Resin-based hard carbon material as well as preparation method and application thereof

Abstract

The invention discloses a resin-based hard carbon material as well as a preparation method and application thereof, and belongs to the technical field of sodium-ion battery negative electrode materials. The preparation method mainly comprises the following steps: pre-oxidizing gel phenolic resin in air, and performing high-temperature carbonization on the gel phenolic resin in a protective atmosphere to obtain the resin-based hard carbon material; the preparation process of the gel phenolic resin comprises the steps that a phenolic resin prepolymer is provided, the prepolymer comprises a phenol compound, a formaldehyde solution and deionized water, and gel phenolic resin is prepared through a heating reaction; the catalyst is anhydrous sodium carbonate; the cross-linking agent is imidazole ionic liquid. The obtained resin-based hard carbon material has good sodium storage performance and cycling stability.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery anode materials, and specifically relates to a method for preparing and applying a hard carbon anode material. Background Technology

[0002] With the deepening of the global energy structure transformation, the large-scale development and utilization of renewable energy (such as wind and solar power) has become a key strategy for addressing climate change and energy security challenges. However, renewable energy power generation is intermittent and unstable, requiring efficient and reliable electrochemical energy storage systems to achieve stable power output and grid peak shaving. Against this backdrop, lithium-ion batteries (LIBs) have dominated the energy storage market for decades due to their high energy density and mature technology. However, lithium-ion batteries (LIBs) are limited by finite and concentrated lithium resources, and will inevitably face bottlenecks caused by lithium scarcity, while sodium resources are abundant. Therefore, sodium-ion batteries (SIBs) will gradually become a viable alternative.

[0003] In sodium-ion batteries, the anode material is one of the key factors determining its electrochemical performance. Because the radius of sodium ions (1.02 Å) is larger than that of lithium ions (0.76 Å), traditional graphite anodes (interlayer spacing of approximately 0.335 nm) struggle to achieve reversible insertion / extraction of sodium ions, resulting in extremely low capacity (<35 mAh / g). Hard carbon materials, due to their disordered carbon layer structure, large interlayer spacing (typically >0.37 nm), and abundant nanopores, can provide more storage sites and better diffusion channels for sodium ions, making them the most promising anode materials for sodium-ion batteries.

[0004] The performance of hard carbon batteries largely depends on the choice of precursors and the preparation process. Currently, the mainstream precursors include three main categories: biomass (such as grapefruit peel, bagasse, and peanut shells), petroleum asphalt, and synthetic resins. While biomass precursors are widely available and inexpensive, their chemical composition and microstructure are significantly affected by the growth environment, season, and region, resulting in poor batch-to-batch consistency of the prepared hard carbon materials, making it difficult to meet the requirements of product uniformity and stability for industrial production. Although petroleum asphalt-based hard carbon has a high carbon yield and good conductivity, its production process typically involves high-temperature coking, which generates large amounts of toxic and harmful substances such as polycyclic aromatic hydrocarbons, posing serious environmental pollution problems. Furthermore, the purity of the raw materials is not high, and impurities (such as sulfur and metal ions) may adversely affect battery performance.

[0005] In contrast, synthetic resins (such as phenolic resins, epoxy resins, and polyimides) have unique advantages as precursors: their molecular structures are highly designable, their purity is extremely high (ash-free and impurity-free), and the hard carbon materials obtained after carbonization exhibit high consistency, structural stability, and reproducibility. These characteristics are crucial for ensuring the consistency and safety of battery products. However, resin-based hard carbon prepared by traditional methods still has significant shortcomings in sodium-ion battery applications: on the one hand, its reversible sodium storage capacity is generally low (usually below 300 mAh / g), making it difficult to meet the requirements of high-energy-density batteries; on the other hand, its capacity decays rapidly during long cycles, and its structural stability needs to be improved. These problems mainly stem from the difficulty of precisely controlling the microstructure of hard carbon (such as interlayer spacing, pore distribution, defect concentration, and graphite crystallite size) in traditional carbonization processes, leading to insufficient sodium-ion storage active sites, sluggish ion transport kinetics, and structural degradation during cycling.

[0006] In existing technologies, the performance of resin-based hard carbon is improved through doping (such as doping with heteroatoms like nitrogen, phosphorus, and sulfur), compositing (compositing with metals / metal oxides), or template methods (using nanotemplates to control the pore structure). These methods are often complex and costly, or introduce inactive substances to reduce tap density, which is not conducive to industrial applications. Furthermore, some methods, while improving initial capacity, sacrifice cycle stability or initial coulombic efficiency. For example, invention patent CN117886299A discloses a method for preparing modified phenolic resin-based hard carbon materials and a sodium-ion battery. This method prepares phenolic resin-based hard carbon in an environmentally friendly and simple process. The modified hard carbon material exhibits short-range ordered and long-range disordered microstructure characteristics, demonstrating excellent cycle stability and high reversible capacity. However, the process route is long and energy-intensive, which is not conducive to scale-up production. Simultaneously, the doping of nitrogen / phosphorus elements reduces the stability of the carbon framework, resulting in unsatisfactory capacity retention under long-term cycling. For example, invention patent CN118164468A discloses a resin-based hard carbon microsphere and its preparation method. The prepared hard carbon microspheres possess excellent first-time efficiency and reversible capacity, while also exhibiting high tap density and low ash content, showing great promise for applications in the field of sodium-ion battery anode materials. However, the spherical morphology leads to a "point contact" conductive network, requiring the addition of more expensive conductive agents to improve conductivity. Furthermore, the spheres are prone to stress concentration during long-term cycling, causing them to crack and resulting in capacity decay.

[0007] Therefore, developing a simple, cost-controllable method for preparing resin-based hard carbon that can simultaneously achieve high reversible capacity and excellent cycle stability has become a critical technical challenge that needs to be addressed to promote the commercial application of sodium-ion batteries. Summary of the Invention

[0008] This invention addresses the shortcomings of existing resin-based hard carbon anode materials, such as insufficient performance, complex modification processes, and high costs, by proposing a resin-based hard carbon material, its preparation method, and its applications.

[0009] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0010] This invention provides a method for preparing a resin-based hard carbon material, comprising the following steps:

[0011] (1) Phenolic compounds, formaldehyde solution and anhydrous sodium carbonate are dissolved in a solvent and stirred to obtain phenolic resin prepolymer;

[0012] (2) Mix the imidazole ionic liquid with the phenolic resin prepolymer, stir and heat to react, and then dry the resulting gel phenolic resin.

[0013] (3) The dried gel phenolic resin is pre-oxidized, and then the pre-oxidized gel phenolic resin is carbonized at high temperature to obtain resin-based hard carbon. The resin-based hard carbon material is obtained by grinding and ball milling.

[0014] In step (1), the molar ratio of phenolic compounds to formaldehyde is 1:1-3, preferably 1:1.5-2; the molar ratio of anhydrous sodium carbonate to phenolic compounds is 1:100-1500, preferably 1:150-250; the mass percentage of the formaldehyde solution is 35-37%; the phenolic compounds are selected from at least one of phenol, resorcinol, bisphenol A, and 3-aminophenol; the solvent is deionized water; and the stirring time is 5-30 min, preferably 10-15 min.

[0015] In step (2), phenolic compounds and formaldehyde undergo a polymerization reaction at high temperature, and imidazole ionic liquids will increase the degree of polymerization.

[0016] The molar ratio of the imidazole ionic liquid to the phenolic compound in the phenolic resin prepolymer is 1:5-20, preferably 1:8-15; the imidazole ionic liquid is selected from at least one of 1-ethyl-2,3-dimethylimidazolium bromide, 1-butyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-octyl-3-methylimidazolium tetrafluoroborate, 1-decyl-3-methylimidazolium tetrafluoroborate, and 1-dodecyl-3-methylimidazolium tetrafluoroborate, preferably at least one of 1-ethyl-2,3-dimethylimidazolium bromide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, and 1-hexyl-3-methylimidazolium tetrafluoroborate;

[0017] The heating reaction is carried out at a temperature of 70-90℃, preferably 80-85℃, for a time of 2-48h, preferably 12-24h; the drying is carried out under vacuum at a temperature of 75-85℃, a vacuum degree of 0.01-0.02MPa, for a time of 2-3h.

[0018] In step (3), the pre-oxidation process increases the oxygen content on the material surface, thereby improving the degree of cross-linking; the heating rate of the pre-oxidation is 5-10℃ / min, preferably 8-10℃ / min, the pre-oxidation temperature is 150-300℃, preferably 200-250℃, and the pre-oxidation time is 5-24h, preferably 10-12h.

[0019] The heating rate for high-temperature carbonization is 3-5℃ / min, preferably 4-5℃ / min; the high-temperature carbonization temperature is 1100-1500℃, preferably 1300-1350℃; the holding time is 0.5-3h, preferably 1-2h; after the holding time, the temperature is reduced to 500℃ at a rate of 5℃ / min, and then allowed to cool naturally to room temperature; the grinding and ball milling are used to reduce the particle size of the hard carbon material to 3-15μm, preferably 5-10μm.

[0020] This invention provides a resin-based hard carbon material prepared using the aforementioned preparation method.

[0021] The present invention also provides the application of the resin-based hard carbon material in sodium-ion battery anode materials.

[0022] The beneficial effects of this invention are:

[0023] 1. This invention creatively proposes a sol-gel method for preparing phenolic resins. The process conditions are mild and the parameters are easy to control, laying the foundation for controllable material preparation. Furthermore, imidazole ionic liquids are added during resin synthesis to adjust the degree of polymerization. Their unique aromatic structure and side chains further promote the formation of a uniform and highly cross-linked three-dimensional gel network, an effect difficult to achieve with traditional polymerization processes. The entire process is well-defined and reproducible, fundamentally overcoming batch fluctuations caused by uneven precursor structures. It possesses excellent potential for process scale-up and provides a reliable path for stable industrial production.

[0024] 2. This invention utilizes ionic liquid regulation to obtain a highly cross-linked and homogeneous gel phenolic resin, providing an ideal precursor for the subsequent carbonization process. This homogeneous structure exhibits excellent thermal stability during pre-carbonization and high-temperature carbonization, effectively suppressing structural collapse and disordered growth. Ultimately, it transforms into a hard carbon material with a rich and stable closed-pore structure and a rationally distributed defect structure, achieving an optimized balance between ordered and disordered regions. The uniformity and stability of its microstructure are the fundamental guarantee for improved performance.

[0025] 3. The hard carbon material prepared by this invention exhibits excellent sodium storage performance and cycle stability. The optimized closed-pore system provides ample and stable sodium ion storage sites, while the highly coherent carbon framework ensures efficient ion and electron conduction, enabling the material to possess both high reversible specific capacity and excellent rate performance. Furthermore, the robust carbon framework effectively buffers volumetric strain during cycling, thereby endowing the material with an ultra-long cycle life and extremely high capacity retention. The hard carbon material prepared by this invention has outstanding comprehensive performance and is particularly suitable as the anode material for high-performance, long-life sodium-ion batteries, solving the problems of low reversible capacity and poor cycle performance of resin-based hard carbon materials in traditional technologies. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The charge-discharge curves of the resin-based hard carbon anode materials prepared in Examples 1, 2 and Comparative Example 1 when used as anodes in sodium-ion batteries are shown.

[0028] Figure 2 The rate performance diagrams show the resin-based hard carbon anode materials prepared in Examples 1, 2, and 1 as anodes in sodium-ion batteries.

[0029] Figure 3 The graph shows the cycle performance of the resin-based hard carbon anode materials prepared in Examples 1, 2 and Comparative Example 1 when used as anodes in sodium-ion batteries. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] A method for preparing a resin-based hard carbon material, comprising the following specific steps:

[0033] (1) Dissolve 2.2g of resorcinol and 3mL of formaldehyde solution (formaldehyde mass fraction is 37%, and the molar ratio of resorcinol to formaldehyde is 1:2) in 10mL of deionized water and stir for 30min to obtain a homogeneous solution;

[0034] (2) Dissolve 0.0106 g of anhydrous sodium carbonate (sodium carbonate to resorcinol molar ratio of 1:200) in the solution obtained in step (1), and stir for 10 min to obtain phenolic resin prepolymer;

[0035] (3) Mix 0.41g of 1-ethyl-2,3-dimethylimidazolium bromide with phenolic resin prepolymer (molar ratio of ionic liquid to resorcinol is 1:10), stir for 10min until fully dispersed, and then carry out the reaction in a reactor at a temperature of 80℃ for 24h to obtain gel phenolic resin. Dry it under vacuum at a temperature of 80℃ and a vacuum degree of 0.01MPa for 2h.

[0036] (4) The dried gel phenolic resin was pre-oxidized at 250°C for 12 hours, and then the pre-oxidized gel phenolic resin was carbonized at high temperature. The pre-oxidized gel phenolic resin was sintered in a tube furnace under an argon atmosphere. The temperature was increased from room temperature to 1300°C at a rate of 5°C / min and held for 2 hours. The cooling process was first reduced to 500°C at a rate of 5°C / min, and then cooled naturally to obtain resin-based hard carbon. The refined resin-based hard carbon material was obtained by grinding and ball milling.

[0037] Example 2

[0038] A method for preparing a resin-based hard carbon material, comprising the following specific steps:

[0039] (1) Dissolve 2.2g of resorcinol and 3mL of formaldehyde solution (formaldehyde mass fraction is 37%, and the molar ratio of resorcinol to formaldehyde is 1:2) in 10mL of deionized water and stir for 30min to obtain a homogeneous solution;

[0040] (2) Dissolve 0.0106 g of anhydrous sodium carbonate (sodium carbonate to resorcinol molar ratio of 1:200) in the solution obtained in step (1), and stir for 10 min to obtain phenolic resin prepolymer;

[0041] (3) Mix 0.396g of 1-ethyl-3-methylimidazolium tetrafluoroborate with phenolic resin prepolymer (molar ratio of ionic liquid to resorcinol is 1:10), stir for 10min until fully dispersed, and then carry out the reaction in a reactor at a temperature of 80℃ for 24h to obtain gel phenolic resin. Dry it under vacuum at a temperature of 80℃ and a vacuum degree of 0.01MPa for 2h.

[0042] (4) The dried gel phenolic resin was pre-oxidized at 250°C for 12 hours, and then the pre-oxidized gel phenolic resin was carbonized at high temperature. The pre-oxidized gel phenolic resin was sintered in a tube furnace under an argon atmosphere. The temperature was increased from room temperature to 1300°C at a rate of 5°C / min and held for 2 hours. The cooling process was first reduced to 500°C at a rate of 5°C / min, and then cooled naturally to obtain resin-based hard carbon. The refined resin-based hard carbon material was obtained by grinding and ball milling.

[0043] Example 3

[0044] A method for preparing a resin-based hard carbon material, comprising the following specific steps:

[0045] (1) Dissolve 2.2g of resorcinol and 2.23mL of formaldehyde solution (formaldehyde mass fraction is 37%, and the molar ratio of resorcinol to formaldehyde is 1:1.5) in 10mL of deionized water and stir for 30min to obtain a homogeneous solution;

[0046] (2) Dissolve 0.0106 g of anhydrous sodium carbonate (sodium carbonate to resorcinol molar ratio of 1:200) in the solution obtained in step (1), and stir for 10 min to obtain phenolic resin prepolymer;

[0047] (3) Mix 0.5125g of 1-ethyl-2,3-dimethylimidazolium bromide with phenolic resin prepolymer (molar ratio of ionic liquid to resorcinol is 1:8), stir for 10min until fully dispersed, and then carry out the reaction in a reactor at a temperature of 80℃ for 24h to obtain gel phenolic resin. Dry it under vacuum at a temperature of 80℃ and a vacuum degree of 0.01MPa for 2h.

[0048] (4) The dried gel phenolic resin was pre-oxidized at 250°C for 12 hours, and then the pre-oxidized gel phenolic resin was carbonized at high temperature. The pre-oxidized gel phenolic resin was sintered in a tube furnace under an argon atmosphere. The temperature was increased from room temperature to 1300°C at a rate of 5°C / min and held for 2 hours. The cooling process was first reduced to 500°C at a rate of 5°C / min, and then cooled naturally to obtain resin-based hard carbon. The refined resin-based hard carbon material was obtained by grinding and ball milling.

[0049] Example 4

[0050] A method for preparing a resin-based hard carbon material, comprising the following specific steps:

[0051] (1) Dissolve 2.2g of resorcinol and 4.76mL of formaldehyde solution (formaldehyde mass fraction is 35%, and the molar ratio of resorcinol to formaldehyde is 1:3) in 20mL of deionized water and stir for 20min to obtain a homogeneous solution;

[0052] (2) Dissolve 1.41 mg of anhydrous sodium carbonate (sodium carbonate to resorcinol molar ratio of 1:1500) in the solution obtained in step (1), and stir for 10 min to obtain phenolic resin prepolymer;

[0053] (3) Mix 0.205g of 1-ethyl-2,3-dimethylimidazolium bromide with phenolic resin prepolymer (molar ratio of ionic liquid to resorcinol is 1:20), stir for 10min until fully dispersed, and then carry out the reaction in a reactor at a temperature of 90℃ for 2h to obtain gel phenolic resin. Dry it under vacuum at a temperature of 75℃ and a vacuum degree of 0.02MPa for 3h.

[0054] (4) The dried gel phenolic resin was pre-oxidized at 150°C for 24 hours, and then the pre-oxidized gel phenolic resin was carbonized at high temperature. The pre-oxidized gel phenolic resin was sintered in a tube furnace under an argon atmosphere. The temperature was increased from room temperature to 1500°C at a heating rate of 3°C / min and held for 0.5 hours. The cooling process was first reduced to 500°C at a rate of 5°C / min, and then cooled naturally to obtain resin-based hard carbon. The refined resin-based hard carbon material was obtained by grinding and ball milling.

[0055] Example 5

[0056] A method for preparing a resin-based hard carbon material, comprising the following specific steps:

[0057] (1) Dissolve 2.2g of resorcinol and 1.54mL of formaldehyde solution (formaldehyde mass fraction is 36%, and the molar ratio of resorcinol to formaldehyde is 1:1) in 5mL of deionized water and stir for 5min to obtain a homogeneous solution.

[0058] (2) Dissolve 0.0212g of anhydrous sodium carbonate (sodium carbonate to resorcinol molar ratio of 1:100) in the solution obtained in step (1), and stir for 10min to obtain phenolic resin prepolymer;

[0059] (3) Mix 0.82g of 1-ethyl-2,3-dimethylimidazolium bromide with phenolic resin prepolymer (molar ratio of ionic liquid to resorcinol is 1:5), stir for 10min until fully dispersed, and then carry out the reaction in a reactor at a temperature of 70℃ for 48h to obtain gel phenolic resin. Dry it under vacuum at a temperature of 85℃, a vacuum degree of 0.01MPa, and a vacuum drying time of 2.5h.

[0060] (4) The dried gel phenolic resin was pre-oxidized at 300℃ for 5h, and then the pre-oxidized gel phenolic resin was carbonized at high temperature. The pre-oxidized gel phenolic resin was sintered in a tube furnace under an argon atmosphere. The temperature was increased from room temperature to 1100℃ at a heating rate of 4℃ / min and held for 3h. The cooling process was first reduced to 500℃ at a rate of 3℃ / min, and then cooled naturally to finally obtain resin-based hard carbon. The refined resin-based hard carbon material was obtained by grinding and ball milling.

[0061] Comparative Example 1

[0062] A method for preparing a resin-based hard carbon material, comprising the following specific steps:

[0063] (1) Dissolve 2.2g of resorcinol and 3mL of formaldehyde solution (formaldehyde mass fraction is 37%, and the molar ratio of resorcinol to formaldehyde is 1:2) in 150mL of ethanol aqueous solution (ethanol and deionized water volume ratio is 1:1), and stir for 30min to obtain a homogeneous solution.

[0064] (2) Dissolve 0.0106 g of anhydrous sodium carbonate (sodium carbonate to resorcinol molar ratio of 1:200) in the solution obtained in step (1), and stir for 10 min to obtain phenolic resin prepolymer;

[0065] (3) Mix 0.41g of 1-ethyl-2,3-dimethylimidazolium bromide with phenolic resin prepolymer (molar ratio of ionic liquid to resorcinol is 1:10), stir for 10min until fully dispersed, then transfer to a flask and heat in an oil bath for reaction at 80℃ for 4h to obtain gel phenolic resin. Dry under vacuum at 80℃ and 0.01MPa for 2h.

[0066] (4) The dried gel phenolic resin was pre-oxidized in air at 250°C for 12 hours, and then the pre-oxidized gel phenolic resin was carbonized at high temperature. The pre-oxidized gel phenolic resin was sintered in a tube furnace under an argon atmosphere. The temperature was increased from room temperature to 1300°C at a rate of 5°C / min and held for 2 hours. The cooling process was first reduced to 500°C at a rate of 5°C / min, and then cooled naturally to obtain resin-based hard carbon. The refined resin-based hard carbon material was obtained by grinding and ball milling.

[0067] Comparative Example 2

[0068] A method for preparing a resin-based hard carbon material, comprising the following specific steps:

[0069] (1) Dissolve 2.2g of resorcinol and 3mL of formaldehyde solution (formaldehyde mass fraction is 37%, and the molar ratio of resorcinol to formaldehyde is 1:2) in 10mL of deionized water and stir for 30min to obtain a homogeneous solution;

[0070] (2) Dissolve 0.0106 g of anhydrous sodium carbonate (sodium carbonate to resorcinol molar ratio of 1:200) in the solution obtained in step (1), and stir for 10 min to obtain phenolic resin prepolymer;

[0071] (3) The phenolic resin prepolymer was transferred to the reactor for heating reaction at a temperature of 80°C for 4 hours to obtain gel phenolic resin. The resin was then dried under vacuum at a temperature of 80°C and a vacuum degree of 0.01 MPa for 12 hours.

[0072] (3) The dried gel phenolic resin was pre-oxidized at 250℃ for 12h, and then the pre-oxidized gel phenolic resin was carbonized at high temperature. The pre-oxidized gel phenolic resin was sintered in a tube furnace under an argon atmosphere. The temperature was increased from room temperature to 1300℃ at a heating rate of 5℃ / min and held for 2h. The cooling process was first reduced to 500℃ at a rate of 5℃ / min, and then cooled naturally to finally obtain resin-based hard carbon. The refined resin-based hard carbon material was obtained by grinding and ball milling.

[0073] Comparative Example 3

[0074] A method for preparing a resin-based hard carbon material, comprising the following specific steps:

[0075] (1) Dissolve 2.2g of 3-aminophenol and 2.23mL of formaldehyde solution (formaldehyde mass fraction is 37%, and the molar ratio of 3-aminophenol to formaldehyde is 1:1.5) in 10mL of deionized water and stir for 30min to obtain a homogeneous solution.

[0076] (2) Dissolve 0.0106 g of anhydrous sodium carbonate (sodium carbonate to 3-aminophenol molar ratio of 1:200) in the solution obtained in step (1), and stir for 10 min to obtain phenolic resin prepolymer;

[0077] (3) Mix 0.5125g of 1-ethyl-2,3-dimethylimidazolium bromide with phenolic resin prepolymer (molar ratio of ionic liquid to 3-aminophenol is 1:8), stir for 10min until fully dispersed, and then carry out the reaction in a reactor at a temperature of 80℃ for 4h to obtain gel phenolic resin. Dry it under vacuum at a temperature of 80℃ and a vacuum degree of 0.01MPa for 2h.

[0078] (4) The dried gel phenolic resin was pre-oxidized at 250°C for 12 hours, and then the pre-oxidized gel phenolic resin was carbonized at high temperature. The pre-oxidized gel phenolic resin was sintered in a tube furnace under an argon atmosphere. The temperature was increased from room temperature to 1300°C at a rate of 5°C / min and held for 2 hours. The cooling process was first reduced to 500°C at a rate of 5°C / min, and then cooled naturally to obtain resin-based hard carbon. The refined resin-based hard carbon material was obtained by grinding and ball milling.

[0079] Implementation Results Example

[0080] The sodium storage performance of 2025 coin cells assembled from resin-based hard carbon materials prepared in Examples 1-3 and Comparative Examples 1-3 was evaluated, as detailed below:

[0081] Electrode slurry was prepared by mixing 0.4 g of hard carbon material, 0.05 g of conductive carbon black, and 0.05 g of binder (carboxymethyl cellulose) in a mass ratio of 8:1:1. This slurry was coated onto aluminum foil to a thickness of 100 μm and vacuum-dried at 80 °C for 24 h. The resulting slurry was then pressed into circular electrode sheets with a diameter of 12 mm. A 2025 coin cell was assembled using sodium foil, glass fiber (GF / D), and 1 M NaPF6 diethylene glycol dimethyl ether as the counter electrode, separator, and electrolyte, respectively.

[0082] The charge-discharge performance of the prepared coin cells was tested using the Blue Battery Testing System. The test temperature was 25℃, the voltage range was 0-2V, the nominal specific capacity was set to 300mAh / g, and the charge-discharge performance was tested at a current density of 0.03A / g. The test results are shown in Table 1.

[0083] Table 1. Charge-discharge performance test results of Examples 1-3 and Comparative Examples 1-3

[0084]

[0085] As can be seen from the table above, the hard carbon anode materials prepared in each embodiment of the present invention all have high reversible capacity and first coulombic efficiency.

[0086] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses the traditional oil bath stirring and heating method to prepare a phenolic resin in powder form, while Example 1 uses the sol-gel method to prepare a gel phenolic resin. The gel-like resin structure is conducive to the generation of more sodium storage sites after carbonization.

[0087] The difference between Comparative Example 2 and Example 2 is that no ionic liquid is added to the prepolymer of Comparative Example 2. It can be seen that the addition of ionic liquid is beneficial to the improvement of the degree of polymerization of resin and the degree of crosslinking during carbonization, thereby improving the sodium storage performance of hard carbon.

[0088] The difference between Comparative Example 3 and Example 3 is that Comparative Example 3 uses 3-aminophenol instead of resorcinol, indicating that 3-aminophenol as a precursor is not easy to polymerize with formaldehyde during heating to form a gel-like phenolic resin, thereby reducing the sodium storage performance.

[0089] Figure 1 The charge-discharge curves of batteries assembled using the hard carbon materials prepared in Examples 1, 2 and Comparative Example 1 are shown at 0.03 A / g. Among them, the reversible capacity of the battery assembled using the hard carbon material prepared in Example 1 reached 335.6 mAh / g.

[0090] Figure 2 To assess the rate performance of batteries assembled using the hard carbon materials prepared in Examples 1, 2, and Comparative Example 1, Example 1 demonstrated outstanding rate performance, exhibiting reversible capacities of 312.8, 301.5, 286.8, 270.8, 252.6, 219.4, and 162 mAh / g at current densities of 0.03, 0.06, 0.15, 0.3, 0.6, 1.5, and 3 A / g, respectively. Specifically, Example 1 still exhibited a reversible capacity of 219.4 mAh / g at a high rate of 1.5 A / g, demonstrating excellent electrochemical performance under high-current charge-discharge conditions. When the current density was reduced back to 0.03 A / g, the reversible capacity rapidly recovered to 310.1 mAh / g, indicating that its internal structure remained stable after high-rate cycling, demonstrating excellent reversibility.

[0091] Figure 3 The cycling performance of batteries assembled using the hard carbon materials prepared in Examples 1, 2 and Comparative Example 1 was measured at 0.3 A / g. Example 1 showed excellent cycling performance, with a reversible capacity retention of 90.1% after 2000 cycles, indicating that the material structure has strong stability.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a resin-based hard carbon material, characterized in that, Includes the following steps: (1) Phenolic compounds, formaldehyde solution and anhydrous sodium carbonate are dissolved in a solvent and stirred to obtain phenolic resin prepolymer; (2) Mix the imidazole ionic liquid with the phenolic resin prepolymer, stir and heat to react, and then dry the resulting gel phenolic resin. (3) The dried gel phenolic resin is pre-oxidized, and then the pre-oxidized gel phenolic resin is carbonized at high temperature to obtain resin-based hard carbon. The resin-based hard carbon material is obtained by grinding and ball milling.

2. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of phenolic compounds to formaldehyde is 1:1-3, the molar ratio of anhydrous sodium carbonate to phenolic compounds is 1:100-1500, and the mass percentage of the formaldehyde solution is 35-37%; the phenolic compounds are selected from at least one of phenol, resorcinol, bisphenol A, and 3-aminophenol.

3. The preparation method according to claim 2, characterized in that: The solvent in step (1) is deionized water, and the stirring time is 5-30 min.

4. The preparation method according to claim 3, characterized in that: In step (2), the molar ratio of the imidazole ionic liquid to the phenolic compound in the phenolic resin prepolymer is 1:5-20. The imidazole ionic liquid is selected from at least one of 1-ethyl-2,3-dimethylimidazolium bromide, 1-butyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-octyl-3-methylimidazolium tetrafluoroborate, 1-decyl-3-methylimidazolium tetrafluoroborate, and 1-dodecyl-3-methylimidazolium tetrafluoroborate.

5. The preparation method according to claim 4, characterized in that: The heating reaction in step (2) is carried out at a temperature of 70-90℃ for 2-48 hours; the drying is carried out under vacuum at a temperature of 75-85℃, a vacuum of 0.01-0.02 MPa for 2-3 hours.

6. The preparation method according to claim 5, characterized in that: The pre-oxidation in step (3) involves heating from room temperature to 150-300℃ at a heating rate of 5-10℃ / min for 5-24 hours.

7. The preparation method according to claim 6, characterized in that: The high-temperature carbonization in step (3) involves heating from room temperature to 1100-1500℃ at a heating rate of 3-5℃ / min and holding at that temperature for 0.5-3h.

8. The preparation method according to claim 7, characterized in that: The grinding and ball milling in step (3) are to reduce the particle size of the hard carbon material to 3-15 μm.

9. A resin-based hard carbon material prepared by the preparation method according to any one of claims 1-8.

10. The application of the resin-based hard carbon material of claim 9 in sodium-ion battery anode materials.

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