Preparation method and application of coal-based hard carbon negative electrode material

Abstract

The application provides a preparation method and application of a coal-based hard carbon negative material and belongs to the technical field of battery materials. The preparation method of the coal-based hard carbon negative material comprises the following steps: firstly, raw coal and graphene slurry are mixed, then water heat reaction is carried out, and then low-temperature carbonization treatment is carried out to obtain a coal-based aerogel; then, macropore filling and micropore filling are sequentially carried out; and then, high-temperature carbonization treatment is carried out to obtain the coal-based hard carbon negative material. In the application, the graphene slurry is used to wrap coal particles in the forming process, the efficiency of electron transmission between the coal particles is improved, macropores and micropores of the aerogel are filled, the pores of the aerogel are effectively filled, a dense carbon layer structure is formed on the surface of the coal-based hard carbon, the conductivity of the coal-based hard carbon is further increased, the true density property of the coal-based hard carbon is improved, and the obtained coal-based hard carbon negative material has excellent electrical conductivity and kinetic property, and the application potential of a secondary battery prepared from the coal-based hard carbon negative material is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a preparation method and application of a coal-based hard carbon negative material. BACKGROUND

[0002] With the rapid development of modern electronic devices, electric vehicles and energy storage systems, the demand for high-performance batteries is increasing. Lithium-ion batteries and sodium-ion batteries, as two mainstream secondary batteries, their performance is largely determined by the electrode material. The characteristics of the negative electrode material have a crucial influence on the key performance indicators of the battery, such as capacity, cycle life, charge and discharge efficiency, etc. In this context, exploring new and efficient negative electrode materials has become one of the hotspots in the field of battery research.

[0003] Traditional negative electrode materials, such as graphite, although to some extent meet the basic needs of the battery, but also have some obvious limitations. For example, the theoretical specific capacity of graphite is relatively limited, which is difficult to meet the requirements of high energy density batteries. Moreover, in the process of large current charging and discharging, graphite is prone to structural collapse and other problems, resulting in the shortening of the cycle life of the battery. These limitations prompt researchers to seek new negative electrode materials with higher specific capacity and better cycle stability.

[0004] Hard carbon materials have shown great potential in the field of battery negative electrode materials due to their unique structure and performance. Hard carbon has a disordered microstructure, which can provide more active sites, thus being beneficial to ion storage and transmission. Compared with traditional graphite materials, hard carbon usually has higher specific capacity and can maintain good structural stability during the cycle process. Based on these advantages, the preparation and optimization of hard carbon materials have become a key research direction.

[0005] Common hard carbon materials include biomass hard carbon and resin-based hard carbon. Compared with biomass hard carbon and resin-based hard carbon, coal-based hard carbon is less studied, but its coal raw material has abundant reserves and stable source, and the prepared hard carbon material has the characteristics of low cost and high compaction, which is a promising negative electrode material. Therefore, coal-based hard carbon negative material shows high capacity in lithium-ion batteries and sodium-ion batteries, and has high application potential.

[0006] However, for coal-based hard carbon, its poor electrical conductivity due to its "card house" and porous structure seriously affects its dynamics, and its complex functional group types and condensed aromatic structure make its electrical conductivity lack obvious.

[0007] Therefore, it is urgent to design a preparation method of coal-based hard carbon negative material to solve the problem of poor electrical conductivity of coal-based hard carbon, so as to improve the dynamics of coal-based hard carbon and obtain a secondary battery with excellent performance. SUMMARY

[0008] In view of the deficiencies of the prior art, the present application aims to provide a preparation method and application of a coal-based hard carbon negative material with high conductivity and kinetic properties.

[0009] One of the purposes of the present application is to provide a preparation method of a coal-based hard carbon negative material, comprising the following steps:

[0010] First, the raw coal and graphene slurry are mixed, then subjected to a hydrothermal reaction, and then subjected to a low-temperature carbonization treatment to obtain a coal-based aerogel;

[0011] Then, macropore filling and micropore filling are sequentially performed, macropore filling is performed using a water-soluble resin, and micropore filling is performed using a deposition gas;

[0012] Then, a high-temperature carbonization treatment is performed to obtain the coal-based hard carbon negative material;

[0013] Preferably, the raw coal is a powdered raw coal.

[0014] Preferably, the graphene slurry comprises an oxidized graphene slurry, and the concentration of the graphene slurry is 10-50 mg / mL.

[0015] Preferably, the weight ratio of the raw coal to the graphene slurry is (1-5):10.

[0016] Preferably, the preparation method further comprises a step of subjecting the raw coal to a crushing treatment, and the fine powder particulate coal with a particle size D50 of 4-10 pm is obtained after the crushing treatment, and then mixed with the graphene slurry.

[0017] Preferably, the reaction temperature of the hydrothermal reaction is 150-250 DEG C, and the reaction time is 2-12 h.

[0018] Preferably, the temperature of the low-temperature carbonization treatment is 550-650 DEG C, and the reaction time is 2-5 h.

[0019] Preferably, the method of macropore filling comprises:

[0020] The coal-based aerogel and the water-soluble resin are mixed, then subjected to a macropore impregnation filling treatment to obtain an impregnated coal-based aerogel.

[0021] Preferably, the concentration of the water-soluble resin is 100-500 g / L.

[0022] Preferably, the weight ratio of the coal-based aerogel to the water-soluble resin is (1-10):100.

[0023] Preferably, the temperature of the macropore impregnation filling treatment is 100-200℃, and the pressure is 0.1-2MPa.

[0024] Preferably, the water-soluble resin comprises one or several of carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, polyurethane resin, acrylic resin or alkyd resin.

[0025] Preferably, the micropore filling method comprises:

[0026] The macropore impregnation filling treatment is followed by a micropore filling treatment of the impregnated coal-based aerogel by chemical vapor deposition to obtain a deposited coal-based aerogel.

[0027] Preferably, the deposition gas comprises methane and / or acetylene.

[0028] Preferably, the flow rate of the deposition gas is 100-500mL / min.

[0029] Preferably, the temperature of the micropore filling treatment is 650-850℃, and the time is 2-5h.

[0030] Preferably, the preparation method further comprises a step of crushing the deposited coal-based aerogel to obtain a coal-based hard carbon precursor with a particle size D50 of 4-7μm.

[0031] Preferably, the temperature of the high-temperature carbonization treatment is 1200-1600℃, and the holding time is 1-10h.

[0032] Preferably, the high-temperature carbonization treatment is carried out in an inert atmosphere.

[0033] The second object of the present application is to provide a use of the coal-based hard carbon negative electrode material obtained by the preparation method as described above in the preparation of a secondary battery.

[0034] The beneficial effects of the present application include:

[0035] In the present application, the mixture of raw coal and graphene slurry is first subjected to a hydrothermal reaction, and the graphene slurry forms on the surface of the coal particles during the hydrothermal reaction and wraps the coal particles. On the one hand, it can hinder the agglomeration of the coal particles and facilitate the uniform dispersion of the coal particles; on the other hand, this wrapping effect can improve the contact between the coal particles and provide a better path for subsequent electron transmission, which can greatly improve the rate of electron transmission between particles; thirdly, the hydrothermal reaction can also promote the adjustment of part of the internal structure of the coal particles and the preliminary carbonization, laying a foundation for subsequent treatment. Then, a low-temperature carbonization treatment is carried out to remove volatile substances in the material, which is conducive to improving the stability of the material and making the material preliminarily form a carbonization structure to obtain a coal-based aerogel with high porosity and low density, which provides a good carrier for subsequent filling treatment.

[0036] Then, the coal-based aerogel is sequentially subjected to macropore filling and micropore filling, effectively filling the pores of the aerogel. Macropore filling is used to fill the larger pores in the coal-based aerogel, which is conducive to increasing the true density and structural stability of the material and reducing the adverse effects of pores on the performance of the material; micropore filling can further refine the pore structure of the material, increase the specific surface area and active sites of the material, and improve the storage capacity of the material for lithium ions and sodium ions and the like. At the same time, macropore filling and micropore filling are also conducive to the formation of a dense carbon layer structure on the pore surface, further increasing the electrical conductivity of the coal-based hard carbon and improving the true density properties of the coal-based hard carbon, and improving the overall performance of the material.

[0037] Then, high-temperature carbonization treatment is performed to further carbonize and crystallize the material, and the components are better combined together to form a more uniform and stable structure.

[0038] The coal-based hard carbon negative electrode material prepared based on this method has a "card house" structure, excellent electrical conductivity and kinetic properties, and improves the application potential of the prepared secondary battery in the fields of passenger cars, energy storage, 3C, etc. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The preparation process flow chart of the coal-based hard carbon negative electrode material provided for Example 1 is shown.

[0040] Figure 2 The micro-morphology diagram of the hard carbon finished product is shown. DETAILED DESCRIPTION

[0041] In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed implementations. However, one skilled in the relevant arts will recognize that implementations can be practiced without one or more of the specific details, or with other methods, components, materials, etc.

[0042] Unless otherwise required by context, the words "including" and "comprising" are to be construed as open-ended, i.e., to the effect that "including but not limited to." Also, the term "coupled" is to be construed in accordance with standard terms of use, i.e., it is permissive and not exclusive.

[0043] References in the specification to "one embodiment" or "an embodiment" or "a preferred embodiment" or "some embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrases "in one embodiment" or "in an embodiment" or "in a preferred embodiment" or "in some embodiments" in various places in the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0044] According to a first aspect of the present invention, a method for preparing a coal-based hard carbon anode material is provided, the method comprising the following steps:

[0045] First, raw coal and graphene slurry are mixed and subjected to hydrothermal reaction, followed by low-temperature carbonization to obtain coal-based aerogel.

[0046] Then, macropore filling and micropore filling were performed sequentially, with water-soluble resin used for macropore filling and deposition gas used for micropore filling.

[0047] Then, high-temperature carbonization is performed to obtain the coal-based hard carbon anode material;

[0048] The raw coal is in powder form.

[0049] In this invention, raw coal and graphene slurry are used. The raw coal serves as the carbon source, giving the resulting anode material a house-of-cards structure. The graphene slurry exhibits high conductivity; its unique two-dimensional structure and excellent electron transport properties contribute to the good conductivity of the final anode material. During the hydrothermal reaction, the graphene slurry, due to its molding characteristics under hydrothermal conditions, can encapsulate coal particles. This encapsulation structure, on the one hand, restricts the agglomeration of coal particles, maintaining a small particle size and good dispersibility in subsequent processing; on the other hand, this encapsulation improves the contact between coal particles, providing a better path for subsequent electron transport and significantly increasing the electron transport rate between particles; thirdly, the unique two-dimensional structure of graphene can form a good interfacial bond with the raw coal, providing protection and support for the coal particles, which is beneficial for forming a structurally stable coal-based aerogel during low-temperature carbonization, allowing the coal-based aerogel to maintain high porosity and low density.

[0050] In this invention, since coal-based aerogels contain a large number of pores, including macropores and micropores, the presence of these pores can easily lead to structural instability or even collapse during subsequent processing. Therefore, this invention employs macropore-filling and micropore-filling techniques to effectively fill the pores in the aerogel. By filling the macropores, the overall structure of the coal-based aerogel becomes more stable, preventing structural collapse due to external forces or temperature changes during subsequent processing. This increases the true density and structural stability of the material, reducing the adverse effects of pores on material properties. Micropore-filling further refines the material's structure, increases its specific surface area and active sites, and improves its storage capacity for lithium ions or sodium ions. Simultaneously, macropore-filling and micropore-filling also facilitate the formation of a dense carbon layer structure on the pore surface, further increasing the conductivity of the coal-based hard carbon and enhancing its true density properties, thereby improving the overall performance of the material.

[0051] In the present application, high-temperature carbonization treatment is performed to further carbonize and crystallize the material, and the components are better combined together to form a more uniform and stable structure.

[0052] The coal-based hard carbon negative electrode material prepared based on the method has a "card house" structure, excellent electrical conductivity and kinetic properties, and improves the application potential of the prepared secondary battery in the fields of passenger cars, energy storage, 3C, etc.

[0053] In a preferred embodiment of the present application, the graphene slurry comprises graphene oxide slurry.

[0054] In the present application, the graphene oxide in the graphene oxide slurry is a curved sheet structure, and a large number of oxygen-containing functional groups are contained on the sheet layer. The oxygen-containing functional groups on the surface of the graphene oxide can form chemical bonding effects such as hydrogen bonds and covalent bonds with the surface of the coal particles, as well as physical adsorption effects such as van der Waals forces, and the graphene oxide can better wrap the coal particles to form a stable composite structure and improve the electron transport efficiency between the particles. During the hydrothermal reaction process, the oxygen-containing functional groups of the graphene oxide can react with the active sites on the surface of the coal particles to promote the interaction between them, and can adjust the pore structure, specific surface area and electrical conductivity of the negative electrode material, and improve the performance stability of the negative electrode material.

[0055] In addition, the graphene oxide has good hydrophilicity and can be more easily dispersed in the hydrothermal reaction system, which is more conducive to fully mixing with the coal particles. Uniform mixing is crucial for preparing high-performance negative electrode materials, which can ensure that each coal particle can be effectively combined with the graphene oxide, so that the performance of the final material is more uniform and consistent.

[0056] In the subsequent carbonization process, the good dispersibility of the graphene oxide also helps to form a more uniform carbon structure and improve the electrical conductivity and mechanical properties of the material. The graphene oxide can also promote the transformation of the carbon structure in the coal particles to a more ordered graphite structure, improving the electrical conductivity and cycle stability of the material.

[0057] In the present application, the raw coal comprises any one or a combination of at least two of anthracite, lean coal, lean coal, coking coal, fat coal, gas coal, weakly caking coal, non-caking coal, long-flame coal or lignite.

[0058] In a preferred embodiment of the present application, the raw coal is long-flame coal.

[0059] In the present application, the long flame coal has lower aromaticity and more branched structure, contains more aliphatic structure and unsaturated bond, forms abundant active sites, is more conducive to reaction with other molecules or groups in the process of forming cross-linked structure and hard carbon structure, promotes the formation and development of structure, and forms abundant pore structure and high specific surface area of hard carbon.

[0060] Specifically, the raw coal and the graphene slurry are stirred and mixed, the stirring and mixing speed is 100-500 rpm, for example, 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm, or a point value between any two of the above; the stirring and mixing time is 2-5 h, for example, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, or a point value between any two of the above.

[0061] Preferably, the concentration of the graphene slurry is 10-50 mg / mL, for example, 10 mg / mL, 15 mg / mL, 20 mg / mL, 25 mg / mL, 30 mg / mL, 35 mg / mL, 40 mg / mL, 45 mg / mL or 50 mg / mL, or a point value between any two of the above.

[0062] Preferably, the solvent of the graphene slurry includes water or a mixture of water and ethanol.

[0063] In the present application, if the concentration of the graphene slurry is too low, it may lead to incomplete wrapping of the coal particles, and it is difficult for the graphene to be effectively formed with the coal raw material when the graphene is formed, and it is difficult to form a good conductive network, greatly reducing the efficiency of electron transport between particles and particles; if the concentration of the graphene slurry is too high, the dispersion ability of the coal raw material in the graphene becomes poor, and a large number of coal particle agglomerates appear, which will lead to that the graphene cannot uniformly wrap the coal particles when mixed with the raw coal, and excessive graphene accumulation may occur locally, while the graphene content in other areas is insufficient, affecting the uniformity and performance stability of the material.

[0064] Preferably, the weight ratio of the raw coal and the graphene slurry is (1-5):10, for example, 1:10, 1.5:10, 2:10, 2.5:10, 3:10, 3.5:10, 4:10, 4.5:10 or 5:10, or a point value between any two of the above.

[0065] In the present application, if the weight ratio of the raw coal and the graphene slurry is too small, i.e. the amount of the graphene slurry is too much, the hard carbon formed is mainly graphene-based, which affects the initial efficiency and reversible capacity of the hard carbon, and may also make the structure of the material too loose, which is prone to collapse in the subsequent processing process, affecting the stability and mechanical properties of the material. In addition, although graphene has high electrical conductivity, excessive graphene may lead to too complex electronic transmission path, thereby reducing the electrical conductivity of the material; it may also affect the embedding and extraction of sodium ions and lithium ions in the material, reducing the charge and discharge performance of the battery.

[0066] If the weight ratio of the raw coal and the graphene slurry is too large, i.e. the amount of the graphene slurry is too small, the amount of coal particles is too much, which affects the grafting behavior between graphenes, making it difficult to form the long-flame coal-based aerogel, which on the one hand is prone to cause the electronic transmission rate to be not obviously improved, and on the other hand is prone to cause defects in the structure of the material, affecting the kinetic performance thereof.

[0067] Preferably, the preparation method further comprises a step of crushing the raw coal, and the fine powder particle coal with a particle size D50 of 4-10 μm, for example 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, and a point value between any two of the above, is obtained after the crushing treatment, and then mixed with the graphene slurry.

[0068] In the present application, the fine powder particle coal with a small particle size is beneficial to the subsequent mixing with the graphene slurry and the reaction, thereby increasing the contact area and the reaction activity.

[0069] In a preferred embodiment of the present application, the reaction temperature of the hydrothermal reaction is 150-250℃.

[0070] In the present application, if the temperature of the hydrothermal reaction is too low, the grafting reaction conditions between the graphene oxides cannot be reached, so that the long-flame coal-based aerogel cannot be formed; if the temperature of the hydrothermal reaction is too high, the long-flame coal-based aerogel after forming will hydrolyze at high temperature.

[0071] In the present application, if the temperature of the hydrothermal reaction is too low, the interaction between the raw coal and the graphene slurry is weakened, the wrapping process becomes slow or even difficult to proceed, it is difficult to form a good composite structure, and the structure reorganization of the coal particles and the carbonization process are also limited, which is easy to lead to the inhomogeneous structure of the coal-based aerogel; if the temperature of the hydrothermal reaction is too high, on the one hand, the coal-based aerogel is prone to hydrolysis, which makes the combination between the graphenes poor, and on the other hand, the reaction is too violent, it is difficult to accurately control the reaction process, which may lead to the inhomogeneous structure of the product, local overheating, excessive carbonization and other problems, and too high temperature may also damage the structure of the coal particles and the graphene oxide, which is easy to make them lose their original performance advantages. Therefore, the reaction temperature of the hydrothermal reaction is 150-250℃, for example, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃ or 250℃, or a point value between any two of the above.

[0072] Preferably, the hydrothermal reaction time is 2-12h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h, or a point value between any two of the above.

[0073] In a preferred embodiment of the present application, the temperature of the low-temperature carbonization treatment is 550-650℃, for example, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃ or 650℃, and a point value between any two of the above.

[0074] In the present application, low-temperature carbonization can remove some volatile substances, open the pores of the aerogel, and help the subsequent liquid-phase impregnation macropore filling and gas-phase deposition micropore filling behaviors. At the same time, low-temperature carbonization can also make the material preliminarily form a carbonized structure, improve the stability of the material, and obtain a coal-based aerogel. If the temperature of the low-temperature carbonization treatment is too low, the carbonization may not be sufficient, the volatile substances in the raw material cannot be fully removed, and the structure formed at low temperature is relatively loose, the stability of the material cannot be effectively improved, the coal-based aerogel cannot be smoothly converted into an intermediate product with a preliminary carbonized structure, the structure formed at low temperature is relatively loose, and the pore structure may not be regular enough to provide a good foundation for the subsequent macropore filling and micropore filling. If the temperature of the low-temperature carbonization treatment is too high, it may lead to excessive carbonization, some beneficial components in the material are destroyed, and the pore structure collapses, the specific surface area decreases. At the same time, excessive carbonization may also make the material too hard to be processed subsequently.

[0075] Preferably, the reaction time of the low-temperature carbonization treatment is 2-5h, for example, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, and a point value between any two of the above.

[0076] In a preferred embodiment of the present application, the method for filling the macropores comprises:

[0077] After mixing the coal-based aerogel and the water-soluble resin, a macropore impregnation filling treatment is performed to obtain an impregnated coal-based aerogel.

[0078] In the present application, the purpose of the macropore filling is to fill the through macropores formed in the aerogel and increase the true density of the formed hard carbon. The macropore refers to a pore with a pore size > 50 nm.

[0079] In the present application, the water-soluble resin has good fluidity and wettability, which is beneficial to the filling in the macropores. After the resin is solidified in the macropores, it can prevent the structure of the aerogel from collapsing due to external force or temperature change during subsequent processing, providing a more uniform and stable basis for the micropore filling treatment, so that the subsequent micropore filling process can be carried out more uniformly.

[0080] Preferably, the water-soluble resin comprises one or more of carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, polyurethane resin, acrylic resin or alkyd resin.

[0081] Preferably, the concentration of the water-soluble resin is 100-500 g / L, for example 100 g / L, 200 g / L, 300 g / L, 400 g / L or 500 g / L, and any point value between any two of the above.

[0082] Preferably, the weight ratio of the coal-based aerogel to the water-soluble resin is (1-10):100, for example 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100 or 10:100, and any point value between any two of the above.

[0083] In the present application, if the weight ratio of the coal-based aerogel to the water-soluble resin is too small, too much resin in the subsequent processing process can make the structure of the material too dense, and the porosity is reduced too much, which can affect the transmission and storage of lithium ions and sodium ions, and reduce the electrochemical performance of the material. If the weight ratio of the coal-based aerogel to the water-soluble resin is too large, the impregnation effect of the water-soluble resin is poor, the internal penetration effect of the coal-based aerogel is poor, which can lead to insufficient filling, and it is difficult to effectively fill the macropores of the coal-based aerogel. It is difficult to form a good composite structure, which affects the pore structure and electrochemical performance of the material.

[0084] Preferably, the temperature of the macropore impregnation filling treatment is 100-200℃, for example 100℃, 120℃, 140℃, 160℃, 180℃ or 200℃, and any point value between any two of the above.

[0085] Preferably, the pressure of the macropore impregnation filling treatment is 0.1-2 MPa, for example 0.1 MPa, 0.5 MPa, 1 MPa, 1.5 MPa or 2 MPa, and a point value between any two of the above.

[0086] In the present application, the macropore impregnation filling treatment is carried out at a temperature of 100-200℃ and a pressure of 0.1-2 MPa, which helps to promote the flowability and wettability of the water-soluble resin, fully wets the pore walls of the coal-based aerogel, and helps the water-soluble resin to enter the interior of the coal-based aerogel, thereby achieving more uniform and sufficient filling.

[0087] In a preferred embodiment of the present application, the method for micropore filling comprises:

[0088] The impregnated coal-based aerogel is subjected to micropore filling treatment by chemical vapor deposition (CVD method), to obtain a deposited coal-based aerogel.

[0089] In the present application, the purpose of micropore filling is to fill pores that cannot be filled by water-soluble resin and form closed pore sites for filling active sodium ions. Among them, micropore refers to pores with a pore size ≤2 nm.

[0090] In the present application, by depositing carbon atoms in the micropores, the size of the micropores becomes more uniform and the porosity decreases. On the one hand, this helps to increase the specific surface area and the number of active sites of the material. On the other hand, the deposited carbon atoms form a continuous carbon network in the micropores, further improving the electrical conductivity of the material. Thirdly, it is also conducive to the formation of a dense carbon layer structure on the surface of the coal-based hard carbon, which not only increases the electrical conductivity of the coal-based hard carbon, but also improves its true density properties.

[0091] Preferably, in the chemical vapor deposition method, the deposition gas comprises methane and / or acetylene.

[0092] Preferably, the flow rate of the deposition gas is 100-500 mL / min, for example 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min or 500 mL / min, and a point value between any two of the above.

[0093] Preferably, the temperature of the micropore filling treatment is 650-850℃, for example 650℃, 700℃, 750℃, 800℃ or 850℃, and a point value between any two of the above; the time of the micropore treatment is 2-5 h, for example 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, and a point value between any two of the above.

[0094] In the present application, if the temperature of the micropore filling treatment is too low, it is difficult for the deposited gas to fully decompose and form effective filling in the micropores, which may result in insufficient filling. In addition, the filling structure formed at low temperature may not be stable enough, and during subsequent processing such as high-temperature carbonization treatment, these unstable filling structures may change or be damaged, affecting the overall performance and stability of the material.

[0095] If the temperature of the micropore filling treatment is too high, the reaction of the deposited gas may be too intense, making it difficult to accurately control the reaction process, which may result in uneven filling, overfilling, or local overheating, etc., easily affecting the skeletal structure properties of the coal-based aerogel, affecting the pore structure and performance of the material. Too high a temperature may also affect the interaction between the deposited gas and the aerogel, resulting in instability of the filling structure.

[0096] In a preferred embodiment of the present application, the preparation method further comprises a step of crushing the deposited coal-based aerogel, and after the crushing treatment, a coal-based hard carbon precursor with a particle size D50 of 4-7 μm is obtained, for example 4 μm, 5 μm, 6 μm or 7 μm, and any point value between any two of the above.

[0097] In the present application, after the macropore filling and micropore filling treatments, the deposited coal-based aerogel obtained may have a large size or uneven particle distribution. By crushing treatment, it is adjusted to a particle with a particle size D50 of 4-7 μm, which is more conducive to subsequent high-temperature carbonization treatment, so that the material can be heated and reacted more uniformly during high-temperature treatment.

[0098] Specifically, the parameters for crushing the deposited coal-based aerogel include: a screw feeding frequency of 20-30 Hz, for example 20 Hz, 22 Hz, 24 Hz, 26 Hz, 28 Hz or 30 Hz, and any point value between any two of the above; a classifier frequency of 60-80 Hz, for example 60 Hz, 65 Hz, 70 Hz, 75 Hz or 80 Hz, and any point value between any two of the above; and an induced draft fan frequency of 40-50 Hz, for example 40 Hz, 42 Hz, 44 Hz, 46 Hz, 48 Hz or 50 Hz, and any point value between any two of the above.

[0099] In a preferred embodiment of the present application, the temperature of the high-temperature carbonization treatment is 1200-1600℃, for example 1200℃, 1300℃, 1400℃, 1500℃ or 1600℃, and any point value between any two of the above.

[0100] Preferably, the holding time of the high-temperature carbonization treatment is 1-10 h, for example 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, and any point value between any two of the above.

[0101] Preferably, the high-temperature carbonization process is carried out in an inert atmosphere, such as nitrogen or argon.

[0102] Preferably, the high-temperature carbonization process has a heating rate of 1-10℃ / min, such as 1℃ / min, 3℃ / min, 5℃ / min, 7℃ / min, or 9℃ / min, and any point value between any two of the above.

[0103] In the present application, a heating rate of 1-10℃ / min is advantageous for uniform heating of the material throughout the heating process, and is advantageous for structural stability and pore adjustment.

[0104] Preferably, the preparation method comprises the following steps:

[0105] (1) The raw coal is crushed to obtain fine powder particles with a particle size D50 of 4-10μm, then mixed with graphene oxide slurry with a concentration of 10-50mg / mL by stirring, then subjected to a hydrothermal reaction at 150-250℃ for 2-12h, and then subjected to a low-temperature carbonization process at 550-650℃ for 2-5h to obtain a coal-based aerogel;

[0106] wherein the weight ratio of raw coal to graphene slurry is (1-5):10, the stirring speed is 100-500rpm, and the stirring time is 2-5h;

[0107] (2) The coal-based aerogel is placed in an impregnation kettle, a water-soluble resin with a concentration of 100-500g / L is added, and a macroporous impregnation filling process is carried out at 100-200℃ and 0.1-2MPa to obtain an impregnated coal-based aerogel; then the impregnated coal-based aerogel is placed in a CVD device, a deposition gas with a flow rate of 100-500mL / min is introduced, and a microporous filling process is carried out at 650-850℃ for 2-5h to obtain a deposited coal-based aerogel; then the deposited coal-based aerogel is subjected to a crushing process to obtain a coal-based hard carbon precursor with a particle size D50 of 4-7μm;

[0108] wherein the weight ratio of coal-based aerogel to water-soluble resin is (1-10):100, and the specific parameters of the crushing process include a screw feed frequency of 20-30Hz, a classifier frequency of 60-80Hz, and an induced draft fan frequency of 40-50Hz;

[0109] (3) The coal-based hard carbon precursor is subjected to a high-temperature carbonization process in an inert atmosphere at a heating rate of 1-10℃ / min to a temperature of 1200-1600℃, and the holding time is 1-10h to obtain the coal-based hard carbon negative electrode material.

[0110] According to a second aspect of the present application, there is provided an application of the coal-based hard carbon negative material prepared by the preparation method of the first aspect in the preparation of a secondary battery.

[0111] Preferably, the secondary battery comprises a lithium ion battery or a sodium ion battery.

[0112] Embodiments

[0113] The present application will be further described in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the related application, and are not a limitation of the application. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0114] In the following embodiments, each raw material component is a commercially available product unless otherwise specified.

[0115] Embodiment 1

[0116] The present embodiment provides a preparation method of a coal-based hard carbon negative material, and a preparation process flow chart of the coal-based hard carbon negative material is as shown in Figure 1 The preparation method comprises the following steps:

[0117] (1) The raw coal is crushed to obtain fine powder particle coal with a particle size D50 of 7 μm, and then mixed with graphene oxide slurry with a concentration of 30 mg / mL by stirring, and then subjected to a hydrothermal reaction at 200 ℃ for 7 h, and then subjected to a low-temperature carbonization treatment at 600 ℃ for 3 h to obtain a coal-based aerogel;

[0118] The raw coal is long flame coal, the solvent of the graphene oxide slurry is water, the weight ratio of the raw coal and the graphene oxide slurry is 3:10, the stirring speed is 300 rpm, and the stirring time is 3 h.

[0119] (2) The coal-based aerogel is placed in an impregnation kettle, a water-soluble resin with a concentration of 300 g / L is added, and subjected to a macropore impregnation filling treatment at 150 ℃ and 1 MPa to obtain an impregnated coal-based aerogel; then the impregnated coal-based aerogel is placed in a CVD device, methane with a flow rate of 300 mL / min is introduced, and subjected to a micropore filling treatment at a temperature of 750 ℃ for 3 h to obtain a deposited coal-based aerogel; and then the deposited coal-based aerogel is subjected to a crushing treatment to obtain a coal-based hard carbon precursor with a particle size D50 of 5 μm;

[0120] The water-soluble resin is a carboxymethyl cellulose aqueous solution with a concentration of 300 g / L, the weight ratio of the coal-based aerogel to the water-soluble resin is 5:100, and the specific parameters of the crushing treatment include a screw feeding frequency of 25 Hz, a classifier frequency of 70 Hz, and an induced draft fan frequency of 45 Hz.

[0121] (3) After being heated to 1400℃ at a heating rate of 5℃ / min in an inert atmosphere, the coal-based hard carbon precursor is subjected to high-temperature carbonization treatment, and the holding time is 5h, to obtain the coal-based hard carbon negative electrode material.

[0122] Example 2

[0123] The present embodiment provides a preparation method of a coal-based hard carbon negative electrode material, which comprises the following steps:

[0124] (1) The raw coal is crushed to obtain fine powder particle coal with a particle size D50 of 8μm, then mixed with graphene oxide slurry with a concentration of 10mg / mL by stirring, then subjected to hydrothermal reaction at 150℃ for 12h, and then subjected to low-temperature carbonization treatment at 550℃ for 2h to obtain coal-based aerogel.

[0125] The raw coal is lean coal, the solvent of the graphene oxide slurry is water, the weight ratio of the raw coal to the graphene oxide slurry is 1:10, the stirring speed is 100rpm, and the stirring time is 2h.

[0126] (2) The coal-based aerogel is placed in an impregnation kettle, water-soluble resin with a concentration of 100g / L is added, and macropore impregnation filling treatment is carried out at 100℃ and 1MPa to obtain impregnated coal-based aerogel; then the impregnated coal-based aerogel is placed in a CVD device, methane with a flow rate of 100mL / min is introduced, and micropore filling treatment is carried out at 650℃ for 5h to obtain deposited coal-based aerogel; then the deposited coal-based aerogel is subjected to crushing treatment to obtain coal-based hard carbon precursor with a particle size D50 of 4μm.

[0127] The water-soluble resin is a carboxymethyl cellulose aqueous solution with a concentration of 100g / L, the weight ratio of the coal-based aerogel to the water-soluble resin is 1:100, and the specific parameters of the crushing treatment include a screw feeding frequency of 20Hz, a classifier frequency of 60Hz, and an induced draft fan frequency of 40Hz.

[0128] (3) After being heated to 1200℃ at a heating rate of 5℃ / min in an inert atmosphere, the coal-based hard carbon precursor is subjected to high-temperature carbonization treatment, and the holding time is 10h, to obtain the coal-based hard carbon negative electrode material.

[0129] Example 3

[0130] The embodiment provides a preparation method of a coal-based hard carbon negative material, and the preparation method comprises the following steps:

[0131] (1) crushing raw coal to obtain fine powder particle coal with a particle size D50 of 10 μm, then stirring and mixing the fine powder particle coal with graphene oxide slurry with a concentration of 50 mg / mL, then performing hydrothermal reaction at 250 DEG C for 2 h, and then performing low-temperature carbonization treatment at 650 DEG C for 5 h to obtain coal-based aerogel;

[0132] In the embodiment, the raw coal is coking coal, the solvent of the graphene oxide slurry is water, the weight ratio of the raw coal to the graphene oxide slurry is 5:10, the stirring and mixing is performed at a rotating speed of 500 rpm for 5 h.

[0133] (2) placing the coal-based aerogel into an impregnation kettle, adding water-soluble resin with a concentration of 500 g / L, and performing macropore impregnation filling treatment at 200 DEG C and 2 MPa to obtain impregnated coal-based aerogel; then placing the impregnated coal-based aerogel in a CVD device, introducing methane with a flow rate of 500 mL / min, and performing micropore filling treatment at 850 DEG C for 2 h to obtain deposited coal-based aerogel; and then performing crushing treatment on the deposited coal-based aerogel to obtain coal-based hard carbon precursor with a particle size D50 of 7 μm;

[0134] In the embodiment, the water-soluble resin is carboxymethyl cellulose aqueous solution with a concentration of 500 g / L, the weight ratio of the coal-based aerogel to the water-soluble resin is 10:100, and the specific parameters of the crushing treatment include a screw feeding frequency of 30 Hz, a classifier frequency of 80 Hz, and an induced draft fan frequency of 50 Hz.

[0135] (3) performing high-temperature carbonization treatment on the coal-based hard carbon precursor in an inert atmosphere at a temperature rising rate of 5 DEG C / min to 1600 DEG C, and keeping the temperature for 1 h to obtain the coal-based hard carbon negative material.

[0136] Embodiment 4

[0137] In the embodiment, the concentration of the graphene oxide slurry is 5 mg / mL.

[0138] The other steps are the same as those in Embodiment 1.

[0139] Embodiment 5

[0140] In the embodiment, the concentration of the graphene oxide slurry is 55 mg / mL.

[0141] The other steps are the same as those in Embodiment 1.

[0142] Embodiment 6

[0143] In this embodiment, the concentration of the graphene oxide slurry is 10 mg / mL.

[0144] The same as Embodiment 1.

[0145] Embodiment 7

[0146] In this embodiment, the concentration of the graphene oxide slurry is 50 mg / mL.

[0147] The same as Embodiment 1.

[0148] Embodiment 8

[0149] In this embodiment, the weight ratio of the raw coal and the graphene oxide slurry is 1:15.

[0150] The same as Embodiment 1.

[0151] Embodiment 9

[0152] In this embodiment, the weight ratio of the raw coal and the graphene oxide slurry is 6:10.

[0153] The same as Embodiment 1.

[0154] Embodiment 10

[0155] In this embodiment, the weight ratio of the raw coal and the graphene oxide slurry is 1:10.

[0156] The same as Embodiment 1.

[0157] Embodiment 11

[0158] In this embodiment, the weight ratio of the raw coal and the graphene oxide slurry is 5:10.

[0159] The same as Embodiment 1.

[0160] Embodiment 12

[0161] In this embodiment, the temperature of the hydrothermal reaction is 100°C.

[0162] The same as Embodiment 1.

[0163] Embodiment 13

[0164] In this embodiment, the temperature of the hydrothermal reaction is 300°C.

[0165] The same as Embodiment 1.

[0166] Embodiment 14

[0167] In this embodiment, the temperature of the hydrothermal reaction is 150°C.

[0168] The same as Embodiment 1.

[0169] Example 15

[0170] In this example, the temperature of the hydrothermal reaction is 250°C.

[0171] The same as Example 1.

[0172] Example 16

[0173] In this example, the weight ratio of the coal-based aerogel and the water-soluble resin is 0.5:100.

[0174] The same as Example 1.

[0175] Example 17

[0176] In this example, the weight ratio of the coal-based aerogel and the water-soluble resin is 15:100.

[0177] The same as Example 1.

[0178] Example 18

[0179] In this example, the weight ratio of the coal-based aerogel and the water-soluble resin is 1:100.

[0180] The same as Example 1.

[0181] Example 19

[0182] In this example, the weight ratio of the coal-based aerogel and the water-soluble resin is 10:100.

[0183] The same as Example 1.

[0184] Example 20

[0185] In this example, the temperature of the micropore filling treatment is 600°C.

[0186] The same as Example 1.

[0187] Example 21

[0188] In this example, the temperature of the micropore filling treatment is 900°C.

[0189] The same as Example 1.

[0190] Example 22

[0191] In this example, the temperature of the micropore filling treatment is 650°C.

[0192] The same as Example 1.

[0193] Example 23

[0194] In this embodiment, the temperature of the micropore filling treatment is 800°C.

[0195] Other than Example 1.

[0196] Example 24

[0197] In this embodiment, the graphene slurry is a non-oxidized graphene slurry.

[0198] Other than Example 1.

[0199] Comparative Example 1

[0200] The difference between this comparative example and Example 1 is that the graphene oxide slurry is replaced by graphene oxide powder.

[0201] Other than Example 1.

[0202] Comparative Example 2

[0203] The difference between this comparative example and Example 1 is that the step of macropore filling is not performed.

[0204] Other than Example 1.

[0205] Comparative Example 3

[0206] The difference between this comparative example and Example 1 is that the step of micropore filling is not performed.

[0207] Other than Example 1.

[0208] Performance test

[0209] First, the coal-based hard carbon negative electrode material provided in the above examples and comparative examples is tested for electrical conductivity; the test for electrical conductivity is performed on the powder material formed by the hard carbon, and the test method is as follows: first, prepare a uniformly dried powder sample and a calibrated powder resistivity testing instrument. The powder is loaded into a container, the container is filled, and the test circuit is connected, and the test is performed with a pressure parameter of 30 MPa and a step size of 2 MPa.

[0210] Then, the coal-based hard carbon negative electrode material is made into a negative electrode sheet, and the preparation method of the negative electrode sheet includes: mixing the prepared hard carbon, conductive carbon black (Super P), carboxymethyl cellulose sodium (CMC), and styrene-butadiene rubber (SBR) in a formula ratio of 91:2:2:5 to prepare a slurry. The prepared slurry is blade-coated on a carbon-coated copper foil, and then transferred to a 65°C air-drying oven until the sheet is dried (about 1-2 h), and then transferred to a vacuum drying oven for drying for 12 h, to obtain the negative electrode sheet.

[0211] Then the negative electrode sheet is assembled with the positive electrode sheet, GF / D glass fiber diaphragm and 1 mol / L NaClO4 electrolyte to obtain a sodium ion button cell.

[0212] The above sodium ion button cell is subjected to electrochemical performance test:

[0213] (1) Kinetic performance test

[0214] The above sodium ion button cell is subjected to kinetic performance test, and the test conditions include: voltage range 0-2 V, and the kinetic properties are obtained by testing under current density 10C charging / 1C discharging.

[0215] (2) Reversible capacity and initial efficiency performance test

[0216] The charge-discharge test is carried out under the voltage range 0-2 V and the current density 30 mA·g −1 to obtain the discharge reversible capacity and the initial efficiency.

[0217] The test results are shown in Table 1.

[0218] Table 1 Test results of examples 1-24 and comparative examples 1-3

[0219]

[0220] Analysis:

[0221] As shown in Table 1, the present application utilizes the characteristics of graphene paste with high electrical conductivity formed under hydrothermal reaction conditions to wrap coal particles during the forming process, greatly improving the efficiency of electron transmission between particles; and by the method of macropore filling and micropore filling, the pores of aerogel are effectively filled, and at the same time a dense carbon layer structure is formed on the surface of the coal-based hard carbon, further increasing the electrical conductivity of the coal-based hard carbon and improving the true density properties of the coal-based hard carbon. The coal-based hard carbon negative material prepared based on this method has excellent electrical conductivity and kinetic properties, improving the application potential of the prepared secondary battery in the fields of passenger cars, energy storage, 3C, etc. The coal-based hard carbon negative material prepared based on the preparation method provided by the present application exhibits excellent electrical conductivity and kinetic performance.

[0222] As shown in Examples 1 and 4-7, if the concentration of graphene oxide paste is too low, the long flame coal-based aerogel formation effect is poor, causing the graphene oxide and flame coal to be not tightly combined, resulting in a decrease in kinetic properties and electrical conductivity properties; if the concentration of graphene oxide paste is too high, the dispersibility of raw coal particles between graphene is insufficient, and the agglomeration of long flame coal particles occurs, affecting the kinetic properties of hard carbon.

[0223] As can be seen from Example 1 and Examples 8-11, if the weight ratio of the raw coal and the graphene slurry is too small, i.e. the amount of the graphene slurry is too much, the formed hard carbon has a high reaction in the electrical conductivity, but the ion transmission of the long flame coal-based hard carbon is slow, resulting in poor kinetic properties of the hard carbon; if the weight ratio of the raw coal and the graphene slurry is too large, i.e. the amount of the graphene slurry is too small, the long flame coal-based aerogel is difficult to form, and the long flame coal particles affect the electrical conductivity of the graphene, resulting in poor electrical conductivity and kinetic properties.

[0224] As can be seen from Example 1 and Examples 12-15, if the temperature of the hydrothermal reaction is too low, the graphene oxide and the raw coal particles are not tightly combined, and the structure of the coal-based aerogel is not uniform, resulting in poor kinetic properties; if the temperature of the hydrothermal reaction is too high, the long flame coal-based aerogel is easily hydrolyzed, resulting in poor combination between the graphenes, over-reaction, and uneven structure of the product, and poor electrical conductivity.

[0225] As can be seen from Example 1 and Examples 16-19, if the weight ratio of the long flame coal-based aerogel and the water-soluble resin is too small, a large amount of the water-soluble resin makes the structure of the material too dense, the porosity is reduced too much, and the subsequent CVD deposition is difficult to enter the inside of the impregnated aerogel, affecting the electrical conductivity of the hard carbon, and further reducing the kinetics; if the weight ratio of the long flame coal-based aerogel and the water-soluble resin is too large, the water-soluble resin cannot be impregnated into the inside of the coal-based aerogel, resulting in a decrease in the capacity, kinetics and electrical conductivity of the hard carbon.

[0226] As can be seen from Example 1 and Examples 20-23, if the temperature of the micropore filling treatment is too low, the deposition gas is difficult to fully decompose and form effective filling in the micropores, resulting in insufficient filling, causing part of the pores to be unable to be closed, and further causing the electrical conductivity and kinetic properties of the hard carbon to decrease; if the temperature of the micropore filling treatment is too high, the skeleton structure is changed, the micropore filling effect is poor, and the electrical conductivity and kinetic properties are affected.

[0227] As can be seen from Example 1 and Comparative Example 1, if the graphene oxide slurry is replaced by graphene oxide powder, the long flame coal-based aerogel cannot be formed, and the long flame coal particles are separated from the graphene, resulting in poor initial efficiency and reversible capacity of the hard carbon, and a decrease in the electrical conductivity and kinetic properties.

[0228] As can be seen from Example 1 and Comparative Example 2, if the step of macropore filling is not performed, a large amount of macropores are produced, the existence of the macropores causes slow electron transmission, and the kinetic properties of the hard carbon are affected.

[0229] As can be seen from Example 1 and Comparative Example 3, if the step of micropore filling is not performed, a large amount of micropores are produced, the reversible capacity and initial efficiency of the hard carbon are decreased, the transmission of the electrons is affected, the electrical conductivity is deteriorated, and the kinetic properties are reduced.

[0230] Applicants declare that the process of the present application is illustrated by the above examples, but the present application is not limited to the above process steps, i.e. it does not mean that the present application must rely on the above process steps to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the raw materials selected by the present application, addition of auxiliary ingredients, selection of specific modes, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing a coal-based hard carbon anode material, characterized in that, The preparation method Includes the following steps: First, raw coal and graphene slurry are mixed and subjected to hydrothermal reaction, followed by low-temperature carbonization to obtain coal-based aerogel. Then, macropore filling and micropore filling were performed sequentially, with water-soluble resin used for macropore filling and deposition gas used for micropore filling. Then, high-temperature carbonization is performed to obtain the coal-based hard carbon anode material; The raw coal is in powder form. The concentration of the graphene slurry is 10-50 mg / mL; The weight ratio of the raw coal and the graphene slurry is (1-5):10; The hydrothermal reaction is carried out at a temperature of 150-250℃ for 2-12 hours. The weight ratio of the coal-based aerogel to the water-soluble resin is (1-10):100; The temperature for micropore filling treatment is 650-850℃, and the time is 2-5 hours. The high-temperature carbonization treatment is carried out at a temperature of 1200-1600℃ and a holding time of 1-10h.

2. The preparation method according to claim 1, characterized in that, The graphene slurry includes graphene oxide slurry; The preparation method further includes the step of pulverizing the raw coal to obtain fine granular coal, which is then mixed with graphene slurry. The particle size D50 of the fine granular coal is 4-10 μm.

3. The preparation method according to claim 1, characterized in that, The low-temperature carbonization treatment is carried out at a temperature of 550-650℃ for a reaction time of 2-5 hours.

4. The preparation method according to claim 1, characterized in that, The method for filling large holes includes: After mixing coal-based aerogel and water-soluble resin, macroporous impregnation and filling treatment is performed to obtain impregnated coal-based aerogel. The concentration of the water-soluble resin is 100-500 g / L; The temperature for the macroporous impregnation and filling treatment is 100-200℃, and the pressure is 0.1-2MPa.

5. The preparation method according to claim 1, characterized in that, The water-soluble resin includes one or more of carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, polyurethane resin, acrylic resin, or alkyd resin.

6. The preparation method according to claim 4, characterized in that, Methods for micropore filling include: Micropore filling treatment of impregnated coal-based aerogel was performed using chemical vapor deposition to obtain deposited coal-based aerogel; The deposited gases include methane and / or acetylene; The flow rate of the deposition gas is 100-500 mL / min.

7. The preparation method according to claim 6, characterized in that, The preparation method further includes a step of pulverizing the deposited coal-based aerogel to obtain a coal-based hard carbon precursor with a particle size D50 of 4-7 μm.

8. The preparation method according to any one of claims 1-7, characterized in that, The high-temperature carbonization process is carried out in an inert atmosphere.

9. The application of a coal-based hard carbon anode material obtained by the preparation method according to any one of claims 1-8 in the preparation of secondary batteries.

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