Composite hard carbon negative electrode material, preparation method thereof and battery

Abstract

The invention provides a composite hard carbon negative electrode material, a preparation method thereof and a battery, and the preparation method comprises the following steps: mixing asphalt and ion exchange resin to obtain a first precursor; performing carbonization treatment on the first precursor to obtain a second precursor; performing nitrogen doping treatment on the second precursor to obtain a third precursor; and performing plasma treatment on the third precursor to obtain the composite hard carbon negative electrode material, the battery comprises the composite hard carbon negative electrode material obtained by the method. The contradiction between the raw material cost and the performance consistency in the prior art is solved, the problem of balance between electronic conductivity and ion transmission is solved, and the problems that dead holes or closed holes exist in the surface of a traditional hard carbon material and cannot be effectively infiltrated by electrolyte, and the contact resistance is large due to particle aggregation are solved.

Description

Technical Field

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

[0002] The preparation and application of existing hard carbon anode materials still face multiple technical bottlenecks. First, there is a contradiction between "stability and cost" in raw material selection. Currently, mainstream biomass raw materials (such as coconut shells and straw) have complex compositions and significant regional variations, making it difficult to guarantee batch-to-batch consistency. While synthetic polymers such as phenolic resins offer high purity and controllable structure, their high cost limits their large-scale industrial application. Inexpensive coal-based or petroleum-based pitch, although high in carbon content and low in cost, tends to form dense soft carbon or graphitized structures after direct carbonization, lacking sufficient pore channels for sodium ion diffusion, resulting in poor sodium storage capacity and rate performance. Second, in terms of preparation processes and microstructure control, traditional single high-temperature carbonization processes cannot simultaneously achieve high capacity and high initial efficiency. On the one hand, higher carbonization temperatures are typically required to improve the graphitization degree and conductivity of materials, but this leads to micropore closure and reduces sodium storage capacity. On the other hand, while low-temperature carbonized hard carbon materials have more defects and higher capacity, they exhibit poor conductivity and a large number of irreversible active sites on their surface, resulting in a low initial coulombic efficiency (ICE). To improve conductivity, existing technologies often employ heteroatom doping (such as nitrogen and phosphorus doping), but this often only addresses electron transport issues and cannot effectively solve the problems of high ion transport resistance and high contact resistance caused by surface micropore closure or particle agglomeration. Furthermore, to improve interface stability, some existing technologies employ surface coating methods, but traditional liquid-phase or solid-phase coating processes easily result in uneven coating layers and make it difficult to precisely control the pore structure of the material surface. Especially for pitch-based or resin-based hard carbon materials, due to the lack of sufficient active functional groups or the presence of closed dead pores on their surface, electrolytes cannot fully wet them, resulting in the ineffective utilization of the internal storage space of the material, which severely restricts the energy density and fast charge / discharge capability of the battery. Summary of the Invention

[0003] This invention provides a composite hard carbon anode material and its preparation method, as well as a battery, to resolve the contradiction between raw material cost and performance consistency in the prior art, to solve the balance problem between electronic conductivity and ion transport, and to solve the problems of dead or closed pores on the surface of traditional hard carbon materials that cannot be effectively wetted by electrolyte, and the high contact resistance caused by particle agglomeration.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a composite hard carbon anode material, the method comprising: mixing asphalt with ion exchange resin to obtain a first precursor; carbonizing the first precursor to obtain a second precursor; doping the second precursor with nitrogen to obtain a third precursor; and subjecting the third precursor to plasma treatment to obtain the composite hard carbon anode material.

[0005] To achieve the above objectives, the present invention also provides the following technical solutions: A composite hard carbon anode material, wherein the composite hard carbon anode material is prepared by the above-described preparation method.

[0006] To achieve the above objectives, the present invention also provides the following technical solutions: A battery comprising a composite hard carbon anode material obtained by the above preparation method, or comprising the above composite hard carbon anode material; the battery is a sodium-ion battery, and its sodium storage capacity at 1C rate is 270-290 mAh / g, its capacity retention rate after 500 cycles is greater than or equal to 85%, and its capacity retention rate at 5C rate is greater than or equal to 70%.

[0007] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. Synergistic optimization of microstructure: Asphalt provides a high-carbon skeleton, while resin (especially waste resin) provides abundant microporous / mesoporous channels and in-situ active sites. The combined capacity of the two is significantly improved compared with that of asphalt alone. 2. Conductive network construction (nitrogen doping): Nitrogen doping significantly improves the powder conductivity, constructs an electron transport bridge, and significantly improves rate performance; 3. Surface modification and interface stabilization (plasma): The plasma treatment in step S4 etched the surface, opened some closed pores and repaired edge defects. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0009] Figure 1 This is a SEM image of the composite hard carbon anode material obtained in Example 1 of the present invention.

[0010] Figure 2 This is a pore size distribution diagram of the composite hard carbon anode material obtained in Example 1 of the present invention. Detailed Implementation

[0011] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be understood that the specific embodiments described herein are only for illustration and explanation of the present invention and are not intended to limit the present invention.

[0012] Any specific numerical values ​​disclosed herein (including the endpoints of numerical ranges) are not limited to their exact values, but should be understood to also include values ​​close to the exact value, such as all possible values ​​within ±5% of the exact value. Furthermore, with respect to the disclosed numerical ranges, one or more new numerical ranges can be obtained by arbitrarily combining the endpoint values ​​of the range, the endpoint values ​​with specific point values ​​within the range, and the specific point values ​​themselves; these new numerical ranges should also be considered as specifically disclosed herein.

[0013] The terminology used in this invention is for the purpose of describing specific exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” as used herein are intended to include the plural forms as well. The terms “comprising,” “including,” “containing,” and “having” are inclusive and thus describe the presence of said features, elements, compositions, steps, integers, operations, and / or components, but do not exclude the presence or inclusion of one or more other features, integers, steps, operations, elements, components, and / or sets thereof. Although the open-ended term “comprising” should be understood as a non-limiting term used to describe and claim the various embodiments described in this invention, in some aspects it may instead be understood as a more restrictive and limiting term, such as “consisting of” or “essentially composed of.” Thus, for any given embodiment describing a composition, material, component, element, feature, integer, operation, and / or process step, the invention also particularly includes embodiments consisting of or substantially consisting of such compositions, materials, components, elements, features, integers, operations, and / or process steps. In the case of “consisting of…”, the alternative embodiments exclude any additional compositions, materials, components, elements, features, integers, operations and / or process steps. In the case of “essentially composed of…”, any additional compositions, materials, components, elements, features, integers, operations and / or process steps that substantially affect the essential and novel characteristics are excluded from such embodiments. However, any compositions, materials, components, elements, features, integers, operations and / or process steps that do not substantially affect the essential and novel characteristics may be included in the embodiments.

[0014] Any method steps, processes, and operations described in this invention should not be construed as necessarily requiring them to be performed in the specific order discussed or shown, unless explicitly specified. It should also be understood that, unless otherwise stated, additional or alternative steps may be used.

[0015] In this invention, except where expressly stated, any matters or issues not mentioned are directly applicable to those known in the art without any modification. Furthermore, any embodiment described in this invention can be freely combined with one or more other embodiments described in this invention, and the resulting technical solutions or concepts are considered part of the original disclosure or original record of this invention, and should not be regarded as new content not disclosed or anticipated by this invention, unless those skilled in the art consider the combination to be clearly unreasonable.

[0016] Unless otherwise stated, the terms used herein have the same meaning as commonly understood by those skilled in the art, and if a term is defined herein and its definition differs from the common understanding in the art, the definition herein shall prevail.

[0017] Unless otherwise stated, "wt%" in this specification refers to "mass fraction".

[0018] First aspect This invention provides a method for preparing a composite hard carbon anode material. The method includes: mixing asphalt with ion exchange resin to obtain a first precursor; carbonizing the first precursor to obtain a second precursor; nitrogen-doping the second precursor to obtain a third precursor; and plasma-treating the third precursor to obtain the composite hard carbon anode material. By employing a composite precursor system of "asphalt + ion exchange resin" combined with a stepwise modification process of "carbonization-nitrogen doping-plasma," a balance between low cost and high performance is achieved. Specifically, the cross-linking structure of the ion exchange resin is used to suppress the ordered stacking of asphalt, constructing a rich sodium-storing microcrystalline structure; nitrogen doping introduces defect sites into the carbon lattice, significantly improving the intrinsic electronic conductivity of the material; and plasma treatment etches the surface, opening closed pores and introducing oxygen-containing functional groups, improving the wettability of the electrolyte. This solves the problems of low capacity of asphalt-based hard carbon, poor consistency of biomass hard carbon, and poor rate performance caused by easy pore blockage in traditional coating processes in the prior art.

[0019] In some embodiments of the present invention, the ion exchange resin described above can be recycled waste ion exchange resin. By using recycled waste ion exchange resin as raw material, the resource utilization of solid waste is realized, significantly reducing the cost of raw materials. At the same time, the residual functional groups in the waste resin are used to assist in pore formation, thereby solving the technical problems of high cost and difficulty in industrialization of pure synthetic resin hard carbon materials.

[0020] It is worth noting that in some embodiments of the present invention, the asphalt can be coal-based asphalt. By selecting coal-based asphalt and utilizing its high carbon content and low cost advantages as the main carbon skeleton, a high carbon yield is achieved, thereby solving the problem of poor product consistency caused by large seasonal differences in biomass precursor production areas, and also avoiding the problem of large fluctuations in petroleum asphalt costs with oil prices.

[0021] In some embodiments of the present invention, the preparation method further includes pretreatment, wherein the raw material asphalt and the raw material ion exchange resin are pretreated separately before mixing. By pretreating the raw materials separately before mixing, precise control of the purity and particle size of the raw materials is achieved, and impurities affecting electrochemical performance are effectively removed, thereby solving the problems of high battery self-discharge rate and poor cycle stability caused by raw material impurities (such as ash and heavy metals).

[0022] In some embodiments of the present invention, the carbonization treatment is a gradient carbonization treatment, which includes three stages: low-temperature devolatilization, medium-temperature crosslinking, and high-temperature carbonization. Through this staged gradient carbonization treatment, a balance between stress release and structural rearrangement during the pyrolysis process is achieved. The low-temperature stage slowly removes volatiles, the medium-temperature stage promotes crosslinking and curing of resin and asphalt molecules, and the high-temperature stage completes the shaping of the disordered layer structure, thereby solving the problems of material structure collapse and reduced micropore count caused by the violent gas release in traditional one-step carbonization methods.

[0023] In some embodiments of the present invention, the nitrogen doping treatment is an ammoniation nitrogen doping treatment, which includes a first stage of introducing an inert gas and a second stage of introducing ammonia. Through this staged ammoniation nitrogen doping treatment, nitrogen atoms are introduced while preserving the integrity of the carbon framework. The first stage of inert gas replacement ensures a pure environment, while the second stage introduces active nitrogen sites using ammonia, thereby solving the problems of poor conductivity and severe polarization at high charge-discharge rates after simple high-temperature carbonization.

[0024] In some embodiments of the present invention, the plasma treatment is performed under an inert atmosphere. By performing plasma treatment under an inert atmosphere, precise control of the etching process is achieved, avoiding the introduction of excessive unstable surface functional groups by reactive gases (such as oxygen), thereby solving the problem of reduced first-efficiency due to excessive surface oxidation.

[0025] In some embodiments of the present invention, the pretreatment involves sequentially crushing, fine crushing, drying, and impurity testing of the raw asphalt. After fine crushing, the asphalt has a D50 of 3–10 μm or 5–7 μm. Vacuum drying is performed at a pressure of -0.080–0.098 MPa or -0.095 MPa, at a temperature of 100–150°C or 120°C, for 2–6 h or 4 h. After testing, the ash content is less than or equal to 2 wt%. By strictly controlling the particle size and moisture content of the asphalt, uniform mixing of asphalt and resin at the microscopic level is achieved, avoiding macroscopic pores caused by moisture evaporation. By controlling the ash content, the residue of electrochemically inert substances is reduced, thereby solving the problem of irreversible capacity loss caused by impurities.

[0026] In some embodiments of the present invention, the pretreatment process involves sequentially performing preliminary cleaning, heavy metal removal, neutral washing, low-temperature drying, and fine pulverization on the raw material ion exchange resin. The preliminary cleaning uses water, ethanol, or acetone as the cleaning solution, with a liquid-to-solid ratio of (1–10):1 or (3–8):1, and an ultrasonic frequency of 30–80 kHz. Heavy metal removal is performed using 0.1–1 mol / L hydrochloric acid at 30–70°C. The low-temperature drying temperature is 50–100°C. After pulverization, the resin D50 is 3–10 μm or 5–7 μm. Through multi-step cleaning and acid washing, deep removal of adsorbed heavy metal ions from the waste resin is achieved, preventing the precipitation and dendrite formation of heavy metals on the negative electrode surface. By controlling the particle size D50 to match the asphalt, the uniformity of the composite precursor is ensured, thereby solving the safety hazards and performance fluctuations caused by direct carbonization of waste resin.

[0027] In some embodiments of the present invention, in the preparation of the first precursor, the mass ratio of the asphalt to the ion exchange resin is (4-8):(6-2). By controlling the mass ratio of asphalt to resin at (4-8):(6-2), an optimal balance between material structure and cost is achieved. An excessively high resin ratio leads to increased cost and decreased compaction density, while an excessively high asphalt ratio easily forms soft carbon, resulting in a decrease in capacity. This ratio range effectively solves the problem of achieving both high capacity and high compaction density in hard carbon materials.

[0028] In some embodiments of the present invention, the preparation of the first precursor is carried out using a ball mill for mixing, with a milling speed of 300–800 rpm and a milling time of 1–10 h. High-energy ball milling mixing achieves mechanical fusion and surface modification of the asphalt and resin particles, enhancing the interfacial bonding force between the two, thereby solving the problem of phase separation and resulting in uneven structure that easily occurs during subsequent carbonization in simple physical mixing.

[0029] In some embodiments of the present invention, in the preparation of the first precursor, the softening point of the asphalt is 160–210°C, the carbon content is greater than or equal to 95 wt%, and the volatile matter content is 25–30 wt%. By selecting asphalt with specific softening points and volatile matter content, suitable fluidity of the asphalt in the early stage of carbonization is achieved to encapsulate resin particles, while retaining sufficient carbon skeleton, thereby solving the problems of excessive asphalt fluidity leading to agglomeration or insufficient fluidity leading to loose bonding.

[0030] In some embodiments of the present invention, in the preparation of the first precursor, the ion exchange resin is a waste styrene-based ion exchange resin with an exchange capacity greater than or equal to 4.5 mmol / g, a water content less than or equal to 10 wt%, and an impurity content less than or equal to 50 ppm. By limiting the exchange capacity and impurity content of the resin, its abundant cross-linking pores are utilized as a "pore-forming agent," while ensuring the high purity of the precursor, thereby solving the problem of uncontrollable final hard carbon pore structure caused by resin quality fluctuations.

[0031] In some embodiments of the present invention, in the gradient carbonization treatment, the low-temperature devolatilization temperature is 200–400°C, the duration is 1–3 hours, and the heating rate is 4–6°C / min. By controlling the low-temperature devolatilization parameters, the stable discharge of moisture and low-molecular-weight volatiles is achieved, avoiding particle breakage caused by rapid gas escape, thereby solving the problem of large-pore defects on the material surface and reduced initial efficiency.

[0032] In some embodiments of the present invention, in the gradient carbonization treatment, the temperature of the intermediate-temperature crosslinking is 500–700°C, the duration is 1–3 h, and the heating rate is 2–4°C / min. By controlling the intermediate-temperature crosslinking parameters, deep crosslinking and solidification of the precursor molecular chains are achieved, fixing the disordered layer structure, thereby solving the problem of difficulty in maintaining the microstructure of hard carbon under high-temperature graphitization trends.

[0033] In some embodiments of the present invention, in the gradient carbonization process, the high-temperature carbonization temperature is 900–1100°C, the duration is 2–5 hours, and the heating rate is 1–3°C / min; the gradient carbonization process is carried out under an argon or nitrogen atmosphere. By controlling the high-temperature carbonization parameters, the interlayer spacing of carbon microcrystals is optimized. This temperature range ensures a high carbonization yield while avoiding the reduction in interlayer spacing caused by excessive graphitization, thereby solving the problem of insufficient interlayer embedding capacity of hard carbon materials during sodium storage.

[0034] In some embodiments of the present invention, the amination nitrogen doping treatment is carried out at a temperature of 700–950°C for 1–5 hours, with a heating rate of 2–10°C / min. By controlling the amination temperature and time, effective doping of nitrogen atoms in the carbon lattice (mainly pyridine nitrogen and pyrrole nitrogen) is achieved, while also providing a certain degree of surface etching, thereby solving the problem of few active sites and slow sodium storage kinetics in single carbon source materials.

[0035] In some embodiments of the present invention, argon or nitrogen is introduced in the first stage of the ammoniation and nitrogen doping treatment. By introducing an inert gas during the heating stage, residual oxygen in the furnace is eliminated, preventing the material from being oxidized and consumed before reaching the reaction temperature, thereby solving the problems of reduced carbon yield and uncontrollable surface properties.

[0036] In some embodiments of the present invention, during the ammoniation nitrogen doping treatment, ammonia gas is introduced in the second stage at a flow rate of 30–80 mL / min or 40–80 mL / min. By precisely controlling the ammonia flow rate, a balance between nitrogen doping amount and cost is achieved. Too low a flow rate results in insignificant doping effect, while too high a flow rate leads to waste and may cause excessive etching of the framework. This range effectively resolves the contradiction between doping efficiency and structural stability.

[0037] In some embodiments of the present invention, the gas flow rate during plasma treatment is 10–80 mL / min or 20–60 mL / min. By controlling the plasma treatment gas flow rate, the plasma concentration is stabilized, ensuring the uniformity of etching and thus solving the problem of large differences in surface properties between batches of products caused by gas flow fluctuations.

[0038] In some embodiments of the present invention, the gas pressure during plasma treatment is 0.1–0.5 MPa or 0.15–0.4 MPa. By controlling the gas pressure, the mean free path of the plasma is adjusted, ensuring that high-energy particles can effectively bombard the particle surface without excessive energy dissipation, thereby solving the problem of insufficient or uneven surface modification depth.

[0039] In some embodiments of the present invention, the plasma treatment duration is 5–20 min or 8–12 min. By controlling the treatment duration, appropriate opening of surface closed pores is achieved. Too short a duration will not effectively open the dead pores, while too long a duration may damage the internal pore structure. This range effectively solves the balance problem between surface opening and maintaining the strength of the internal framework.

[0040] In some embodiments of the present invention, the plasma treatment power is 100–200 W or 120–180 W. By controlling the plasma power, precise control of particle bombardment energy is achieved. This power range is sufficient to break the C / C bonds on the surface and introduce defects, but not enough to destroy the main framework, thus solving the problem of difficulty in precisely controlling the surface micropore size in general physical activation.

[0041] In some embodiments of the present invention, in order to further reduce the impact of inactive impurities on battery cycle stability and reduce the probability of side reactions, the ash content of the coal-based pitch is preferably controlled to be less than or equal to 0.5 wt%, and the carbon content is preferably greater than or equal to 95 wt%. Using such high-purity, high-carbon pitch raw materials helps to form a more uniform and dense carbon microcrystalline framework during subsequent carbonization, thereby significantly improving the first-cycle coulombic efficiency of the material while ensuring high capacity.

[0042] It should be noted that although the preferred embodiment of the present invention describes in detail a gradient carbonization process comprising three stages: low-temperature devolatilization, medium-temperature crosslinking, and high-temperature carbonization, this does not mean that the carbonization treatment of the present invention is limited to this. Those skilled in the art will understand that, depending on equipment conditions or cost control requirements, conventional continuous temperature-programmed carbonization methods or other known carbonization techniques can also be used, as long as effective carbonization and structural fusion of asphalt and ion exchange resin can be achieved, all of which should be covered within the scope of protection of the present invention. Similarly, although the nitrogen doping treatment preferably employs gas-phase ammoniation to achieve uniform surface and shallow doping, without departing from the concept of the present invention, nitrogen can also be introduced by mixing solid nitrogen sources such as urea and melamine in the precursor and decomposing them in situ at high temperature.

[0043] The plasma treatment step introduced in this invention plays a crucial role in improving the sodium storage kinetics of the material. The mechanism is as follows: the high-energy particle beam of the low-temperature plasma can physically bombard and chemically etch the surface of the carbon material. On the one hand, it effectively removes the amorphous carbon layer sealed on the surface during carbonization, opening up blocked channels and significantly reducing the number of dead pores. On the other hand, this etching effect tends to construct microporous structures with pore sizes ranging from 0.5 to 1.5 nm on the material surface and near the surface. Studies have shown that micropores within this size range are most conducive to sodium ion insertion / extraction behavior, significantly reducing the ion transport barrier. Simultaneously, plasma treatment can also repair dangling bond defects at the carbon layer edges, and combined with the simultaneously introduced nitrogen doping sites, synergistically improve the electronic conductivity and interfacial wettability of the material, thereby achieving excellent rate performance and cycling stability.

[0044] Second aspect This invention provides a composite hard carbon anode material, which is prepared by the above-described preparation method. The composite hard carbon anode material obtained by this method possesses a unique "asphalt-resin" composite framework and a nitrogen-rich open-pore structure on its surface, achieving a balance between high capacity, high initial efficiency, and excellent rate performance. This solves the problem that the overall performance of existing hard carbon anode materials is insufficient to meet the requirements of power batteries.

[0045] In some embodiments of the present invention, the specific surface area of ​​the composite hard carbon anode material is 1–20 m² / g or 2–10 m² / g. By controlling the specific surface area within a specific range, a balance is achieved between the electrolyte contact area and the consumption by side reactions. An excessively large specific surface area leads to excessive sodium ion consumption during SEI film formation (low initial efficiency), while an excessively small specific surface area results in insufficient ion flux (poor rate performance). This range effectively solves the problem of mutual constraint between initial efficiency and rate performance.

[0046] In some embodiments of the present invention, the average pore size of the composite hard carbon anode material is 0.3–1.5 nm or 0.4–1 nm. By constructing a suitable average pore size, rapid insertion and extraction of sodium ions are achieved, while limiting the co-intercalation of solvent molecules, thereby solving the problem of graphite layer peeling or structural damage and reduced cycle life caused by solvent co-intercalation.

[0047] In some embodiments of the present invention, the median particle size D50 of the composite hard carbon anode material is 4–10 μm or 5–7 μm. By controlling the median particle size, the smoothness and compaction density of the electrode coating are achieved. A suitable particle size helps to shorten the ion diffusion path while ensuring electrical contact between particles, thus solving the problems of slow diffusion due to excessively large particle size and easy agglomeration and difficulty in pulping due to excessively small particle size.

[0048] In some embodiments of the present invention, the true density of the composite hard carbon anode material is 1.4–1.6 g / cm³, and the tap density is 0.5–0.9 g / cm³ or 0.6–0.8 g / cm³. By increasing the tap density of the material, the volumetric energy density is improved, thereby solving the problem that the high porosity of traditional hard carbon materials leads to low volumetric energy density, limiting their application in space-constrained scenarios.

[0049] In some embodiments of the present invention, the closed-pore volume of the composite hard carbon anode material is 0.20–0.30 cm³ / g. By constructing a rich closed-pore volume, high-capacity storage of sodium ions in the "plateau region" is achieved, thereby solving the technical problem that hard carbon materials mainly rely on interlayer adsorption, resulting in high operating voltage and limited overall battery energy density.

[0050] In some embodiments of the present invention, the nitrogen content of the composite hard carbon anode material is 1.5~2.5 wt%. By maintaining an appropriate amount of nitrogen doping, the electronic conductivity and surface wettability are improved, and the additional defect sites provide pseudocapacitance contributions, thereby solving the problem of excessive capacity decay under high-rate charge and discharge.

[0051] In some embodiments of the present invention, the powder conductivity of the composite hard carbon anode material is 100–150 S / m. This higher powder conductivity reduces the battery's internal resistance and polarization, thereby solving the problems of severe heat generation and voltage hysteresis in hard carbon anodes under high current conditions.

[0052] In some embodiments of the present invention, the ash content of the composite hard carbon anode material is less than or equal to 0.8 wt%. This extremely low ash content maximizes the proportion of active material, reduces side reactions catalyzed by impurities, and thus solves the problems of continuous electrolyte decomposition and gas swelling during long-cycle operation.

[0053] Third aspect This invention provides a battery comprising a composite hard carbon anode material obtained by the above-described preparation method, or comprising the above-described composite hard carbon anode material; the battery is a sodium-ion battery, and its sodium storage capacity at 1C rate is 270-290 mAh / g, its capacity retention rate after 500 cycles is greater than or equal to 85%, and its capacity retention rate at 5C rate is greater than or equal to 70%. By applying the composite hard carbon anode material, the sodium-ion battery achieves excellent fast-charging capability and long cycle life while maintaining high energy density, thereby solving the industry problem that existing sodium-ion batteries cannot meet the long life and rapid replenishment requirements of electric vehicles and large-scale energy storage.

[0054] Example It is worth noting that, unless otherwise specified, the raw materials and equipment used in the embodiments of this invention can all be obtained through general commercial channels.

[0055] Jaw crusher: Wuxi Qingxin Powder Equipment Co., Ltd., Model: ZG.

[0056] Airflow mill: Kunshan Qiangdi Crushing Equipment Co., Ltd., Model: QDB-150.

[0057] Double cone vacuum dryer: Jiangsu Yutong Drying Engineering Co., Ltd., Model: SZG-100.

[0058] Ultrasonic cleaning tank; Changzhou Langbo Instrument Manufacturing Co., Ltd., Model: LB-100.

[0059] Acid-resistant reactor: Shanghai Fuding Technology Co., Ltd.

[0060] Hydrochloric acid: Sinopharm Chemical Reagent Co., Ltd., Model: AR, 36~38%.

[0061] Blower dryer: Shanghai Yiheng Scientific Instruments Co., Ltd., Model: BPG-2000L.

[0062] Ball mill: Wuxi Qingxin Powder Equipment Co., Ltd., Model: SQM-SJ-30L.

[0063] Box furnace: Shanghai Ruijing Machinery Equipment Co., Ltd., Model: RGQ-1600-50.

[0064] Rotary kiln: Xianyang Hongfeng Kiln Equipment Co., Ltd., Model: HF-RL45.

[0065] Example 1 S01: 10 kg of asphalt (softening point 160-210℃, carbon content greater than or equal to 95 wt%, volatile matter content 25-30 wt%) is crushed to a particle size of 5-10 mm by a jaw crusher, and then the powder is further pulverized by an air jet mill to control the D50 particle size of the asphalt to 5-7 μm. The pulverized asphalt is then placed in a double cone vacuum dryer and dried at 120℃ and -0.095 MPa for 4 hours to remove moisture. After the above treatment, the asphalt is obtained for use. S02: 10 kg of recycled waste ion exchange resin (gel type, non-macroporous, exchange capacity greater than 4.5 mmol / g, water content less than 10 wt%, ferric ion content less than 50 ppm, and divalent copper ion content less than 50 ppm) was placed in an ultrasonic cleaning tank for ultrasonic cleaning. The mass ratio of cleaning water to waste ion exchange resin was controlled at 5:1, the ultrasonic cleaning frequency was 50 kHz, the water temperature during ultrasonic cleaning was 40 ℃, and the cleaning time was 1 h. After the initial cleaning, the resin was transferred to an acid-resistant reactor and treated in 0.5 mol / L hydrochloric acid at 40 ℃ at 150 rpm for 2 h to remove heavy metal ions. The resin after heavy metal ion removal was immersed in deionized water and stirred and washed for 2 h to remove dust. Then, the above-mentioned liquid was separated into solid and liquid by atmospheric pressure filtration. The obtained resin was placed in a blower dryer and dried at 80 ℃ for 6 h. Then, the obtained material was pulverized by an air jet mill to obtain ion exchange resin with a D50 of 5-7 μm. S1, the above asphalt and ion exchange resin are added into a ball mill at a mass ratio of 7:3 and mixed thoroughly at a speed of 450 rpm for 2 hours to obtain the first precursor; S2, the first precursor obtained in step S1 is placed in a box furnace for gradient heating carbonization. Under nitrogen protection, the temperature is first increased to 300°C at a heating rate of 4°C / min and held for 2 hours for low-temperature devolatilization carbonization; then the temperature is increased to 600°C at a heating rate of 3°C / min and held for 1.5 hours for medium-temperature crosslinking carbonization; finally, the temperature is increased to 1000°C at a heating rate of 2°C / min for high-temperature carbonization, and after 3 hours, the temperature is lowered to obtain the second precursor. S3. The second precursor obtained in step S2 is placed in a rotary kiln for ammoniation and nitrogen doping treatment. It is first heated to 800°C at a heating rate of 2°C / min, and nitrogen gas is simultaneously introduced as a protective gas at a flow rate of 50 mL / min during this heating process. After reaching 800°C, the nitrogen gas is stopped and ammonia gas is introduced at a flow rate of 50 mL / min. After maintaining the temperature for 2 hours, the ammoniation and nitrogen doping treatment is completed. Then, it is naturally cooled to room temperature and discharged to obtain the third precursor. S4. The third precursor obtained in step S3 is placed in a plasma processor, argon gas is introduced and the pressure of argon gas is maintained at 0.2 MPa, the power of the plasma processor is 150 W and the flow rate is 40 mL / min. After 10 min, the composite hard carbon anode material is obtained.

[0066] Example 2 S01: 10 kg of asphalt (softening point 160-210℃, carbon content greater than or equal to 95 wt%, volatile matter content 25-30 wt%) is crushed to a particle size of 5-10 mm by a jaw crusher, and then the powder is further pulverized by an air jet mill to control the D50 particle size of the asphalt to 5-7 μm. The pulverized asphalt is then placed in a double cone vacuum dryer and dried at 120℃ and -0.095 MPa for 4 hours to remove moisture. After the above treatment, the asphalt is obtained for use. S02: 10 kg of recycled waste ion exchange resin (gel type, non-macroporous, exchange capacity greater than 4.5 mmol / g, water content less than 10 wt%, ferric ion content less than 50 ppm, and divalent copper ion content less than 50 ppm) was placed in an ultrasonic cleaning tank for ultrasonic cleaning. The mass ratio of cleaning water to waste ion exchange resin was controlled at 4:1, the ultrasonic cleaning frequency was 50 kHz, the water temperature during ultrasonic cleaning was 40 ℃, and the cleaning time was 1 h. After the initial cleaning, the resin was transferred to an acid-resistant reactor and treated in 0.4 mol / L hydrochloric acid at 40 ℃ at 150 rpm for 2 h to remove heavy metal ions. The resin that had been treated with heavy metal ions was then soaked in deionized water and stirred and washed for 2 h to remove dust. Then, the above-mentioned liquid was separated into solid and liquid by atmospheric pressure filtration. The obtained resin was placed in a blower dryer and dried at 80 ℃ for 6 h. Then, the obtained material was pulverized by an air jet mill to obtain ion exchange resin with a D50 of 5-7 μm. S1, the above asphalt and ion exchange resin are added into a ball mill at a mass ratio of 8:2 and mixed thoroughly at a speed of 450 rpm for 2 hours to obtain the first precursor; S2, the first precursor obtained in step S1 is placed in a box furnace for gradient heating carbonization. Under nitrogen protection, the temperature is first raised to 300°C at a rate of 4°C / min and held for 2 hours for low-temperature devolatilization carbonization; then the temperature is raised to 600°C at a rate of 3°C / min and held for 1.5 hours for medium-temperature crosslinking carbonization; finally, the temperature is raised to 1100°C at a rate of 2°C / min for high-temperature carbonization, and after 4 hours, the temperature is lowered to obtain the second precursor. S3. The second precursor obtained in step S2 is placed in a rotary kiln for ammoniation and nitrogen doping treatment. It is first heated to 850°C at a heating rate of 3°C / min, and nitrogen gas is simultaneously introduced as a protective gas at a flow rate of 50 mL / min during this heating process. After reaching 850°C, the nitrogen gas is stopped and ammonia gas is introduced at a flow rate of 50 mL / min. The ammoniation and nitrogen doping treatment is completed after maintaining the temperature for 1.5 hours. Then, it is naturally cooled to room temperature and discharged to obtain the third precursor. S4. The third precursor obtained in step S3 is placed in a plasma processor, argon gas is introduced and the pressure of argon gas is maintained at 0.2 MPa, the power of the plasma processor is 150 W and the flow rate is 40 mL / min. After 10 min, the composite hard carbon anode material is obtained.

[0067] Example 3 S01: 10 kg of asphalt (softening point 160-210℃, carbon content greater than or equal to 95 wt%, volatile matter content 25-30 wt%) is crushed to a particle size of 5-10 mm by a jaw crusher, and then the powder is further pulverized by an air jet mill to control the D50 particle size of the asphalt to 5-7 μm. The pulverized asphalt is then placed in a double cone vacuum dryer and dried at 120℃ and -0.095 MPa for 4 hours to remove moisture. After the above treatment, the asphalt is obtained for use. S02: 10 kg of recycled waste ion exchange resin (gel type, non-macroporous, exchange capacity greater than 4.5 mmol / g, water content less than 10 wt%, ferric ion content less than 50 ppm, and divalent copper ion content less than 50 ppm) was placed in an ultrasonic cleaning tank for ultrasonic cleaning. The mass ratio of cleaning water to waste ion exchange resin was controlled at 6:1, the ultrasonic cleaning frequency was 50 kHz, the water temperature during ultrasonic cleaning was 40 ℃, and the cleaning time was 1 h. After the initial cleaning, the resin was transferred to an acid-resistant reactor and treated in 0.6 mol / L hydrochloric acid at 40 ℃ at 150 rpm for 2 h to remove heavy metal ions. The resin after heavy metal ion removal was immersed in deionized water and stirred and washed for 2 h to remove dust. Then, the above-mentioned liquid was separated into solid and liquid by atmospheric pressure filtration. The obtained resin was placed in a blower dryer and dried at 80 ℃ for 6 h. Then, the obtained material was pulverized by an air jet mill to obtain ion exchange resin with a D50 of 5-7 μm. S1, the above asphalt and ion exchange resin are added into a ball mill at a mass ratio of 6:4 and mixed thoroughly at a speed of 400 rpm for 3 hours to obtain the first precursor; S2, the first precursor obtained in step S1 is placed in a box furnace for gradient heating carbonization. Under nitrogen protection, the temperature is first raised to 350°C at a heating rate of 5.5°C / min and held for 1 hour for low-temperature devolatilization carbonization; then the temperature is raised to 650°C at a heating rate of 4°C / min and held for 1 hour for medium-temperature crosslinking carbonization; finally, the temperature is raised to 1000°C at a heating rate of 3°C / min for high-temperature carbonization, and after 3 hours, the temperature is lowered to obtain the second precursor. S3. The second precursor obtained in step S2 is placed in a rotary kiln for ammoniation and nitrogen doping treatment. It is first heated to 800°C at a heating rate of 4°C / min, and nitrogen gas is simultaneously introduced as a protective gas at a flow rate of 60 mL / min during this heating process. After reaching 800°C, the nitrogen gas is stopped and ammonia gas is introduced at a flow rate of 50 mL / min. After maintaining the temperature for 2 hours, the ammoniation and nitrogen doping treatment is completed. Then, it is naturally cooled to room temperature and discharged to obtain the third precursor. S4. The third precursor obtained in step S3 is placed in a plasma processor, argon gas is introduced and the pressure of argon gas is maintained at 0.3 MPa, the power of the plasma processor is 130 W and the flow rate is 50 mL / min. After 9 min, the composite hard carbon anode material is obtained.

[0068] Example 4 S01: 10 kg of asphalt (softening point 160-210℃, carbon content greater than or equal to 95 wt%, volatile matter content 25-30 wt%) is crushed to a particle size of 5-10 mm by a jaw crusher, and then the powder is further pulverized by an air jet mill to control the D50 particle size of the asphalt to 5-7 μm. The pulverized asphalt is then placed in a double cone vacuum dryer and dried at 120℃ and -0.095 MPa for 4 hours to remove moisture. After the above treatment, the asphalt is obtained for use. S02: 10 kg of recycled waste ion exchange resin (gel type, non-macroporous, exchange capacity greater than 4.5 mmol / g, water content less than 10 wt%, ferric ion content less than 50 ppm, and divalent copper ion content less than 50 ppm) was placed in an ultrasonic cleaning tank for ultrasonic cleaning. The mass ratio of cleaning water to waste ion exchange resin was controlled at 6:1, the ultrasonic cleaning frequency was 50 kHz, the water temperature during ultrasonic cleaning was 40 ℃, and the cleaning time was 1 h. After the initial cleaning, the resin was transferred to an acid-resistant reactor and treated in 0.5 mol / L hydrochloric acid at 40 ℃ at 150 rpm for 2 h to remove heavy metal ions. The resin after heavy metal ion removal was immersed in deionized water and stirred and washed for 2 h to remove dust. Then, the above-mentioned liquid was separated into solid and liquid by atmospheric pressure filtration. The obtained resin was placed in a blower dryer and dried at 80 ℃ for 6 h. Then, the obtained material was pulverized by an air jet mill to obtain ion exchange resin with a D50 of 5-7 μm. S1, the above asphalt and ion exchange resin are added into a ball mill at a mass ratio of 5:5 and mixed thoroughly at a speed of 450 rpm for 2 hours to obtain the first precursor; S2, the first precursor obtained in step S1 is placed in a box furnace for gradient heating carbonization. Under nitrogen protection, the temperature is first raised to 250°C at a heating rate of 5°C / min and held for 1.5 hours for low-temperature devolatilization carbonization; then the temperature is raised to 550°C at a heating rate of 2°C / min and held for 2 hours for medium-temperature crosslinking carbonization; finally, the temperature is raised to 900°C at a heating rate of 1°C / min for high-temperature carbonization, and after 2 hours, the temperature is lowered to obtain the second precursor. S3. The second precursor obtained in step S2 is placed in a rotary kiln for ammoniation and nitrogen doping treatment. It is first heated to 900°C at a heating rate of 5°C / min, and nitrogen gas is simultaneously introduced as a protective gas at a flow rate of 50 mL / min during this heating process. After reaching 900°C, the nitrogen gas is stopped and ammonia gas is introduced at a flow rate of 70 mL / min. After maintaining the temperature for 2.5 hours, the ammoniation and nitrogen doping treatment is completed. Then, it is naturally cooled to room temperature and discharged to obtain the third precursor. S4. The third precursor obtained in step S3 is placed in a plasma processor, argon gas is introduced and the pressure of argon gas is maintained at 0.25 MPa, the power of the plasma processor is 170 W and the flow rate is 30 mL / min. After 11 min, the composite hard carbon anode material is obtained.

[0069] Example 5 S01: 10 kg of asphalt (softening point 160-210℃, carbon content greater than or equal to 95 wt%, volatile matter content 25-30 wt%) is crushed to a particle size of 5-10 mm by a jaw crusher, and then the powder is further pulverized by an air jet mill to control the D50 particle size of the asphalt to 5-7 μm. The pulverized asphalt is then placed in a double cone vacuum dryer and dried at 120℃ and -0.095 MPa for 4 hours to remove moisture. After the above treatment, the asphalt is obtained for use. S02: 10 kg of recycled waste ion exchange resin (gel type, non-macroporous, exchange capacity greater than 4.5 mmol / g, water content less than 10 wt%, ferric ion content less than 50 ppm, and divalent copper ion content less than 50 ppm) was placed in an ultrasonic cleaning tank for ultrasonic cleaning. The mass ratio of cleaning water to waste ion exchange resin was controlled at 4:1, the ultrasonic cleaning frequency was 50 kHz, the water temperature during ultrasonic cleaning was 40 ℃, and the cleaning time was 1 h. After the initial cleaning, the resin was transferred to an acid-resistant reactor and treated in 0.5 mol / L hydrochloric acid at 40 ℃ at 150 rpm for 2 h to remove heavy metal ions. The resin after heavy metal ion removal was immersed in deionized water and stirred and washed for 2 h to remove dust. Then, the above-mentioned liquid was separated into solid and liquid by atmospheric pressure filtration. The obtained resin was placed in a blower dryer and dried at 80 ℃ for 6 h. Then, the obtained material was pulverized by an air jet mill to obtain ion exchange resin with a D50 of 5-7 μm. S1, the above asphalt and ion exchange resin are added into a ball mill at a mass ratio of 7:3 and mixed thoroughly at a speed of 500 rpm for 1 hour to obtain the first precursor; S2, the first precursor obtained in step S1 is placed in a box furnace for gradient heating carbonization. Under nitrogen protection, the temperature is first raised to 300°C at a rate of 4°C / min and held for 2 hours for low-temperature devolatilization carbonization; then the temperature is raised to 650°C at a rate of 3°C / min and held for 2 hours for medium-temperature crosslinking carbonization; finally, the temperature is raised to 1000°C at a rate of 2°C / min for high-temperature carbonization, and after 3 hours, the temperature is lowered to obtain the second precursor. S3. The second precursor obtained in step S2 is placed in a rotary kiln for ammoniation and nitrogen doping treatment. It is first heated to 800°C at a heating rate of 2°C / min, and nitrogen gas is simultaneously introduced as a protective gas at a flow rate of 50 mL / min during this heating process. After reaching 800°C, the nitrogen gas is stopped and ammonia gas is introduced at a flow rate of 50 mL / min. After maintaining the temperature for 2 hours, the ammoniation and nitrogen doping treatment is completed. Then, it is naturally cooled to room temperature and discharged to obtain the third precursor. S4. The third precursor obtained in step S3 is placed in a plasma processor, argon gas is introduced and the pressure of argon gas is maintained at 0.2 MPa, the power of the plasma processor is 170 W and the flow rate is 50 mL / min. After 11 min, the composite hard carbon anode material is obtained.

[0070] Comparative Example 1 S01: 10 kg of asphalt (softening point 160-210℃, carbon content greater than or equal to 95 wt%, volatile matter content 25-30 wt%) is crushed to a particle size of 5-10 mm by a jaw crusher, and then the powder is further pulverized by an air jet mill to control the D50 particle size of the asphalt to 5-7 μm. The pulverized asphalt is then placed in a double cone vacuum dryer and dried at 120℃ and -0.095 MPa for 4 hours to remove moisture. After the above treatment, the asphalt is obtained for use. S1, the above asphalt is put into a ball mill and mixed thoroughly at a speed of 450 rpm for 2 hours to obtain the first precursor; S2, the first precursor obtained in step S1 is placed in a box furnace for gradient heating carbonization. Under nitrogen protection, the temperature is first raised to 300°C at a rate of 4°C / min and held for 2 hours for low-temperature devolatilization carbonization; then the temperature is raised to 600°C at a rate of 3°C / min and held for 1.5 hours for medium-temperature crosslinking carbonization; finally, the temperature is raised to 1100°C at a rate of 2°C / min for high-temperature carbonization, and after 4 hours, the temperature is lowered to obtain the second precursor. S3. The second precursor obtained in step S2 is placed in a rotary kiln for ammoniation and nitrogen doping treatment. It is first heated to 850°C at a heating rate of 3°C / min, and nitrogen gas is simultaneously introduced as a protective gas at a flow rate of 50 mL / min during this heating process. After reaching 850°C, the nitrogen gas is stopped and ammonia gas is introduced at a flow rate of 50 mL / min. The ammoniation and nitrogen doping treatment is completed after maintaining the temperature for 1.5 hours. Then, it is naturally cooled to room temperature and discharged to obtain the third precursor. S4. The third precursor obtained in step S3 is placed in a plasma processor, argon gas is introduced and the pressure of argon gas is maintained at 0.2 MPa, the power of the plasma processor is 150 W and the flow rate is 40 mL / min. After 10 min, hard carbon anode material is obtained.

[0071] Comparative Example 2 S01: 10 kg of asphalt (softening point 160-210℃, carbon content greater than or equal to 95 wt%, volatile matter content 25-30 wt%) is crushed to a particle size of 5-10 mm by a jaw crusher, and then the powder is further pulverized by an air jet mill to control the D50 particle size of the asphalt to 5-7 μm. The pulverized asphalt is then placed in a double cone vacuum dryer and dried at 120℃ and -0.095 MPa for 4 hours to remove moisture. After the above treatment, the asphalt is obtained for use. S02: 10 kg of recycled waste ion exchange resin (gel type, non-macroporous, exchange capacity greater than 4.5 mmol / g, water content less than 10 wt%, ferric ion content less than 50 ppm, and divalent copper ion content less than 50 ppm) was placed in an ultrasonic cleaning tank for ultrasonic cleaning. The mass ratio of cleaning water to waste ion exchange resin was controlled at 4:1, the ultrasonic cleaning frequency was 50 kHz, the water temperature during ultrasonic cleaning was 40 ℃, and the cleaning time was 1 h. After the initial cleaning, the resin was transferred to an acid-resistant reactor and treated in 0.4 mol / L hydrochloric acid at 40 ℃ at 150 rpm for 2 h to remove heavy metal ions. The resin that had been treated with heavy metal ions was then soaked in deionized water and stirred and washed for 2 h to remove dust. Then, the above-mentioned liquid was separated into solid and liquid by atmospheric pressure filtration. The obtained resin was placed in a blower dryer and dried at 80 ℃ for 6 h. Then, the obtained material was pulverized by an air jet mill to obtain ion exchange resin with a D50 of 5-7 μm. S1, the above asphalt and ion exchange resin are added into a ball mill at a mass ratio of 8:2 and mixed thoroughly at a speed of 450 rpm for 2 hours to obtain the first precursor; S2, the first precursor obtained in step S1 is placed in a box furnace and heated for carbonization. Under nitrogen protection, the temperature is first raised to 1000℃ at a heating rate of 2℃ / min and held for 3 hours to directly carry out high-temperature carbonization. After 4 hours, the temperature is lowered and the second precursor is obtained. S3. The second precursor obtained in step S2 is placed in a rotary kiln for ammoniation and nitrogen doping treatment. It is first heated to 850°C at a heating rate of 3°C / min, and nitrogen gas is simultaneously introduced as a protective gas at a flow rate of 50 mL / min during this heating process. After reaching 850°C, the nitrogen gas is stopped and ammonia gas is introduced at a flow rate of 50 mL / min. The ammoniation and nitrogen doping treatment is completed after maintaining the temperature for 1.5 hours. Then, it is naturally cooled to room temperature and discharged to obtain the third precursor. S4. The third precursor obtained in step S3 is placed in a plasma processor, argon gas is introduced and the pressure of argon gas is maintained at 0.2 MPa, the power of the plasma processor is 150 W and the flow rate is 40 mL / min. After 10 min, hard carbon anode material is obtained.

[0072] Comparative Example 3 S01: 10 kg of asphalt (softening point 160-210℃, carbon content greater than or equal to 95 wt%, volatile matter content 25-30 wt%) is crushed to a particle size of 5-10 mm by a jaw crusher, and then the powder is further pulverized by an air jet mill to control the D50 particle size of the asphalt to 5-7 μm. The pulverized asphalt is then placed in a double cone vacuum dryer and dried at 120℃ and -0.095 MPa for 4 hours to remove moisture. After the above treatment, the asphalt is obtained for use. S02: 10 kg of recycled waste ion exchange resin (gel type, non-macroporous, exchange capacity greater than 4.5 mmol / g, water content less than 10 wt%, ferric ion content less than 50 ppm, and divalent copper ion content less than 50 ppm) was placed in an ultrasonic cleaning tank for ultrasonic cleaning. The mass ratio of cleaning water to waste ion exchange resin was controlled at 4:1, the ultrasonic cleaning frequency was 50 kHz, the water temperature during ultrasonic cleaning was 40 ℃, and the cleaning time was 1 h. After the initial cleaning, the resin was transferred to an acid-resistant reactor and treated in 0.4 mol / L hydrochloric acid at 40 ℃ at 150 rpm for 2 h to remove heavy metal ions. The resin that had been treated with heavy metal ions was then soaked in deionized water and stirred and washed for 2 h to remove dust. Then, the above-mentioned liquid was separated into solid and liquid by atmospheric pressure filtration. The obtained resin was placed in a blower dryer and dried at 80 ℃ for 6 h. Then, the obtained material was pulverized by an air jet mill to obtain ion exchange resin with a D50 of 5-7 μm. S1, the above asphalt and ion exchange resin are added into a ball mill at a mass ratio of 8:2 and mixed thoroughly at a speed of 450 rpm for 2 hours to obtain the first precursor; S2, the first precursor obtained in step S1 is placed in a box furnace for gradient heating carbonization. Under nitrogen protection, the temperature is first raised to 300°C at a rate of 4°C / min and held for 2 hours for low-temperature devolatilization carbonization; then the temperature is raised to 600°C at a rate of 3°C / min and held for 1.5 hours for medium-temperature crosslinking carbonization; finally, the temperature is raised to 1100°C at a rate of 2°C / min for high-temperature carbonization, and after 4 hours, the temperature is lowered to obtain the second precursor. S3. The second precursor obtained in step S2 is placed in a plasma processor, argon gas is introduced and the pressure of argon gas is maintained at 0.2 MPa, the power of the plasma processor is 150 W and the flow rate is 40 mL / min. After 10 min, hard carbon anode material is obtained.

[0073] Comparative Example 4 S01: 10 kg of asphalt (softening point 160-210℃, carbon content greater than or equal to 95 wt%, volatile matter content 25-30 wt%) is crushed to a particle size of 5-10 mm by a jaw crusher, and then the powder is further pulverized by an air jet mill to control the D50 particle size of the asphalt to 5-7 μm. The pulverized asphalt is then placed in a double cone vacuum dryer and dried at 120℃ and -0.095 MPa for 4 hours to remove moisture. After the above treatment, the asphalt is obtained for use. S02: 10 kg of recycled waste ion exchange resin (gel type, non-macroporous, exchange capacity greater than 4.5 mmol / g, water content less than 10 wt%, ferric ion content less than 50 ppm, and divalent copper ion content less than 50 ppm) was placed in an ultrasonic cleaning tank for ultrasonic cleaning. The mass ratio of cleaning water to waste ion exchange resin was controlled at 4:1, the ultrasonic cleaning frequency was 50 kHz, the water temperature during ultrasonic cleaning was 40 ℃, and the cleaning time was 1 h. After the initial cleaning, the resin was transferred to an acid-resistant reactor and treated in 0.4 mol / L hydrochloric acid at 40 ℃ at 150 rpm for 2 h to remove heavy metal ions. The resin that had been treated with heavy metal ions was then soaked in deionized water and stirred and washed for 2 h to remove dust. Then, the above-mentioned liquid was separated into solid and liquid by atmospheric pressure filtration. The obtained resin was placed in a blower dryer and dried at 80 ℃ for 6 h. Then, the obtained material was pulverized by an air jet mill to obtain ion exchange resin with a D50 of 5-7 μm. S1, the above asphalt and ion exchange resin are added into a ball mill at a mass ratio of 8:2 and mixed thoroughly at a speed of 450 rpm for 2 hours to obtain the first precursor; S2, the first precursor obtained in step S1 is placed in a box furnace for gradient heating carbonization. Under nitrogen protection, the temperature is first raised to 300°C at a rate of 4°C / min and held for 2 hours for low-temperature devolatilization carbonization; then the temperature is raised to 600°C at a rate of 3°C / min and held for 1.5 hours for medium-temperature crosslinking carbonization; finally, the temperature is raised to 1100°C at a rate of 2°C / min for high-temperature carbonization, and after 4 hours, the temperature is lowered to obtain the second precursor. S3. The second precursor obtained in step S2 is placed in a rotary kiln for ammoniation and nitrogen doping treatment. It is first heated to 850°C at a heating rate of 3°C / min, and nitrogen gas is simultaneously introduced as a protective gas at a flow rate of 50 mL / min during the heating process. After reaching 850°C, the nitrogen gas is stopped and ammonia gas is introduced at a flow rate of 50 mL / min. After maintaining the temperature for 1.5 hours, the ammoniation and nitrogen doping treatment is completed. Then, it is naturally cooled to room temperature and discharged to obtain hard carbon anode material.

[0074] Comparative Example 5 S01: 10 kg of asphalt (softening point 160-210℃, carbon content greater than or equal to 95 wt%, volatile matter content 25-30 wt%) is crushed to a particle size of 5-10 mm by a jaw crusher, and then the powder is further pulverized by an air jet mill to control the D50 particle size of the asphalt to 5-7 μm. The pulverized asphalt is then placed in a double cone vacuum dryer and dried at 120℃ and -0.095 MPa for 4 hours to remove moisture. After the above treatment, the asphalt is obtained for use. S02: 10 kg of recycled waste ion exchange resin (gel type, non-macroporous, exchange capacity greater than 4.5 mmol / g, water content less than 10 wt%, ferric ion content less than 50 ppm, and divalent copper ion content less than 50 ppm) was placed in an ultrasonic cleaning tank for ultrasonic cleaning. The mass ratio of cleaning water to waste ion exchange resin was controlled at 4:1, the ultrasonic cleaning frequency was 50 kHz, the water temperature during ultrasonic cleaning was 40 ℃, and the cleaning time was 1 h. After the initial cleaning, the resin was transferred to an acid-resistant reactor and treated in 0.4 mol / L hydrochloric acid at 40 ℃ at 150 rpm for 2 h to remove heavy metal ions. The resin that had been treated with heavy metal ions was then soaked in deionized water and stirred and washed for 2 h to remove dust. Then, the above-mentioned liquid was separated into solid and liquid by atmospheric pressure filtration. The obtained resin was placed in a blower dryer and dried at 80 ℃ for 6 h. Then, the obtained material was pulverized by an air jet mill to obtain ion exchange resin with a D50 of 5-7 μm. S1, the above asphalt and ion exchange resin are added into a ball mill at a mass ratio of 1:9 and mixed thoroughly at a speed of 450 rpm for 2 hours to obtain the first precursor; S2, the first precursor obtained in step S1 is placed in a box furnace for gradient heating carbonization. Under nitrogen protection, the temperature is first raised to 300°C at a rate of 4°C / min and held for 2 hours for low-temperature devolatilization carbonization; then the temperature is raised to 600°C at a rate of 3°C / min and held for 1.5 hours for medium-temperature crosslinking carbonization; finally, the temperature is raised to 1100°C at a rate of 2°C / min for high-temperature carbonization, and after 4 hours, the temperature is lowered to obtain the second precursor. S3. The second precursor obtained in step S2 is placed in a rotary kiln for ammoniation and nitrogen doping treatment. It is first heated to 850°C at a heating rate of 3°C / min, and nitrogen gas is simultaneously introduced as a protective gas at a flow rate of 50 mL / min during this heating process. After reaching 850°C, the nitrogen gas is stopped and ammonia gas is introduced at a flow rate of 50 mL / min. The ammoniation and nitrogen doping treatment is completed after maintaining the temperature for 1.5 hours. Then, it is naturally cooled to room temperature and discharged to obtain the third precursor. S4. The third precursor obtained in step S3 is placed in a plasma processor, argon gas is introduced and the pressure of argon gas is maintained at 0.2 MPa, the power of the plasma processor is 150 W and the flow rate is 40 mL / min. After 10 min, the composite hard carbon anode material is obtained.

[0075] Test Example 1 The composite hard carbon anode material obtained in Example 1 was characterized by SEM using a Zeiss Sigma 500 scanning electron microscope at a voltage of 1.00 kV. The obtained SEM images are shown below. Figure 1 As shown.

[0076] Test Example 2 The hard carbon anode materials obtained in Examples 1-5 and Comparative Examples 1-5 were characterized and tested as follows: (1) Characterization of specific surface area and pore structure: The specific surface area was determined by the American Mack fully automatic adsorption-desorption instrument (model ASAP2460). The adsorbate for the specific surface area test was nitrogen gas, and the measurement temperature was 77K. The specific surface area was calculated by the BET method. The adsorbate for the micropore size test was carbon dioxide, the measurement temperature was 273K, the powder degassing temperature was 300℃, and the relative pressure range P / P0 was 0~1, which was obtained by DFT model analysis. The tests were conducted on Examples 1-5 and Comparative Examples 1-5 according to the above method, and the relevant test results are as follows. Figure 2 As shown; (2) D50 particle size test: obtained by laser particle size diffractometer (Mastersize2000, Malvern 2000); (3) True density: The true density of the hard carbon anode material was measured using a fully automatic true density analyzer of the American CANTA UltraPYC1200e and denoted as ρ true density; The formula for calculating the closed-cell volume (V_closed-cell) is: V_closed-cell = (1 / ρ_true density) - (1 / 2.26). (4) Tap density: The tap density of the above-mentioned hard carbon anode material was measured by tapping using an FZS4-4B tap density tester. (5) Nitrogen content test: The nitrogen content of the composite hard carbon anode material was measured using an ON-3000 oxygen and nitrogen analyzer; (6) Powder conductivity: The conductivity of the composite hard carbon anode material was measured using an MCP-PD51 powder conductivity meter.

[0077] Test Example 3 Electrochemical performance test: Hard carbon anode materials prepared in Examples 1-5 and Comparative Examples 1-5 were weighed, ground and mixed according to a mass ratio of anode material to conductive agent (name: SP, manufacturer: Yirui Stone (Shanghai) Investment Management Co., Ltd., model: SUPERPLi) and binder (name: PVDF, manufacturer: Arkema (Changshu) Fluorochemical Co., Ltd., model: 716A) of 90:5:5. NMP (N-Methyl-2-pyrrolidone) was used as solvent to prepare a viscous and uniform slurry. The slurry was then coated onto copper foil using a scraping method. The coated copper foil was then placed in a vacuum oven at 80°C and dried for 12 hours. Cut the dried copper foil into pieces with an area of ​​2cm. 2 The working electrode is made of a circular sheet; at room temperature, a sodium metal sheet is used as the negative electrode and the counter electrode, the electrode sheet prepared above is used as the working electrode, a GE Whatman glass fiber membrane is used as the diaphragm, and a 1 mol / L NaPF6 / EC+DMC solution (volume ratio of 1:1) is used as the electrolyte. Assemble CR2032 button batteries in a vacuum glove box and seal them tightly with a mechanical seal; after the assembled batteries are left to stand at room temperature for 24 hours, electrochemical tests are started; constant current charge and discharge experiments are carried out in the LAND battery testing system, with a charge and discharge voltage window of 0~2.0V, a discharge rate of 1C or 5C, and a charge rate of 0.1C. The discharge capacity and initial discharge efficiency of Examples 1-5 and Comparative Examples 1-5 were measured according to conventional testing methods in the art. Specifically, constant current charge-discharge experiments were conducted on a LAND battery testing system with a charge-discharge voltage window of 0-2.0V, a discharge rate of 1C or 5C, and a charge rate of 0.1C. The initial coulombic efficiency was calculated as: initial discharge capacity / initial charge capacity × 100%; cycle retention was calculated as: 500th discharge capacity / 2nd discharge capacity × 100%; and rate retention was calculated as: 5C discharge capacity / 1C discharge capacity × 100%.

[0078] Table 1. Performance of the hard carbon anode materials obtained in each embodiment.

[0079] Table 2 shows the performance of the hard carbon anode materials obtained in each embodiment.

[0080] As can be seen from Examples 1-5 of this invention, the present invention achieves effective control over the pore structure and specific surface area of ​​the hard carbon composite material through the synergistic effect between various process steps. The sodium-ion battery made from the prepared hard carbon composite material as the negative electrode material exhibits high capacity and cycle retention. This indicates that the present invention achieves high-value recycling of asphalt and waste ion exchange resin, and also solves the problem of high raw material costs for sodium-ion battery negative electrode materials.

[0081] Compared with the test results of Examples 1-5, the capacity and retention rate of Comparative Example 1 decreased significantly at 1C and 5C. This is because: Comparative Example 1 did not use waste ion exchange resin compounding, but only pure asphalt. After carbonization, the asphalt was mainly composed of "dense amorphous carbon" and there were no micropore / mesopore communication channels provided by the resin, which affected the sodium ion diffusion efficiency. It relied only on the trace amount of heteroatomic N in the asphalt itself (<0.3wt%). Although the ammoniation stage could supplement some N, the final N content was only 0.6wt% due to the few defects on the asphalt surface (no active sites provided by the resin), which led to a significant decrease in its capacity and retention rate.

[0082] Compared with the test results of Examples 1-5, Comparative Example 2 showed an increase in specific surface area and a decrease in capacity and retention rate. This is because: the rapid heating in one step caused small resin molecules to escape in a concentrated manner, forming a large number of ineffective micropores, which could not provide a smooth channel for sodium ions, thus leading to the problem of increased specific surface area and decreased capacity and retention rate.

[0083] Compared with the test results of Examples 1-5, the ratio of Comparative Example 3 is within a suitable range, but its powder conductivity and capacity retention at 5C decreased significantly. This is because: the N atoms introduced by in-situ ammoniation can build "conductive bridges" and improve electron transport efficiency; due to the low N content (0.7wt%), the conductive network of Comparative Example 3 is incomplete, and the conductivity drops from 120S / m to 55S / m, resulting in a significant decrease in capacity retention.

[0084] Compared with the test results of Examples 1 to 5, Comparative Example 4 had the same nitrogen content, but its specific surface area increased, and its powder conductivity and capacity retention also decreased significantly. This is because: without plasma etching, the particles agglomerated severely, and the contact resistance between particles increased during the tableting test, which in turn caused the conductivity to drop from 120 S / m to 80 S / m. During cycling, due to poor contact, the 500-cycle retention rate dropped from 88.6% to 81.2%.

[0085] Compared with the test results of Examples 1-5, Comparative Example 5 showed an increase in specific surface area, a decrease in powder conductivity and capacity retention. This is because when the resin content increased to 90%, although the specific surface area and N content were increased, micropores proliferated, the carbon skeleton broke down, and the conductivity dropped sharply, leading to a deterioration in overall performance.

[0086] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. Furthermore, specific examples have been used in the specification to illustrate the principles and implementation methods of the present invention. The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention, and the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing a composite hard carbon anode material, characterized in that, The preparation method includes: The asphalt was mixed with the ion exchange resin to obtain the first precursor; The first precursor is subjected to carbonization treatment to obtain the second precursor; The second precursor is subjected to nitrogen doping to obtain the third precursor; The third precursor is subjected to plasma treatment to obtain the composite hard carbon anode material.

2. The preparation method according to claim 1, characterized in that, It has at least one of the following characteristics: The preparation method further includes pretreatment, wherein the raw material asphalt and the raw material ion exchange resin are pretreated separately before mixing the asphalt with the ion exchange resin. The carbonization process is a gradient carbonization process, which includes three stages: low-temperature devolatilization, medium-temperature crosslinking, and high-temperature carbonization. The nitrogen doping treatment is an ammoniated nitrogen doping treatment, which includes a first stage of introducing an inert gas and a second stage of introducing ammonia gas. The plasma treatment is performed under an inert atmosphere.

3. The preparation method according to claim 2, characterized in that, In the pretreatment process, the raw asphalt is sequentially subjected to coarse crushing, fine crushing, drying, and impurity testing. After fine crushing, the asphalt D50 is 3–10 μm or 5–7 μm. Vacuum drying is performed at a pressure of -0.080–0.098 MPa or -0.095 MPa, a drying temperature of 100–150℃ or 120℃, and a drying time of 2–6 h or 4 h. After testing, the ash content is less than or equal to 2 wt%. In the pretreatment, the raw material ion exchange resin is subjected to preliminary cleaning, heavy metal removal, neutral washing, low-temperature drying, and fine pulverization in sequence. The preliminary cleaning uses water, ethanol, or acetone as the cleaning solution, with a liquid-to-solid ratio of (1-10):1 or (3-8):1, and an ultrasonic frequency of 30-80kHz. The heavy metal removal is performed using hydrochloric acid with a concentration of 0.1-1mol / L at 30-70℃. The low-temperature drying temperature is 50-100℃. After pulverization, the resin D50 is 3-10μm or 5-7μm.

4. The preparation method according to claim 2, characterized in that, The preparation of the first precursor has at least one of the following characteristics: The mass ratio of the asphalt to the ion exchange resin is (4-8):(6-2). The mixture was mixed using a ball mill at a speed of 300–800 rpm for 1–10 hours. The asphalt has a softening point of 160–210°C, a carbon content greater than or equal to 95 wt%, and a volatile matter content of 25–30 wt%. The ion exchange resin is a waste styrene-based ion exchange resin with an exchange capacity greater than or equal to 4.5 mmol / g, a water content less than or equal to 10 wt%, and an impurity content less than or equal to 50 ppm.

5. The preparation method according to claim 2, characterized in that, The gradient carbonization process has at least one of the following characteristics: The low-temperature devolatilization is carried out at a temperature of 200–400°C for 1–3 hours, with a heating rate of 4–6°C / min. The intermediate-temperature crosslinking temperature is 500–700℃, the duration is 1–3 hours, and the heating rate is 2–4℃ / min; The high-temperature carbonization is carried out at a temperature of 900–1100°C for 2–5 hours, with a heating rate of 1–3°C / min; the gradient carbonization process is performed under an argon or nitrogen atmosphere.

6. The preparation method according to claim 2, characterized in that, The nitrogen doping treatment with ammonia has at least one of the following characteristics: The ammoniation nitrogen doping treatment is performed at a temperature of 700–950°C for 1–5 hours, with a heating rate of 2–10°C / min. Argon or nitrogen gas is introduced in the first stage; In the second stage, ammonia gas is introduced at a flow rate of 30–80 mL / min or 40–80 mL / min.

7. The preparation method according to claim 2, characterized in that, The plasma processing has at least one of the following characteristics: The gas flow rate is 10–80 mL / min or 20–60 mL / min; The gas pressure is 0.1–0.5 MPa or 0.15–0.4 MPa; The duration of the plasma treatment is 5–20 min or 8–12 min; The power of the plasma treatment is 100-200W or 120-180W.

8. A composite hard carbon anode material, characterized in that, The composite hard carbon anode material is prepared by any one of claims 1 to 7.

9. The composite hard carbon anode material as described in claim 8, characterized in that, It has at least one of the following characteristics: The specific surface area of ​​the composite hard carbon anode material is 1-20 m² / g or 2-10 m² / g. The average pore size of the composite hard carbon anode material is 0.3–1.5 nm or 0.4–1 nm; The median particle size D50 of the composite hard carbon anode material is 4–10 μm or 5–7 μm. The true density of the composite hard carbon anode material is 1.4–1.6 g / cm³, and the tap density is 0.5–0.9 g / cm³ or 0.6–0.8 g / cm³. The closed-cell volume of the composite hard carbon anode material is 0.20–0.30 cm³ / g; The nitrogen content of the composite hard carbon anode material is 1.5~2.5 wt%; The powder conductivity of the composite hard carbon anode material is 100-150 S / m; The ash content of the composite hard carbon anode material is less than or equal to 0.8 wt%.

10. A battery, characterized in that, The battery comprises a composite hard carbon anode material obtained by the preparation method according to any one of claims 1 to 7, or comprises a composite hard carbon anode material according to claim 8 or 9; The battery is a sodium-ion battery, and its sodium storage capacity at 1C rate is 270-290 mAh / g, its capacity retention rate after 500 cycles is greater than or equal to 85%, and its capacity retention rate at 5C rate is greater than or equal to 70%.

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