Hard carbon negative electrode material precursor, hard carbon negative electrode material, preparation method of hard carbon negative electrode material and battery

Abstract

The invention relates to the technical field of batteries, in particular to a hard carbon negative electrode material precursor, a hard carbon negative electrode material, a preparation method of the hard carbon negative electrode material and a battery. The hard carbon negative electrode material precursor comprises a cross-linking product, and the cross-linking product comprises an amide polymer and a cross-linking product of the hard carbon precursor; the hard carbon precursor comprises carboxyl and / or hydroxyl functional groups; the amide group and the carboxyl functional group in the amide polymer, or the amide group and the hydroxyl functional group in the amide polymer interact through hydrogen bonds and form a double-network cross-linked three-dimensional structure. The preparation method of the hard carbon negative electrode material precursor comprises the following steps: mixing a hard carbon precursor, an amide monomer, a cross-linking agent and a solvent to obtain a mixture, and carrying out polymerization reaction on the mixture under photocatalysis to obtain the hard carbon negative electrode material precursor. The hard carbon negative electrode material is obtained by carbonizing a hard carbon negative electrode material precursor. The hard carbon negative electrode material provided by the invention has the characteristics of high capacity and low potential platform capacity ratio.

Description

Technical Field

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

[0002] Sodium-ion batteries (SIBs) are expected to become a low-cost alternative to dominant lithium-ion batteries due to their abundant sodium resources, excellent low-temperature performance, and fast charging ability. In sodium-ion batteries, although several cathode materials such as layered oxides, polyanionic compounds, and Prussian blue materials have been well developed, the lack of high-performance anode materials with high sodium (Na) storage capacity and low cost is the main challenge for the development of large-energy SIBs.

[0003] Generally, graphite is the main anode material for commercial lithium-ion batteries. However, the insertion of sodium ions into graphite to form binary graphite intercalation compounds (b-GICs) is thermodynamically unfavorable. That is, graphite anode materials have been successfully applied in lithium-ion batteries, but their application in sodium-ion batteries is limited because sodium ions are difficult to embed in them. Therefore, the development of anode materials with high sodium capacity is the key to promoting sodium-ion battery technology. Among them, hard carbon is considered a promising anode material for sodium-ion batteries due to its large interlayer spacing, good structural stability, and low cost. However, existing hard carbon materials have deficiencies such as low capacity and low initial efficiency, which limit their further development in the field of sodium-ion battery anodes.

[0004] Therefore, there is an urgent need to develop a new hard carbon anode material for sodium-ion batteries with high capacity and a low proportion of the potential plateau capacity. Summary of the Invention

[0005] In view of this, the present invention aims to at least solve one of the technical problems in the related art to some extent. For this purpose, the present invention provides a precursor of a hard carbon negative electrode material, a hard carbon negative electrode material, a preparation method thereof, and a battery, and the hard carbon negative electrode material has the characteristics of high capacity and a low proportion of the potential plateau capacity.

[0006] To solve the above technical problems, the present application is implemented as follows: According to the first aspect of the present application, the present invention provides a precursor of a hard carbon negative electrode material, and the precursor of the hard carbon negative electrode material includes a cross-linked product, and the cross-linked product includes a cross-linked product of an amide polymer and a hard carbon precursor; The hard carbon precursor includes a carboxyl group and / or a hydroxyl functional group; The amide groups in the amide polymer and the carboxyl functional groups interact with each other through hydrogen bonds to form a three-dimensional structure with double-network crosslinking. Alternatively, the amide groups in the amide polymer and the hydroxyl functional groups interact with each other through hydrogen bonds to form a three-dimensional structure with double-network crosslinking.

[0007] In any embodiment, the amide polymer includes polyacrylamide.

[0008] In any embodiment, the hard carbon precursor includes saccharides.

[0009] In any embodiment, the hard carbon precursor includes at least one of sodium alginate, chitosan, cellulose, or β-cyclodextrin.

[0010] In any embodiment, the mass ratio of the amide polymer to the hard carbon precursor is (1 to 50):(1 to 100).

[0011] The second aspect of the present application provides a method for preparing a precursor of a hard carbon negative electrode material, including the following steps: Mix a hard carbon precursor, an amide monomer, a crosslinking agent, and a solvent to obtain a mixture, and subject the mixture to a polymerization reaction under photocatalysis to obtain a precursor of a hard carbon negative electrode material; Wherein, the hard carbon precursor includes carboxyl and / or hydroxyl functional groups; The amide monomer polymerizes to form an amide polymer. The amide groups in the amide polymer and the carboxyl functional groups interact with each other through hydrogen bonds to form a three-dimensional structure with double-network crosslinking. Alternatively, the amide groups in the amide polymer and the hydroxyl functional groups interact with each other through hydrogen bonds to form a three-dimensional structure with double-network crosslinking.

[0012] In any embodiment, the mixture further includes an initiator.

[0013] In any embodiment, the mass ratio of the hard carbon precursor, the amide monomer, the crosslinking agent, and the initiator is (1 to 100):(1 to 50):(0.1 to 10):(0.1 to 10).

[0014] In any embodiment, the amide monomer includes at least one of acrylamide, N-n-propylacrylamide, N-isopropylacrylamide, N,N-diethylacrylamide, N-cyclopropylacrylamide, N-methylacrylamide, or N-ethylacrylamide.

[0015] In any embodiment, the hard carbon precursor includes at least one of sodium alginate, chitosan, cellulose, or β-cyclodextrin.

[0016] In any embodiment, the crosslinking agent includes at least one of tetramethylethylenediamine, N,N'-methylenebisacrylamide, or ethylene glycol dimethacrylate.

[0017] In any embodiment, the solvent includes at least one of water, ethanol, acetone, toluene, ether, N,N'-dimethylformamide, or ethylene glycol monomethyl ether.

[0018] In any embodiment, the initiator includes at least one of azobisisobutyronitrile, ammonium persulfate, azodiisovaleronitrile, or hydrogen peroxide.

[0019] In any embodiment, the photocatalysis method includes at least one of ultraviolet photocatalysis or gamma-ray photocatalysis.

[0020] In any embodiment, the photocatalysis time is 10 min to 300 min.

[0021] The third aspect of the present application provides a method for preparing a hard carbon anode material, including the following steps: carbonizing a hard carbon anode material precursor to obtain a hard carbon anode material; Wherein, the hard carbon anode material precursor includes the above-mentioned hard carbon anode material precursor or the hard carbon anode material precursor prepared by the above method.

[0022] In any embodiment, before the carbonization treatment, the method further includes: Drying and pulverizing the hard carbon anode material to obtain an intermediate, and then carbonizing the intermediate to obtain the hard carbon anode material.

[0023] In any embodiment, the drying treatment includes vacuum drying, and the temperature of the vacuum drying is 50°C to 100°C.

[0024] In any embodiment, the pulverizing treatment includes at least one of jet milling, mechanical grinding, ball milling, or roller press milling.

[0025] In any embodiment, the specific surface area of the intermediate is 50 to 200 m 2 / g.

[0026] In any embodiment, the median particle size of the intermediate is 5 μm to 10 μm.

[0027] In any embodiment, the true density of the intermediate is 1.8 to 2.2 g / cm 3 .

[0028] In any embodiment, the temperature of the carbonization treatment is 1000°C to 1600°C, the heating rate of the carbonization treatment is 0.1 to 10°C / min, and the heat preservation time of the carbonization treatment is 1 h to 10 h.

[0029] In any embodiment, the specific surface area of the hard carbon negative electrode material is 2 to 10 m 2 / g.

[0030] In any embodiment, the median particle size of the hard carbon negative electrode material is 3 μm to 6 μm.

[0031] In any embodiment, the true density of the hard carbon negative electrode material is 1.5 to 1.7 g / cm 3 .

[0032] The fourth aspect of the present application provides a hard carbon negative electrode material, which is prepared by using the preparation method of the hard carbon negative electrode material as described above.

[0033] The fifth aspect of the present application provides a battery, including a negative electrode sheet, where the negative electrode sheet includes the hard carbon negative electrode material prepared by using the preparation method of the hard carbon negative electrode material as described above, or includes the hard carbon negative electrode material as described above.

[0034] Through the above technical solutions, the beneficial technical effects of the present invention are as follows: (1) In the embodiments of the present application, the provided hard carbon negative electrode material precursor and its preparation method mainly consist of a cross-linked product of an amide polymer and a hard carbon precursor. The hard carbon precursor contains carboxyl and / or hydroxyl functional groups. The amide polymers are interconnected on the surface of the hard carbon precursor to form a three-dimensional molecular chain and a stable network structure, improving the strength and hardness of the material. And the amide functional groups in the side chains of the amide polymers can form a three-dimensional structure of double-network cross-linking through hydrogen bond interaction layer by layer with the hydroxyl or carboxyl groups in the hard carbon precursor material, thereby obtaining a hard carbon negative electrode material precursor with developed pores, providing a larger storage space for subsequent Na + and being beneficial to the insertion of Na + , thereby improving the capacity of the material and the proportion of the low-potential platform capacity.

[0035] (2) In the embodiments of the present application, the provided hard carbon negative electrode material and its preparation method are mainly obtained by carbonizing the hard carbon negative electrode material precursor with the three-dimensional structure of double-grid cross-linking described above. During the carbonization process, the three-dimensional structure of double-network cross-linking in the hard carbon negative electrode material precursor, that is, the short-range ordered graphite-like microcrystals, gradually form long-range disordered coiled carbon chains, and wind and contract to form a large number of closed pores. The large number of closed pores provide more storage space for Na + , thereby enhancing Na +The storage capacity at the low potential plateau simultaneously improves the capacity of the material.

[0036] Other features and advantages of the present invention will be described in detail in the following detailed implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following detailed implementation, they are used to explain the present invention, but do not constitute a limitation to the present invention.

[0038] Figure 1 Shown is the SEM image (scanning electron microscope image) of the hard carbon negative electrode material obtained in Example 1.

[0039] Figure 2 Shown is the TEM image (transmission electron microscope image) of the hard carbon negative electrode material obtained in Example 1.

[0040] Figure 3 Shown is the XRD pattern (X-ray diffraction pattern) of the hard carbon negative electrode material obtained in Example 1.

[0041] Figure 4 Shown is the Raman spectrum of the hard carbon negative electrode material obtained in Example 1.

[0042] Figure 5 Shown is the structural schematic diagram of sodium alginate in the present invention.

[0043] Figure 6 Shown is the structural schematic diagram of the precursor of the hard carbon negative electrode material in the present invention.

[0044] Figure 7 Shown is the enlarged schematic diagram of the structure of the precursor of the hard carbon negative electrode material in the present invention, which represents acrylamide.

[0045] Figure 8 Shown is the enlarged schematic diagram of the structure of the precursor of the hard carbon negative electrode material in the present invention, which represents a saccharide carbon source hard carbon precursor containing a carboxyl functional group.

[0046] Figure 9 Shown is the enlarged schematic diagram of the structure of the precursor of the hard carbon negative electrode material in the present invention, which represents a crosslinking agent. DETAILED DESCRIPTION OF THE INVENTION

[0047] The present invention discloses a precursor of a hard carbon negative electrode material, a hard carbon negative electrode material, a preparation method thereof, and a battery. Those skilled in the art can draw on the content of this article and appropriately modify process parameters to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those related can obviously make changes or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0048] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, 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.

[0049] 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 of each range or individual point values, 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.

[0050] If there is no special instruction, all implementation manners and optional implementation manners of this 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 this application can be combined with each other to form a new technical solution.

[0051] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended or 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 it can only include or comprise the listed components.

[0052] In sodium-ion batteries, although several cathode materials such as layered oxides, polyanion compounds, and Prussian blue have been well developed, there is a lack of high-performance anode materials with high sodium storage capacity and low cost. Among the anode materials for sodium-ion batteries, "hard carbon", as a non-graphitizable carbon, has become the most suitable SIB anode microstructure due to its randomly distributed turbostratic structure, which has a large interlayer spacing (exceeding 0.37 nm) and closed nanopores. Generally, hard carbon is synthesized from thermosetting precursors (such as cellulose, peanut shells, sucrose, glucose, phenolic resins, starch, anthracite, etc.) through high-temperature carbonization. During the pyrolysis process, carbon layers in the precursor are prone to form turbostratic layers and disordered microstructures composed of surface defects, nanopores or voids, and graphite domains. During the curing process, Na ions are first adsorbed on the defect sites of hard carbon in the inclined region (0.1 - 1 V vs Na / Na + ) and then form quasi-metallic Na clusters in the plateau region (0 - 0.1 V vs Na / Na + ). Currently, the extensive research on hard carbon can be summarized into the following aspects: 1) understanding the charge storage mechanism of hard carbon and enhancing Na + transfer kinetics by introducing heteroatoms (such as O, N, S, P), pores or defects; 2) optimizing the electrode-electrolyte interface; 3) improving the reversible Na storage capacity and initial Coulomb efficiency by adjusting the pore structure. Despite these studies, these hard carbon electrodes still exhibit a relatively low plateau capacity at ≈0.1 V (Na + / Na), and the plateau capacity plays a key role in determining the working voltage and energy density of a fully charged battery. Therefore, there is an urgent need to develop a hard carbon anode material for sodium-ion batteries with high capacity and a low proportion of the potential plateau capacity.

[0053] In view of this, the present application proposes a precursor of a hard carbon anode material, a hard carbon anode material, its preparation method, and a battery. The hard carbon anode material has the characteristics of high capacity and a low proportion of the potential plateau capacity. The following provides a more specific description of the present application and optional implementation manners.

[0054] [Precursor of Hard Carbon Anode Material] In some embodiments, a precursor of a hard carbon anode material is provided. The precursor of the hard carbon anode material includes a cross-linked product, and the cross-linked product includes a cross-linked product of an amide polymer and a hard carbon precursor.

[0055] The hard carbon precursor contains carboxyl and / or hydroxyl functional groups; for example, the hard carbon precursor may contain carboxyl functional groups, or may contain hydroxyl functional groups, or may contain both carboxyl functional groups and hydroxyl functional groups.

[0056] The amide groups and carboxyl functional groups in the amide polymer interact with each other through hydrogen bonding to form a three-dimensional structure with double-network crosslinking. Alternatively, the amide groups and the hydroxyl functional groups in the amide polymer interact with each other through hydrogen bonding to form a three-dimensional structure with double-network crosslinking.

[0057] In this application, the provided hard carbon anode material precursor can be used to prepare a hard carbon anode material. For example, the hard carbon anode material can be obtained by carbonizing the hard carbon anode material precursor. Particularly, the hard carbon anode material precursor contains a cross-linked product of an amide polymer and a hard carbon precursor, which can endow the hard carbon anode material precursor with a three-dimensional structure with double-network crosslinking, and further enable the hard carbon anode material to be a three-dimensional network hard carbon anode material. The present invention mainly utilizes the amide groups (or amino groups) on the side chains of the amide polymer to cross-link with the carboxyl groups or hydroxyl groups on the hard carbon precursor through hydrogen bonding to form a double-network three-dimensional structure, thereby improving the capacity or other electrochemical properties of the prepared hard carbon anode material.

[0058] Specifically, the hard carbon anode material precursor of the present invention is mainly composed of a cross-linked product of an amide polymer and a hard carbon precursor. Among them, the amide polymer can be formed by polymerizing amide monomers. After polymerization, the amide monomers form linear molecular chains, which are gradually connected to form three-dimensional molecular chains and a stable network structure under the action of a cross-linking agent, thereby enhancing the strength and hardness of the material. At the same time, the side chains of the amide polymer carry amide groups (or amino groups) functional groups, and the hard carbon precursor contains carboxyl groups and / or hydroxyl groups. The carboxyl groups or hydroxyl groups in the hard carbon precursor can interact with the amide groups in the side chains of the amide polymer through hydrogen bonding to form a three-dimensional structure with double-network crosslinking through layer-by-layer self-assembly. That is, the amide polymer has a network structure, and at the same time, the amide polymer and the hard carbon precursor can be cross-linked to form a network structure, thereby obtaining a three-dimensional structure with double-network crosslinking, and further obtaining a hard carbon anode material precursor with developed pores, providing conditions for the subsequent preparation of a hard carbon anode material with a large number of closed pores.

[0059] Therefore, the hard carbon anode material precursor provided in this application selects a hard carbon precursor containing carboxyl groups and / or hydroxyl groups, and at the same time introduces an amide polymer. The amide groups in the amide polymer form a three-dimensional structure with double-network crosslinking with the carboxyl groups or hydroxyl groups in the hard carbon precursor through hydrogen bonding, providing a large number of pore structures for the hard carbon anode material precursor, providing conditions for the subsequent preparation of a hard carbon anode material with a large number of closed pores, and facilitating the improvement of the low-potential platform capacity of the hard carbon anode material.

[0060] In this application, the term "amide polymer" refers to a class of high-molecular compounds containing amide bonds (-CONH-) in the main chain of the molecule.

[0061] In this application, the term "carboxyl group" refers to the -COOH group.

[0062] In the present application, the term "hydroxyl group" refers to the -OH group.

[0063] In the present application, the term "crosslinked product" refers to a product in which crosslinked polymer molecular chains are connected through chemical bonds or other strong interactions to form a three-dimensional network structure.

[0064] In some specific embodiments, amide polymers include, but are not limited to, polyacrylamide. The polyacrylamide can be polymerized from amide monomers. The polyacrylamide has a network structure and stable structure. By adding polyacrylamide, it is beneficial to improve the sodium ion storage performance of the finally prepared hard carbon negative electrode material and increase the capacity of the hard carbon negative electrode material.

[0065] In some specific embodiments, the hard carbon precursor includes, but is not limited to, sugars.

[0066] Optionally, in some specific embodiments, the hard carbon precursor includes at least one of sodium alginate, chitosan, cellulose, or β-cyclodextrin.

[0067] Preferably, the hard carbon precursor is selected from sodium alginate. The sodium alginate is more likely to undergo a crosslinking reaction with polyacrylamide to obtain a hard carbon negative electrode material precursor with more excellent performance.

[0068] Of course, it is not limited thereto, but other similar sugar carbon sources can also be used as long as the purpose of the present application is not restricted.

[0069] In the present application, a sugar carbon source with rich carboxyl or hydroxyl functional groups is selected as the hard carbon precursor. After mixing these sugar carbon sources with amide monomers such as acrylamide, the acrylamide is polymerized under photocatalysis to form a three-dimensional structure polymer chain with amide functional groups on the side chain; at the same time, the amide groups on the side chain and the carboxyl or hydroxyl groups carried by the biomass-derived hard carbon precursor such as the sugar carbon source are self-assembled layer by layer through hydrogen bonds or chemical bond interactions to form a three-dimensional structure with a double network crosslinking, thereby obtaining a hard carbon negative electrode material precursor with developed pores.

[0070] In some specific embodiments, the mass ratio of the amide polymer to the hard carbon precursor is (1 to 50):(1 to 100). Preferably, the mass ratio of the amide polymer to the hard carbon precursor is (5 to 30):(1 to 100). As an example, the mass ratio of the amide polymer to the hard carbon precursor can be any one of the point values or the range values between any two of 1:1, 1:2, 5:22, 8:35, 10:55, 15:63, 35:52, 40:75, 50:92. By controlling the masses of the amide polymer and the hard carbon precursor within the above ranges, the hard carbon precursor material can have a large number of pore structures, and then a hard carbon negative electrode material with a large number of Na + storage spaces can be prepared, improving the storage capacity of sodium ions at the low potential plateau. If the content of the amide polymer is too high, the crosslinking density of the crosslinked product formed by the amide polymer and the hard carbon precursor will be too large, and the grids in the three-dimensional structure will be densely packed, and then the pores in the crosslinked product will be reduced, resulting in a decrease in the Na + storage space in the subsequent hard carbon negative electrode material, thus resulting in a decrease in the plateau capacity and a significant decrease in the first discharge capacity; if the content of the amide polymer is too low, the crosslinking density of the crosslinked product formed by the amide polymer and the hard carbon precursor will be too low, and the grids in the three-dimensional structure will be relatively loose, and then a small number of large pores will be formed in the crosslinked product, and thus the specific surface area will also be relatively large, resulting in a decrease in the first efficiency of the subsequent hard carbon negative electrode material.

[0071] That is, by controlling the mass ratio of the amide polymer, the crosslinking degree of the amide polymer and the hard carbon precursor is adjusted to ensure that the hard carbon negative electrode material precursor has a large number of pore structures, providing conditions for the subsequent hard carbon negative electrode material with a large number of closed pores, so that the hard carbon negative electrode material has a large number of Na + storage spaces, improving the storage capacity of sodium ions at the low potential plateau, and then improving the capacity of the hard carbon negative electrode material and the proportion of the low potential plateau capacity.

[0072] [Preparation method of hard carbon negative electrode material precursor] In some embodiments, the present application provides a preparation method of a hard carbon negative electrode material precursor, including the following steps: Mix the hard carbon precursor, the amide monomer, the crosslinking agent and the solvent to obtain a mixture, and carry out a polymerization reaction on the mixture under photocatalysis to obtain the hard carbon negative electrode material precursor; wherein, the hard carbon precursor includes carboxyl and / or hydroxyl functional groups; The amide monomer polymerizes to form an amide polymer, and the amide groups in the amide polymer interact with the carboxyl functional groups through hydrogen bonds and form a three-dimensional structure of double-network crosslinking, or the amide groups interact with the hydroxyl functional groups through hydrogen bonds and form a three-dimensional structure of double-network crosslinking.

[0073] In this application, after mixing a hard carbon precursor, an amide monomer, a crosslinking agent, and a solvent, a polymerization reaction is initiated under photocatalysis to prepare a precursor of a hard carbon negative electrode material. That is, a method for photocatalytically constructing a three-dimensional network precursor of a hard carbon negative electrode material is provided, which can improve the reversible specific capacity, low-potential plateau capacity, first efficiency, and other properties of the finally prepared hard carbon negative electrode material.

[0074] This preparation method has a simple process, is convenient to operate, has strong feasibility, and is easy to industrialize; through this method, a precursor of a hard carbon negative electrode material with a double-network three-dimensional structure can be prepared, which has good structural stability, has more sodium storage spaces, and has good electrochemical properties.

[0075] It should be understood that all the characteristics and advantages described above for the "precursor of the hard carbon negative electrode material" also apply to the "preparation method of the precursor of the hard carbon negative electrode material", and will not be elaborated here one by one.

[0076] In this application, a hard carbon precursor containing carboxyl and / or hydroxyl functional groups is mixed with an amide monomer. Among them, the amide monomer undergoes a polymerization reaction under photocatalysis to generate linear amide polymer molecular chains, and then under the action of a crosslinking agent, the linear amide polymer molecular chains are connected to each other to form a three-dimensional molecular chain and form a stable network structure, further enhancing the strength and hardness of the material; at the same time, the amide groups in the side chains of the amide polymer and the carboxyl or hydroxyl functional groups in the hard carbon precursor form a three-dimensional structure of double-network crosslinking through hydrogen bonding through layer-by-layer self-assembly, thereby obtaining a precursor of a hard carbon negative electrode material with developed pores, providing conditions for the subsequent preparation of a hard carbon negative electrode material with a large number of closed pores, and increasing the storage space of Na + in the hard carbon negative electrode material, which is beneficial to the insertion of Na + and thus improves the capacity of the material and the proportion of the low-potential plateau capacity.

[0077] In some specific embodiments, the mixture further includes an initiator. That is, by mixing a hard carbon precursor, an amide monomer, a crosslinking agent, an initiator, and a solvent, a mixture can be obtained.

[0078] As an example, a hard carbon precursor, an amide monomer, a crosslinking agent, and an initiator are sequentially added to a stirring kettle containing a solvent and uniformly dispersed, and then transferred to a reaction kettle and the polymerization reaction of an amide monomer such as acrylamide is initiated under photocatalysis to form a three-dimensional structure polymer chain with amide functional groups in the side chains; at the same time, the amide groups in the side chains and the carboxyl or hydroxyl groups carried by the biomass-derived hard carbon precursor form a three-dimensional network crosslinked hard carbon negative electrode material precursor with developed pores through hydrogen bonding through layer-by-layer self-assembly.

[0079] Optionally, the initiator includes, but is not limited to, any one of azobisisobutyronitrile, ammonium persulfate, azobisisoheptonitrile, or hydrogen peroxide, or a combination of two or more of them in any proportion.

[0080] In some specific embodiments, the mass ratio of the hard carbon precursor, amide monomer, crosslinking agent, and initiator is (1 to 100):(1 to 50):(0.1 to 10):(0.1 to 10). As an example, the mass ratio of the hard carbon precursor, amide monomer, crosslinking agent, and initiator can be 1:1:0.1:0.1, 2:1:0.1:0.1, 5:1:0.1:0.1, 10:1:0.1:0.1, 35:1:0.1:0.1, 50:1:0.1:0.1, 100:1:0.1:0.1, 100:5:0.1:0.1, 100:10:0.1:0.1, 100:30:0.1:0.1, 100:50:0.1:0.1, 100:50:1:1, 100:50:10:10, any one of these values or the range between any two of them. By adjusting the mass ratio of the hard carbon precursor, amide monomer, crosslinking agent, and initiator within the above range, the pore size and number of the hard carbon negative electrode material precursor can be increased, providing a large amount of storage space for the subsequent insertion of Na + to improve the capacity of the material and the proportion of the low-potential platform capacity. In addition, by controlling the dosage ratio of the hard carbon precursor and amide monomer within the above range, conditions can be provided for the subsequent sintering of the hard carbon negative electrode material from the hard carbon negative electrode material precursor. The dosages of the hard carbon precursor and amide monomer directly affect the molecular weight of the crosslinked product. The larger the molecular weight of the crosslinked product, the greater the crosslinking strength of the crosslinked product, and thus the strength of the crosslinked product will also increase, with small structural changes during the sintering process, ensuring that the three-dimensional structure of the double-network crosslinking in the hard carbon negative electrode material precursor is not damaged during the sintering process.

[0081] In some specific embodiments, the amide monomer includes, but is not limited to, any one of acrylamide, N-n-propylacrylamide, N-isopropylacrylamide, N,N-diethylacrylamide, N-cyclopropylacrylamide, N-methylacrylamide, or N-ethylacrylamide, or a combination of two or more of them in any proportion.

[0082] Preferably, the amide monomer is selected from acrylamide. The use of acrylamide monomer is mainly because it has a crosslinkable double bond and can easily undergo a crosslinking reaction to form a polymer through photoinduction, with a simple and safe method.

[0083] In some specific embodiments, the hard carbon precursor includes, but is not limited to, any one of sodium alginate, chitosan, cellulose, or β-cyclodextrin, or a combination of two or more of them in any proportion.

[0084] In some specific embodiments, the crosslinking agent includes, but is not limited to, any one of tetramethylethylenediamine, N,N'-methylenebisacrylamide, or ethylene glycol dimethacrylate, or a combination of two or more of them in any proportion.

[0085] In some specific embodiments, the solvent includes, but is not limited to, any one of water, ethanol, acetone, toluene, ether, N,N'-dimethylformamide, or ethylene glycol monomethyl ether, or a combination of two or more of them in any proportion.

[0086] However, this application is not limited to these amide monomers, hard carbon precursors, crosslinking agents, initiators, and solvents. This application can also use other amide monomers, hard carbon precursors, crosslinking agents, and solvent initiators that can be used as precursors for hard carbon anode materials. Any one of the above substances can be used alone, or two or more of them can be used in combination.

[0087] In some specific embodiments, the photocatalysis method includes, but is not limited to, at least one of ultraviolet photocatalysis or gamma-ray photocatalysis.

[0088] In some specific embodiments, the photocatalysis time is 10 min to 300 min. As an example, the photocatalysis time can be any one of the point values of 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 150 min, 200 min, 250 min, 300 min, or the range value between any two of them.

[0089] Thus, controlling the above process parameters within the given ranges is beneficial to preparing a high-quality precursor for the hard carbon anode material, providing favorable conditions for finally preparing the hard carbon anode material, and further improving the performance of the hard carbon anode material of this application. Those skilled in the art can selectively adjust one or more of the above process parameters according to the actual production situation.

[0090] As an example, the preparation of the precursor for the hard carbon anode material includes: Disperse 1 to 100 g of a hard carbon precursor such as sodium alginate, chitosan, cellulose or β-cyclodextrin, 1 to 50 g of an amide monomer such as acrylamide, N-n-propylacrylamide, N-isopropylacrylamide, N,N-diethylacrylamide, N-cyclopropylacrylamide, N-methylacrylamide or N-ethylacrylamide, 0.1 to 10 g of a crosslinking agent such as tetramethylethylenediamine, N,N'-methylenebisacrylamide or ethylene glycol dimethacrylate, 0.1 to 10 g of an initiator such as azobisisobutyronitrile, ammonium persulfate, azobisisoheptonitrile or hydrogen peroxide and a solvent such as water, ethanol, acetone, toluene, ether, N,N'-dimethylformamide or ethylene glycol monomethyl ether, and then perform photocatalysis, such as polymerization reaction for 10 to 300 min by ultraviolet photocatalysis or gamma ray photocatalysis, to obtain a hard carbon anode material precursor.

[0091] Optionally, the schematic structural diagram of sodium alginate is as Figure 5 shown.

[0092] Taking sodium alginate as the hard carbon precursor and acrylamide as the amide monomer as an example, the three-dimensional structure of the double-network crosslinked hard carbon anode material precursor obtained is described. It should be understood that here sodium alginate is taken as an example for description, and other saccharide carbon source precursors containing carboxyl or hydroxyl functional groups also have similar structures. The structure of the hard carbon anode material precursor with the three-dimensional structure of double-network crosslinking is as Figure 6 shown; the enlarged schematic diagram of the structure of the hard carbon anode material precursor is as Figures 7 to 9 shown.

[0093] Figure 6 In , the -N-H-O- structure indicated by the arrow is the three-dimensional network crosslinked structure formed by the carboxyl functional group on the hard carbon precursor and the amide group on acrylamide through hydrogen bond interaction.

[0094] [Preparation method of hard carbon anode material] In some embodiments, the present application provides a method for preparing a hard carbon anode material, including the following steps: carbonizing the hard carbon anode material precursor to obtain the hard carbon anode material; wherein, the hard carbon anode material precursor includes the above-mentioned hard carbon anode material precursor or the hard carbon anode material precursor prepared by the above-mentioned method.

[0095] The hard carbon anode material of the present invention can be obtained by carbonizing the above-mentioned hard carbon anode material precursor, and thus has at least all the characteristics and advantages of the above-mentioned hard carbon anode material precursor.

[0096] In this application, a hard carbon precursor containing carboxyl and / or hydroxyl functional groups is mixed with an amide monomer. The amide monomer undergoes a polymerization reaction under photocatalysis to form a linear amide polymer molecular chain. Then, under the action of a crosslinking agent, the linear amide polymer molecular chains are interconnected to form a three-dimensional molecular chain and a stable network structure, further enhancing the strength and hardness of the material. At the same time, the amide groups in the side chains of the amide polymer and the carboxyl or hydroxyl functional groups in the hard carbon precursor form a three-dimensional structure with double-network crosslinking through hydrogen bonding via layer-by-layer self-assembly. After carbonization treatment of the three-dimensional structure with double-network crosslinking, a hard carbon negative electrode material with well-developed pores is obtained. During its preparation, the crosslinking degree of the hard carbon negative electrode material can be regulated by adjusting the mass ratio of the amide monomer such as acrylamide. And during the carbonization process, as the temperature rises, short-range ordered graphite-like microcrystals gradually form long-range disordered coiled carbon chains, which wind and contract to form a large number of closed pores. A large number of closed pores provide more storage space for Na + and thus improve the storage capacity of Na + at the low potential plateau while enhancing the capacity of the material.

[0097] In some specific embodiments, before the carbonization treatment, the method further includes: performing a drying treatment and a pulverization treatment on the hard carbon negative electrode material to obtain an intermediate, and then performing a carbonization treatment on the intermediate to obtain the hard carbon negative electrode material.

[0098] As an example, after the hard carbon negative electrode material precursor is prepared, the hard carbon negative electrode material precursor is first placed in an oven for vacuum drying treatment, and then pulverized to obtain an intermediate. Then, the intermediate is placed in a high-temperature carbonization furnace and subjected to high-temperature carbonization treatment under the protection of an inert atmosphere to obtain the hard carbon negative electrode material.

[0099] In some specific embodiments, the drying treatment includes, but is not limited to, vacuum drying, and the temperature of the vacuum drying is 50°C to 100°C. As an example, the temperature of the vacuum drying can be any one of the point values of 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C or the range value between any two of them.

[0100] In some specific embodiments, the pulverization treatment includes at least one of jet milling, mechanical grinding, ball milling or roller press milling.

[0101] In some specific embodiments, the specific surface area of the obtained intermediate is 50 to 200 m 2 / g; the median particle size of the intermediate is 5 μm to 10 μm; the true density of the intermediate is 1.8 to 2.2 g / cm 3 . As an example, the specific surface area of the intermediate can be 50 m2 / g, 80 m 2 / g, 100 m 2 / g, 120 m 2 / g, 150 m 2 / g, 160 m 2 / g, 180 m 2 / g, 200 m 2 Any one of the point values in / g or the range value between any two of them; the median particle size of the intermediate can be any one of the point values of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or the range value between any two of them; the true density of the intermediate can be 1.8 g / cm 3 , 1.9 g / cm 3 , 2.0 g / cm 3 , 2.1 g / cm 3 , 2.2 g / cm 3 Any one of the point values in or the range value between any two of them. By controlling the surface area, median particle size and vacuum density of the intermediate within the above ranges, conditions are provided for the subsequent preparation of a hard carbon negative electrode material with a large number of closed pores, enabling the hard carbon precursor to provide more storage space for Na + and improving the storage capacity of Na + at the low potential plateau while enhancing the capacity of the material.

[0102] In some specific embodiments, the temperature of the carbonization treatment is 1000 °C to 1600 °C, the heating rate of the carbonization treatment is 0.1 to 10 °C / min, and the holding time of the carbonization treatment is 1 h to 10 h. As an example, the temperature of the carbonization treatment can be any one of the point values of 1000, 1080, 1100, 1200, 1500, 1200, 1500, 1300, 1360, 1400, 1480, 1500, 1550, 1600 °C or the range value between any two of them; the heating rate of the carbonization treatment can be any one of the point values of 0.1 °C / min, 0.5 °C / min, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min or the range value between any two of them; the holding time of the carbonization treatment can be any one of the point values of 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h or the range value between any two of them. By adjusting the parameters of the carbonization treatment within the above ranges, the three-dimensional structure of the double-network crosslinking formed by the amide polymer and the hard carbon precursor with carboxyl and / or hydroxyl groups can gradually form long-range disordered coiled carbon chains and contract to form a large number of closed pores, providing a large amount of storage space for Na + and thus enhancing Na+ The storage capacity at the low potential plateau. If the carbonization temperature is too high, the three-dimensional structure of the double network cross-linking formed by the amide polymer and the hard carbon precursor with carboxyl and / or hydroxyl groups will be destroyed at high temperature, resulting in the inability to obtain the double grid structure; if the carbonization temperature is too low, the three-dimensional structure of the double network cross-linking cannot gradually form long-range disordered coiled carbon chains, and thus a large number of closed pores cannot be formed by contraction.

[0103] In some specific embodiments, the specific surface area of the hard carbon negative electrode material is 2 - 10 m 2 / g, the median particle size of the hard carbon negative electrode material is 3 μm - 6 μm, and the true density of the hard carbon negative electrode material is 1.5 - 1.7 g / cm 3 . As an example, the specific surface area of the hard carbon negative electrode material can be 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, any one of these point values or the range value between any two of them; the median particle size of the hard carbon negative electrode material can be any one of 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm or the range value between any two of them; the true density of the hard carbon negative electrode material can be 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , any one of these point values or the range value between any two of them. By controlling the surface area, median particle size, and vacuum density of the hard carbon negative electrode material within the above ranges, it can be ensured that the hard carbon negative electrode material can provide more storage space for Na + , improve the storage capacity of Na + at the low potential plateau while enhancing the capacity of the material.

[0104] Therefore, controlling the above process parameters within the given ranges is beneficial to preparing high-quality hard carbon negative electrode materials, and can further improve the storage capacity and capacity of the hard carbon negative electrode material of the present application for Na + at the low potential plateau. Those skilled in the art can selectively adjust one or more of the above process parameters according to the actual production situation.

[0105] [Hard Carbon Negative Electrode Material] In some embodiments, the present application provides a hard carbon negative electrode material, which is prepared by the preparation method of the hard carbon negative electrode material as described above.

[0106] It should be understood that all the features and advantages described above for the "precursor of the hard carbon negative electrode material" or the "preparation method of the hard carbon negative electrode material" also apply to the "hard carbon negative electrode material", and will not be repeated here one by one.

[0107] [Battery] In some embodiments, the present application provides a battery, including a negative electrode sheet, which includes the hard carbon negative electrode material prepared by the preparation method of the hard carbon negative electrode material as described above, or includes the hard carbon negative electrode material as described above.

[0108] Since the negative electrode sheet includes the hard carbon negative electrode material provided by the embodiments of the present application, it can exhibit good electrochemical performance, such as high first charge-discharge capacity, excellent first Coulomb efficiency and other performances.

[0109] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed 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 disposed 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 stacked on any one of the two surfaces of the negative electrode current collector.

[0110] The present application does not particularly limit 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 made of a foil material with a surface coating layer.

[0111] 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. The present application does not particularly limit the types of the conductive agent and the binder in the negative electrode active material layer, as long as the purpose of the present application can be achieved.

[0112] In some embodiments, the above 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.

[0113] In the embodiments of the present application, for the specific materials, structures, etc. of the positive electrode sheet, the separator and the electrolyte in the battery, no limitation is made, and the components and structures known to those skilled in the art and applicable to secondary batteries can be selected, as long as the purpose of the present application can be achieved.

[0114] In the embodiments of the present application, the battery mentioned may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may be a battery cell, or the battery may include a battery module (or battery pack), etc.

[0115] In some embodiments, the battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet. The electrode assembly may be a wound structure or a stacked structure, and the embodiments of the present application do not limit this.

[0116] In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module.

[0117] In some embodiments, the battery may be a battery pack, and the battery pack may include a box body and battery cells, and the battery cells or battery modules are accommodated in the box body.

[0118] It should be understood that multiple battery cells can be assembled into a battery module or a battery pack, and the number of battery cells contained in the battery module or battery pack can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module or battery pack.

[0119] In some embodiments, the battery may be an energy storage device. The energy storage device includes an energy storage container, an energy storage cabinet, etc.

[0120] In the embodiments of the present application, the preparation method of the battery cell or the battery is well known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a stacking process, the electrode assembly is placed in an outer package, dried and then injected with electrolyte, and after processes such as vacuum packaging, standing, forming, and shaping, a battery cell is obtained. Optionally, multiple battery cells can further be connected in series, in parallel, or in a hybrid connection to form a battery module. Optionally, multiple battery modules can be connected in series, in parallel, or in a hybrid connection to form a battery pack. Optionally, in some embodiments, multiple battery cells can also directly form a battery pack.

[0121] The present invention will be further described in detail below through embodiments. The raw materials used in the embodiments can all be obtained through commercial channels.

[0122] Example 1 The preparation of the hard carbon negative electrode material includes the following steps: Sodium alginate, acrylamide, tetramethylethylenediamine, and azodiisobutyronitrile were added successively to a stirring kettle containing deionized water in a mass ratio of 100:35:0.1:0.1 and dispersed evenly. Subsequently, it was transferred to a reaction kettle and then under ultraviolet light irradiation, acrylamide was catalytically polymerized. The reaction time was 35 min. After the reaction was complete, it was placed in a 60 °C oven for vacuum drying, and the dried material was pulverized by an air jet mill to obtain an intermediate with a median particle size of 4.53 μm, a specific surface area of 50.07 m 2 / g, and a true density of 1.9 g / cm 3 . Then, the intermediate was placed in a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature was increased from room temperature to 1400 °C at a heating rate of 2 °C / min, and the holding time was 4 h. After cooling to room temperature, it was sieved through a 300-mesh sieve to obtain a hard carbon anode material with a median particle size of 3.58 μm, a specific surface area of 3.96 m 2 / g, and a true density of 1.57 g / cm 3 .

[0123] The SEM image (SEM model: Tescan Mira3, manufactured by Tescan, Czech Republic) of the hard carbon anode material obtained in Example 1 is as shown in Figure 1 . As can be seen from Figure 1 , the hard carbon anode material prepared in Example 1 is irregular block-shaped black particles, and the particle sizes are uniform.

[0124] The TEM image (TEM model: Talos F200X, manufactured by ThermoFisher, USA) of the hard carbon anode material obtained in Example 1 is as shown in Figure 2 . As can be seen from Figure 2 , it can be seen from the transmission electron microscope that the hard carbon anode material prepared in Example 1 has abundant nanopores and a graphite-like interlayer structure, which is beneficial to the migration and storage of sodium ions. That is, as can be seen from Figure 2 , the formation process of the short-range ordered graphite-like microcrystals in the product prepared in the embodiment of the present invention is mainly a short-range ordered graphite-like microcrystal structure, which gradually grows into a long-range disordered coiled carbon chain.

[0125] The XRD pattern (XRD model: D8 ADVANCE, manufactured by BRUKER, Germany) of the hard carbon anode material obtained in Example 1 is as shown in Figure 3 . As can be seen from Figure 3 , the peak positions of the XRD of the sample material include two broad peaks located at 2θ ≈ 23° (002) and 2θ ≈ 43° (100). That is, two typical characteristic peaks appear at 25° and 43° in the hard carbon anode material obtained in Example 1, which are related to the (002) and (100) crystal planes of hard carbon respectively.

[0126] The Raman graph of the hard carbon anode material obtained in Example 1 (Raman model: HR800, Horiba JobinYvon, France) is as Figure 4 shown. As can be seen from Figure 4 , the Raman spectrum of the hard carbon anode material obtained in Example 1 shows two typical peaks, which respectively represent disordered or defective graphite bands (D peak, 1350 cm -1 ), and crystalline graphite bands (G peak, 1580 cm -1 ). The degree of carbon structural order is 1.05 as indicated by the integral intensity ratio (ID / IG).

[0127] The hard carbon anode material obtained in Example 1 was assembled into a half-cell to test its electrochemical performance. The specific operation steps are as follows: Weigh 19 g of the active material (i.e., the hard carbon anode material), 5.0 g of conductive carbon black Super P, and 5.0 g of binder (2.5% carboxymethyl cellulose CMC), and magnetically stir at a speed of 500 rpm to mix the slurry evenly. After coating, place it in a vacuum oven at 80 °C and dry for 8 h to remove moisture; use a sodium sheet as the counter electrode, a polypropylene microporous membrane as the separator, and an electrolyte prepared by mixing a ternary solvent of 1M NaClO4 in a volume ratio of EC:DMC:PC = 1:1:1 to assemble the battery. The battery test conditions are as follows: the voltage range is 0.0 - 2.0 V. During the first week of cycling, the working steps are set as constant current discharge at 0.1C, constant current discharge at 0.05C, constant current discharge at 0.02C, and constant current charge at 0.1C; during subsequent cycling, the working steps are set as constant current discharge at 0.2C, constant current discharge at 0.1C, constant current discharge at 0.05C, constant current discharge at 0.02C, and constant current charge at 0.2C. The electrochemical performance test results are shown in Table 1.

[0128] Example 2 The preparation of the hard carbon anode material includes the following steps: Chitosan, acrylamide, tetramethylethylenediamine, and ammonium persulfate were added to a stirring kettle containing deionized water in a mass ratio of 100:20:0.1:0.1 and dispersed evenly. Subsequently, it was transferred to a reaction kettle and then under ultraviolet light irradiation, acrylamide was catalytically polymerized. The reaction time was 20 min. After the reaction was complete, it was placed in a 60 °C oven for vacuum drying, and the dried material was pulverized by an air flow pulverizer to obtain a median particle size of 4.04 μm, a specific surface area of 70.57 m 2 / g, and a true density of 1.9 g / cm 3The intermediate product is then placed into a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature is increased from room temperature to 1400 °C at a heating rate of 2 °C / min, and the holding time is 4 h. After cooling to room temperature, it is sieved through a 300-mesh sieve to obtain a hard carbon negative electrode material with a median particle size of 3.53 μm and a specific surface area of 5.07 m 2 / g and a true density of 1.5 g / cm 3 .

[0129] The hard carbon negative electrode material obtained in Example 2 is assembled into a half-cell. The test conditions are the same as those in Example 1, and the electrochemical performance test results are shown in Table 1.

[0130] Example 3 Preparation of the hard carbon negative electrode material includes the following steps: Chitosan, acrylamide, N,N'-methylenebisacrylamide, and azobisisobutyronitrile are sequentially added to a stirring kettle containing deionized water in a mass ratio of 100:25:0.1:0.1 and uniformly dispersed. Subsequently, it is transferred to a reaction kettle and then under ultraviolet light irradiation, acrylamide is catalytically polymerized. The reaction time is 25 min. After the reaction is complete, it is placed in a 60 °C oven for vacuum drying, and the dried material is pulverized by an air flow pulverizer to obtain an intermediate product with a median particle size of 4.53 μm and a specific surface area of 40.07 m 2 / g and a true density of 2.0 g / cm 3 The intermediate product is then placed into a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature is increased from room temperature to 1400 °C at a heating rate of 2 °C / min, and the holding time is 4 h. After cooling to room temperature, it is sieved through a 300-mesh sieve to obtain a hard carbon negative electrode material with a median particle size of 4.36 μm and a specific surface area of 4.89 m 2 / g and a true density of 1.5 g / cm 3 .

[0131] The hard carbon negative electrode material obtained in Example 3 is assembled into a half-cell. The test conditions are the same as those in Example 1, and the electrochemical performance test results are shown in Table 1.

[0132] Example 4 Preparation of the hard carbon negative electrode material includes the following steps: Cellulose, acrylamide, ethylene glycol dimethacrylate, and azobisisoheptonitrile are sequentially added to a stirring kettle containing deionized water in a mass ratio of 100:30:0.1:0.1 and uniformly dispersed. Subsequently, it is transferred to a reaction kettle and then under ultraviolet light irradiation, acrylamide is catalytically polymerized. The reaction time is 30 min. After the reaction is complete, it is placed in a 60 °C oven for vacuum drying, and the dried material is pulverized by an air flow pulverizer to obtain an intermediate product with a median particle size of 3.53 μm and a specific surface area of 44.87 m2 / g, the true density is 1.9 g / cm 3 of the intermediate, and then the intermediate is placed in a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature is raised from room temperature to 1400 °C at a heating rate of 2 °C / min, and the holding time is 4 h. After cooling to room temperature, it is sieved through a 300-mesh sieve to obtain a median particle size of 4.37 μm and a specific surface area of 3.88 m 2 / g, the true density is 1.5 g / cm 3 of the hard carbon negative electrode material.

[0133] The hard carbon negative electrode material obtained in Example 4 is assembled into a half-cell, and the test conditions are the same as those in Example 1. The electrochemical performance test results are shown in Table 1.

[0134] Example 5 Preparation of the hard carbon negative electrode material, including the following steps: Cellulose, acrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate are sequentially added to a stirring kettle containing deionized water in a mass ratio of 100:40:0.1:0.1 and dispersed evenly. Subsequently, it is transferred to a reaction kettle and then the polymerization reaction of acrylamide is catalytically initiated under ultraviolet light irradiation. The reaction time is 40 min. After the reaction is complete, it is placed in a 60 °C oven for vacuum drying, and the dried material is pulverized by an air flow pulverizer to obtain a median particle size of 5.93 μm and a specific surface area of 39.65 m 2 / g, the true density is 1.9 g / cm 3 of the intermediate, and then the intermediate is placed in a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature is raised from room temperature to 1400 °C at a heating rate of 2 °C / min, and the holding time is 4 h. After cooling to room temperature, it is sieved through a 300-mesh sieve to obtain a median particle size of 4.69 um and a specific surface area of 7.56 m 2 / g, the true density is 1.5 g / cm 3 of the hard carbon negative electrode material.

[0135] The hard carbon negative electrode material obtained in Example 5 is assembled into a half-cell, and the test conditions are the same as those in Example 1. The electrochemical performance test results are shown in Table 1.

[0136] Example 6 Preparation of the hard carbon negative electrode material, including the following steps: Sodium alginate, acrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate were added sequentially to a stirring kettle containing deionized water in a mass ratio of 100:50:0.1:0.1 and uniformly dispersed. Subsequently, it was transferred to a reaction kettle and then under ultraviolet light irradiation, acrylamide was catalytically polymerized. The reaction time was 50 min. After the reaction was complete, it was placed in a 60 °C oven for vacuum drying. After the dried material was pulverized by an air flow pulverizer, an intermediate with a median particle size of 4.94 μm, a specific surface area of 44.07 m2 / g, and a true density of 1.9 g / cm3 was obtained. Then, the intermediate was placed in a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature was raised from room temperature to 1400 °C at a heating rate of 2 °C / min, and the holding time was 4 h. After cooling to room temperature, it was sieved through a 300-mesh sieve to obtain a hard carbon negative electrode material with a median particle size of 5.34 μm, a specific surface area of 6.99 m 2 / g and a true density of 1.5 g / cm 3 .

[0137] The hard carbon negative electrode material obtained in Example 6 was assembled into a half-cell, and the test conditions were the same as those in Example 1. The electrochemical performance test results are shown in Table 1.

[0138] Example 7 Preparation of the hard carbon negative electrode material, including the following steps: Sodium alginate, N-n-propylacrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate were added sequentially to a stirring kettle containing deionized water in a mass ratio of 100:35:0.1:0.1 and uniformly dispersed. Subsequently, it was transferred to a reaction kettle and then under ultraviolet light irradiation, N-n-propylacrylamide was catalytically polymerized. The reaction time was 50 min. After the reaction was complete, it was placed in a 60 °C oven for vacuum drying. After the dried material was pulverized by an air flow pulverizer, an intermediate with a median particle size of 4.53 μm, a specific surface area of 50.07 m 2 / g and a true density of 1.9 g / cm 3 was obtained. Then, the intermediate was placed in a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature was raised from room temperature to 1400 °C at a heating rate of 2 °C / min, and the holding time was 4 h. After cooling to room temperature, it was sieved through a 300-mesh sieve to obtain a hard carbon negative electrode material with a median particle size of 5.34 μm, a specific surface area of 6.99 m 2 / g and a true density of 1.5 g / cm 3 .

[0139] The hard carbon negative electrode material obtained in Example 7 was assembled into a half-cell, and the test conditions were the same as those in Example 1. The electrochemical performance test results are shown in Table 1.

[0140] Example 8 Preparation of the hard carbon negative electrode material comprises the following steps: Sodium alginate, acrylamide, tetramethylethylenediamine, and ammonium persulfate are sequentially added into a stirring kettle containing deionized water in a mass ratio of 100:5:0.1:0.1 and uniformly dispersed. Subsequently, it is transferred to a reaction kettle and then under ultraviolet light irradiation, acrylamide is catalytically polymerized. The reaction time is 5 min. After the reaction is complete, it is placed in a 60°C oven for vacuum drying, and the dried material is pulverized by a jet mill to obtain an intermediate product with a median particle size of 7.53 μm, a specific surface area of 35.07 m 2 / g, and a true density of 1.9 g / cm 3 Then, the intermediate product is placed in a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature is raised from room temperature to 1100°C at a heating rate of 2°C / min, and the holding time is 4 h. After cooling to room temperature, it is sieved through a 300-mesh sieve to obtain a hard carbon negative electrode material with a median particle size of 7.63 μm, a specific surface area of 15.74 m 2 / g, and a true density of 1.5 g / cm 3

[0141] The hard carbon negative electrode material obtained in Example 8 is assembled into a half-cell. The test conditions are the same as those in Example 1, and the electrochemical performance test results are shown in Table 1.

[0142] Example 9 Preparation of the hard carbon negative electrode material comprises the following steps: Sodium alginate, acrylamide, ethylene glycol dimethacrylate, and ammonium persulfate are sequentially added into a stirring kettle containing deionized water in a mass ratio of 100:10:0.1:0.1 and uniformly dispersed. Subsequently, it is transferred to a reaction kettle and then under ultraviolet light irradiation, acrylamide is catalytically polymerized. The reaction time is 120 min. After the reaction is complete, it is placed in a 60°C oven for vacuum drying, and the dried material is pulverized by a jet mill to obtain an intermediate product with a median particle size of 7.53 μm, a specific surface area of 80.14 m 2 / g, and a true density of 1.9 g / cm 3 Then, the intermediate product is placed in a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature is raised from room temperature to 1200°C at a heating rate of 2°C / min, and the holding time is 4 h. After cooling to room temperature, it is sieved through a 300-mesh sieve to obtain a hard carbon negative electrode material with a median particle size of 8.34 μm, a specific surface area of 1.68 m 2 / g, and a true density of 1.5 g / cm 3

[0143] The hard carbon negative electrode material obtained in Example 9 is assembled into a half-cell. The test conditions are the same as those in Example 1, and the electrochemical performance test results are shown in Table 1. ​​

[0144] Example 10 Preparation of the hard carbon negative electrode material includes the following steps: Sodium alginate, acrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate were sequentially added to a stirring kettle containing deionized water in a mass ratio of 100:60:0.1:0.1 and uniformly dispersed. Subsequently, it was transferred to a reaction kettle and then under ultraviolet light irradiation, acrylamide was catalytically polymerized. The reaction time was 150 min. After the reaction was complete, it was placed in a 60 °C oven for vacuum drying. After the dried material was pulverized by a jet mill, an intermediate with a median particle size of 6.65 μm, a specific surface area of 23.04 m 2 / g, and a true density of 1.9 g / cm 3 was obtained. Then the intermediate was placed in a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature was raised from room temperature to 1500 °C at a heating rate of 2 °C / min, and the holding time was 4 h. After cooling to room temperature, it was sieved through a 300-mesh sieve to obtain a hard carbon negative electrode material with a median particle size of 8.99 μm, a specific surface area of 1.25 m 2 / g, and a true density of 1.5 g / cm 3

[0145] The hard carbon negative electrode material obtained in Example 10 was assembled into a half-cell. The test conditions were the same as those in Example 1, and the results of the electrochemical performance test are shown in Table 1.

[0146] Example 11 Preparation of the hard carbon negative electrode material includes the following steps: Sodium alginate, acrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate were sequentially added to a stirring kettle containing deionized water in a mass ratio of 100:100:0.1:0.1 and uniformly dispersed. Subsequently, it was transferred to a reaction kettle and then under ultraviolet light irradiation, acrylamide was catalytically polymerized. The reaction time was 180 min. After the reaction was complete, it was placed in a 60 °C oven for vacuum drying. After the dried material was pulverized by a jet mill, an intermediate with a median particle size of 9.53 μm, a specific surface area of 46.24 m 2 / g, and a true density of 1.9 g / cm 3 was obtained. Then the intermediate was placed in a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature was raised from room temperature to 1500 °C at a heating rate of 2 °C / min, and the holding time was 4 h. After cooling to room temperature, it was sieved through a 300-mesh sieve to obtain a hard carbon negative electrode material with a median particle size of 9.38 um, a specific surface area of 0.92 m 2 / g, and a true density of 1.5 g / cm 3

[0147] ​​The hard carbon negative electrode material obtained in Example 11 was assembled into a half-cell, and the test conditions were the same as those in Example 1. The results of the electrochemical performance test are shown in Table 1.

[0148] Comparative Example 1 The preparation of the hard carbon negative electrode material includes the following steps: Sodium alginate was placed in a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature was raised from room temperature to 1400 °C at a heating rate of 2 °C / min, and the holding time was 4 h. After cooling to room temperature, it was sieved through a 300-mesh sieve to obtain a hard carbon negative electrode material with a median particle size of 1.38 μm, a specific surface area of 1.86 m 2 / g, and a true density of 1.5 g / cm 3 of the hard carbon negative electrode material.

[0149] The hard carbon negative electrode material obtained in Comparative Example 1 was assembled into a half-cell, and the test conditions were the same as those in Example 1. The results of the electrochemical performance test are shown in Table 1.

[0150] Comparative Example 2 The preparation of the hard carbon negative electrode material includes the following steps: Coconut shell, acrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate were sequentially added to a stirring kettle containing deionized water according to a mass ratio of 100:100:0.1:0.1 and uniformly dispersed. Subsequently, it was transferred to a reaction kettle and then irradiated with ultraviolet light to catalyze the polymerization of acrylamide. The reaction time was 180 min. After the reaction was complete, it was placed in a 60 °C oven for vacuum drying, and the dried material was pulverized by an air flow pulverizer to obtain an intermediate with a median particle size of 7.53 μm, a specific surface area of 61.57 m 2 / g, and a true density of 1.9 g / cm 3 The intermediate was then placed in a high-temperature carbonization furnace filled with a nitrogen atmosphere. The carbonization temperature was raised from room temperature to 1400 °C at a heating rate of 2 °C / min, and the holding time was 4 h. After cooling to room temperature, it was sieved through a 300-mesh sieve to obtain a hard carbon negative electrode material with a median particle size of 7.88 μm, a specific surface area of 5.92 m 2 / g, and a true density of 1.5 g / cm 3 of the hard carbon negative electrode material.

[0151] The hard carbon negative electrode material obtained in Comparative Example 2 was assembled into a half-cell, and the test conditions were the same as those in Example 1. The results of the electrochemical performance test are shown in Table 1.

[0152] Performance Test The batteries prepared in the above examples and comparative examples were subjected to performance tests, which specifically included: (1)Specific surface area test: The test is carried out by the nitrogen adsorption - desorption method. Specifically, the hard carbon anode material is adsorbed below the boiling point temperature of the adsorbate, and a P / P value is given. After reaching the adsorption equilibrium, the adsorption volume V is measured (by measuring the volume difference of a known amount of gas before and after adsorption, and then obtaining the gas adsorption amount). Through a series of measured values of P / Po and V, many points are obtained, and the data points are connected to obtain the isothermal adsorption curve; conversely, by reducing the vacuum to desorb the adsorbed gas, the desorption curve can be obtained. The specific surface area and pore size distribution information are calculated by substituting the adsorption - desorption curve into different statistical models.

[0153] (2)First discharge capacity and first charge capacity test: 0.1C discharge capacity test: Constant current discharge at 0.1C until 0V, and then stand for 5 min. The capacity measured in this step is the 0.1C discharge capacity (denoted as C0), which is the first discharge capacity.

[0154] 0.1C charge capacity: Constant current and constant voltage charge at 0.1C until 2.0V, with the cut - off current of 0.05C, and then stand for 5 min. The capacity measured in this step is the 0.1C charge capacity (denoted as C1), which is the first charge capacity.

[0155] (3)Low - potential plateau capacity test: The low - potential plateau capacity corresponds to the gram capacity between 0 - 0.1V of the charge curve; among them, the data of the low - potential plateau capacity is directly read from the charge - discharge test data, which is the capacity data corresponding to 0.1V of the charge curve.

[0156] (4)First Coulombic efficiency: First Coulombic efficiency = First discharge capacity / First charge capacity * 100%.

[0157] The test results are shown in Table 1.

[0158] Table 1 Electrochemical performance test results of examples and comparative examples It can be seen from the data in Table 1 that the capacity and initial efficiency of Examples 1 - 11 are generally better than those of Comparative Examples 1 - 2, and the highest capacity can reach 330 mAh·g -1 Above, the initial efficiency of Example 1 can reach more than 90%, indicating that the hard carbon anode material prepared by constructing a three - dimensional structure of double - network cross - linking to regulate more closed pores has significantly improved capacity and initial efficiency. The specific reason analysis is as follows: It can be seen from Examples 1 to 6 and Examples 8 to 11 that as the mass ratio of the hard carbon precursor to acrylamide increases, the reversible capacity of the hard carbon negative electrode material shows a trend of first increasing and then decreasing, and the change trend of the proportion of the low-potential platform capacity also corresponds to it. This is because acrylamide undergoes a polymerization reaction under photocatalysis, crosslinks on the surface of the hard carbon precursor to form a three-dimensional structure, and self-assembles with the carboxyl functional groups on its surface to form a double-network crosslinked three-dimensional structure. During the high-temperature carbonization process, this double-network crosslinked structure gradually forms long-range disordered coiled carbon chains, which wind and contract to form a large number of closed pores, thereby increasing the storage capacity of sodium ions at the low-potential platform. When the mass ratio of acrylamide continues to increase, due to the excessive crosslinking density of its molecular chains, the carbon layers are densely stacked after high-temperature carbonization, and the closed pore volume is greatly reduced, resulting in a decrease in the platform capacity, so the first discharge capacity also decreases significantly; when the mass ratio of acrylamide is too low, the degree of crosslinking is too low, resulting in a relatively loose network formed. After high-temperature carbonization, a small number of large pores are formed on the surface of the hard carbon negative electrode material, and the specific surface area is also relatively large, resulting in a decrease in the first efficiency. Among them, the change in the photocatalysis time is mainly considered due to the increase in the amount of acrylamide used, and the photocatalysis time is also increased to ensure sufficient polymerization.

[0159] It can be seen from Comparative Examples 1 to 2 that in Comparative Example 1, sodium alginate was directly carbonized to obtain a hard carbon negative electrode material. The first charge-discharge capacity, low-potential platform capacity, and Coulomb efficiency of this hard carbon negative electrode material are all lower than those of Example 1, indicating that the capacity and first efficiency of the hard carbon negative electrode material prepared by constructing a double-network crosslinked three-dimensional structure and then regulating more closed pores are significantly improved; in Comparative Example 2, the first charge-discharge capacity, low-potential platform capacity, and Coulomb efficiency of the hard carbon negative electrode material are all lower than those of Example 1. This is because coconut shell is used as the hard carbon precursor, and the content of oxygen-containing functional groups in the coconut shell is relatively small. After subsequent carbonization treatment, almost no oxygen-containing functional groups exist, and they cannot be connected with the amide polymer to form a three-dimensional molecular chain on the surface of the hard carbon precursor and form a stable network structure, thus unable to improve the capacity and first efficiency of the material.

[0160] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A precursor of a hard carbon anode material, characterized in that, The hard carbon negative electrode material precursor includes a cross-linked product, and the cross-linked product includes a cross-linked product of an amide polymer and a hard carbon precursor; The hard carbon precursor includes carboxyl and / or hydroxyl functional groups; The amide groups in the amide polymer and the carboxyl functional groups interact through hydrogen bonds to form a three-dimensional structure of double-network cross-linking, or the amide groups in the amide polymer and the hydroxyl functional groups interact through hydrogen bonds to form a three-dimensional structure of double-network cross-linking.

2. The hard carbon anode material precursor according to claim 1, wherein The amide polymer includes polyacrylamide; and / or, The hard carbon precursor includes saccharides.

3. The hard carbon negative electrode material precursor according to claim 1 or 2, characterized in that, The hard carbon precursor includes at least one of sodium alginate, chitosan, cellulose, or β-cyclodextrin; and / or, The mass ratio of the amide polymer to the hard carbon precursor is (1 to 50):(1 to 100).

4. A method for preparing a precursor of a hard carbon anode material, characterized in that, It includes the following steps: Mix a hard carbon precursor, an amide monomer, a cross-linking agent, and a solvent to obtain a mixture, and carry out a polymerization reaction on the mixture under photocatalysis to obtain a hard carbon negative electrode material precursor; Among them, the hard carbon precursor includes carboxyl and / or hydroxyl functional groups; The amide monomer polymerizes to form an amide polymer, and the amide groups in the amide polymer and the carboxyl functional groups interact through hydrogen bonds to form a three-dimensional structure of double-network cross-linking, or the amide groups in the amide polymer and the hydroxyl functional groups interact through hydrogen bonds to form a three-dimensional structure of double-network cross-linking.

5. The preparation method of the hard carbon anode material precursor according to claim 4, wherein An initiator is also included in the mixture; The mass ratio of the hard carbon precursor, the amide monomer, the cross-linking agent, and the initiator is (1 to 100):(1 to 50):(0.1 to 10):(0.1 to 10).

6. The preparation method of the hard carbon anode material precursor according to claim 5, characterized in that, The preparation method satisfies at least one of the following conditions (1) to (7): (1) The amide monomer includes at least one of acrylamide, N-n-propylacrylamide, N-isopropylacrylamide, N,N-diethylacrylamide, N-cyclopropylacrylamide, N-methylacrylamide, or N-ethylacrylamide; (2) The hard carbon precursor includes at least one of sodium alginate, chitosan, cellulose, or β-cyclodextrin; (3) The cross-linking agent includes at least one of tetramethylethylenediamine, N,N'-methylenebisacrylamide, or ethylene glycol dimethacrylate; (4) The solvent includes at least one of water, ethanol, acetone, toluene, ether, N,N'-dimethylformamide, or ethylene glycol monomethyl ether; (5) The initiator includes at least one of azobisisobutyronitrile, ammonium persulfate, azobisisoheptonitrile, or hydrogen peroxide; (6) The photocatalysis method includes at least one of ultraviolet light photocatalysis or gamma ray photocatalysis; (7) The photocatalysis time is 10 min to 300 min.

7. A method for preparing a hard carbon negative electrode material, characterized in that, Carry out carbonization treatment on the hard carbon negative electrode material precursor to obtain a hard carbon negative electrode material; Among them, the hard carbon negative electrode material precursor includes the hard carbon negative electrode material precursor described in any one of claims 1 to 3 or the hard carbon negative electrode material precursor prepared by the method described in any one of claims 4 to 6.

8. The preparation method of the hard carbon negative electrode material according to claim 7, wherein The preparation method satisfies at least one of the following conditions (1) to (8): Before the carbonization treatment, the method further includes: drying and pulverizing the hard carbon negative electrode material to obtain an intermediate, and then carbonizing the intermediate to obtain the hard carbon negative electrode material; (2) The drying treatment includes vacuum drying, and the temperature of the vacuum drying is 50°C to 100°C; (3) The pulverizing treatment includes at least one of jet milling, mechanical grinding, ball milling or roller press milling; (4) The specific surface area of the intermediate is 50 to 200 m 2 / g; and / or, The median particle size of the intermediate is 5 μm to 10 μm; and / or, The true density of the intermediate is 1.8 to 2.2 g / cm 3 ; (5) The temperature of the carbonization treatment is 1000°C to 1600°C, the heating rate of the carbonization treatment is 0.1 to 10 °C / min, and the holding time of the carbonization treatment is 1 h to 10 h; (6) The specific surface area of the hard carbon negative electrode material is 2 to 10 m 2 / g; (7) The median particle size of the hard carbon negative electrode material is 3 μm to 6 μm; The true density of the hard carbon negative electrode material is 1.5 to 1.7 g / cm 3 .

9. 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 7 to 8.

10. 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 7 to 8, or includes the hard carbon negative electrode material according to claim 9.

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