Preparation method of sodium ion battery hard carbon negative electrode material

Abstract

The application discloses a preparation method of a sodium ion battery hard carbon negative electrode material and belongs to the sodium ion battery field. In the application, inorganic strong acid iron salt, chain carbon source and stabilizer are dispersed in N,N-dimethylformamide, heated and stirred to obtain a precursor solution, and the precursor solution is spray dried to obtain a precursor. The precursor, sodium salt organic matter, inorganic strong acid zinc salt and dimethyl imidazole are dissolved in methanol, and centrifugation, washing and vacuum drying are sequentially performed to obtain a precursor coating. The precursor coating is subjected to two-step high-temperature calcination under an argon atmosphere, and is subjected to suction filtration, water washing and vacuum drying to obtain the sodium ion battery hard carbon negative electrode material. The application can generate the hard carbon negative electrode material with rich closed pore structures, stable solid-state electrolyte interfaces and sufficient active sites. The characteristics jointly act to greatly improve the sodium storage capacity and structural stability of the sodium ion battery negative electrode, and further improve the initial coulomb efficiency and specific capacity of the sodium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion batteries, specifically relating to a method for preparing a hard carbon anode material for sodium-ion batteries. Background Technology

[0002] Electrochemical energy storage systems have demonstrated enormous application potential and a broad prospect for large-scale energy storage due to their advantages in addressing the uneven temporal and spatial distribution of renewable energy. Through efficient energy storage and intelligent release, electrochemical energy storage systems help balance the intermittent supply of renewable energy sources such as wind and solar power, 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 superior cycle stability, have become the mainstream rechargeable battery technology in the market, widely used in electric vehicles and portable electronic devices. However, the relatively low abundance of lithium resources in the Earth's crust and their significant geographical unevenness limit the feasibility and sustainability of lithium-ion batteries in broader large-scale energy storage applications.

[0003] Sodium-ion batteries are increasingly being considered a promising candidate technology for electrochemical energy storage systems due to their low cost, abundant sodium resources, and wide geographical distribution. Furthermore, sodium and lithium, being elements in the same group of the periodic table, share similar chemical properties and electrochemical behaviors, making sodium-ion batteries theoretically a viable alternative to lithium-ion batteries. With the accelerated commercialization of sodium-ion batteries, the demand for high-performance hard carbon anode materials is growing, bringing with it a series of technical and research challenges. Currently, further breakthroughs are needed in optimizing the electrochemical performance and improving the initial coulombic efficiency (ICE) of hard carbon anodes.

[0004] Chinese patent document CN116544386A discloses a starch-based hard carbon sodium-ion battery anode material, its preparation method, and its applications. This material possesses a widely distributed closed-pore structure, significantly enhancing its sodium desodiumation and intercalation capabilities, further improving its specific capacity. However, this material exhibits some oxygen-containing functional groups and defects, which can trap sodium. + This leads to irreversible capacity loss. Chinese patent document CN117735521A discloses a hard carbon anode material, its preparation method, applications, and a sodium-ion battery. This hard carbon anode material possesses suitable pore size distribution and specific surface area, exhibiting excellent electrochemical performance when applied to batteries. However, the solid electrolyte interface (SEI) formed at the interface between the hard carbon and the electrolyte consumes irreversible sodium ions, resulting in low ICE (internal capacity loss). Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing hard carbon anode materials for sodium-ion batteries. This invention can generate hard carbon anode materials with abundant pore structure, stable solid-state electrolyte interface, and sufficient active sites. These characteristics work together to significantly improve the sodium storage capacity and structural stability of sodium-ion battery anodes, thereby improving the initial coulombic efficiency and specific capacity of sodium-ion batteries.

[0006] To achieve the above-mentioned objective, this invention provides a method for preparing a hard carbon anode material for sodium-ion batteries, comprising the following steps:

[0007] (1) Disperse inorganic strong acid iron salt, chain carbon source and stabilizer in N,N-dimethylformamide, heat and stir to obtain precursor solution, spray dry the precursor solution to obtain precursor;

[0008] (2) The precursor, sodium salt organic matter, inorganic strong acid zinc salt and dimethylimidazole were dissolved in methanol, and centrifuged, washed and vacuum dried in sequence to obtain the precursor coating.

[0009] (3) The precursor coating was subjected to a first step of high-temperature calcination under an argon atmosphere, then carbon dioxide gas was introduced, and a second step of high-temperature calcination was carried out. After cooling, it was washed in 2M dilute hydrochloric acid, then washed with water until neutral, and then vacuum dried to obtain the sodium-ion battery hard carbon anode material.

[0010] Preferably, in step (1), the inorganic strong acid ferric 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; and the stabilizer is one of hexadecyltrimethylammonium bromide, polyethylene glycol, and citric acid. The molar concentration of the inorganic strong acid ferric salt in the precursor solution is 0.01–0.5 mol / L, the mass ratio of the inorganic strong acid ferric salt, stabilizer, and chain carbon source is 1:1–1.7:2–3, the heating and stirring temperature is 80–90°C, and the time is 6–10 h.

[0011] Preferably, in step (2), the sodium salt organic compound is one of disodium phthalate, disodium ethylenediaminetetraacetate, trisodium citrate, and sodium tartrate, and the inorganic strong acid zinc salt is one of zinc chloride, zinc sulfate, and zinc nitrate. The mass ratio of the precursor, sodium salt organic compound, inorganic strong acid zinc salt, and dimethylimidazole is 1:0.1-0.6:1-5:2-10.

[0012] Preferably, in step (3), the first high-temperature calcination conditions are: heating to 600-800℃, heating rate of 2-5℃ / min, and holding time of 1-4h; the second high-temperature calcination conditions are: heating to 1000-1500℃, heating rate of 5-10℃ / min, and holding time of 1-2h; the concentration of dilute hydrochloric acid is 2M; and the vacuum drying conditions are: temperature of 70-90℃ and time of 8-12h.

[0013] The beneficial effects of this invention are as follows:

[0014] 1. The technical solution provided by this invention involves combining inorganic strong acid iron salts with a chain carbon source, followed by high-temperature calcination and carbon dioxide gas etching to generate an iron carbide and hard carbon composite material. Iron carbide itself has high reactivity and therefore excellent sodium storage capacity. Combining it with hard carbon can further increase the overall sodium storage capacity of the negative electrode material. The addition of iron carbide effectively improves the conductivity of the hard carbon negative electrode, which enhances the material utilization efficiency 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 maintain the structural integrity of hard carbon during charge and discharge, reducing material expansion and contraction 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 storage and penetration capacity of sodium, further improving battery performance.

[0015] 2. The technical solution provided by this invention allows the addition of sodium salt organic matter to react with the hard carbon surface, forming a stable SEI layer. This helps reduce irreversible sodium ion loss during the first charge and discharge process, thereby significantly improving the initial coulombic efficiency of the battery. This stable SEI layer reduces the repeated formation of the SEI during battery cycling, avoiding excessive consumption of sodium ions and electrolyte, which affects battery performance. The stable SEI layer prevents direct contact between the hard carbon anode and the electrolyte, reducing side reactions and thus improving battery safety. Due to the protective effect of the SEI layer, the structural integrity of the hard carbon anode is maintained, reducing volume expansion and contraction during charge and discharge, thereby improving the cycle stability of the battery.

[0016] 3. The technical solution provided by this invention employs a two-step calcination method during the carbonization process. Initially, the precursor coating is pyrolyzed under argon gas. Inorganic strong acid iron salt and chain carbon source form iron carbide particles. Then, carbon dioxide gas is introduced to further increase the number and volume of closed pores at higher temperatures. This closed-pore environment provides more storage sites for sodium ions, which can effectively insert and extract sodium ions during battery charging and discharging. Simultaneously, the zinc metal formed by the inorganic strong acid zinc salt at high temperatures vaporizes, forming micropores. These porous environments significantly improve the sodium storage capacity of the hard carbon anode. The presence of closed pores helps form a stable sodium ion insertion platform at lower voltages. Due to the increased number and volume of closed pores, the initial coulombic efficiency of the hard carbon anode in sodium-ion batteries is improved. This means that irreversible capacity loss during the first charge-discharge process is reduced, and the battery efficiency and energy utilization 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 anode during this process. This helps maintain the structural integrity of the electrode and reduces structural degradation during charge-discharge cycles.

[0017] 4. The hard carbon anode material for sodium-ion batteries prepared by the technical solution provided in this invention exhibits outstanding performance in sodium-ion battery anodes. 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. Simultaneously, the ICE (intercalation efficiency) can be maintained at 92.0–96.5% under 0.1 A / g cycling conditions. Attached Figure Description

[0018] Figure 1 The image shows a scanning electron microscope (SEM) image of the hard carbon anode material for sodium-ion batteries prepared in Example 1.

[0019] Figure 2 The image shows the X-ray diffraction (XRD) pattern of the hard carbon anode material for sodium-ion batteries prepared in Example 1.

[0020] Figure 3 The rate performance diagram shows the sodium-ion battery hard carbon anode material prepared in Example 1. Detailed Implementation

[0021] The present invention will be described in detail below with reference to embodiments and comparative examples, but the present invention is not limited thereto. Example 1

[0022] (1) Ferric chloride, epoxy resin, and hexadecyltrimethylammonium bromide were dispersed in 50 ml of N,N-dimethylformamide, and then heated and stirred at 90 °C for 8 h to obtain a precursor solution. The molar concentration of ferric chloride in the precursor solution was 0.01 mol / L, and the mass ratio of ferric chloride, hexadecyltrimethylammonium bromide, and epoxy resin was 1:1.3:2. The precursor solution was spray-dried to obtain the precursor.

[0023] (2) The precursor, disodium phthalate, zinc chloride, and dimethylimidazole were dissolved in methanol and stirred overnight. Then, the mixture was centrifuged, washed, and dried to obtain the precursor-coated product. The mass ratio of the precursor, disodium phthalate, zinc chloride, and dimethylimidazole was 1:0.6:1:10.

[0024] (3) The precursor coating was placed in a tube furnace and heated to 650°C at a heating rate of 2°C / min in an argon atmosphere for 3 hours to obtain a carbonized product. Then carbon dioxide gas was introduced and heated to 1500°C at a heating rate of 10°C / min for 1 hour. After cooling, it was washed in 2M dilute hydrochloric acid, then further filtered and washed with water, and vacuum dried at 90°C for 12 hours to finally obtain the sodium-ion battery hard carbon anode material. Example 2

[0025] (1) Ferric nitrate, polyacrylonitrile, and polyethylene glycol were dispersed in 50 ml of N,N-dimethylformamide, and then heated and stirred at 80 °C for 10 h to obtain a precursor solution. The molar concentration of ferric nitrate in the precursor solution was 0.1 mol / L, and the mass ratio of ferric nitrate, polyethylene glycol, and polyacrylonitrile was 1:1:2. The precursor solution was spray-dried to obtain the precursor.

[0026] (2) The precursor, disodium ethylenediaminetetraacetate, zinc nitrate, and dimethylimidazole were dissolved in methanol and stirred overnight. Then, the mixture was centrifuged, washed, and dried to obtain the precursor-coated product. The mass ratio of the precursor, disodium ethylenediaminetetraacetate, zinc nitrate, and dimethylimidazole was 1:0.1:5:2.

[0027] (3) The precursor coating was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min in an argon atmosphere for 1 hour to obtain a carbonized product. Then carbon dioxide gas was introduced and heated to 1200°C at a heating rate of 5°C / min for 2 hours. After cooling, it was washed in 2M dilute hydrochloric acid, then further filtered and washed with water, and vacuum dried at 80°C for 10 hours to finally obtain the sodium-ion battery hard carbon anode material. Example 3

[0028] (1) Ferric sulfate, polyaniline, and citric acid were dispersed in 50 ml of N,N-dimethylformamide, and then heated and stirred at 85 °C for 6 h to obtain a precursor solution. The molar concentration of ferric sulfate in the precursor solution was 0.5 mol / L, and the mass ratio of ferric sulfate, citric acid, and polyaniline was 1:1.7:3. The precursor solution was then spray-dried to obtain the precursor.

[0029] (2) The precursor, trisodium citrate, zinc sulfate, and dimethylimidazole were dissolved in methanol and stirred overnight. Then, the mixture was centrifuged, washed, and dried to obtain the precursor-coated product. The mass ratio of the precursor, disodium ethylenediaminetetraacetate, zinc sulfate, and dimethylimidazole was 1:0.6:5:2.

[0030] (3) The precursor coating was placed in a tube furnace and heated to 600°C at a heating rate of 3°C / min in an argon atmosphere for 4 hours to obtain carbonized products. Then carbon dioxide gas was introduced and heated to 1000°C at a heating rate of 5°C / min for 1 hour. After cooling, it was washed in 2M dilute hydrochloric acid, then further filtered and washed with water, and vacuum dried at 70°C for 9 hours to finally obtain the sodium-ion battery hard carbon anode material. Example 4

[0031] (1) Ferric nitrate, phenolic resin, and polyethylene glycol were dispersed in 50 ml of N,N-dimethylformamide, and then heated and stirred at 90 °C for 7 h to obtain a precursor solution. The molar concentration of ferric nitrate in the precursor solution was 0.2 mol / L, and the mass ratio of ferric nitrate, polyethylene glycol, and phenolic resin was 1:1:3. The precursor solution was then spray-dried to obtain the precursor.

[0032] (2) The precursor, sodium tartrate, zinc chloride and dimethylimidazole were dissolved in methanol and stirred overnight. Then, the mixture was centrifuged, washed and dried to obtain the precursor-coated product. The mass ratio of the precursor, disodium phthalate, zinc chloride and dimethylimidazole was 1:0.1:1:10.

[0033] (3) The precursor coating was placed in a tube furnace and heated to 800°C at a heating rate of 4°C / min in an argon atmosphere for 2 hours to obtain a carbonized product. Then carbon dioxide gas was introduced and heated to 1500°C at a heating rate of 10°C / min for 2 hours. After cooling, it was washed in 2M dilute hydrochloric acid, then further filtered and washed with water, and vacuum dried at 80°C for 8 hours to finally obtain the sodium-ion battery hard carbon anode material. Comparative Example 1

[0034] This comparative example does not include inorganic strong acid iron salts, but all other processes are the same as in Example 1. Comparative Example 2

[0035] This comparative example does not include any sodium salt organic matter, but all other processes are consistent with those in Example 1. Comparative Example 3

[0036] In this comparative example, no carbon dioxide was introduced; all other procedures were the same as in Example 1.

[0037] Performance testing:

[0038] The negative electrode materials obtained according to the examples and comparative examples were directly used as negative electrode sheets, with a sodium metal sheet as the counter electrode, a 1 mol / L NaPF6 EC / DMC (1:1 Vol%) solution as the electrolyte, and Whatman adhesive-free glass fiber filter paper as the separator. A 2032-type button cell was assembled in a glove box under an argon atmosphere. The test results are shown in Table 1.

[0039]

[0040] The sodium-ion battery hard carbon anode material obtained in Example 1 was subjected to scanning electron microscopy (SEM) testing, and the resulting SEM images are shown below. Figure 1As shown in the figure, the sodium-ion battery hard carbon anode material of this invention has a blocky structure and a porous surface. This porous structure is attributed to carbon dioxide etching technology, which creates abundant closed pores in the hard carbon material, providing more active sites for sodium ion storage. These sites can effectively insert and extract sodium ions during battery charging and discharging, thus significantly improving the sodium storage capacity of the hard carbon anode. In this invention, a two-step calcination method is used during carbonization. Initially, the precursor coating is decomposed under a lower temperature argon atmosphere, and inorganic strong acid iron salts and chain carbon sources form iron carbide particles. At higher temperatures, the carbon further decomposes, and the microlattice further curls to form a closed-pore environment. Carbon dioxide gas assists in increasing the number and volume of closed pores. This closed-pore environment provides more storage sites for sodium ions, which can effectively insert and extract sodium ions during battery charging and discharging. If a one-step calcination method is used, the iron carbide particles may be too large, resulting in a reduction of active sites. Furthermore, the zinc metal formed by the inorganic strong acid zinc salt at high temperatures vaporizes, creating micropores. These porous environments significantly enhance the sodium storage capacity of the hard carbon anode. The presence of closed pores helps form a stable sodium-ion intercalation platform at lower voltages. Due to the increase in the number and volume of closed pores, the initial coulombic efficiency of the hard carbon anode in sodium-ion batteries is improved. This means that irreversible capacity loss during the first charge-discharge cycle is reduced, and the battery efficiency and energy utilization 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 anode during this process. This helps maintain the structural integrity of the electrode and reduces structural degradation during charge-discharge cycles.

[0041] Adding sodium salt organic matter to the precursor coating allows it to react with the hard carbon surface, forming an SEI layer that helps reduce irreversible sodium ion loss during the first charge and discharge cycle, thus significantly improving the battery's initial coulombic efficiency. A stable SEI layer reduces the repeated formation of the SEI during battery cycling, which typically leads to additional sodium ion and electrolyte consumption, affecting battery performance. A stable SEI layer also prevents direct contact between the hard carbon anode and the electrolyte, reducing side reactions and improving battery safety. Furthermore, the protective effect of the SEI layer maintains the structural integrity of the hard carbon anode, reducing volume expansion and contraction during charge and discharge, thereby improving the battery's cycle stability.

[0042] The sodium-ion battery hard carbon anode material prepared in Example 1 was analyzed by XRD, and the results are shown in [the table / document / etc.]. Figure 2 The XRD pattern reveals a carbon peak at approximately 25° and Fe3C. The weak characteristic peak of Fe3C in the XRD is due to the small size of the Fe3C nanoparticles and their good dispersion in the material.

[0043] The prepared hard carbon anode material was subjected to electrochemical tests, such as... Figure 3 As shown in the table, the hard carbon anode material prepared in Example 1 exhibited specific capacities of 468.1, 436.9, 373.2, 295.5, 271.0, and 226.9 mAh / g at current densities of 0.1, 0.2, 0.5, 1, 2, and 5 A / g, respectively, with an ICE of 96.5% at 0.1 A / g, demonstrating excellent charge-discharge performance. The same tests were performed on the materials from Examples 2 to 4, and the results were similar to those of Example 1 (Table 1). The difference in ICE retention rate among the samples from each example at a current density of 0.1 A / g did not exceed 5%.

[0044] Compared to the sample in Comparative Example 1, the examples showed better performance under different rate and ICE conditions, indicating that Fe3C has high reactivity and therefore excellent sodium storage capacity. Combining it with hard carbon can further increase the overall sodium storage capacity of the anode material. The addition of Fe3C effectively improves the conductivity of the hard carbon anode, which enhances the material utilization efficiency and promotes the rapid diffusion of sodium ions, thereby improving the battery's charge and discharge efficiency. Simultaneously, Fe3C helps maintain the structural integrity of the hard carbon during charge and discharge, reducing material expansion and contraction caused by volume changes, which helps enhance the battery's cycle life. Furthermore, Fe3C has high surface wettability to the electrolyte, which helps improve sodium storage and permeation capacity, further improving battery performance (Table 1). In addition, regarding Comparative Example 2, since the anode material lacks sodium salt organic matter, the sodium content in the SEI... + This leads to a significant reduction in cycle reversibility and ICE retention. Example 3 exhibits superior electrochemical performance compared to Comparative Example 3, indicating that the numerous closed pores formed by CO2 etching play a crucial role in the sodium storage performance of hard carbon.

[0045] The specific embodiments described above provide a further detailed explanation of the present invention; however, these descriptions should not be construed as limiting the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon anode material for sodium-ion batteries, characterized in that, Includes the following steps: (1) Disperse inorganic strong acid iron salt, chain carbon source and stabilizer in N,N-dimethylformamide, heat and stir to obtain precursor solution, spray dry the precursor solution to obtain precursor; (2) The precursor, sodium salt organic matter, inorganic strong acid zinc salt and dimethylimidazole were dissolved in methanol, and centrifuged, washed and vacuum dried in sequence to obtain the precursor coating. (3) The precursor coating was subjected to a first step of high-temperature calcination under an argon atmosphere, then carbon dioxide gas was introduced, and a second step of high-temperature calcination was carried out. After cooling, it was washed in 2M dilute hydrochloric acid, then washed with water until neutral, and then vacuum dried to obtain the sodium-ion battery hard carbon anode material.

2. The method for preparing the hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that, In step (1), the inorganic strong acid ferric 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; and the stabilizer is one of hexadecyltrimethylammonium bromide, polyethylene glycol, and citric acid. The molar concentration of the inorganic strong acid ferric salt in the precursor solution is 0.01–0.5 mol / L, the mass ratio of the inorganic strong acid ferric salt, stabilizer, and chain carbon source is 1:1–1.7:2–3, the heating and stirring temperature is 80–90°C, and the time is 6–10 h.

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

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

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