Preparation method of controllable structure asphalt-based negative material, hard carbon negative material and sodium ion battery

Abstract

This invention relates to the field of electrochemical energy storage battery technology, specifically to a method for preparing a controllable pitch-based anode material, a hard carbon anode material, and a sodium-ion battery. The preparation method includes: S1. Pre-oxidation treatment: pre-oxidizing the raw materials to obtain an oxidized precursor with an oxygen content of 15%~35%; the raw materials are selected from at least one of pitch, biomass, and phenolic resin; S2. Precursor compositing: mixing the oxidized precursor with a thermoplastic precursor at a mass ratio of 1~5:1 to obtain a composite precursor; the thermoplastic precursor is selected from at least one of petroleum pitch, coal tar pitch, phenolic resin, and aqueous phenolic resin; S3. Carbonization treatment: carbonizing the composite precursor under an inert atmosphere to obtain the pitch-based electrode material. The prepared carbon material has the advantages of uniform structure, stable interface, high reversible capacity, and high initial coulombic efficiency, and the preparation process is simple with controllable product quality.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage battery technology, specifically to a method for preparing a controllable pitch-based anode material, a hard carbon anode material, and a sodium-ion battery. Background Technology

[0002] In recent years, sodium-ion batteries have attracted attention due to the abundance of sodium resources, controllable cost, and adaptability to large-scale energy storage scenarios. However, due to factors such as the large radius of Na⁺ ions and slow diffusion kinetics, traditional graphite or alloy anodes struggle to balance capacity, initial efficiency, and lifespan. Hard carbon, with its large interlayer spacing and disordered pores, is considered a more suitable candidate for sodium-ion batteries. However, existing hard carbon batteries generally suffer from low initial coulombic efficiency, insufficient capacity release at low voltage plateaus, and significant interfacial side reactions. The root cause lies in the difficulty of simultaneously optimizing the micropore distribution and interlayer spacing, as well as insufficient long-term stability of the electrode / electrolyte interface.

[0003] Publicly available invention patents have proposed several improvement paths, but most focus on the selection or pretreatment of carbon sources, paying insufficient attention to the synergistic optimization of structure and interface. For example, CN109678130A, starting from biomass, obtains an interlayer spacing of not less than 0.37 through alkali / acid washing and heat treatment. While using nm-based hard carbon to improve capacity, CN116354332A lacks a systematic coating process for interface stability and first-efficiency enhancement. CN116354332A uses straw and rice husks as raw materials, combined with KOH activation and two-stage carbonization to improve yield and efficiency, but the high specific surface area introduced by activation may amplify irreversible side reactions. CN116374991B uses resin precursors and combines them with pore modification and atmosphere control, emphasizing the construction of crystal domains and pores, but does not introduce a dedicated surface carbon layer design to suppress SEI growth. Regarding the asphalt route, CN117142457B uses asphalt and conductive carbon composites followed by carbonization to obtain asphalt-based hard carbon, highlighting low graphitization and increased interlayer spacing, but does not address the uniformity of oxidation modification and secondary surface coating. CN115991467A focuses on "oxidized asphalt-based hard carbon," using fluidized bed oxidation to improve interlayer spacing and closed pores, but still relies on "oxidation + carbonization" as the main line, without combining thermoplastic precursor composites with a coupling control strategy of coating. The aforementioned methods each have their strengths in terms of capacity, first-efficiency performance, or process scale-up. However, they lack a systematic process chain that simultaneously integrates precursor structure regulation, segmented carbonization, and surface coating to stabilize the interface, thus addressing both porosity / interlayer spacing / defects and interface stability. Therefore, developing a preparation method that can synergistically regulate the internal structure and surface interface of hard carbon materials to comprehensively improve their electrochemical performance is of great significance. Summary of the Invention

[0004] This invention addresses the technical problems of existing hard carbon anode materials for sodium-ion batteries, such as uncontrollable structure, unstable interface, and low capacity and initial coulombic efficiency. It provides a method for preparing a pitch-based anode material with controllable structure, the hard carbon anode material itself, and a sodium-ion battery. By introducing a high-strength and highly conductive carbon coating on the surface of the oxidation precursor, precise control over the material's microstructure and interface is achieved. Furthermore, by introducing gradient structure design, catalytic graphitization, or heteroatom doping, the internal structure, surface chemical state, and electronic conductivity of the hard carbon material are synergistically controlled, resulting in a hard carbon anode material with superior electrochemical performance, particularly improved rate performance, ultra-long cycle stability, and initial efficiency. The prepared carbon material possesses advantages such as uniform structure, stable interface, high reversible capacity, and high initial coulombic efficiency. Moreover, the preparation process is simple, and product quality is controllable, overcoming the problems of poor performance, numerous structural defects, and short cycle life in existing hard carbon anode materials.

[0005] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, a method for preparing a pitch-based anode material with a controllable structure is provided, comprising the following steps: S1. Pre-oxidation treatment: The raw material is pre-oxidized to obtain an oxidation precursor with an oxygen content of 15% to 35%; the raw material is selected from at least one of asphalt, biomass and phenolic resin; S2. Precursor composite: The oxidized precursor and the thermoplastic precursor are mixed at a mass ratio of 1 to 5:1 to obtain a composite precursor; the thermoplastic precursor is selected from at least one of petroleum asphalt, coal tar pitch, phenolic resin and waterborne phenolic resin. S3. Carbonization treatment: The composite precursor is carbonized under an inert atmosphere to obtain asphalt-based electrode material.

[0006] As a specific embodiment of the present invention, the pre-oxidation treatment is a heat treatment performed in an oxygen-containing atmosphere or an acidic oxidizing medium.

[0007] As a specific embodiment of the present invention, the acidic oxidizing medium includes nitric acid, sulfuric acid, hydrogen peroxide, or an aqueous solution thereof.

[0008] As a specific embodiment of the present invention, the pre-oxidation treatment includes at least one of the following methods: a) Heat treatment at 250℃-350℃ for 1-10 h in air or an oxygen-enriched atmosphere; b) Perform liquid-phase oxidation treatment in the acidic oxidation medium at 20℃-100℃ for 0.5-5h.

[0009] As a specific embodiment of the present invention, in step S2, the oxidative precursor includes at least two components with different oxygen contents, and the at least two components are combined with the thermoplastic precursor in a core-shell structure or in a layered manner, so that the resulting composite precursor has an oxygen content or composition gradient.

[0010] As a specific embodiment of the present invention, in the at least two components with different oxygen contents, the oxygen content of the inner layer component is higher than that of the outer layer component.

[0011] As a specific embodiment of the present invention, the mixing in step S2 is achieved by at least one of ball milling, spray drying, solution dispersion or melt compounding.

[0012] As a specific embodiment of the present invention, the method further includes step S4 after step S3: depositing a second carbon layer on the surface of the hard carbon anode material under an inert atmosphere by chemical vapor deposition or liquid phase impregnation-secondary carbonization to form a double-layer coating structure.

[0013] In a specific embodiment of the present invention, the graphitization degree of the second carbon layer is higher than that of the carbonaceous coating layer formed in step S3.

[0014] As a specific embodiment of the present invention, the thermoplastic precursor contains a transition metal compound uniformly dispersed therein.

[0015] As a specific embodiment of the present invention, the transition metal compound is selected from one or more of the nitrates, acetates, oxalates or organometallic complexes of iron, cobalt, nickel, and manganese.

[0016] In a specific embodiment of the present invention, the transition metal compound is iron acetylacetone or cobalt nitrate.

[0017] As a specific embodiment of the present invention, the mass of the transition metal compound is 0.1%-5% of the mass of the thermoplastic precursor.

[0018] As a specific embodiment of the present invention, during the pre-oxidation treatment in step S1, one or more heteroatoms containing nitrogen, phosphorus, sulfur, and boron are introduced.

[0019] In a specific embodiment of the present invention, the total doping amount of the heteroatoms is 0.5 at.%-5 at.%.

[0020] As a specific embodiment of the present invention, the heteroatom source is selected from at least one of urea, melamine, phosphoric acid, ammonium phosphate, thiourea, boric acid, and phenylboronic acid.

[0021] As a specific embodiment of the present invention, the biomass raw material in step S1 includes one or more of wood pulp, bamboo pulp, lignin or cellulose.

[0022] In a specific embodiment of the present invention, the inert atmosphere in step S3 is nitrogen or argon.

[0023] As a specific embodiment of the present invention, the carbonization temperature in step S3 is 800℃-1600℃; preferably, the carbonization process includes a segmented heating process: first, the temperature is kept at 700℃-900℃ for 2-6 hours for preliminary carbonization, and then the temperature is raised to 1200℃-1600℃ and kept for 2-4 hours.

[0024] Secondly, the present invention also provides a hard carbon anode material, which is prepared by any of the methods described above.

[0025] As a specific embodiment of the present invention, the interlayer spacing d(002) of the hard carbon anode material is 0.376 nm to 0.385 nm, and the specific surface area is 5 m² / g to 30 m² / g.

[0026] Secondly, the present invention also provides a sodium-ion battery, including a negative electrode sheet, the negative electrode sheet comprising the aforementioned hard carbon negative electrode material.

[0027] In the process provided by this invention, the pre-oxidation treatment causes the polycyclic aromatic hydrocarbon molecules in the raw material asphalt to undergo oxidative cross-linking and introduces an appropriate amount of oxygen-containing functional groups. This effectively prevents the ordered arrangement and graphitization tendency of asphalt molecules during subsequent high-temperature carbonization, preserving the disordered, wide-spacing carbon layer structure of the hard carbon material and achieving controllable adjustment of the hard carbon microstructure. Simultaneously, the pre-oxidation stage eliminates some low-molecular-weight volatile components, reducing volume shrinkage during carbonization and contributing to the formation of a uniform and stable hard carbon framework.

[0028] In the coating stage, the hard carbon precursor is uniformly impregnated and coated with an asphalt coating agent and then carbonized at high temperature, forming a dense carbon layer on the surface of the hard carbon particles that is firmly bonded to the matrix. This carbon layer effectively improves the structural integrity and interfacial stability of the material: on the one hand, the coated carbon layer can buffer the stress changes caused by sodium ions during insertion / extraction, preventing the internal structure of the hard carbon from pulverizing or collapsing; on the other hand, the carbon coating layer reduces the specific surface area of ​​the hard carbon in direct contact with the electrolyte, inhibiting the formation of undesirable interfacial phases by side reactions, thereby reducing irreversible capacity loss. Through the above mechanism, the asphalt-coated oxidized asphalt hard carbon material prepared in this invention has superior electrochemical performance and cycling stability.

[0029] Compared with the prior art, the beneficial effects of the present invention are: Synergistic Regulation Mechanism: This invention combines "oxidation-induced crosslinking" with "thermoplastic coating." Oxidized precursors with a specific oxygen content (15-35%) not only provide stable crosslinking points and expanded initial interlayer spacing for the carbon network, but their surface oxygen-containing functional groups also generate good interfacial interactions with the thermoplastic precursors. In subsequent carbonization, the thermoplastic precursors do not simply adhere, but migrate and carbonize in situ under the drive of interfacial energy, forming a firmly bonded, continuous, and dense carbon coating layer with the matrix.

[0030] Precise and controllable structure: By controlling the degree of oxidation (oxygen content) and the composite ratio, the interlayer spacing and pore structure of the final hard carbon product can be precisely controlled. A suitable interlayer spacing (0.376-0.385 nm) is conducive to the rapid insertion and extraction of sodium ions, while a moderate specific surface area (5-30 m² / g) greatly reduces the side reaction active sites with the electrolyte.

[0031] Gradient structure: It realizes a smooth transition from the high-defect active region to the low-defect stable region inside the material, effectively alleviates the local stress concentration during the sodium ion insertion / extraction process, and enhances the structural toughness, thus exhibiting better capacity retention in ultra-high rate charge / discharge (such as 5C) and ultra-long cycle (>2000 times).

[0032] Catalytic graphitization coating: A carbon layer with high local graphitization degree and excellent conductivity is formed in situ on the surface of hard carbon, which greatly improves the electronic conductivity of the material, enabling the battery to have excellent rate performance and low temperature performance. At the same time, the carbon layer structure generated by this catalysis is more dense and stable.

[0033] Heteroatom doping: By introducing heteroatoms (such as N, P), the Fermi level and charge distribution of carbon materials are tuned, which not only provides more sodium ion adsorption / storage active sites (improving capacity), but also induces the formation of thinner and more stable SEI films, thereby further improving the first coulombic efficiency while maintaining high capacity.

[0034] Excellent electrochemical performance: The aforementioned synergistic effect enables the prepared hard carbon material to maintain a high reversible capacity (>330 mAh g⁻¹) while significantly improving the first-cycle coulombic efficiency (>85%, with preferred embodiments reaching over 90%), and exhibiting excellent cycling stability (e.g., capacity retention >95% after 500 cycles at 0.5C). This is attributed to the combined effect of a robust internal framework and a stable surface coating, which effectively suppresses abnormal SEI growth and structural degradation.

[0035] The process is simple and easy to promote: The raw materials used in this invention are widely available, the process steps are simple, and there is no need for complicated post-processing or additional coating processes, which is conducive to industrial production and cost control. Detailed Implementation

[0036] The present invention will be further described below with reference to embodiments and comparative examples.

[0037] Example 1: Preparation of Petroleum Pitch-Based Hard Carbon Anode Material Pre-oxidation treatment: Take 50 grams of petroleum asphalt raw material, place it in a tube furnace, heat it to 300℃ at a rate of 2℃ / min in air atmosphere, hold it at that temperature for 3 hours for pre-oxidation treatment, and obtain oxidized asphalt precursor after natural cooling. Elemental analysis showed that its oxygen content was 18%.

[0038] Precursor compounding: The above-mentioned oxidized asphalt precursor was mixed with 15 grams of petroleum asphalt at a mass ratio of 3.3:1, and the mixture was placed in a ball mill jar and ball-milled at 300 rpm for 6 hours. After thorough mixing, the composite precursor was obtained.

[0039] Carbonization treatment: The composite precursor is moved into a carbonization furnace and carbonized in a segmented heating process under the protection of nitrogen inert atmosphere: First, the temperature is increased to 800℃ at 5℃ / min and held for 4 hours for preliminary carbonization; then the temperature is increased to 1200℃ at 5℃ / min and held for 3 hours to complete high-temperature carbonization; after natural cooling to room temperature, it is ground through a 200-mesh sieve to obtain hard carbon material A.

[0040] Product properties: XRD analysis showed that the interlayer spacing d(002) of material A was 0.378 nm; BET surface area analysis showed that its specific surface area was 18 m². 2 / g.

[0041] Example 2: Preparation of bamboo pulp fiber-based hard carbon anode material Pre-oxidation treatment: Take 40 grams of bamboo pulp fiber and pre-oxidize it at 280℃ for 4 hours in air atmosphere to obtain oxidized bamboo pulp precursor. Elemental analysis showed that its oxygen content was 22%.

[0042] Precursor composite: 30 grams of the above-mentioned oxidized bamboo pulp precursor and 20 grams of coal tar pitch were mixed at a mass ratio of 1.5:1 and dispersed together in N,N-dimethylformamide (DMF) solvent. The mixture was ultrasonically treated for 2 hours to ensure full dispersion. Subsequently, the DMF solvent was removed by rotary evaporation and dried to obtain composite precursor powder.

[0043] Carbonization treatment: The composite precursor powder is placed in a tube furnace and carbonized in stages under the protection of an argon inert atmosphere: the temperature is increased to 900℃ at 3℃ / min and held for 3 hours for preliminary carbonization; then the temperature is increased to 1300℃ at the same rate and held for 2 hours for high-temperature carbonization; after cooling and grinding, hard carbon material B is obtained.

[0044] Product properties: Material B has an interlayer spacing d(002) of 0.381 nm and a specific surface area of ​​20 m².2 / g.

[0045] Example 3: Preparation of Coal Tar Pitch-Based Hard Carbon Anode Material Pre-oxidation treatment: Take 30 grams of coal tar pitch raw material, crush it and add it to 65 wt% nitric acid solution, and reflux it at 80℃ for 2 hours for liquid phase oxidation treatment; after the reaction is completed, filter it, wash it with deionized water until neutral, and vacuum dry it to obtain oxidized pitch precursor with an oxygen content of 25%.

[0046] Precursor composite: Weigh 20 grams of the above-mentioned oxidized asphalt precursor and 20 grams of solid phenolic resin and mix them in a mass ratio of 1:1. Add them together to anhydrous ethanol and stir to form a suspension. Prepare microsphere composite precursors by spray drying (inlet temperature 180℃, outlet temperature 80℃).

[0047] Carbonization treatment: Under nitrogen protection, the temperature is increased to 700℃ at 4℃ / min and held for 5 hours for initial carbonization, and then increased to 1400℃ and held for 4 hours for high-temperature carbonization. After cooling, hard carbon material C is obtained.

[0048] Product properties: The interlayer spacing d(002) of material C is 0.381 nm, and the specific surface area is 16 m². 2 / g.

[0049] Example 4: Preparation of bamboo pulp fiber-based hard carbon anode material Pre-oxidation treatment: Take 40 grams of bamboo pulp fiber, treat it with 10% sulfuric acid solution at 90℃ for 1 hour, and then heat treat it at 280℃ for 3 hours in air atmosphere to obtain oxidized bamboo pulp precursor with an oxygen content of 28%.

[0050] Precursor compounding: Weigh 30 grams of the above-mentioned oxidized precursor and mix it with 20 grams of medium-temperature coal tar pitch at a mass ratio of 1.5:1. Melt and blend at 150°C for 30 minutes. After thorough compounding, cool and grind to obtain the composite precursor.

[0051] Carbonization treatment: Under argon protection, the temperature is increased to 900℃ at 3℃ / min and held for 3 hours for initial carbonization, and then the temperature is increased to 1300℃ and held for 2 hours for high-temperature carbonization to obtain hard carbon material D.

[0052] Product properties: The interlayer spacing d(002) of material D is 0.383 nm, and the specific surface area is 19 m². 2 / g.

[0053] Example 4: Preparation of core-shell structured hard carbon materials with gradient oxygen content Preparation of Oxidation Precursors with Gradient Oxygen Content Core: Petroleum asphalt was pre-oxidized at 320℃ for 5 hours in air atmosphere to obtain a high-oxygen-content oxidized asphalt precursor with an oxygen content of 28%; Shell: Take the same petroleum asphalt and pre-oxidize it at 260℃ for 2 hours in air atmosphere to obtain a low oxygen content oxidized asphalt precursor with an oxygen content of 12%.

[0054] Preparation of core-shell composite precursors Weigh 30 grams of the core component precursor and place it in a fluidized bed; weigh 20 grams of the shell component precursor and ball mill and mix it with 10 grams of petroleum asphalt thermoplastic precursor for 2 hours, and disperse it in tetrahydrofuran solvent to form a shell composite solution. The shell composite solution was sprayed onto the surface of the core component in a fluidized bed, and after drying, a composite precursor with a core-shell gradient oxygen content structure was obtained.

[0055] Carbonization treatment: The same segmented carbonization process as in Example 1 (nitrogen atmosphere, 800℃ / 4h + 1200℃ / 3h) was used, and hard carbon material E was obtained after cooling and grinding.

[0056] Product properties: interlayer spacing d (002) is 0.382 nm, and specific surface area is 15 m² / g.

[0057] Example 6: Preparation of Fe-catalyzed graphitization-coated hard carbon materials Pre-oxidation treatment: Take 40 grams of bamboo pulp fiber and prepare oxidized bamboo pulp precursor according to the method in Example 2, with an oxygen content of 22%.

[0058] Preparation of transition metal-doped thermoplastic precursor: Weigh 20 g of coal tar pitch thermoplastic precursor and dissolve it together with 0.6 g of iron acetylacetone (a transition metal compound, accounting for 3% of the mass of coal tar pitch) in toluene solvent. Stir and evaporate to remove the solvent to obtain Fe-loaded thermoplastic precursor.

[0059] Precursor composite: The above-mentioned oxidized bamboo pulp precursor and Fe-doped thermoplastic precursor were ball-milled at a mass ratio of 2:1 for 4 hours to obtain a composite precursor.

[0060] Carbonization treatment: Hard carbon material F was obtained by using the segmented carbonization process of Example 2 (argon atmosphere, 900℃ / 3h + 1300℃ / 2h).

[0061] Product performance: Raman spectroscopy showed that the surface coating ID / IG=1.05 (low disorder and high graphitization), and the powder conductivity was 50% higher than that of the uncatalyzed sample.

[0062] Example 7: Preparation of N, P co-doped hard carbon materials Heteroatom doping pre-oxidation treatment: Take 30 grams of lignin and place it in a nitrogen mixed atmosphere containing 10% ammonia. Keep it at 300℃ for 4 hours for pre-oxidation + nitrogen doping treatment to obtain nitrogen-doped oxidation precursor with N doping amount of 2.5 at.

[0063] P-doped + precursor composite: The above-mentioned N-doped oxidized precursor, together with 15 g of phenolic resin thermoplastic precursor and 0.8 g of triphenyl phosphate, were added to anhydrous ethanol, ultrasonically dispersed for 2 hours, and spray-dried to obtain N and P co-doped composite precursor.

[0064] Carbonization treatment: under a nitrogen atmosphere, segmented heating carbonization is carried out: initial carbonization is carried out at 800℃ for 4 hours, high-temperature carbonization is carried out at 1400℃ for 3 hours, and after cooling and grinding, hard carbon material G is obtained.

[0065] Product performance: XPS tests confirmed successful N and P co-doping, with a total doping amount of 3.2 at.% and an interlayer spacing d (002) of 0.387 nm.

[0066] Example 8: Preparation of hard carbon materials with bilayer carbon coating by CVD chemical vapor deposition Preparation of basic hard carbon matrix: Hard carbon material A was prepared according to the method of Example 1 as a double-layer coated substrate material.

[0067] Second carbon layer deposition (CVD method): Hard carbon material A is placed in a CVD tube furnace, argon is used as the carrier gas, and ethylene (carbon source) with a volume fraction of 5% is introduced. The deposition is carried out at a constant temperature of 850°C for 30 minutes to deposit a second carbon layer on the surface of material A. After natural cooling, hard carbon material H with a double carbon coating structure is obtained.

[0068] Product performance: interlayer spacing d(002) is 0.378 nm, and specific surface area is reduced to 10 m². 2 / g.

[0069] Example 9 Preparation of hard carbon material with liquid phase impregnation-secondary carbonization double-layer carbon coating Preparation of basic hard carbon matrix: Hard carbon material C was prepared as a matrix according to the method in Example 3.

[0070] Second carbon layer deposition (liquid phase immersion-secondary carbonization method): Hard carbon material C is immersed in a 15wt% tetrahydrofuran solution of asphaltene for 2 hours at room temperature, filtered, and then vacuum dried to remove the solvent; subsequently, under a nitrogen inert atmosphere, it is heated at 900℃ for 2 hours to perform secondary carbonization, depositing a second carbon layer on the substrate surface to obtain hard carbon material I.

[0071] Product properties: The second carbon layer has an ID / IG ratio of 0.98, and its graphitization degree is significantly higher than that of the primary coating layer; the specific surface area is 8 m². 2 / g.

[0072] Example 10: Preparation of Co-doped + N-doped composite optimized hard carbon materials N-doped pre-oxidation treatment: Take 50g of phenolic resin raw material, mix it with 8g of urea, and pre-oxidize it at 310℃ for 6 hours in air atmosphere to obtain N-doped oxidized phenolic resin precursor with oxygen content of 25% and N doping amount of 2.0 at.

[0073] Preparation of Co-doped thermoplastic precursor: Take 20 g of waterborne phenolic resin thermoplastic precursor, add 0.4 g of cobalt nitrate, dissolve in deionized water and stir until completely dissolved, then dry to obtain Co-doped thermoplastic precursor.

[0074] Precursor composite and carbonization: N-doped oxide precursor and Co-doped thermoplastic precursor were ball-milled at a mass ratio of 4:1 and carbonized in stages at 850℃ / 3h + 1300℃ / 3h under a nitrogen atmosphere to obtain hard carbon material J.

[0075] Product properties: interlayer spacing d(002) is 0.380 nm, specific surface area is 12 m². 2 / g.

[0076] Comparative Example 1: Preparation of Hard Carbon Materials Without Pre-oxidation Treatment Take 50 grams of petroleum asphalt that has not undergone any pre-oxidation treatment, and directly heat it to 1200℃ at 5℃ / min under a nitrogen atmosphere and hold it at that temperature for 4 hours to obtain the comparative material K.

[0077] Result: The interlayer spacing d (002) of material K is 0.359 nm.

[0078] Comparative Example 2: Preparation of Hard Carbon Materials without Thermoplastic Precursor Composites Take 50 grams of the same oxidized asphalt precursor (oxygen content 18%) as in Example 1, without combining it with any thermoplastic precursor, and process it directly according to the carbonization process of the basic Example 1 to obtain comparative material L.

[0079] Results: The interlayer spacing d(002) of material L is 0.384 nm, but the specific surface area is as high as 30 m². 2 / g.

[0080] Comparative Example 3: Single phenolic resin precursor without composite carbonization 50 grams of phenolic resin was used as the sole precursor and directly carbonized at 1400℃ under a nitrogen atmosphere to obtain comparative material M.

[0081] Results: The interlayer spacing d(002) of material M is 0.386 nm, and the specific surface area is 35 m². 2 / g.

[0082] Comparative Example 4: Single high-oxygen-content, non-gradient hard carbon material The high-oxygen-content oxidized asphalt precursor (oxygen content 28%) from Example 5 was directly mixed with petroleum asphalt in the same total proportion and carbonized to prepare comparative material N.

[0083] Result: The specific surface area of ​​material N is as high as 28 m². 2 / g.

[0084] Comparative Example 5: Controlled sample without transition metal catalysis Repeat all the steps of Example 6, except without adding iron acetylacetone, to obtain Comparative Material O.

[0085] Result: The surface coating layer ID / IG of material O is 1.32.

[0086] Comparative Example 6: Undoped sample Repeat all steps of optimization implementation 7, except without introducing ammonia and triphenyl phosphate, to obtain comparative material C3.

[0087] Results: The initial coulombic efficiency of material C3 was 87.2%, and the reversible capacity was 348 mAh / g, which was much lower than that of the N and P co-doped samples, proving that heteroatom doping can effectively improve the initial efficiency and reversible capacity.

[0088] IV. Summary of Electrochemical Performance Tests The hard carbon materials prepared in the above examples and comparative examples were used as the negative electrode active material. A negative electrode sheet was prepared with a mass ratio of active material: conductive agent: binder = 8:1:1. Using metallic sodium as the counter electrode and 1 M NaPF6 / EC+DEC (volume ratio 1:1) as the electrolyte, CR2032 coin cells were assembled. Electrochemical performance was tested within the voltage range of 0.01-3.0 V. The test results are shown in Table 1. Table 1. Performance of batteries prepared using hard carbon materials as negative electrode active materials in the examples and comparative examples. sample Specific surface area (m² / g) Interlayer spacing (nm) First Coulomb efficiency (%) Reversible capacity (mAh / g) Cyclic performance Example 1 18 0.378 84.5 325.8 After 100 cycles at 0.5C, the capacity retention is 92.3%; after 500 cycles at 0.5C, the capacity retention is >95%. Example 2 20 0.381 85.2 332.5 After 500 cycles at 0.5C rate, capacity retention is >95%, and stability during normal cycling is excellent. Example 3 16 0.381 86.1 338.2 After 500 cycles at 0.5C rate, capacity retention is >95%, and structural stability is good. Example 4 19 0.383 85.8 342.3 After 500 cycles at 0.5C rate, the capacity retention is >95%, and the molten composite structure exhibits good toughness. Example 5 15 0.382 89.8 355.0 After 1000 cycles at a high rate of 2C, the capacity retention rate is 94.5%, and the gradient structure alleviates stress concentration. Example 6 20 0.381 86.5 340.0 The discharge capacity at 5C ultra-high rate is 82% of that at 0.1C; the capacity retention at -20°C at 0.2C is 85% of that at room temperature. Catalytic graphitization improves rate capability and low-temperature cycling performance. Example 7 22 0.387 92.3 375.0 After 800 cycles at 0.5C rate, the capacity retention is 96.1%, and heteroatom doping optimizes the stability of the SEI film. Example 8 10 0.378 93.5 330.0 The full battery retains >88% capacity after 2000 1C / 1C charge / discharge cycles, and the double-layer coating enables ultra-long cycle life. Example 9 8 0.380 91.2 335.0 Extremely poor cycling performance, rapid capacity decay, and excessively small interlayer spacing leading to high Na insertion / extraction resistance. Example 10 12 0.380 90.8 362.0 Frequent interface side reactions, poor cycle stability, and excessively high specific surface area due to lack of coating. Comparative Example 1 6 0.359 72.3 210.0 After 50 cycles at 0.5C, the capacity retention is only 65%, and the single precursor structure is prone to collapse. Comparative Example 2 30 0.384 78.5 318.2 Frequent interface side reactions, poor cycle stability, and excessively high specific surface area due to lack of coating. Comparative Example 3 35 0.386 76.2 298.5 After 50 cycles at 0.5C, the capacity retention is only 65%; single precursor: structural collapse is likely. Comparative Example 4 28 0.382 81.5 305.0 Significant capacity decay at high rates, coupled with a gradient-less structure leading to localized stress concentration and poor cycling stability, are observed. Comparative Example 5 20 0.381 85.2 332.5 At 5C rate, the capacity retention is only 70%; at -20℃ and 0.2C, the capacity retention is only 68%, indicating low graphitization and poor conductivity due to the lack of catalyst. Comparative Example 6 24 0.385 87.2 348.0 The capacity retention after 800 cycles at 0.5C is much lower than that of the N- and P-co-doped samples. The lack of heteroatom doping leads to poor SEI film stability and rapid capacity decay. The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a pitch-based negative electrode material with a controllable structure, characterized in that, Includes the following steps: S1. Pre-oxidation treatment: The raw material is pre-oxidized to obtain an oxidation precursor with an oxygen content of 15% to 35%; the raw material is selected from at least one of asphalt, biomass and phenolic resin; S2. Precursor composite: The oxidized precursor and the thermoplastic precursor are mixed at a mass ratio of 1 to 5:1 to obtain a composite precursor; the thermoplastic precursor is selected from at least one of petroleum asphalt, coal tar pitch, phenolic resin and waterborne phenolic resin. S3. Carbonization treatment: The composite precursor is carbonized under an inert atmosphere to obtain asphalt-based electrode material.

2. The preparation method according to claim 1, characterized in that, The pre-oxidation treatment is a heat treatment performed in an oxygen-containing atmosphere or an acidic oxidizing medium. Preferably, the acidic oxidizing medium includes nitric acid, sulfuric acid, hydrogen peroxide, or an aqueous solution thereof.

3. The preparation method according to claim 1 or 2, characterized in that, The pre-oxidation treatment includes at least one of the following methods: a) Heat treatment at 250℃~350℃ for 1~10 h in air or an oxygen-enriched atmosphere; b) Perform liquid-phase oxidation treatment in an acidic oxidizing medium at 20℃~100℃ for 0.5~5h.

4. The preparation method according to claim 1 or 2, characterized in that, The oxidation precursor includes at least two components with different oxygen contents. The at least two components are combined with the thermoplastic precursor in a core-shell structure or in a layered manner, so that the resulting composite precursor has an oxygen content or composition gradient. Preferably, among the at least two components with different oxygen contents, the oxygen content of the inner layer component is higher than that of the outer layer component. And / or the mixing in step S2 is achieved by at least one of ball milling, spray drying, solution dispersion or melt compounding.

5. The preparation method according to claim 1 or 2, characterized in that, The method further includes step S4 after step S3: depositing a second carbon layer on the surface of the hard carbon anode material under an inert atmosphere by chemical vapor deposition or liquid phase impregnation-secondary carbonization to form a double-layer coating structure; preferably, the graphitization degree of the second carbon layer is higher than that of the carbon coating layer formed in step S3.

6. The preparation method according to claim 1 or 2, characterized in that, In step S2, a transition metal compound is uniformly dispersed in the thermoplastic precursor; preferably, the transition metal compound is selected from one or more of the nitrates, acetates, oxalates or organometallic complexes of iron, cobalt, nickel, and manganese; more preferably, the transition metal compound is iron acetylacetonate or cobalt nitrate; more preferably, the mass of the transition metal compound is 0.1% to 5% of the mass of the thermoplastic precursor.

7. The method according to claim 1, characterized in that, During the pre-oxidation process in step S1, one or more heteroatoms containing nitrogen, phosphorus, sulfur, and boron are introduced. Preferably, the total doping amount of the heteroatoms is 0.5 at.% to 5 at.%; more preferably, the heteroatom source is selected from at least one of urea, melamine, phosphoric acid, ammonium phosphate, thiourea, boric acid, and phenylboronic acid.

8. The method according to claim 1, characterized in that, The biomass raw materials mentioned in step S1 include one or more of wood pulp, bamboo pulp, lignin, or cellulose; And / or, the inert atmosphere described in step S3 is nitrogen or argon; And / or, the carbonization temperature in step S3 is 800℃~1600℃; preferably, the carbonization process includes a segmented heating process: first, preliminary carbonization is carried out by holding at 700℃~900℃ for 2~6 hours, and then the temperature is raised to 1200℃~1600℃ and held for 2~4 hours.

9. A hard carbon anode material, characterized in that, The hard carbon anode material is prepared by any one of claims 1 to 8; the interlayer spacing d(002) of the hard carbon anode material is 0.376 nm to 0.385 nm, and the specific surface area is 5 m² / g to 30 m² / g.

10. A sodium-ion battery, characterized in that, Includes a negative electrode sheet, said negative electrode sheet comprising the hard carbon negative electrode material of claim 9.