Preparation method of negative electrode material, negative electrode material, negative electrode plate and battery

Abstract

The invention provides a preparation method of a negative electrode material, the negative electrode material, a negative electrode plate and a battery, and the preparation method comprises the following steps: S1, mixing biomass or a biomass derivative as a hard carbon precursor with sodium silicate, acrylamide, an initiator and a cross-linking agent in a solvent, uniformly stirring, and carrying out a free radical polymerization reaction under a photocatalytic condition to obtain a mixed solution; the first precursor is obtained; s2, the first precursor is soaked in a water-soluble calcium salt solution for a hybrid cross-linking reaction, then acidification is conducted, a second precursor is obtained, and a third precursor of a double-network cross-linked structure is obtained after drying, smashing and sieving; and S3, carbonizing the third precursor in an inert atmosphere, and cooling to obtain the hard carbon negative electrode material, at least solving the technical problems of enhancing the sodium ion adsorption capacity, improving the voltage platform capacity, further improving the electrochemical conversion efficiency and reasonably controlling the cost.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a method for preparing a negative electrode material, a negative electrode material, a negative electrode sheet, and a battery. Background Art

[0002] With the development of new energy technologies, secondary batteries have become one of the important ways to achieve low-carbon emissions. Lithium-ion batteries have been the main power source for low-carbon transportation such as hybrid electric vehicles and electric vehicles. However, in order to cope with the depletion of future lithium resources, the industry is also working hard to find reliable alternative batteries for lithium batteries. Sodium-ion batteries have recently received considerable attention in the field of large-scale energy storage (such as energy storage systems) because, compared with lithium-ion batteries, sodium-ion batteries have the characteristics of low cost and abundant distribution.

[0003] Graphite is often used as the negative electrode material for lithium-ion batteries. However, since sodium-graphite intercalation compounds are not easily formed and the absorption of sodium ions in graphite is extremely small, it is difficult to use graphite as the anode in sodium-ion batteries to manufacture high-energy density electrode materials. Therefore, a large amount of research has also been carried out in the industry to develop potential anode materials for lithium-ion batteries and sodium-ion batteries, including carbon-based, alloy-based, and metal oxide-based materials. Among them, hard carbon composed of amorphous carbon domains with irregular orientations and a small number of graphite layers approximately parallelly stacked has become one of the more promising anode materials because of its low cost, easy synthesis, high stability during sodium ion insertion and deinsertion, and the ability to be produced using renewable resources (such as wood, macroalgae, and fruit shells). In addition, the large spacing between the basal planes of graphite layers and the defects and micropores present in hard carbon provide favorable positions for the absorption of sodium ions, enabling a relatively high reversible capacity to be obtained. More importantly, hard carbon has a low-voltage plateau capacity below 0.1 V, which is not possessed by other types of carbon (such as soft carbon), making it more favorable for the development of high-energy density electrodes for full batteries.

[0004] However, in the specific preparation process of the negative electrode material for sodium-ion batteries, it often faces great challenges in ensuring good transport performance and ion diffusion kinetics performance of sodium ions at low temperatures or high charging rates. Moreover, the structure of hard carbon materials cannot be well regulated in the process, which will affect the performance of the fabricated electrode sheets and batteries. The current process in the industry of performing a self-boosting reaction in a closed reactor to control the formed hard carbon structure not only has a high cost but also a low production efficiency, and cannot meet the requirements of actual production. Summary of the Invention

[0005] In view of this, an embodiment of the present application provides a method for preparing a negative electrode material, a negative electrode material, a negative electrode sheet, and a battery to solve at least one problem in the background art, and at least solves the technical problems of enhancing the sodium ion adsorption capacity, improving the voltage plateau capacity, thereby improving the electrochemical conversion efficiency and reasonably controlling the cost.

[0006] In a first aspect, a method for preparing a negative electrode material is provided, including: S1: Using biomass or biomass derivatives as hard carbon precursors, mixing them with sodium silicate, acrylamide, an initiator, and a crosslinking agent in a solvent, stirring evenly, and then undergoing a free radical polymerization reaction under photocatalytic conditions to obtain the first precursor; S2: Soaking the first precursor in a water-soluble calcium salt solution for a hybridization crosslinking reaction, and then acidifying it to obtain a second precursor. After drying, pulverizing, and sieving, a third precursor with a double-network crosslinked structure is obtained; S3: Carbonizing the third precursor under an inert atmosphere and then cooling it to obtain a hard carbon negative electrode material.

[0007] Optionally, step S1 satisfies at least one of the following characteristics: (1) The biomass or the biomass derivative includes at least one of sodium alginate, chitosan, cellulose, and β-cyclodextrin; (2) The mass ratio of the hard carbon precursor, the sodium silicate, the acrylamide, the initiator, and the crosslinking agent is 100: (1 - 5): (1 - 50): (0.5 - 2): (0.1 - 2); (3) The initiator includes at least one of azobisisobutyronitrile, ammonium persulfate, azobisisoheptonitrile, and hydrogen peroxide; (4) The crosslinking agent includes at least one of tetramethylethylenediamine, N,N'-methylenebisacrylamide, and ethylene glycol dimethacrylate; (5) The solvent is deionized water.

[0008] Optionally, step S1 satisfies at least one of the following characteristics: (1) The photocatalytic conditions include: using a photocatalytic method of ultraviolet light and / or gamma rays; (2) The photocatalytic time of the photocatalytic conditions is 10 min - 300 min.

[0009] Optionally, step S2 satisfies at least one of the following characteristics: (1) The water-soluble calcium salt used in the water-soluble calcium salt solution includes at least one of calcium nitrate, calcium lactate, calcium chloride, and calcium dihydrogen phosphate; (2) The mass percentage concentration of the water-soluble calcium salt dissolved in the water-soluble calcium salt solution is 1% - 20%; (3) The immersion time of the first precursor in the water-soluble calcium salt solution is 5 min - 120 min; (4) The acid solution used for acidification includes at least one of hydrochloric acid, sulfuric acid, and nitric acid; (5) The molar concentration of the acid solution used for acidification is 0.1 mol / L - 3 mol / L; (6) The acidification reaction time of the acidification is 5 min - 120 min; (7) The hybrid cross-linking reaction is an organic-inorganic hybrid reaction.

[0010] Optionally, step S2 satisfies at least one of the following characteristics: (1) The drying treatment method of the drying is: vacuum drying treatment in an oven at 50°C - 100°C; (2) The comminution method of the comminution includes at least one of jet milling, mechanical grinding, ball milling, and roller press milling; (3) The sieving method of the sieving is: sieving under the condition of a 100-mesh - 300-mesh sieve.

[0011] Optionally, step S3 satisfies at least one of the following characteristics: (1) The inert gas of the inert atmosphere includes at least one of argon, nitrogen, and helium; (2) The carbonization temperature of the carbonization is 1000°C - 1600°C; (3) The carbonization heating rate of the carbonization is 0.1°C / min - 10°C / min; (4) The carbonization holding time of the carbonization is 1 h - 10 h.

[0012] Optionally, in step S3, before carbonization, the third precursor satisfies the following characteristics: (1) The specific surface area of the third precursor is 4 m 2 / g - 500 m 2 / g, the median particle size of the third precursor is 5 μm - 50 μm, and the true density of the third precursor is 1.8 g / cm 3 -2.2 g / cm 3 ; (2) After carbonization, the third precursor satisfies the following characteristics: the specific surface area of the hard carbon negative electrode material is 2 m 2 / g - 15 m 2 / g, the median particle size of the hard carbon negative electrode material is 5 μm - 10 μm, and the true density of the hard carbon negative electrode material is 1.4 g / cm 3 -1.8 g / cm 3 .

[0013] In a second aspect, a negative electrode material is provided, which is prepared by the method for preparing a negative electrode material described in any of the above solutions.

[0014] In a third aspect, a negative electrode sheet is provided, which includes the negative electrode material prepared by the method for preparing a negative electrode material described above.

[0015] In a fourth aspect, a battery is provided, which includes the negative electrode sheet described in the above solution.

[0016] The method for preparing a negative electrode material, the negative electrode material, the negative electrode sheet, and the battery provided by the embodiments of the present application have at least obtained the following beneficial technical effects: First, by introducing acrylamide monomer to undergo a free radical polymerization reaction, a polymer layer is formed on the surface of the hard carbon precursor. The amino functional groups on the polymer chain form hydrogen bonds with the carboxyl and hydroxyl groups on the surface of the hard carbon precursor to form a first precursor with a double-network crosslinked three-dimensional network structure. The addition of an initiator can initiate the free radical polymerization of acrylamide monomer under photocatalysis, while the crosslinking agent can promote the crosslinking of acrylamide single chains to form a corresponding three-dimensional network structure, thereby obtaining a network structure with well-developed pores. The photocatalytic condition can more effectively play a catalytic role when acrylamide monomer undergoes a free radical polymerization reaction, and can further accelerate the free radical polymerization reaction process, making the reaction more sufficient and efficient, thereby shortening the synthesis time and improving production efficiency. Moreover, the photocatalytic method is easy to obtain and has the advantages of sustainable energy, relatively small pollution, and environmental friendliness; Second, the first precursor with a double-network crosslinked three-dimensional organizational structure is immersed in a water-soluble calcium salt solution. The dissolved calcium ions can form calcium silicate particles with the sodium silicate inorganic molecules introduced into the hard carbon, and also interact with the hard carbon precursor and silicate ions to form an organic-inorganic hybrid crosslinked structure. The calcium silicate particles form a multi-nanowire structure under acid induction, and many tiny pores will form on the surface of calcium silicate. This nanowire structure will be abundantly attached to the hard carbon precursor, greatly increasing the specific surface area of the finally prepared hard carbon negative electrode material. Thereby, the adsorption capacity of the negative electrode material for sodium ions can be greatly improved, and the reversible capacity of the negative electrode material can be significantly enhanced; Furthermore, by further combining carbonization treatment, it can ensure that the crystal structure and electrochemical performance of the third precursor with a specific organizational structure obtained by preparation reach the best state, not only optimizing the particle morphology and conductivity of the negative electrode material, but also improving the energy density and output power of the battery, and further enhancing the stability and cycle life of the battery.

[0017] The additional aspects and advantages of the present application will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present application. Description of the Drawings

[0018] The accompanying drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings: Figure 1 is a schematic flowchart of a method for preparing a negative electrode material provided by an embodiment of the present application; Figure 2 is an SEM image of the hard carbon negative electrode material obtained by performance testing in Example 1 of the present application; Figure 3 is a TEM image of the hard carbon negative electrode material obtained by performance testing in Example 1 of the present application; Figure 4 is an XRD pattern of the hard carbon negative electrode material obtained by performance testing in Example 1 of the present application; Figure 5 is a charge-discharge curve of a half-cell of the hard carbon negative electrode material obtained by performance testing in Example 1 of the present application. Detailed Embodiments

[0019] In order to make the technical solutions and beneficial effects of the present invention more obvious and understandable, the following will be described in detail by combining the accompanying drawings and listing specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are generally in accordance with conventional experimental conditions. The reagents and raw materials used in the present invention are commercially available unless otherwise specified.

[0020] In the following description, a large number of specific details are given to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present application, some technical features known to the art are not described; that is, not all features of the actual embodiments are described here, and the well-known functions and steps are not described in detail.

[0021] The purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present application. The terms "comprising" and / or "including", when used in this specification, determine the presence of the described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. When used herein, the term "and / or" includes any and all combinations of the related listed items.

[0022] To thoroughly understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. The preferred embodiments of this application are described in detail below. However, in addition to these detailed descriptions, this application may have other implementation manners.

[0023] Unless otherwise defined, the technical and scientific terms used in this application have the same meanings as those of the technical and scientific terms in the technical field to which this application belongs.

[0024] For those not specified with specific techniques or conditions in the following embodiments, they are generally carried out according to the conventional techniques or conditions described in the literature in this field, or according to the conditions recommended in the product manual and by the manufacturer. The numerical ranges in the following embodiments include the endpoint values.

[0025] As described in the background art, hard carbon has many advantages in the development and preparation of sodium-ion batteries. However, in order to obtain a high charge-discharge Coulomb efficiency and reversible specific capacity, it is necessary to consider how to specifically achieve an excellent preparation and formation structure by using hard carbon materials to optimize the charge-discharge platform capacity. In fact, during the research and development process of proposing the solution of this invention, the inventors did not get stuck in the technical ideas of complex and high-cost processes such as using a closed pressure-increasing reaction to control the formation structure or traditional atomic doping. Instead, through various in-depth analysis, comparison studies, and relevant experimental verifications, it was found that: after uniformly mixing raw materials such as hard carbon precursors, sodium silicate, acrylamide, initiators, and crosslinking agents and stirring them evenly, first, the addition of the initiator initiates the free radical polymerization of acrylamide monomers under photocatalysis, so that the acrylamide monomers form linear molecular chains after polymerization, and under the action of the crosslinking agent, they are connected to each other and gradually form a three-dimensional molecular chain and a stable network structure. At the same time, the amino functional groups on the side chains of polyacrylamide and the carboxyl and hydroxyl groups on the hard carbon precursors are crosslinked with each other through hydrogen bonding to form a double-network crosslinked structure (i.e., a three-dimensional organizational structure of double-network crosslinking).

[0026] Furthermore, after introducing sodium silicate inorganic molecules into hard carbon and soaking it in a soluble calcium salt solution, calcium ions react with silicate ions alone to form calcium silicate particles. At the same time, they also interact with the hard carbon precursor and silicate ions to form an organic-inorganic hybrid cross-linked structure. Finally, the calcium silicate particles gradually form nanowires under acid induction. These nanowires adhere to the hard carbon, resulting in many tiny pores on the surface, thereby greatly increasing the specific surface area of the finally prepared hard carbon negative electrode material, and thus greatly improving the adsorption capacity for sodium ions. Through experimental verification, the hard carbon negative electrode material prepared using this solution has a turbulent structure composed of short-range ordered and long-range disordered parallel carbon layers inside. This organizational structure makes it possible to form more micropores, thereby being able to adsorb more sodium ions, and thus also improving the energy density of the sodium-ion battery. The battery electrode sheet made of this hard carbon negative electrode material was tested and obtained a relatively high first charge-discharge specific capacity and charge-discharge efficiency.

[0027] Based on this, the embodiments of the present application provide a preparation method for a negative electrode material, as Figure 1 shown. The preparation method of the negative electrode material includes several preparation steps from step S1 to step S3. The operation process of each step will be specifically described below.

[0028] S1. Use biomass or biomass derivatives as the hard carbon precursor, mix them with sodium silicate, acrylamide, initiator, and cross-linking agent in a solvent, stir evenly, and then carry out a free radical polymerization reaction under photocatalytic conditions to obtain a first precursor.

[0029] By introducing acrylamide monomer to carry out a free radical polymerization reaction, a polymer layer is formed on the surface of the hard carbon precursor. The amino functional groups on the polymer chain form hydrogen bonds with the carboxyl and hydroxyl groups on the surface of the hard carbon precursor to form a first precursor with a three-dimensional network body structure of double network cross-linking, so as to prepare for the subsequent reaction with the calcium salt solution.

[0030] In some embodiments, the biomass or biomass derivatives used include one or more (referring to two or more in the embodiments) combinations of sodium alginate, chitosan, cellulose, β-cyclodextrin, etc., or any other feasible biomass or biomass derivatives. The embodiments of the present application do not make special limitations on this. Biomass and its derivatives refer to various organisms formed through photosynthesis, including all animals, plants, and microorganisms. Biomass energy is the form of energy in which solar energy is stored in biomass in the form of chemical energy. It is an energy source with rich sources, low consumption, low price, and high carbon content. Therefore, using this kind of raw material can also reduce the preparation raw material cost to a certain extent.

[0031] In some embodiments, sodium silicate uses sodium silicate raw materials in a smaller particle form, which can enhance the cross-linking effect. In some embodiments, the particle size of the sodium silicate can be selected in the range of 40 nm to 60 nm, preferably in the range of 48 nm to 52 nm. For example, the particle size is about 50 nm, etc. The sodium silicate raw materials within this particle size range have a better promoting and enhancing effect on the cross-linking reaction. In some embodiments, the initiator can be one or a combination of azobisisobutyronitrile, ammonium persulfate, azobisisoheptonitrile, and hydrogen peroxide. In some embodiments, the cross-linking agent can be one or a combination of tetramethylethylenediamine, N,N'-methylenebisacrylamide, and ethylene glycol dimethacrylate. In some embodiments, the solvent used can be deionized water. It should be noted that without departing from the inventive concept of the present application, any other feasible initiator, cross-linking agent, or solvent can also be used, and the embodiments of the present application do not specifically limit them. The addition of the initiator can initiate the free radical polymerization of acrylamide monomers under photocatalysis, while the cross-linking agent can promote the cross-linking of acrylamide single chains to form a corresponding three-dimensional network structure, thereby obtaining a network structure with developed pores.

[0032] In some embodiments, the mass ratio of the hard carbon precursor, sodium silicate, acrylamide, initiator, and cross-linking agent can be set to 100:(1 - 5):(1 - 50):(0.5 - 2):(0.1 - 2). For example, it can be 100:1:5:0.5:0.5, 100:2:10:1:1, 100:3:30:1.5:1.5, or 100:4:50:2:2, etc. Controlling the mass ratio of the hard carbon precursor, sodium silicate, acrylamide, initiator, and cross-linking agent within the above range can not only ensure sufficient free radical polymerization reactions between the hard carbon precursor and sodium silicate and acrylamide, with a reasonable proportion of the initiator, but also better promote the free radical polymerization of acrylamide monomers under photocatalysis. The appropriate proportion of the cross-linking agent is more conducive to the formation of a three-dimensional network structure during the cross-linking of acrylamide single chains. And by controlling the proportion of the cross-linking agent, the cross-linking degree of the formed three-dimensional network can also be controlled, which is beneficial to preparing an ideal network structure with relatively rich and developed pores. Specific different implementation manners can be formulated using any possible combination ratio or any other feasible ratio within the above ratio range.

[0033] In actual preparation, a hard carbon precursor solution, a sodium silicate solution, an acrylamide solution, an initiator solution, and a crosslinker solution with certain mass concentrations can be respectively prepared. Among them, solvents such as deionized water can be used. This can better promote the dissolution and mixing of reactants, facilitate the control of the reaction rate, and improve the uniformity and sufficiency of the reaction. Further, the mass percentage concentration of the hard carbon precursor solution can be 10% - 50%. The mass percentage concentration of the sodium silicate solution can be 1% - 10%. The mass percentage concentration of the acrylamide solution can be 5% - 25%. The mass percentage concentration of the initiator solution can be 0.5% - 5%. The mass percentage concentration of the crosslinker solution can be 0.1% - 10%.

[0034] In some embodiments, for the photocatalytic conditions of the free radical polymerization reaction, ultraviolet photocatalysis or gamma ray photocatalysis can be used. Selecting appropriate photocatalytic conditions can more effectively play a catalytic role during the free radical polymerization reaction of acrylamide monomers, making the reaction more sufficient and efficient. Moreover, due to the relatively low pollution of the photocatalytic method, it has the advantage of environmental friendliness. Among them, the ultraviolet photocatalysis method has the advantages of easy access to the light source, low cost, and low environmental pollution. The gamma ray photocatalysis method, due to the relatively strong and high-energy gamma ray radiation, can accelerate the free radical polymerization reaction process, thereby shortening the synthesis time and improving production efficiency. It also has the advantages of easy access and sustainable energy. It should be noted that any other feasible corresponding light source photocatalysis method can also be used as long as it can achieve the reaction catalytic function effect. The embodiments of the present application do not make special limitations on this.

[0035] In some embodiments, the specific photocatalytic time of the photocatalytic conditions can be selected within the following time range: 10 min - 300 min. For example, the photocatalytic time can be set to values such as 10 min, 20 min, 50 min, 80 min, 100 min, 130 min, 150 min, 200 min, 240 min, 280 min, 300 min, etc. Other feasible value parameters can also be selected. An appropriate photocatalytic time can better exert the photocatalytic effect of the light source during the reaction, making the free radical polymerization reaction more sufficient and efficient, which is also beneficial to obtaining a more ideal crosslinking reaction effect subsequently.

[0036] S2: Immerse the first precursor in a water-soluble calcium salt solution for a hybrid crosslinking reaction, and then acidify it to obtain a second precursor. After drying, pulverizing, and sieving, a third precursor with a double-network crosslinked structure is obtained.

[0037] First, immerse the first precursor with a dual-network cross-linked three-dimensional tissue structure prepared in the previous step in a water-soluble calcium salt solution. The dissolved calcium ions can form calcium silicate particles with the sodium silicate inorganic molecules introduced into the hard carbon, and at the same time, they also interact with the hard carbon precursor and silicate ions to form an organic-inorganic hybrid cross-linked structure. The calcium silicate particles form a multi-nanowire structure under acid induction, and many tiny pores will form on the surface of the calcium silicate. This nanowire structure will adhere to a large amount inside and on the surface of the hard carbon tissue structure. And through experimental verification, after acid treatment, the specific surface area of the third precursor increases significantly, and thus the specific surface area of the finally prepared hard carbon negative electrode material increases significantly, thereby greatly improving the adsorption capacity of the negative electrode material for sodium ions and also greatly increasing the reversible capacity of the negative electrode material.

[0038] In some embodiments, the hybrid cross-linking reaction that occurs when the first precursor is immersed in the water-soluble calcium salt solution is an organic-inorganic hybrid reaction. In some embodiments, this organic-inorganic hybrid reaction is an organic-inorganic hybrid cross-linking reaction. Through this reaction, an organic-inorganic hybrid cross-linked polymer with a developed pore structure and a dual-network cross-linked structure with multiple nanowires attached can be obtained, that is, the second precursor with high adsorption capacity is prepared.

[0039] In some embodiments, the water-soluble calcium salt used in the water-soluble calcium salt solution can be a combination of one or more of calcium nitrate, calcium lactate, calcium chloride, and calcium dihydrogen phosphate, or any other feasible water-soluble calcium salt solution can also be used, as long as it can provide a source of dissolved calcium ions and meet the aforementioned reaction requirements. The embodiments of the present application do not make special limitations on this.

[0040] In some embodiments, the mass percentage concentration of the water-soluble calcium salt dissolved in the water-soluble calcium salt solution is 1% - 20%. For example, it can take values such as 1%, 5%, 8%, 10%, 15%, 20%, etc., or any other feasible preparation ratio can also be selected. The embodiments of the present application do not make limitations. By controlling the appropriate mass percentage concentration of the water-soluble calcium salt, it is more able to ensure the provision of sufficient dissolved calcium ions to promote the reaction of generating calcium silicate particles, ensure the generation of sufficient nanowire tissue, and also avoid excessive dissolution and save the preparation cost.

[0041] In some embodiments, the immersion time of the first precursor in the water-soluble calcium salt solution ranges from 5 min to 120 min. For example, it can take values such as 5 min, 10 min, 30 min, 60 min, 90 min, 120 min, etc., or any other feasible value parameters can also be selected. The embodiments of the present application do not make limitations. An appropriate immersion time is beneficial to the generation of a sufficient amount of calcium silicate particles and promotes the sufficient reaction of interacting with the hard carbon precursor and silicate ions to form an organic-inorganic hybrid cross-linked structure.

[0042] In some embodiments, the acid solution used for the acidification treatment includes a combination of one or more of hydrochloric acid, sulfuric acid, and nitric acid. In some embodiments, the acidification reaction time for the acidification ranges from 5 min to 120 min. For example, it can be 5 min, 15 min, 40 min, 55 min, 80 min, 120 min, etc. Other any value parameters can also be selected, and the embodiments of the present application do not make limitations. An appropriate acidification reaction time can better ensure an effective acid induction effect, promote the formation of sufficient multiple nanowire structures, and further provide more sodium ion adsorption sites.

[0043] Thus, through the operation process of hybridizing and crosslinking the first precursor prepared from the hard carbon precursor with the water-soluble calcium salt solution by soaking and then acidifying, especially by setting a relatively appropriate concentration ratio of the calcium salt solution, soaking time, or acidification time, it can ensure that sufficient dissolved calcium ions react fully with silicate ions to form calcium silicate nanoparticles, and after acidification, more micropores are formed by the formed nanowires, greatly increasing the specific surface area, which is obviously more conducive to the adsorption of sodium ions.

[0044] In some embodiments, the drying treatment method for drying the prepared second precursor is: under the temperature condition of 50°C - 100°C, vacuum drying treatment is carried out in an oven. The specific temperature setting can be 50°C, 60°C, 75°C, 90°C, 100°C, etc. Other any feasible value parameters can also be selected, and the embodiments of the present application do not make limitations. The temperature of 50°C - 100°C is a relatively appropriate drying treatment temperature because this temperature range is sufficient to meet the effect of drying the second precursor and fully removing moisture. If the temperature is too low, the expected drying effect cannot be achieved, and if the temperature is too high, energy will be wasted, which is not conducive to cost savings.

[0045] In some embodiments, after the drying treatment of the second precursor, it is also crushed and sieved to obtain a third precursor. In some embodiments, the specific crushing method can be a combination of one or more of air crushing, mechanical grinding, ball milling, and roller press milling, or other any feasible crushing process methods, and the embodiments of the present application do not make special limitations. In some embodiments, the specific sieving method for sieving can be sieving under the condition of a sieve mesh size of 100 mesh - 300 mesh, such as 100 mesh, 120 mesh, 150 mesh, 200 mesh, 260 mesh, 300 mesh, etc. Other any feasible sieve mesh sizes can also be used, and the embodiments of the present application do not make special limitations. By performing particle crushing in an appropriate manner and screening under the condition of a suitable sieve mesh size, solid particles with a uniform particle size distribution can be obtained, which can ensure uniform heating during the subsequent carbonization process and make the physicochemical properties of the carbonized material have good consistency.

[0046] S3: Carbonize the third precursor in an inert atmosphere and then cool it to obtain a hard carbon negative electrode material.

[0047] Based on the above-prepared third precursor, through carbonization treatment at an appropriate temperature in an inert atmosphere, it is possible to ensure that the crystal structure and electrochemical performance of the third precursor with the specific organizational structure prepared above reach the optimal state, not only optimizing the particle morphology and conductivity of the anode material, but also improving the energy density and output power of the battery, thereby enhancing the stability and cycle life of the battery.

[0048] In some embodiments, the inert gas in the inert atmosphere used includes one or a combination of argon, nitrogen, helium, etc., and other any feasible inert gas can also be used, and the embodiments of the present application do not make special limitations. In some embodiments, the third precursor is specifically treated by high-temperature carbonization in an inert atmosphere. In some embodiments, the carbonization temperature range for carbonization is 1000°C - 1600°C. In some embodiments, the setting range of the carbonization heating rate is 0.1°C / min - 10°C / min. In some embodiments, the carbonization holding time range for carbonization is 1h - 10h. In some embodiments, the third precursor after carbonization treatment can be cooled to room temperature, such as a temperature value selected within the temperature range between 20°C and 30°C, or any other feasible temperature, and the embodiments of the present application do not make special limitations. In some embodiments, after cooling, it can also be sieved again under the condition of a screen size of 100 mesh - 300 mesh, specifically, 100 mesh, 125 mesh, 155 mesh, 190 mesh, 270 mesh, 300 mesh, etc. can be selected, or any other feasible screen size can also be used, so as to further precisely control to obtain a hard carbon anode material that meets the expected particle size and performance requirements.

[0049] The precise control of the high-temperature carbonization treatment method and appropriate treatment conditions can not only optimize the organizational structure and performance of the anode material, but also achieve high crystallinity and high specific surface area on the surface of the anode material, which is an important means to further improve the comprehensive performance of the prepared anode material and the battery.

[0050] In some embodiments, before carbonization treatment, the specific surface area range of the third precursor is 4m 2 / g - 500m 2 / g, the median particle size range of the third precursor is 5μm - 50μm, and the true density range of the third precursor is 1.8g / cm 3 - 2.2g / cm 3 ; after carbonization treatment, the specific surface area of the prepared hard carbon anode material is 2m 2 / g - 15m 2 / g, the median particle size of the prepared hard carbon anode material is 5μm - 10μm, and the true density of the prepared hard carbon anode material is 1.4g / cm 3 - 1.8g / cm 3。By controlling the above key performance characterization parameters for preparing the anode material, the prepared hard carbon anode material can achieve the expected material performance effects. The change in specific surface area before and after indicates that after high-temperature carbonization, the specific surface area of hard carbon decreases significantly. Combining the change in true density values before and after can further illustrate that a large number of open pores gradually form into micropores or closed pores, thereby increasing the plateau region capacity of the prepared hard carbon material. Controlling the median particle size within an appropriate range is for kinetic performance considerations. If the particle size is too large, the kinetics cannot be improved. If the particle size is too small, the specific surface area of hard carbon will be too large, which will lead to a serious gas generation risk in the subsequent manufactured battery cells. Therefore, by appropriately controlling this material index range, the performance of the prepared product can be further optimized and guaranteed.

[0051] In addition, some embodiments of the present application also provide an anode material prepared by the preparation method of the anode material provided by any of the above embodiments. It should be understood that all the features and advantages of the preparation method of the anode material described in the above embodiments equally apply to the anode material in the embodiments of the present application and will not be elaborated here one by one.

[0052] In addition, based on the anode material with a developed pore structure and a dual-network cross-linked structure with multiple nanowires attached prepared by any of the above embodiments, some embodiments of the present application also provide an anode sheet and a battery made therefrom, and after corresponding performance tests and verifications, not only a high low-potential plateau capacity is obtained, but also relatively excellent first charge-discharge specific capacity and first Coulomb efficiency are obtained.

[0053] It should be understood that since the anode sheet of the battery in the embodiments of the present application includes the anode material prepared by the preparation method of the anode material described in any of the above embodiments or includes the anode material described in the above embodiments, the beneficial effects of the anode material described in any of the above embodiments equally apply to this battery.

[0054] In some embodiments, the battery can be a secondary battery, and the secondary battery can be a sodium-ion secondary battery. Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and de-embedded back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0055] The technical solution of the present application will be further described below in conjunction with multiple embodiments and comparative examples. First of all, it should be noted that steps S1, S2, and S3 in the preparation method of the negative electrode material provided by the embodiment solution of the present application are respectively implemented as operation steps (1), operation step (2), operation step (3), operation step (4), and operation step (5) in the following embodiments. Similarly, in the corresponding comparative examples, it can be seen that the step numbers (1) to (5) are only for the convenience of representation and description, and should not be understood as a limitation or conflicting description or representation of steps S1, S2, and S3 in the foregoing embodiments. Example 1

[0056] (1) Sodium alginate, sodium silicate, acrylamide, azobisisobutyronitrile, and tetramethylethylenediamine were sequentially added to a stirring kettle containing deionized water in a mass ratio of 100:1:1:0.5:0.1 and uniformly dispersed to obtain a prepolymerization mixture; (2) The prepolymerization mixture obtained in step (1) was poured into a glass petri dish with a diameter of 200 mm to make it evenly distributed, and then under the action of an ultraviolet lamp, acrylamide was catalytically initiated to undergo a free radical polymerization reaction. The catalytic reaction time (i.e., the photocatalytic time) was 10 min to obtain a first precursor with a well-developed pore double-network cross-linked structure; (3) The first precursor obtained in step (2) was immersed in a calcium nitrate solution with a mass percentage concentration of 1% for 5 min to carry out an organic-inorganic hybrid cross-linking reaction, and then transferred to a 0.1 mol / L hydrochloric acid solution for an acidification reaction. The reaction time was 5 min to obtain a second precursor with a double-network cross-linked three-dimensional structure with nanowire distribution; (4) The second precursor obtained in step (3) was placed in a 50 °C oven for vacuum drying treatment, and then airflow pulverized and sieved through 300 meshes to obtain a third precursor; (5) The third precursor obtained in step (4) was placed in a high-temperature carbonization furnace, and under the protection of a nitrogen atmosphere, it was heated from room temperature to 1000 °C at a heating rate of 0.1 °C / min, and the holding time was 2 h. After carbonization, it was cooled to room temperature and sieved through 300 meshes to obtain a hard carbon negative electrode material.

[0057] Exemplarily, the specific performance test conditions and processes are as follows: The nitrogen-doped hard carbon anode material obtained in this example was assembled into a half-cell to test its electrochemical performance. The specific operation steps were as follows: Weigh 19 g of the active material, 5.0 g of the conductive agent (Super P, carbon black conductive agent), and 5.0 g of the binder (2.5% CMC, sodium carboxymethyl cellulose binder). Magnetically stir the slurry at a speed of 500 rpm to mix it evenly. After coating, place it in a vacuum oven at 80 °C and dry it 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 1 M NaClO4 in a volume ratio of EC (ethylene carbonate solvent): DMC (dimethyl carbonate solvent): PC (propylene carbonate solvent) of 1:1:1 for battery assembly. The battery test conditions were as follows: The voltage range was 0 - 2.0 V. The specific steps were as follows: Constant current discharge at 0.1C to 0 V to obtain the first discharge specific capacity; Constant current charge at 0.1C to 2.0 V to obtain the first charge specific capacity; The low potential plateau charge specific capacity was the charge specific capacity corresponding to when the voltage reached 0.8 V during constant current charge at 0.1C; The first Coulombic efficiency = (first discharge specific capacity / first charge specific capacity) * 100%. The final electrochemical performance test results are shown in Table 1 below.

[0058] Specific surface area test method: Refer to GB / T 21650.2 - 2008 for testing. Use a fully automatic gas adsorption instrument for testing, and utilize the Brunauer - Emmett - Teller (BET) multi - molecular layer adsorption model algorithm to obtain the specific surface area of the sample to be tested. Example 2

[0059] (1) Sodium alginate, sodium silicate, acrylamide, azobisisobutyronitrile, and tetramethylethylenediamine were added to a stirring kettle containing deionized water in a mass ratio of 100:1.5:50:2:2 in sequence and dispersed evenly to obtain a prepolymerization mixture. (2) Pour the prepolymerization mixture obtained in step (1) into a glass petri dish with a diameter of 200 mm to make it distribute evenly. Subsequently, under the action of an ultraviolet lamp, catalyze and initiate the free - radical polymerization reaction of acrylamide. The catalytic reaction time was 300 min to obtain a first precursor with a well - developed pore double - network cross - linked structure. (3) Immerse the first precursor obtained in step (2) in a 20% calcium nitrate solution for 120 min to carry out an organic - inorganic hybrid cross - linking reaction. Then transfer it to a 2 mol / L hydrochloric acid solution for an acidification reaction. The acidification reaction time was 120 min to obtain a second precursor with a double - network cross - linked three - dimensional structure with nanowire distribution. (4) Place the second precursor obtained in step (3) in a 100 °C oven for vacuum drying treatment. Subsequently, crush it with air flow and sieve it through a 100 - mesh sieve to obtain a third precursor. (5) The third precursor obtained in step (4) is placed in a high-temperature carbonization furnace and heated from room temperature to 1600 °C at a heating rate of 10 °C / min under a nitrogen atmosphere protection, with a holding time of 10 h. After carbonization, it is cooled to room temperature and sieved through a 100-mesh sieve to obtain the hard carbon anode material.

[0060] The specific performance test conditions and operation procedures of the hard carbon anode material obtained in this example are the same as those in Example 1, and the final electrochemical performance test results are shown in Table 1 below. Example 3

[0061] (1) Cellulose, sodium silicate, acrylamide, azobisisobutyronitrile, and tetramethylethylenediamine are sequentially added to a stirring kettle containing deionized water according to a mass ratio of 100:2:25:1.5:0.5 and uniformly dispersed to obtain a prepolymerization mixture; (2) The prepolymerization mixture obtained in step (1) is poured into a glass petri dish with a diameter of 200 mm to make it evenly distributed, and then under the action of an ultraviolet lamp, acrylamide is catalytically initiated to undergo a free radical polymerization reaction for 20 min to obtain a first precursor with a well-developed pore double-network cross-linked structure; (3) The first precursor obtained in step (2) is soaked in a 5% calcium nitrate solution for 60 min to carry out an organic-inorganic hybrid cross-linking reaction, and then transferred to a 1 mol / L hydrochloric acid solution for an acidification reaction for 60 min to obtain a second precursor with a double-network cross-linked three-dimensional structure with nanowire distribution; (4) The second precursor obtained in step (3) is placed in a 60 °C oven for vacuum drying treatment, then ball-milled and sieved through a 200-mesh sieve to obtain a third precursor; (5) The third precursor obtained in step (4) is placed in a high-temperature carbonization furnace and heated from room temperature to 1100 °C at a heating rate of 0.1 °C / min under a nitrogen atmosphere protection, with a holding time of 5 h. After carbonization, it is cooled to room temperature and sieved through a 200-mesh sieve to obtain the hard carbon anode material.

[0062] The specific performance test conditions and operation procedures of the hard carbon anode material obtained in this example are the same as those in Example 1, and the final electrochemical performance test results are shown in Table 1 below. Example 4

[0063] (1) Chitosan, sodium silicate, acrylamide, azobisisobutyronitrile, and tetramethylethylenediamine are sequentially added to a stirring kettle containing deionized water according to a mass ratio of 100:2.5:50:2:2 and uniformly dispersed to obtain a prepolymerization mixture; (2) Pour the pre-polymerized mixture obtained in step (1) into a glass petri dish with a diameter of 200 mm to make it evenly distributed, and then under the action of gamma rays, catalyze and initiate the free radical polymerization reaction of acrylamide. The catalytic reaction time is 40 min to obtain a first precursor with a well-developed porous double-network cross-linked structure; (3) Immerse the first precursor obtained in step (2) in a 5% calcium lactate solution for 30 min to carry out an organic-inorganic hybrid cross-linking reaction, and then transfer it to a 0.1 mol / L sulfuric acid solution for an acidification reaction. The reaction time is 10 min to obtain a second precursor with a double-network cross-linked three-dimensional structure with nanowire distribution; (4) Put the second precursor obtained in step (3) into an oven at 70 °C for vacuum drying treatment, then mechanically grind and sieve it through 300 meshes to obtain a third precursor; (5) Put the third precursor obtained in step (4) into a high-temperature carbonization furnace, and under the protection of an argon atmosphere, heat it from room temperature to 1300 °C at a heating rate of 0.1 °C / min, keep the temperature for 6 h, cool it to room temperature after carbonization, and sieve it through 300 meshes to obtain a hard carbon negative electrode material.

[0064] The specific performance test conditions and operation procedures of the hard carbon negative electrode material obtained in this example are the same as those in Example 1, and the final electrochemical performance test results are shown in Table 1 below. Example 5

[0065] (1) Add β-cyclodextrin, sodium silicate, acrylamide, ammonium persulfate, and ethylene glycol dimethacrylate to a stirring kettle containing deionized water in a mass ratio of 100:3:40:1:1 in sequence and disperse them evenly to obtain a pre-polymerized mixture; (2) Pour the pre-polymerized mixture obtained in step (1) into a glass petri dish with a diameter of 200 mm to make it evenly distributed, and then under the action of an ultraviolet lamp, catalyze and initiate the free radical polymerization reaction of acrylamide. The catalytic reaction time is 100 min to obtain a first precursor with a well-developed porous double-network cross-linked structure; (3) Immerse the first precursor obtained in step (2) in an 8% calcium chloride solution for 20 min to carry out an organic-inorganic hybrid cross-linking reaction, and then transfer it to a 2.5 mol / L nitric acid solution for an acidification reaction. The reaction time is 20 min to obtain a second precursor with a double-network cross-linked three-dimensional structure with nanowire distribution; (4) Put the second precursor obtained in step (3) into an oven at 80 °C for vacuum drying treatment, then roll and grind it and sieve it through 300 meshes to obtain a third precursor; (5) The third precursor obtained in step (4) is placed in a high-temperature carbonization furnace. Under the protection of a nitrogen atmosphere, it is heated from room temperature to 1500 °C at a heating rate of 2 °C / min, held for 5 h, cooled to room temperature after carbonization, and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0066] The specific performance test conditions and operation procedures of the hard carbon anode material obtained in this example are the same as those in Example 1. The final electrochemical performance test results are shown in Table 1 below. Example 6

[0067] (1) Sodium alginate, sodium silicate, acrylamide, azobisisobutyronitrile, and tetramethylethylenediamine are sequentially added to a stirring kettle containing deionized water according to a mass ratio of 100:5:40:0.6:1.5 and uniformly dispersed to obtain a prepolymerization mixture; (2) The prepolymerization mixture obtained in step (1) is poured into a glass petri dish with a diameter of 200 mm to make it evenly distributed. Subsequently, under the action of an ultraviolet lamp, acrylamide is catalytically initiated to undergo a free radical polymerization reaction. The catalytic reaction time is 80 min to obtain a first precursor with a well-developed pore double-network cross-linked structure; (3) The first precursor obtained in step (2) is soaked in a 15% calcium nitrate solution for 15 min to carry out an organic-inorganic hybrid cross-linking reaction. Subsequently, it is transferred to a 3 mol / L hydrochloric acid solution for an acidification reaction. The reaction time is 15 min to obtain a second precursor with a double-network cross-linked three-dimensional structure with nanowire distribution; (4) The second precursor obtained in step (3) is placed in an oven at 90 °C for vacuum drying treatment, followed by air flow pulverization and sieving through a 300-mesh sieve to obtain a third precursor; (5) The third precursor obtained in step (4) is placed in a high-temperature carbonization furnace. Under the protection of a helium atmosphere, it is heated from room temperature to 1400 °C at a heating rate of 3 °C / min, held for 4 h, cooled to room temperature after carbonization, and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0068] The specific performance test conditions and operation procedures of the hard carbon anode material obtained in this example are the same as those in Example 1. The final electrochemical performance test results are shown in Table 1 below.

[0069] Comparative Example 1 (1) Sodium alginate, acrylamide, azobisisobutyronitrile, and tetramethylethylenediamine are sequentially added to a stirring kettle containing deionized water according to a mass ratio of 100:30:0.5:0.1 and uniformly dispersed to obtain a prepolymerization mixture; (2) Pour the pre-polymerized mixture obtained in step (1) into a glass petri dish with a diameter of 200 mm to make it evenly distributed, and then under the action of an ultraviolet lamp, catalyze and initiate the free radical polymerization reaction of acrylamide. The catalytic reaction time is 10 min to obtain a first precursor with a well-developed pore double-network cross-linked structure; (3) Immerse the first precursor obtained in step (2) in a 1% calcium nitrate solution for 5 min to carry out an organic-inorganic hybrid cross-linking reaction, and then transfer it to a 0.1 mol / L hydrochloric acid solution for acidification reaction. The reaction time is 5 min to obtain a second precursor; (4) Put the second precursor obtained in step (3) into an oven at 50 °C for vacuum drying treatment, and then perform air flow pulverization and sieving through 300 meshes to obtain a third precursor; (5) Put the third precursor obtained in step (4) into a high-temperature carbonization furnace, and under the protection of a nitrogen atmosphere, heat it from room temperature to 1000 °C at a heating rate of 0.1 °C / min, keep the temperature for 2 h, cool it to room temperature after carbonization, and sieve it through 300 meshes to obtain a hard carbon negative electrode material.

[0070] The specific performance test conditions and operation procedures of the hard carbon negative electrode material obtained in this comparative example are the same as those in Example 1, and the final electrochemical performance test results are shown in Table 1 below.

[0071] Comparative Example 2 (1) Add cellulose, sodium silicate, acrylamide, azobisisobutyronitrile, and tetramethylethylenediamine to a stirring kettle containing deionized water in a mass ratio of 100:10:15:0.5:0.1 in sequence and disperse them evenly to obtain a pre-polymerized mixture; (2) Pour the pre-polymerized mixture obtained in step (1) into a glass petri dish with a diameter of 200 mm to make it evenly distributed, and then under the action of an ultraviolet lamp, catalyze and initiate the free radical polymerization reaction of acrylamide. The catalytic reaction time is 20 min to obtain a first precursor with a well-developed pore double-network cross-linked structure; (3) Carry out an acidification reaction on the first precursor obtained in step (2) in a 1 mol / L hydrochloric acid solution. The reaction time is 60 min to obtain a second precursor; (4) Put the second precursor obtained in step (3) into an oven at 60 °C for vacuum drying treatment, and then perform air flow pulverization and sieving through 200 meshes to obtain a third precursor; (5) Put the third precursor obtained in step (4) into a high-temperature carbonization furnace, and under the protection of a nitrogen atmosphere, heat it from room temperature to 1100 °C at a heating rate of 0.1 °C / min, keep the temperature for 5 h, cool it to room temperature after carbonization, and sieve it through 200 meshes to obtain a hard carbon negative electrode material.

[0072] The specific performance test conditions and operation procedures of the hard carbon anode material obtained in this example are the same as those in Example 1, and the final electrochemical performance test results are shown in Table 1 below.

[0073] Comparative Example 3 (1)Sodium alginate, sodium silicate, acrylamide, azobisisobutyronitrile, and tetramethylethylenediamine were added to a stirring kettle containing deionized water in a mass ratio of 100:10:35:0.5:0.1 in sequence and uniformly dispersed to obtain a prepolymerization mixture; (2)The prepolymerization mixture obtained in step (1) was poured into a glass petri dish with a diameter of 200 mm to make it evenly distributed, and then under the action of an ultraviolet lamp, acrylamide was catalytically initiated to undergo a free radical polymerization reaction, and the catalytic reaction time was 10 min to obtain a first precursor with a well-developed pore double-network cross-linked structure; (3)The first precursor obtained in step (2) was soaked in a 1% calcium nitrate solution for 5 min to carry out an organic-inorganic hybrid cross-linking reaction to obtain a second precursor; (4)The second precursor obtained in step (3) was placed in a 50 °C oven for vacuum drying treatment, and then airflow pulverized and sieved through a 300-mesh sieve to obtain a third precursor; (5)The third precursor obtained in step (4) was placed in a high-temperature carbonization furnace, and under the protection of a nitrogen atmosphere, it was heated from room temperature to 1000 °C at a heating rate of 0.1 °C / min, the holding time was 2 h, after carbonization, it was cooled to room temperature, and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0074] The specific performance test conditions and operation procedures of the hard carbon anode material obtained in this example are the same as those in Example 1, and the final electrochemical performance test results are shown in Table 1 below.

[0075] Table 1

[0076] In addition, Figure 2 shows the SEM image of the hard carbon anode material prepared in Example 1 obtained through performance testing; Figure 3 shows the TEM image of the hard carbon anode material prepared in Example 1 obtained through performance testing; Figure 4 shows the XRD pattern of the hard carbon anode material prepared in Example 1 obtained through performance testing.

[0077] Based on the electrochemical performance test result data obtained for the anode materials prepared in all the examples and comparative examples shown in Table 1 above under the corresponding test conditions, and in combination with Figures 2 to 4 , the following experimental conclusions can be drawn: 1) First, comparing the specific surface area of the third precursor obtained after acidification in Examples 1 to 6 with the specific surface area of the hard carbon negative electrode material obtained after carbonization, the specific surface area of the hard carbon negative electrode material decreased. Combining with the decrease in the true density range value, it shows that a large number of open pores in the hard carbon negative electrode material gradually formed micropores or closed pores after being treated by this preparation process. Further referring to Figure 2 the SEM image of the prepared hard carbon negative electrode material (for example) shown in Figure 3 and the microstructure shown in the TEM image (for example) shown in Figure 4 , it can also be seen that there are many turbulent structures composed of short-range and long-range disordered parallel carbon layers distributed in the finally prepared hard carbon negative electrode material. And as an example, combining with the XRD pattern shown in Figure 5 it can be seen that the negative electrode material prepared in this application has two characteristic peaks of hard carbon materials. Among them, the positions of the two characteristic peaks include two broad peaks at about 2θ = 23° (002) and about 2θ = 43° (100). As can be seen from the above, in the negative electrode material prepared in this application, the degree of disorder of the hard carbon tissue is relatively high, and this kind of structure tends to form more micropores. This also indicates that the double-network cross-linked three-dimensional structure with multiple nanowire distributions generated by the preparation is beneficial to the formation of micropores, so that sodium ions can be stored more effectively, and obviously can improve the sodium storage capacity of the negative electrode material; 3) Comparing Examples 1 to 6 with Comparative Example 1, as the key raw materials for preparing sodium-ion batteries and sodium-ion anode materials, the data on the addition amount of the sodium source and its mass ratio to the hard carbon precursor, that is, the ratio of sodium silicate to the hard carbon precursor which is also a key preparation raw material, shows that the larger the addition amount of sodium silicate and the larger the mass ratio of sodium silicate to the hard carbon precursor, the larger the specific surface area of the third precursor obtained after acidification. This also indicates that while interacting with the hard carbon precursor and silicate ions to form an organic-inorganic hybrid cross-linked structure, calcium silicate particles form a multi-nanowire structure under acid induction, enabling calcium silicate particles with many micropores on the surface to adhere to the hard carbon, promoting an increase in the specific surface area of the hard carbon anode material, thereby greatly improving the adsorption capacity for sodium ions, and consequently, the corresponding reversible capacity is also significantly increased. Furthermore, considering the same ratio of sodium silicate to the hard carbon precursor, but with or without the addition of soluble calcium salts for the hybrid cross-linking reaction as one of the differential preparation factors, comparing Example 3 with Comparative Example 2 shows that the reversible capacity of the hard carbon anode material without being soaked in soluble calcium salts is significantly lower, which indirectly verifies that organic-inorganic hybrid cross-linking can enhance the strength of the cross-linked structure, thus promoting the increase in reversible capacity.

[0078] It should be noted that the anode material examples, battery examples, preparation method examples of the anode material, anode sheet application examples of the anode material in the battery, and battery application examples provided in this application belong to the same concept; among the technical features in the technical solutions recorded in each example, they can be arbitrarily combined without conflict.

[0079] It should be understood that the above examples are all exemplary and do not cover all possible implementation manners. Without departing from the scope of the present disclosure, various deformations and changes can also be made based on the above examples. Similarly, the technical features of the above examples can also be arbitrarily combined to form additional examples of the present invention that may not be explicitly described. Therefore, the above examples only represent several implementation manners of the present invention and do not limit the protection scope of the present invention patent.

Claims

1. A preparation method of a negative electrode material, characterized in that, Including: S1: Using biomass or biomass derivatives as hard carbon precursors, mixing them with sodium silicate, acrylamide, initiator, and crosslinker in a solvent, stirring evenly, and then undergoing a free radical polymerization reaction under photocatalytic conditions to obtain a first precursor; S2: Immersing the first precursor in a water-soluble calcium salt solution for a hybrid crosslinking reaction, followed by acidification to obtain a second precursor. After drying, pulverizing, and sieving, a third precursor with a double-network crosslinked structure is obtained; S3: Carbonizing the third precursor in an inert atmosphere and then cooling to obtain a hard carbon anode material.

2. The preparation method of the negative electrode material according to claim 1, wherein, Step S1 satisfies at least one of the following characteristics: (1) The biomass or biomass derivative includes at least one of sodium alginate, chitosan, cellulose, and β-cyclodextrin; (2) The mass ratio of the hard carbon precursor, sodium silicate, acrylamide, initiator, and crosslinker is 100: (1 - 5): (1 - 50): (0.5 - 2): (0.1 - 2); (3) The initiator includes at least one of azobisisobutyronitrile, ammonium persulfate, azobisisoheptonitrile, and hydrogen peroxide; (4) The crosslinker includes at least one of tetramethylethylenediamine, N,N'-methylenebisacrylamide, and ethylene glycol dimethacrylate; (5) The solvent is deionized water.

3. The preparation method of the negative electrode material according to claim 1, characterized in that, Step S1 satisfies at least one of the following characteristics: (1) The photocatalytic conditions include: using a photocatalytic method with ultraviolet light and / or gamma rays; (2) The photocatalytic time under the photocatalytic conditions is 10 min - 300 min.

4. The preparation method of the negative electrode material according to claim 1, characterized in that, Step S2 satisfies at least one of the following characteristics: (1) The water-soluble calcium salt used in the water-soluble calcium salt solution includes at least one of calcium nitrate, calcium lactate, calcium chloride, and calcium dihydrogen phosphate; (2) The mass percentage concentration of the water-soluble calcium salt dissolved in the water-soluble calcium salt solution is 1% - 20%; (3) The soaking time of the first precursor in the water-soluble calcium salt solution is 5 min - 120 min; (4) The acid solution used for acidification includes at least one of hydrochloric acid, sulfuric acid, and nitric acid; (5) The molar concentration of the acid solution used for acidification is 0.1 mol / L - 3 mol / L; (6) The acidification reaction time for acidification is 5 min - 120 min; (7) The hybrid crosslinking reaction is an organic-inorganic hybrid reaction.

5. The method for preparing the negative electrode material according to claim 1, wherein Step S2 satisfies at least one of the following characteristics: (1) The drying treatment method for drying is: vacuum drying treatment in an oven at 50°C - 100°C; (2) The pulverizing method for pulverizing includes at least one of jet milling, mechanical grinding, ball milling, and roller press milling; (3) The sieving method for sieving: sieving under the condition of a 100 - 300 mesh sieve.

6. The preparation method of the negative electrode material according to claim 1, wherein Step S3 satisfies at least one of the following characteristics: (1) The inert gas in the inert atmosphere includes at least one of argon, nitrogen, and helium; (2) The carbonization temperature for carbonization is 1000°C - 1600°C; (3) The carbonization heating rate for carbonization is 0.1°C / min - 10°C / min; (4) The carbonization holding time for carbonization is 1 h - 10 h.

7. The preparation method of the negative electrode material according to claim 1, characterized in that, In step S3, before carbonization, the third precursor satisfies the following characteristics: (1) The specific surface area of the third precursor is 4 m 2 / g - 500 m 2 / g, the median particle size of the third precursor is 5 μm - 50 μm, and the true density of the third precursor is 1.8 g / cm 3 - 2.2 g / cm 3 ; (2)After carbonization, the third precursor satisfies the following characteristics: the specific surface area of the hard carbon negative electrode material is 2 m 2 / g - 15 m 2 / g, the median particle size of the hard carbon negative electrode material is 5 μm - 10 μm, and the true density of the hard carbon negative electrode material is 1.4 g / cm 3 - 1.8 g / cm 3 .

8. A negative electrode material, characterized in that, Prepared by the method for preparing a negative electrode material according to any one of claims 1 to 7.

9. A negative electrode sheet, characterized in that, Includes the negative electrode material according to claim 8.

10. A battery, characterized in that, Includes the negative electrode sheet according to claim 9.

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