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

Abstract

The present application provides a preparation method of a negative electrode material, a negative electrode material, a negative electrode sheet and a battery, the preparation method comprising: 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, stirring evenly, and subjecting the mixture to 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 hybrid cross-linking reaction, and then acidifying the first precursor to obtain a second precursor, which is dried, crushed and sieved to obtain a third precursor with a double network cross-linked structure; S3: carbonizing the third precursor under an inert atmosphere and then cooling it to obtain a hard carbon negative electrode material, which at least solves the technical problems of enhancing the sodium ion adsorption capacity, increasing the voltage platform capacity, thereby 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 in particular to a method for preparing a negative electrode material, the negative electrode material, a negative electrode sheet and a battery. Background Art

[0002] With the development of new energy technologies, secondary batteries have become a key approach to achieving low-carbon emissions. Lithium-ion batteries have been the primary power source for low-carbon transportation, such as hybrid and electric vehicles. However, to address the future depletion of lithium resources, the industry is working to identify reliable alternatives to lithium batteries. Sodium-ion batteries have recently garnered considerable attention in large-scale energy storage applications, such as energy storage systems, due to their low cost and abundant distribution compared to lithium-ion batteries.

[0003] Graphite is commonly used as anode material for lithium-ion batteries. However, due to the difficulty in forming sodium-graphite intercalation compounds, graphite absorbs minimal sodium ions, making it difficult to use graphite as anode material for sodium-ion batteries to produce high-energy-density electrodes. Consequently, extensive research has been conducted to develop potential anode materials for lithium-ion and sodium-ion batteries, including carbon-based, alloy-based, and metal oxide-based materials. Among them, hard carbon, composed of amorphous carbon domains formed by irregularly oriented, nearly parallel stacking of a small number of graphite layers, has emerged as one of the most promising anode materials due to its low cost, ease of synthesis, high stability during sodium ion insertion and deinsertion, and availability of renewable resources (such as wood, macroalgae, and fruit shells). Furthermore, the large spacing between the basal planes of the graphite layers, as well as the defects and micropores present in hard carbon, provide favorable sites for sodium ion absorption, resulting in high reversible capacity. Importantly, hard carbon exhibits a low-voltage plateau capacity below 0.1V, which is not found in other carbon types (such as soft carbon), making it advantageous for developing high-energy-density electrodes for full batteries.

[0004] However, in the specific preparation and implementation of sodium-ion battery negative electrode materials, ensuring that sodium ions have good transport performance and ion diffusion kinetics at low temperatures or high charging rates often faces major challenges. In addition, the structure of hard carbon materials cannot be well controlled in the process, which affects the performance of the finished electrode and battery. The current process used in the industry to conduct a self-pressurized reaction in a closed reactor to control the formation of a hard carbon structure is not only costly but also has low production efficiency and cannot meet the needs of actual production. Summary of the Invention

[0005] In view of this, the embodiments of the present application provide 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 existing in the background technology, which at least solves the technical problems of enhancing the sodium ion adsorption capacity, increasing the voltage platform 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, comprising:

[0007] 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, stirring evenly, and then performing a free radical polymerization reaction under photocatalytic conditions to obtain the first precursor;

[0008] S2: soaking the first precursor in a water-soluble calcium salt solution to perform a hybrid cross-linking reaction, and then acidifying to obtain a second precursor, which is then dried, crushed, and sieved to obtain a third precursor with a double network cross-linking structure;

[0009] S3: carbonizing the third precursor under an inert atmosphere and then cooling it to obtain a hard carbon negative electrode material.

[0010] Optionally, step S1 satisfies at least one of the following characteristics:

[0011] (1) The biomass or the biomass derivative includes at least one of sodium alginate, chitosan, cellulose, and β-cyclodextrin;

[0012] (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);

[0013] (3) The initiator includes at least one of azobisisobutyronitrile, ammonium persulfate, azobisisoheptylonitrile, and hydrogen peroxide;

[0014] (4) The cross-linking agent includes at least one of tetramethylethylenediamine, N,N'-methylenebisacrylamide, and ethylene glycol dimethacrylate;

[0015] (5) The solvent is deionized water.

[0016] Optionally, step S1 satisfies at least one of the following characteristics:

[0017] (1) The photocatalytic conditions include: using ultraviolet light and / or gamma ray photocatalysis;

[0018] (2) The photocatalytic time of the photocatalytic conditions is 10 min to 300 min.

[0019] Optionally, step S2 satisfies at least one of the following characteristics:

[0020] (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;

[0021] (2) The mass percentage concentration of the water-soluble calcium salt dissolved in the water-soluble calcium salt solution is 1%-20%;

[0022] (3) The first precursor is immersed in the water-soluble calcium salt solution for 5 min to 120 min;

[0023] (4) The acid solution used for the acidification includes at least one of hydrochloric acid, sulfuric acid, and nitric acid;

[0024] (5) The molar concentration of the acid solution used in the acidification is 0.1 mol / L-3 mol / L;

[0025] (6) The acidification reaction time of the acidification is 5 min to 120 min;

[0026] (7) The hybrid cross-linking reaction is an organic-inorganic hybrid reaction.

[0027] Optionally, step S2 satisfies at least one of the following characteristics:

[0028] (1) The drying method is: vacuum drying in an oven at 50°C-100°C;

[0029] (2) The pulverization method includes at least one of air flow pulverization, mechanical grinding, ball milling, and roller milling;

[0030] (3) The sieving method is as follows: sieving on a 100-300 mesh sieve.

[0031] Optionally, step S3 satisfies at least one of the following characteristics:

[0032] (1) The inert gas of the inert atmosphere includes at least one of argon, nitrogen, and helium;

[0033] (2) The carbonization temperature of the carbonization is 1000°C-1600°C;

[0034] (3) The carbonization heating rate of the carbonization is 0.1°C / min-10°C / min;

[0035] (4) The carbonization heat preservation time of the carbonization is 1h-10h.

[0036] Optionally, in step S3, the third precursor before carbonization satisfies the following characteristics:

[0037] (1) The specific surface area of the third precursor is 4m 2 / g-500m 2 / g, the median particle size of the third precursor is 5μm-50μm, and the true density of the third precursor is 1.8g / cm 3 -2.2g / cm 3 ;

[0038] (2) After carbonization, the third precursor satisfies the following characteristics: the specific surface area of the hard carbon negative electrode material is 2m 2 / g-15m 2 / g, the median particle size of the hard carbon negative electrode material is 5μm-10μm, and the true density of the hard carbon negative electrode material is 1.4g / cm 3 -1.8g / cm 3 .

[0039] In a second aspect, a negative electrode material is provided, which is prepared by the negative electrode material preparation method described in any of the above schemes.

[0040] In a third aspect, a negative electrode sheet is provided, comprising the negative electrode material prepared by the above-mentioned method for preparing the negative electrode material.

[0041] In a fourth aspect, a battery is provided, comprising the negative electrode sheet described in the above solution.

[0042] The negative electrode material preparation method, negative electrode material, negative electrode sheet, and battery provided in the embodiments of the present application achieve at least the following beneficial technical effects:

[0043] First, acrylamide monomers are introduced to undergo free radical polymerization, thereby forming a layer of polymer on the surface of the hard carbon precursor. The amino functional groups on the polymer chains hydrogen bond with the carboxyl and hydroxyl groups on the surface of the hard carbon precursor to form a first precursor with a double-network cross-linked three-dimensional network structure. The addition of an initiator can trigger the free radical polymerization of the 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. The photocatalytic conditions can more effectively catalyze the free radical polymerization reaction of the acrylamide monomers, further accelerate the free radical polymerization reaction process, make the reaction more complete and efficient, thereby shortening the synthesis time and improving production efficiency. In addition, the photocatalytic method is easy to obtain and has the advantages of energy sustainability, relatively low pollution, and environmental friendliness.

[0044] Secondly, the first precursor with a double-network cross-linked 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. 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 multiple nanowire structures under acid induction. Many tiny pores will form on the surface of the calcium silicate. This nanowire structure will be attached to the hard carbon precursor in large quantities, greatly increasing the specific surface area of the final hard carbon negative electrode material. This can greatly improve the negative electrode material's adsorption capacity for sodium ions, thereby greatly improving the reversible capacity of the negative electrode material.

[0045] Furthermore, further combined with carbonization treatment can ensure that the crystal structure and electrochemical performance of the third precursor with a specific organizational structure prepared are in the optimal state, which not only optimizes the particle morphology and conductivity of the negative electrode material, but also can increase the energy density and output power of the battery, further improving the stability and cycle life of the battery.

[0046] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The drawings described herein are used to provide a further understanding of the present application and constitute 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 on the present application. In the drawings:

[0048] Figure 1 A schematic diagram of a process for preparing a negative electrode material according to an embodiment of the present application;

[0049] Figure 2 This is a SEM image of the hard carbon negative electrode material prepared in Example 1 of the present application obtained through performance testing;

[0050] Figure 3 This is a TEM image of the hard carbon negative electrode material prepared in Example 1 of the present application obtained through performance testing;

[0051] Figure 4 This is the XRD pattern of the hard carbon negative electrode material prepared in Example 1 of the present application obtained through performance testing;

[0052] Figure 5 This is a half-cell charge and discharge curve obtained through performance testing of the hard carbon negative electrode material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0053] In order to make the technical solutions and beneficial effects of the present invention more clearly understood, the following is a detailed description of the invention by referring to the accompanying drawings and listing specific embodiments. It should be understood that these embodiments are intended only to illustrate the present invention and are not intended to limit the scope of the invention. The experimental methods in the following examples where specific conditions are not specified are generally based on conventional experimental conditions. Unless otherwise specified, the reagents and raw materials used in the present invention are commercially available.

[0054] In the following description, numerous specific details are provided to provide a more thorough understanding of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced without one or more of these details. In other instances, certain technical features known in the art are not described to avoid confusion with the present application; that is, all features of actual embodiments are not described herein, nor are well-known functions and steps described in detail.

[0055] The terminology used herein is intended only to describe specific embodiments and is not intended to limit the present application. The terms "comprising" and / or "including," when used in this specification, identify the presence of the recited features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. As used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0056] In order to fully understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solution of the present application. The preferred embodiments of the present application are described in detail below. However, in addition to these detailed descriptions, the present application may also have other implementation methods.

[0057] Unless otherwise defined, technical and scientific terms used in this application have the same meanings as those in the technical field to which this application belongs.

[0058] In the following examples, if no specific techniques or conditions are specified, the methods are generally carried out according to conventional techniques or conditions described in the literature in the field, or according to the product instructions and the conditions recommended by the manufacturer. The numerical ranges in the following examples are all inclusive.

[0059] As described in the background, hard carbon has many advantages in the development and preparation of sodium-ion batteries. However, in order to achieve high charge-discharge coulombic efficiency and reversible specific capacity, it is necessary to consider how to achieve an excellent preparation and formation structure of hard carbon materials to optimize the charge-discharge platform capacity. In fact, in the development process of the solution proposed in the present invention, the inventors did not fall into the existing technical ideas of using closed boost reaction to control the formation of structure or traditional atomic doping, which are complex and costly processes. Instead, through various in-depth analysis and comparative studies and relevant experimental verification, they found that after the hard carbon precursor is mixed and stirred with raw materials such as sodium silicate, acrylamide, initiator, and cross-linking agent, the addition of initiator first triggers the free radical polymerization of acrylamide monomer under photocatalysis, so that the acrylamide monomer polymerizes to form linear molecular chains. Under the action of the cross-linking agent, the acrylamide monomers gradually connect to form three-dimensional molecular chains and form a stable network structure. At the same time, the amino functional groups of the polyacrylamide side chains cross-link with the carboxyl and hydroxyl groups on the hard carbon precursor through hydrogen bonding to form a double network cross-linked structure (i.e., a double network cross-linked three-dimensional structure).

[0060] Furthermore, after introducing sodium silicate inorganic molecules into the hard carbon, it is soaked in a soluble calcium salt solution. The calcium ions then react with silicate ions 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, forming many tiny pores on the surface. This greatly increases the specific surface area of the final hard carbon negative electrode material, thereby greatly improving the adsorption capacity of sodium ions. Experimental verification shows that the hard carbon negative electrode material prepared using this scheme has a turbulent structure composed of short-range ordered and long-range disordered parallel carbon layers. This organizational structure makes it possible to form more micropores, thereby enabling the adsorption of more sodium ions, thereby improving the energy density of the sodium ion battery. The battery electrode made of this hard carbon negative electrode material has been tested and obtained a high first charge and discharge specific capacity and charge and discharge efficiency.

[0061] Based on this, the present invention provides a method for preparing a negative electrode material. Figure 1 As shown, the preparation method of the negative electrode material includes several preparation steps from step S1 to step S3, and the operation process of each step will be specifically described in detail below.

[0062] S1. Biomass or a biomass derivative as a hard carbon precursor is mixed with sodium silicate, acrylamide, an initiator and a cross-linking agent in a solvent, stirred evenly, and then a free radical polymerization reaction occurs under photocatalytic conditions to obtain a first precursor.

[0063] By introducing acrylamide monomers to undergo free radical polymerization, a layer of polymer is formed on the surface of the hard carbon precursor. The amino functional groups on the polymer chain hydrogen bond with the carboxyl and hydroxyl groups on the surface of the hard carbon precursor to form a first precursor with a double-network cross-linked three-dimensional network structure, in preparation for the subsequent reaction with the calcium salt solution.

[0064] In some embodiments, the biomass or biomass derivatives used include one or more of sodium alginate, chitosan, cellulose, and β-cyclodextrin (each of which refers to a combination of two or more), or any other feasible biomass or biomass derivatives, which are not particularly limited in the embodiments of this application. Biomass and its derivatives refer to various organisms formed by photosynthesis, including all plants, animals, and microorganisms. Biomass energy is the energy form of solar energy stored in biomass in the form of chemical energy. It has abundant sources, low consumption, low price, and high carbon content. Therefore, this type of raw material can also reduce the cost of preparing raw materials to a certain extent.

[0065] In some embodiments, sodium silicate uses a sodium silicate raw material in the form of smaller particles, which can enhance the cross-linking effect. In some embodiments, the particle size of the sodium silicate can be selected between 40nm-60nm, preferably between 48nm-52nm, for example, the particle size is about 50nm, etc. The sodium silicate raw material under this particle size range has a better promoting and enhancing effect on the cross-linking reaction. In some embodiments, the initiator can be a combination of one or more of azobisisobutyronitrile, ammonium persulfate, azobisisoheptanenitrile and hydrogen peroxide. In some embodiments, the cross-linking agent can be a combination of one or more 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 are not specifically limited to it. The addition of initiator can trigger free radical polymerization of acrylamide monomer under photocatalysis, while the cross-linker can promote the cross-linking of acrylamide single chains to form a corresponding three-dimensional network structure, thereby obtaining a network structure with well-developed pores.

[0066] In some embodiments, the mass ratio of the hard carbon precursor, sodium silicate, acrylamide, initiator and cross-linker 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-linker within the above range can not only ensure sufficient free radical polymerization reaction between the hard carbon precursor and sodium silicate and acrylamide, but also a reasonable proportion of initiator can better promote the free radical polymerization of acrylamide monomer under photocatalysis. The appropriate proportion of cross-linker is more conducive to the formation of a three-dimensional network structure during the cross-linking process of acrylamide single chains, and by controlling the proportion of cross-linker, the cross-linking degree of the formed three-dimensional network can also be controlled, which is conducive to the preparation of an ideal network structure with relatively rich and developed pores. Different specific implementation methods can be prepared using any possible combination ratio within the above ratio range or any other feasible ratio.

[0067] In actual preparation, a hard carbon precursor solution, sodium silicate solution, acrylamide solution, initiator solution and crosslinker solution of certain mass concentrations can be prepared respectively, wherein the solvent can be, for example, deionized water. This can better promote the dissolution and mixing of the reactants, facilitate the control of the reaction rate, and improve the uniformity and sufficiency of the reaction. Furthermore, 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%.

[0068] In some embodiments, the specific photocatalytic conditions for the free radical polymerization reaction can be ultraviolet light photocatalysis or gamma ray photocatalysis. The selection of appropriate photocatalytic conditions can more effectively catalyze the free radical polymerization reaction of acrylamide monomer, making the reaction more sufficient and efficient. In addition, the photocatalytic method has the advantages of being environmentally friendly due to its relatively low pollution. Among them, the ultraviolet light photocatalytic method has the advantages of easy access to light sources, low cost, and low environmental pollution. The gamma ray photocatalytic method has the advantages of being able to accelerate the free radical polymerization process due to the strong and high energy radiation of gamma rays, thereby shortening the synthesis time and improving production efficiency. It also has the advantages of being easy to obtain and sustainable energy. It should be noted that any other feasible corresponding light source photocatalytic method can also be used, as long as it can achieve its reaction catalytic function effect. The embodiments of the present application are not particularly limited to this.

[0069] In some embodiments, the specific photocatalytic time of the photocatalytic conditions can be selected within the following time range: 10min-300min, for example, the photocatalytic time is set to 10min, 20min, 50min, 80min, 100min, 130min, 150min, 200min, 240min, 280min, 300min, etc., or any other feasible value parameters can be selected. Appropriate photocatalytic time can better exert the photocatalytic effect of the light source during the reaction process, making the free radical polymerization reaction more sufficient and efficient, which is also conducive to obtaining a more ideal cross-linking reaction effect later.

[0070] S2: Soaking the first precursor in a water-soluble calcium salt solution to carry out a hybrid cross-linking reaction, and then acidifying it to obtain a second precursor, which is then dried, crushed, and sieved to obtain a third precursor with a double network cross-linking structure.

[0071] First, the first precursor with a double-network cross-linked three-dimensional organizational structure prepared in the previous step 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 cross-linked structure. The calcium silicate particles form multiple nanowire structures under acid induction, and many tiny pores are formed on the surface of the calcium silicate. This nanowire structure will be attached to the inside and surface of the hard carbon organizational structure in large quantities. Experimental verification shows that after acidification treatment, the specific surface area of the third precursor is greatly increased, and the specific surface area of the hard carbon negative electrode material finally obtained is greatly increased, thereby greatly improving the adsorption capacity of the negative electrode material for sodium ions, and the reversible capacity of the negative electrode material is also greatly improved.

[0072] In some embodiments, the hybrid crosslinking reaction that occurs when the first precursor is immersed in a water-soluble calcium salt solution is an organic-inorganic hybrid reaction. In some embodiments, the organic-inorganic hybrid reaction is an organic-inorganic hybrid crosslinking reaction, which can produce an organic-inorganic hybrid crosslinked polymer having a well-developed porous structure and a double-network crosslinked structure with multiple nanowires attached, thereby producing a second precursor with high adsorption capacity.

[0073] 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 be used, as long as it can provide a source of dissolved calcium ions and meet the aforementioned reaction requirements. This embodiment of the present application is not particularly limited to this.

[0074] In some embodiments, the water-soluble calcium salt is dissolved in the water-soluble calcium salt solution at a mass percentage concentration of 1%-20%, for example, 1%, 5%, 8%, 10%, 15%, 20%, etc., or any other feasible formulation ratio may be selected, and the present application is not limited thereto. By controlling the appropriate mass percentage concentration of the water-soluble calcium salt, it is possible to better ensure that sufficient dissolved calcium ions are provided to promote the reaction of forming calcium silicate particles and to ensure the formation of sufficient nanowire tissue without excessive dissolution, thereby saving preparation costs.

[0075] In some embodiments, the soaking time of the first precursor in the aqueous calcium salt solution ranges from 5 min to 120 min, and can be, for example, 5 min, 10 min, 30 min, 60 min, 90 min, 120 min, and the like. Any other feasible value parameter can also be selected, and the present application is not limited thereto. A suitable soaking time is conducive to the formation of sufficient calcium silicate particles and promotes sufficient reaction with the hard carbon precursor and silicate ions to form an organic-inorganic hybrid crosslinked structure.

[0076] 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 of the acidification treatment ranges from 5 min to 120 min, and can be, for example, 5 min, 15 min, 40 min, 55 min, 80 min, 120 min, etc., or any other value parameter can be selected, and the present application embodiment is not limited thereto. An appropriate acidification reaction time can better ensure an effective acid induction effect, promote the formation of sufficient multiple nanowire structures, and thus provide more sodium ion adsorption pores.

[0077] It can be seen from this that by soaking the first precursor prepared from the hard carbon precursor in a water-soluble calcium salt solution to fully undergo hybridization and cross-linking reaction and then acidifying, especially by setting a more appropriate calcium salt solution concentration ratio, soaking time or acidification time, it can be ensured that sufficient dissolved calcium ions react with silicate ions to fully form calcium silicate nanoparticles, and after acidification, the nanowires formed carry more micropores, thereby greatly increasing the specific surface area, which is obviously more conducive to the adsorption of sodium ions.

[0078] In some embodiments, the drying treatment method for drying the prepared second precursor is: vacuum drying in an oven at a temperature of 50°C-100°C. The specific temperature setting can be 50°C, 60°C, 75°C, 90°C, 100°C, etc., or any other feasible value parameters can be selected. The embodiments of the present application are not limited thereto. The temperature of 50°C-100°C is a more appropriate drying treatment temperature because this temperature range is sufficient to dry the second precursor and fully remove moisture. If the temperature is too low, the expected drying effect cannot be achieved. If the temperature is too high, energy will be wasted, which is not conducive to cost savings.

[0079] In certain embodiments, after the second precursor is dried, it is crushed and sieved to obtain a third precursor. In certain embodiments, the specific crushing method can adopt one or more combinations of air flow crushing, mechanical grinding, ball milling, roller milling, or any other feasible crushing process method, and the present application embodiment is not particularly limited. In certain embodiments, the specific sieving method can be sieved under the conditions of a sieve size of 100 mesh to 300 mesh, such as 100 mesh, 120 mesh, 150 mesh, 200 mesh, 260 mesh, 300 mesh, etc., or any other feasible sieve size can be adopted, and the present application embodiment is not particularly limited. By carrying out particle crushing in an appropriate manner and screening under suitable sieve size conditions, it is possible to obtain solid particles with uniform particle size distribution, and it is possible to ensure that the heat is evenly distributed during the subsequent carbonization process, so that the physical and chemical properties of the material after carbonization have good consistency.

[0080] S3: carbonizing the third precursor under an inert atmosphere and then cooling it to obtain a hard carbon negative electrode material.

[0081] Based on the third precursor prepared as described above, carbonization treatment at an appropriate temperature in an inert atmosphere can ensure that the crystal structure and electrochemical performance of the third precursor with a specific organizational structure prepared above reach the optimal state, which not only optimizes the particle morphology and electrical conductivity of the negative electrode material, but also can increase the energy density and output power of the battery, thereby improving the stability and cycle life of the battery.

[0082] In some embodiments, the inert gas in the inert atmosphere used includes a combination of one or more of argon, nitrogen, and helium, and any other feasible inert gas may also be used, which is not particularly limited in the embodiments of the present application. In some embodiments, the third precursor is treated by high-temperature carbonization under an inert atmosphere. In some embodiments, the carbonization temperature range for carbonization is 1000°C-1600°C. In some embodiments, the carbonization heating rate is set in the range of 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, for example, a temperature value selected in the temperature range between 20°C and 30°C, or any other feasible temperature, which is not particularly limited in the embodiments of the present application. In some embodiments, after cooling, the material can be sieved again using a sieve size of 100-300 mesh. Specifically, 100 mesh, 125 mesh, 155 mesh, 190 mesh, 270 mesh, 300 mesh, etc. can be selected. Any other feasible sieve size can also be used to further precisely control the hard carbon negative electrode material to meet the expected particle size and performance requirements.

[0083] High-temperature carbonization treatment and precise control of appropriate treatment conditions can not only optimize the microstructure and performance of the negative electrode material, but also achieve high crystallinity and high specific area on the surface of the negative electrode material. This is an important means to further improve the preparation of negative electrode materials and the overall performance of the resulting batteries.

[0084] In some embodiments, before carbonization, the specific surface area of the third precursor is in the range of 4 m 2 / g-500m 2 / g, the median particle size of the third precursor is in the range of 5μm-50μm, and the true density of the third precursor is in the range of 1.8g / cm 3 -2.2g / cm 3 After carbonization treatment, the specific surface area of the hard carbon negative electrode material is 2m 2 / g-15m 2 / g, the median particle size of the hard carbon negative electrode material is 5μm-10μm, and the true density of the hard carbon negative electrode material is 1.4g / cm 3 -1.8g / cm 3By controlling the above-mentioned key performance characterization parameters of the negative electrode material, the prepared hard carbon negative electrode material can achieve the expected material performance effect. The change in specific surface area before and after shows that after high-temperature carbonization, the specific surface area of hard carbon decreases significantly. Combined with the change in true density before and after, it can be further explained that a large number of open pores gradually form micropores or closed pores, thereby improving the platform area capacity of the prepared hard carbon material; and controlling the median particle size within an appropriate range is based on 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 serious gas production risks in the subsequent battery cells. Therefore, by properly controlling this material indicator range, the performance of the prepared product can be further optimized and guaranteed.

[0085] In addition, some embodiments of the present application further provide a negative electrode material prepared by the negative electrode material preparation method provided in any of the above embodiments. It should be understood that all the features and advantages of the negative electrode material preparation method described in the above embodiments are also applicable to the negative electrode material in the embodiments of the present application and will not be described in detail here.

[0086] In addition, based on the negative electrode material having a developed pore structure and a double-network cross-linked structure with multiple nanowires attached, prepared according to any of the above-mentioned embodiments, some embodiments of the present application also provide negative electrode sheets and batteries made therefrom, and after corresponding performance testing and verification, not only a higher low-potential platform capacity is obtained, but also a relatively excellent first charge and discharge specific capacity and first coulombic efficiency are obtained.

[0087] It should be understood that since the negative electrode sheet of the battery in the embodiment of the present application includes the negative electrode material prepared by the preparation method of the negative electrode material described in any of the above embodiments or includes the negative electrode material described in the above embodiments, the beneficial effects of the negative electrode material described in any of the above embodiments are applicable to the battery.

[0088] In some embodiments, the battery may be a secondary battery, which may be a sodium ion secondary battery. Typically, a secondary battery comprises 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 intercalated and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte acts as an ion conductor between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, primarily to prevent a short circuit between the positive and negative electrodes while allowing ions to pass through.

[0089] The technical solution of the present application is further described below in conjunction with a number of embodiments and comparative examples. First, it should be noted that steps S1, S2, and S3 in the method for preparing the negative electrode material provided in the embodiment of the present application are respectively implemented as operation steps (1), (2), (3), (4), and (5) in the following embodiment. Similarly, in the corresponding comparative examples, it can be seen that the step numbers (1) to (5) are only for the purpose of convenient representation and description, and should not be understood as a limitation or conflicting description or representation of steps S1, S2, and S3 in the aforementioned embodiment. Example 1

[0090] (1) Sodium alginate, sodium silicate, acrylamide, azobisisobutyl cyanide, and tetramethylethylenediamine were added into a stirring kettle containing deionized water in a mass ratio of 100:1:1:0.5:0.1 and uniformly dispersed to obtain a prepolymer mixture;

[0091] (2) The prepolymer mixture obtained in step (1) was poured into a glass culture dish with a diameter of 200 mm to make it uniformly distributed, and then catalyzed and initiated a free radical polymerization reaction of acrylamide under the action of ultraviolet light. The catalytic reaction time (i.e., photocatalytic time) was 10 minutes to obtain a first precursor with a double-network cross-linked structure with well-developed pores;

[0092] (3) Soaking the first precursor obtained in step (2) in a 1% by mass calcium nitrate solution for 5 minutes to perform an organic-inorganic hybrid crosslinking reaction, and then transferring it to a 0.1 mol / L hydrochloric acid solution for an acidification reaction for 5 minutes to obtain a second precursor having a double-network crosslinked three-dimensional structure with nanowire distribution;

[0093] (4) The second precursor obtained in step (3) was placed in a 50°C oven for vacuum drying, and then air flow crushed and sieved through 300 mesh to obtain a third precursor;

[0094] (5) The third precursor obtained in step (4) was placed in a high-temperature carbonization furnace, and the temperature was raised from room temperature to 1000°C at a heating rate of 0.1°C / min under nitrogen atmosphere, and the temperature was kept at this temperature for 2 hours. After carbonization, the precursor was cooled to room temperature and sieved through 300 mesh to obtain a hard carbon negative electrode material.

[0095] For example, the specific performance test conditions and process are as follows:

[0096] The nitrogen-doped hard carbon negative electrode material obtained in this example was assembled into a half-cell to test its electrochemical performance. The specific operation steps were as follows: 19 g of active material, 5.0 g of conductive agent (Super P, carbon black conductive agent) and 5.0 g of binder (2.5% CMC, sodium carboxymethyl cellulose binder) were weighed, and the slurry was mixed by magnetic stirring at a speed of 500 rpm. After coating, the slurry was dried in a vacuum oven at 80°C for 8 hours to remove moisture. The battery was assembled using a sodium sheet as the counter electrode, a polypropylene microporous membrane as the separator, and an electrolyte solution of a three-component mixed solvent of 1M NaClO4 in a volume ratio of 1:1:1 of EC (ethylene carbonate solvent): DMC (dimethyl carbonate solvent): PC (propylene carbonate solvent);

[0097] The battery test conditions are: voltage range 0-2.0V, and the specific steps are: 0.1C constant current discharge to 0V to obtain the first discharge specific capacity; 0.1C constant current charge to 2.0V to obtain the first charge specific capacity; the low potential platform charge specific capacity is the corresponding charge specific capacity when the voltage reaches 0.8V during 0.1C constant current charging; 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.

[0098] Specific surface area test method: Refer to GB / T 21650.2-2008 for testing, use a fully automatic gas adsorption instrument for testing, and use 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

[0099] (1) Sodium alginate, sodium silicate, acrylamide, azobisisobutyl cyanide, and tetramethylethylenediamine were added into a stirring kettle containing deionized water in a mass ratio of 100:1.5:50:2:2 and uniformly dispersed to obtain a prepolymer mixture;

[0100] (2) The prepolymer mixture obtained in step (1) was poured into a glass culture dish with a diameter of 200 mm to make it evenly distributed, and then catalyzed by ultraviolet light to initiate a free radical polymerization reaction of acrylamide. The catalytic reaction time was 300 min, and a first precursor with a double-network cross-linked structure with well-developed pores was obtained;

[0101] (3) Soaking the first precursor obtained in step (2) in a 20% calcium nitrate solution for 120 minutes to perform an organic-inorganic hybrid crosslinking reaction, and then transferring it to a 2 mol / L hydrochloric acid solution for an acidification reaction for 120 minutes to obtain a second precursor having a double-network crosslinked three-dimensional structure with nanowire distribution;

[0102] (4) The second precursor obtained in step (3) was placed in a 100°C oven for vacuum drying, and then air flow crushed and sieved through 100 mesh to obtain a third precursor;

[0103] (5) The third precursor obtained in step (4) was placed in a high-temperature carbonization furnace, and the temperature was raised from room temperature to 1600°C at a heating rate of 10°C / min under nitrogen atmosphere, and the temperature was kept at this temperature for 10 h. After carbonization, the precursor was cooled to room temperature and sieved through 100 mesh to obtain a hard carbon negative electrode material.

[0104] 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. The final electrochemical performance test results are shown in Table 1 below. Example 3

[0105] (1) Cellulose, sodium silicate, acrylamide, azobisisobutyl cyanide, and tetramethylethylenediamine were added into a stirring kettle containing deionized water in a mass ratio of 100:2:25:1.5:0.5 and uniformly dispersed to obtain a prepolymer mixture;

[0106] (2) The prepolymer mixture obtained in step (1) was poured into a glass culture dish with a diameter of 200 mm to make it evenly distributed, and then acrylamide was catalyzed and initiated to undergo free radical polymerization under the action of ultraviolet light for 20 minutes to obtain a first precursor having a double-network cross-linked structure with well-developed pores;

[0107] (3) The first precursor obtained in step (2) was immersed in a 5% calcium nitrate solution for 60 minutes to perform an organic-inorganic hybrid crosslinking reaction, and then transferred to a 1 mol / L hydrochloric acid solution for an acidification reaction for 60 minutes to obtain a second precursor having a double-network crosslinked three-dimensional structure with nanowire distribution;

[0108] (4) The second precursor obtained in step (3) was placed in a 60°C oven for vacuum drying, and then ball milled and sieved through 200 mesh to obtain a third precursor;

[0109] (5) The third precursor obtained in step (4) was placed in a high-temperature carbonization furnace, and the temperature was raised from room temperature to 1100°C at a heating rate of 0.1°C / min under nitrogen atmosphere, and the temperature was kept at this temperature for 5 hours. After carbonization, the precursor was cooled to room temperature and sieved through 200 mesh to obtain a hard carbon negative electrode material.

[0110] 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. The final electrochemical performance test results are shown in Table 1 below. Example 4

[0111] (1) Chitosan, sodium silicate, acrylamide, azobisisobutyl cyanide, and tetramethylethylenediamine were added into a stirring tank containing deionized water in a mass ratio of 100:2.5:50:2:2 and uniformly dispersed to obtain a prepolymer mixture;

[0112] (2) The prepolymer mixture obtained in step (1) was poured into a glass culture dish with a diameter of 200 mm to make it uniformly distributed, and then catalyzed by gamma rays to initiate a free radical polymerization reaction of acrylamide. The catalytic reaction time was 40 minutes, and a first precursor having a double network cross-linked structure with well-developed pores was obtained;

[0113] (3) Soaking the first precursor obtained in step (2) in a 5% calcium lactate solution for 30 minutes to perform an organic-inorganic hybrid crosslinking reaction, and then transferring it to a 0.1 mol / L sulfuric acid solution for an acidification reaction for 10 minutes to obtain a second precursor having a double-network crosslinked three-dimensional structure with nanowire distribution;

[0114] (4) The second precursor obtained in step (3) was placed in a 70°C oven for vacuum drying, and then mechanically ground and sieved through 300 mesh to obtain a third precursor;

[0115] (5) The third precursor obtained in step (4) was placed in a high-temperature carbonization furnace, and the temperature was raised from room temperature to 1300°C at a heating rate of 0.1°C / min under argon atmosphere, and the temperature was kept at this temperature for 6 hours. After carbonization, the precursor was cooled to room temperature and sieved through 300 mesh to obtain a hard carbon negative electrode material.

[0116] 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. The final electrochemical performance test results are shown in Table 1 below. Example 5

[0117] (1) β-cyclodextrin, sodium silicate, acrylamide, ammonium persulfate, and ethylene glycol dimethacrylate were added sequentially into a stirring kettle containing deionized water in a mass ratio of 100:3:40:1:1 and uniformly dispersed to obtain a prepolymer mixture;

[0118] (2) The prepolymer mixture obtained in step (1) was poured into a glass culture dish with a diameter of 200 mm to make it evenly distributed, and then catalyzed by ultraviolet light to initiate a free radical polymerization reaction of acrylamide. The catalytic reaction time was 100 min, and a first precursor having a double-network cross-linked structure with well-developed pores was obtained;

[0119] (3) Soaking the first precursor obtained in step (2) in an 8% calcium chloride solution for 20 minutes to perform an organic-inorganic hybrid crosslinking reaction, and then transferring it to a 2.5 mol / L nitric acid solution for an acidification reaction for 20 minutes to obtain a second precursor having a double-network crosslinked three-dimensional structure with nanowire distribution;

[0120] (4) The second precursor obtained in step (3) was placed in an oven at 80°C for vacuum drying, then crushed by roller mill and sieved through 300 mesh to obtain a third precursor;

[0121] (5) The third precursor obtained in step (4) was placed in a high-temperature carbonization furnace, and the temperature was raised from room temperature to 1500°C at a heating rate of 2°C / min under nitrogen atmosphere, and the temperature was kept at this temperature for 5 hours. After carbonization, the precursor was cooled to room temperature and sieved through 300 mesh to obtain a hard carbon negative electrode material.

[0122] 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. The final electrochemical performance test results are shown in Table 1 below. Example 6

[0123] (1) Sodium alginate, sodium silicate, acrylamide, azobisisobutyronitrile, and tetramethylethylenediamine were added into a stirring kettle containing deionized water in a mass ratio of 100:5:40:0.6:1.5 and uniformly dispersed to obtain a prepolymer mixture;

[0124] (2) The prepolymer mixture obtained in step (1) was poured into a glass culture dish with a diameter of 200 mm to make it evenly distributed, and then acrylamide was catalyzed and initiated to undergo free radical polymerization under the action of ultraviolet light. The catalytic reaction time was 80 min, and a first precursor having a double-network cross-linked structure with well-developed pores was obtained;

[0125] (3) Soaking the first precursor obtained in step (2) in a 15% calcium nitrate solution for 15 minutes to perform an organic-inorganic hybrid crosslinking reaction, and then transferring it to a 3 mol / L hydrochloric acid solution for an acidification reaction for 15 minutes to obtain a second precursor having a double-network crosslinked three-dimensional structure with nanowire distribution;

[0126] (4) The second precursor obtained in step (3) was placed in a 90°C oven for vacuum drying, and then air flow crushed and sieved through 300 mesh to obtain a third precursor;

[0127] (5) The third precursor obtained in step (4) was placed in a high-temperature carbonization furnace, and the temperature was raised from room temperature to 1400°C at a heating rate of 3°C / min under the protection of a helium atmosphere, and the temperature was kept at this temperature for 4 hours. After carbonization, the precursor was cooled to room temperature and sieved through 300 mesh to obtain a hard carbon negative electrode material.

[0128] 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. The final electrochemical performance test results are shown in Table 1 below.

[0129] Comparative Example 1

[0130] (1) Sodium alginate, acrylamide, azobisisobutyronitrile, and tetramethylethylenediamine were added into a stirring kettle containing deionized water in a mass ratio of 100:30:0.5:0.1 and uniformly dispersed to obtain a prepolymer mixture;

[0131] (2) The prepolymer mixture obtained in step (1) was poured into a glass culture dish with a diameter of 200 mm to make it evenly distributed, and then catalyzed by ultraviolet light to initiate a free radical polymerization reaction of acrylamide. The catalytic reaction time was 10 min, and a first precursor with a double-network cross-linked structure with well-developed pores was obtained;

[0132] (3) Soaking the first precursor obtained in step (2) in a 1% calcium nitrate solution for 5 minutes to perform an organic-inorganic hybrid crosslinking reaction, and then transferring it to a 0.1 mol / L hydrochloric acid solution for an acidification reaction for 5 minutes to obtain a second precursor;

[0133] (4) The second precursor obtained in step (3) was placed in a 50°C oven for vacuum drying, and then air flow crushed and sieved through 300 mesh to obtain a third precursor;

[0134] (5) The third precursor obtained in step (4) was placed in a high-temperature carbonization furnace, and the temperature was raised from room temperature to 1000°C at a heating rate of 0.1°C / min under nitrogen atmosphere, and the temperature was kept at this temperature for 2 hours. After carbonization, the precursor was cooled to room temperature and sieved through 300 mesh to obtain a hard carbon negative electrode material.

[0135] 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. The final electrochemical performance test results are shown in Table 1 below.

[0136] Comparative Example 2

[0137] (1) Cellulose, sodium silicate, acrylamide, azobisisobutyl cyanide, and tetramethylethylenediamine were added into a stirring kettle containing deionized water in a mass ratio of 100:10:15:0.5:0.1 and uniformly dispersed to obtain a prepolymer mixture;

[0138] (2) The prepolymer mixture obtained in step (1) was poured into a glass culture dish with a diameter of 200 mm to make it evenly distributed, and then catalyzed by ultraviolet light to initiate a free radical polymerization reaction of acrylamide. The catalytic reaction time was 20 min, and a first precursor with a double network cross-linking and well-developed pores was obtained;

[0139] (3) The first precursor obtained in step (2) was subjected to an acidification reaction in a 1 mol / L hydrochloric acid solution for 60 min to obtain a second precursor;

[0140] (4) The second precursor obtained in step (3) was placed in a 60°C oven for vacuum drying, and then air flow crushed and sieved through 200 mesh to obtain a third precursor;

[0141] (5) The third precursor obtained in step (4) was placed in a high-temperature carbonization furnace, and the temperature was raised from room temperature to 1100°C at a heating rate of 0.1°C / min under nitrogen atmosphere, and the temperature was kept at this temperature for 5 hours. After carbonization, the precursor was cooled to room temperature and sieved through 200 mesh to obtain a hard carbon negative electrode material.

[0142] 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. The final electrochemical performance test results are shown in Table 1 below.

[0143] Comparative Example 3

[0144] (1) Sodium alginate, sodium silicate, acrylamide, azobisisobutyronitrile, and tetramethylethylenediamine were added into a stirring kettle containing deionized water in a mass ratio of 100:10:35:0.5:0.1 and uniformly dispersed to obtain a prepolymer mixture;

[0145] (2) The prepolymer mixture obtained in step (1) was poured into a glass culture dish with a diameter of 200 mm to make it evenly distributed, and then catalyzed by ultraviolet light to initiate a free radical polymerization reaction of acrylamide. The catalytic reaction time was 10 min, and a first precursor with a double-network cross-linked structure with well-developed pores was obtained;

[0146] (3) Soaking the first precursor obtained in step (2) in a 1% calcium nitrate solution for 5 minutes to perform an organic-inorganic hybrid crosslinking reaction to obtain a second precursor;

[0147] (4) The second precursor obtained in step (3) was placed in a 50°C oven for vacuum drying, and then air flow crushed and sieved through 300 mesh to obtain a third precursor;

[0148] (5) The third precursor obtained in step (4) was placed in a high-temperature carbonization furnace, and the temperature was raised from room temperature to 1000°C at a heating rate of 0.1°C / min under nitrogen atmosphere, and the temperature was kept at this temperature for 2 hours. After carbonization, the precursor was cooled to room temperature and sieved through 300 mesh to obtain a hard carbon negative electrode material.

[0149] 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. The final electrochemical performance test results are shown in Table 1 below.

[0150] Table 1

[0151]

[0152] in addition, Figure 2 The SEM image of the hard carbon negative electrode material prepared in Example 1 obtained through performance testing is shown; Figure 3 The TEM image of the hard carbon negative electrode material prepared in Example 1 obtained through performance testing is shown; Figure 4 The XRD pattern of the hard carbon negative electrode material prepared in Example 1 obtained through performance testing is shown.

[0153] According to the negative electrode materials prepared in all the embodiments and comparative examples shown in Table 1 above, the electrochemical performance test results obtained under the corresponding test conditions are combined with Figures 2 to 4 , the following experimental conclusions can be drawn:

[0154] 1) First, the specific surface area of the third precursor obtained after acidification in Examples 1 to 6 is compared 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 is reduced, and the true density range value is also reduced. This shows that after the preparation process, a large number of open pores in the hard carbon negative electrode material gradually form micropores or closed pores. Figure 2 The SEM image of the hard carbon negative electrode material prepared as shown (as an example) and Figure 3 The microstructure of the TEM image shown (as an example) also shows that the hard carbon negative electrode material finally prepared has a turbulent structure composed of short-range, ordered and long-range disordered parallel carbon layers. Figure 4 The XRD pattern shown shows that the negative electrode material prepared in the present application has two characteristic peaks of hard carbon material, wherein the two characteristic peak positions include two broad peaks located at about 2θ of 23° (002) and about 2θ of 43° (100). As can be seen from the above, in the negative electrode material prepared in the present application, the hard carbon structure has a high degree of disorder, and this structure tends to form more micropores. This also shows that the prepared double-network cross-linked three-dimensional structure with multiple nanowire distribution is conducive to the formation of micropores, thereby more effectively storing sodium ions, which can obviously improve the sodium storage capacity of the negative electrode material.

[0155] 2) Further referring to the hard carbon negative electrode materials prepared in Examples 1 to 6 in Table 1, the tests also obtained higher first charge specific capacity, first discharge specific capacity, low potential platform charge specific capacity and first coulombic efficiency, and compared with the hard carbon negative electrode materials prepared under the same preparation conditions of Comparative Examples 1 to 3 (the respective difference variable factors are used as a comparison, Comparative Example 1 does not add sodium silicate, Comparative Example 2 does not add soluble calcium salt for hybrid cross-linking reaction, and Comparative Example 3 does not combine acidification treatment to promote the generation of nanowires under acid-induced conditions), the first charge specific capacity, first discharge specific capacity, low potential platform charge specific capacity and first coulombic efficiency are compared. It can be seen that the three performance data dimensions have been greatly improved; and as an example, combined with Figure 5 The half-cell charge-discharge curves shown also show that a relatively wide low-potential platform charge capacity is obtained, which further verifies that the hard carbon negative electrode materials prepared by the specific preparation processes of Examples 1 to 6 have achieved relatively excellent expected electrochemical performance effects in electrode and battery applications.

[0156] 3) Comparing Examples 1 to 6 with Comparative Example 1, as key raw materials for preparing sodium ion batteries and sodium ion negative electrode materials, the amount of sodium source added 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 raw material for preparation, it can be seen that when the amount of sodium silicate added is greater and the mass ratio of sodium silicate to the hard carbon precursor is greater, the specific surface area of the third precursor obtained after acidification is also greater, which also shows that while interacting with the hard carbon precursor and silicate ions to form an organic-inorganic hybrid cross-linked structure, the calcium silicate particles form a multiple nanowire structure under acid induction, so that the surface Calcium silicate particles with many micropores on the surface are attached to the hard carbon, which increases the specific surface area of the hard carbon negative electrode material, thereby greatly improving the adsorption capacity of sodium ions, and thus the corresponding reversible capacity is also greatly improved; furthermore, combining the same ratio of sodium silicate and hard carbon precursor, but with or without the addition of soluble calcium salt for hybrid cross-linking reaction as one of the different preparation factors, by comparing Example 3 with Comparative Example 2, it can be seen that the reversible capacity of the hard carbon negative electrode material that has not been soaked in soluble calcium salt is significantly lower, which indirectly verifies that organic-inorganic hybrid cross-linking can improve the strength of the cross-linking structure, thereby promoting the improvement of reversible capacity.

[0157] It should be noted that the negative electrode material embodiments and battery embodiments provided in this application, the negative electrode material preparation method embodiments, the negative electrode material negative electrode sheet application embodiments in batteries, and the battery application embodiments belong to the same concept; the technical features in the technical solutions recorded in each embodiment can be combined arbitrarily unless there is a conflict.

[0158] It should be understood that the above embodiments are exemplary and are not intended to include all possible implementations. Various modifications and changes may be made to the above embodiments without departing from the scope of the present disclosure. Similarly, the various technical features of the above embodiments may be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments merely express several implementations of the present invention and do not limit the scope of protection of the patent of the present invention.

Claims

1. A method for preparing a negative electrode material, characterized in that: include: S1: Biomass or biomass derivatives containing carboxyl and / or hydroxyl groups are used as a hard carbon precursor, mixed with sodium silicate, acrylamide, an initiator, and a cross-linking agent in a solvent, stirred evenly, and then subjected to a free radical polymerization reaction under photocatalytic conditions to obtain a first precursor; S2: soaking the first precursor in a water-soluble calcium salt solution to carry out a hybrid cross-linking reaction, and then acidifying to obtain a second precursor, which is then dried, crushed, and sieved to obtain a third precursor with a double network cross-linked structure; the molar concentration of the acid solution used for the acidification is 0.1 mol / L-3 mol / L; and the acidification reaction time is 5 min-120 min; S3: carbonizing the third precursor under an inert atmosphere and then cooling it to obtain a hard carbon negative electrode material.

2. The method for preparing the negative electrode material according to claim 1, wherein: 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, azobisisoheptylonitrile, and hydrogen peroxide; (4) The cross-linking agent includes at least one of tetramethylethylenediamine, N,N'-methylenebisacrylamide, and ethylene glycol dimethacrylate; (5) The solvent is deionized water.

3. The method for preparing the negative electrode material according to claim 1, wherein: Step S1 satisfies at least one of the following characteristics: (1) The photocatalytic conditions include: using ultraviolet light and / or gamma ray photocatalysis; (2) The photocatalytic time of the photocatalytic conditions is 10 min to 300 min.

4. 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 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 first precursor is immersed in the water-soluble calcium salt solution for 5 min to 120 min; (4) The acid solution used for the acidification includes at least one of hydrochloric acid, sulfuric acid, and nitric acid; (5) The hybrid cross-linking 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 method is: vacuum drying in an oven at 50°C-100°C; (2) The pulverization method includes at least one of air flow pulverization, mechanical grinding, ball milling, and roller milling; (3) The sieving method is as follows: sieving on a 100-300 mesh sieve.

6. The method for preparing the negative electrode material according to claim 1, wherein: 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 heat preservation time of the carbonization is 1h-10h.

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

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

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

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

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