Preparation method of hard carbon negative electrode material, hard carbon negative electrode material and battery

Abstract

The present invention relates to the technical field of batteries, and specifically relates to a preparation method of a hard carbon negative electrode material, a hard carbon negative electrode material, and a battery. A preparation method of a hard carbon negative electrode material, the method comprising: pyrolyzing raw materials to obtain a pretreated material; the raw materials comprising wood pulp and / or bamboo pulp, and the environmental atmosphere of the pyrolysis treatment comprising hydrogen; successively subjecting the pretreated material to a purification treatment and a pulverization treatment to obtain a pulverized material; mixing the fluidized pulverized material with a fluidized coating agent to obtain a carbonization precursor; and carbonizing the carbonization precursor to obtain the hard carbon negative electrode material. A hard carbon negative electrode material is prepared by using this method. The solution of the present invention can improve the coating effect of the hard carbon negative electrode material, reduce the defect concentration of the material, improve the uniformity of the coating, and improve the first Coulomb efficiency of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular, to a preparation method of a hard carbon negative electrode material, a hard carbon negative electrode material, and a battery. Background Art

[0002] Sodium-ion batteries are favored in the energy storage field due to the more abundant resources, relatively lower manufacturing costs, and easier accessibility of "sodium". Currently, the electrochemical performance of the negative electrode materials for sodium-ion (Na + ) batteries still cannot meet the actual industrial needs. Due to the relatively large radius and atomic mass of Na + , there are defects such as poor sodium ion deintercalation kinetics performance, poor cycle stability, and low initial efficiency. Therefore, conventional graphite negative electrode materials or silicon-based negative electrode materials are difficult to be used in sodium-ion batteries.

[0003] Among the negative electrode materials developed for sodium-ion batteries, hard carbon and soft carbon are more common. Both belong to disordered carbon materials. The difference is that hard carbon has a lower degree of graphitization, a more abundant disordered structure, and a larger carbon layer spacing, which is convenient for providing more active sites for the insertion of Na + . Thus, in the development of the negative electrode material system for sodium-ion batteries, due to its high degree of disorder, large layer spacing (the carbon layer spacing can reach 0.36 - 0.40 nm), rich pore structure, abundant resources, and renewable characteristics, hard carbon has become an ideal material for the negative electrode material of sodium-ion batteries.

[0004] Although hard carbon negative electrode materials have certain advantages in sodium-ion batteries, the existing hard carbon negative electrode materials still have some deficiencies. Especially in terms of the performance of biomass hard carbon materials, their capacity is relatively low, and the initial Coulombic efficiency is relatively low, so most of them are still in the research stage and have not been applied on a large scale in practice. Therefore, the existing hard carbon negative electrode materials used in sodium-ion batteries still need to be improved and developed. Summary of the Invention

[0005] In view of this, the present invention aims to solve at least one of the technical problems in the related art to some extent. For this reason, the present invention provides a preparation method of a hard carbon negative electrode material, a hard carbon negative electrode material, and a battery, which can improve the coating uniformity and coating effect, and can alleviate the problems of relatively low capacity and relatively low initial Coulombic efficiency of the existing hard carbon negative electrode materials.

[0006] To solve the above technical problems, the present application is implemented as follows:

[0007] The first aspect of the present application provides a preparation method of a hard carbon negative electrode material, and the method includes:

[0008] Performing pyrolysis treatment on raw materials to obtain a pretreated material; the raw materials include wood pulp and / or bamboo pulp, and the ambient atmosphere of the pyrolysis treatment includes hydrogen;

[0009] The pre-treated material is successively subjected to purification treatment and pulverization treatment to obtain a pulverized material;

[0010] The fluidized pulverized material is mixed with a fluidized coating agent to obtain a carbonization precursor;

[0011] The carbonization precursor is subjected to carbonization treatment to obtain the hard carbon negative electrode material.

[0012] In any embodiment, the pyrolysis treatment satisfies at least one of the following characteristics (1) to (5): (1) The ambient atmosphere of the pyrolysis treatment includes hydrogen or a mixed gas, and the mixed gas includes at least one of a mixed gas of hydrogen and argon, a mixed gas of hydrogen and nitrogen, or a mixed gas of hydrogen and helium, and the volume ratio of hydrogen in the mixed gas is 5% to 10%; (2) The concentration of oxygen in the atmosphere of the pyrolysis treatment is ≤100 ppm; (3) The heating rate of the pyrolysis treatment is 1 °C / min to 5 °C / min; (4) The pyrolysis temperature of the pyrolysis treatment is 200 °C to 600 °C; (5) The pyrolysis time of the pyrolysis treatment is 0.5 h to 10 h.

[0013] In any embodiment, the particle size range of the raw material is 1 mm to 30 mm.

[0014] In any embodiment, the wood pulp includes softwood pulp and / or hardwood pulp.

[0015] In any embodiment, the softwood pulp includes at least one of black pine pulp, Chinese red pine pulp, Chinese white pine pulp, Chinese pine pulp, Yunnan pine pulp, masson pine pulp, Chinese arborvitae pulp, Chinese fir pulp, fir pulp or cedar pulp.

[0016] In any embodiment, the hardwood pulp includes at least one of camphorwood pulp, magnolia grandiflora pulp, nanmu pulp, castanopsis sclerophylla pulp, Chinese wingnut pulp, plane tree pulp, elm pulp, paulownia pulp, sophora japonica pulp, ginkgo pulp or Chinese white poplar pulp.

[0017] In any embodiment, the purification treatment includes: successively subjecting the pre-treated material to pickling, water washing and drying.

[0018] In any embodiment, the pulverization treatment is carried out by means of pneumatic pulverization treatment.

[0019] In any embodiment, the acid in the pickling includes at least one of hydrochloric acid, nitric acid, hydrofluoric acid or sulfuric acid.

[0020] In any embodiment, the hydrogen ion concentration of the acid in the pickling is 0.5 mol / L to 1.5 mol / L.

[0021] In any embodiment, the gas source for airflow pulverization includes compressed air, and the pressure of the compressed air is 0.2 MPa to 1.0 MPa.

[0022] In any embodiment, the particle size D v of the pulverized material ranges from 7 μm to 10 μm.

[0023] In any embodiment, the step of obtaining the carbonization precursor includes: spraying a coating agent solution into the fluidized bed reactor through the nozzle of the fluidized bed reactor, transporting the pulverized material into the fluidized bed reactor through compressed gas to make the pulverized material in a fluidized state, and mixing the coating agent in the coating agent solution with the fluidized pulverized material in the fluidized bed reactor to obtain the carbonization precursor.

[0024] In any embodiment, the step of obtaining the carbonization precursor satisfies at least one of the following characteristics (1) to (7): (1) The coating agent in the coating agent solution includes at least one of asphalt, glucose, phenolic resin, epoxy resin, or phenolic epoxy resin; (2) The solvent in the coating agent solution includes at least one of water, ethanol, tetrahydrofuran, N,N-dimethylformamide, n-hexane, xylene, carbon disulfide, or trichloroethylene; (3) The compressed gas includes at least one of dry nitrogen, argon, or helium; (4) The flow rate of the compressed gas is 0.3 m / s to 5 m / s; (5) The pressure of the nozzle is 0.2 MPa to 2 MPa; (6) The temperature of the mixing is 100 °C to 300 °C; (7) The time of the mixing is 0.5 h to 2 h.

[0025] In any embodiment, the carbonization treatment includes a first carbonization stage and a second carbonization stage carried out in sequence.

[0026] In any embodiment, during the first carbonization stage, the carbonization atmosphere includes at least one of nitrogen, argon, or helium, the concentration of oxygen in the carbonization atmosphere is ≤ 100 ppm, the heating rate is 1 °C / min to 10 °C / min, the carbonization temperature is 600 °C to 900 °C, and the holding time is 1 h to 10 h.

[0027] In any embodiment, during the second carbonization stage, the carbonization atmosphere includes at least one of nitrogen, argon, or helium, the concentration of oxygen in the carbonization atmosphere is ≤ 100 ppm, the heating rate is 1 °C / min to 10 °C / min, the carbonization temperature is 1000 °C to 1500 °C, and the holding time is 1 h to 8 h.

[0028] The second aspect of the present application provides a hard carbon negative electrode material, which is prepared by using the preparation method of the aforementioned hard carbon negative electrode material; the hard carbon negative electrode material includes a hard carbon matrix and a carbon coating layer coated on the surface of the hard carbon matrix.

[0029] In any embodiment, the particle size D of the hard carbon matrix v is in the range of 5 μm to 10 μm.

[0030] In any embodiment, the thickness range of the carbon coating layer is 2 nm to 10 nm.

[0031] The third aspect of the present application provides a battery, which includes a negative electrode sheet, and the negative electrode sheet includes the hard carbon negative electrode material prepared by using the preparation method of the aforementioned hard carbon negative electrode material, or includes the aforementioned hard carbon negative electrode material.

[0032] Implementing the technical solutions of the present invention has at least the following beneficial effects:

[0033] In the present application, the preparation method of the provided hard carbon negative electrode material synthesizes the hard carbon negative electrode material by processes such as pyrolysis treatment, purification, coating, and carbonization. Among them, the pyrolysis treatment is carried out in a hydrogen atmosphere. Hydrogen can reduce the oxygen-containing functional groups in raw materials such as wood pulp or bamboo pulp precursors, reducing the influence of oxygen elements in the material on the hard carbon negative electrode material; at the same time, after the pyrolysis ends, a large number of small molecules escape, leaving a large number of pores inside the material, providing conditions for subsequent coating; and, the coating is carried out in the form of fluidized coating. This fluidized coating can make the coated object in a fluidized state, ensuring full contact between the coating agent and the coated object, ensuring the uniformity of the coating, shortening the coating time, and also reducing the dosage of the coating agent. Through fluidized coating, the specific surface area of the material can be reduced, the interface of the material can be improved, and the electrochemical stability of the material can be enhanced. Therefore, the hard carbon negative electrode material prepared by this method has uniform coating, fewer surface defects of the material, less consumption of electrolyte during the first charge-discharge process, and thus a higher initial Coulomb efficiency and a higher specific capacity.

[0034] The additional aspects and advantages of the present application will be partially given in the following description, partially will become obvious from the following description, or will be understood through the practice of the present invention. Description of the Drawings

[0035] Figure 1 Shown is the scanning electron microscope image of the hard carbon negative electrode material provided in Embodiment 1 of the present invention.

[0036] Figure 2 Shown is the charge-discharge curve of the hard carbon negative electrode material provided in Embodiment 1 of the present invention.

[0037] Figure 3The XRD pattern of the hard carbon negative electrode material provided by Embodiment 1 of the present invention is shown below. Detailed implementation manners

[0038] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments of the present application are only used to illustrate the present application and not to limit the scope of the present application.

[0039] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values or individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0040] If there is no special instruction, all implementation manners and optional implementation manners of the present application can be combined with each other to form a new technical solution. If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0041] If there is no special instruction, all steps of the present application can be carried out in sequence or randomly, and preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or can also include steps (a), (c) and (b), or can also include steps (c), (a) and (b), etc.

[0042] If there is no special instruction, the "including" and "comprising" mentioned in the present application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0043] In the development of the anode material system for sodium-ion batteries, hard carbon has become an ideal anode material for sodium-ion batteries due to its advantages such as high disorder degree, large interlayer spacing, rich pore structure, abundant and renewable resources. Biomass materials such as wood and bamboo are one of the good hard carbon precursor materials, and China has rich forest resources and the advantage of being renewable. Wood pulp, made from wood as raw material through mechanical or chemical processing, has rich carbon content and natural pore structure, which can provide an effective channel for electron transport, so it has the potential advantage as a hard carbon material precursor. However, due to the large number of pore structures in wood pulp, it brings a high concentration of defects, resulting in a low initial Coulomb efficiency and poor cycle stability of the anode material synthesized from it, affecting the long-term use performance of sodium-ion batteries. To address this pain point, it has become a widespread consensus to introduce coating agents such as asphalt and glucose for coating treatment in order to reduce the specific surface area and defect concentration of the material and improve the initial Coulomb efficiency of the material. For example, the patent with the publication number CN109935792A discloses a method for composite surface modification of anode materials, in which the main material and the coating agent are coated by a solid-solid mixing and long-time high-speed stirring method. Although the operation is simple, the solid-solid mixing effect is poor, and there are easy dead corners in the coating process, resulting in uneven coating and affecting the performance of the finally prepared anode material. In view of this, a reasonable coating method is crucial for improving the material performance.

[0044] Therefore, the inventors of the present application fully considered the characteristics of hard carbon materials, adopted a special coating method to improve the coating effect, and then improved the performance of the material such as capacity and initial efficiency to effectively alleviate the above problems. In view of this, the present application provides a preparation method of a hard carbon anode material, a hard carbon anode material and a battery, and the present application will be described in detail below.

[0045] In some embodiments, the present application provides a preparation method of a hard carbon anode material, and the method includes the following steps:

[0046] Pyrolyze the raw materials to obtain a pretreated material; the raw materials include wood pulp and / or bamboo pulp, and the environmental atmosphere for pyrolysis treatment includes hydrogen;

[0047] Perform purification treatment and pulverization treatment on the pretreated material in sequence to obtain a pulverized material;

[0048] Mix the fluidized pulverized material with the fluidized coating agent to obtain a carbonization precursor;

[0049] Perform carbonization treatment on the carbonization precursor to obtain a hard carbon anode material.

[0050] The preparation method of the hard carbon anode material provided in this application has the characteristics of environmental friendliness from the perspective of raw materials. It is applicable to the preparation of biomass-based hard carbon materials, that is, biomass can be used as a precursor to prepare the hard carbon anode material. In particular, using wood pulp or bamboo pulp biomass materials as raw materials to prepare the hard carbon anode material has excellent properties such as rich resources, wide sources, short growth cycles, renewable green materials, wide distribution, fast growth, early maturity, and high strength. It is the biomass resource with the largest reserves on the earth, which can ensure the stable supply of raw materials and is applicable to the practical industrial production plan for solving the anode material of sodium-ion batteries at low cost and on a large scale. In addition, its preparation process has the characteristics of low energy consumption and low emissions, meeting the current demand for green development. From the perspective of green and recyclable, the strategy of using biomass to synthesize electrode materials is of great significance. Moreover, due to the problems such as high-concentration defects brought by the large number of pore structures existing in the existing wood pulp, the method of the present invention is more applicable when using wood pulp as the raw material, which can further promote the development of preparing hard carbon anode materials from wood pulp, enabling the wood pulp-derived hard carbon anode material to exhibit good electrochemical performance and being more conducive to its application in sodium-ion batteries.

[0051] The preparation method of the hard carbon anode material provided in this application has the characteristics of reasonable process from the perspective of process. It includes pyrolysis treatment (preferably low-temperature pyrolysis in a hydrogen atmosphere) of raw materials such as wood pulp or bamboo pulp, and then purification treatment, pulverization treatment, fluidized coating treatment, and carbonization treatment (preferably two-step high-temperature carbonization treatment). This application adopts the scheme of fluidized coating of wood pulp to improve the coating effect, reduce the defect concentration of the material, and improve the first Coulomb efficiency of the material. Among them, fluidization refers to the state in which solid particles are suspended by the action of a gas flow. In this state, introducing a coating agent can ensure sufficient contact between the coating agent and the main material, avoiding the existence of coating dead corners; at the same time, the particles are in a suspended state, and a good coating effect can be achieved in a short time. At the same time, this application uses the above fluidized coating in combination with low-temperature pyrolysis treatment and two-step high-temperature carbonization process to reduce the defects of wood pulp-derived hard carbon, and then a wood pulp-derived hard carbon material with a high first Coulomb efficiency can be obtained. Specifically:

[0052] (1) The biomass raw material used in the present invention is wood pulp or bamboo pulp. There are certain oxygen-containing functional groups in the wood pulp, which will have a certain impact on the performance of the finally prepared hard carbon anode material. Therefore, the present invention adds a pyrolysis treatment step for the wood pulp raw material before the fluidized coating treatment, and uses a hydrogen atmosphere in the pyrolysis treatment. Hydrogen can reduce the oxygen-containing functional groups in raw materials such as wood pulp or bamboo pulp precursors, reducing the influence of oxygen elements in the material on the hard carbon anode material. At the same time, after the pyrolysis is completed, a large number of small molecules escape, leaving a large number of pores inside the material, providing conditions for subsequent coating. The present invention selects wood pulp, which is rich in resources and renewable, as the precursor, improving the utilization rate of wood pulp and reducing the environmental pressure. And compared with the existing preparation methods, the present invention uses the method of pyrolyzing the wood pulp raw material in a hydrogen atmosphere, which can overcome the deficiencies of the existing methods, not only effectively improving the resource utilization efficiency of the biomass raw material, but also significantly improving the electrochemical performance of the hard carbon anode material.

[0053] (2) After the pyrolysis treatment in the present invention, a purification treatment and a pulverization treatment are carried out before coating, which can be used to remove impurity elements in the material, improve the purity of the material, obtain the matrix material with the required particle size, facilitate the exertion of the electrical properties of the material, and thus facilitate the improvement of the electrochemical performance of the finally prepared hard carbon anode material.

[0054] (3) The present invention does not use the method of solid-solid mixing and long-time high-speed stirring for coating, but uses the fluidized coating method for coating. This fluidized coating can make the coated object in a fluidized state, ensuring full contact between the coating agent and the coated object, ensuring the uniformity of coating, shortening the coating time, and also reducing the dosage of the coating agent. Through fluidized coating, the specific surface area of the material can be reduced, the interface of the material can be improved, and the electrochemical stability of the material can be enhanced. Thus, compared with the traditional coating method, the present invention adopts the fluidized coating technical solution, shortening the time used for coating, ensuring the uniformity of coating, reducing the dosage of the coating agent, and improving the coating effect.

[0055] (4) In the preferred embodiment of the present invention, the carbonization treatment preferably adopts two-step carbonization. This carbonization process uses two-step carbonization. The medium-temperature carbonization can promote the growth and development of graphite microcrystals, laying a foundation for the formation of closed pores in the later high-temperature carbonization. The high-temperature carbonization can provide sufficient energy for the rearrangement of carbon atoms, thereby reducing the defects of the wood pulp-derived hard carbon and obtaining a wood pulp-derived hard carbon material with a high initial Coulomb efficiency.

[0056] In addition, this preparation method has a simple process, is easy to operate, has strong feasibility, is green and environmentally friendly, has a low cost, and is easy to realize industrialization. The hard carbon anode material prepared by this method has good electrochemical performance.

[0057] Therefore, based on the above, the hard carbon negative electrode material prepared by the method of the present invention has uniform coating, good coating effect, fewer surface defects of the material, less electrolyte consumption during the first charge-discharge process, and thus a higher initial Coulomb efficiency, and has a higher specific capacity.

[0058] The hard carbon negative electrode material prepared by the present invention has a core-shell structure, wherein the inner core is made of hard carbon, and the outer shell or shell layer includes a carbon coating layer (carbon material layer). Among them, hard carbon is used as the inner core, and the hard carbon in the present application is a biomass-based hard carbon material, that is, the precursor of hard carbon can use biomass such as wood pulp, and it is a hard carbon material derived from biomass such as wood pulp.

[0059] In the present application, the carbon coating layer is formed or coated on at least part of the surface of the hard carbon matrix, which can play a role in protecting or improving the matrix, and can be used to improve the structural stability of the hard carbon negative electrode material, improve the initial Coulomb efficiency of the hard carbon negative electrode material, and reduce the specific surface area of the negative electrode material. The carbon coating layer being coated or formed on at least part of the surface of the hard carbon matrix means that the carbon coating layer can completely encapsulate the hard carbon matrix within the carbon coating layer, or it can also be that the carbon coating layer only coats a part of the outer surface of the hard carbon matrix; that is, the carbon coating layer can completely coat the hard carbon matrix, or can coat a part of the surface of the hard carbon matrix, preferably completely coat.

[0060] Setting a carbon coating layer on the surface of the hard carbon matrix can use the carbon coating layer to reduce the specific surface area, increase the mechanical strength and conductivity of the material, effectively slow down the structural degradation of the negative electrode material during the repeated sodiation / desodiation process, improve the structural stability of the negative electrode material, and improve the initial Coulomb efficiency of the negative electrode material.

[0061] In some specific embodiments, the preparation method of the hard carbon negative electrode material specifically includes the following steps (a) to (e):

[0062] Step (a): Perform pyrolysis treatment.

[0063] In some embodiments, in step (a), the raw material is subjected to low-temperature pyrolysis treatment to obtain a pretreated material; optionally, before the raw material is subjected to low-temperature pyrolysis treatment, the raw material is first cut into pieces so that the particle size is within a preset range.

[0064] Exemplarily, first cut raw materials such as wood pulp and / or bamboo pulp into pieces so that the particle size is within the range of 1 mm to 30 mm, which is convenient for subsequent processing and improves the utilization rate of the raw material. For example, the particle size can be 1 mm, 5 mm, 8 mm, 10 mm, 12 mm, 15 mm, 20 mm, 25 mm, 30 mm, etc., and of course it can also be other values within the above range, which are not limited here.

[0065] In some embodiments, in step (a), the raw material used may be wood pulp, or may be bamboo pulp, or may be a mixture of wood pulp and bamboo pulp; preferably, the raw material is wood pulp.

[0066] Optionally, wood pulp can be classified into softwood pulp and hardwood pulp according to beating characteristics. That is, the wood pulp in the present application can be softwood pulp, or can be hardwood pulp, or can be a combination of softwood pulp and hardwood pulp.

[0067] In some embodiments, softwood pulp includes, but is not limited to, any one or a combination of at least two of black pine pulp, Chinese red pine pulp, Chinese white pine pulp, Chinese pine pulp, Yunnan pine pulp, masson pine pulp, Chinese arborvitae pulp, spruce pulp, fir pulp or cedar pulp.

[0068] In some embodiments, hardwood pulp includes, but is not limited to, any one or a combination of at least two of camphorwood pulp, magnolia grandiflora pulp, nanmu pulp, castanopsis sclerophylla pulp, Chinese wingnut pulp, plane tree pulp, zelkova serrata pulp, paulownia pulp, sophora japonica pulp, ginkgo pulp or Chinese white poplar pulp.

[0069] By selecting the above several kinds of wood pulp, it has the advantages of low cost, wide source, easy access, natural environmental protection, etc.

[0070] In some embodiments, in step (a), the environmental atmosphere for pyrolysis treatment includes hydrogen (H2) or a mixed gas, and the mixed gas includes at least one of a mixed gas of hydrogen and argon (Ar), a mixed gas of hydrogen and nitrogen (N2), or a mixed gas of hydrogen and helium. As an example, the pyrolysis treatment can be carried out in an H2 atmosphere, or can be carried out in a mixed gas atmosphere of H2 and Ar, or can be carried out in a mixed gas atmosphere of H2 and N2.

[0071] Optionally, the volume fraction of hydrogen in the mixed gas is 5% - 10%; for example, the volume fraction of hydrogen in the mixed gas is 5%, 6%, 7%, 8%, 9%, 10%, etc. Of course, it can also be other values within the above range, which are not limited here.

[0072] In the present application, low-temperature pyrolysis uses a hydrogen atmosphere, which can reduce the oxygen-containing functional groups in the wood pulp precursor and reduce the influence of oxygen elements in the material on the hard carbon anode material; at the same time, after pyrolysis, a large number of small molecules escape, leaving a large number of pores inside the material, providing conditions for subsequent coating.

[0073] In some embodiments, in step (a), the pyrolysis temperature of the pyrolysis treatment is 200°C to 600°C; the pyrolysis time of the pyrolysis treatment is 0.5 h to 10 h; the heating rate of the pyrolysis treatment is 1°C / min to 5°C / min. As an example, the pyrolysis temperature can be 200°C, 300°C, 400°C, 500°C, 600°C, etc., and of course it can also be other values within the above range, which are not limited herein; the pyrolysis time can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, etc.; the heating rate can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, etc., and of course it can also be other values within the above range, which are not limited herein.

[0074] In some embodiments, in step (a), the concentration of oxygen in the atmosphere of the pyrolysis treatment is ≤100 ppm; as an example, the oxygen concentration during the pyrolysis process can be 90 ppm, 80 ppm, 70 ppm, 50 ppm or less than 50 ppm, etc.

[0075] By controlling conditions such as the pyrolysis temperature, time, and oxygen concentration during the above pyrolysis treatment, it is helpful to obtain a suitable pore structure. The small molecule gases escaping during or after the pyrolysis process will induce pores inside the hard carbon, which can further improve the electrochemical performance of the hard carbon anode material product.

[0076] Step (b): Perform purification treatment.

[0077] In some embodiments, in step (b), the pretreated material is sequentially subjected to pickling, water washing, and drying. Specifically, the purification treatment includes: subjecting the pretreated material obtained in step (a) to pickling purification in a reaction kettle to remove impurities in the material. After the pickled material is washed with water to neutrality, it is filtered and dried to obtain a purified material.

[0078] Optionally, in step (b), the acid in the pickling includes at least one of hydrochloric acid, nitric acid, hydrofluoric acid, or sulfuric acid.

[0079] Optionally, in step (b), the hydrogen ion (H + ) concentration of the acid in the pickling is 0.5 mol / L to 1.5 mol / L, for example, 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.5 mol / L, etc.

[0080] Optionally, in step (b), during the purification treatment, the solid content of the slurry in the purification reaction kettle is 20 - 40%, the temperature is controlled at 60 - 100°C, and the reaction time is controlled at 1 - 10 h.

[0081] In the above purification treatment, the specific operating conditions of water washing or drying can be carried out in a conventional manner, and the embodiments of the present application do not limit this.

[0082] Thus, through the above purification treatment steps, it can be used to remove impurity elements in the material, improve the purity of the material, and further facilitate the improvement of the electrochemical performance of the prepared hard carbon anode material.

[0083] Step (c): Perform comminution treatment.

[0084] In some embodiments, in step (c), the purified material obtained in step (b) is comminuted in a jet mill to obtain a comminuted material.

[0085] In this application, the comminution treatment adopts the method of jet milling. While reducing the particle size of the material, it can further homogenize the material, with good comminution effect, high efficiency, controllable particle size range, good dispersibility, and high energy utilization rate.

[0086] In some embodiments, in step (c), the gas source for jet milling includes compressed air, and the pressure of the compressed air is 0.2 MPa to 1.0 MPa. That is, the gas source of the jet mill is compressed air, and the pressure of this compressed air is 0.2 MPa to 1.0 MPa. For example, it can be 0.2 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.8 MPa, 1 MPa, etc.

[0087] In some embodiments, in step (c), the particle size D v 50 of the comminuted material ranges from 7 μm to 10 μm. As an example, the particle size D v 50 of the comminuted material is 7 μm, 8 μm, 9 μm, 10 μm, etc. Of course, it can also be other values within the above range, which are not limited here.

[0088] Optionally, the comminuted material is sieved through a 300 - 500 mesh sieve, preferably through a 300 - 400 mesh sieve, and the undersize is collected for the next process.

[0089] In this application, jet milling the purified material to obtain a comminuted material within a preset particle size range can make subsequent coating easier and more uniform. For example, by making the particle size D v 50 of the comminuted material range from 7 μm to 10 μm, within this particle size range, the size is appropriate, which is conducive to the exertion of the electrical properties of the material. If the particle size of the comminuted material is too small, the defects will increase, affecting the initial efficiency. If the particle size of the comminuted material is too large, the rate performance will be reduced.

[0090] Step (d): Perform coating treatment.

[0091] In some embodiments, in step (d), the comminuted material obtained in step (c) and the coating agent are coated in a fluidized bed reactor to obtain a coating material with a low specific surface area, that is, a carbonization precursor is obtained.

[0092] Specifically, this step (d) includes: spraying a coating agent solution into the fluidized bed reactor through the nozzle of the fluidized bed reactor, transporting the crushed material obtained in step (c) into the fluidized bed reactor by compressed gas, making the crushed material in a fluidized state, and mixing the coating agent in the coating agent solution with the fluidized crushed material in the fluidized bed reactor to obtain a carbonization precursor.

[0093] During the coating treatment using a fluidized bed reactor, the crushed material obtained in step (c) can be first transported into the fluidized bed reactor by compressed gas. Optionally, the compressed gas includes at least one of dried nitrogen, dried argon, or dried helium. Preferably, the compressed gas is selected from dried nitrogen or dried argon. Optionally, the flow rate of the compressed gas is 0.3 m / s to 5 m / s. For example, it can be 0.3 m / s, 0.5 m / s, 1 m / s, 1.5 m / s, 2 m / s, 3 m / s, 4 m / s, 5 m / s, etc. Preferably, the flow rate of the compressed gas is set in sections. For example, the flow rate of the compressed gas in the first stage is set at 1.5 m / s to 5 m / s. After all the crushed material enters the fluidized bed reactor, the flow rate of the compressed gas is adjusted to 0.3 m / s to 1.5 m / s to ensure that the crushed material is in a fluidized state. Then, the heating system of the fluidized bed reaction equipment is turned on to make the temperature in the fluidized bed reactor be at a certain value in the range of 100°C to 300°C. For example, the temperature of the mixture can be 100°C, 120°C, 150°C, 180°C, 200°C, 250°C, 300°C, etc. Of course, it can also be other values within the above range, which are not limited here. The heating preferably adopts the method of oil bath heating. The coating agent solution (solution containing the coating agent) is sprayed into the fluidized bed reactor through the nozzle. Optionally, the pressure at the nozzle (spray orifice) is 0.2 MPa to 2 MPa. For example, it can be 0.2 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.8 MPa, 1 MPa, 1.5 MPa, 2 MPa, etc. The reaction time between the above-mentioned crushed material and the coating agent in the fluidized bed reactor is 0.5 h to 2 h. For example, it can be 0.5 h, 0.8 h, 1 h, 1.5 h, 2 h, etc. After the reaction ends, the heating is stopped, and the coated material is collected through the material receiving port.

[0094] Thus, through the above-mentioned fluidized bed coating method, the surface properties of the hard carbon material can be effectively improved, and the coating effect can be enhanced.

[0095] Optionally, in step (d), the coating agent solution is a solution obtained by dissolving the coating agent in a solvent. The coating agent includes, but is not limited to, any one or at least two combinations of organic carbon sources such as pitch, glucose, phenolic resin, epoxy resin, or phenolic epoxy resin. Preferably, the coating agent is selected from one or more of pitch, glucose, or phenolic resin.

[0096] Optionally, in step (d), the coating ratio of the coating agent used is 2% to 20%, for example, it can be 2%, 5%, 8%, 10%, 15%, 18%, 20%, etc. Of course, it can also be other values within the above range, which are not limited here. The fluidized coating scheme can reduce the dosage of the coating agent.

[0097] Optionally, in step (d), the solvent in the coating agent solution includes, but is not limited to, any one or a combination of at least two of water, ethanol, tetrahydrofuran, N,N-dimethylformamide, n-hexane, xylene, carbon disulfide, or trichloroethylene.

[0098] The above solvents can select corresponding solvents according to different coating agents. As an example, when the coating agent is glucose, water can be used as the solvent, that is, glucose needs to be dissolved in water such as deionized water. When the coating agent is materials such as asphalt and phenolic resin, organic solvents can be used for dissolution, that is, materials such as asphalt and phenolic resin need to be dissolved in organic solvents, and the organic solvent can be one or more of alcohols, tetrahydrofuran, N,N-dimethylformamide, n-hexane, xylene, carbon disulfide, or trichloroethylene, etc.

[0099] In this application, a fluidized coating scheme is adopted. This fluidized coating makes the coated object in a fluidized state, ensuring sufficient contact between the coating agent and the coated object, ensuring the uniformity of coating, shortening the coating time, and also reducing the dosage of the coating agent. In addition, through fluidized coating, the specific surface area of the material can be reduced, the interface of the material can be improved, and the electrochemical stability of the material can be enhanced.

[0100] Step (e): Perform carbonization treatment.

[0101] In some embodiments, in step (e), the carbonization treatment includes a first carbonization stage and a second carbonization stage carried out in sequence; wherein the first carbonization stage is a medium-temperature carbonization stage, and the second carbonization stage is a high-temperature carbonization stage. As an example, the carbonization precursor obtained in step (d) is placed in a high-temperature carbonization furnace for carbonization, which is divided into medium-temperature pre-carbonization and high-temperature carbonization. After the medium-temperature carbonization is completed, it is directly heated to carry out high-temperature carbonization, and there is no need to discharge materials during the process, obtaining a hard carbon negative electrode for sodium-ion batteries, that is, obtaining a hard carbon negative electrode material.

[0102] The two-step carbonization in this carbonization process can improve the electrical properties of the hard carbon negative electrode material. The medium-temperature carbonization in the first carbonization stage can promote the growth and development of graphite microcrystals, laying a foundation for the formation of closed pores in the later high-temperature carbonization; the high-temperature carbonization in the second stage provides sufficient energy for the rearrangement of carbon atoms, which is beneficial to the insertion and extraction of sodium ions in the material, thus facilitating the improvement of the first Coulomb efficiency and capacity.

[0103] In some embodiments, in step (e), during the first carbonization stage, i.e., during medium-temperature carbonization, the carbonization atmosphere includes at least one of nitrogen, argon, or helium, preferably nitrogen and / or argon; the oxygen concentration in the carbonization atmosphere ≤ 100 ppm, for example, the oxygen concentration in this carbonization atmosphere can be 90 ppm, 80 ppm, 70 ppm, 50 ppm, or less than 50 ppm, etc.; the heating rate is 1 °C / min to 10 °C / min, the carbonization temperature is 600 °C to 900 °C, and the heat preservation time is 1 h to 10 h.

[0104] As an example, the carbonization temperature for medium-temperature carbonization can be 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, etc. Of course, it can also be other values within the above range, which are not limited herein; the carbonization time for medium-temperature carbonization can be 1 h, 2 h, 5 h, 6 h, 8 h, 10 h, etc. Of course, it can also be other values within the above range, which are not limited herein. The heating rate for medium-temperature carbonization is 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 8 °C / min, 10 °C / min, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0105] In some embodiments, in step (e), during the second carbonization stage, i.e., during high-temperature carbonization, the carbonization atmosphere includes at least one of nitrogen, argon, or helium, preferably nitrogen and / or argon; the oxygen concentration in the carbonization atmosphere ≤ 100 ppm, for example, the oxygen concentration in this carbonization atmosphere can be 90 ppm, 80 ppm, 70 ppm, 50 ppm, or less than 50 ppm, etc.; the heating rate is 1 °C / min to 10 °C / min, the carbonization temperature is 1000 °C to 1500 °C, and the heat preservation time is 1 h to 8 h.

[0106] As an example, the carbonization temperature for high-temperature carbonization can be 1000 °C, 1100 °C, 1200 °C, 1300 °C, 1400 °C, 1500 °C, etc. Of course, it can also be other values within the above range, which are not limited herein; the carbonization time for high-temperature carbonization can be 1 h, 2 h, 5 h, 6 h, 7 h, 8 h, etc. Of course, it can also be other values within the above range, which are not limited herein. The heating rate for high-temperature carbonization is 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 8 °C / min, 10 °C / min, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0107] By controlling conditions such as the temperature, time, and heating rate of medium-temperature carbonization and high-temperature carbonization in the preparation process of the above hard carbon negative electrode material, it helps to obtain a hard carbon negative electrode material with excellent performance, and can further improve the electrochemical performance of the hard carbon negative electrode material product.

[0108] In summary, the hard carbon anode material synthesized by the method of the present invention has the advantages of low defect concentration, high first Coulomb efficiency, and strong cycle stability.

[0109] In some embodiments, the present application provides a hard carbon anode material, which is prepared by using the preparation method of the aforementioned hard carbon anode material.

[0110] In the present application, the hard carbon anode material includes a hard carbon matrix and a carbon coating layer coated on the surface of the hard carbon matrix.

[0111] It should be understood that all the features and advantages described above for the "preparation method of hard carbon anode material" equally apply to the "hard carbon anode material", and will not be elaborated herein one by one.

[0112] In some embodiments, the particle size D v 50 of the hard carbon matrix ranges from 5 μm to 10 μm. As an example, the particle size D v 50 of the hard carbon matrix is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0113] By controlling the particle size of the hard carbon matrix within the above range, it is beneficial to make the structure of the prepared material more uniform and the performance more stable, which is more conducive to the long-term cycle stability of battery charge and discharge or more conducive to the comprehensive electrochemical performance of the battery.

[0114] In some embodiments, the thickness range of the carbon coating layer is 2 nm to 10 nm. Further, the thickness of the carbon coating layer is 3 nm to 9 nm. As an example, the thickness of the carbon coating layer can be any point value among 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm or the range value between any two of them.

[0115] In the present application, the thickness of the carbon coating layer can be adjusted according to the size of the inner hard carbon matrix. A suitable thickness of the carbon coating layer can not only ensure good processing performance of the anode material, but also avoid the excessive thickness of the carbon coating layer and excessive coating material, which may affect the timely release of active ions, the electrochemical performance of the battery core, or increase the cost. Or it can also avoid the too thin thickness of the carbon coating layer, which is not enough to effectively play the modification effect of the carbon coating layer, that is, it can avoid reducing the first efficiency of the material and the specific surface area of the material due to too thin thickness.

[0116] In some embodiments, the present application provides a battery, which includes a negative electrode sheet, and the negative electrode sheet includes the hard carbon anode material prepared by the preparation method of the aforementioned hard carbon anode material, or includes the aforementioned hard carbon anode material.

[0117] Since the negative electrode sheet in the battery includes the hard carbon negative electrode material provided by the embodiments of the present application, it can exhibit good electrochemical performance, such as a relatively high first charge-discharge capacity, excellent first Coulomb efficiency, and a relatively low surface defect concentration.

[0118] The above-mentioned battery can be a secondary battery or a primary battery, preferably a secondary battery. For example, the above-mentioned battery can be a sodium-ion battery, etc. The battery structure of the present application includes but is not limited to a soft-pack sodium-ion battery, a square hard-shell battery, a cylindrical hard-shell battery, etc.

[0119] In some embodiments, the above-mentioned battery further includes a positive electrode sheet, an electrolyte, and a separator. That is, the battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator.

[0120] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is provided on the two opposite surfaces of the negative electrode current collector. It can be understood that the negative electrode active material layer can also be laminated on any one of the two surfaces of the negative electrode current collector.

[0121] The present application places no particular limitation on the material of the negative electrode current collector, as long as the purpose of the present application can be achieved, and it can be selected according to actual needs. As an example, the negative electrode current collector can be made of metal materials such as aluminum, copper, nickel, stainless steel, nickel-plated steel, etc., or can be a foil material with a surface coating layer; or a composite current collector can also be used, and the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy on a polymer material substrate such as polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, etc.

[0122] In some embodiments, the negative electrode active material layer includes the hard carbon negative electrode material provided by the present application as described above. Further, the negative electrode active material layer may optionally further include a conductive agent. Further, the negative electrode active material layer may optionally further include a binder.

[0123] In the embodiments of the present application, there are no particular limitations on the types of conductive agents and binders in the negative electrode active material layer, as long as the objectives of the present application can be achieved. For example, the binder may include, but is not limited to, one or more of polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, styrene-butadiene copolymer (styrene-butadiene rubber), polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, or sodium hydroxymethyl cellulose. The conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, graphene, or conductive polymers. The above-mentioned conductive carbon black includes Ketjen black, acetylene black, etc., and the above-mentioned carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0124] The present application does not particularly limit the mass ratio of the hard carbon negative electrode material, conductive agent, and binder in the negative electrode active material layer. Those skilled in the art can select according to actual needs as long as the objectives of the present application can be achieved.

[0125] In the embodiments of the present application, in the battery, there are no limitations on the specific materials, structures, etc. of the positive electrode sheet, separator, and electrolyte. Components and structures known in the art that can be used in secondary batteries can be selected as long as the objectives of the present application can be achieved.

[0126] The battery of the present application further includes a packaging case for accommodating the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components known in the art in sodium ion batteries. The present application does not limit the above-mentioned other components. The present application has no particular limitations on the packaging case, and it can be a packaging case well-known in the art as long as the objectives of the present application can be achieved.

[0127] The present invention has no special limitations on the preparation method of the battery, and the technical solution of preparing a battery such as a secondary battery well-known to those skilled in the art can be adopted.

[0128] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation of the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For reagents or instruments not specified as to the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0129] Example 1

[0130] The preparation of the hard carbon negative electrode material includes the following steps:

[0131] (a)Weigh 1000 g of spruce wood pulp and cut it into pieces with a particle size of 30 mm. Then, place the spruce wood pulp pieces in a pre-carbonization furnace for low-temperature pyrolysis treatment. A mixed gas of hydrogen and argon is introduced, and the volume fraction of hydrogen in the mixed gas is 5%, and the oxygen concentration is 90 ppm. During the pyrolysis treatment, the heating rate is 5 °C / min, the pyrolysis temperature is 400 °C, and the holding time is 6 h to obtain a pre-treated material.

[0132] (b)Place the pre-treated material obtained after pyrolysis in a reaction kettle and carry out acid washing and purification with hydrochloric acid. The concentration of the acid H + is 1.5 mol / L, the solid content is 20%, the acid washing temperature is 100 °C, and the acid washing time is 2 h. After the acid-washed material is washed with water to neutrality, it is filtered and dried by suction to obtain a purified material.

[0133] (c)Add the obtained purified material to a jet mill for grinding. The gas source for jet grinding is compressed air, the pressure of the compressed gas is 0.6 MPa, and the ground material is sieved through a 300-mesh sieve, and the material under the sieve is collected; that is, a ground material is obtained, and the particle size D v 50 of the ground material is 9 μm.

[0134] (d)Add the obtained ground material to a fluidized bed reactor, and nitrogen is used as the carrier gas source. That is, the ground material is transported to the fluidized bed reactor through compressed nitrogen, and the flow rate of the compressed nitrogen is 1.5 m / s. After all the material to be coated (ground material) is brought into the fluidized bed reactor, the gas flow rate is adjusted to 0.8 m / s. Then, turn on the heating system of the fluidized bed reaction equipment, set the temperature in the fluidized bed reactor to 260 °C, and after the temperature is stable, select pitch as the coating agent. The pitch is dissolved in trichloroethylene, and the mass ratio of the pitch is 4% of the material to be coated (ground material). The coating agent solution is sprayed into the fluidized reactor through a nozzle, the pressure at the nozzle is 1.1 MPa, and the coating time is 0.5 h to obtain a carbonization precursor.

[0135] (e)Place the obtained carbonization precursor in a carbonization furnace for carbonization treatment. The oxygen concentration during the carbonization treatment is 50 ppm; the atmosphere during the carbonization treatment is a nitrogen atmosphere. The carbonization is divided into medium-temperature carbonization and high-temperature carbonization. The heating rate of medium-temperature carbonization is 5 °C / min, the medium-temperature carbonization temperature is 700 °C, and the holding time is 4 h; the heating rate of high-temperature carbonization is 3 °C / min, the high-temperature carbonization temperature is 1400 °C, and the holding time is 4 h. After the carbonization is completed, spruce wood pulp-derived hard carbon is obtained, that is, a hard carbon negative electrode material is obtained.

[0136] Example 2

[0137] The preparation of the hard carbon negative electrode material includes the following steps:

[0138] (a) Weigh 1500 g of camphor wood pulp and cut it into pieces with a particle size of 10 mm. Then, place the camphor wood pulp pieces in a pre-carbonization furnace for low-temperature pyrolysis treatment. Introduce a hydrogen atmosphere with an oxygen concentration of 60 ppm. During the pyrolysis treatment, the heating rate is 5 °C / min, the pyrolysis temperature is 500 °C, and the holding time is 5 h to obtain a pre-treated material.

[0139] (b) Place the pre-treated material obtained after pyrolysis in a reaction kettle and perform acid washing and purification using nitric acid. The concentration of the acid H + is 1.0 mol / L, the solid content is 20%, the acid washing temperature is 80 °C, and the acid washing time is 4 h. After the acid-washed material is washed with water to neutrality and then filtered and dried by suction, a purified material is obtained.

[0140] (c) Add the obtained purified material to a jet mill for pulverization. The gas pressure of the gas source for jet pulverization is 0.8 MPa. After pulverization, the material passes through a 300-mesh sieve, and the material under the sieve is collected; that is, a pulverized material is obtained, and the particle size D v 50 of the pulverized material is 8 μm.

[0141] (d) Add the obtained pulverized material to a fluidized bed reactor. Nitrogen is used as the carrier gas source. That is, the pulverized material is transported to the fluidized bed reactor by compressed nitrogen. The flow rate of the compressed nitrogen is 1.3 m / s. After all the material to be coated (pulverized material) is brought into the fluidized bed reactor, adjust the gas flow rate to 0.5 m / s. Then, turn on the heating system of the fluidized bed reaction equipment and set the temperature in the fluidized bed reactor to 200 °C. After the temperature is stable, select phenolic resin as the coating agent. The phenolic resin is dissolved in ethanol, and the mass ratio of the phenolic resin is 5% of the material to be coated (pulverized material). Spray the coating agent solution into the fluidized reactor through a nozzle. The pressure at the nozzle is 1.0 MPa, and the coating time is 1.5 h to obtain a carbonization precursor.

[0142] (e) Place the obtained carbonization precursor in a carbonization furnace for carbonization treatment. The oxygen concentration during the carbonization treatment is 40 ppm; the atmosphere during the carbonization treatment uses a nitrogen atmosphere. Carbonization is divided into medium-temperature carbonization and high-temperature carbonization. The heating rate of medium-temperature carbonization is 5 °C / min, the medium-temperature carbonization temperature is 800 °C, and the holding time is 6 h; the heating rate of high-temperature carbonization is 3 °C / min, the high-temperature carbonization temperature is 1300 °C, and the holding time is 4 h. After carbonization is completed, camphor wood pulp-derived hard carbon is obtained, that is, a hard carbon negative electrode material is obtained.

[0143] Example 3

[0144] Preparation of the hard carbon negative electrode material includes the following steps:

[0145] (a)Weigh 600 g of cedar wood pulp and cut it into pieces with a particle size of 15 mm; then, place the cedar wood pulp pieces in a pre-carbonization furnace for low-temperature pyrolysis treatment. Introduce a hydrogen atmosphere with an oxygen concentration of 85 ppm. During the pyrolysis treatment, the heating rate is 3 °C / min, the pyrolysis temperature is 600 °C, and the holding time is 4 h to obtain a pre-treated material.

[0146] (b)Place the pre-treated material obtained after pyrolysis in a reaction kettle and carry out acid washing and purification with nitric acid. The concentration of the acid H + is 1.2 mol / L, the solid content is 30%, the acid washing temperature is 60 °C, and the acid washing time is 6 h. After the acid-washed material is washed with water to neutrality, it is filtered by suction and dried to obtain a purified material.

[0147] (c)Add the obtained purified material to a jet mill for pulverization. The gas source for jet pulverization is compressed air, the pressure of the compressed gas is 0.5 MPa, and the pulverized material is passed through a 300-mesh sieve, and the material under the sieve is collected; that is, a pulverized material is obtained, and the particle size D v 50 of the pulverized material is 10 μm.

[0148] (d)Add the obtained pulverized material to a fluidized bed reactor, and nitrogen is used as the carrier gas source. That is, the pulverized material is transported to the fluidized bed reactor by compressed nitrogen. The flow rate of the compressed nitrogen is 3.0 m / s. After all the material to be coated (pulverized material) is brought into the fluidized bed reactor, the gas flow rate is adjusted to 0.7 m / s; then, turn on the heating system of the fluidized bed reaction equipment, set the temperature in the fluidized bed reactor to 180 °C. After the temperature is stable, select glucose as the coating agent. Glucose is dissolved in deionized water, and the mass ratio of glucose is 10% of the material to be coated (pulverized material). The coating agent solution is sprayed into the fluidized reactor through a nozzle, the pressure at the nozzle is 0.7 MPa, and the coating time is 2 h to obtain a carbonization precursor.

[0149] (e)Place the obtained carbonization precursor in a carbonization furnace for carbonization treatment. The oxygen concentration during the carbonization treatment is 30 ppm; the atmosphere during the carbonization treatment uses a nitrogen atmosphere. Carbonization is divided into medium-temperature carbonization and high-temperature carbonization. The heating rate of medium-temperature carbonization is 5 °C / min, the medium-temperature carbonization temperature is 700 °C, and the holding time is 6 h; the heating rate of high-temperature carbonization is 2 °C / min, the high-temperature carbonization temperature is 1500 °C, and the holding time is 4 h. After carbonization, cedar wood pulp-derived hard carbon is obtained, that is, a hard carbon negative electrode material is obtained.

[0150] Example 4

[0151] The preparation of the hard carbon negative electrode material in Example 4 was carried out according to the preparation method of Example 1 above, with the only difference being that:

[0152] In step (a), 1000 g of spruce wood pulp was weighed and cut into pieces with a particle size of 30 mm. Then, the spruce wood pulp pieces were placed in a pre-carbonization furnace for low-temperature pyrolysis treatment. A mixed gas of hydrogen and argon was introduced, and the volume fraction of hydrogen in the mixed gas was 8%, and the oxygen concentration was 60 ppm. During the pyrolysis treatment, the heating rate was 3 °C / min, the pyrolysis temperature was 200 °C, and the holding time was 10 h to obtain a pretreated material.

[0153] Example 5

[0154] The preparation of the hard carbon negative electrode material of Example 5 was carried out according to the preparation method of Example 1 above, with the only difference being that:

[0155] In step (a), 1000 g of spruce wood pulp was weighed and cut into pieces with a particle size of 30 mm. Then, the spruce wood pulp pieces were placed in a pre-carbonization furnace for low-temperature pyrolysis treatment. A mixed gas of hydrogen and nitrogen was introduced, and the volume fraction of hydrogen in the mixed gas was 10%, and the oxygen concentration was 80 ppm. During the pyrolysis treatment, the heating rate was 4 °C / min, the pyrolysis temperature was 600 °C, and the holding time was 4 h to obtain a pretreated material.

[0156] Example 6

[0157] The preparation of the hard carbon negative electrode material of Example 6 was carried out according to the preparation method of Example 1 above, with the only difference being that:

[0158] In step (d), the obtained crushed material was added to a fluidized bed reactor, and nitrogen was used as the carrier gas source. That is, the crushed material was transported to the fluidized bed reactor by compressed nitrogen, and the flow rate of the compressed nitrogen was 2.5 m / s. After all the material to be coated (crushed material) was brought into the fluidized bed reactor, the gas flow rate was adjusted to 0.5 m / s. Then, the heating system of the fluidized bed reaction equipment was turned on, and the temperature in the fluidized bed reactor was set to 120 °C. After the temperature was stabilized, pitch was selected as the coating agent. The pitch was dissolved in trichloroethylene, and the mass ratio of the pitch was 10% of the material to be coated (crushed material). The coating agent solution was sprayed into the fluidized reactor through a nozzle, the pressure at the nozzle was 0.8 MPa, and the coating time was 1 h to obtain a carbonization precursor.

[0159] Example 7

[0160] The preparation of the hard carbon negative electrode material of Example 7 was carried out according to the preparation method of Example 1 above, with the only difference being that:

[0161] In step (d), the obtained crushed material is added to a fluidized bed reactor, and nitrogen is used as the carrier gas source. That is, the crushed material is transported to the fluidized bed reactor by compressed nitrogen. The flow rate of the compressed nitrogen is 3.5 m / s. After all the material to be coated (crushed material) is carried into the fluidized bed reactor, the gas flow rate is adjusted to 1.2 m / s. Then, the heating system of the fluidized bed reaction equipment is turned on, and the temperature in the fluidized bed reactor is set to 300 °C. After the temperature is stabilized, asphalt is selected as the coating agent. The asphalt is dissolved in trichloroethylene, and the mass ratio of the asphalt is 18% of the material to be coated (crushed material). The coating agent solution is sprayed into the fluidized reactor through a nozzle. The pressure at the nozzle is 1.6 MPa, and the coating time is 2 h to obtain a carbonization precursor.

[0162] Example 8

[0163] The preparation of the hard carbon anode material of Example 8 was carried out according to the preparation method of Example 1 above, with the only difference being that:

[0164] In step (e), the obtained carbonization precursor is placed in a carbonization furnace for carbonization treatment. The oxygen concentration during the carbonization treatment is 55 ppm; the atmosphere during the carbonization treatment is a nitrogen atmosphere. The carbonization is divided into medium-temperature carbonization and high-temperature carbonization. The heating rate of medium-temperature carbonization is 8 °C / min, the medium-temperature carbonization temperature is 600 °C, and the holding time is 8 h; the heating rate of high-temperature carbonization is 6 °C / min, the high-temperature carbonization temperature is 1000 °C, and the holding time is 6 h. After the carbonization is completed, spruce pulp-derived hard carbon is obtained, that is, the hard carbon anode material is obtained.

[0165] Example 9

[0166] The preparation of the hard carbon anode material of Example 9 was carried out according to the preparation method of Example 1 above, with the only difference being that:

[0167] In step (e), the obtained carbonization precursor is placed in a carbonization furnace for carbonization treatment. The oxygen concentration during the carbonization treatment is 60 ppm; the atmosphere during the carbonization treatment is a nitrogen atmosphere. The carbonization is divided into medium-temperature carbonization and high-temperature carbonization. The heating rate of medium-temperature carbonization is 3 °C / min, the medium-temperature carbonization temperature is 900 °C, and the holding time is 3 h; the heating rate of high-temperature carbonization is 3 °C / min, the high-temperature carbonization temperature is 1500 °C, and the holding time is 2 h. After the carbonization is completed, spruce pulp-derived hard carbon is obtained, that is, the hard carbon anode material is obtained.

[0168] Comparative Example 1

[0169] The preparation of the hard carbon anode material includes the following steps:

[0170] (a)Weigh 1000 g of spruce wood pulp and cut it into pieces with a particle size of 30 mm. Then, place the spruce wood pulp pieces in a pre-carbonization furnace for low-temperature pyrolysis treatment. Introduce a mixture of hydrogen and argon, with the volume fraction of hydrogen in the mixture being 5% and the oxygen concentration being 90 ppm. During the pyrolysis treatment, the heating rate is 5 °C / min, the pyrolysis temperature is 400 °C, and the holding time is 6 h to obtain a pre-treated material.

[0171] (b)Place the pre-treated material obtained after pyrolysis in a reaction kettle and carry out acid washing and purification with hydrochloric acid. The concentration of the acid H + is 1.5 mol / L, the solid content is 20%, the acid washing temperature is 100 °C, and the acid washing time is 2 h. After the acid-washed material is washed with water to neutrality and then filtered and dried by suction, a purified material is obtained.

[0172] (c)Add the obtained purified material to a jet mill for pulverization. The gas source for jet pulverization is compressed air, the pressure of the compressed gas is 0.6 MPa, and the pulverized material passes through a 300-mesh sieve. Collect the material under the sieve; that is, a pulverized material is obtained, and the particle size D v 50 of the pulverized material is 9 μm.

[0173] (d)Place the obtained pulverized material in a carbonization furnace for carbonization treatment. The oxygen concentration during the carbonization treatment is 50 ppm; the atmosphere during the carbonization treatment uses a nitrogen atmosphere. The carbonization is divided into medium-temperature carbonization and high-temperature carbonization. The heating rate for medium-temperature carbonization is 5 °C / min, the medium-temperature carbonization temperature is 700 °C, and the holding time is 4 h; the heating rate for high-temperature carbonization is 3 °C / min, the high-temperature carbonization temperature is 1400 °C, and the holding time is 4 h. After the carbonization is completed, spruce wood pulp-derived hard carbon is obtained, that is, a hard carbon negative electrode material is obtained.

[0174] The main difference between Comparative Example 1 and Example 1 is that Comparative Example 1 omits the fluidized coating step, that is, the obtained material is spruce wood pulp-derived hard carbon without a carbon coating layer.

[0175] Comparative Example 2

[0176] The preparation of the hard carbon negative electrode material includes the following steps:

[0177] (a)Weigh 1000 g of spruce wood pulp and cut it into pieces with a particle size of 30 mm. Then, place the spruce wood pulp pieces in a pre-carbonization furnace for low-temperature pyrolysis treatment. Introduce a mixture of hydrogen and argon, with the volume fraction of hydrogen in the mixture being 5% and the oxygen concentration being 90 ppm. During the pyrolysis treatment, the heating rate is 5 °C / min, the pyrolysis temperature is 400 °C, and the holding time is 6 h to obtain a pre-treated material.

[0178] (b)Place the pre-treated material obtained after pyrolysis in a reaction kettle and carry out acid washing and purification with hydrochloric acid. The concentration of the acid H +The concentration is 1.5 mol / L, the solid content is 20%, the pickling temperature is 100 °C, and the pickling time is 2 h. The pickled material is washed with water until neutral and then filtered by suction and dried to obtain the purified material.

[0179] (c) Add the obtained purified material to a jet mill for comminution. The gas source for jet milling is compressed air, the pressure of the compressed gas is 0.6 MPa, and the comminuted material is sieved through a 300-mesh sieve, and the material under the sieve is collected; that is, the comminuted material is obtained, and the particle size D v 50 of the comminuted material is 9 μm.

[0180] (d) Carry out solid-solid mixing of the obtained comminuted material and the coating agent asphalt; wherein, the mass of asphalt is 4% of the mass of the comminuted material; after adding 50% of the mass of the comminuted material to be coated into the high-speed mixer cavity, then add asphalt into the high-speed mixer cavity, and finally add the remaining comminuted material to be coated into the cavity; the high-speed mixer is first stirred at 200 rpm for 15 min, and then stirred at 800 rpm for 90 min. After the stirring is completed, the coating is completed, and the carbonization precursor is obtained after discharging.

[0181] (e) Place the obtained carbonization precursor in a carbonization furnace for carbonization treatment. The oxygen concentration during the carbonization treatment is 50 ppm; the atmosphere during the carbonization treatment is a nitrogen atmosphere. The carbonization is divided into medium-temperature carbonization and high-temperature carbonization. The heating rate of medium-temperature carbonization is 5 °C / min, the medium-temperature carbonization temperature is 700 °C, and the holding time is 4 h; the heating rate of high-temperature carbonization is 3 °C / min, the high-temperature carbonization temperature is 1400 °C, and the holding time is 4 h. After the carbonization is completed, cloud spruce pulp-derived hard carbon is obtained, that is, the hard carbon negative electrode material is obtained.

[0182] The main difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, a conventional coating method is adopted during the coating treatment, that is, the fluidized coating method is not adopted.

[0183] Comparative Example 3

[0184] The preparation of the hard carbon negative electrode material includes the following steps:

[0185] (a) Weigh 1000 g of cloud spruce pulp, cut it into pieces with a particle size of 30 mm to obtain the pretreated material.

[0186] (b) Place the pretreated material in a reaction kettle and carry out pickling and purification with hydrochloric acid. The H + concentration of the acid is 1.5 mol / L, the solid content is 20%, the pickling temperature is 100 °C, and the pickling time is 2 h. The pickled material is washed with water until neutral and then filtered by suction and dried to obtain the purified material.

[0187] (c) The obtained purified material was added to a jet mill for pulverization. However, during the pulverization, it was found that due to the omission of the low-temperature pyrolysis step, the hardness of the wood pulp was poor, similar to the state of cotton, and it was difficult to break it into small particle sizes. Foaming occurred during the crushing process, resulting in the inability to complete the pulverization and obtain the material with the required particle size.

[0188] Steps (d) to (e) are the same as those in Example 1.

[0189] The main difference between Comparative Example 3 and Example 1 is that Comparative Example 3 omitted the low-temperature pyrolysis treatment step, resulting in the inability to smoothly complete the jet pulverization and obtain the material with the required particle size.

[0190] Comparative Example 4

[0191] Preparation of the hard carbon negative electrode material includes the following steps:

[0192] (a) Weigh 1000 g of spruce wood pulp and cut it into pieces with a particle size of 30 mm; then, place the spruce wood pulp pieces in a pre-carbonization furnace for low-temperature pyrolysis treatment. The atmosphere for low-temperature pyrolysis is nitrogen, the oxygen concentration is 90 ppm. During the pyrolysis treatment, the heating rate is 5 °C / min, the pyrolysis temperature is 400 °C, and the holding time is 6 h to obtain the pretreatment material.

[0193] Steps (b) to (e) are the same as those in Example 1.

[0194] The main difference between Comparative Example 4 and Example 1 is that hydrogen was not introduced during the low-temperature pyrolysis treatment step in Comparative Example 4.

[0195] Comparative Example 5

[0196] The preparation of the hard carbon negative electrode material in Comparative Example 5 was carried out according to the preparation method of Example 1 above, with the only difference being:

[0197] In step (e), the obtained carbonization precursor was placed in a carbonization furnace for carbonization treatment. The oxygen concentration during the carbonization treatment was 60 ppm; the atmosphere during the carbonization treatment was a nitrogen atmosphere, the heating rate was 3 °C / min, the high-temperature carbonization temperature was 1400 °C, and the holding time was 4 h.

[0198] The main difference between Comparative Example 5 and Example 1 is that Comparative Example 5 used one-step carbonization in the carbonization treatment step.

[0199] Test Example

[0200] 1. Preparation of sodium-ion batteries

[0201] (1) The hard carbon negative electrode materials prepared in the above examples and comparative examples were used as the negative electrode active materials, acetylene black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder.

[0202] Mix the negative electrode active material, conductive agent, and binder in a mass ratio of 91.6:1.8:6.6 to obtain a mixed material. Stir the mixed material evenly in N-methylpyrrolidone (NMP) to obtain the corresponding negative electrode slurry. Uniformly coat the negative electrode slurry on the negative electrode current collector copper foil, and after processes such as drying (drying in an oven at 110°C for 4 h) and pressing, obtain a negative electrode sheet.

[0203] (2)Provide a sodium metal foil as the counter electrode.

[0204] (3)Provide an electrolyte, which is prepared by dissolving 1.0 mol / L of NaPF6 in an organic solvent composed of ethylene carbonate (EC) + dimethyl carbonate (DMC) + fluoroethylene carbonate (FEC) (the volume ratio of EC, DMC, and FEC is 4.5:4.5:1).

[0205] (4)Assemble in the order of the negative electrode sheet, separator, and sodium metal foil, and infiltrate them with the electrolyte respectively, and assemble a button cell in a glove box filled with an argon atmosphere.

[0206] 2. Perform performance tests on the above hard carbon negative electrode material and battery

[0207] (1)Specific surface area test: Perform specific surface area tests on the hard carbon negative electrode materials prepared in the above examples and comparative examples, and use the nitrogen isothermal adsorption and desorption test method to test the specific surface area of the materials. For example, under the action of pressure, nitrogen performs reversible physical adsorption with the porous material. By measuring the change amount of the adsorbate and the relative pressure before and after adsorption, and then using the multi-molecular layer adsorption model (the equation model of the multi-molecular layer adsorption theory proposed by Brunauer, Emmet, and Teller), calculate the specific surface area of the sample to be tested.

[0208] (2)First discharge capacity, first charge capacity, and Coulomb efficiency test: Under the constant temperature condition of 25°C, perform constant current discharge at a rate of 0.1C to 0V, and record the discharge capacity at this time as the first-cycle (first) discharge capacity; continue to charge at a constant current of 0.1C to 2V, and record the charge capacity at this time as the first-cycle (first) charge capacity, and record the charge capacity at this time as the first-cycle (first) charge capacity; the first Coulomb efficiency = first-cycle charge specific capacity / first-cycle discharge specific capacity * 100%.

[0209] (3)Capacity retention rate (cycling performance) test: Under the constant temperature condition of 25 °C, discharge at a constant current density of 1C to 0V, and then charge at a constant current of 1C to 2V. This is a complete charge-discharge cycle, denoted as 1 cycle. Repeat this process until the number of cycles equals 200 cycles, then end the test and record the charging capacity of the 200th cycle. Then, the capacity retention rate of the 200th cycle = charging capacity of the 200th cycle / charging capacity of the 1st cycle * 100%.

[0210] The test results are shown in Table 1 below.

[0211] Table 1

[0212]

[0213] As can be seen from Table 1, compared with Comparative Examples 1-5, the coin-type half-cells prepared with the hard carbon negative electrode materials provided in Examples 1-9 all have relatively high initial discharge capacities, the first inventory efficiency exceeds 90%, and the cycling capacity retention rate of the battery is improved.

[0214] Through the analysis and comparison of Example 1 with Comparative Example 1 and Comparative Example 2, it can be known that without using the fluidized coating method, the coating effect and coating uniformity are reduced. Benefiting from the uniform fluidized coating of Example 1 of the present invention, the specific surface area of the material after fluidized coating is the smallest, and the first Coulomb efficiency of the prepared hard carbon negative electrode material is higher, and it has more excellent cycling performance.

[0215] Through the analysis and comparison of Example 1 with Comparative Example 3, it can be known that Comparative Example 3 omits the low-temperature pyrolysis step, so the hardness of the wood pulp is poor and it is difficult to break it into small particle sizes. It will foam during the crushing process, similar to the state of cotton, being too soft to smoothly complete the jet milling, that is, the jet milling cannot achieve the crushing effect and the required particle size of the substance cannot be obtained, which affects the subsequent coating treatment, increases the specific surface area of the material, and reduces the first efficiency and cycling performance. This shows that through the low-temperature pyrolysis step, the hardness of the wood pulp can be increased, the crushing process can be effectively completed, and the influence of oxygen elements in the material on the hard carbon negative electrode material can be reduced; at the same time, after the pyrolysis ends, a large number of small molecules escape, leaving a large number of pores inside the material, providing conditions for the subsequent coating. And, through the analysis and comparison of Example 1 with Comparative Example 4, it can be known that if hydrogen is not introduced during the low-temperature pyrolysis process of Comparative Example 4, the oxygen-containing functional groups in the wood pulp raw material cannot be reduced; while Example 1 uses a hydrogen atmosphere during the low-temperature pyrolysis process, which can reduce the oxygen-containing functional groups in the wood pulp precursor, and the reduction of oxygen-containing functional groups can improve the first Coulomb efficiency of the material and improve the cycling performance.

[0216] Through the analysis and comparison of Example 1 and Comparative Example 5, it can be seen that two-step carbonization is adopted in Example 1, and the medium-temperature carbonization therein promotes the growth and development of graphite microcrystals, laying a foundation for the formation of closed pores during the subsequent high-temperature carbonization. Therefore, the first charging capacity and the first Coulombic efficiency of Example 1 are higher, and the cycle capacity retention rate is also improved.

[0217] In addition, Figure 1 Figure 5 shows the scanning electron microscope image of the hard carbon negative electrode material (spruce pulp-derived hard carbon negative electrode material) prepared in Example 1 of the present invention. It can be seen from Figure 1 it that the material retains the tubular structure of the fiber. After fluidized bed coating, the voids of the material are reduced and the defects are decreased.

[0218] Figure 2 Figure 6 shows the charge-discharge curve of the hard carbon negative electrode material (spruce pulp-derived hard carbon negative electrode material) prepared in Example 1 of the present invention. It can be seen from Figure 2 it that under the charge-discharge condition of 0.1C, the first-cycle discharge specific capacity is 323.8 mAh / g, the first-cycle charge specific capacity is 300.2 mAh / g, and the first Coulombic efficiency is 92.7%. This shows that the spruce pulp-based hard carbon negative electrode material prepared in Example 1 has a high reversible capacity and a high first efficiency.

[0219] Figure 3 Figure 7 shows the XRD pattern of the hard carbon negative electrode material (spruce pulp-derived hard carbon negative electrode material) prepared in Example 1 of the present invention. It can be seen from Figure 3 it that the full width at half maximum of the diffraction peak (002) is relatively large and the angle is relatively small, indicating that the material has a high degree of disorder and a large interlayer spacing, which is suitable for the insertion and extraction of sodium ions within the carbon layer.

[0220] The parts not detailed in the present invention are well-known technologies to those skilled in the art.

[0221] The basic principles of the present invention have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, advantages, effects, etc. mentioned in the present invention are only examples and not limitations. It cannot be considered that these advantages, advantages, effects, etc. are essential for each embodiment of the present invention. In addition, the above-disclosed specific details are only for the purpose of illustration and easy understanding, rather than limitations. The above details do not limit the present invention to necessarily adopt the above specific details to implement.

[0222] It should be noted that the term "and / or" or " / " used herein is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. The singular forms "a", "the" and "said" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0223] In the specific embodiments and claims, a list of items connected by terms such as "at least one of", "at least a", "at least a kind of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0224] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a hard carbon negative electrode material, characterized in that, The method includes: Performing pyrolysis treatment on raw materials to obtain a pretreated material; the raw materials include wood pulp and / or bamboo pulp, and the ambient atmosphere of the pyrolysis treatment includes hydrogen; Successively performing purification treatment and pulverization treatment on the pretreated material to obtain a pulverized material; Mixing the fluidized pulverized material with a fluidized coating agent to obtain a carbonization precursor; specifically obtaining the carbonization precursor includes: spraying a coating agent solution into a fluidized bed reactor through a nozzle of the fluidized bed reactor, and conveying the pulverized material into the fluidized bed reactor through compressed gas to make the pulverized material in a fluidized state, and mixing the coating agent in the coating agent solution with the fluidized pulverized material in the fluidized bed reactor to obtain the carbonization precursor; Performing carbonization treatment on the carbonization precursor, and the carbonization treatment includes a first carbonization stage and a second carbonization stage performed successively; during the first carbonization stage, the carbonization temperature is 600°C to 900°C, and the heat preservation time is 1h to 10h; during the second carbonization stage, the carbonization temperature is 1000°C to 1500°C, and the heat preservation time is 1h to 8h; obtaining the hard carbon negative electrode material.

2. The preparation method of the hard carbon negative electrode material according to claim 1, characterized in that, The pyrolysis treatment satisfies at least one of the following characteristics (1) to (5): (1) The ambient atmosphere of the pyrolysis treatment includes hydrogen or a mixed gas, and the mixed gas includes at least one of a mixed gas of hydrogen and argon, a mixed gas of hydrogen and nitrogen, or a mixed gas of hydrogen and helium, and the volume ratio of hydrogen in the mixed gas is 5% to 10%; (2) The concentration of oxygen in the atmosphere of the pyrolysis treatment ≤ 100 ppm; (3) The heating rate of the pyrolysis treatment is 1°C / min to 5°C / min; (4) The pyrolysis temperature of the pyrolysis treatment is 200°C to 600°C; (5) The pyrolysis time of the pyrolysis treatment is 0.5h to 10h.

3. The preparation method of the hard carbon negative electrode material according to claim 1, wherein The particle size range of the raw materials is 1mm to 30mm; and / or, The wood pulp includes softwood pulp and / or hardwood pulp; The softwood pulp includes at least one of black pine pulp, Chinese pine pulp, Korean pine pulp, Chinese white pine pulp, Yunnan pine pulp, masson pine pulp, Platycladus orientalis pulp, spruce pulp, fir pulp or cedar pulp; The hardwood pulp includes at least one of camphorwood pulp, magnolia grandiflora pulp, nanmu pulp, castanopsis sclerophylla pulp, Chinese wingnut pulp, plane tree pulp, zelkova serrata pulp, paulownia pulp, sophora japonica pulp, ginkgo pulp or populus tomentosa pulp.

4. The preparation method of the hard carbon negative electrode material according to claim 1, characterized in that, The purification treatment includes: successively performing pickling, water washing and drying on the pretreated material; and / or, The pulverization treatment adopts the method of air flow pulverization.

5. The preparation method of the hard carbon negative electrode material according to claim 4, characterized in that The acid in the pickling includes at least one of hydrochloric acid, nitric acid, hydrofluoric acid or sulfuric acid; and / or, The hydrogen ion concentration of the acid in the pickling is 0.5mol / L to 1.5mol / L; and / or, The gas source of the air flow pulverization includes compressed air, and the pressure of the compressed air is 0.2MPa to 1.0MPa; and / or, The particle size D of the crushed material v is in the range of 7 μm to 10 μm for 50.

6. The preparation method of the hard carbon negative electrode material according to claim 1, characterized in that, The step of obtaining the carbonization precursor satisfies at least one of the following characteristics (1) to (7): (1) The coating agent in the coating agent solution includes at least one of asphalt, glucose, phenolic resin, epoxy resin, or phenolic epoxy resin; (2) The solvent in the coating agent solution includes at least one of water, ethanol, tetrahydrofuran, N,N-dimethylformamide, n-hexane, xylene, carbon disulfide, or trichloroethylene; (3) The compressed gas includes at least one of dry nitrogen, argon, or helium; (4) The flow rate of the compressed gas is 0.3 m / s to 5 m / s; (5) The pressure of the nozzle is 0.2 MPa to 2 MPa; (6) The temperature of the mixing is 100 °C to 300 °C; (7) The time of the mixing is 0.5 h to 2 h.

7. The preparation method of the hard carbon negative electrode material according to any one of claims 1 to 6, characterized in that, During the first carbonization stage, the carbonization atmosphere includes at least one of nitrogen, argon, or helium, the concentration of oxygen in the carbonization atmosphere is ≤ 100 ppm, and the heating rate is 1 °C / min to 10 °C / min; and / or, During the second carbonization stage, the carbonization atmosphere includes at least one of nitrogen, argon, or helium, the concentration of oxygen in the carbonization atmosphere is ≤ 100 ppm, and the heating rate is 1 °C / min to 10 °C / min.

8. A hard carbon negative electrode material, characterized in that, The hard carbon negative electrode material is prepared by the preparation method of the hard carbon negative electrode material according to any one of claims 1 to 7; The hard carbon negative electrode material includes a hard carbon matrix and a carbon coating layer coated on the surface of the hard carbon matrix.

9. A battery, comprising a negative electrode sheet, characterized in that, The negative electrode sheet includes the hard carbon negative electrode material prepared by the preparation method of the hard carbon negative electrode material according to any one of claims 1 to 7, or includes the hard carbon negative electrode material according to claim 8.

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