carbon negative electrode; the existence of closed pores helps to form a stable sodium ion insertion platform at a lower voltage. Due to the increase in the number and volume of closed pores, the initial Coulomb efficiency of the hard carbon negative electrode in the sodium-ion battery is improved, which means that the irreversible capacity loss during the first charge and discharge process of the battery is reduced, and the efficiency and energy utilization rate of the battery are improved; the assistance of carbon dioxide not only increases the number and volume of closed pores, but also maintains the original morphology of the hard carbon negative electrode during this process, which helps to maintain the structural integrity of the electrode and reduce the structural degradation during the charge and discharge cycle.

[0025] Adding sodium salt organic matter during the precursor coating can react with the surface of hard carbon, and the formed SEI layer helps to reduce the irreversible sodium ion loss during the first charge and discharge process, thus significantly improving the initial Coulomb efficiency of the battery; the stable SEI layer reduces the repeated formation of SEI during the battery cycling process, which usually leads to the consumption of additional sodium ions and electrolyte and affects the battery performance; the stable SEI layer can prevent the direct contact between the hard carbon negative electrode and the electrolyte, reduce the occurrence of side reactions, and thus improve the safety of the battery; due to the protection of the SEI layer, the structural integrity of the hard carbon negative electrode is maintained, reducing the volume expansion and contraction during charge and discharge, and thus improving the cycle stability of the battery.

[0026] The hard carbon negative electrode material of the sodium ion battery prepared in Example 1 was analyzed by XRD, and the results are shown in Figure 2 . By observing the spectrum, a carbon peak at about 25° and Fe 3 C can be detected. The weak characteristic peak of Fe 3 C in XRD is due to the small size of Fe 3 C nanoparticles and their good dispersion state in the material.

[0027] The prepared hard carbon negative electrode material was subjected to electrochemical tests, as shown in Figure 3 . The specific capacities of the hard carbon negative electrode material prepared in Example 1 at current densities of 0.1, 0.2, 0.5, 1, 2, and 5 A / g were 468.1, 436.9, 373.2, 295.5, 271.0, and 226.9 mAh / g, respectively. The ICE was 96.5% under the condition of 0.1 A / g, showing excellent charge and discharge performance. The same tests were carried out on the materials of Examples 2-4, and the results were similar to those of Example 1 (Table 1). The difference in the ICE retention rate of the samples of each example under the current density of 0.1 A / g did not exceed 5%.

[0028] Compared with the sample of Comparative Example 1, the examples had better performance under different magnification and ICE conditions, indicating that Fe 3 C has high reactivity and thus has excellent sodium storage capacity. Combining it with hard carbon can further increase the sodium storage capacity of the overall negative electrode material; the addition of Fe 3 C effectively improves the conductivity of the hard carbon negative electrode, which enhances the utilization efficiency of the material and promotes the rapid diffusion of sodium ions, thus improving the charge and discharge efficiency of the battery; at the same time, Fe 3 C helps to maintain the structural integrity of hard carbon during charge and discharge, reducing the material expansion and contraction caused by volume changes, which helps to enhance the cycle life of the battery; in addition, Fe 3C has a high surface wettability to the electrolyte, which helps to improve the sodium storage and penetration ability and further enhance the battery performance (Table 1). In addition, for Comparative Example 2, since there is no sodium salt organic matter in the negative electrode material, Na in the SEI is consumed, which in turn has a significant impact on reducing the cycle reversibility and ICE retention. The example has more excellent electrochemical performance than Comparative Example 3, which indicates that a large number of closed pores formed by CO etching play an important role in the sodium storage performance of hard carbon. + 2

[0029] The specific embodiments described above further illustrate the present invention in detail, but these descriptions should not be construed as limitations on the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.​​

Claims

1. A method for preparing a hard carbon negative electrode material for a sodium ion battery, characterized in that: The steps include: (1) dispersing an inorganic strong acid iron salt, a chain carbon source and a stabilizer in N,N-dimethylformamide, heating and stirring to obtain a precursor solution, and spray drying the precursor solution to obtain a precursor; (2) dissolving the precursor, sodium salt organic matter, inorganic strong acid zinc salt and dimethylimidazole in methanol, centrifuging, washing and vacuum drying in sequence to obtain the precursor coating; (3) The precursor coating is subjected to the first step of high-temperature calcination in an argon atmosphere, and then carbon dioxide gas is introduced, followed by the second step of high-temperature calcination. After cooling, it is washed in 2M dilute hydrochloric acid, and then washed with water until neutral. After vacuum drying, a hard carbon negative electrode material for a sodium ion battery is obtained.

2. The method for preparing a hard carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: In the step (1), the inorganic strong acid iron salt is one of ferric chloride, ferric sulfate, and ferric nitrate; the chain carbon source is one of polyacrylonitrile, phenolic resin, epoxy resin, and polyaniline; the stabilizer is one of hexadecyltrimethylammonium bromide, polyethylene glycol, and citric acid; the molar concentration of the inorganic strong acid iron salt in the precursor solution is 0.01 to 0.5 mol / L, the mass ratio of the inorganic strong acid iron salt, the stabilizer, and the chain carbon source is 1:1 to 1.7:2 to 3, the heating and stirring temperature is 80 to 90°C, and the time is 6 to 10 hours.

3. The method for preparing a hard carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: In the step (2), the sodium salt organic matter is one of disodium phthalate, disodium ethylenediaminetetraacetic acid, trisodium citrate, and sodium tartrate; the inorganic strong acid zinc salt is one of zinc chloride, zinc sulfate, and zinc nitrate; and the mass ratio of the precursor, the sodium salt organic matter, the inorganic strong acid zinc salt, and dimethylimidazole is 1:0.1-0.6:1-5:2-10.

4. The method for preparing a hard carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: In the step (3), the first step of high temperature calcination conditions are: heating to 600-800°C, heating rate of 2-5°C / min, holding time of 1-4h, the second step of high temperature calcination conditions are: heating to 1000-1500°C, heating rate of 5-10°C / min, holding time of 1-2h; vacuum drying conditions are: temperature of 70-90°C, holding time of 8-12h.

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