Modified starch-based hard carbon material, and preparation method and application thereof

Abstract

The application relates to the technical field of energy storage materials, and particularly discloses a modified starch-based hard carbon material and a preparation method and application thereof. The preparation method of the modified starch-based hard carbon material comprises the following steps of S1, mixing starch and a crosslinking agent at a certain proportion, dispersing the mixture in deionized water, and then freeze-drying to obtain a precursor powder; S2, pyrolyzing the obtained precursor powder at low temperature in an argon environment, pre-carbonizing the precursor powder at a proper temperature to obtain a pre-carbonized sample; and S3, dispersing the obtained pre-carbonized sample and a reinforcing agent in a solvent, mixing uniformly, carbonizing at high temperature, and then washing with water and drying to obtain the modified starch-based hard carbon material. The starch is crosslinked at low temperature, and then crosslinked and carbonized at high temperature, so that the hard carbon material with a large specific surface area, active sites and a proper interlayer spacing is obtained. When used as a negative electrode material, the specific capacity, energy density and discharge current of the hard carbon material are far superior to those of a commercial hard carbon material, and the application of the biomass hard carbon is provided with a broader prospect.

Description

Technical Field

[0001] This invention belongs to the field of energy storage materials technology, specifically relating to a modified starch-based hard carbon material and its preparation method and application. Background Technology

[0002] With the growing global demand for sustainable energy storage solutions, sodium-ion batteries have become an important complement to lithium-ion batteries due to their abundant resources and cost-effectiveness. Among various advanced sodium-ion battery anode candidate materials, hard carbon has become the preferred material for commercial sodium-ion batteries due to its structural stability, high safety, and excellent cycle stability. Hard carbon has a "house of cards" structure, composed of many aromatic plate-like structures stacked in a disordered manner to form a highly disordered amorphous structure, which provides the structural basis for its excellent electrochemical performance in sodium-ion batteries. Compared with graphite anodes commonly used in lithium-ion batteries, hard carbon has an expanded interlayer spacing, which facilitates sodium ion insertion and extraction. At the same time, the highly disordered phase defects and the unique closed-cell structure of hard carbon also provide additional sodium storage capacity. Hard carbon can usually be prepared by high-temperature carbonization of precursors such as biomass, bitumen, resin, and anthracite. As a sodium-ion battery anode, its sodium storage specific capacity can reach 300-400 mAh / g. However, due to the inhomogeneity of raw material composition and structure, the performance of hard carbon materials prepared from them exhibits instability. In addition, biomass hard carbon often has many irreversible side reactions during charging and discharging, which leads to a low initial coulombic efficiency. This is all related to the complex, variable and difficult-to-control microstructure of hard carbon.

[0003] Studies have found that the sodium storage capacity of hard carbon at high voltages (V>0.1V) can be achieved by doping with elements such as O, N, P, and S. These dopants not only introduce more defect structures into the hard carbon but also increase the interlayer spacing, providing more active sites for sodium ion insertion and extraction. Furthermore, the strong electronegativity of heteroatoms can enhance the adsorption capacity of hard carbon for sodium ions. Chinese patent CN118439588A discloses a method for preparing hard carbon from starch, characterized by using a staged pyrolysis method. However, its preparation process is complex, and its initial charge specific capacity at low current densities is low, which is not conducive to sodium ion storage. Chinese patent CN118439586A reports a starch-based hard carbon with excellent rate performance, but it uses sulfuric acid in its preparation process, which is not conducive to large-scale production and environmental protection requirements.

[0004] Chinese patent CN114956043A proposes a method to prepare hard carbon materials for sodium-ion batteries by impregnating a mixture of starch, phosphate, and water, followed by etching under a CO2 atmosphere. This method has a simple synthesis process and high yield, but the performance graph shows poor reversible capacity and capacity retention. The initial charge capacity is 320 mAh / g, and the capacity drops to approximately 300 mAh / g after 50 cycles. Furthermore, the degree of CO2 etching must be carefully controlled to prevent insufficient or excessive etching, which could result in hard carbon with almost no closed pores or excessively large pore sizes.

[0005] While numerous existing reports have provided methods for improving the reversible specific capacity and first-efficiency of hard carbon sodium-ion batteries, preparing hard carbon with even higher reversible specific capacity remains a challenge. Furthermore, most current hard carbon preparation methods are cumbersome and difficult to reproduce; therefore, it is essential to explore a simple, environmentally friendly, and high-performance method for hard carbon preparation. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a modified starch-based hard carbon material, its preparation method, and its application. This modified starch-based hard carbon material is cross-linked at low temperature and then cross-linked and carbonized at high temperature, thereby preparing a hard carbon material with a larger specific surface area, active sites, and appropriate interlayer spacing. This hard carbon material is far superior to commercial hard carbon materials in terms of specific capacity, energy density, and discharge current, providing a broader prospect for the application of biomass hard carbon.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of this invention is to provide a method for preparing a modified starch-based hard carbon material, comprising the following steps:

[0009] S1. Mix starch and crosslinking agent in a certain proportion, disperse the mixture in deionized water, and then freeze-dry to obtain precursor powder; the crosslinking agent is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, thiourea, and phosphoric acid;

[0010] S2. After the precursor powder obtained in step S1 is pyrolyzed at low temperature in an argon atmosphere, it is pre-carbonized at an appropriate temperature to obtain a pre-carbonized sample.

[0011] S3. Disperse the pre-carbonized sample obtained in step S2 with the reinforcing agent in a solvent, mix well, carbonize at high temperature, wash with water and dry to obtain modified starch-based hard carbon material.

[0012] The reinforcing agent is one or more of asphalt, graphene, and benzene-containing organic compounds;

[0013] The solvent is one or more of tetrahydrofuran, ethanol, glycerol and diethyl ether.

[0014] Furthermore, the starch includes one or more of corn starch, wheat starch, pea starch, and tapioca starch.

[0015] Furthermore, the mass ratio of the starch to the crosslinking agent is 1:1 to 10:1.

[0016] Furthermore, in step S2, the pyrolysis temperature is 100℃~300℃, and the pyrolysis time is 5h~24h.

[0017] Furthermore, in step S2, the pre-carbonization temperature is 400℃~1000℃, and the pre-carbonization time is 1h~2h.

[0018] Furthermore, in step S3, the carbonization temperature is 1200℃~1500℃, the heating rate is 3~5℃ / min, and the carbonization time is 2h~3h.

[0019] A second objective of the present invention is to provide a modified starch-based hard carbon material obtained by the above-described preparation method.

[0020] A third object of the present invention is to provide an electrode comprising the above-described modified starch-based hard carbon material and a conductive agent.

[0021] Furthermore, the conductive agent is one or more of Superp, Ketjen Black, carbon nanotubes, and carbon nanofibers.

[0022] A fourth objective of this invention is to provide a lithium, sodium, or potassium ion battery or capacitor that uses the aforementioned modified starch-based hard carbon material as the negative electrode material.

[0023] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows:

[0024] (1) The present invention provides a modified starch-based hard carbon material. Using readily available and inexpensive crosslinking agents doped with N, P, and S elements, and starch as raw materials, the material undergoes low-temperature crosslinking followed by high-temperature crosslinking and carbonization. The resulting hard carbon material exhibits a large specific surface area, active sites, and appropriate interlayer spacing. This anode material significantly outperforms commercial hard carbon materials in terms of specific capacity, energy density, and discharge current. On one hand, phosphates, thiourea, and phosphoric acid are fully considered as crosslinking agents to maintain the original morphology of the starch particles. On the other hand, considering that the decomposition of phosphates, thiourea, and phosphoric acid leads to the opening of pores on the hard carbon surface, asphalt, graphene, and benzene-containing compounds are used to coat the hard carbon surface to further reduce its specific surface area, thereby improving the sodium storage performance of the hard carbon. After improvement, freeze-drying treatment was found to maintain the original starch particle morphology, and the crosslinking agent doping provided a large number of active sites for the electrochemical sodium storage process of the hard carbon. Simultaneously, asphalt, graphene, and benzene-containing organic compounds further reduced the specific surface area of ​​the hard carbon. Ultimately, the sodium storage performance of optimized hard carbon was greatly improved, with a reversible capacity of 350 mAh / g and a capacity retention rate of 98.5%, making it an excellent hard carbon candidate material suitable for large-scale production.

[0025] (2) Phosphates, thiourea, and phosphoric acid act as crosslinking agents, catalysts, and heteroatom dopants. Their catalytic and crosslinking effects advance the pyrolysis of crosslinked starch (compared to uncrosslinked starch), allowing hard carbon to retain the granular structure of starch during pyrolysis. Furthermore, heteroatom doping not only exposes more active sites on the hard carbon, but also, with the decomposition of the crosslinking agent at high temperatures, a large amount of gas escapes from the hard carbon particles, creating numerous vacancies on the surface of the particles, ultimately resulting in a large specific surface area for the prepared hard carbon. Finally, the abundant mesoporous structure provides additional ion transport pathways for sodium ions. These characteristics are all beneficial for sodium ion storage.

[0026] (3) A small amount of asphalt, graphene and benzene-containing organic matter are used as reinforcing agents. Their main function is to mix with hard carbon and further seal the openings formed by previous pyrolysis through coating. This will reduce the specific surface area of ​​hard carbon and further improve the first efficiency of hard carbon.

[0027] (4) The modified starch-based hard carbon prepared by this method exhibits excellent reversible capacity (350 mAh / g) at low current density (0.1C) and excellent rate performance (134 mAh / g at 0.3 A / g current density and 50 mAh / g specific capacity at 1.5 A / g current density). Its reversible capacity and rate performance are far superior to commercial hard carbon materials. It has important application value in medical devices, electric vehicle equipment, and aerospace.

[0028] (5) Freeze-drying allows water to sublimate directly from a solid state to a gaseous state, which can greatly improve the uniformity of mixing starch and cross-linking agent and maintain the natural microporous structure and granular morphology of biomass. In contrast, drying evaporates water from a liquid state by heating, which can damage the microstructure of starch due to high temperature, thus easily causing problems such as starch granule collapse and deformation.

[0029] (6) The preparation method provided by the present invention has few steps, the solvent is simple and readily available, it has good controllability, high production efficiency and low cost, and can be used for large-scale industrial production. Attached Figure Description

[0030] Figure 1 SEM image of the modified starch-based hard carbon material prepared in Example 2;

[0031] Figure 2 This is a rate performance diagram of the modified starch-based hard carbon material prepared in Example 2;

[0032] Figure 3 The graph shows the cycling performance of the modified starch-based hard carbon material prepared in Example 2.

[0033] Figure 4 SEM image of the hard carbon material prepared in Comparative Example 1. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments and accompanying drawings are described in further detail below. Where specific test methods, instruments, or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0035] The preparation process of the modified starch-based hard carbon material provided by this invention includes low-temperature crosslinking and high-temperature carbonization. Specifically, the crosslinked starch prepared by this invention is first crosslinked at low temperature and then crosslinked and carbonized at high temperature.

[0036] The modified starch-based hard carbon prepared by this invention has a large specific surface area and active sites, as well as an appropriate interlayer spacing. When used as a hard carbon anode material, it is far superior to commercial hard carbon materials in terms of specific capacity, energy density, and discharge current, providing a broader prospect for the application of biomass hard carbon.

[0037] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0038] Example 1

[0039] This embodiment provides a method for preparing a modified starch-based hard carbon material. The specific steps are as follows:

[0040] Step (1) Sieve the starch through a 1200-mesh sieve to obtain starch granules with a particle size distribution of 15-20 μm;

[0041] Step (2) Weigh starch and thiourea into a beaker at a mass ratio of 3:1, then add an appropriate amount of deionized water and stir with a magnetic stirrer until a uniform, white dispersion is formed. The stirred dispersion is then evaporated to a slurry state in an oil bath at 60°C, and then freeze-dried in a freeze dryer for 24 hours.

[0042] Step (3) After freeze-drying, the sample was cross-linked at 180℃ in an argon atmosphere for 10 hours and pre-carbonized at 600℃ in an argon atmosphere for 2 hours.

[0043] Step (4) Disperse the pre-carbonized sample and asphalt in tetrahydrofuran, and then stir with a magnetic stirrer for 12 hours;

[0044] Step (5) The sample obtained in step (4) is placed in an argon atmosphere at 1300℃ for carbonization for 2 hours;

[0045] Step (6) Disperse the obtained hard carbon in deionized water, sonicate for 1 hour, and then dry it in an oven to obtain the final product.

[0046] Example 2

[0047] This embodiment provides a method for preparing a modified starch-based hard carbon material. The specific steps are as follows:

[0048] Step (1) Sieve the starch through a 1200-mesh sieve to obtain starch granules with a particle size distribution of 15-20 μm;

[0049] Step (2) Weigh starch and diammonium hydrogen phosphate into a beaker at a mass ratio of 5:1, then add an appropriate amount of deionized water and stir with a magnetic stirrer until a uniform, white dispersion is formed. The stirred dispersion is then evaporated to a slurry state in an oil bath at 60°C, and then freeze-dried in a freeze dryer for 24 hours.

[0050] Step (3) After freeze-drying, the sample was cross-linked at 180℃ in an argon atmosphere for 10 hours and pre-carbonized at 800℃ in an argon atmosphere for 2 hours.

[0051] Step (4) The pre-carbonized sample and graphene were dispersed in ethanol and then stirred with a magnetic stirrer for 24 hours.

[0052] Step (5) The sample obtained in step (4) is placed in an argon atmosphere at 1300℃ for carbonization for 2 hours;

[0053] Step (6) Disperse the obtained hard carbon in deionized water, sonicate for 1 hour, and then dry it in an oven to obtain the final product.

[0054] Example 3

[0055] This embodiment provides a method for preparing a modified starch-based hard carbon material. The specific steps are as follows:

[0056] Step (1) Sieve the starch through a 1200-mesh sieve to obtain starch granules with a particle size distribution of 15-20 μm;

[0057] Step (2) Weigh starch and ammonium dihydrogen phosphate in a beaker at a mass ratio of 10:1, then add an appropriate amount of deionized water and stir with a magnetic stirrer until a uniform, white dispersion is formed. The stirred dispersion is then evaporated to a slurry state in an oil bath at 60°C, and then freeze-dried in a freeze dryer for 24 hours.

[0058] Step (3) After freeze-drying, the sample was cross-linked at 180℃ in an argon atmosphere for 6 hours and pre-carbonized at 800℃ in an argon atmosphere for 2 hours.

[0059] Step (4) Separate the pre-carbonized sample and graphene into ethanol, and then stir with a magnetic stirrer for 12 hours;

[0060] Step (5) The sample obtained in step (4) is placed in an argon atmosphere at 1200℃ for carbonization for 2 hours;

[0061] Step (6) Disperse the obtained hard carbon in deionized water, sonicate for 1 hour, and then dry it in an oven to obtain the final product.

[0062] Example 4

[0063] This embodiment provides a method for preparing a modified starch-based hard carbon material. The specific steps are as follows:

[0064] Step (1) Sieve the starch through a 1200-mesh sieve to obtain starch granules with a particle size distribution of 15-20 μm;

[0065] Step (2) Weigh starch and thiourea into a beaker at a mass ratio of 5:1, then add an appropriate amount of deionized water and stir with a magnetic stirrer until a uniform, white dispersion is formed. The stirred dispersion is then evaporated to a slurry state in an oil bath at 60°C, and then freeze-dried in a freeze dryer for 24 hours.

[0066] Step (3) After freeze-drying, the sample was cross-linked at 120℃ in an argon atmosphere for 10 hours and pre-carbonized at 900℃ in an argon atmosphere for 2 hours.

[0067] Step (4) Disperse the pre-carbonized sample and asphalt in tetrahydrofuran, and then stir with a magnetic stirrer for 24 hours;

[0068] Step (5) The sample obtained in step (4) is placed in an argon atmosphere at 900℃ for carbonization for 2 hours;

[0069] Step (6) Disperse the obtained hard carbon in deionized water, sonicate for 1 hour, and then dry it in an oven to obtain the final product.

[0070] Example 5

[0071] This embodiment provides a method for preparing a modified starch-based hard carbon material. The specific steps are as follows:

[0072] Step (1) Sieve the starch through a 1200-mesh sieve to obtain starch granules with a particle size distribution of 15-20 μm;

[0073] Step (2) Weigh starch and phosphoric acid into a beaker at a mass ratio of 10:1, then add an appropriate amount of deionized water and stir with a magnetic stirrer until a uniform, white dispersion is formed. The stirred dispersion is then evaporated to a slurry state in an oil bath at 60°C, and then freeze-dried in a freeze dryer for 24 hours.

[0074] Step (3) After freeze-drying, the sample was cross-linked at 250℃ in an argon atmosphere for 10 hours and pre-carbonized at 800℃ in an argon atmosphere for 2 hours.

[0075] Step (4) Disperse the pre-carbonized sample with benzoic acid in glycerol and then stir with a magnetic stirrer for 24 hours;

[0076] Step (5) Place the sample obtained in step (4) in an argon atmosphere at 1000℃ for carbonization for 2 hours;

[0077] Step (6) Disperse the obtained hard carbon in deionized water, sonicate for 1 hour, and then dry it in an oven to obtain the final product.

[0078] Example 6

[0079] This embodiment provides a method for preparing a modified starch-based hard carbon material. The specific steps are as follows:

[0080] Step (1) Sieve the starch through a 1200-mesh sieve to obtain starch granules with a particle size distribution of 15-20 μm;

[0081] Step (2) Weigh starch and diammonium hydrogen phosphate into a beaker at a mass ratio of 5:1, then add an appropriate amount of deionized water and stir with a magnetic stirrer until a uniform, white dispersion is formed. The stirred dispersion is then evaporated to a slurry state in an oil bath at 60°C, and then freeze-dried in a freeze dryer for 24 hours.

[0082] Step (3) After freeze-drying, the sample was cross-linked at 180℃ in an argon atmosphere for 10 hours and pre-carbonized at 800℃ in an argon atmosphere for 2 hours.

[0083] Step (4) Disperse the pre-carbonized sample with terephthalic acid in ethanol and then stir with a magnetic stirrer for 24 hours;

[0084] Step (5) The sample obtained in step (4) is placed in an argon atmosphere at 1300℃ for carbonization for 2 hours;

[0085] Step (6) Disperse the obtained hard carbon in deionized water, sonicate for 1 hour, and then dry it in an oven to obtain the final product.

[0086] Example 7

[0087] This embodiment provides a method for preparing a modified starch-based hard carbon material. The specific steps are as follows:

[0088] Step (1) Sieve the starch through a 1200-mesh sieve to obtain starch granules with a particle size distribution of 15-20 μm;

[0089] Step (2) Weigh starch and ammonium dihydrogen phosphate in a beaker at a mass ratio of 10:1, then add an appropriate amount of deionized water and stir with a magnetic stirrer until a uniform, white dispersion is formed. The stirred dispersion is then evaporated to a slurry state in an oil bath at 60°C, and then freeze-dried in a freeze dryer for 24 hours.

[0090] Step (3) After freeze-drying, the sample was cross-linked at 160℃ in an argon atmosphere for 8 hours and pre-carbonized at 800℃ in an argon atmosphere for 2 hours.

[0091] Step (4) Disperse the pre-carbonized sample with p-methylbenzoic acid in ethanol, and then stir with a magnetic stirrer for 24 hours;

[0092] Step (5) The sample obtained in step (4) is placed in an argon atmosphere at 1400℃ for carbonization for 2 hours;

[0093] Step (6) Disperse the obtained hard carbon in deionized water, sonicate for 1 hour, and then dry it in an oven to obtain the final product.

[0094] Comparative Example 1

[0095] Compared to Example 2, no crosslinking agent was added, but the other steps were the same.

[0096] Comparative Example 2

[0097] Compared to Example 2, starch and crosslinking agent were directly mixed as powders, and then directly subjected to low-temperature crosslinking at 180°C, with the other steps remaining the same.

[0098] Comparative Example 3

[0099] Compared with Example 2, the low-temperature crosslinking time was changed to 5 hours, while the other steps remained the same.

[0100] Comparative Example 4

[0101] Compared with Example 2, the low-temperature crosslinking time was changed to 20h, while the other steps remained the same.

[0102] Comparative Example 5

[0103] Compared with Example 2, the low-temperature crosslinking temperature was changed to 200°C, while the other steps remained the same.

[0104] Comparative Example 6

[0105] Compared with Example 2, the low-temperature crosslinking temperature was changed to 250°C, while the other steps remained the same.

[0106] The starch-based hard carbon prepared in Examples 1-7 and Comparative Examples 1-6 was used as the negative electrode for sodium-ion batteries, and the preparation method is as follows:

[0107] Assembly of sodium / lithium / potassium ion batteries: Using the porous hard carbon prepared above as the negative electrode material, sodium / lithium / potassium half-cells were assembled separately. Modified starch-based hard carbon material, conductive agent, and PVDF were weighed at a mass ratio of 8:1:1, and an appropriate amount of NMP was added for grinding for 20 min. Copper foil / aluminum foil / aluminum foil were selected as current collectors, and the slurry was uniformly coated onto the surface of the current collector using a coating method. The cells were then placed in a vacuum drying oven and kept at 80℃ for at least 12 h to remove the solvent. After drying, circular electrode sheets with a diameter of 12 mm were cut, weighed, and transferred to a glove box. The mass load of a single electrode was approximately 1–1.3 mg. The battery components are 2032 button cells. The entire packaging process is carried out in an argon-protected glove box (water and oxygen content are both below 0.01 ppm). The components are assembled in the following order: positive electrode shell, electrode, separator paper, sodium / lithium / potassium sheet, gasket, spring sheet, and negative electrode shell. The electrolyte is a 1 mol / L NaPF6 solution (1:1 ethylene carbonate EC, diethyl carbonate DEC, and 5% fluoroethylene carbonate FEC) / LiPF6 (1:1:1 propylene carbonate PC, methyl ethyl carbonate EMC, and dimethyl carbonate DMC) / KPF6 (1:1:1 propylene carbonate PC, methyl ethyl carbonate EMC, and dimethyl carbonate DMC, and 5.0% fluoroethylene carbonate FEC), with a volume of 100 μL. The separator is Whatman (GF / D) / Celgard 2400 / Whatman (GF / A). After assembly, the battery is sealed in a sealing machine. The sealed battery is left to stand at room temperature for more than 12 hours before electrochemical testing is performed. The purpose is to allow the electrolyte to fully penetrate the electrode material.

[0108] The electrochemical performance of the prepared battery anode was tested, and the results are shown in Table 1.

[0109] Table 1. Performance Comparison of Various Examples and Comparative Examples

[0110]

[0111]

[0112] As shown in Table 1, in Examples 1-3, by changing the ratio of starch to crosslinking agent, the reversible capacity and coulombic efficiency reached their optimal values ​​at a ratio of 5:1, with a reversible specific capacity of 350 mAh / g and a coulombic efficiency of 81%. This indicates that for starch-based hard carbon anode materials, an appropriate ratio of crosslinking agent to starch may be key to improving their reversible capacity. In Examples 4 and 5, the crosslinking temperatures were set to 120℃ and 250℃, respectively, resulting in reversible specific capacities of less than 300 mAh / g. This suggests that excessively high crosslinking temperatures affect the structural stability of the starch product, while excessively low temperatures prevent the crosslinking agent from effectively crosslinking, both of which are detrimental to improving the sodium storage performance of hard carbon. Examples 5 and 6 compared the effects of different reinforcing agents on the sodium storage performance of hard carbon, showing that after coating modification, the coulombic efficiency of hard carbon was significantly improved compared to the unmodified form. Figure 1 The image shows the SEM image of the hard carbon sample prepared in Example 2. It can be seen that the morphology of the optimized cross-linked starch is maintained. It can also be seen that many starch particles are aggregated after cross-linking, which further reduces the specific surface area of ​​the prepared hard carbon. Figure 2 The rate performance graph corresponding to Example 2 shows that it has good rate performance. Its specific capacity at 0.1C, 0.2C, 0.5C, 1C, 2C and 5C is 380mAh / g, 330mAh / g, 220mAh / g, 135mAh / g, 87mAh / g and 50mAh / g, respectively. After 10 cycles at each current density and then returning to 0.1C, it can be seen that its current density is maintained at 382mAh / g, showing excellent "fast charging and fast discharging" capability. Figure 3 The graph shows the cycle performance of the sample in Example 2. It can be seen that the initial charge of the sample was 350 mAh / g, and after 50 charge-discharge cycles, the capacity retention rate was 98.5%, which shows excellent capacity retention.

[0113] In Comparative Example 1, uncrosslinked hard carbon was used as the negative electrode material for sodium-ion batteries, and conductive carbon black was used as the conductive agent. Its reversible capacity was 240 mAh / g, and its specific capacity at 0.3 A / g was 75 mAh / g, which made it impossible to apply under high current and high power conditions. Figure 4The SEM image of Comparative Example 1 shows that it is entirely composed of a layered structure, which is unfavorable for sodium ion storage. The hard carbon sample prepared in Comparative Example 2 exhibited the worst reversible capacity and rate performance among all examples. This is mainly because insufficient powder mixing ensured uniform mixing of starch and crosslinking agent, affecting crosslinking effect, morphology retention, and ultimately leading to poor electrochemical performance. Comparative Examples 3 and 4 further compared and analyzed the effect of low-temperature crosslinking time on the final electrochemical sodium storage performance of hard carbon. It can be seen that excessively short low-temperature crosslinking has no significant crosslinking effect, while excessively long crosslinking does not significantly improve the sodium storage performance of hard carbon. Furthermore, excessively long processing times also consume a large amount of energy. The comparison showed that 10 hours is the optimal low-temperature crosslinking time. Comparative Examples 5 and 6 compared the effect of different crosslinking temperatures on the sodium storage performance of hard carbon when diammonium hydrogen phosphate was used as the crosslinking agent. It can be seen that as the crosslinking temperature increases, the sodium storage performance of hard carbon deteriorates. This may be because the crosslinking agent decomposes prematurely, leading to the failure of its catalytic effect.

[0114] Where there is no conflict, the above embodiments and features described herein can be combined with each other.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a modified starch-based hard carbon material, characterized in that, Includes the following steps: S1. Mix starch and diammonium hydrogen phosphate at a mass ratio of 5:1, disperse them in deionized water, and then freeze-dry to obtain precursor powder; S2. The precursor powder obtained in step S1 is pyrolyzed at low temperature in an argon atmosphere at a temperature of 180℃ for 10 h; then it is pre-carbonized at 800℃ for 2 h to obtain a pre-carbonized sample. S3. The pre-carbonized sample obtained in step S2 is dispersed with graphene in ethanol solvent, mixed well, and then carbonized at 1300℃. After carbonization, it is washed with water and dried to obtain modified starch-based hard carbon material. The heating rate of carbonization is 3~5℃ / min, and the carbonization time is 2 h.

2. The preparation method according to claim 1, characterized in that, The starch includes one or more of corn starch, wheat starch, pea starch, and tapioca starch.

3. A modified starch-based hard carbon material prepared by the preparation method described in claim 1.

4. An electrode, characterized in that, It includes the modified starch-based hard carbon material as described in claim 3, and a one-dimensional or two-dimensional conductive agent.

5. The electrode as described in claim 4, characterized in that, The one-dimensional or two-dimensional conductive agent is one or more of carbon black, carbon whiskers, carbon fibers, carbon nanotubes, or graphene.

6. A lithium, sodium, or potassium-ion battery or capacitor, characterized in that, The modified starch-based hard carbon material described in claim 3 is used as the negative electrode material.

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