Covalently bridged bicontinuous hard carbon negative electrode material and preparation method and application thereof

Abstract

The application discloses a kind of covalent bridging double continuous hard carbon negative electrode material and its preparation method and application, belong to electrochemical energy storage material field.The application breaks through the long-range disorder structure of biomass hard carbon by "template-self-assembly-reconstruction" three-stage reaction, realizes atomic level cooperation of electron and ion in hard carbon matrix, enhances in-situ mechanical interlocking and chemical bridging between heteroatom doped carbon dots and hard carbon matrix graphite domains using precursor design, triggers topological reconstruction of carbon skeleton through acid washing purification and high-temperature carbonization process, and realizes precise fusion of C-C covalent bond.The graphitized nanodomains grown in this process provide a fast transmission channel for electrons, and the topological defects and heteroatoms produced provide a fast transmission channel for sodium ion adsorption and surface migration.The prepared material exhibits excellent reversible capacity, first coulombic efficiency and rate performance.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage materials, specifically relating to a covalently bridged dual continuous hard carbon anode material, its preparation method, and its application. Background Technology

[0002] Hard carbon is considered the most promising anode material for sodium-ion batteries due to its low cost and abundant sodium resources. However, the low intrinsic conductivity and tortuous ion diffusion paths caused by the disordered carbon framework can lead to severe kinetic polarization effects, making it difficult for hard carbon to meet the rate performance and cycle life requirements of commercial fast charging. Traditional modification methods, such as pore formation, widening the interlayer spacing, or heteroatom doping, usually require balancing the mismatch between electron conduction and ion transport to avoid introducing a large number of irreversible defects that would reduce the initial coulombic efficiency and tap density.

[0003] Studies have shown that heterostructures with covalent bridging can effectively enhance electronic interactions, mechanical connections, and interfacial charge transport, thus exhibiting significant advantages in fields such as electrocatalysis and energy storage. This provides a novel approach to fundamentally solve the interfacial transport problem in carbon-based composite materials. However, applying this "covalent bridging" design concept to complex and disordered hard carbon materials, and constructing covalently bonded graphite domain nanodomains containing heteroatom defects within hard carbon through molecular engineering to synergistically optimize electron and ion transport, remains a significant unexplored challenge.

[0004] Therefore, developing a hard carbon material with a stable and efficient dual-continuous transport structure and its preparation method is of vital importance for overcoming the performance bottleneck of sodium-ion battery anodes and promoting their industrialization. The purpose of this invention is precisely to solve the fundamental problems existing in the prior art. Summary of the Invention

[0005] One of the objectives of this invention is to address the core problem of electron-ion transport mismatch in existing hard carbon materials by providing a hard carbon anode material with a "covalent quantum bridging" structure, thereby solving the problems of poor rate performance and cycle stability of hard carbon anode materials.

[0006] The second objective of this invention is to provide a method for the batch preparation of the material with controllable process.

[0007] A third objective of this invention is to provide the application of the material as a negative electrode in high-performance sodium-ion batteries.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] In a first aspect, the covalently bridged dual continuous hard carbon anode material of the present invention uses hard carbon derived from biomass carbon source as a three-dimensional framework, wherein highly graphitized nanofunctional domains are uniformly embedded through covalent bonds to form an electron-ion dual continuous transport network.

[0010] in:

[0011] The highly graphitized nanofunctional domains have a size of 5-15 nm and are formed by the high-temperature catalytic graphitization of in-situ generated carbon dots.

[0012] The highly graphitized nanofunctional domains and the hard carbon matrix are precisely fused at the atomic level through C-C covalent bonds, forming a stable covalent bridging interface.

[0013] At the edges and bridging interfaces of the highly graphitized nanodomains, heteroatom functional groups and topological defects are selectively enriched, forming active channels for ion adsorption and rapid migration.

[0014] The closed-pore volume of the bicontinuous hard carbon material is significantly higher than that of traditional hard carbon, and the closed-pore structure is formed by the carbon dots as rigid templates and the synergistic control of a multi-step carbonization-purification process.

[0015] Secondly, the method for preparing the covalently bridged dual continuous hard carbon anode material of the present invention includes the following steps:

[0016] Step 1: Mix the carbon source and carbon dot precursor, and obtain mixed precursor powder after pretreatment;

[0017] Step 2: Under an inert atmosphere, the mixed precursor powder is subjected to a first continuous two-step step carbonization treatment to obtain a hard carbon intermediate.

[0018] Step 3: The hard carbon intermediate is subjected to acid washing to remove impurities and vacuum drying to obtain a purified porous hard carbon intermediate;

[0019] Step 4: Under an inert atmosphere, the purified porous hard carbon intermediate is subjected to a second high-temperature carbonization treatment to obtain the final bicontinuous hard carbon material.

[0020] In step 1, the carbon source is selected from any one or more of bamboo powder, coconut shell, corn stalk, reed, distiller's grains, palm shell, walnut shell, starch, and soybean gum.

[0021] Furthermore, the carbon source is crushed by a crusher and passed through a 100-400 mesh sieve with a particle size of 50-150 μm, and then transferred to an oven at 80-140 ℃ to dry for 5-15 h.

[0022] In step 1, the carbon dot precursor is classified into B-source precursor, N-source precursor, O-source precursor, P-source precursor, S-source precursor and F-source precursor according to the type of heteroatom provided, and the carbon dot precursor is selected from one or a combination of several of them.

[0023] Furthermore:

[0024] The B-source precursor is selected from one or more of boric acid, borax, sodium borate, and sodium borohydride;

[0025] The N-source precursor is selected from one or more of urea, melamine, ammonium chloride, dopamine, aniline, L-glutamic acid, ethylenediamine, polyethyleneimine, 1,3-diaminopropane, and folic acid.

[0026] The O-source precursor is selected from one or more of citric acid, glucose, 2,5-dimethoxycarbonyl-1,4-cyclohexanedione, salicylic acid, tartaric acid, and ascorbic acid.

[0027] The P-source precursor is selected from one or more of phosphoric acid, phytic acid, sodium hydrogen phosphate, tributyl phosphate, diammonium hydrogen phosphate, and hydroxyethyl diphosphonic acid.

[0028] The S-source precursor is selected from one or more sulfur-containing amino acids such as thiourea, dimethyl sulfoxide, acesulfame potassium, carbon disulfide, thioacetamide, and cysteine.

[0029] The F-source precursor is selected from one or more of polyvinylidene fluoride, ammonium fluoride, 3,4-diaminofluorobenzene, and levofloxacin.

[0030] Furthermore, the mass ratio of the carbon dot precursor to the carbon source is (10-100):100.

[0031] Furthermore, the pretreatment adopts a mechanical mixing method, in which the carbon source and carbon point precursor in the specified proportions are physically mixed by high-energy ball milling or three-dimensional mixing ball milling for 2-8 hours, with the rotation speed set at 500-3000 rpm.

[0032] In step 2, the inert atmosphere is argon or nitrogen; the heating rate in the first stage is 0.5-5 ℃ / min, the carbonization temperature is 100-300 ℃, and the holding time is 1-5 h; the heating rate in the second stage is 2-10 ℃ / min, the carbonization temperature is 500-800 ℃, and the holding time is 1-5 h.

[0033] During the first carbonization process, if the carbonization time is too short, the carbonization temperature is too low, or the heating rate is too fast, the energy required for carbon point growth will be insufficient, and the carbon source and the formed carbon points will have difficulty forming a stable cross-linking network. If the carbonization time is too long, the carbonization temperature is too high, or the heating rate is too slow, the carbon points will form too many graphitized nanodomains. A highly graphitized structure is not conducive to sodium ion storage.

[0034] During the first carbonization process, the carbon source and carbon dot precursor undergo polymerization and carbonization reactions. By controlling the appropriate carbonization reaction time, carbonization temperature and heating rate, carbon dots rich in heteroatom functional groups can be generated in situ on the surface of the carbon source, and a stable cross-linked network can be formed through hydrogen bonding and preliminary physicochemical reactions.

[0035] Step 3, the acid washing and impurity removal process includes the following steps:

[0036] The hard carbon intermediate was added to an acid solution and magnetically stirred at 200-500 r / min for 5-20 h at 30-100℃. The solution was then filtered and washed with deionized water until the pH of the filtrate was 7.0 and the conductivity was less than 20 μS / cm. Finally, it was dried in a vacuum oven at 80-150℃ for 8-20 h.

[0037] The acid solution is selected from any one or more of hydrochloric acid, hydrofluoric acid, phosphoric acid, and oxalic acid solutions with a mass fraction of 5-30%.

[0038] In step 3, the acid concentration, leaching temperature, and leaching time used in the impurity removal process must be appropriate. Excessive acid concentration, excessively long leaching time, or excessively high leaching temperature will damage the pore structure and carbon skeleton of the hard carbon intermediate, forming more unfavorable irreversible sodium storage sites. Insufficient acid concentration, excessively short leaching time, or excessively low leaching temperature will not effectively remove residual tar and impurities, leading to aggravated side reactions.

[0039] In step 3, appropriate acid etching can effectively remove residual SiO2, tar and ash, enabling the construction of abundant and interconnected ion transport channels inside the hard carbon.

[0040] In step 4, the inert atmosphere is argon or nitrogen, the heating rate is 0.5-10 ℃ / min, the carbonization temperature is 1100-1700 ℃, and the carbonization time is 2-10 h.

[0041] Second high-temperature carbonization-induced carbon skeleton sp 3 -sp 2Through topological reconstruction, the carbon layer gradually twists to form abundant closed pores. At the same time, the highly graphitized nanodomains formed by carbon dots through the defect-mediated mechanism achieve precise fusion of C-C covalent bonds with the carbon substrate. The highly graphitized nanodomains grown in this process can provide a fast transport channel for electrons, and the generated topological defects and pyridine / pyrrole N also provide a fast transport path for the adsorption and surface migration of sodium ions.

[0042] Thirdly, the present invention also provides a sodium-ion battery, using the covalently bridged dual continuous hard carbon material as the negative electrode. Specifically, the covalently bridged dual continuous hard carbon material, conductive agent, and binder are mixed in a mass ratio of (8-9.5):(0-1):(0.5-1) to prepare a slurry, which is then coated onto a current collector, dried, and rolled to serve as the negative electrode. This slurry is then assembled with a sodium sheet or a sodium-based positive electrode to form a sodium-ion half-cell or a full-cell battery.

[0043] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0044] 1. The core of the preparation of the covalently bridged dual-continuous hard carbon anode material of this invention lies in the uniform composite of various biomass precursors (carbon sources) and carbon dot precursors, and the in-situ growth of carbon dots. Cross-linking carbonization and deep purification are achieved during subsequent carbonization and acid washing processes. Finally, high-temperature carbonization completes the covalent bridging of carbon dots and the hard carbon matrix, forming a stable and ideal microstructure. This three-stage design of "template-self-assembly-reconstruction" overcomes the limitation of long-range disorder in biomass hard carbon, constructing a clearly partitioned dual-continuous transport network in the hard carbon. This achieves atomic-level synergy between electron channels and ion channels (nanocavities). Graphitized nanodomains are responsible for ultrafast electron transport, while their edge active sites are responsible for rapid ion migration. This fundamentally solves the problem of hard carbon kinetic mismatch.

[0045] 2. In preparing the covalently bridged dual-continuous hard carbon anode material, this invention first performs a two-step step-low-temperature pre-carbonization treatment on the mixed precursor powder obtained in step 1, followed by acid washing to remove impurities, and finally a second high-temperature carbonization. This invention generates heteroatom-doped carbon dots through the first-stage low-temperature carbonization of the mixed precursor powder, and these carbon dots are initially anchored to the bamboo powder framework undergoing initial pyrolysis through physical adsorption and chemical bonding, constructing a molecularly uniformly dispersed carbon dot-carbon source composite precursor. This ingenious "precursor engineering" ensures the effective fixation of carbon dots on the bamboo powder surface. During the second-stage low-temperature carbonization, complex interactions occur between the carbon dots and the bamboo carbon framework, including physical anchoring, covalent bonding, π-π stacking, and catalytic graphitization. These interactions not only establish preliminary mechanical and chemical connections between the two but, more importantly, lay the structural foundation for the subsequent full covalent bridging and highly graphitized nanodomain formation under the second high-temperature treatment. This multi-step, progressive bridging strategy avoids the problem of carbon dot structure destruction or uneven distribution caused by direct high-temperature treatment. The second high-temperature carbonization drives carbon atom rearrangement, with carbon dots acting as nucleation centers, co-forming with the bamboo carbon framework to form covalent, highly graphitized "quantum bridges." This invention uses mixed precursor powder, hard carbon intermediate, and porous hard carbon intermediate as the control targets, and employs the "synergistic coupling of the first continuous step-low temperature carbonization and the second high-temperature carbonization" as the control method. The aim is to prepare hard carbon materials with ideal graphite nanodomains by controlling the mixed precursor powder and hard carbon intermediate. Compared with traditional technologies, the preparation method has a clear principle and controllable process. The material structure can be finely controlled by adjusting the type of precursor and process parameters. It is applicable to various biomass carbon sources, possesses good universality and scalability, is simple and flexible, and requires no new equipment.

[0046] 3. This invention uses the prepared covalently bridged dual continuous hard carbon anode material as the anode material to prepare sodium-ion batteries, achieving a synergistic breakthrough in specific capacity, first-time efficiency, fast charge and discharge capability, and cycle life. Attached Figure Description

[0047] Figure 1 This is a process flow diagram for preparing the covalently bridged dual continuous hard carbon anode material of the present invention.

[0048] Figure 2 The image shows a TEM image of CDs in the hard carbon anode material prepared in Example 1.

[0049] Figure 3 This is a STEM image of the hard carbon anode material prepared in Example 1.

[0050] Figure 4 The images show the XRD patterns of the hard carbon anode materials prepared in Example 1 and Comparative Example 1.

[0051] Figure 5Raman diagrams of the hard carbon anode materials prepared in Example 1 and Comparative Example 1.

[0052] Figure 6 The first charge-discharge curves of sodium-ion batteries assembled with the hard carbon anode materials prepared in Example 1 and Comparative Example 1 at a current density of 30 mA / g.

[0053] Figure 7 Rate performance of sodium-ion batteries assembled with hard carbon anode materials prepared in Example 1 and Comparative Example 1 at current densities of 30-6000 mA / g.

[0054] Figure 8 The graph shows the cycling performance of sodium-ion batteries assembled with the hard carbon anode materials prepared in Example 1 and Comparative Example 1 at a current density of 300 mA / g.

[0055] Figure 9 The long-cycle performance of sodium-ion batteries assembled with the hard carbon anode materials prepared in Example 1 and Comparative Example 1 at a current density of 6000 mA / g is shown in the figure. Detailed Implementation

[0056] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0057] The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. The solutions disclosed herein will be explained below in conjunction with the embodiments. Those skilled in the art will understand that the following embodiments are only for illustrating the present disclosure and should not be considered as limiting the scope of the present disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] The technical solution of the present invention will be further analyzed and explained through specific embodiments below.

[0059] Example 1:

[0060] refer to Figure 1 The schematic diagram shown illustrates the fabrication process. The method for preparing the covalently bridged dual continuous hard carbon anode material in this embodiment includes the following steps:

[0061] 1. The carbon precursor (1 g citric acid, 2 g urea) and the carbon source (10 g bamboo powder) were mixed in a high-energy ball mill at 1000 rpm for 3 h to obtain mixed precursor powder.

[0062] 2. Under an Ar atmosphere, the mixed precursor powder was subjected to a first-stage carbonization treatment at 200 °C at a rate of 2 °C / min for 2 h, followed by a second-stage carbonization treatment at 600 °C at a rate of 5 °C / min for 3 h, to obtain a hard carbon intermediate.

[0063] 3. The hard carbon intermediate was immersed in a 20% (w / w) acid solution (the mass ratio of HCl to HF in the solute was 1:1), heated to 40 °C on a magnetic stirrer and stirred at 350 r / min for 6 h. The solution was washed multiple times with deionized water until the pH of the filtrate was ~7.0 and the conductivity was less than 20 μS / cm. Finally, it was dried in a vacuum oven at 80 °C for 8 h to obtain the purified porous hard carbon intermediate.

[0064] 4. Under an Ar atmosphere, the purified porous hard carbon intermediate was subjected to a second carbonization treatment at a rate of 5 °C / min to 1300 °C for 3 h to obtain a bicontinuous hard carbon material.

[0065] The hard carbon anode materials of Examples 2-22 and Comparative Examples 1-5 are the same as those of Example 1, except for the experimental parameters listed in the table.

[0066] Table 1 below shows some of the experimental parameters in the preparation methods of hard carbon anode materials in Examples 1-22 and Comparative Examples 1-5.

[0067]

[0068]

[0069] Wherein, " / " indicates that no acid was added; in all different embodiments, an acid solution with a mass fraction of 20% was used, and the acid content in the table is the mass percentage of different acids in the solute.

[0070] The hard carbon materials prepared in Examples 1-22 and Comparative Examples 1-5 were assembled into sodium-ion batteries, specifically including the following steps:

[0071] A uniform slurry was prepared by mixing hard carbon material, acetylene black, styrene-butadiene rubber, and carboxymethyl cellulose (92:3:3.5:1.5), which was then coated onto copper foil to a thickness of 100 μm. The slurry was dried in a vacuum oven at 80 ℃ for 10 h and cut into 14 mm diameter circular electrode sheets. CR2032 button half-cells were assembled in a vacuum glove box (water and oxygen levels <0.01 ppm), using a sodium sheet as the counter electrode, Whatman glass fiber as the separator, and NP-035 (1.0 M NaPF6 in DME) electrolyte. Before testing, the button cells were allowed to stand for 10 h and then tested using a Newway battery testing system, with a voltage range of 0.001–3.0 V.

[0072] The sodium storage performance data of the hard carbon anodes prepared in Examples 1-22 and Comparative Examples 1-5 are summarized in Table 2 below.

[0073]

[0074] As can be seen from Table 2, compared with Comparative Examples 1-5, the hard carbon materials obtained in Examples 1-22 exhibit high reversible capacity and ICE. It can be seen that through the ingenious combination of precursor molecule design and multi-step precise thermal treatment, the synergistic construction of electron and ion transport pathways at the atomic scale was achieved in the hard carbon anode material, thus solving the problem of improving electrochemical performance.

[0075] Figure 2 The TEM image of carbon dots in the hard carbon anode material prepared in Example 1 shows that the carbon dots have clear lattice stripes and a typical interplanar spacing of 0.21 nm, which is similar to the crystal structure of graphene (100) crystal plane. The size and distribution of the carbon dots are reasonable and uniform.

[0076] Figure 3 The image shows a STEM image of the hard carbon anode material prepared in Example 1. It can be seen that the graphitized nanodomains formed after the carbon dots are carbonized at high temperature have clear graphite diffraction fringes and are directly fused with the hard carbon matrix. No amorphous boundary was observed at the interface, which proves that the highly graphitized nanodomains and the hard carbon matrix are bridged and fused together by covalent bonds at high temperature.

[0077] Figure 4 The XRD patterns of the hard carbon anode materials prepared in Example 1 and Comparative Example 1 show that they both have two typical amorphous carbon (002) and (100) crystal planes. Furthermore, the (002) peak of the hard carbon anode material prepared in Example 1 shifts to a lower angle, indicating a larger carbon interlayer spacing.

[0078] Figure 5 Raman plots of the hard carbon anode materials prepared in Example 1 and Comparative Example 1, at ~1345 and ~1590 cm⁻¹. -1 Both exhibited characteristic peaks of the D and G bands of hard carbon, with the hard carbon anode material prepared in Example 1 showing higher A peaks. D1 / A G and A D3 / A G The ratio indicates that it contains higher levels of in-plane defects and oxygen-containing groups.

[0079] Figure 6 The first charge-discharge curves of the hard carbon anode materials prepared in Example 1 and Comparative Example 1 at a current density of 30 mA / g show that the reversible specific capacity of the hard carbon anode material prepared in Example 1 is as high as 391.1 mAh / g, the ICE is as high as 92%, and the plateau capacity is 278.5 mAh / g.

[0080] Figure 7 The rate performance graphs for the hard carbon anode materials prepared in Example 1 and Comparative Example 1 at current densities of 30-6000 mA / g show that the hard carbon anode material prepared in Example 1 has a reversible specific capacity of 250.8 mAh / g at 6 A / g, while the hard carbon anode material prepared in Comparative Example 1 has only 140.6 mAh / g.

[0081] Figure 8 The graph shows the cycling performance of the hard carbon anode materials prepared in Example 1 and Comparative Example 1 at a current density of 300 mA / g. It can be seen that the hard carbon anode material prepared in Example 1 still has a high sodium storage performance of 331.6 mAh / g after 400 cycles, with a capacity retention rate as high as 94.4%.

[0082] Figure 9 The graphs show the long-cycle performance of the hard carbon anode materials prepared in Example 1 and Comparative Example 1 at a current density of 6000 mA / g. It can be seen that the hard carbon anode material prepared in Example 1 exhibits excellent cycling stability, with a capacity retention of up to 83.5% after 15000 cycles. This is attributed to the dual-continuous structure of the hard carbon anode material prepared in Example 1, which simultaneously promotes sodium ion diffusion and electron transport, and the enhanced reaction kinetics due to N doping.

[0083] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0084] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for preparing a covalently bridged dual continuous hard carbon anode material, comprising the following steps: Step 1: Mix the carbon source and carbon dot precursor, and obtain mixed precursor powder after pretreatment; Step 2: Under an inert atmosphere, the mixed precursor powder is subjected to a first continuous two-step step carbonization treatment to obtain a hard carbon intermediate. Step 3: The hard carbon intermediate is subjected to acid washing to remove impurities and vacuum drying to obtain a purified porous hard carbon intermediate; Step 4: Under an inert atmosphere, the purified porous hard carbon intermediate is subjected to a second high-temperature carbonization treatment to obtain the final bicontinuous hard carbon material. In step 1, the carbon source is selected from any one or more of bamboo powder, coconut shell, corn stalk, reed, distiller's grains, palm shell, walnut shell, starch, and soybean gum; the carbon dot precursor is classified into B source precursor, N source precursor, O source precursor, P source precursor, S source precursor, and F source precursor according to the type of heteroatom provided, and the carbon dot precursor is selected from one or more of these combinations; the mass ratio of the carbon dot precursor to the carbon source is (10-100):

100. In step 2, the inert atmosphere is argon or nitrogen; the heating rate in the first stage is 0.5-5℃ / min, the carbonization temperature is 100-300℃, and the holding time is 1-5 h; the heating rate in the second stage is 2-10℃ / min, the carbonization temperature is 500-800℃, and the holding time is 1-5 h. Step 3, the acid washing and impurity removal process includes the following steps: The hard carbon intermediate is added to an acid solution and magnetically stirred at 200-500 r / min for 5-20 h at 30-100℃. The solution is then filtered and washed with deionized water until the pH of the filtrate is 7.0 and the conductivity is below 20 μS / cm. Finally, it is vacuum dried at 80-150℃. The acid solution is selected from any one or more of hydrochloric acid, hydrofluoric acid, phosphoric acid, and oxalic acid solutions with a mass fraction of 5-30%. In step 4, the inert atmosphere is argon or nitrogen, the heating rate is 0.5-10℃ / min, the carbonization temperature is 1100-1700℃, and the carbonization time is 2-10 h.

2. The preparation method according to claim 1, characterized in that: The B-source precursor is selected from one or more of boric acid, borax, sodium borate, and sodium borohydride; The N-source precursor is selected from one or more of urea, melamine, ammonium chloride, dopamine, aniline, L-glutamic acid, ethylenediamine, polyethyleneimine, 1,3-diaminopropane, and folic acid. The O-source precursor is selected from one or more of citric acid, glucose, 2,5-dimethoxycarbonyl-1,4-cyclohexanedione, salicylic acid, tartaric acid, and ascorbic acid. The P-source precursor is selected from one or more of phosphoric acid, phytic acid, sodium hydrogen phosphate, tributyl phosphate, diammonium hydrogen phosphate, and hydroxyethyl diphosphonic acid. The S-source precursor is selected from one or more sulfur-containing amino acids such as thiourea, dimethyl sulfoxide, acesulfame potassium, carbon disulfide, thioacetamide, and cysteine. The F-source precursor is selected from one or more of polyvinylidene fluoride, ammonium fluoride, 3,4-diaminofluorobenzene, and levofloxacin.

3. The preparation method according to claim 1, characterized in that: In step 1, the pretreatment adopts a mechanical mixing method, in which the carbon source and carbon point precursor in the specified proportions are ball-milled and mixed for 2-8 hours, with the rotation speed set at 500-3000 rpm.

4. A covalently bridged dual continuous hard carbon anode material, prepared according to any one of the preparation methods described in claims 1-3, characterized in that: The covalently bridged dual continuous hard carbon anode material uses hard carbon derived from biomass carbon source as a three-dimensional framework, in which highly graphitized nanofunctional domains are uniformly embedded through covalent bonds to form an electron-ion dual continuous transport network. The highly graphitized nanofunctional domains have a size of 5-15 nm and are formed by the high-temperature catalytic graphitization of in-situ generated carbon dots. The highly graphitized nanofunctional domains and the hard carbon matrix are precisely fused at the atomic level through C-C covalent bonds, forming a stable covalent bridging interface. At the edges and bridging interfaces of the highly graphitized nanodomains, heteroatom functional groups and topological defects are selectively enriched, forming active channels for ion adsorption and rapid migration.

5. A sodium-ion battery comprising the covalently bridged dual continuous hard carbon anode material as described in claim 4.

Images