Ternary crosslinking-regulated highly doped nanosheet hard carbon materials, their preparation methods and applications

Abstract

This invention belongs to the field of battery materials technology and discloses a highly doped nanosheet hard carbon material based on ternary crosslinking regulation, its preparation method, and its application. A resin-based material, a nitrogen-containing heterocyclic organic ligand, and a crosslinking agent are uniformly dispersed in a solvent. A Lewis acid catalyst is added under an acidic environment to carry out a crosslinking reaction, yielding a ternary crosslinking precursor. The ternary crosslinking precursor is transferred to a sealed reaction vessel and subjected to solvothermal treatment at a temperature higher than the solvent's boiling point to obtain a reconstructed precursor. The reconstructed precursor is then subjected to gradient-heating pre-oxidation treatment in an atmosphere containing nitrogen, sulfur, and / or phosphorus heteroatoms to obtain a stabilized precursor. The stabilized precursor is then subjected to gradient-heating carbonization treatment in an inert atmosphere to obtain the highly doped nanosheet hard carbon material. This invention optimizes the structural order, heteroatom distribution, and pore structure matching of the hard carbon material, and the prepared highly doped nanosheet hard carbon material exhibits excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to hard carbon materials, specifically to highly doped nanosheet hard carbon materials based on ternary crosslinking regulation, their preparation methods, and applications. Background Technology

[0002] Hard carbon materials are considered one of the most promising anode materials for sodium-ion batteries due to their large interlayer spacing, abundant defect structure, and good low-potential sodium storage capacity. Currently, the main methods for preparing hard carbon materials include biomass carbonization and resin pyrolysis.

[0003] For biomass carbonization, biomass carbon materials are typically derived from natural resources such as lignocellulose, algae, or agricultural waste. Porous carbon materials can be obtained through simple carbonization or activation treatment. This method is simple and low-cost, but due to the complex composition and uncontrollable structure of biomass itself, non-uniform pore structures and random defect distributions easily form during carbonization, resulting in poor batch-to-batch stability and difficulty in precisely controlling interlayer spacing and sodium storage active sites. Furthermore, the numerous open pores in biomass carbon easily trigger continuous decomposition reactions in the electrolyte during the first cycle, leading to significant irreversible capacity loss and generally low initial coulombic efficiency.

[0004] For resin pyrolysis, resin-based carbon materials are typically obtained through simple resin pre-oxidation and high-temperature carbonization steps. The resulting resin-based hard carbon materials (such as urea-formaldehyde resin and phenolic resin) have been widely used in recent years to prepare structurally uniform hard carbon anode materials due to their relatively controllable molecular structures. However, these methods mostly employ single resins or simple blend systems, resulting in limited cross-linking structures within the precursor. During carbonization, structural shrinkage or collapse easily occurs, making it difficult to form a continuous and stable carbon framework. Heteroatoms such as nitrogen and oxygen are easily removed or locally enriched during high-temperature carbonization, leading to uneven distribution of active sites and consequently affecting sodium ion adsorption and interfacial reaction processes.

[0005] In addition, some studies have improved the material properties by introducing nitrogen- or oxygen-containing organic molecules to dope and modify hard carbon, or by constructing specific porous structures using template methods. However, these methods often suffer from complex processes, cumbersome steps, or high costs. For example, template-assisted methods typically require additional template introduction and removal processes, which not only increases the difficulty of the process but may also introduce impurities or damage the integrity of the carbon framework. Simple doping strategies, on the other hand, are mostly physical mixing or single chemical introductions, lacking a mechanism for fixing the structure of heteroatoms in the precursor stage, resulting in low doping efficiency and insufficient stability.

[0006] From a structural control perspective, existing methods for preparing hard carbon materials generally suffer from the following problems: First, the carbon layer stacking structure is disordered and unevenly distributed, making it difficult to precisely control the interlayer spacing, which restricts the sodium ion insertion and diffusion process. Second, there is a mismatch in pore structure types, with an excessively high proportion of open pores or insufficient closed pores, which affects the low-potential sodium storage capacity and exacerbates electrolyte side reactions. Third, the microstructure lacks continuity, and the material is prone to block agglomeration or lamellar fragmentation, making it difficult to effectively mitigate volume changes during cycling, thus leading to structural degradation. At the electrochemical performance level, these structural defects further manifest as low initial coulombic efficiency, poor rate performance, and insufficient cycling stability. Especially under high current density or long cycling conditions, the solid electrolyte interphase (SEI) is prone to continuous growth or rupture, leading to a continuous increase in charge transfer impedance and intensified polarization, severely limiting the application of hard carbon materials in practical energy storage systems.

[0007] Therefore, how to achieve multi-component synergistic crosslinking in the precursor structure design stage, thereby constructing a stable carbon skeleton structure during carbonization, while simultaneously achieving efficient introduction and uniform distribution of heteroatoms, and synergistically controlling interlayer spacing, pore structure and interface behavior, has become a key technical problem that urgently needs to be solved in the field of hard carbon anode materials. Summary of the Invention

[0008] The purpose of this invention is to address the problems existing in the prior art by providing a method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking regulation. By constructing a ternary crosslinking network, solvothermal treatment, and gradient heat treatment, the structural order, heteroatom distribution, and pore structure matching of the hard carbon materials are optimized, thereby improving the electrochemical performance of the hard carbon materials.

[0009] To achieve the above objectives, the present invention adopts the following technical solutions.

[0010] This invention provides a method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking regulation, comprising the following steps: Construction of ternary crosslinking precursor: The resin-based material, nitrogen-containing heterocyclic organic ligand and crosslinking agent are uniformly dispersed in a solvent, and a Lewis acid catalyst is added under acidic conditions to carry out the crosslinking reaction to obtain the ternary crosslinking precursor; Solvothermal-induced structural reconstruction: The ternary cross-linked precursor was transferred to a closed reaction vessel and subjected to solvothermal treatment at a temperature higher than the boiling point of the solvent at atmospheric pressure to obtain the reconstructed precursor. Gradient pre-oxidation treatment: The reconstructed precursor is subjected to gradient heating pre-oxidation treatment at 170~300℃ in an atmosphere containing nitrogen, sulfur and / or phosphorus heteroatoms to obtain a stabilized precursor; Gradient carbonization treatment: The stabilized precursor is subjected to gradient heating carbonization treatment in an inert atmosphere at 400~1000℃ to obtain highly doped nanosheet hard carbon materials.

[0011] In this invention, there is a clear synergistic relationship between the various steps: the construction of the ternary crosslinked precursor network forms the basis for structural regulation; then, the ordered reconstruction of the precursor is achieved through solvothermal treatment; next, the structure is stabilized and locked through gradient pre-oxidation treatment, promoting heteroatom fixation; finally, the carbon skeleton is constructed through gradient carbonization treatment. Through the above multi-stage synergistic regulation, the resulting hard carbon material achieves optimization in terms of structural order, heteroatom distribution, and pore structure matching, thereby exhibiting high initial coulombic efficiency, excellent rate performance, and long-term cycling stability in electrochemical performance.

[0012] In one possible implementation, the above-described step of constructing a ternary crosslinked precursor involves building a ternary crosslinked network using a resin-based material, a nitrogen-containing heterocyclic organic ligand, and a crosslinking agent. This allows for the uniform distribution of nitrogen, oxygen, and other heteroatoms at the molecular scale during the precursor stage, ensuring their stable retention during subsequent pre-oxidation and carbonization processes. The mass ratio of the resin-based material, the nitrogen-containing heterocyclic organic ligand, and the crosslinking agent is 100:(15-20):(12-20). In some preferred embodiments, the mass ratio may be 100:18:15, 100:20:18, 100:16:20, 100:18:16, 100:15:18, or 100:20:12. The resin-based material is the main component providing the carbon source and skeletal support; the resin-based material is at least one of phenolic modified amino resin, ketone-aldehyde resin, polyamide resin, phosphorus-containing modified resin, boron-containing modified resin, etc.; further, the phenolic modified amino resin includes rosin-modified phenolic resin, cashew nut phenolic amine epoxy resin, phenol-modified urea-formaldehyde resin, resorcinol-modified amino resin, nonylphenol-modified amino resin, etc., and the ketone-aldehyde resin includes cyclohexanone-formaldehyde resin, acetone-formaldehyde resin, etc. Resins, polyaldehyde resins, polyketone resins, etc., wherein the polyamide resins include polyamide-imide resins, hyperbranched polyamide resins, polyamide-amine resins, semi-aromatic polyamide resins, modified nylon resins, etc., wherein the phosphorus-containing modified resins include phosphate ester modified amino resins, DOPO modified resins, hypophosphite modified resins, polyphosphate ester resins, phosphaphenanthrene structure modified resins, etc., and wherein the boron-containing modified resins include boric acid modified resins, borate ester modified resins, boron phenolic resins, boronoxane modified resins, etc. The nitrogen-containing heterocyclic organic ligand is used to introduce nitrogen and participate in cross-linking reactions; the nitrogen-containing heterocyclic organic ligand is at least one of imidazole compounds, triazine compounds, or nitrogen-containing heterocyclic small molecule compounds; further, the imidazole compounds include benzimidazole, 2-methylimidazolium, imidazole, 2-ethylimidazolium, 2-phenylimidazolium, etc., the triazine compounds include melamine, benzomelamine, cyanuric acid chloride, 2,4-diamino-6-hydroxy-1,3,5-triazine, 2,4-diamino-6-methoxy-1,3,5-triazine, etc., and the nitrogen-containing heterocyclic small molecule compounds include 1,2,4-triazole, pyridine, pyrrole, pyrazine, pyrimidine, etc.The crosslinking agent is used to increase the network crosslinking density and enhance the structural stability of the precursor; the crosslinking agent is at least one of epoxy compounds, isocyanate compounds, organic acid anhydride compounds, or silane coupling agents; further, the epoxy compounds include glycerol triglycidyl ether, ethylene glycol diglycidyl ether, bisphenol A diglycidyl ether, etc.; the isocyanate compounds include isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, etc.; the organic acid anhydride compounds include pyromellitic dianhydride, maleic anhydride, phthalic anhydride, succinic anhydride, etc.; and the silane coupling agent compounds include γ-glycidyl etheroxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, etc. The Lewis acid catalyst is used to promote hydroxymethylation and polycondensation reactions, thereby constructing a uniform three-dimensional cross-linked structure at the molecular scale; the amount of the Lewis acid catalyst is 2.0 to 3.0 wt% based on the mass of the resin-based material. In some preferred embodiments, the amount of the Lewis acid catalyst may be 2.0 wt%, 2.2 wt%, 2.5 wt%, 2.8 wt%, or 3.0 wt%; the Lewis acid catalyst includes at least one of metal halide Lewis acids, metal trifluoromethanesulfonate Lewis acids, and boron-based Lewis acids; further, the metal halide Lewis acids include at least one of zinc chloride, zinc bromide, aluminum trichloride, aluminum tribromide, ferric chloride, ferric chloride, tin tetrachloride, and titanium tetrachloride; the metal trifluoromethanesulfonate Lewis acids include at least one of zinc trifluoromethanesulfonate, aluminum trifluoromethanesulfonate, ferric trifluoromethanesulfonate, magnesium trifluoromethanesulfonate, and scandium trifluoromethanesulfonate; the boron-based Lewis acids include at least one of boron trifluoride, boron trifluoride diethyl ether complex, boron trichloride, tris(pentafluorophenyl)boron, and triphenylboron.

[0013] Furthermore, in the step of constructing the ternary crosslinking precursor, the solvent is ethanol or a mixture of ethanol and water; the pH of the acidic environment is 3-5, which can be adjusted by using an acidic ethanol solution with a concentration of 0.1-0.5 mol / L. Examples of suitable acidic ethanol solutions include hydrochloric acid ethanol solution, nitric acid ethanol solution, phosphoric acid ethanol solution, acetic acid ethanol solution, and formic acid ethanol solution. The crosslinking reaction temperature is 60-70℃, and the reaction time is 4-6 h.

[0014] In one possible implementation, the solvothermal-induced structural reconstruction step serves to promote the spatial rearrangement of precursor molecular chains and the densification of cross-linked networks through thermal induction, transforming the original cross-linked structure from a loose state into an ordered network with a certain orientation, thereby providing a structural basis for the subsequent formation of the carbon skeleton and suppressing local collapse or uneven shrinkage that occurs during carbonization, resulting in a structurally stable reconstructed precursor.

[0015] Furthermore, the solvent heat treatment temperature is 120–200°C, and the time is 4–12 h.

[0016] In one possible implementation, the above-mentioned gradient pre-oxidation treatment step causes partial oxidation and cross-linking solidification of the organic structure in the reconstructed precursor, thereby obtaining a stabilized precursor. This step achieves "locking" of the precursor structure by gradually increasing the temperature, which on the one hand inhibits the rapid shrinkage and collapse of the structure during the subsequent high-temperature carbonization process, and on the other hand promotes the stable embedding of heteroatoms such as nitrogen and oxygen in the carbon skeleton, thereby improving the heteroatom doping efficiency and reducing their loss at high temperatures.

[0017] Furthermore, the gradient heating pre-oxidation process involves heating at 170–300℃ in 2–4 stages, with a heating rate of 1–5℃ / min and a holding time of 0.5–2 h for each stage.

[0018] Furthermore, the atmosphere containing nitrogen, sulfur, and / or phosphorus heteroatoms comes from at least one of ammonia, N2O, SO2, trimethyl phosphate vapor, CH3CN vapor, etc.; the atmosphere containing nitrogen, sulfur, and / or phosphorus heteroatoms also includes air; the volume flow rate ratio of the nitrogen, sulfur, and / or phosphorus heteroatoms in the atmosphere to the volume flow rate of air is 5:95 to 20:80.

[0019] In one possible implementation, the aforementioned gradient carbonization process gradually transforms the three-dimensional cross-linked network in the precursor into a carbon skeleton structure with nanosheets as basic units, forming a moderately expanded interlayer spacing and a porous structure system dominated by closed nanopores. By using a gradient heating method, the gradual evolution and orderly construction of the carbon skeleton can be achieved, thereby avoiding structural breakage or excessive disorder that occurs during traditional rapid carbonization processes.

[0020] Furthermore, the gradient heating carbonization process involves heating in 2 to 4 stages from 400 to 1000℃, with a heating rate of 2 to 10℃ / min and a holding time of 1 to 3 hours for each stage.

[0021] Furthermore, the inert atmosphere is at least one of nitrogen, argon, or helium.

[0022] This invention also provides highly doped nanosheet hard carbon materials prepared by any of the methods described above. The prepared highly doped nanosheet hard carbon materials have the following structural features: (1) the material is formed by continuous stacking of nanosheets to form a stable sheet-like framework structure, which can provide continuous electron transport channels; (2) the material has a pore structure mainly composed of closed nanopores, which can serve as a low-potential sodium storage space and effectively suppress electrolyte side reactions; (3) nitrogen, oxygen and other heteroatoms are uniformly distributed in the carbon framework in various chemical states, forming high-density polar active sites. These structural features are the basis for achieving high initial coulombic efficiency, excellent rate performance and long-term cycling stability.

[0023] The present invention also provides the application of the above-mentioned highly doped nanosheet hard carbon material in the preparation of batteries, which can be used as a negative electrode material for sodium-ion batteries and can significantly improve the overall electrochemical performance of the battery.

[0024] Compared with existing hard carbon material preparation methods and comparative materials, this invention achieves systematic optimization in precursor structure construction, carbon skeleton evolution path, and interfacial reaction regulation through a combination of ternary crosslinking control and gradient heat treatment, thus exhibiting significant advantages in electrochemical performance and engineering applicability. (1) In terms of material composition and heteroatom regulation, compared with the existing single resin or simple blend system where heteroatoms are easily removed or locally enriched, resulting in uneven distribution of active sites, this invention constructs a ternary crosslinking network through resin-based materials, nitrogen-containing heterocyclic organic ligands and crosslinking agents, so that nitrogen, oxygen and other heteroatoms are uniformly distributed at the molecular scale in the precursor stage, and multiple nitrogen and oxygen chemical states coexist, which can significantly enhance the control of Na + It enhances adsorption capacity and improves interfacial reaction uniformity, thereby effectively reducing irreversible capacity loss in the first cycle and improving initial coulombic efficiency.

[0025] (2) In terms of carbon skeleton structure regulation, compared with existing hard carbon materials, which are prone to block agglomeration or structural breakage due to lack of effective cross-linking regulation, resulting in discontinuous conductive network and aggravated cycle decay, this invention achieves the stepwise stabilization of precursor structure through solvothermal reconstruction and gradient pre-oxidation treatment, so that a continuous sheet bundle skeleton structure composed of stacked nanosheets is formed during carbonization. This structure not only provides a continuous electron transport channel, but also effectively relieves volume stress during cycling.

[0026] (3) In terms of pore structure and sodium storage behavior, compared with the existing hard carbon materials, which have an excessively high proportion of open pores or mismatched pore structure, which easily leads to increased irreversible capacity loss and decreased cycle stability, the material of the present invention forms a hierarchical pore structure system with closed nanopores as the main component and interconnected pores as the auxiliary component. Among them, the closed nanopores provide a stable reversible sodium storage space in the low potential region and effectively inhibit the continuous decomposition reaction of the electrolyte in the pores; the interconnected pores are beneficial to electrolyte wetting and ion transport. Therefore, the hard carbon material provided by the present invention exhibits a higher capacity contribution in the low potential region and a significantly improved first-cycle coulombic efficiency.

[0027] (4) In terms of kinetic performance, compared with existing hard carbon materials, which exhibit significant capacity decay under high-rate conditions, leading to diffusion limitation and polarization accumulation problems, the hard carbon material provided by this invention, relying on the synergistic effect of nanosheet bundle structure and high-density polar sites, significantly reduces Na+. +The diffusion path and diffusion barrier enable it to maintain a high capacity output under high current density conditions and achieve good capacity recovery during rate recovery.

[0028] (5) In terms of interface stability, compared with existing hard carbon materials, which are prone to forming unstable interface films due to uneven surface structure or unreasonable distribution of active sites, resulting in a continuous increase in interface impedance, the hard carbon material provided by the present invention can induce the formation of a uniform, dense and stable solid electrolyte interface (SEI) film with a small change in charge transfer impedance with cycling, thereby effectively suppressing polarization growth and extending cycle life.

[0029] (6) Based on the experimental results, it can be seen that the hard carbon material provided by the present invention exhibits high reversible capacity and significantly improved initial coulombic efficiency during the first charge and discharge cycle. In the long cycle test, the capacity retention rate is significantly better than that of the comparative material. In the rate performance test, it still maintains stable output under high current density and has good capacity recovery capability after rate recovery. These experimental results fully verify the effectiveness of the present invention in terms of structural control and performance improvement.

[0030] (7) The raw materials used in this invention are widely available and the process flow is controllable. It does not require complex templates or additional removal steps, has good repeatability and scalability potential, and is beneficial to practical engineering applications.

[0031] The aforementioned structural advantages have been verified in the first-cycle coulomb efficiency, rate performance, and long-cycle tests of the embodiments described later. Attached Figure Description

[0032] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 SEM images of Examples 1-6; Figure 2 These are SEM images for comparative examples 1-5; Figure 3 HRTEM images of Examples 1-6; Figure 4 The HRTEM images are for comparative examples 1-5; Figure 5 Example 1 at 10 A·g -1 Ultra-long cycle tests were conducted under these conditions. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of this invention, and not all of them.

[0035] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0036] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0037] Existing methods mostly employ single resins or simple physical mixtures, which have limited internal cross-linking structures. During heat treatment, they are prone to disordered shrinkage or local collapse, resulting in unclear carbon skeleton evolution paths. It is difficult to construct carbon skeleton structures with continuity and stability, and at the same time, it is impossible to achieve uniform anchoring of heteroatoms at the molecular scale, resulting in low doping efficiency and limiting material properties.

[0038] Furthermore, existing hard carbon materials suffer from difficulties in coordinating the interlayer and pore structures during carbonization, generally exhibiting problems such as insufficient or excessively disordered interlayer spacing and an imbalance in the ratio of closed to open pores. This restricts the insertion and diffusion of sodium ions and triggers side reactions of the electrolyte within the pore structure, resulting in low initial coulombic efficiency and poor cycling stability. Traditional processes lack phased control over the carbon framework formation process, making it difficult to achieve controllable evolution of the structure from precursor to carbon material.

[0039] Furthermore, in terms of interfacial reactions and kinetic behavior, due to the uneven distribution of heteroatoms and microstructural defects, existing hard carbon materials are prone to forming uneven and unstable solid electrolyte interfacial (SEI) films during charge and discharge, resulting in a continuous increase in interfacial impedance, restricted charge transfer and intensified polarization, especially under high-rate or long-cycle conditions, the performance degradation is obvious.

[0040] To address the aforementioned technical problems, this invention provides a method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking regulation, comprising four steps: constructing a ternary crosslinking precursor, solvothermal-induced structural reconstruction, gradient pre-oxidation treatment, and gradient carbonization treatment. (1) By introducing resin-based materials, nitrogen-containing heterocyclic organic ligands and crosslinking agents in the precursor stage to construct a ternary crosslinking network, and achieving molecular-scale structural fixation under the synergistic effect of Lewis acid catalysis and acidic environment, the structure can be effectively inherited and transformed into a continuous carbon skeleton structure in the subsequent heat treatment process.

[0041] (2) By solvothermal induced reconstruction and gradient pre-oxidation treatment, the precursor structure is stabilized step by step, the structural collapse and heteroatom loss during carbonization are suppressed, and on this basis, a hard carbon material with appropriate interlayer spacing, continuous nanosheet skeleton and high proportion of closed nanopores is constructed through gradient carbonization process, thereby achieving effective control of sodium storage behavior at the structural level.

[0042] (3) By uniformly introducing and stably anchoring high-density nitrogen, oxygen and other heteroatoms, the polar site distribution and interfacial reaction behavior on the material surface are regulated, and a uniform and stable interfacial film structure is induced to form, reducing charge transfer impedance and improving sodium ion diffusion dynamics, thereby achieving a comprehensive improvement in the material's initial coulombic efficiency, rate performance and long-cycle stability.

[0043] In summary, this invention provides a method for preparing hard carbon anodes by constructing a synergistic design system of "precursor cross-linking structure - heat treatment evolution path - microstructure regulation - interface behavior optimization", which can systematically improve the overall performance of hard carbon anodes and provides a new technical approach for the development of high-performance sodium-ion battery anode materials.

[0044] Example 1 This embodiment provides a method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking control, including the following steps: S1, Construction of ternary crosslinking precursor: Weigh 100g of rosin-modified phenolic resin (Baolin Chemical, 221#), 18g of benzimidazole and 15g of glycerol triglycidyl ether, disperse them in 1800g of anhydrous ethanol, stir at room temperature for 30min to mix them evenly; then add 2.5g of zinc chloride as Lewis acid catalyst, adjust the pH of the system to about 3.8 with a 0.2 mol / L hydrochloric acid ethanol solution, and continue to react at 65℃ for 4h to obtain the ternary crosslinking precursor.

[0045] S2, Solvothermal-induced structural reconstruction: The ternary crosslinked precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 165 °C for 8 h. After naturally cooling to room temperature, it was filtered and vacuum dried at 70 °C for 12 h to obtain the reconstructed precursor. S3, Gradient Pre-oxidation Treatment: The reconstructed precursor was placed in a tube furnace and subjected to gradient pre-oxidation treatment in an air / NH3 mixed atmosphere (NH3 to air volume flow rate ratio of 10:90). Specific conditions were: 2℃•min -1 Heat to 180℃ and hold for 1 hour, then increase the temperature by 1℃•min. -1 Heat to 230℃ and hold for 1 hour, then reduce temperature by 1℃•min. -1 The temperature was raised to 280℃ and held for 0.5 hours to obtain a stabilized precursor. S4, Gradient carbonization treatment: The stabilized precursor is subjected to gradient carbonization treatment under an argon atmosphere. The specific conditions are: 5℃•min -1 Heat to 450℃ and hold for 1 hour, then increase the temperature by 5℃•min. -1 Heat to 700℃ and hold for 1 hour, then reduce to 5℃·min. -1 The temperature was raised to 850℃ and held for 2 hours. After natural cooling, a high nitrogen and oxygen doped nanosheet hard carbon material was obtained, which was denoted as sample HC-1.

[0046] Example 2 This embodiment provides a method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking control, including the following steps: S1, Construction of ternary crosslinking precursor: Weigh 100g of cashew phenol-modified phenolic amine epoxy resin (Shanghai Zhipu Chemical Co., Ltd., HG-8003T), 20g of 2-methylimidazole and 18g of isophorone diisocyanate, disperse them in 2000g of anhydrous ethanol, and stir at room temperature for 40 min to mix them evenly; then add 3.0g of aluminum trichloride as Lewis acid catalyst, adjust the pH of the system to about 4.2 with 0.2mol / L nitric acid ethanol solution, and continue to react at 70 ℃ for 5h to obtain ternary crosslinking precursor.

[0047] S2, Solvothermal-induced structural reconstruction: The ternary crosslinked precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 170℃ for 10h. After naturally cooling to room temperature, it was filtered and vacuum dried at 65℃ for 10h to obtain the reconstructed precursor. S3, Gradient Pre-oxidation Treatment: The reconstructed precursor is placed in a tube furnace and subjected to gradient pre-oxidation treatment in an air / N2O mixed atmosphere (N2O to air volume flow rate ratio of 10:90). Specific conditions are: 2℃•min -1 Heat to 190℃ and hold for 1 hour, then increase the temperature by 2℃•min. -1 Heat to 240℃ and hold for 1 hour, then reduce to 2℃•min. -1 The temperature was raised to 290℃ and held for 0.5 hours to obtain a stabilized precursor. S4, Gradient carbonization treatment: The stabilized precursor is subjected to gradient carbonization treatment in a nitrogen / argon mixed inert atmosphere (nitrogen to argon volume flow rate ratio of 10:90), specifically under the following conditions: 5℃•min -1 Heat to 400℃ and hold for 1 hour, then increase the temperature by 5℃•min. -1 Heat to 650℃ and hold for 1 hour, then reduce temperature to 5℃·min. -1 The temperature was raised to 900℃ and held for 2 hours. After natural cooling, a high nitrogen and oxygen doped nanosheet hard carbon material was obtained, which was denoted as sample HC-2.

[0048] Example 3 This embodiment provides a method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking control, including the following steps: S1, Construction of ternary crosslinking precursor: Weigh 100g of polyketide resin (Yantai Mangosteen New Material Co., Ltd., SZ120), 16g of imidazole and 20g of pyromellitic dianhydride, disperse them in 1600g of anhydrous ethanol, and stir at room temperature for 40 min to mix them evenly; then add 2.0g of zinc chloride as Lewis acid catalyst, adjust the pH of the system to about 3.6 with a 0.2mol / L phosphoric acid ethanol solution, and continue to react at 60 ℃ for 4h to obtain the ternary crosslinking precursor.

[0049] S2, Solvothermal-induced structural reconstruction: The ternary crosslinked precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 160℃ for 6 hours. After naturally cooling to room temperature, it was filtered and vacuum dried at 60℃ for 12 hours to obtain the reconstructed precursor. S3, Gradient Pre-oxidation Treatment: The reconstructed precursor is placed in a tube furnace and subjected to gradient pre-oxidation treatment in an air / SO2 mixed atmosphere (SO2 to air volume flow rate ratio of 10:90). Specific conditions are: 2℃•min -1 Heat to 170℃ and hold for 1 hour, then increase the temperature by 1℃•min. -1 Heat to 220℃ and hold for 1 hour, then reduce temperature by 1℃•min. -1 The temperature was raised to 270℃ and held for 1 hour to obtain the stabilized precursor. S4, Gradient carbonization treatment: The stabilized precursor is subjected to gradient carbonization treatment under a nitrogen atmosphere. The specific conditions are: 5℃•min -1 Heat to 420℃ and hold for 1 hour, then increase the temperature by 5℃•min. -1 Heat to 680℃ and hold for 1 hour, then reduce temperature to 5℃·min. -1 The temperature was raised to 820℃ and held for 2.5 hours. After natural cooling, a high nitrogen and oxygen doped nanosheet hard carbon material was obtained, which was designated as sample HC-3.

[0050] Example 4 This embodiment provides a method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking control, including the following steps: S1, Construction of ternary crosslinking precursor: Weigh 100g polyaldehyde resin (Jinan Changtai Chemical Co., Ltd., CT-A81), 18g 2-ethylimidazole and 16g hexamethylene diisocyanate, disperse them in 1700g anhydrous ethanol, stir at room temperature for 40min to mix them evenly; then add 2.8g ferric chloride as Lewis acid catalyst, adjust the pH of the system to about 4.0 with 0.2mol / L acetic acid ethanol solution, and continue to react at 68 ℃ for 5h to obtain ternary crosslinking precursor.

[0051] S2, Solvothermal-induced structural reconstruction: The ternary crosslinked precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 175℃ for 8 hours. After naturally cooling to room temperature, it was filtered and vacuum dried at 70℃ for 10 hours to obtain the reconstructed precursor. S3, Gradient Pre-oxidation Treatment: The reconstructed precursor was placed in a tube furnace and subjected to gradient pre-oxidation treatment in an air / trimethyl phosphate (trimethyl phosphate to air volume flow rate ratio of 10:90) mixed atmosphere. The specific conditions were: 5℃•min -1 Heat to 185℃ and hold for 1 hour, then increase the temperature by 1℃•min. -1 Heat to 235℃ and hold for 1 hour, then reduce to 3℃·min. -1 The temperature was raised to 285℃ and held for 0.5 hours to obtain a stabilized precursor. S4, Gradient carbonization treatment: The stabilized precursor is subjected to gradient carbonization treatment in a helium / argon mixed inert atmosphere (helium to argon volume flow rate ratio of 10:90), specifically under the following conditions: 5℃•min -1 Heat to 430℃ and hold for 1 hour, then increase the temperature by 5℃·min. -1 Heat to 700℃ and hold for 1 hour, then reduce to 5℃·min. -1 The temperature was raised to 880℃ and held for 2 hours. After natural cooling, a high nitrogen and oxygen doped nanosheet hard carbon material was obtained, which was designated as sample HC-4.

[0052] Example 5 This embodiment provides a method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking control, including the following steps: S1, Construction of ternary crosslinking precursor: Weigh 100g of polyamide-imide resin (Xinfuda Composite Material, T8100), 15g of 1,2,4-triazole and 18g of maleic anhydride, disperse them in 1500g of anhydrous ethanol, and stir at room temperature for 40 min to mix them evenly; then add 2.2g of zinc chloride as Lewis acid catalyst, adjust the pH of the system to about 3.9 with a 0.2mol / L formic acid ethanol solution, and continue to react at 62 ℃ for 6h to obtain the ternary crosslinking precursor.

[0053] S2, Solvothermal-induced structural reconstruction: The ternary crosslinked precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 155℃ for 10h. After natural cooling to room temperature, it was filtered and vacuum dried at 65℃ for 12h to obtain the reconstructed precursor. S3, Gradient Pre-oxidation Treatment: The reconstructed precursor was placed in a tube furnace and subjected to gradient pre-oxidation treatment in a mixed atmosphere of air / NH3 / trimethyl phosphate (volume flow ratio of air, NH3 and trimethyl phosphate was 80:10:10). The specific conditions were: 3℃•min -1 Heat to 180℃ and hold for 1 hour, then increase the temperature by 2℃•min. -1 Heat to 230℃ and hold for 1 hour, then reduce temperature by 1℃•min. -1 The temperature was raised to 275℃ and held for 1 hour to obtain the stabilized precursor. S4, Gradient carbonization treatment: The stabilized precursor is subjected to gradient carbonization treatment in a nitrogen / argon mixed inert atmosphere (nitrogen to argon volume flow rate ratio of 10:90), specifically under the following conditions: 5℃•min -1 Heat to 400℃ and hold for 1 hour, then increase the temperature by 5℃•min. -1 Heat to 650℃ and hold for 1 hour, then reduce temperature to 5℃·min. -1 The temperature was raised to 830℃ and held for 3 hours. After natural cooling, a high nitrogen and oxygen doped nanosheet hard carbon material was obtained, which was designated as sample HC-5.

[0054] Example 6 This embodiment provides a method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking control, including the following steps: S1, Construction of ternary crosslinking precursor: Weigh 100g of hyperbranched polyamide resin (Wuhan Hyperbranched Resin Technology Co., Ltd., HPN202), 20g of 2-methylimidazole and 12g of γ-glycidyl etheroxypropyltrimethoxysilane, disperse them in 1900g of anhydrous ethanol, and stir at room temperature for 40 min to mix them evenly; then add 2.5g of aluminum trichloride as Lewis acid catalyst, adjust the pH of the system to about 4.1 with a 0.2mol / L hydrochloric acid ethanol solution, and continue to react at 66 ℃ for 4h to obtain the ternary crosslinking precursor.

[0055] S2, Solvothermal-induced structural reconstruction: The ternary crosslinked precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 168℃ for 9 hours. After naturally cooling to room temperature, it was filtered and vacuum dried at 60℃ for 12 hours to obtain the reconstructed precursor. S3, Gradient Pre-oxidation Treatment: The reconstructed precursor is placed in a tube furnace and subjected to gradient pre-oxidation treatment in an air / N2O / CH3CN vapor mixed atmosphere (air, N2O and CH3CN vapor volume flow ratio of 80:10:10). Specific conditions are: 5℃•min -1 Heat to 175℃ and hold for 1 hour, then increase the temperature by 3℃•min. -1 Heat to 225℃ and hold for 1 hour, then reduce to 2℃•min. -1 The temperature was raised to 280℃ and held for 0.5 hours to obtain a stabilized precursor. S4, Gradient carbonization treatment: The stabilized precursor is subjected to gradient carbonization treatment under an argon atmosphere. The specific conditions are: 5℃•min -1 Heat to 420℃ and hold for 1 hour, then increase the temperature by 5℃•min. -1 Heat to 720℃ and hold for 1 hour, then reduce temperature to 5℃·min. -1 The temperature was raised to 900℃ and held for 2 hours. After natural cooling, a high nitrogen and oxygen doped nanosheet hard carbon material was obtained, which was designated as sample HC-6.

[0056] Example 7 This embodiment provides a method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking control, including the following steps: S1, Construction of ternary crosslinking precursor: Weigh 100g of DOPO modified resin (Shenzhen Xingkaiyue Biotechnology Co., Ltd., G184), 20g of melamine and 18g of bisphenol A diglycidyl ether, disperse them in 2000g of anhydrous ethanol, and stir at room temperature for 40 min to mix them evenly; then add 2.5g of zinc trifluoromethanesulfonate as Lewis acid catalyst, adjust the pH of the system to about 4.0 with a 0.2mol / L hydrochloric acid ethanol solution, and continue to react at 65 ℃ for 4h to obtain the ternary crosslinking precursor.

[0057] S2, Solvothermal-induced structural reconstruction: The ternary crosslinked precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 165℃ for 10h. After naturally cooling to room temperature, it was filtered and vacuum dried at 60℃ for 12h to obtain the reconstructed precursor. S3, Gradient Pre-oxidation Treatment: The reconstructed precursor was placed in a tube furnace and subjected to gradient pre-oxidation treatment in an air / NH3 mixed atmosphere (NH3 to air volume flow rate ratio of 20:80). Specific conditions were: 5℃•min -1 Heat to 180℃ and hold for 0.5 hours, then reduce temperature by 3℃·min. -1 Heat to 250℃ and hold for 0.5 hours, then reduce temperature by 2℃•min. -1 The temperature was raised to 300℃ and held for 1 hour to obtain the stabilized precursor. S4, Gradient carbonization treatment: The stabilized precursor is subjected to gradient carbonization treatment under an argon atmosphere. The specific conditions are: 5℃•min -1 Heat to 450℃ and hold for 1 hour, then increase the temperature by 5℃•min. -1 Heat to 750℃ and hold for 2 hours, then reduce temperature to 5℃·min. -1 The temperature was raised to 1000℃ and held for 1 hour. After natural cooling, a high nitrogen and oxygen doped nanosheet hard carbon material was obtained, which was designated as sample HC-7.

[0058] Example 8 This embodiment provides a method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking control, including the following steps: S1, Construction of ternary crosslinking precursor: Weigh 100g boron phenolic resin (Bengbu Tianyu High Temperature Resin Materials Co., Ltd., FB-90), 18g 2,4-diamino-6-methoxy-1,3,5-triazine and 15g hexamethylene diisocyanate, disperse them in 2000g anhydrous ethanol, and stir at room temperature for 40 min to mix them evenly; then add 3.0g boron trifluoride as Lewis acid catalyst, adjust the pH of the system to about 3.5 with a 0.2mol / L hydrochloric acid ethanol solution, and continue to react at 70 ℃ for 4h to obtain the ternary crosslinking precursor.

[0059] S2, Solvothermal-induced structural reconstruction: The ternary crosslinked precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 160℃ for 8 hours. After naturally cooling to room temperature, it was filtered and vacuum dried at 60℃ for 12 hours to obtain the reconstructed precursor. S3, Gradient Pre-oxidation Treatment: The reconstructed precursor was placed in a tube furnace and subjected to gradient pre-oxidation treatment in an air / NH3 mixed atmosphere (NH3 to air volume flow rate ratio of 20:80). Specific conditions were: 5℃•min -1 Heat to 170℃ and hold for 1 hour, then increase the temperature by 3℃•min. -1 Heat to 230℃ and hold for 1 hour, then reduce to 2℃·min. -1 The temperature was raised to 280℃ and held for 1 hour to obtain the stabilized precursor. S4, Gradient carbonization treatment: The stabilized precursor is subjected to gradient carbonization treatment under an argon atmosphere. The specific conditions are: 10℃•min -1 Heat to 450℃ and hold for 3 hours, then increase the temperature by 3℃•min. -1 Heat to 650℃ and hold for 1 hour, then reduce temperature to 5℃·min. -1 The temperature was raised to 1000℃ and held for 1 hour. After natural cooling, a high nitrogen and oxygen doped nanosheet hard carbon material was obtained, which was designated as sample HC-8.

[0060] Comparative Example 1 This comparative example provides a method for preparing a hard carbon material, comprising the following steps: S1. To construct the precursor, 100g of rosin-modified phenolic resin (Baolin Chemical, 221#) and 15g of glycerol triglycidyl ether were weighed and dispersed in 1800g of anhydrous ethanol. The mixture was stirred at room temperature for 30 min to ensure homogeneity. Subsequently, 2.5g of zinc chloride was added as a Lewis acid catalyst. The pH of the system was adjusted to approximately 3.8 using a 0.2mol / L hydrochloric acid-ethanol solution, and the reaction was continued at 65℃ for 4 h to obtain the precursor.

[0061] S2, Solvothermal-induced structural reconstruction: The precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 165 °C for 8 h. After natural cooling to room temperature, it was filtered and vacuum dried at 70 °C for 12 h to obtain the reconstructed precursor. S3, Gradient Pre-oxidation Treatment: The reconstructed precursor was placed in a tube furnace and subjected to gradient pre-oxidation treatment in an air / NH3 mixed atmosphere (NH3 to air volume flow rate ratio of 10:90). Specific conditions were: 2℃•min -1 Heat to 180℃ and hold for 1 hour, then increase the temperature by 1℃•min. -1 Heat to 230℃ and hold for 1 hour, then reduce temperature by 1℃•min. -1 The temperature was raised to 280℃ and held for 0.5 hours to obtain a stabilized precursor. S4, Gradient carbonization treatment: The stabilized precursor is subjected to gradient carbonization treatment under an argon atmosphere. The specific conditions are: 5℃•min -1 Heat to 450℃ and hold for 1 hour, then increase the temperature by 5℃•min. -1 Heat to 700℃ and hold for 1 hour, then reduce to 5℃·min. -1 The temperature was raised to 850℃ and held for 2 hours. After natural cooling, hard carbon material was obtained, which was denoted as sample C-1.

[0062] This comparative example is used to illustrate that: after removing the nitrogen-containing heterocyclic organic ligand based on Example 1, although the precursor system can still form a certain cross-linked structure, the source of high-density nitrogen active sites in the material is weakened, which is not conducive to the efficient introduction and stable retention of nitrogen, and thus affects the polar site distribution, interfacial film uniformity and sodium storage kinetics of the final material.

[0063] Comparative Example 2 This comparative example provides a method for preparing a hard carbon material, including the following steps: S1, Precursor construction: Weigh 100g of rosin-modified phenolic resin (Baolin Chemical, 221#) and 18g of benzimidazole, disperse them in 1800g of anhydrous ethanol, and stir at room temperature for 30 min to mix them evenly; then add 2.5g of zinc chloride as a Lewis acid catalyst, adjust the pH of the system to about 3.8 with a 0.2mol / L hydrochloric acid ethanol solution, and continue to react at 65℃ for 4h to obtain the precursor.

[0064] S2, Solvothermal-induced structural reconstruction: The precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 165 °C for 8 h. After natural cooling to room temperature, it was filtered and vacuum dried at 70 °C for 12 h to obtain the reconstructed precursor. S3, Gradient Pre-oxidation Treatment: The reconstructed precursor was placed in a tube furnace and subjected to gradient pre-oxidation treatment in an air / NH3 mixed atmosphere (NH3 to air volume flow rate ratio of 10:90). Specific conditions were: 2℃•min -1 Heat to 180℃ and hold for 1 hour, then increase the temperature by 1℃•min. -1 Heat to 230℃ and hold for 1 hour, then reduce temperature by 1℃•min. -1 The temperature was raised to 280℃ and held for 0.5 hours to obtain a stabilized precursor. S4, Gradient carbonization treatment: The stabilized precursor is subjected to gradient carbonization treatment under an argon atmosphere. The specific conditions are: 5℃•min -1 Heat to 450℃ and hold for 1 hour, then increase the temperature by 5℃•min. -1 Heat to 700℃ and hold for 1 hour, then reduce to 5℃·min. -1 The temperature was raised to 850℃ and held for 2 hours. After natural cooling, hard carbon material was obtained, which was denoted as sample C-2.

[0065] This comparative example is used to illustrate that: after removing the crosslinking agent based on Example 1, the crosslinking density of the three-dimensional network in the precursor system decreases, the structural fixation ability weakens, and local collapse or disordered shrinkage is more likely to occur during heat treatment, which is not conducive to the formation of nanosheet bundle framework and closed nanopore structure, and ultimately leads to a decrease in material structure uniformity and cycle stability.

[0066] Comparative Example 3 This comparative example provides a method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking control, including the following steps: S1, Construction of the precursor: Weigh 100g of rosin-modified phenolic resin (Baolin Chemical, 221#), 18g of benzimidazole and 15g of glycerol triglycidyl ether, disperse them in 1800g of anhydrous ethanol, and stir at room temperature for 30 min to mix them evenly; then adjust the pH of the system to about 3.8 with a 0.2mol / L hydrochloric acid ethanol solution, and continue to react at 65℃ for 4h to obtain the precursor.

[0067] S2, Solvothermal-induced structural reconstruction: The precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 165 °C for 8 h. After natural cooling to room temperature, it was filtered and vacuum dried at 70 °C for 12 h to obtain the reconstructed precursor. S3, Gradient Pre-oxidation Treatment: The reconstructed precursor was placed in a tube furnace and subjected to gradient pre-oxidation treatment in an air / NH3 mixed atmosphere (NH3 to air volume flow rate ratio of 10:90). Specific conditions were: 2℃•min -1 Heat to 180℃ and hold for 1 hour, then increase the temperature by 1℃•min. -1 Heat to 230℃ and hold for 1 hour, then reduce temperature by 1℃•min. -1 The temperature was raised to 280℃ and held for 0.5 hours to obtain a stabilized precursor. S4, Gradient carbonization treatment: The stabilized precursor is subjected to gradient carbonization treatment under an argon atmosphere. The specific conditions are: 5℃•min -1 Heat to 450℃ and hold for 1 hour, then increase the temperature by 5℃•min. -1 Heat to 700℃ and hold for 1 hour, then reduce to 5℃·min. -1 The temperature was raised to 850℃ and held for 2 hours. After natural cooling, hard carbon material was obtained, which was designated as sample C-3.

[0068] This comparative example illustrates that, based on Example 1, removing the Lewis acid catalyst inhibits the polycondensation and crosslinking reactions in the precursor, reduces network construction efficiency, and hinders the formation of a uniform and stable precursor structure. This, in turn, affects the structural inheritance during subsequent solvothermal reconstruction and heat treatment, ultimately reducing the controllability of the material's microstructure.

[0069] Comparative Example 4 This comparative example provides a method for preparing a hard carbon material, including the following steps: S1, Construction of ternary crosslinking precursor: Weigh 100g of rosin-modified phenolic resin (Baolin Chemical, 221#), 18g of benzimidazole and 15g of glycerol triglycidyl ether, disperse them in 1800g of anhydrous ethanol, stir at room temperature for 30 min to mix them evenly; then add 2.5g of zinc chloride as Lewis acid catalyst, adjust the pH of the system to about 3.8 with a 0.2mol / L hydrochloric acid ethanol solution, and continue to react at 65℃ for 4h to obtain the ternary crosslinking precursor.

[0070] S2, Solvothermal-induced structural reconstruction: The ternary crosslinked precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 165 °C for 8 h. After naturally cooling to room temperature, it was filtered and vacuum dried at 70 °C for 12 h to obtain the reconstructed precursor. S3, Pre-oxidation treatment: The reconstructed precursor is placed in a tube furnace and pre-oxidized in an air atmosphere. The specific conditions are: 2℃•min -1 The temperature was raised to 230℃ and held for 2 hours to obtain the stabilized precursor. S4, Gradient carbonization treatment: The stabilized precursor is subjected to gradient carbonization treatment under an argon atmosphere. The specific conditions are: 5℃•min -1 Heat to 450℃ and hold for 1 hour, then increase the temperature by 5℃•min. -1 Heat to 700℃ and hold for 1 hour, then reduce to 5℃·min. -1 The temperature was raised to 850℃ and held for 2 hours. After natural cooling, hard carbon material was obtained, which was designated as sample C-4.

[0071] This comparative example is used to illustrate that, based on Example 1, after removing the nitrogen-containing atmosphere-assisted pre-oxidation, the heteroatom stabilization and structure locking process of the material in the pre-oxidation stage is weakened, which is not conducive to the further fixation of nitrogen and the improvement of the thermal stability of the precursor, and ultimately affects the heteroatom retention rate and interface control capability of the material.

[0072] Comparative Example 5 This comparative example provides a method for preparing a hard carbon material, including the following steps: S1, Construction of ternary crosslinking precursor: Weigh 100g of rosin-modified phenolic resin (Baolin Chemical, 221#), 18g of benzimidazole and 15g of glycerol triglycidyl ether, disperse them in 1800g of anhydrous ethanol, stir at room temperature for 30 min to mix them evenly; then add 2.5g of zinc chloride as Lewis acid catalyst, adjust the pH of the system to about 3.8 with a 0.2mol / L hydrochloric acid ethanol solution, and continue to react at 65℃ for 4h to obtain the ternary crosslinking precursor.

[0073] S2, Solvothermal-induced structural reconstruction: The ternary crosslinked precursor was transferred to a 2L polytetrafluoroethylene-lined reactor and subjected to solvothermal-induced reconstruction at 165 °C for 8 h. After naturally cooling to room temperature, it was filtered and vacuum dried at 70 °C for 12 h to obtain the reconstructed precursor. S3, Gradient Pre-oxidation Treatment: The reconstructed precursor was placed in a tube furnace and subjected to gradient pre-oxidation treatment in an air / NH3 mixed atmosphere (NH3 to air volume flow rate ratio of 10:90). Specific conditions were: 2℃•min -1 Heat to 180℃ and hold for 1 hour, then increase the temperature by 1℃•min. -1 Heat to 230℃ and hold for 1 hour, then reduce temperature by 1℃•min. -1 The temperature was raised to 280℃ and held for 0.5 hours to obtain a stabilized precursor. S4, Carbonization treatment: The stabilized precursor is carbonized under an argon atmosphere, specifically at 5℃•min. -1 The temperature was raised to 850℃ and held for 2 hours. After natural cooling, hard carbon material was obtained, which was designated as sample C-5.

[0074] This comparative example is used to illustrate that: after removing the gradient carbonization step based on Example 1, the conversion process of the precursor to the hard carbon framework lacks phased regulation, which can easily lead to rapid shrinkage of local structures or uneven evolution of the carbon framework, which is not conducive to the formation of continuous nanosheet framework and high proportion of closed nanopores, thereby affecting sodium storage behavior and rate performance.

[0075] Structural and performance characterization 1. Structural characterization Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses were performed on the ternary crosslinked high nitrogen and oxygen doped nanosheet hard carbon materials prepared in Examples 1-6 and the hard carbon materials prepared in Comparative Examples 1-5. The results are as follows: Figures 1-4 As shown.

[0076] from Figure 1 and Figure 2The SEM images shown reveal that the samples obtained in Examples 1-6 all exhibited sheet-like carbon framework characteristics to varying degrees. Example 1 showed the most regular structure, with the sample consisting of a continuous stack of nanosheets forming a bundle-like framework. The sheet size distribution was relatively concentrated, with clear boundaries and good connectivity between the sheets. Examples 2-6 generally maintained a nanosheet-dominated structure, but due to differences in resin-based materials, crosslinking agent type, heteroatom-containing atmosphere, and gradient carbonization path, there were certain differences in local sheet thickness, bundle density, and surface roughness. In contrast, the sample obtained in Comparative Example 1 showed broken and loosely stacked sheets; Comparative Example 2 tended to form a dense blocky or locally shell-like structure; Comparative Example 3 was dominated by wrinkled aggregates with significantly insufficient continuity; Comparative Example 4, due to the removal of nitrogen-containing atmosphere-assisted pre-oxidation, showed local shrinkage and collapse on the sample surface; and Comparative Example 5, due to the removal of gradient carbonization, showed many irregular shrinkage bodies and framework fracture areas. These results indicate that the synergistic effect of the ternary crosslinking network, heteroatom-containing pre-oxidation atmosphere, and gradient carbonization path are important conditions for constructing a continuous nanosheet bundle-like framework.

[0077] from Figure 3 and Figure 4 The HRTEM results show that Example 1 exhibits continuous and relatively clear layered striations, indicating that the carbon skeleton was well inherited and reconstructed during heat treatment. Local closed cavities formed by stacked nanosheets can be observed within its layers, corresponding to closed nanopore structures. Layered striations were also observed in Examples 2-6, but the continuity and curvature of the striations differed. In comparison, the striations in Comparative Example 1 were shorter and more curved, indicating insufficient crosslinking density leading to a decrease in the skeleton's support capacity. While the striations in Comparative Example 2 were longer, the local stacking was too dense, indicating densification shrinkage during thermal evolution. The striations in Comparative Example 3 were the most disordered, reflecting that the carbon skeleton mainly underwent disordered carbonization when multi-component synergistic regulation was lacking. Comparative Examples 4 and 5 showed increased striation discontinuities and local carbon layer fusion, respectively, indicating that pre-oxidation stabilization and gradient carbonization significantly promoted the complete formation of the nanosheet skeleton.

[0078] 2. Electrochemical testing methods The samples obtained in Examples 1-6 and Comparative Examples 1-5 were mixed with acetylene black and polyvinylidene fluoride at a mass ratio of 80:10:10, respectively, and N-methylpyrrolidone was added to prepare a slurry (solid-liquid ratio of 2:3). The slurry was uniformly coated onto a copper foil current collector, dried under vacuum at 70°C for 12 h, and then punched into circular electrode sheets with a diameter of 14 mm. The active material loading was controlled at 1.4-1.7 mg·cm³. -2 Using metallic sodium as the counter electrode and glass fiber as the diaphragm, 1 mol·L⁻¹ -1NaClO4 / EC:DMC:EMC (volume ratio 1:1:1, containing 2% FEC) was used as the electrolyte. CR2032 coin cell half-cells were assembled in an argon-atmospheric glove box. The constant current charge-discharge test voltage range was 0.01–3.0 V.

[0079] 3. First charge-discharge test The half-cells assembled in Examples 1-6 and Comparative Examples 1-5 were subjected to the first cycle of constant current charge-discharge test, and the results of representative samples are shown in Table 1.

[0080] Table 1. Test results of the first charge-discharge performance of each sample.

[0081] As shown in Table 1, Example 1 exhibited higher reversible capacity and significantly improved initial coulombic efficiency during the first discharge cycle, indicating that irreversible sodium loss was effectively suppressed. Although the specific capacity levels of Examples 2-6 varied due to changes in resin-based materials, crosslinking agents, or heteroatom atmospheres, they were generally superior to the comparative examples, demonstrating the good universality of the system covered by the outline of this invention. Comparative Example 1, lacking benzimidazole, had a decreased number of surface active sites, resulting in increased irreversible loss in the first cycle; Comparative Example 2, lacking crosslinking agents, had decreased structural inheritance, leading to enhanced electrolyte side reactions; Comparative Example 3, lacking multi-component synergistic crosslinking, had the lowest overall first-cycle efficiency; Comparative Examples 4 and 5 respectively demonstrated that nitrogen-containing atmosphere-assisted pre-oxidation and gradient carbonization played crucial roles in improving the first-cycle efficiency.

[0082] 4. Ratio Performance Test The rate performance of Examples 1-6 and Comparative Examples 1-5 was tested at 0.1C and 10C, and the results are shown in Table 2.

[0083] Table 2. Ratio Performance Test Table for Each Sample

[0084] As shown in Table 2, Example 1 exhibits a smaller capacity decay during the gradual increase of current density and demonstrates good capacity recovery capability after rate recovery, indicating that its Na + The transport channels are continuous and the structure recovers well. Examples 2-6 also exhibit superior rate response compared to the comparative examples, indicating that good kinetic performance can be obtained within the range of resin-based materials, crosslinking agents, and heteroatom-containing heat treatment conditions defined in this invention. Comparative Example 1 suffers from insufficient crosslinking density, resulting in layer breakage and discontinuous diffusion channels; Comparative Example 2 suffers from limited ion transport due to localized densification; Comparative Example 3 suffers from poor interlayer spacing and pore structure matching due to the lack of a ternary synergistic network; Comparative Examples 4 and 5 demonstrate that the absence of a pre-oxidizing atmosphere and gradient carbonization pathway significantly amplifies the polarization effect at high rates.

[0085] 6. Long-cycle performance test Examples 1-6 and Comparative Examples 1-5 were tested at 0.1 A·g. -1 Long-cycle performance tests were conducted under certain conditions, and Example 1 was further tested at 10 A·g. -1 Under these conditions, ultra-long cycle tests were performed, and the results are as follows: Figure 5 As shown in Table 3.

[0086] Table 3. Long-cycle performance test results for each sample

[0087] From Table 3 and Figure 5 It can be seen that Example 1 exhibits significantly better capacity retention during long-term cycling, maintaining a high reversible capacity even after 2000 cycles. This indicates that the synergistic effect of the ternary crosslinking network, heteroatom-containing pre-oxidation, and gradient carbonization can effectively maintain structural integrity and interfacial stability. Although Examples 2-6 show some differences under different precursor systems, their overall cycle life is better than that of the comparative examples. Comparative Examples 1-3 mainly suffer from gradual framework degradation during cycling due to precursor network defects. Comparative Examples 4 and 5 further demonstrate that the pre-oxidation and carbonization pathways have a significant impact on long-term interfacial stability.

[0088] Based on the above structural characterization and electrochemical test results, Examples 1-6 demonstrate the effectiveness of the synergistic route established in this invention, which involves the construction of a ternary precursor (resin-based material—nitrogen-containing heterocyclic organic ligand—crosslinking agent), solvothermal-induced reconstruction, pre-oxidation in a heteroatom-containing atmosphere, and gradient carbonization. Examples 1-6 further illustrate that the resin-based material, crosslinking agent, and heat treatment path defined in this invention can all achieve the construction of high nitrogen-oxygen-doped nanosheet hard carbon structures, exhibiting good process versatility. Comparative Examples 1-5 demonstrate the necessity of the key technical features of this invention from the perspectives of lacking nitrogen-containing heterocyclic organic ligands, lacking crosslinking agents, lacking multi-component synergistic precursors, lacking heteroatom-containing pre-oxidation, and lacking gradient carbonization, respectively.

[0089] The above research results show that the ternary crosslinking-regulated high nitrogen and oxygen doped nanosheet hard carbon material and its preparation method proposed in this invention not only have clear advantages in structural regulation, but also exhibit high first-cycle coulombic efficiency, excellent rate performance and good long-cycle stability in sodium-ion battery anode applications, and have high application feasibility and industrialization potential.

[0090] The present invention has been described according to the above embodiments. It should be understood that the above embodiments do not limit the present invention in any way. All technical solutions obtained by equivalent substitution or equivalent transformation fall within the scope of the present invention.

Claims

1. A method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking regulation, characterized in that, Includes the following steps: Construction of ternary crosslinking precursor: The resin-based material, nitrogen-containing heterocyclic organic ligand and crosslinking agent are uniformly dispersed in a solvent, and a Lewis acid catalyst is added under acidic conditions to carry out the crosslinking reaction to obtain the ternary crosslinking precursor; Solvothermal-induced structural reconstruction: The ternary cross-linked precursor was transferred to a closed reaction vessel and subjected to solvothermal treatment at a temperature higher than the boiling point of the solvent at atmospheric pressure to obtain the reconstructed precursor. Gradient pre-oxidation treatment: The reconstructed precursor is subjected to gradient heating pre-oxidation treatment at 170~300℃ in an atmosphere containing nitrogen, sulfur and / or phosphorus heteroatoms to obtain a stabilized precursor; Gradient carbonization treatment: The stabilized precursor is subjected to gradient heating carbonization treatment in an inert atmosphere at 400-1000℃ to obtain highly doped nanosheet hard carbon materials.

2. The method for preparing highly doped nanosheet hard carbon material based on ternary crosslinking control according to claim 1, characterized in that, The mass ratio of the resin-based material, the nitrogen-containing heterocyclic organic ligand, and the crosslinking agent is 100:(15~20):(12~20); the resin-based material is at least one of phenolic modified amino resin, ketone-aldehyde resin, polyamide resin, phosphorus-containing modified resin, and boron-containing modified resin; the nitrogen-containing heterocyclic organic ligand is used to introduce nitrogen and participate in the crosslinking reaction; the nitrogen-containing heterocyclic organic ligand is at least one of imidazole compounds, triazine compounds, or nitrogen-containing heterocyclic small molecule compounds; the crosslinking agent is at least one of epoxy compounds, isocyanate compounds, organic acid anhydride compounds, or silane coupling agents.

3. The method for preparing highly doped nanosheet hard carbon material based on ternary crosslinking control according to claim 2, characterized in that, The phenolic modified amino resin includes rosin-modified phenolic resin, cashew nut shell phenolic amine epoxy resin, phenol-modified urea-formaldehyde resin, resorcinol-modified amino resin, and nonylphenol-modified amino resin; the ketone-aldehyde resin includes cyclohexanone-formaldehyde resin, acetone-formaldehyde resin, polyaldehyde resin, and polyketone resin; the phosphorus-containing modified resin includes phosphate ester-modified amino resin, DOPO-modified resin, hypophosphite-modified resin, polyphosphate ester resin, and phosphaphenanthrene-structure-modified resin; the polyamide resin includes polyamide-imide resin, hyperbranched polyamide resin, polyamide-amine resin, semi-aromatic polyamide resin, and modified nylon resin; the boron-containing modified resin includes boric acid-modified resin, borate ester-modified resin, boron phenolic resin, and boronoxane-modified resin; the imidazole compounds include benzimidazole, 2-methylimidazole, imidazole, 2-ethylimidazole, and 2-phenylimidazole; the triazine compounds... The compounds include melamine, benzomelamine, chlorocyanurate, 4,6-diamino-2-hydroxy-1,3,5-triazine, and 2,4-diamino-6-methoxy-1,3,5-triazine; the nitrogen-containing heterocyclic small molecule compounds include 1,2,4-triazole, pyridine, pyrrole, pyrazine, and pyrimidine; the epoxy compounds include glycerol triglycidyl ether, ethylene glycol diglycidyl ether, and bisphenol A diglycidyl ether; the isocyanate compounds include isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate; the organic acid anhydride compounds include pyromellitic dianhydride, maleic anhydride, phthalic anhydride, and succinic anhydride; and the silane coupling agent compounds include γ-glycidyl etheroxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

4. The method for preparing highly doped nanosheet hard carbon materials based on ternary crosslinking control according to any one of claims 1 to 3, characterized in that, The solvent is ethanol or a mixture of ethanol and water; the pH value of the acidic environment is 3~5; the crosslinking reaction temperature is 60~70℃, and the crosslinking reaction time is 4~6h.

5. The method for preparing highly doped nanosheet hard carbon material based on ternary crosslinking control according to claim 4, characterized in that, The solvent heat treatment temperature is 120–200℃, and the time is 4–12 h.

6. The method for preparing highly doped nanosheet hard carbon material based on ternary crosslinking control according to claim 1, characterized in that, The gradient heating pre-oxidation process involves heating at 170–300℃ in 2–4 stages, with a heating rate of 1–5℃ / min and a holding time of 0.5–2 h for each stage.

7. The method for preparing highly doped nanosheet hard carbon material based on ternary crosslinking control according to claim 6, characterized in that, The atmosphere containing nitrogen, sulfur, and / or phosphorus heteroatoms is derived from at least one of ammonia, N2O, SO2, trimethyl phosphate vapor, and CH3CN vapor; the atmosphere containing nitrogen, sulfur, and / or phosphorus heteroatoms also includes air, and the volume flow ratio of the atmosphere containing nitrogen, sulfur, and / or phosphorus heteroatoms to air is 5:95 to 20:

80.

8. The method for preparing highly doped nanosheet hard carbon material based on ternary crosslinking control according to claim 1, characterized in that, The gradient heating carbonization process involves heating in 2 to 4 stages from 400 to 1000°C at a rate of 2 to 10°C / min, with each stage lasting 1 to 3 hours. The inert atmosphere is at least one of nitrogen, argon, or helium.

9. A highly doped nanosheet hard carbon material, characterized in that, It is prepared by the method according to any one of claims 1 to 8.

10. The application of the highly doped nanosheet hard carbon material of claim 9 in the preparation of batteries.

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