A hard carbon anode material, its preparation method and application

Abstract

This invention provides a hard carbon anode material with a graphite-like layer structure having an interlayer spacing d002 ≥ 0.385 nm. The hard carbon anode material exhibits closed-pore, microporous, mesoporous, and macroporous structures. Closed-pore structures are channels with an opening diameter d ≤ 0.35 nm; microporous structures are channels with an opening diameter 0.35 nm < d ≤ 2 nm; mesoporous structures are channels with an opening diameter 2 nm < d ≤ 50 nm; and macroporous structures are channels with an opening diameter d > 50 nm. The porosity of the hard carbon anode material is 20-60%. The pore volume of the closed-pore structure accounts for > 2% of the total pore volume of the hard carbon anode material, the pore volume of the macroporous structure accounts for < 65% of the total pore volume of the hard carbon anode material, and the ratio of the pore volume of the microporous structure to the pore volume of the mesoporous structure is 10-150. It exhibits particularly excellent performance in electrochemical properties such as low-temperature, rate, and cycle performance.

Description

Technical Field

[0001] This invention relates to the field of anode material technology, specifically to a hard carbon anode material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries share similar electrochemical working principles and technical characteristics with lithium-ion batteries. Compared to the relative scarcity of lithium on Earth, sodium is abundant, widely distributed, and inexpensive. Due to its superior electrochemical kinetics and stability compared to lithium-ion batteries, sodium-ion battery systems exhibit significantly better performance in low-temperature conditions, rate capability, and safety. This gives them a clear advantage in specific scenarios, making them a competitive force in energy storage, start-stop systems, and low-power applications, and a focus of attention in the current new energy industry. Among numerous anode materials, hard carbon materials are considered the optimal match for sodium-ion battery anode materials due to their larger interlayer spacing, diverse sodium storage mechanisms, high capacity, and low voltage platform.

[0003] Researchers studying the energy storage mechanism of hard carbon have discovered that larger interlayer spacing and abundant closed-cell / microporous structures can significantly improve the sodium storage kinetics of hard carbon anodes, thereby enhancing the overall performance of sodium-ion batteries, including rate capability, low-temperature performance, and cycle capacity. Traditional biomass materials, such as coconut shells and reeds, which are widely available, possess rich porous structures after carbonization. However, the high proportion of mesopores and macropores is unfavorable for sodium ion storage. Furthermore, the structural and compositional uncertainties of natural bio-based hard carbon precursors affect the stability of hard carbon anode materials. Given their structural stability, controllability, and low ash content, synthetic resins have become a new source of hard carbon precursors, attracting considerable research attention.

[0004] Several research results have been achieved in the development of hard carbon anodes based on synthetic resin precursors. For example, patent CN112225194B involves dissolving phenolic resin in an organic solvent, mixing it with a conductive agent, and then drying it. A pre-oxidation process is introduced before high-temperature carbonization to introduce a large number of oxygen-containing functional groups, resulting in a cross-linked framework structure and simultaneously improving the conductivity and mechanical strength of the hard carbon material. Patent CN109742383B mixes liquid phenolic resin with ethanol, performs hydrothermal curing, then pulverizes and carbonizes at high temperature to obtain a hard carbon material. The pore structure of the hard carbon material can be optimized by adjusting the ratio of phenolic resin to ethanol. For example, articles such as Adv. Mater. 2025, 37, 2501434, Adv. Funct. Mater. 2024, 34, 2403642, and Nat Commun 16, 3634 (2025) have conducted in-depth research on the pore structure of hard carbon anodes and its influence on electrical performance, pointing out the positive impact of closed-pore or microporous structures on the performance of hard carbon anodes.

[0005] However, existing optimization schemes for the pore structure of polymer-based hard carbon anodes often involve introducing other additives to aid pore formation. For example, ethanol organic solvents, asphalt, carbon dot materials, and metal oxides are added to phenolic resins to optimize pore size. These additional additives often lack electrochemical activity or even have adverse effects. In response, patents such as CN117069091A and CN118954471A attempt to design the molecular structure of the phenolic resin precursor by introducing N, S, and O functional groups. On the one hand, this strengthens the degree of polymer crosslinking, inhibits the graphitization process, and promotes the formation of micropores during high-temperature carbonization. On the other hand, the electronegativity of the heterogeneous elements disrupts the π-π conjugation of the molecular chains, reducing the degree of ordered graphite stacking, and combined with steric hindrance, increases the interlayer spacing of graphite. This improves the sodium storage performance of the hard carbon anode material. However, in our actual experiments, we found that there are many factors that affect the structure of hard carbon anodes. Simply designing the molecular structure is often not practical. It is necessary to combine specific polymer precursor preparation processes and carbonization process control to achieve structural optimization and performance improvement of hard carbon anodes.

[0006] Therefore, it is necessary to improve the intrinsic chemical structure of the phenolic resin-based polymer hard carbon precursor, and combine the preparation method of the resin precursor with the subsequent carbonization process to try to obtain hard carbon anode materials with large graphite interlayer spacing and abundant closed-pore and microporous structures, thereby improving the overall electrochemical performance of resin-based hard carbon anodes. Summary of the Invention

[0007] This invention addresses the problems in existing hard carbon anode materials where uncontrollable interlayer spacing and pore structure of the graphite layer lead to reduced kinetic performance, resulting in significantly poor cycle life, rate capability, and low-temperature performance. It proposes a resin-based hard carbon anode material and applies it to sodium-ion batteries. This invention innovatively inserts functionalized segments containing special functional groups into the chain structure of the resin-based polymer precursor. By controlling the number and type of functionalized segments embedded in the polymer precursor, and combining this with a specific carbonization process, the microstructure of the corresponding resin-based hard carbon anode is jointly regulated and optimized, thereby affecting the electrical performance of the hard carbon anode. Regarding the design of the chemical structure of the resin polymer precursor, this invention, on the one hand, achieves the doping of N, O, S, and P as heterogeneous elements through the use of functionalized additives, thereby increasing the interlayer spacing of the graphite-like layers in hard carbon and reducing the energy barrier for sodium ion insertion into the hard carbon graphite-like layers. On the other hand, the presence of heterogeneous functional groups can regulate the degree and length of crosslinking of graphite-like layer segments during high-temperature carbonization, promoting the formation of short-range disordered micro-graphite structures, which is beneficial for forming abundant micropores or closed-pore structures in the hard carbon anode. To achieve the above-mentioned improvements, we also optimized the subsequent carbonization process and added an optimization control process for particle size before high-temperature carbonization. When the resin-based hard carbon anode prepared by the above method is applied to sodium-ion battery anode materials, it exhibits good electrochemical performance, especially in low-temperature, rate, and cycle performance.

[0008] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a hard carbon anode material, wherein the interlayer spacing d002 of the graphite-like layer structure of the hard carbon anode material is ≥0.385 nm. The hard carbon anode material has a pore structure including closed-pore structures, micropore structures, mesopore structures, and macropore structures. The closed-pore structure is a channel with an opening diameter d ≤0.35 nm, the micropore structure is a channel with an opening diameter of 0.35 nm < d ≤ 2 nm, the mesopore structure is a channel with an opening diameter of 2 nm < d ≤ 50 nm, and the macropore structure is a channel with an opening diameter d > 50 nm. The porosity of the hard carbon anode material is 20-60%, the pore volume of the closed-pore structure accounts for >2% of the total pore volume of the hard carbon anode material, the pore volume of the macropore structure accounts for <65% of the total pore volume of the hard carbon anode material, and the ratio of the pore volume of the micropore structure to the pore volume of the mesopore structure is 10-150.

[0009] This invention exhibits superior kinetic performance by controlling the graphite-like interlayer spacing and pore structure in hard carbon anode materials. Specifically, it demonstrates excellent low-temperature performance, rate performance, and cycling stability, while also possessing a high plateau / slope capacity ratio. The larger graphite interlayer spacing facilitates reversible sodium ion insertion / extraction and mitigates volume expansion during cycling. Unlike conventional hard carbon anode materials prepared from a wide range of biomass materials, which have a high proportion of mesoporous and macroporous structures, this invention simultaneously limits the hard carbon anode material to have a high micropore-to-closed-pore ratio. In particular, the high volumetric proportion of closed-pore structures helps promote the sodium ion desolvation process, improves the filling and deposition efficiency of sodium ions in the pores, enhances the sodium ion insertion kinetics and reversibility, optimizes the formation of the solid electrolyte interphase (SEI) film, and constructs a stable SEI film. The hard carbon anode material in this invention also possesses certain mesoporous and macroporous structures, forming a multi-level pore system with the aforementioned micropores and closed pores, synergistically improving the overall performance of the electrode. This hierarchical porous structure synergistically combines micropore / closed-pore-dominated sodium storage behavior with mesopore / macropore-dominated mass transfer processes, maintaining a high plateau capacity while further optimizing kinetic performance and cycle stability under full-cell conditions. The high proportion of closed-pore structures provides ample nanoscale enclosed space, effectively providing active sites for sodium ion deposition and contributing significantly to the plateau capacity. It also reduces the direct contact area between the electrode material and the electrolyte, thus suppressing side reactions and improving initial coulombic efficiency and cycle stability. Furthermore, this invention controls the ratio of micropore volume to mesopore volume to be greater than 10, meaning that micropores, primarily responsible for sodium ion adsorption and storage, dominate the porous structure. This structural feature ensures high sodium ion deposition / dissolution kinetics and reversible sodium storage capacity, contributing to the overall electrical performance improvement of the hard carbon anode. On the other hand, the appropriate amount of mesopores serves as a necessary ion transport channel, ensuring that sodium ions can quickly reach the interior of the material. This structure maintains high specific capacity while optimizing ion migration pathways, resulting in superior high-rate charge-discharge performance and long-term cycle life. The aforementioned structural advantages synergistically enhance the sodium ion insertion / extraction kinetics in hard carbon anode materials, thereby comprehensively improving their electrochemical performance at cycling, rate, and low temperatures.

[0010] As a further preferred embodiment, the percentage of closed-pore structure volume in the pore structure of the hard carbon anode material is 5% to 15% of the total pore volume of the hard carbon anode material, and the ratio of microporous structure volume to mesoporous structure volume is 25 to 100.

[0011] This invention can further limit the pore volume of the closed-pore structure and the pore volume ratio between the microporous and mesoporous structures. When the pore volume ratio of the closed-pore structure is increased to more than 5%, a richer array of nanoscale closed spaces is formed inside the material. These high-proportion, appropriately sized closed cavities provide a large number of active sites for sodium ion filling and deposition, promoting the sodium ion desolvation process, enhancing the sodium ion intercalation kinetics and reversibility, and constructing a stable SEI film. Since the closed-pore structure does not have open channels, it can significantly reduce the effective contact area between the electrode material and the electrolyte, thereby physically inhibiting the continuous decomposition of the electrolyte on the active surface. This is crucial for constructing a stable solid electrolyte interphase (SEI) film and is the structural basis for simultaneously achieving high initial coulombic efficiency and long cycle life. At the same time, increasing the pore volume ratio of micropores to mesopores to more than 25, the micropores, which dominate the pore structure of the material, provide a huge specific surface area, which is more conducive to improving the sodium ion intercalation and deintercalation kinetics. The few but essential mesopores serve as a crucial pathway for the rapid migration of ions within the electrode material, ensuring the efficient transport of sodium ions to the vast microporous adsorption surface. This extremely high pore volume ratio between the microporous and mesoporous structures microscopically optimizes ion migration dynamics, enabling sodium ions to be rapidly captured and released even under high-current conditions of rapid charge and discharge, resulting in superior rate performance and excellent cycle stability.

[0012] As an example, the pore structure, pore size, and pore volume of the hard carbon anode material can be obtained through a combination of gas (N2 / CO2) adsorption-desorption testing, He gas permeation, and mercury porosimetry. Specifically, N2 gas adsorption-desorption testing is mainly for mesoporous structures, CO2 gas adsorption-desorption testing is mainly for microporous structures, mercury porosimetry is used for macroporous structure characterization, and He gas permeation is used for closed-pore structure testing. The interlayer spacing of the hard carbon can be obtained through XRD testing, and the shift of the characteristic peak at 23° of the (002) crystal plane is calculated using the Bragg equation.

[0013] Secondly, the present invention also provides a method for preparing the hard carbon anode material described in the first aspect, the method comprising the following steps: S1. Phenolic compounds and aldehyde compounds are reacted under alkaline conditions to obtain phenolic resin prepolymers; Functionalized additives and aldehyde compounds were reacted under alkaline conditions and with a halide metal salt catalyst to obtain functional block prepolymers. A functional block prepolymer, comprising 4-45% of the phenolic resin prepolymer, is added to a phenolic resin prepolymer and reacted under alkaline catalytic conditions to obtain a linear block polymer with an AABAA structure, wherein A is the phenolic resin prepolymer and B is the functional block prepolymer. Block-structured linear polymers were cured at high temperature to obtain block-modified phenolic resin-based hard carbon precursors; The functionalized additives are selected from one or more of aminophenolic compounds, benzoic acid compounds, benzenesulfonic acid compounds, and phenyl phosphate compounds; S2: The block-modified phenolic resin-based hard carbon precursor prepared in S1 is pre-sintered and crushed at a temperature of 100~400℃ to obtain a pre-oxidized product. The particle size D50 of the pre-oxidized product is 0.4~2.5μm and the particle size SPAN value is ≤2.1. The pre-oxidized powder is first kept at 400~850℃ for 5~9h, and then kept at 900~1700℃ for 2~7h to complete the two-step carbonization to obtain hard carbon anode material.

[0014] This invention innovatively achieves effective control over the molecular framework of the precursor by precisely embedding functionalized segments containing heterogeneous elements such as N, O, S, and P into the phenolic resin backbone. These functional blocks play a crucial role in the high-temperature carbonization process: on the one hand, their introduction effectively expands the graphite-like interlayer spacing of the final carbonized product; on the other hand, the selective decomposition and volatilization of these blocks at specific temperatures can create abundant closed-pore and microporous structures in situ within the carbon matrix. During the polymerization stage, the precise control of the molar incorporation ratio of the phenolic resin prepolymer to the functional block prepolymer lays the molecular foundation for the subsequent formation of an ideal hierarchical porous structure. This ratio range is the key basis for obtaining linear polymers with specific AABAA structures and for structural optimization: if the functional block ratio is too low, it will be difficult to effectively form sufficient closed-pore and microporous structures during subsequent carbonization; conversely, if the ratio is too high, it will lead to overdevelopment of closed-pores and micropores, or even structural defects, crowding out necessary ion transport channels, which is detrimental to electrolyte wetting and rapid ion migration. In the pre-carbonization stage, pre-oxidation treatment, precise particle size control, and a narrow particle size range (lower SPAN value) ensured high uniformity in morphology and reactivity of the precursor particles, guaranteeing the uniform evolution of the material structure during subsequent carbonization. Controlling the pre-sintering temperature between 100 and 400°C helped form appropriate mesopores and macropores in the product, serving as macroscopic channels for ion transport. Simultaneously, more uniform and complete heat conduction and gas volatilization resulted in a narrower pore size distribution, which facilitated the convergence of the pore size distribution towards closed-pore and micropore regions. During the carbonization stage, a two-step carbonization process was employed, with detailed limits on the temperature and time based on fundamental parameters such as the characteristics and doping ratio range of the phenolic resin prepolymer and functional block prepolymer. This guided the orderly decomposition of functional blocks and the directional reconstruction of the carbon skeleton, thereby synergistically optimizing the interlayer spacing and the formation of a multi-level pore structure, and controlling the porosity of the hard carbon anode material within a certain range. The systematic control of the above preparation scheme ensured that the obtained hard carbon anode material simultaneously possessed an expanded graphite-like interlayer spacing, a high proportion of closed-pore / microporous structures, and excellent particle uniformity. The selection of functional block prepolymers and optimization of their intercalation ratios, the optimization and control of particle size of the pre-oxidation products before carbonization, and the optimization of carbonization process conditions synergistically promoted the rapid and stable intercalation-deintercalation kinetics of sodium ions in the material. Ultimately, this enabled the material to exhibit excellent plateau capacity, initial coulombic efficiency, rate performance, low-temperature performance, and long cycle life in sodium-ion batteries.

[0015] As a further embodiment, in S1, a functional block prepolymer with a molecular weight range of 50-1200Mn is added to a phenolic resin prepolymer with a molecular weight range of 2000-20000Mn, accounting for 15-40% of the phenolic resin prepolymer, and reacted under alkaline catalytic conditions to obtain a block-structured linear polymer. This invention further optimizes the incorporation ratio of functional block prepolymers and limits the molecular weight of phenolic resin prepolymers and functional block prepolymers within a certain range. This allows for the regulation of the crosslinking degree and length of graphite-like layer segments during high-temperature carbonization, further promoting the formation of short-range disordered micro-graphite structures. This, in turn, is more conducive to the formation of abundant micropores or closed-pore structures in hard carbon anodes.

[0016] As a further preferred embodiment, in S1, a functional block prepolymer with a molecular weight range of 300±100Mn is added to a phenolic resin prepolymer with a molecular weight range of 5000±1000Mn, accounting for 25~30% of the phenolic resin prepolymer, and reacted under alkaline catalytic conditions to obtain a block-structured linear polymer.

[0017] This invention can further limit the molar percentage of functional block prepolymers in the phenolic resin prepolymer while also limiting the molecular weight ranges of the phenolic resin prepolymer and the functional block prepolymer. When the proportion of functional block prepolymers in the phenolic resin prepolymer is further controlled at 25-30%, and the molecular weights of both are further limited to a narrow range, an optimal balance between the spatial distribution of functional blocks and the distribution of chemically active sites can be achieved from the perspective of precursor molecules. This can effectively regulate the microstructure of the final hard carbon material. Under this preferred ratio, the phenolic resin prepolymer with a larger molecular weight forms the main chain segment, mainly contributing to the formation of the basic carbon skeleton and graphite-like structure of the hard carbon material. Its moderate molecular weight is beneficial for forming regular graphite-like domains with large interlayer spacing during subsequent curing and carbonization. The lower molecular weight of the functional block prepolymer allows it to be more flexibly embedded between the main chain segments or at specific sites. During heat treatment, these small molecule blocks rich in specific functional groups preferentially decompose or generate specific steric hindrance effects, thereby precisely creating a series of closed-pore and microporous structures within the carbon framework. This enables synergistic control over the interlayer spacing and hierarchical pore structure of hard carbon materials with graphite-like structures, which is key to obtaining excellent electrochemical performance. The sufficient number of functional blocks is crucial for efficiently creating pores and expanding the interlayer spacing of graphite-like layers during carbonization, ensuring a sufficient number of closed-pores and micropores to provide high plateau capacity. Simultaneously, the heteroatoms they contain are uniformly embedded in the carbon framework, effectively expanding the interlayer spacing of the graphite-like structures. This ratio avoids insufficient pore development due to too few functional blocks, as well as over-enrichment of pore structures and accumulation of defects in the carbon framework due to too many. This structural balance ensures, on the one hand, that sodium ions have sufficient and highly active storage sites, and on the other hand, maintains continuous channels for rapid ion and electron migration, thus synergistically optimizing the sodium storage capacity and reaction kinetics of the material at the microstructural level.

[0018] As an example, the molecular weights of the phenolic resin prepolymer A and the phenolic resin prepolymer B can be characterized using gel permeation chromatography (GPC).

[0019] As a further embodiment, the phenolic resin prepolymer in S1 is prepared by reacting phenolic compounds and aldehyde compounds at a molar ratio of 1:0.8 to 1:1.5 under alkaline conditions at pH 8 to 12 at 60 to 95°C for 2 to 5 hours to obtain the phenolic resin prepolymer; the functional block prepolymer in S1 is prepared by reacting functionalized additives and aldehyde compounds at a molar ratio of 1:0.8 to 1:1.5. A functional block prepolymer is obtained by reacting a phenolic resin prepolymer with a halide metal salt catalyst at a molar ratio of 1:1.5 under alkaline conditions at pH 8-12 at 50-85°C for 0.5-2 hours. A functional block prepolymer (25-30% molar fraction of the phenolic resin prepolymer) is added to the separated phenolic resin prepolymer and reacted at 80-110°C for 4-9 hours under alkaline catalysis at pH 7.5-13 to obtain a block-structured linear polymer. The block-structured linear polymer is then cured at 110-160°C for 9-13 hours to obtain a block-modified phenolic resin-based hard carbon precursor. The functional additive is selected from one or more of aminophenolic compounds, benzoic acid compounds, benzenesulfonic acid compounds, and phenyl phosphate compounds.

[0020] This invention can further limit the reaction environment in the preparation methods of phenolic resin prepolymers and functional block prepolymers, for example, by limiting the molar ratio of phenolic compounds and aldehyde compounds, and parameters such as pH, reaction time, and reaction temperature during the reaction process. This allows for the acquisition of phenolic resin prepolymers and functional block prepolymers with target molecular weights, avoiding the problems of excessively low molecular weight due to excessively low pH or short reaction time, and excessively high molecular weight due to excessively high pH or long reaction time. These issues directly or indirectly affect the graphite chain structure in the subsequent preparation of block-structured linear polymers. The optimization of the crosslinking degree, initial length, and microstructure of the graphite segments makes it easier to form rich micropores or closed-pore structures in the hard carbon anode formed after subsequent carbonization. Based on the above, the present invention further limits the temperature and reaction time of high-temperature curing. This step also lays the foundation for obtaining hard carbon anode materials with suitable porosity and pore structure distribution through subsequent pre-oxidation and carbonization. It avoids the initial pores from not shrinking effectively due to excessively low high-temperature curing temperature, resulting in high porosity, and also avoids excessively high temperature or excessively long curing time, resulting in the formation of too many pores and too many macropore structures.

[0021] As a further example, the aminophenolic compound is selected from one or more of p-aminophenol, m-aminophenol, o-aminophenol, and p-acetylaminophenol.

[0022] As a further example, the benzoic acid compound is selected from one or more of benzoic acid, p-hydroxybenzoic acid, o-hydroxybenzoic acid, p-aminobenzoic acid, phthalic acid, and 2,4-dihydroxybenzoic acid.

[0023] As a further example, the benzenesulfonic acid compound is selected from one or more of benzenesulfonic acid, p-toluenesulfonic acid, p-hydroxybenzenesulfonic acid, dodecylbenzenesulfonic acid, p-aminobenzenesulfonic acid, and 1,3-benzenedisulfonic acid.

[0024] As a further example, the phenyl phosphate compound is selected from one or more of phenylphosphonic acid, (4-hydroxyphenyl)phosphonic acid, and triphenyl phosphate.

[0025] As a further preferred example, the aldehyde compound is exemplary selected from one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, acrolein, glutaraldehyde, cinnamaldehyde, cyclohexylformaldehyde, benzaldehyde, and p-methylbenzaldehyde.

[0026] As a further preferred example, the phenolic compound is exemplary selected from one or more of phenol, cresol, hydroquinone, and resorcinol.

[0027] As a further embodiment, the halide metal salt includes one of copper halide, iron halide, and zinc halide; As a further preferred embodiment, the halide metal salt is selected from one or more copper halide salts.

[0028] As a further embodiment, the preparation method of the phenolic resin prepolymer in S1 is to mix phenolic compounds and aldehyde compounds at a molar ratio of 1:1~ A phenolic resin prepolymer is obtained by reacting a phenolic resin mixture at a ratio of 1:1.1 under alkaline catalytic conditions of pH 9-11 at 80-90℃ for 3-4 hours. The functional block prepolymer in S1 is prepared by reacting functionalized additives and aldehyde compounds at a molar ratio of 1:1 to 1:1.2 under alkaline conditions of pH 8-10 with copper chloride (CuCl2) catalysis at 60-80℃ for 1-2 hours to obtain the functional block prepolymer. A functional block prepolymer (25-30% molar fraction of the phenolic resin prepolymer) is added to the separated phenolic resin prepolymer, and the mixture is reacted at 90-100℃ under alkaline catalysis of pH 11-13 for 5-8 hours to obtain a block-structured linear polymer. The block-structured linear polymer is then cured at 120-150℃ for 10-12 hours to obtain a block-modified phenolic resin-based hard carbon precursor.

[0029] This invention further limits the amount of raw materials and reaction conditions in the preparation methods of phenolic resin prepolymer and functional block prepolymer in S1. It also limits CuCl2 as the catalyst in the preparation process of the functional block prepolymer and specifies the reaction conditions in the block copolymerization and curing processes. In the synthesis of the phenolic resin prepolymer, a precise molar ratio of 1:1 to 1:1.1 and a suitable alkaline environment ensure the formation of a linear prepolymer with moderate molecular weight and uniform reactivity, providing a regular basis for the main carbon skeleton. In the preparation of the functional block prepolymer, the introduction of CuCl2 forms a highly efficient catalytic-reaction system, promoting the formation of the target low molecular weight functional prepolymer at specific pH and temperature. Simultaneously, through the block action of functionalized additives, it lays the foundation for directional decomposition and precise pore formation in the subsequent carbonization process. The above lays the foundation for the initial raw materials used to form a high graphite-like interlayer spacing and a high proportion of closed-cell and microporous structures. The subsequent block copolymerization step is one of the key components of the entire molecular design. Under strongly alkaline conditions, functional blocks are connected to the main chain through easily broken bonds. Their 25-30% molar proportion achieves an optimal balance between the density of pore-forming sites and the integrity of the carbon skeleton, while also facilitating the formation of controllable proportions of closed-cell and microporous structures. Finally, a curing process of 10-12 hours at 120-150°C successfully transforms the precisely designed linear polymer into a solid precursor with a stable three-dimensional crosslinked network. This curing condition ensures sufficient crosslinking to maintain the structural stability of the precursor during carbonization while avoiding pore closure caused by excessive crosslinking. This allows the precursor to preferentially decompose functional blocks within a specific temperature range during subsequent carbonization, creating a large number of uniformly sized closed pores and micropores in situ and directionally within the carbon matrix. Simultaneously, the doping of heteroatoms effectively expands the interlayer spacing of the graphite-like structure, while a moderately formed cross-linked network ensures the structural stability of the carbon framework during pore formation. This precise control at the molecular scale is crucial for achieving the ideal pore structure and excellent sodium storage performance of the hard carbon anode material described in this invention, enabling it to exhibit high plateau capacity, superior rate performance, and long cycle life in sodium-ion batteries.

[0030] As a further preferred embodiment, the halide metal salt catalyst is a copper halide salt; and the functionalized additive is an aminophenol compound.

[0031] This invention uses copper halide salts as catalysts for the reaction, exhibiting higher catalytic activity. The copper ions (Cu) in the copper halide... 2+ As a Lewis acid, Cu can coordinate with the carbonyl oxygen atom in aldehydes, activating the formaldehyde molecule and making it more susceptible to nucleophilic attack. Meanwhile, Cu... 2+ It can also react with the amino group (-NH2) or phenoxy group (-O) in the preferred aminophenolic compounds of this application. -Coordination enhances nucleophilicity. Under weakly alkaline conditions, CuCl2 can lower the reaction energy barrier through coordination, promoting the hydroxymethylation reaction of formaldehyde with amino groups (forming N-hydroxymethyl) or phenolic hydroxyl groups (forming O-hydroxymethyl), thereby accelerating the formation of prepolymers. Furthermore, aminophenolic compounds, as a source of heterogeneous elements in functionalized segments, mainly provide elements such as N and O. Compared to elements such as S and P, N and O have more suitable atomic sizes, enabling them to form more stable and uniform doping in the carbon framework. The introduction of N atoms effectively expands the interlayer spacing of graphite-like structures. Meanwhile, the O functional groups help form a more stable cross-linked structure in the pre-oxidation stage, inhibiting excessive graphitization of the carbon framework at high temperatures, creating favorable conditions for the formation and stable retention of closed-pore and microporous structures. More importantly, there is a unique synergistic effect between copper halide salts and aminophenolic compounds. In the synthesis stage of functional block prepolymers, Cu... 2+ The coordination with the amino group in aminophenol can guide the molecular chain to adopt a specific conformation and undergo decomposition behavior during the subsequent carbonization process. This can more precisely and efficiently induce the formation of uniformly sized and concentrated closed-pore and microporous structures, rather than disordered macropores or mesopores. This precise control at the molecular scale is a further optimization of achieving the ideal pore structure with a high closed-pore / micropore ratio and a high micropore / mesopore volume ratio as described in this invention.

[0032] As a further example, the phenolic resin prepolymer and the functional block prepolymer prepared in S1 can be separated by the following method: Phenolic resin prepolymer was obtained by reacting phenolic compounds and aldehyde compounds under alkaline conditions. The phenolic resin prepolymer was added to petroleum ether solvent, stirred vigorously, allowed to stand, and filtered to obtain the separated phenolic resin prepolymer. The functional block prepolymer obtained by reacting functionalized additives and aldehyde compounds under alkaline conditions and catalysis by copper chloride (CuCl2) was added to petroleum ether solvent, stirred vigorously, allowed to stand, and filtered to obtain the separated functional block prepolymer.

[0033] As a further preferred example, the prepared phenolic resin prepolymer and functional block prepolymer can be separated by the following method: The prepared phenolic resin prepolymer and functional block prepolymer were added to petroleum ether solvent and stirred vigorously at a speed of more than 500 rpm for 1 hour. After standing for 3 hours, the phenolic resin prepolymer and functional block prepolymer appeared at the bottom of the mixed solution as powder and flocculent precipitates, respectively. After filtration, the separated phenolic resin prepolymer and functional block prepolymer were obtained.

[0034] As a further embodiment, the crushing step in S2 involves ball milling at a speed of 500-1300 ppm with zirconium beads having a diameter of 2-6 mm. The ratio of the pre-sintered product to the zirconium beads is 1:10-10:1, and the ball milling time is 4-10 hours to obtain the pre-oxidized product.

[0035] As a further preferred embodiment, the pre-oxidized product has a unimodal particle size distribution, a particle size D50 of 0.5~2μm, and a particle size SPAN value ≤1.5.

[0036] As an example, the particle size of the pre-oxidized product can be measured by a laser particle size analyzer.

[0037] The SPAN value is calculated using the following formula: SPAN = (D90 - D10) / D50.

[0038] This invention further limits the particle size of the pre-oxidized product, confining the particle size within a certain range and a narrower range. This ensures that each particle receives highly consistent heat treatment conditions during the subsequent high-temperature carbonization process, thereby producing a hard carbon material with stable and controllable graphite-like interlayer spacing and pore structure. If the particle size distribution is too wide, the excessively uneven particle size makes it easier for more mesopores and macropores to form during carbonization, leading to differential structural evolution, uneven microstructure of the material, and consequently, inconsistent reaction kinetics within the electrode.

[0039] As a further embodiment, the carbonization step in S2 involves heating from room temperature to 500-800°C and holding at that temperature for 6-8 hours, then heating to 900-1500°C and holding for 3-5 hours, followed by cooling to room temperature to obtain the hard carbon anode material.

[0040] This invention further limits the carbonization temperature, carbonization time, and holding time. It employs a specific stepped heating program and holding time to guide the orderly decomposition of functional blocks and the directional reconstruction of the carbon skeleton, thereby synergistically optimizing the interlayer spacing and the formation of multi-level pore structures. This significantly affects the proportion of mesopores and macropores in the material and optimizes its porosity. The further optimizations of this invention avoid excessively high carbonization temperatures, which can lead to over-graphitization, enlarged pore sizes, and the formation of excessive mesopores and macropores. Increased graphitization also reduces interlayer spacing, hindering sodium ion insertion / extraction. It also avoids excessively low carbonization temperatures, which result in more defects and increased side reactions, affecting the initial capacity. Furthermore, it avoids excessively short holding times, which lead to insufficient decomposition, low pore volume, and excessive closed pores, resulting in low capacity. Finally, it avoids excessively long holding times, which can cause micropores / closed pores to tend to transform into mesopores and macropores.

[0041] As a further preferred embodiment, the heating rate in the carbonization step of S2 is 0.5-3℃ / min.

[0042] This invention further optimizes the heating rate during the carbonization process, avoiding problems such as excessive heating rate, rapid gas volatilization, easy "pore bursting", formation of large pores, wide pore size distribution, and difficulty in sodium ion filling.

[0043] As a further preferred embodiment, the preparation method includes the following steps: S1. Phenolic compounds and aldehyde compounds are reacted at a molar ratio of 1:1 to 1:1.1 under alkaline catalytic conditions of pH 9-11 at 80-90℃ for 3-4 hours to obtain phenolic resin prepolymer; The functionalized additives, aminophenolic compounds and aldehyde compounds, were reacted at a molar ratio of 1:1 to 1:1.2 under alkaline conditions (pH 8-10) and catalyzed by copper chloride (CuCl2) at 60-80°C for 1-2 hours to obtain a functionalized block prepolymer. The amount of copper chloride used was 0.2-1.3% of the total mass of the functionalized additives, aminophenolic compounds and aldehyde compounds. A functional block prepolymer, comprising 25-30% of the phenolic resin prepolymer molar fraction, was added to the separated phenolic resin prepolymer and reacted at 90-100℃ for 5-8 hours under alkaline catalysis at pH 11-13 to obtain a block-structured linear polymer. Block-structured linear polymers were cured at a high temperature of 120~150℃ for 10~12h to obtain block-modified phenolic resin-based hard carbon precursors.

[0044] S2: The block phenolic resin-based hard carbon precursor prepared in S1 is pre-sintered at a temperature of 100~400℃ for 10~14h. The zirconium beads were ball-milled at a diameter of 2-6 mm and a rotation speed of 600-1100 ppm. The ratio of the pre-sintered product to the zirconium beads was 1:10-10:1, and the ball milling time was 5-9 h to obtain the pre-oxidized product. The particle size D50 of the pre-oxidized product was 0.5-1.5 μm, and the particle size SPAN value was ≤1.5. The pre-oxidized powder is first heated from room temperature to 500~800℃ and held at this temperature for 6~8 h, then heated to 900~1500℃ and held for 3~5 h, with a heating rate of 0.5-3℃ / min, and then cooled to room temperature to obtain the hard carbon anode material.

[0045] Thirdly, the present invention also provides a negative electrode sheet, wherein the negative electrode sheet comprises the hard carbon negative electrode material described in the first aspect or the hard carbon negative electrode material prepared by the hard carbon negative electrode material preparation method described in the second aspect.

[0046] Fourthly, the present invention also provides a sodium-ion battery comprising the hard carbon negative electrode sheet described in the third aspect.

[0047] The features and beneficial effects of this invention are as follows: This invention achieves precise control over the microstructure of hard carbon anodes by precisely regulating the molecular structure of phenolic resin-based precursors. This avoids the negative impact of uncertainties in the structure and composition of traditional natural biomass-based precursors, such as coconut shells, reeds, coal, lignin, and cellulose, on hard carbon anodes. The block-modified phenolic resin-based hard carbon anode material prepared by this invention has a larger graphite-like interlayer spacing and a higher proportion of micropores. The larger graphite interlayer spacing facilitates sodium ion insertion / extraction, while the higher proportion of micropores is beneficial for the "sodium ion desolvation process," "SEI film optimization," and "sodium ion pore-filling deposition process." This effectively improves the kinetics of sodium ion insertion / extraction in hard carbon anodes, resulting in better low-temperature, rate, and cycling performance, increasing the plateau / ramp capacity ratio, and thus improving the overall electrical performance of hard carbon anodes.

[0048] To effectively achieve the aforementioned improvements, this invention also provides a method for preparing the modified resin precursor and a subsequent carbonization process. By limiting the proportion of functional blocks in the chain segments, the problems of increased defects due to the addition of too many heterofunctional groups affecting the first-cycle efficiency of the battery and the formation of excessive gas during carbonization affecting the formation of micropores can be avoided. By optimizing the particle size of the pre-oxidized powder, the problems of excessively large particles, internal thermal stress, and gas accumulation leading to mesopores, macropores, cracks, and uneven pore size distribution during carbonization can be avoided, thus ensuring the optimization effect of hard carbon pore size. This invention also uses a carbonization temperature control process to ensure the optimization of the hard carbon structure. A lower carbonization temperature avoids the problems of reduced interlayer spacing and increased pore size caused by excessive graphitization; slow heating allows precursor molecules sufficient time for slow, orderly thermal decomposition and rearrangement, generating more crosslinking points and defects, thereby forming a richer and more complex micropore network; and a reasonable holding time allows the pyrolysis reaction to proceed fully and the carbon structure to relax. Extending the heat preservation time usually makes the carbon structure more stable, the pores merge, and the pore size distribution tends to be concentrated, but too long a time may lead to pore shrinkage and reduction.

[0049] This invention combines molecular science-level regulation technology with existing hard carbon anode processes, which significantly improves the electrical performance of hard carbon anodes and has process feasibility and compatibility, while also being economical and feasible for industrial production. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention, 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.

[0051] Figure 1 TEM and SEM images of the hard carbon anode prepared in Example 1; Figure 1 Image a is a TEM image of the hard carbon anode prepared in Example 1; Figure 1 Image b is a SEM image of the hard carbon anode prepared in Example 1.

[0052] Figure 2 The aperture distribution diagrams are for Example 1 and Comparative Example 1. Detailed Implementation

[0053] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0054] As a specific example of the implementation of this invention, detailed cases are provided below.

[0055] Example 1: Preparation of modified phenolic resin precursor: Step 1, Preparation of phenolic resin prepolymer: 94.1g of phenol and 33g of formaldehyde were added to 500g of ultrapure water, KOH was added to adjust the pH to about 10, and the mixture was kept at a constant temperature of 85℃ in a water bath for 3.5h to obtain a phenolic resin prepolymer containing hydroxymethyl groups; Step 2, Preparation of functionalized intercalated prepolymer: 10.9g of functional additive 4-aminophenol and 3g of formaldehyde were added to 50g of ultrapure water, KOH powder was added to adjust the pH to about 8.5, and 0.1g of CuCl2 catalyst was added. The mixture was kept at a constant temperature of 65℃ in a water bath for 1h to obtain a functional block prepolymer containing hydroxymethyl groups; Step 3, Separation: The phenolic resin prepolymer and functional block prepolymer obtained by the above method were added to 3 times their volume of petroleum ether solvent respectively. The mixture was stirred vigorously at a speed of 500 rpm or higher for 1 hour, allowed to stand for 3 hours, and then filtered to obtain two prepolymers. Step four, block copolymerization: 25% of the functional block prepolymer (theoretical molar fraction of phenolic resin prepolymer) was added to a 20 wt% aqueous solution of the above phenolic resin prepolymer. The reaction was carried out at pH 12 and 95°C under KOH catalysis for 7 hours to form a block-structured linear polymer. Step five, curing: The solution obtained in step four was transferred to a hydrothermal reactor and cured at 140°C for 11 hours. After curing, the solution was filtered and washed to obtain the block-modified phenolic resin-based hard carbon precursor powder required in Example 1. Preparation of modified hard carbon anode material: Step 1, pre-oxidation and refining: 50g of the above-mentioned block-modified phenolic resin hard carbon precursor was placed in a muffle furnace and pre-sintered in air atmosphere. The sintering temperature was controlled at 300℃ and held for 12h. The cooled pre-oxidized product was ball-milled, with a ball-to-material ratio of 2:1. The mass of zirconium beads with diameters of 2 / 4 / 6mm were 60g, 30g, and 10g, respectively. The ball milling speed was 800rpm and the ball milling time was 8h to obtain pre-oxidized powder. Step 2, High-temperature carbonization: The pre-oxidized powder is transferred to a tube furnace and subjected to a high-temperature carbonization process under an argon atmosphere. The temperature is first raised from room temperature to 650°C and held at this temperature for 8 hours. Then, the temperature is raised to 1100°C and held for 4 hours for high-temperature pyrolysis carbonization. The heating rate is controlled to be a slow 1.5°C / min throughout the process. After the high-temperature carbonization process is completed, the material is naturally cooled to room temperature to obtain the hard carbon anode material with the optimized microstructure.

[0056] Example 2: Preparation of modified phenolic resin precursor: Step 1, preparation of phenolic resin prepolymer: same as in Example 1; Step 2, preparation of functionalized intercalated prepolymer monomer: 13.81g of functional additive p-hydroxybenzoic acid and 3g of formaldehyde were added to 50g of ultrapure water, KOH powder was added to adjust the pH to about 9, and 0.1g of CuCl2 catalyst was added. The mixture was kept at a constant temperature of 60℃ in a water bath and reacted for 1h to obtain a functional block prepolymer containing hydroxymethyl groups; Step 3, separation: same as in Example 1; Step 4, block copolymerization: 25% of the functional block prepolymer (theoretical molar fraction of the prepolymer) was added to a 20wt% aqueous solution of the above prepolymer. The mixture was reacted at pH=13 and temperature of 90℃ under KOH catalysis for 8h to form a block-structured linear polymer; Step 5, curing: same as in Example 1; Preparation of modified hard carbon anode material: Modified hard carbon anode material can be obtained by using the same preparation method as in Example 1.

[0057] Example 3: Preparation of modified phenolic resin precursor: Step 1, preparation of phenolic resin prepolymer: same as Example 1; Step 2, preparation of functionalized intercalated prepolymer monomer: 17.42g of functional additive p-hydroxybenzenesulfonic acid and 3g of formaldehyde were added to 50g of ultrapure water, KOH powder was added to adjust the pH to about 9.5, and 0.1g of CuCl2 catalyst was added. The mixture was kept at a constant temperature of 65℃ in a water bath and reacted for 1h to obtain a functional block prepolymer containing hydroxymethyl; Step 3, separation: same as Example 1; Step 4, block copolymerization: 25% of the functional block prepolymer (theoretical molar fraction of the prepolymer) was added to a 25wt% aqueous solution of the above prepolymer. The mixture was reacted at pH=12.5 and temperature of 95℃ under KOH catalysis for 8h to form a block-structured linear polymer; Step 5, curing: same as Example 1; Preparation of modified hard carbon anode material: Modified hard carbon anode material can be obtained by using the same preparation method as in Example 1.

[0058] Example 4: Preparation of modified phenolic resin precursor: Step 1, preparation of phenolic resin prepolymer: same as Example 1; Step 2, preparation of functionalized intercalated prepolymer monomer: 17.41g of functional additive (4-hydroxyphenyl)phosphonic acid and 3g of formaldehyde were added to 50g of ultrapure water, KOH powder was added to adjust the pH value to about 10, and 0.1g of CuCl2 catalyst was added. The mixture was kept at a constant temperature of 60℃ in a water bath and reacted for 1h to obtain a functional block prepolymer containing hydroxymethyl; Step 3, separation: same as Example 1; Step 4, block copolymerization: 23% of the functional block prepolymer (theoretical molar fraction of the prepolymer) was added to a 20wt% aqueous solution of the above prepolymer. The mixture was reacted at pH=13 and temperature of 95℃ under KOH catalysis for 8h to form a block-structured linear polymer; Step 5, curing: same as Example 1; Preparation of modified hard carbon anode material: Modified hard carbon anode material can be obtained by using the same preparation method as in Example 1.

[0059] Example 5: Preparation of modified phenolic resin precursor: Same as Example 1, except that in step one, the pH was adjusted to about 10, the water bath temperature was kept constant at 92°C, and the reaction was carried out for 5 hours. By increasing the pH and temperature of the prepolymer reaction environment and extending the reaction time, a high molecular weight prepolymer can be obtained. Its molecular weight was characterized by gel permeation chromatography (GPC), and its molecular weight was about 10,000 Mn. Preparation of hard carbon anode material: The hard carbon anode material of Comparative Example 4 can be obtained by using the same preparation method as in Example 1.

[0060] Example 6: Preparation of modified phenolic resin precursor: Same as Example 1, except for step two, the pH value is adjusted to about 11, and 0.1g CuCl2 catalyst is added. The reaction is carried out at a constant temperature of 83°C in a water bath for 2 hours. By increasing the pH and temperature of the prepolymer reaction environment and extending the reaction time, a high molecular weight prepolymer can be obtained. Its molecular weight is characterized by gel permeation chromatography (GPC), and its molecular weight is about 1200Mn. Preparation of hard carbon anode material: The hard carbon anode material of Comparative Example 5 can be obtained by using the same preparation method as in Example 1.

[0061] Example 7: Preparation of modified phenolic resin precursor: Same as Example 1, except for step four, block copolymerization: Add 4% of the functional block prepolymer (theoretical molar fraction of the prepolymer) to the 20wt% aqueous solution of the above prepolymer, react at pH=12 and temperature 95℃ under KOH catalysis for 7h to form a block structure linear polymer. Preparation of hard carbon anode material: The hard carbon anode material of Comparative Example 5 can be obtained by using the same preparation method as in Example 1.

[0062] Example 8: Preparation of modified phenolic resin precursor: Same as Example 1, except for step four, block copolymerization: Add 45% of the functional block prepolymer (theoretical molar fraction of the prepolymer) to the above prepolymer aqueous solution at 20wt% and react at pH=12 and 95℃ for 7h under KOH catalysis to form a block structure linear polymer. Preparation of hard carbon anode material: The hard carbon anode material of Comparative Example 5 can be obtained by using the same preparation method as in Example 1.

[0063] Example 9: Preparation of modified phenolic resin precursor: The same preparation method as in Example 1 was used; Preparation of hard carbon anode material: Same as in Example 1, except for step one, pre-oxidation and refining: 50g of the above-mentioned block-modified phenolic resin hard carbon precursor 1 was placed in a muffle furnace and pre-sintered in air atmosphere. The sintering temperature was controlled at 300℃ and held for 12h. The cooled pre-oxidized product was ball-milled, with a ball-to-material ratio controlled at 1:10. The mass of zirconium beads with diameters of 2 / 4 / 6mm were 60g, 30g, and 10g, respectively. The ball milling speed was 500ppm and the ball milling time was 8h to obtain pre-oxidized powder.

[0064] Example 10: Preparation of modified phenolic resin precursor: The same preparation method as in Example 1 was used; Preparation of hard carbon anode material: Same as in Example 1, except for step one, pre-oxidation refining: 50g of the above-mentioned block-modified phenolic resin hard carbon precursor 1 was placed in a muffle furnace and pre-sintered in air atmosphere. The sintering temperature was controlled at 300℃ and held for 12h. The cooled pre-oxidized product was ball-milled, with a ball-to-material ratio controlled at 10:1. The mass of zirconium beads with diameters of 2 / 4 / 6mm were 60g, 30g, and 10g, respectively. The ball milling speed was 1300ppm and the ball milling time was 8h to obtain pre-oxidized powder.

[0065] Example 11: Preparation of modified phenolic resin precursor: The same preparation method as in Example 1 was used; Preparation of hard carbon anode material: Same as in Example 1, except for step two, high-temperature carbonization: The above pre-oxidized powder is transferred to a tube furnace and subjected to high-temperature carbonization under an argon atmosphere. First, the temperature is raised from room temperature to 400°C and held at this temperature for 8 hours. Then, the temperature is raised to 900°C and held for 4 hours to carry out high-temperature pyrolysis carbonization. The heating rate is controlled to be a slow increase of 1.5°C / min throughout the process. After the above high-temperature carbonization process is completed, the material is naturally cooled to room temperature to obtain the above-mentioned hard carbon anode material with optimized microstructure.

[0066] Example 12: Preparation of modified phenolic resin precursor: The same preparation method as in Example 1 was used; Preparation of hard carbon anode material: Same as in Example 1, except for step two, high-temperature carbonization: The above pre-oxidized powder is transferred to a tube furnace and subjected to high-temperature carbonization under an argon atmosphere. First, the temperature is raised from room temperature to 850°C and held at this temperature for 8 hours. Then, the temperature is raised to 1700°C and held for 4 hours for high-temperature pyrolysis carbonization. The heating rate is controlled to be a slow rise of 1.5°C / min throughout the process. After the above high-temperature carbonization process is completed, the material is naturally cooled to room temperature to obtain the above-mentioned hard carbon anode material with optimized microstructure.

[0067] Example 13: Preparation of modified phenolic resin precursor: The same preparation method as in Example 1 was used; Preparation of hard carbon anode material: Same as in Example 1, except for step two, high-temperature carbonization: The above pre-oxidized powder is transferred to a tube furnace and subjected to high-temperature carbonization under an argon atmosphere. First, the temperature is raised from room temperature to 650°C and held at this temperature for 5 hours. Then, the temperature is raised to 1100°C and held for 2 hours to carry out high-temperature pyrolysis carbonization. The heating rate is controlled to be a slow increase of 1.5°C / min throughout the process. After the above high-temperature carbonization process is completed, the material is naturally cooled to room temperature to obtain the above-mentioned hard carbon anode material with optimized microstructure.

[0068] Example 14: Preparation of modified phenolic resin precursor: The same preparation method as in Example 1 was used; Preparation of hard carbon anode material: Same as in Example 1, except for step two, high-temperature carbonization: The above pre-oxidized powder is transferred to a tube furnace and subjected to high-temperature carbonization under an argon atmosphere. First, the temperature is raised from room temperature to 650°C and held at this temperature for 9 hours. Then, the temperature is raised to 1100°C and held for 7 hours to carry out high-temperature pyrolysis carbonization. The heating rate is controlled to be a slow increase of 1.5°C / min throughout the process. After the above high-temperature carbonization process is completed, the material is naturally cooled to room temperature to obtain the above-mentioned hard carbon anode material with optimized microstructure.

[0069] Example 15: Preparation of modified phenolic resin precursor: The same preparation method as in Example 1 was used; Preparation of hard carbon anode material: Same as in Example 1, except for step two, high-temperature carbonization: The above pre-oxidized powder is transferred to a tube furnace and subjected to high-temperature carbonization under an argon atmosphere. First, the temperature is raised from room temperature to 500°C and held at this temperature for 7 hours. Then, the temperature is raised to 1500°C and held for 3 hours to carry out high-temperature pyrolysis carbonization. The heating rate is controlled to be a slow increase of 1.5°C / min throughout the process. After the above high-temperature carbonization process is completed, the material is naturally cooled to room temperature to obtain the above-mentioned hard carbon anode material with optimized microstructure.

[0070] Example 16: Preparation of modified phenolic resin precursor: The same preparation method as in Example 1 was used; Preparation of hard carbon anode material: Same as in Example 1, except for step two, high-temperature carbonization: The above pre-oxidized powder is transferred to a tube furnace and subjected to high-temperature carbonization under an argon atmosphere. First, the temperature is raised from room temperature to 500°C and held at this temperature for 7 hours. Then, the temperature is raised to 1500°C and held for 3 hours to carry out high-temperature pyrolysis carbonization. The heating rate is controlled to be 3°C / min throughout the process. After the above high-temperature carbonization process is completed, the material is naturally cooled to room temperature to obtain the above-mentioned hard carbon anode material with optimized microstructure.

[0071] Example 17: Preparation of modified phenolic resin precursor: Same as in Example 1; Preparation of hard carbon anode material: The same method as in Example 1 is used, except that in step two, the heating rate is 5℃ / min for rapid heating.

[0072] Comparative Example 1: Preparation of Phenolic Resin Precursor: Step 1, Preparation of Phenolic Resin Prepolymer: Same as in Example 1; Step 2, Separation: Same as in Example 1; Step 3, Copolymerization: The prepolymer obtained in Step 2 was prepared into a 20wt% aqueous solution, and reacted for 7 hours under KOH catalysis, pH=12, temperature 95℃, to form a linear polymer; Step 4, Curing: The solution obtained in Step 3 was transferred into a high-pressure reactor and cured at 140℃ for 11 hours to obtain the phenolic resin-based hard carbon precursor corresponding to Comparative Example 1; Preparation of hard carbon anode material: Modified hard carbon anode material can be obtained by using the same preparation method as in Example 1.

[0073] Comparative Example 2: Preparation of modified phenolic resin precursor: Same as Example 1, except that in step four, the proportion of functional block prepolymer added is 50%; Preparation of hard carbon anode material: The hard carbon anode material of Comparative Example 2 can be obtained by using the same preparation method as in Example 1.

[0074] Comparative Example 3: Preparation of modified phenolic resin precursor: Same as Example 1, except that in step four, the proportion of functional block prepolymer added is 3%; Preparation of hard carbon anode material: The hard carbon anode material of Comparative Example 3 can be obtained by using the same preparation method as in Example 1.

[0075] Comparative Example 4: Preparation of modified phenolic resin precursor: Same as Example 1, except for step one, the pH was adjusted to about 13, the water bath temperature was kept constant at 96℃, and the reaction was carried out for 8 hours. By increasing the pH and temperature of the prepolymer reaction environment and extending the reaction time, a high molecular weight prepolymer can be obtained. Its molecular weight was characterized by gel permeation chromatography (GPC) and was about 100,000 Mn. Preparation of hard carbon anode material: The hard carbon anode material of Comparative Example 4 can be obtained by using the same preparation method as in Example 1.

[0076] Comparative Example 5: Preparation of modified phenolic resin precursor: Same as Example 1, except for step two, the pH value was adjusted to about 12, and 0.1g CuCl2 catalyst was added. The reaction was carried out at a constant temperature of 86℃ in a water bath for 3 hours. By increasing the pH and temperature of the prepolymer reaction environment and extending the reaction time, a high molecular weight prepolymer can be obtained. Its molecular weight was characterized by gel permeation chromatography (GPC), and its molecular weight was about 20,000 Mn. Preparation of hard carbon anode material: The hard carbon anode material of Comparative Example 5 can be obtained by using the same preparation method as in Example 1.

[0077] Comparative Example 6: Preparation of modified phenolic resin precursor: Same as in Example 1; Preparation of hard carbon anode material: The process was the same as in Example 1, except for the ball milling conditions of the pre-oxidized product. The ball-to-material ratio was controlled at 1:1, and the masses of zirconium beads with diameters of 6, 8, and 10 mm were 5 g, 15 g, and 35 g, respectively. The milling speed was 500 ppm, and the milling time was 3 h to obtain pre-oxidized powder. The particle size distribution was measured using a Malvern laser particle size analyzer, with a D50 of 7.4 μm and a SPAN of 1.48.

[0078] Comparative Example 7: Preparation of modified phenolic resin precursor: Same as in Example 1; Preparation of hard carbon anode material: The process was the same as in Example 1, except for the ball milling conditions of the pre-oxidized product. The ball-to-material ratio was controlled at 2:1, and the masses of zirconium beads with diameters of 1 / 2 / 3 mm were 70 g, 5 g, and 25 g, respectively. The milling speed was 800 ppm, and the milling time was 8 h to obtain pre-oxidized powder. The particle size distribution was measured using a Malvern laser particle size analyzer, with D50 = 0.9 μm and SPAN = 2.6.

[0079] Comparative Example 8: Preparation of modified phenolic resin precursor: Same as in Example 1; Preparation of hard carbon anode material: The same as in Example 1 is used, except that in step two, one-step carbonization is used, the carbonization temperature is 1450℃, and the temperature is maintained at this temperature for 12h for high-temperature pyrolysis carbonization. During the process, the heating rate is controlled to be a slow heating rate of 1.5℃ / min. After the above high-temperature carbonization process is completed, the material is naturally cooled to room temperature to obtain the hard carbon anode material.

[0080] Comparative Example 9: Preparation of modified phenolic resin precursor: Same as in Example 1; Preparation of hard carbon anode material: The same as in Example 1 is used, except that in step two, one-step carbonization is used, the carbonization temperature is 900℃, and the temperature is maintained at this temperature for 12h for high-temperature pyrolysis carbonization. During the process, the heating rate is controlled to be a slow heating rate of 1.5℃ / min. After the above high-temperature carbonization process is completed, the hard carbon anode material is obtained by naturally cooling to room temperature.

[0081] Comparative Example 10: Preparation of modified phenolic resin precursor: Same as in Example 1; Preparation of hard carbon anode material: The same method as in Example 1 is used, except that in step two, the temperature is raised to 1100℃ and then held for 1.5 hours.

[0082] Comparative Example 11: Preparation of modified phenolic resin precursor: Same as in Example 1; Preparation of hard carbon anode material: The same method as in Example 1 is used, except that in step two, the temperature is raised to 650℃ and then held for 10 hours.

[0083] The following tests were performed on Examples 1-17 and Comparative Examples 1-11: (1) The prepared hard carbon anode material, carbon black, SBR, and CMC were homogenized and mixed in a mass ratio of 95:1.5:1.5:2 to prepare an electrode paste. The prepared electrode paste was uniformly coated on aluminum foil and vacuum dried at 80°C for 12 hours, then cut into pieces. The electrode is 12, and the loading of active material is controlled at 3-4 mg / cm³. 2 Electrode plates were obtained. Then, coin cells were assembled in an argon-filled glove box. Sodium metal was used as the counter electrode, glass fiber as the separator, and 1M NaClO4, EC:DEC (vol = 1:1) was used as the electrolyte. Charge-discharge performance was tested using a Newway battery testing system with a test voltage range of 0-3V and a nominal specific capacity of 350mAh / g. The test results are shown in Table 2.

[0084] (2) The particle size distribution of the pre-oxidized powder was tested using a Mastersizer 3000 laser particle size analyzer. The dry test mode was used with Aero S (dry sampler). The sample amount was 0.015 g, the injection pressure was 3 Bar, the injection rate was 20%, the shading degree was 5%, the refractive index of the medium was 1.0, the refractive index of the sample was 1.85, the sample absorptivity was 0.85, and the SPAN was calculated using the formula SPAN = (D90-D10) / D50.

[0085] The molecular weight of prepolymers and block prepolymers was determined by GPC gel permeation chromatography using deionized water as the mobile phase. The molecular weight Mn of the prepolymer was then determined. To calculate the D002 interlayer spacing, we first obtained the peak value of (002) from the XRD pattern, then calculated θ = (2θ) / 2, and finally substituted it into the formula D002 = λ / (2 sinθ) for calculation.

[0086] He gas permeation can test the closed-pore volume of materials with a pore size <0.35 nm using a Microtrac BELPYCNO analyzer. The principle is based on the small atomic radius and high permeability of He gas to obtain the cavity volume of the material. The calculation formula is Vc = 1 / ρ - 1 / 2.26, where Vc is the closed-pore volume of hard carbon, with units of m³. 2 / g, ρ is the true density of the material, ρ=m / (Vc+Vs), Vs represents the volume of the material skeleton, where (Vc+Vs) can be calculated from the difference between the apparent volume and the cavity volume.

[0087] The macropores of the hard carbon anode material were characterized using a Microtrac BELPORE MP mercury porosimeter. According to the Mashburn equation P = -(2γcosθ) / r, the pressure range can be set from 0 to 14.71 MPa to characterize the pore structure of the macropore region >50 nm.

[0088] N2 gas adsorption-desorption technology can be used to characterize the mesoporous structure of hard carbon materials (mainly mesopores with pore sizes of 2-50 nm, including a small number of micropores > 0.7 nm). When the medium gas is replaced with CO2, it can be used to characterize the microporous structure of hard carbon materials (mainly micropores in the range of 0.35 nm-2 nm, especially sensitive to micropores < 0.7 nm). The corresponding operating temperatures are 77 K and 273 K, respectively, both using a Microtrac BELSORP MAX-II analytical instrument. The corresponding specific surface area (SSA) and pore size were calculated by the BET (N2) method and the NLDFT (CO2) method, respectively. The corresponding pore volume was calculated by the Barrett-Joyner-Halenda method and the Horvath-Kawazoe method, respectively. The test results are shown in Tables 1 and 2.

[0089] Table 1

[0090] Table 2

[0091] Table 3

[0092] As can be seen from Examples 1-17 and Comparative Examples 1-11, combined with the data in Tables 1-3, this invention can simultaneously regulate the preparation process and high-temperature carbonization process of block-modified phenolic resin-based hard carbon precursors, thereby systematically optimizing the microstructure of the hard carbon anode material and ultimately achieving a comprehensive improvement in its electrochemical performance. Under the conditions defined by this invention, the phenolic resin with functional block design and heteroatom doping increases the D002 interlayer spacing and optimizes its pore structure. This allows for the formation of more closed-pore structures, resulting in a larger micropore to mesopore ratio, which is more conducive to improving the sodium ion storage capacity and kinetic performance. Ultimately, this significantly improves the overall electrochemical performance, especially the plateau capacity, first-efficiency, rate capability, and low-temperature performance.

[0093] A comparison of Examples 1-17 and Comparative Example 1 shows that when the functional block-designed phenolic resin is doped with heteroatoms, the D002 interlayer spacing is increased, and its pore structure is optimized, forming more closed-pore structures. The ratio of micropores to mesopores is larger, promoting the desolvation process of sodium ions, enhancing the intercalation kinetics and reversibility of sodium ions, and constructing a stable SEI film; it is also more conducive to improving the sodium ion storage capacity and kinetic performance. In Comparative Example 1, because the phenolic resin prepolymer did not undergo the intercalation design of the functional block prepolymer, its microstructure and electrochemical performance were comprehensively degraded, with a graphite-like interlayer spacing d002 of only 0.368 nm, significantly smaller than that of Example 1. This directly proves that the effective expansion of the graphite interlayer spacing by heteroatoms in the functional blocks is the key to this invention. At the same time, the closed-pore ratio in Comparative Example 1 is as low as 0.32%, while that in Example 1 is as high as 5.51%. This indicates that the preferential decomposition and volatilization of functional blocks at specific carbonization temperatures is the core mechanism for creating abundant closed pores in situ. Precursors without the intercalation design of block prepolymers will find it difficult to form effective nanoscale closed spaces. The cross-linking effect between blocks disrupts the regular graphite layered structure and promotes the formation of micropores, with a micropore / mesopore ratio of only 4.61, far lower than the 35.5 in Example 1. At the same time, its mesopore volume is relatively high, indicating that the pores are mainly open mesopores, which is not conducive to sodium ion filling and SEI film stability, thus showing a comprehensive decline in electrochemical performance. This confirms the synergistic advantages of the intercalation design of the functional block prepolymer of this invention in improving sodium storage capacity, optimizing reaction kinetics, and improving first-efficiency in structures with large interlayer spacing and high closed-pore / micropore ratio.

[0094] Depend on Figure 1 and Figure 2 It can be seen that the hard carbon anode material prepared in Example 1 of the present invention has a large graphite-like interlayer spacing, forming more closed-pore and microporous structures.

[0095] A comparison of Examples 1-17 and Comparative Examples 2-5 shows that the block arrangement and quantity of functional segments are closely related to the structure of the hard carbon anode. Too many or too few blocks, and the length of the co-intercalated segments, all affect the degree and manner of polymer chain crosslinking, thus affecting the degree of graphitization and consequently the interlayer spacing and micropore structure. In Comparative Example 2, with an excessively high proportion of functional block prepolymer, although a larger interlayer spacing was achieved, its closed-cell ratio was extremely low, and the initial coulombic efficiency and cycle retention rate decreased significantly. This indicates that an excessively high proportion of functional blocks introduces too many defects, severely disrupting the continuity and stability of the carbon skeleton. Although the interlayer spacing is enlarged, it cannot form effective closed-cell sodium storage sites, and it also exacerbates side reactions, impairing initial efficiency and cycle life. Conversely, the parameters of Comparative Example 3 at a lower proportion are similar to those of Comparative Example 1, indicating that a too low proportion cannot effectively exert the pore-forming and layer-expanding effects, and the introduction effect of functional blocks cannot be effectively exerted at a low proportion. The comparison between Comparative Examples 4 and 5 reveals the crucial role of molecular weight control. The interlayer spacing of Comparative Examples 4 and 5 was much smaller than that of Example 1, with a closed-cell ratio of only 0.32% in both cases, resulting in a comprehensive deterioration in performance. This demonstrates that excessively high molecular weight severely restricts the movement and rearrangement of polymer chains during heat treatment, making it difficult for heteroatoms to effectively exert their steric hindrance effect. At the same time, functional blocks are also unable to accurately form nanopores in the carbon matrix, ultimately leading to severely poor closed-cell development in the material structure.

[0096] A comparison of Example 1 and Comparative Examples 6-7 shows that before high-temperature carbonization, the particle size properties of the powder affect the hard carbon anode structure. Smaller particle size and smaller SPAN result in more uniform and sufficient heat conduction and gas volatilization, and a narrower pore size distribution, which is conducive to the pore size distribution moving towards closed-pore and microporous regions. Conversely, larger particles have a larger SPAN value, and internal inhomogeneity makes it easier to form mesopores, macropores, and cracks. Based on this, controlling the pre-sintering temperature at 100~400℃ and limiting the ball milling parameters in the crushing step helps to form appropriate mesopore and macropore spaces in the product, serving as macroscopic channels for ion transport. At the same time, due to more uniform and sufficient heat conduction and gas volatilization, the narrower pore size distribution is conducive to the pore size distribution moving towards closed-pore and microporous regions.

[0097] As can be seen from the comparison between Example 1 and Comparative Examples 8-11, the present invention innovatively adopts a two-step carbonization process and limits the carbonization temperature and carbonization holding time, thereby guiding the orderly decomposition of functional blocks and the directional reconstruction of the carbon skeleton, thereby synergistically optimizing the interlayer spacing and the formation of multi-level pore structures, and controlling the porosity of the hard carbon anode material within a certain range.

[0098] A comparison of Examples 1 and 5-8 shows that the present invention can further limit the molar percentage of the functional block prepolymer in the phenolic resin prepolymer, while also limiting the molecular weight range of the phenolic resin prepolymer and the functional block prepolymer. When the proportion of the functional block prepolymer in the phenolic resin prepolymer is further controlled at 25-30%, and the molecular weights of both are further limited to a narrow range, an optimal balance between the spatial distribution of functional blocks and the distribution of chemically active sites can be achieved from the perspective of precursor molecules. This can effectively regulate the microstructure of the final hard carbon material. Under this preferred ratio, the phenolic resin prepolymer with a larger molecular weight forms the main chain segment, mainly contributing to the formation of the basic carbon skeleton and graphite-like structure of the hard carbon material. Its moderate molecular weight is beneficial for forming regular graphite-like domains with large interlayer spacing during subsequent curing and carbonization. The lower molecular weight of the functional block prepolymer allows it to be more flexibly embedded between the main chain segments or at specific sites. During heat treatment, these small molecule blocks rich in specific functional groups preferentially decompose or generate specific steric hindrance effects, thereby precisely creating a series of closed-pore and microporous structures within the carbon framework. This enables synergistic control over the interlayer spacing and hierarchical pore structure of hard carbon materials with graphite-like structures, which is key to obtaining excellent electrochemical performance. The sufficient number of functional blocks is crucial for efficiently creating pores and expanding the interlayer spacing of graphite-like layers during carbonization, ensuring a sufficient number of closed-pores and micropores to provide high plateau capacity. Simultaneously, the heteroatoms they contain are uniformly embedded in the carbon framework, effectively expanding the interlayer spacing of the graphite-like structures. This ratio avoids insufficient pore development due to too few functional blocks, as well as over-enrichment of pore structures and accumulation of defects in the carbon framework due to too many. This structural balance ensures, on the one hand, that sodium ions have sufficient and highly active storage sites, and on the other hand, maintains continuous channels for rapid ion and electron migration, thus synergistically optimizing the sodium storage capacity and reaction kinetics of the material at the microstructural level. Compared to Example 5, Example 1 further optimized the chain length of the main chain segments, which can further optimize the basic carbon skeleton and graphite-like structure of the hard carbon material, and is more conducive to the formation of regular graphite-like domains with large interlayer spacing during subsequent curing and carbonization. Compared to Example 6, Example 1 further optimized the chain length of the blocks, which further avoids structural defects and pore structure defects in the graphite-like domains caused by excessively long embedding. Therefore, by further using a phenolic resin prepolymer with a molecular weight range of 5000±1000Mn and adding a functional block prepolymer with a molecular weight range of 300±100Mn at a molar ratio of 25~30% of the phenolic resin prepolymer, a hard carbon anode material with a higher pore volume of closed structure and a higher ratio of microporous structure pore volume to mesoporous structure pore volume can be obtained.

[0099] As can be seen from the comparison between Examples 1 and Examples 9-10, the present invention can further optimize the pre-oxidation pulverization process and optimize the ball-to-material ratio and rotation speed during the ball milling process. When the particle size D50 of the pre-oxidized product obtained by further optimization is 0.5~1.5μm and the particle size SPAN value is ≤1.5, it further avoids the formation of more mesopores and macropores after subsequent carbonization due to excessively large particle size and distribution range. It also avoids the differential structural evolution caused by uneven heat distribution during subsequent carbonization, which leads to uneven microstructure of the material and poor reaction kinetics performance inside the electrode.

[0100] A comparison of Examples 1 and 11-14 shows that the present invention further optimizes the holding temperature and time. In Example 12, due to the high holding temperature, excessive graphitization is likely to occur, resulting in larger pore sizes, a higher proportion of macropores, and smaller interlayer spacing. In Example 11, due to the excessively low holding temperature, there are more defects, and the increased side reactions affect the initial efficiency capacity. In Example 13, due to the excessively short holding time, decomposition is insufficient, resulting in low pore volume, manifested as low porosity and low capacity. In Example 14, the long holding time makes micropores / closed pores more prone to transforming into mesopores and macropores. Therefore, the present invention further limits the carbonization temperature and holding time. The present invention adopts a specific stepped heating program and holding time to guide the orderly decomposition of functional blocks and the directional reconstruction of the carbon skeleton, thereby synergistically optimizing the interlayer spacing and the formation of multi-level pore structures, focusing on affecting the proportion of mesopores and macropores in the material, and optimizing the porosity of the material.

[0101] As can be seen from the comparison of Examples 1, 16 and 17, the present invention further optimizes the heating rate in the carbonization process, avoiding problems such as excessive heating rate, rapid gas volatilization, easy "pore bursting", formation of large pores, wide pore size distribution, and unfavorable sodium ion filling.

[0102] As can be seen from Examples 1-4, when copper halide salts are used as catalysts for the reaction, they exhibit higher catalytic activity, and the copper ions (Cu) in the copper halide... 2+ As a Lewis acid, Cu can coordinate with the carbonyl oxygen atom in aldehydes, activating the formaldehyde molecule and making it more susceptible to nucleophilic attack. Meanwhile, Cu... 2+It can also coordinate with the amino groups (-NH2) or phenolic oxy groups (-O-) in the preferred aminophenolic compounds, enhancing nucleophilicity. Under weakly alkaline conditions, CuCl2 can lower the reaction energy barrier through coordination, promoting the hydroxymethylation reaction of formaldehyde with amino groups (forming N-hydroxymethyl) or phenolic hydroxy groups (forming O-hydroxymethyl), thereby accelerating the formation of the prepolymer. Furthermore, aminophenolic compounds, as a source of heterogeneous elements in functionalized segments, mainly provide elements such as N and O. Compared to elements such as S and P, N and O have more suitable atomic sizes, enabling them to form more stable and uniform doping in the carbon framework. The introduction of N atoms effectively expands the interlayer spacing of graphite-like structures. Meanwhile, the O functional groups help form a more stable cross-linked structure during the pre-oxidation stage, inhibiting excessive graphitization of the carbon framework at high temperatures, creating favorable conditions for the formation and stable retention of closed-pore and microporous structures. More importantly, there is a unique synergistic effect between copper halide salts and aminophenolic compounds. In the synthesis stage of functional block prepolymers, CuCl2... 2+ The coordination with the amino group in aminophenol can guide the molecular chain to adopt a specific conformation and undergo decomposition behavior during the subsequent carbonization process. This can more precisely and efficiently induce the formation of uniformly sized and concentrated closed-pore and microporous structures, rather than disordered macropores or mesopores. This precise control at the molecular scale is a further optimization of achieving the ideal pore structure with a high closed-pore / micropore ratio and a high micropore / mesopore volume ratio as described in this invention.

[0103] In summary, this invention, through precise design at the precursor molecular level, innovatively embeds functionalized segments containing heterogeneous elements such as nitrogen and oxygen into the phenolic resin backbone, and synergistically optimizes subsequent particle grinding and two-step carbonization processes, successfully preparing a hard carbon anode material with a unique microstructure. This material possesses a significantly expanded graphite-like interlayer spacing, a high volumetric closed-pore structure, and an extremely high micropore / mesopore volume ratio. This synergistic structure effectively improves the sodium-ion storage capacity, insertion / extraction kinetics, and interfacial stability, ultimately enabling the material to exhibit comprehensive electrochemical performance in sodium-ion batteries, including high initial efficiency, high plateau capacity, excellent rate performance, and long cycle life. This solves the problems of uncontrollable structure and difficulty in achieving balanced performance in traditional hard carbon materials.

[0104] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A hard carbon anode material, characterized in that, The interlayer spacing d002 of the graphite-like layer structure of the hard carbon anode material is ≥0.385 nm. The hard carbon anode material has a pore structure including closed-pore, microporous, mesoporous, and macroporous structures. The closed-pore structure is a channel with an opening diameter of d ≤0.35 nm, the microporous structure is a channel with an opening diameter of 0.35 nm < d ≤ 2 nm, the mesoporous structure is a channel with an opening diameter of 2 nm < d ≤ 50 nm, and the macroporous structure is a channel with an opening diameter of d > 50 nm. The porosity of the hard carbon anode material is 20-60%. The pore volume of the closed-pore structure accounts for >2% of the total pore volume of the hard carbon anode material, the pore volume of the macroporous structure accounts for <65% of the total pore volume of the hard carbon anode material, and the ratio of the pore volume of the microporous structure to the pore volume of the mesoporous structure is 10-150.

2. The hard carbon anode material according to claim 1, characterized in that, In the pore structure of the hard carbon anode material, the percentage of the pore volume of the closed-pore structure to the total pore volume of the hard carbon anode material is 5% to 15%, and the ratio of the pore volume of the microporous structure to the pore volume of the mesoporous structure is 25 to 100.

3. A method for preparing the hard carbon anode material according to any one of claims 1 to 2, characterized in that, Includes the following steps: S1. Phenolic compounds and aldehyde compounds are reacted under alkaline conditions to obtain phenolic resin prepolymers; Functionalized additives and aldehyde compounds were reacted under alkaline conditions and with a halide metal salt catalyst to obtain functional block prepolymers. A functional block prepolymer, comprising 4-45% of the phenolic resin prepolymer, is added to a phenolic resin prepolymer and reacted under alkaline catalytic conditions to obtain a linear block polymer with an AABAA structure, wherein A is the phenolic resin prepolymer and B is the functional block prepolymer. Block-structured linear polymers were cured at high temperature to obtain block-modified phenolic resin-based hard carbon precursors; The functionalized additives are selected from one or more of aminophenolic compounds, benzoic acid compounds, benzenesulfonic acid compounds, and phenyl phosphate compounds; S2: The block-modified phenolic resin-based hard carbon precursor prepared in S1 is pre-sintered and crushed at a temperature of 100~400℃ to obtain a pre-oxidized product. The particle size D50 of the pre-oxidized product is 0.4~2.5μm and the particle size SPAN value is ≤2.

1. The pre-oxidized powder is first kept at 400~850℃ for 5~9h, and then kept at 900~1700℃ for 2~7h to complete the two-step carbonization to obtain hard carbon anode material.

4. The preparation method according to claim 3, characterized in that, In S1, a functional block prepolymer with a molecular weight range of 50-1200Mn is added to a phenolic resin prepolymer with a molecular weight range of 2000-20000Mn, accounting for 15-40% of the phenolic resin prepolymer. The reaction is carried out under alkaline catalytic conditions to obtain a block-structured linear polymer. Preferably, in S1, a functional block prepolymer with a molecular weight range of 300±100Mn is added to a phenolic resin prepolymer with a molecular weight range of 5000±1000Mn, accounting for 25~30% of the phenolic resin prepolymer, and reacted under alkaline catalytic conditions to obtain a block-structured linear polymer. Preferably, the phenolic resin prepolymer in S1 is prepared by reacting phenolic compounds and aldehyde compounds at a molar ratio of 1:0.8 to 1:1.5 under alkaline conditions at pH 8 to 12 at 60 to 95°C for 2 to 5 hours to obtain the phenolic resin prepolymer; the functional block prepolymer in S1 is prepared by reacting functionalized additives and aldehyde compounds at a molar ratio of 1:0.8 to 1:1.

5. A functional block prepolymer is obtained by reacting a phenolic resin prepolymer with a halide metal salt catalyst at a molar ratio of 1:1.5 under alkaline conditions at pH 8-12 at 50-85°C for 0.5-2 hours. A functional block prepolymer (25-30% molar fraction of the phenolic resin prepolymer) is added to the separated phenolic resin prepolymer and reacted at 80-110°C for 4-9 hours under alkaline catalysis at pH 7.5-13 to obtain a block-structured linear polymer. The block-structured linear polymer is then cured at 110-160°C for 9-13 hours to obtain a block-modified phenolic resin-based hard carbon precursor. The functional additive is selected from one or more of aminophenolic compounds, benzoic acid compounds, benzenesulfonic acid compounds, and phenyl phosphate compounds.

5. The preparation method according to claim 3, characterized in that, The aminophenolic compounds include one or more of p-aminophenol, m-aminophenol, o-aminophenol, and p-acetaminophenol; Preferably, the benzoic acid compounds include one or more of benzoic acid, p-hydroxybenzoic acid, o-hydroxybenzoic acid, p-aminobenzoic acid, phthalic acid, and 2,4-dihydroxybenzoic acid; Preferably, the benzenesulfonic acid compound includes one or more of benzenesulfonic acid, p-toluenesulfonic acid, p-hydroxybenzenesulfonic acid, dodecylbenzenesulfonic acid, p-aminobenzenesulfonic acid, and 1,3-benzenedisulfonic acid; Preferably, the phenyl phosphate compound includes one or more of phenylphosphonic acid, (4-hydroxyphenyl)phosphonic acid, and triphenyl phosphate; Preferably, the aldehyde compounds include one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, acrolein, glutaraldehyde, cinnamaldehyde, cyclohexylformaldehyde, benzaldehyde, and p-methylbenzaldehyde; Preferably, the phenolic compound includes one or more of phenol, cresol, hydroquinone, and resorcinol; Preferably, the halide metal salt includes one of copper halide, iron halide, and zinc halide; More preferably, the halide metal salt is selected from one or more copper halide salts.

6. The preparation method according to claim 3, characterized in that, The preparation method of the phenolic resin prepolymer in S1 is to mix phenolic compounds and aldehyde compounds in a molar ratio of 1:

1. The phenolic resin prepolymer is obtained by reacting a mixture of functional additives and aldehyde compounds at a molar ratio of 1:1 to 1:1.2 at 80-90°C for 3-4 hours under alkaline catalysis at pH 9-11. The functional block prepolymer in S1 is prepared by reacting the functional additives and aldehyde compounds at 60-80°C for 1-2 hours under alkaline conditions at pH 8-10 and catalysis by copper halide salts to obtain the functional block prepolymer. 25-30% of the functional block prepolymer is added to the separated phenolic resin prepolymer, and the mixture is reacted at 90-100°C for 5-8 hours under alkaline catalysis at pH 11-13 to obtain a block-structured linear polymer. The block-structured linear polymer is then cured at 120-150°C for 10-12 hours to obtain a block-modified phenolic resin-based hard carbon precursor. Preferably, the halide metal salt catalyst is a copper halide salt; the functionalized additive is an aminophenol compound; Preferably, the phenolic resin prepolymer and the functional block prepolymer prepared in S1 can be separated by the following method: Phenolic resin prepolymer was obtained by reacting phenolic compounds and aldehyde compounds under alkaline conditions. The phenolic resin prepolymer was added to petroleum ether solvent, stirred vigorously, allowed to stand, and filtered to obtain the separated phenolic resin prepolymer. The functional block prepolymer obtained by reacting functionalized additives and aldehyde compounds under alkaline conditions and catalysis by copper chloride (CuCl2) was added to petroleum ether solvent, stirred vigorously, allowed to stand, and filtered to obtain the separated functional block prepolymer. More preferably, the prepared phenolic resin prepolymer and functional block prepolymer can be separated by the following method: The prepared phenolic resin prepolymer and functional block prepolymer were added to petroleum ether solvent and stirred vigorously at a speed of more than 500 rpm for 1 hour. After standing for 3 hours, the phenolic resin prepolymer and functional block prepolymer appeared at the bottom of the mixed solution as powder and flocculent precipitates, respectively. After filtration, the separated phenolic resin prepolymer and functional block prepolymer were obtained.

7. The preparation method according to claim 3, characterized in that, The crushing step in S2 involves ball milling at a speed of 500-1300ppm with zirconium beads having a diameter of 2-6mm. The ratio of the pre-sintered product to the zirconium beads is 1:10-10:1, and the ball milling time is 4-10h to obtain the pre-oxidized product. Preferably, the pre-oxidized product has a unimodal particle size distribution, a particle size D50 of 0.5~2μm, and a particle size SPAN value ≤1.5; Preferably, the carbonization step in S2 is to raise the temperature from room temperature to 500~800℃ and hold it at that temperature for 6~8 h, raise the temperature to 900~1500℃ and hold it for 3~5 h, and then cool it to room temperature to obtain the hard carbon anode material. Preferably, the heating rate in the carbonization step of S2 is 0.5-3℃ / min.

8. The preparation method according to claim 3, characterized in that, The preparation method includes the following steps: S1. Phenolic compounds and aldehyde compounds are reacted at a molar ratio of 1:1 to 1:1.1 under alkaline catalytic conditions of pH 9-11 at 80-90℃ for 3-4 hours to obtain phenolic resin prepolymer; The functionalized additives, aminophenolic compounds and aldehyde compounds, were reacted at a molar ratio of 1:1 to 1:1.2 under alkaline conditions (pH 8-10) and catalyzed by copper chloride (CuCl2) at 60-80°C for 1-2 hours to obtain a functionalized block prepolymer. The amount of copper chloride used was 0.2-1.3% of the total mass of the functionalized additives, aminophenolic compounds and aldehyde compounds. A functional block prepolymer, comprising 25-30% of the phenolic resin prepolymer molar fraction, was added to the separated phenolic resin prepolymer and reacted at 90-100℃ for 5-8 hours under alkaline catalysis at pH 11-13 to obtain a block-structured linear polymer. Block-structured linear polymers were cured at a high temperature of 120~150℃ for 10~12h to obtain block-modified phenolic resin-based hard carbon precursors. S2: The block phenolic resin-based hard carbon precursor prepared in S1 is pre-sintered at a temperature of 100~400℃ for 10~14h. The zirconium beads were ball-milled at a diameter of 2-6 mm and a rotation speed of 600-1100 ppm. The ratio of the pre-sintered product to the zirconium beads was 1:10-10:1, and the ball milling time was 5-9 h to obtain the pre-oxidized product. The particle size D50 of the pre-oxidized product was 0.5-1.5 μm, and the particle size SPAN value was ≤1.

5. The pre-oxidized powder is first heated from room temperature to 500~800℃ and held at this temperature for 6~8 h, then heated to 900~1500℃ and held for 3~5 h, with a heating rate of 0.5-3℃ / min, and then cooled to room temperature to obtain the hard carbon anode material.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the hard carbon negative electrode material according to any one of claims 1 to 2 or the hard carbon negative electrode material prepared by the method of preparing the hard carbon negative electrode material according to any one of claims 3 to 8.

10. A sodium-ion battery comprising the hard carbon negative electrode sheet as described in claim 9.

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