An integrally formed hard carbon negative electrode material, a preparation method therefor, and an application thereof

Abstract

The application discloses an integrally-formed hard carbon negative material and a preparation method and application thereof, and belongs to the technical field of sodium ion battery materials. Specifically, biomass such as starch is used as a carbon source, esterification is performed by using an esterification agent, and an electrode sheet is directly pressed, so that the integrally-formed hard carbon negative electrode is directly obtained through carbonization. The hard carbon material prepared by using the integrally-forming technology can be directly used as a battery negative electrode, significantly simplifies a production process, is favorable for reducing manufacturing costs, improving production efficiency, and improving structural consistency and electrochemical performance of the electrode. In addition, the electrode conductivity can be improved, sodium storage kinetics, sodium storage capacity and cycle stability of the hard carbon negative electrode are improved, so that the working requirements of the sodium ion battery are met. Furthermore, the integrally-formed hard carbon negative electrode prepared by the application has the advantages of high stability, low cost, environmental friendliness, high energy utilization rate and the like, and has a wide application prospect in the field of sodium ion batteries.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to an integrally formed hard carbon anode material, its preparation method, and its application. Background Technology

[0002] With the continuous growth of energy demand, the research and development of energy storage technology has received increasing attention. Lithium-ion batteries, due to their high energy density and long lifespan, have been widely used in mobile devices, electric vehicles, and renewable energy storage. However, the scarcity and uneven distribution of lithium metal resources have led to increasing interest in sodium-ion batteries as an alternative. Sodium-ion batteries offer advantages such as abundant sodium resources and low cost, making them an important research direction for future energy storage technology. Furthermore, sodium-ion batteries exhibit more stable performance under extreme environments, thus demonstrating superior performance compared to lithium-ion batteries in certain specific application scenarios.

[0003] However, the commercialization of sodium-ion batteries still faces many technical challenges, particularly in the selection and preparation of anode materials. Traditional anode materials are mostly graphite-based, but due to the larger radius of sodium ions, intercalation and deintercalation in graphite are more difficult compared to lithium ions, resulting in poorer performance in sodium-ion batteries. Hard carbon materials, due to their excellent structural properties, have become an ideal choice for anode materials in sodium-ion batteries. Hard carbon materials possess high specific surface area, good electrical conductivity, and a large pore structure. Furthermore, their structural diversity allows for greater tunability, enabling them to better accommodate the intercalation and deintercalation of sodium ions, thereby improving battery performance.

[0004] Existing methods for preparing hard carbon electrode sheets often involve stepwise mixing of slurry, coating, and cutting. This process is not only complex and time-consuming (12-24 hours), but also costly, and its energy efficiency and environmental friendliness need improvement. From a process perspective, this method is not only environmentally and health-insensitive and economically inefficient, but also highly complex. From an electrode structure perspective, traditional processes result in hard carbon electrodes with insufficient structural stability. Due to limited interfacial bonding between the binder and hard carbon particles, and uneven slurry dispersion, the internal electrode structure cannot withstand the volume changes caused by lithium-ion insertion / extraction during battery charging and discharging. This leads to problems such as electrode pulverization and active material shedding. These process and structural defects ultimately result in shortened battery cycle life, rapid capacity decay, increased internal resistance, and decreased rate performance, failing to meet the requirements of long-cycle and high-stability power batteries and energy storage batteries, thus hindering large-scale industrial applications. The optimization strategies commonly adopted from an industrial and materials perspective are water-based binder replacement technology and continuous production process upgrades. The strategy for optimizing electrode structure stability from a materials perspective is to modify the surface of hard carbon materials and design composite electrode structures. Summary of the Invention

[0005] To address the problems in existing technologies, such as impurities in the active material of the electrode sheet and side reactions between NMP and the electrolyte, which lead to poor battery stability and rate performance, this invention provides a method for preparing an integrated hard carbon anode material and its application.

[0006] This invention uses biomass materials as a carbon source, an oxide template as a pore-forming medium, and a tablet press to directly press starch with added esterification agent into electrode sheets. Finally, the electrode sheet is directly synthesized through a two-step carbonization process. Specifically, biomass starch is used as the carbon source because it is low-cost and renewable, effectively reducing resource consumption and economic costs in the production process. Esterification and cross-linking allow the starch to maintain its spherical morphology, reducing the specific surface area of ​​the material and improving the initial coulombic efficiency. After pressing the starch mixed with esterification agent into electrode sheets using a tablet press, the sintered sample fully possesses the characteristics of an electrode sheet. Traditionally, the active material needs to be mixed with a binder (PVDF), a conductive agent (NMP), and the active material to obtain a slurry, which is then coated onto aluminum foil to obtain a hard carbon negative electrode sheet. However, this integrated preparation not only eliminates the need for the slurry and current collector to combine, preventing separation of the electrode and current collector due to uneven coating or binder failure, but also avoids the problems of NMP recovery when dissolving PVDF and potential side reactions with the electrolyte. This method not only significantly improves the anode loading, compaction density, structural stability, interfacial stability, and compatibility of hard carbon materials, promoting charge transfer, enhancing the wettability of the electrode-electrolyte interface, and improving electrode conductivity, but also enhances the sodium storage kinetics, sodium storage capacity, and cycle stability of hard carbon anodes. Furthermore, the integrated molding technology not only significantly shortens the production time and improves the efficiency of the entire electrochemical material production process, but also serves as a green and environmentally friendly electrode preparation method, effectively reducing the NMP recovery issues associated with traditional methods, making the preparation of hard carbon materials more efficient and energy-saving.

[0007] The specific technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] This invention provides a method for integrally molding hard carbon anode materials, comprising the following steps:

[0009] (1) Mix starch with an esterifying agent to obtain mixed starch;

[0010] (2) Press the mixed starch into electrode sheet material;

[0011] (3) The electrode sheet material is pre-carbonized in an inert gas atmosphere to obtain a pre-carbonized material;

[0012] (4) The pre-carbonized material is heated in an inert gas atmosphere to carry out secondary carbonization to obtain the integrated molded hard carbon material.

[0013] By adopting the aforementioned technical solution, this invention achieves cross-linking of biomass raw material starch with an esterifying agent, enabling the starch to maintain its spherical morphology, reducing the specific surface area of ​​the material, and improving the initial coulombic efficiency. A secondary high-temperature sintering process removes the oxides formed during the initial sintering of the esterifying agent, transforming the open pores in the material into closed pores. The integrated molding and pressing process prevents electrode and current collector separation and some side reactions caused by uneven coating or binder failure in traditional preparation methods. Through integrated molding technology, high-performance hard carbon materials are obtained efficiently and environmentally, possessing advantages such as high efficiency, low cost, environmental friendliness, and high energy utilization, showing broad application prospects in the field of sodium-ion batteries.

[0014] The following are preferred technical solutions of the present invention:

[0015] Preferably, in step (1), the starch is natural starch, selected from one or more of cereal starches (wheat starch, corn starch, rice starch, sorghum starch), tuber starches (potato starch, cassava starch, and sweet potato starch), legume starches (mung bean starch, pea starch), and other plant starches (sago starch, kudzu starch); using starch as a raw material has a wide range of sources and has excellent economic advantages and environmental value;

[0016] And / or, the esterifying agent is selected from one or more of magnesium acetate, zinc acetate, copper acetate, magnesium sulfate, zinc sulfate, copper sulfate, succinic anhydride, maleic anhydride, sodium tripolyphosphate, and ketene.

[0017] Preferably, the mass ratio of starch to esterifying agent is 2:0.2~1, more preferably 2:0.25~1, and even more preferably 2:0.25.

[0018] Preferably, in step (1), the mixing time is 1 to 96 hours; more preferably, the starch and esterifying agent are mixed by stirring in deionized water to make the mixture more thorough and uniform, preferably at a stirring rate of 100-500 r / min; even more preferably, after mixing with water, the mixture is dehydrated and dried by a freeze dryer to make the starch and esterifying agent evenly distributed and dried.

[0019] Preferably, in step (2), the electrode sheet thickness is 0.05~2mm. If it is too thin, the pore structure may collapse during the carbonization process. If it is too thick, the carbonization will be uneven and the internal oxide template will be difficult to remove, making it difficult for the material to form open pores. Consequently, it will be difficult to convert the open pores into closed pores at high temperatures, and the pore utilization rate will decrease. More preferably, the tableting condition is that the pressure set by the tablet press is 2~500 MPa.

[0020] Preferably, in step (3), the pre-carbonization conditions are: heating rate of 2~10℃ / min, holding temperature of 300~800℃, and holding time of 2~15 h. During this process, the esterifying agent molecules promote the cross-linking reaction between starch molecules. If the esterification cross-linking time is too long, it may lead to excessively dense connections between molecular chains, thereby hindering the formation of mesopores and micropores, resulting in an unsuitable decrease in the porosity and specific surface area of ​​the material. At the same time, during the pre-carbonization process, the esterifying agent is further converted into oxides, which serve as pore-forming agents.

[0021] Preferably, in steps (3) and (4), the inert gas is at least one of argon (Ar), nitrogen (N2), and helium (He).

[0022] Preferably, in step (4), the secondary carbonization conditions are: heating rate of 2~10 ℃ / min, holding temperature of 1000~1500℃, and holding time of 1~10 h.

[0023] Preferably, in step (4), the particle size (spherical morphology) of the integrally formed hard carbon anode material is 0.2~10 μm, and the specific surface area is 2~100 m². 2 g -1 The pore size is 0.3~50 nm and the carbon interlayer spacing is 0.36~0.60 nm.

[0024] The present invention provides an integrally formed hard carbon anode material prepared according to any of the above methods.

[0025] Preferably, the specific surface area of ​​the material is 2~100m². 2 g -1 This invention, by employing a suitable specific surface area, can effectively improve the capacity and conductivity of hard carbon materials while avoiding excessive electrolyte consumption due to a larger specific surface area. This avoids the risk of pore closure or structural collapse during cycling, leading to rapid capacity decay, thereby effectively improving the cycling performance of the material.

[0026] Preferably, the material has a particle size of 0.2~10 μm, a pore size of 0.3~50 nm, a porosity of 10%~90%, and a carbon interlayer spacing of 0.36~0.60 nm.

[0027] The present invention also provides an application of any of the above-mentioned integrally molded hard carbon anode materials or integrally molded hard carbon anode materials prepared by any of the above-mentioned preparation methods in the field of sodium-ion batteries.

[0028] Based on the above technical solution, the present invention has the following beneficial effects:

[0029] (1) Using natural biomass materials such as cereal starch and potato starch has the advantages of low cost, large quantity and renewability, which effectively reduces resource consumption and economic costs in the production process.

[0030] (2) Compared with the uncontrollable pore size distribution caused by the traditional KOH activation method, the oxide template pore-forming technology can generate a hierarchical pore structure, effectively improve the diffusion coefficient of sodium ions and their insertion and extraction efficiency, thereby significantly improving the overall performance of the battery.

[0031] (3) By pioneering the use of integrated molding technology as a green and energy-saving electrode sheet manufacturing method, it can not only significantly shorten the time and improve the efficiency of the entire electrochemical process, but also serve as a green and environmentally friendly electrode sheet preparation method, effectively reducing the problem of NMP recovery in traditional methods, making the preparation of hard carbon materials more efficient and energy-saving; at the same time, the integrated method of this invention further and significantly improves the electrochemical performance of the material compared with traditional electrode sheet preparation methods.

[0032] The preparation method of this invention achieves uniform and efficient pore formation and green energy-saving preparation of hard carbon materials through the synergistic effect of oxide template pore-forming and integrated hard carbon anode technology, which are both indispensable. Furthermore, the resulting hard carbon materials have more suitable and superior structural parameters such as specific surface area and carbon interlayer spacing, thereby further improving the electrochemical performance of the materials and demonstrating broad market application prospects. At the same time, the preparation method of this invention is simple, rapid, and efficient, suitable for large-scale industrial production. Attached Figure Description

[0033] Figure 1 SEM image (50 μm) of the hard carbon anode material prepared in Example 1;

[0034] Figure 2 SEM image (1 μm) of the hard carbon anode material prepared in Example 1;

[0035] Figure 3 XRD images of the hard carbon anode material prepared in Example 1;

[0036] Figure 4 Cycle capacity diagrams of sodium-ion batteries assembled with the hard carbon anode materials prepared in Example 1 and Comparative Example 1 under different rate conditions. Detailed Implementation

[0037] To better clarify and understand the objectives, process solutions, and advantages of this invention, the technical solutions and implementation methods of this invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solutions of this invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of this invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining this invention and do not limit this invention. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] Unless otherwise specified, the experimental methods and conditions used in the embodiments of this invention are conventional methods and conditions. The materials, reagents, instruments, and equipment used in the embodiments, unless otherwise specified, are all conventional substances or equipment known to those skilled in the art and can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention's content can all achieve the stated reactions and obtain the desired products. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of this invention.

[0039] Example 1

[0040] (1) Mix corn starch raw material (Chengdu Kelong Chemical Co., Ltd.) and magnesium acetate and dissolve them in deionized water. The mass ratio of raw material to esterification agent is 2:0.25. The mixed raw material is stirred at 300 rpm for 48 hours to form premixed starch.

[0041] (2) Place the premixed starch suspension obtained in step (1) in a freeze dryer, start the machine, keep the temperature at -55℃, freeze for 12 hours, and then vaporize it under a high pressure of 5 MPa for 48 hours to finally obtain freeze-dried mixed starch precursor powder.

[0042] (3) The freeze-dried mixed starch precursor powder was placed in a tablet press and pressed into an electrode sheet with a thickness of 1 mm. The pressure was set to 250 MPa. Then, it was rapidly heated in an argon atmosphere for pre-carbonization. The heating rate was 2℃ / min, the holding temperature was 800℃, and the holding time was 8 h.

[0043] (4) The material was rapidly carbonized by heating in an argon-filled atmosphere. The secondary carbonization conditions were: heating rate of 2 °C / min, holding temperature of 1500 °C, and holding time of 5 h. Finally, an integrated biomass hard carbon anode material was obtained. The particle size of the hard carbon material was 0.2~9 μm, and the specific surface area was 78.4 m². 2 g-1 It has a porosity of 27%, a pore size of 0.7~50 nm, and a carbon interlayer spacing of 0.38~0.60 nm.

[0044] Example 2

[0045] (1) Mix potato starch raw material and zinc acetate and dissolve in deionized water. The mass ratio of raw material to esterifying agent is 2:1. Stir the mixed raw material at 100 rpm for 96 h to form premixed starch.

[0046] (2) Place the premixed starch suspension obtained in step (1) in a freeze dryer, start the machine, keep the temperature at -100℃, freeze for 12h, and then vaporize it under 2MPa pressure for 72h to finally obtain freeze-dried mixed starch precursor powder.

[0047] (3) The freeze-dried mixed starch precursor powder was placed in a tablet press and pressed into an electrode sheet with a thickness of 0.05 mm. The pressure was set to 500 MPa. Then, it was rapidly heated in an argon atmosphere for pre-carbonization. The heating rate was 10 °C / min, the holding temperature was 300 °C, and the holding time was 15 h.

[0048] (4) The material was rapidly carbonized by heating in an argon-filled atmosphere. The secondary carbonization conditions were: heating rate of 10 °C / min, holding temperature of 1000 °C, and holding time of 10 h. Finally, an integrated biomass hard carbon anode material was obtained. The particle size of the hard carbon material was 0.4~9 μm, and the specific surface area was 100 m². 2 g -1 It has a porosity of 24%, a pore size of 0.6~40 nm, and a carbon interlayer spacing of 0.37~0.60 nm.

[0049] Example 3

[0050] (1) Mix wheat starch raw material and maleic anhydride and dissolve in deionized water. The mass ratio of raw material to esterifying agent is 2:0.5. Stir the mixed raw material at 500 rpm for 1 hour to form premixed starch.

[0051] (2) Place the premixed starch suspension obtained in step (1) in a freeze dryer, start the machine, keep the temperature at -55℃, freeze for 12 hours, and then vaporize it under a high pressure of 10 MPa for 24 hours to finally obtain freeze-dried mixed starch precursor powder.

[0052] (3) The freeze-dried mixed starch precursor powder was placed in a tablet press and pressed into an electrode sheet with a thickness of 2 mm. The pressure was set to 2 MPa. Then, it was rapidly heated in an argon atmosphere for pre-carbonization. The heating rate was 2℃ / min, the holding temperature was 800℃, and the holding time was 2 h.

[0053] (4) The material was rapidly carbonized by heating in an argon-filled atmosphere. The secondary carbonization conditions were: heating rate of 2℃ / min, holding temperature of 1500℃, and holding time of 1 h. Finally, an integrated biomass hard carbon anode material was obtained. The particle size of the hard carbon material was 0.4~8μm, and the specific surface area was 95.6 m². 2 g -1 It has a porosity of 22%, a pore size of 0.5~40 nm, and a carbon interlayer spacing of 0.39~0.60 nm.

[0054] Example 4

[0055] (1) Mix mung bean starch raw material and magnesium sulfate and dissolve in deionized water. The mass ratio of raw material to esterifying agent is 2:0.25. Stir the mixed raw material at 100 rpm for 1 h to form premixed starch.

[0056] (2) Place the premixed starch suspension obtained in step (1) in a freeze dryer, start the machine, keep the temperature at -100℃, freeze for 12 hours, and then vaporize it under a high pressure of 2 MPa for 24 hours to finally obtain freeze-dried mixed starch precursor powder.

[0057] (3) The freeze-dried mixed starch precursor powder was placed in a tablet press and pressed into an electrode sheet with a thickness of 0.05 mm. The pressure was set to 500 MPa. Then, it was rapidly heated in an argon atmosphere for pre-carbonization. The heating rate was 2℃ / min, the holding temperature was 300℃, and the holding time was 2 h.

[0058] (4) The material was rapidly carbonized by heating in an argon-filled atmosphere. The secondary carbonization conditions were: heating rate of 2 °C / min, holding temperature of 1000 °C, and holding time of 1 h. Finally, an integrated biomass hard carbon anode material was obtained. The particle size of the hard carbon material was 0.4~8 μm, and the specific surface area was 80 m². 2 g -1 It has a porosity of 28%, a pore size of 0.3~45 nm, and a carbon interlayer spacing of 0.37~0.59 nm.

[0059] Example 5

[0060] (1) Mix sago starch raw material and sodium tripolyphosphate and dissolve in deionized water. The mass ratio of raw material to esterifying agent is 2:0.5. Stir the mixed raw material at 500 rpm for 48 h to form premixed starch.

[0061] (2) Place the premixed starch suspension obtained in step (1) in a freeze dryer, start the machine, keep the temperature at -55℃, freeze for 12h, and then vaporize it under 8MPa pressure for 48h to finally obtain freeze-dried mixed starch precursor powder.

[0062] (3) The freeze-dried mixed starch precursor powder was placed in a tablet press and pressed into an electrode sheet with a thickness of 1 mm. The pressure was set to 250 MPa. Then, it was rapidly heated in an argon atmosphere for pre-carbonization. The heating rate was 2 ℃ / min, the holding temperature was 800 ℃, and the holding time was 2 h.

[0063] (4) The material was rapidly carbonized by heating in an argon-filled atmosphere. The secondary carbonization conditions were: heating rate of 2 °C / min, holding temperature of 1300 °C, and holding time of 6 h. Finally, an integrated biomass hard carbon anode material was obtained. The particle size of the hard carbon material was 0.4~8 μm, and the specific surface area was 96.2 m². 2 g -1 It has a porosity of 19%, a pore size of 0.6~50 nm, and a carbon interlayer spacing of 0.37~0.59 nm.

[0064] Example 6

[0065] (1) Mix corn starch raw material and ketone in deionized water. The mass ratio of raw material to esterifying agent is 2:1. Stir the mixed raw material at 100 rpm for 48 h to form premixed starch.

[0066] (2) Place the premixed starch suspension obtained in step (1) in a freeze dryer, start the machine, keep the temperature at -100℃, freeze for 12 hours, and then vaporize it under a high pressure of 2 MPa for 48 hours to finally obtain freeze-dried mixed starch precursor powder.

[0067] (3) The freeze-dried mixed starch precursor powder was placed in a tablet press and pressed into an electrode sheet with a thickness of 1 mm. The pressure was set to 250 MPa. Then, it was rapidly heated in an argon atmosphere for pre-carbonization. The heating rate was 10 ℃ / min, the holding temperature was 300 ℃, and the holding time was 8 h.

[0068] (4) The material was rapidly carbonized by heating in an argon-filled atmosphere. The secondary carbonization conditions were: heating rate of 2 °C / min, holding temperature of 1000 °C, and holding time of 5 h. Finally, an integrated biomass hard carbon anode material was obtained. The particle size of the hard carbon material was 0.2~8 μm, and the specific surface area was 40 m². 2 g -1 It has a porosity of 20%, a pore size of 0.6~40 nm, and a carbon interlayer spacing of 0.37~0.59 nm.

[0069] Comparative Example 1

[0070] (1) Mix corn starch raw material and magnesium acetate and dissolve them in deionized water. The mass ratio of raw material to esterification agent is 2:0.25. The mixed raw material is stirred at 300 rpm for 48 h to form premixed starch.

[0071] (2) Place the premixed starch suspension obtained in step (1) in a freeze dryer, start the machine, keep the temperature at -55℃, freeze for 12 hours, and then vaporize it under a high pressure of 5 MPa for 48 hours to finally obtain freeze-dried mixed starch precursor powder.

[0072] (3) The freeze-dried mixed starch precursor powder was placed in a tablet press and pressed into electrode sheets with a thickness of 1 mm. The pressure was set to 250 MPa. Then, it was rapidly heated in an argon atmosphere for pre-carbonization. The heating rate was 2 °C / min, the holding temperature was 800 °C, and the holding time was 8 h. Finally, an integrated biomass hard carbon anode material was obtained. The particle size of the hard carbon material was 0.6~10 μm, and the specific surface area was 10.6 m². 2 g -1 It has a porosity of 13%, a pore size of 0.6~10nm, and a carbon interlayer spacing of 0.34~0.56nm.

[0073] Comparative Example 2

[0074] (1) Mix corn starch raw material and maleic anhydride and dissolve in deionized water. The mass ratio of raw material to esterifying agent is 2:1. Stir the mixed raw material at 100 rpm for 96 h to form premixed starch.

[0075] (2) Place the premixed starch suspension obtained in step (1) in a freeze dryer, start the machine, keep the temperature at -100℃, freeze for 12h, and then vaporize it under 2MPa pressure for 72h to finally obtain freeze-dried mixed starch precursor powder.

[0076] (3) The powdered precursor was mixed with potassium hydroxide (KOH) solution at room temperature with a mass ratio of 4:1 and a treatment time of 6 h. The treated precursor powder was then placed in a tablet press and pressed into electrode sheets with a thickness of 0.05 mm. The pressure was set to 500 MPa. Then, the sheets were rapidly heated in an argon atmosphere for pre-carbonization. The heating rate was 10 ℃ / min, the holding temperature was 300 ℃, and the holding time was 15 h.

[0077] (4) The material was rapidly carbonized by heating in an argon-filled atmosphere. The secondary carbonization conditions were: heating rate of 10 °C / min, holding temperature of 1000 °C, and holding time of 10 h. Finally, an integrated biomass hard carbon anode material was obtained. The particle size of the hard carbon material was 0.8~10 μm, and the specific surface area was 268 m². 2 g -1 It has a porosity of 55%, a pore size of 0.5~75 nm, and a carbon interlayer spacing of 0.35~0.57 nm.

[0078] Comparative Example 3

[0079] (1) Mix corn starch raw material and magnesium acetate and dissolve in deionized water. The mass ratio of raw material to esterifying agent is 2:0.25. Stir the mixed raw material at 500 rpm for 96 hours to form premixed starch.

[0080] (2) Place the premixed starch suspension obtained in step (1) in a freeze dryer, start the machine, keep the temperature at -55℃, freeze for 12 hours, and then vaporize it under a high pressure of 10 MPa for 24 hours to finally obtain freeze-dried mixed starch precursor powder.

[0081] (3) The freeze-dried mixed starch precursor powder was pre-carbonized by rapidly heating in an argon atmosphere. The heating rate was 2℃ / min, the holding temperature was 800℃, and the holding time was 2 h.

[0082] (4) The material was rapidly carbonized by heating in an argon-filled atmosphere. The secondary carbonization conditions were: heating rate of 2℃ / min, holding temperature of 1500℃, and holding time of 1 h. The resulting biomass hard carbon anode material had a particle size of 0.8~10μm and a specific surface area of ​​29.4 m². 2 g -1 It has a porosity of 33%, a pore size of 20~250nm, and a carbon interlayer spacing of 0.34~0.57nm.

[0083] Comparative Example 4

[0084] (1) Mix corn starch raw material and magnesium acetate and dissolve in deionized water. The mass ratio of raw material to esterification agent is 2:0.25. The mixed raw material is stirred at 300 rpm for 48 hours to form premixed starch.

[0085] (2) Place the premixed starch suspension obtained in step (1) into a freeze dryer, start the machine, keep the temperature at -55℃, freeze for 12 hours, and then vaporize it under a high pressure of 5 MPa for 48 hours to finally obtain freeze-dried mixed starch precursor powder.

[0086] (3) The freeze-dried mixed starch precursor powder was pre-carbonized by rapidly heating in an argon atmosphere. The heating rate was 2℃ / min, the holding temperature was 800℃, and the holding time was 8 h.

[0087] (4) The material was rapidly carbonized by heating in an argon-filled atmosphere. The secondary carbonization conditions were: heating rate of 2 °C / min, holding temperature of 1500 °C, and holding time of 5 h. The resulting biomass hard carbon anode material had a particle size of 0.9~10 μm and a specific surface area of ​​33.9 m². 2 g -1 It has a porosity of 30%, a pore size of 25~280nm, and a carbon interlayer spacing of 0.35~0.55nm.

[0088] Test Example: Battery Assembly and Performance Testing

[0089] Traditional preparation methods for hard carbon anode materials in Comparative Examples 3 and 4: The hard carbon anode material, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) obtained in the corresponding comparative examples were accurately weighed according to a mass ratio of 8:1:1 and placed in N-methylpyrrolidone (NMP) to ensure a solid content of 25%. Next, the mixture was transferred to a homogenizer and homogenized at 1780 rpm. After homogenization, 1 g of the resulting slurry was uniformly coated onto an aluminum foil current collector using a 150 μm scraper, ensuring an active material loading of ~2 mg / cm³. -2 Subsequently, the coated aluminum foil was first dried in a 70°C forced-air drying oven for 2 hours, and then transferred to a 120°C vacuum drying oven for another 12 hours. After the drying process, the resulting electrode sheet was compacted on a roller press to a thickness of 1 mm. Finally, the compacted electrode sheet was cut into 12 mm diameter pieces to serve as electrode plates.

[0090] Sodium-ion battery assembly: In a glove box filled with argon gas and with humidity and oxygen concentration below 0.01 ppm, the positive electrode shell, the integrally molded electrode sheets of the above embodiments and comparative examples, as well as the conventional stepwise slurry electrode sheets of Comparative Examples 3 and 4, the electrolyte (1 mol / L NaPF6 in DME = 100 vol%), the glass fiber separator (Whatman GF / D), the sodium sheet, the gasket, the spring sheet, and the negative electrode shell were assembled sequentially. Finally, a 50 kg cm⁻¹ solution was used. -2 Encapsulation is performed under pressure.

[0091] Place the assembled sodium-ion battery on the Xinwei battery tester and test it at a rate of 0.02 A g within the voltage range of 0.01~2.5 V. -1 Activate for three cycles, then use 1 A g -1 Long-cycle testing was conducted. The rate testing used a 0.02 A g... -1 0.05 Ag -1 0.1 A g -1 0.2 A g -1 0.5 A g -1 1 A g -1 0.02 Ag -1 Current density.

[0092] The hard carbon anode material prepared according to the above method is shown in Table 1.

[0093] Table 1 Comparison of structural parameters of different hard carbon anode materials

[0094]

[0095] Note: * indicates that the electrode sheet thickness is 1mm and the active material thickness on the electrode sheet is 0.1×10⁻⁶. -6 mm.

[0096] Combining the data in the table and the appendix Figures 1-4It can be seen that the hard carbon anode material obtained by rapid carbonization through a combination of oxide template pore-forming and integrated molding can have its structural parameters adjusted by changing parameters. A suitable specific surface area can improve initial efficiency, reduce irreversible sodium loss, and extend cycle life. In contrast, the specific surface areas of the hard carbon materials obtained without pore-forming and with traditional KOH pore-forming in the comparative examples show two extremes. In Comparative Example 1, the low specific surface area means a limited number of active sites and pores, leading to a significant reduction in sodium ion adsorption and intercalation capacity. Insufficient pores result in difficulty in electrolyte penetration, long sodium ion transport paths, and severe polarization at high rates. In Comparative Example 2, the high specific surface area easily leads to a significant increase in the contact area with the electrolyte, triggering uncontrollable SEI film formation, consuming active sodium and electrolyte, and easily causing pore closure or structural collapse during cycling, resulting in rapid capacity decay. Comparative Examples 3 and 4 show that, compared to Example 1, the electrode prepared by the traditional method is not only time-consuming and labor-intensive, but also produces materials with larger pore sizes, affecting ion diffusion efficiency.

[0097] Meanwhile, the particle size in the examples and comparative examples ranged from 0.2 to 10 μm. The pore size distribution in the examples consisted of a combination of micropores and mesopores, with micropores dominating. In Comparative Example 1, the hard carbon anode material obtained without pore formation had mostly open pores, with only a few closed pores. Combined with the electrochemical performance data in Table 2, this resulted in a moderate battery capacity, poor ion diffusion kinetics, and limited rate performance. In Comparative Examples 2-4, the high porosity led to reduced mechanical strength, making the material prone to structural collapse during long-term charge-discharge cycles and resulting in poor cycle stability. Furthermore, Comparative Examples 3 and 4, which used conventional methods to prepare electrode sheets, showed that even adjusting other parameters could not effectively improve their electrochemical performance, let alone significantly improve it to the level of Example 1. Moreover, Comparative Examples 3-4 revealed the conventional technical rule that the larger the particle size distribution, the lower the electrochemical performance of the electrode sheets prepared using conventional methods. Regarding the interlayer spacing of the hard carbon materials, the interlayer spacing in the examples ranged from 0.37 to 0.60 nm, a significant improvement compared to the comparative examples, which could reduce Na... + Diffusion resistance is reduced, sodium storage capacity is enhanced, and rate and cycle performance are improved, resulting in a high-capacity, long-life sodium-ion battery system.

[0098] The electrochemical properties were prepared and measured according to the above method, and the results are shown in Table 2.

[0099] Table 2 Comparison of electrochemical performance of different hard carbon anode materials

[0100]

[0101] The materials described in Examples 1-6 of this invention were tested under the corresponding test conditions of the test examples, and all met the following requirements: at 0.02 Ag... -1The initial discharge specific capacity at current density is not less than 440 mA hg -1 The initial coulomb efficiency is no less than 70%, in 1A g -1 The initial discharge specific capacity at current density is not less than 170 mA hg -1 After 1000 cycles, the discharge specific capacity is not less than 150 mA hg. -1 The cycle capacity retention rate is no less than 85%. In contrast, the battery tested in Comparative Example 1, at 0.02 A g... -1 The initial discharge specific capacity at the current density was low, and the coulombic efficiency was below 70%. In contrast, the battery tested in Comparative Example 2 had a high initial discharge specific capacity of 530.75 mA hg due to its large specific surface area. -1 However, the first-cycle coulomb efficiency was extremely low, at only 37.9%. At the same time, the capacity retention of comparative batteries 1 to 4 was low, and their cycle performance and rate performance were poor.

[0102] The hard carbon anode material obtained in Example 1 was used in a 0.02 A g test. -1 0.05 Ag -1 0.1 A g -1 0.2 A g -1 0.5 A g -1 1 A g -1 0.02 Ag -1 The specific capacitance at the current density is 461.79 mA hg. -1 319.32 mA hg -1 304.04 mA hg -1 287.39 mA hg -1 252.31 mA hg -1 199.01 mA hg -1 280.12 mA hg -1 The performance of Examples 2-6 shows the same trend as that of Example 1. However, in Comparative Examples 1-4, such as... Figure 4 As shown, the battery capacity is significantly lower than that of the embodiments of the present invention under different current densities, and the coulombic efficiency is low.

[0103] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims.

Claims

1. A method for integrally forming a hard carbon negative electrode material, characterized by, The steps include the following: (1) Mix starch with esterifying agent to obtain mixed starch; the mass ratio of starch to esterifying agent is 2:0.2~1; the esterifying agent is selected from one or more of magnesium acetate, zinc acetate, copper acetate, magnesium sulfate, zinc sulfate, copper sulfate, succinic anhydride, maleic anhydride, sodium tripolyphosphate, and ketene. (2) Press the mixed starch into electrode sheet material; use a tablet press to press the electrode sheet into a tablet, with the pressure set to 2~500Mpa and the electrode sheet thickness to be 0.05~2mm; (3) The electrode sheet material is pre-carbonized in an inert gas atmosphere to obtain pre-carbonized material; the pre-carbonization conditions are: heating rate of 2~10 ℃ / min, holding temperature of 300~800℃, and holding time of 2~15h. (4) The pre-carbonized material is heated in an inert gas atmosphere to carry out secondary carbonization to obtain the integrated molded hard carbon material. The secondary carbonization conditions are: heating rate of 2~10 ℃ / min, holding temperature of 1000~1500℃, and holding time of 1~10 h.

2. The method of claim 1, wherein: In step (1), the starch is selected from one or more of cereal starch, potato starch, legume starch and other plant starches.

3. The method of claim 2, wherein: The mass ratio of starch to esterifying agent is 2:0.25~1.

4. The method of claim 1, wherein: In step (1), the mixing time is 1 to 96 hours.

5. An integrally formed hard carbon anode material prepared by the method according to any one of claims 1-4.

6. The integrally formed hard carbon anode material of claim 5, wherein, The specific surface area of the material is 2-100 m 2 g -1 .

7. The application of an integrally formed hard carbon anode material prepared by the method of any one of claims 1-4 in the field of sodium-ion batteries.

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