A starch-based hard carbon material based on a heat-conducting medium, and a preparation method and applications thereof

Abstract

The application belongs to the technical field of sodium ion batteries, and provides a starch-based hard carbon material based on a heat-conducting medium, and a preparation method and application thereof.The preparation method comprises the following steps: subjecting the heat-conducting medium to ball milling or freeze-drying treatment to obtain pretreated heat-conducting medium; mixing the carbon precursor and the pretreated heat-conducting medium, and then performing pre-oxidation treatment under tumbling treatment, followed by separating the heat-conducting medium and the oxidation product; and sequentially performing carbonization and acid pickling treatment on the oxidation product under a protective atmosphere to obtain the starch-based hard carbon material.The heat-conducting medium can physically isolate starch particles and prevent them from agglomerating; the heat-conducting medium and tumbling treatment help to conduct heat and improve the oxidation efficiency of starch; and the heat-conducting medium is easy to separate and can be reused.The obtained hard carbon negative electrode material maintains a spherical morphology and has high reversible capacity and a first coulomb efficiency.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a starch-based hard carbon material based on a thermally conductive medium, its preparation method, and its application. Background Technology

[0002] The ever-increasing demand for energy has spurred the development of safe, inexpensive, and scalable high-performance battery technologies. Lithium-ion batteries, due to the limited and uneven distribution of lithium resources, struggle to meet this demand. Sodium-ion batteries, sharing similar characteristics with lithium-ion batteries, show great potential for application. However, sodium... + radius Compared to Li + Large. Graphite, as a mature commercial anode material for lithium-ion batteries, Na... + Intercalation between graphite layers is difficult, and the thermodynamic properties of sodium-based graphite intercalation compounds are unstable. Therefore, there is an urgent need to develop high-performance anode materials to meet the practical applications of sodium-ion batteries.

[0003] Hard carbon (HCs) possesses advantages such as large interlayer spacing, abundant defects, and internal pores, making it a promising anode material for sodium-ion batteries. Starch, as a widely available biomass material, is abundant in yield and low in cost, making it an ideal precursor for hard carbon materials. Furthermore, starch itself has a spherical morphology that is retained during hard carbon preparation, providing numerous active sites for sodium ion insertion and extraction, which is beneficial for improving the battery's initial coulombic efficiency and reversible specific capacity. However, direct high-temperature carbonization of starch can lead to foaming and coalescence. To avoid foaming during starch carbonization, a prolonged oxidative cross-linking treatment is required before carbonization. Traditional processes, such as air oxidation, have limited contact between starch particles and air, resulting in poor oxidation effects and requiring longer processing cycles or higher oxidation temperatures, leading to increased energy consumption. In addition, high-temperature oxidation reactions are intense, easily causing starch melting and foaming during oxidation. Liquid-phase oxidation is difficult to meet the needs of large-scale production and often requires the addition of additional oxidants, which are difficult to recover, increasing processing steps and production costs. Existing processes significantly limit the large-scale production of starch-based hard carbon materials, restricting their application in sodium-ion batteries.

[0004] Therefore, it is of great significance to develop a starch oxidation pretreatment and hard carbon-based hard carbon anode material that can maintain the spherical morphology of starch, has high oxidation efficiency, and is simple and easy to operate. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art by providing a starch-based hard carbon material based on a thermally conductive medium, its preparation method, and its application.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a starch-based hard carbon material based on a thermally conductive medium, comprising the following steps:

[0008] 1) The starch was dried to obtain a carbon precursor;

[0009] The heat-conducting medium is ball-milled or freeze-dried to obtain a pretreated heat-conducting medium.

[0010] 2) After mixing the carbon precursor and the pretreated heat-conducting medium, the mixture is pre-oxidized under tumbling conditions, and then the heat-conducting medium and oxidation products are separated.

[0011] 3) The oxidation products are sequentially carbonized and acid-washed under a protective atmosphere to obtain starch-based hard carbon material;

[0012] The heat-conducting medium in step 1) is a water-soluble salt;

[0013] In step 2), the mass ratio of the carbon precursor to the pretreated heat-conducting medium is 1:1 to 20.

[0014] Preferably, the starch is potato starch, cassava starch, pea starch, wheat starch, sorghum starch, rice starch, or corn starch.

[0015] Preferably, the drying temperature in step 1) is 30–90°C, and the drying time is 2–36 h.

[0016] The heat-conducting medium is sodium chloride, potassium chloride, magnesium chloride, sodium carbonate, potassium carbonate, or potassium sulfate.

[0017] Preferably, the ball milling speed in step 1) is 100-800 r / min, the ball milling time is 1-24 h, and the ball milling is followed by sieving with a mesh size of 100-500 mesh.

[0018] Preferably, a surfactant is added during the freeze-drying process in step 1), the surfactant being polyether, and the mass ratio of polyether to the heat-conducting medium being 0.015 to 0.05:1; the freeze-drying temperature is -50 to -40°C, and the freeze-drying time is 6 to 24 hours; after freeze-drying, the material is sieved, and the sieve mesh size is 100 to 600 mesh.

[0019] Preferably, in step 2), under the condition of tumbling treatment, water is continuously added for pre-oxidation treatment, with water added once every 25 to 35 minutes, and 4 to 6 mL each time.

[0020] Preferably, the temperature of the pre-oxidation treatment is 150–400℃, the heating rate is 2–20℃ / min, the pre-oxidation treatment time is 1–24h, and the number of pre-oxidation treatments is 2–6.

[0021] Preferably, the protective atmosphere in step 3) is argon or nitrogen, the carbonization temperature is 1100–2600℃, the carbonization time is 1–10 h, and the heating rate to the carbonization temperature is 0.5–20℃ / min.

[0022] The present invention also provides a starch-based hard carbon material based on a thermally conductive medium prepared by the aforementioned preparation method.

[0023] The present invention also provides the application of the starch-based hard carbon material based on the thermally conductive medium in sodium-ion batteries.

[0024] The beneficial effects of this invention include the following:

[0025] 1) This invention, by adjusting the size of the heat-conducting medium and replacing it with a medium of different thermal conductivity, can effectively physically isolate starch particles, uniformly conduct heat, and ensure that the starch particles are heated evenly during oxidation, avoiding melting and foaming caused by excessively high local temperatures, thus promoting starch stabilization. Furthermore, the heat-conducting medium is easy to separate and remove; after dissolving it in deionized water, the precipitate yields hard carbon material, and the solution can be dried to obtain a reusable heat-conducting medium. This process is simple, low-cost, sustainable, and environmentally friendly. The size of the heat-conducting medium can be controlled using ball milling / freeze-drying and sieving processes. Adding polyether F-127 for freeze-drying allows polyether F-127 to increase solution viscosity and inhibit crystal nucleation and growth by adsorbing onto the crystal surface, thereby obtaining an ultrafine heat-conducting medium. Replacing the heat-conducting medium with one of different thermal conductivity can achieve even better oxidation results.

[0026] 2) This invention employs a tumbling process to ensure thorough and uniform mixing of the carbon precursor and the heat-conducting medium. This process also increases the contact between starch particles and oxygen, deepening the oxidation process and introducing more electrochemically active oxygen-containing functional groups, thereby improving the electrochemical performance of the assembled sodium-ion battery. As a result, while ensuring the oxidation effect, the pre-oxidation time is significantly shortened, reducing energy consumption and cost during the preparation process. The heat-conducting medium and tumbling process also help conduct heat and improve the starch oxidation efficiency.

[0027] 3) Compared with single oxidation-annealing, the multi-stage oxidation-annealing treatment of the present invention greatly deepens the oxidation degree, effectively suppresses the foaming and agglomeration of starch particles that may occur during carbonization, preserves the natural spherical morphology of starch particles, significantly improves carbon yield, and has high reversible capacity and first coulombic efficiency.

[0028] 4) The method of the present invention is simple, environmentally friendly, energy-saving, efficient and feasible. The hard carbon material prepared has a good spherical morphology, which provides a large number of active sites for the insertion and extraction of sodium ions. By controlling parameters such as the ratio of carbon precursor and heat-conducting medium, oxidation heating rate, oxidation temperature and holding time, the assembled sodium-ion battery can have a high reversible specific capacity and initial coulombic efficiency. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the preparation method of starch-based hard carbon material based on a thermally conductive medium according to the present invention;

[0030] Figure 2 This is a photograph of Example 1 before pre-oxidation treatment;

[0031] Figure 3 This is a photograph of the product after pre-oxidation treatment in Example 1;

[0032] Figure 4 SEM images of the hard carbon material prepared in Example 1;

[0033] Figure 5 SEM images of the hard carbon material prepared for Comparative Example 1;

[0034] Figure 6 SEM images of the hard carbon materials prepared for Comparative Example 2;

[0035] Figure 7 The first charge-discharge curve of the sodium-ion button battery assembled in Example 1 at a current density of 20 mA / g is shown. Detailed Implementation

[0036] This invention provides a method for preparing a starch-based hard carbon material based on a thermally conductive medium, comprising the following steps:

[0037] 1) The starch was dried to obtain a carbon precursor;

[0038] The heat-conducting medium is ball-milled or freeze-dried to obtain a pretreated heat-conducting medium.

[0039] 2) After mixing the carbon precursor and the pretreated heat-conducting medium, the mixture is pre-oxidized under tumbling conditions, and then the heat-conducting medium and oxidation products are separated.

[0040] 3) The oxidation products are sequentially carbonized and acid-washed under a protective atmosphere to obtain starch-based hard carbon material;

[0041] The heat-conducting medium in step 1) is a water-soluble salt;

[0042] In step 2), the mass ratio of the carbon precursor to the pretreated heat-conducting medium is 1:1 to 20.

[0043] In this invention, the starch is preferably potato starch, cassava starch, pea starch, wheat starch, sorghum starch, rice starch, or corn starch.

[0044] In this invention, the drying temperature in step 1) is preferably 30-90°C, more preferably 40-80°C, and even more preferably 50-60°C; the drying time is preferably 2-36 hours, more preferably 8-28 hours, and even more preferably 10-24 hours.

[0045] In this invention, the heat-conducting medium is preferably sodium chloride, potassium chloride, magnesium chloride, sodium carbonate, potassium carbonate, or potassium sulfate.

[0046] In this invention, the ball milling speed in step 1) is preferably 100-800 r / min, more preferably 200-600 r / min, and even more preferably 300-500 r / min; the ball milling time is preferably 1-24 h, more preferably 5-20 h, and even more preferably 8-12 h; after ball milling, the material is sieved, and the sieve mesh size is preferably 100-500 mesh, more preferably 200-400 mesh, and even more preferably 300 mesh.

[0047] In this invention, a surfactant is added during the freeze-drying process in step 1). The surfactant is preferably a polyether, and the polyether is preferably polyether F-127 (poloxam, polyoxyethylene polyoxypropylene). The mass ratio of polyether to the heat-conducting medium is preferably 0.015 to 0.05:1, more preferably 0.025 to 0.045:1, and more preferably 0.03 to 0.04:1. The freeze-drying temperature is preferably -50 to -40°C, more preferably -48 to -42°C, and more preferably -46 to -45°C. The freeze-drying time is preferably 6 to 24 hours, more preferably 10 to 22 hours, and more preferably 12 to 20 hours. After freeze-drying, the material is sieved, and the sieve mesh size is preferably 100 to 600 mesh, more preferably 200 to 500 mesh, and more preferably 300 to 400 mesh.

[0048] In this invention, the mass ratio of the carbon precursor and the pretreated heat-conducting medium in step 2) is preferably 1:2 to 15, more preferably 1:3 to 12, and even more preferably 1:4 to 9.

[0049] In step 2) of the present invention, it is preferred that water is continuously added for pre-oxidation under the condition of tumbling treatment, with water added once every 25 to 35 minutes, and 4 to 6 mL each time, and more preferably once every 30 minutes, with 5 mL each time; after pre-oxidation, the mixture is naturally cooled to room temperature.

[0050] In this invention, the temperature of the pre-oxidation treatment is preferably 150–400°C, more preferably 180–360°C, and even more preferably 200–300°C; the heating rate is preferably 2–20°C / min, more preferably 5–15°C / min, and even more preferably 8–12°C / min; the pre-oxidation treatment time is preferably 1–24 h, more preferably 3–20 h, and even more preferably 4–16 h; and the number of pre-oxidation treatments is preferably 2–6 times, more preferably 3–5 times, and even more preferably 4 times.

[0051] In this invention, the separation in step 2) is preferably achieved by dissolving the heat-conducting medium and the oxidation product in deionized water, taking the precipitate to obtain the oxidation product, and drying the solution to obtain a reusable heat-conducting medium.

[0052] In this invention, the protective atmosphere in step 3) is preferably argon or nitrogen; the carbonization temperature is preferably 1100–2600℃, more preferably 1300–2200℃, and even more preferably 1500–20300℃; the carbonization time is preferably 1–10 h, more preferably 3–9 h, and even more preferably 5–8 h; the heating rate to the carbonization temperature is preferably 0.5–20℃ / min, more preferably 2–15℃ / min, and even more preferably 5–10℃ / min.

[0053] In this invention, the acid used in the pickling treatment in step 3) is preferably an acetic acid solution, hydrochloric acid, sulfuric acid solution, or nitric acid solution, and the mass concentration of the acid is preferably 0.5-5%, more preferably 1-4%, and even more preferably 2-3%.

[0054] The present invention also provides a starch-based hard carbon material based on a thermally conductive medium prepared by the aforementioned preparation method.

[0055] The present invention also provides the application of the starch-based hard carbon material based on the thermally conductive medium in sodium-ion batteries.

[0056] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] 10g of corn starch was dried in an electric heating drying oven at 60℃ for 10h to obtain a carbon precursor; 50g of sodium chloride was ball-milled at 500r / min for 4h, and then sieved through a 500-mesh standard sieve to obtain a pretreated heat transfer medium.

[0059] The carbon precursor was blended with a pre-treated heat-conducting medium and pre-oxidized under tumbling conditions by continuously adding a trace amount of deionized water (5 mL every 30 min). The temperature was increased to 200℃ at a rate of 5℃ / min and held for 1 h. Then the temperature was increased to 240℃ at a rate of 5℃ / min and held for 1 h. Finally, the temperature was increased to 260℃ at a rate of 5℃ / min and held for 4 h. After pre-oxidation, the temperature was allowed to cool naturally to room temperature.

[0060] The heat-conducting medium and oxidation products were dissolved in deionized water, and the precipitate was collected to obtain the oxidation products. The solution was dried to obtain a reusable heat-conducting medium. The oxidation products were carbonized under an argon atmosphere, with the temperature increased to 800℃ at a rate of 5℃ / min, and then increased to 1400℃ at a rate of 5℃ / min, and held at 1400℃ for 4 hours. After cooling to room temperature, the materials were acid-washed with a 2% hydrochloric acid solution to obtain starch-based hard carbon material.

[0061] A slurry was prepared by mixing starch-based hard carbon material, acetylene black, and sodium carboxymethyl cellulose aqueous solution (mass concentration of 2%) in a mass ratio of 92:3:5. The slurry was coated, dried, and cut to obtain electrode sheets. A sodium metal counter electrode was used, and a 1.0 mol / L NaPF6 solution (solvent consisting of diethyl carbonate and ethylene carbonate in a volume ratio of 1:1) was used as the electrolyte to assemble a sodium-ion button battery.

[0062] Electrochemical performance tests were conducted on the sodium-ion button battery at a temperature of 25°C, a current density of 20 mA / g, and a voltage range of 0.001–2.5 V. Table 1 shows that the sodium-ion button battery assembled in this embodiment has a first-charge specific capacity of 366.7 mAh / g and an initial coulombic efficiency of 83.9%.

[0063] Example 2

[0064] 10g of wheat starch was dried in an electric heating oven at 60℃ for 8 hours to obtain a carbon precursor. 2.5g of polyether F-127 and 50g of sodium chloride were mixed and added to 300mL of deionized water, then frozen into a solid at -50℃. The solid was pre-cooled to -50℃ in a vacuum freeze-drying oven and treated for 24 hours, followed by sieving through a 600-mesh standard sieve.

[0065] The carbon precursor was blended with a pre-treated heat-conducting medium. Under tumbling conditions, a trace amount of deionized water was continuously added (5 mL every 30 min) for pre-oxidation treatment. The temperature was increased to 220℃ at a rate of 7℃ / min and held for 1.5 h. Then, the temperature was increased to 260℃ at a rate of 7℃ / min and held for 1.5 h. Finally, the temperature was increased to 320℃ at a rate of 7℃ / min and held for 6 h. After pre-oxidation, the temperature was naturally cooled to room temperature.

[0066] The heat-conducting medium and oxidation products were dissolved in deionized water, and the precipitate was collected to obtain the oxidation products. The solution was dried to obtain a reusable heat-conducting medium. The oxidation products were carbonized under an argon atmosphere, with the temperature increased to 900℃ at a rate of 6℃ / min, and then increased to 1500℃ at a rate of 3℃ / min, and held at 1500℃ for 4 hours. After cooling to room temperature, the materials were acid-washed with a 3% sulfuric acid solution to obtain starch-based hard carbon material.

[0067] A slurry was prepared by mixing starch-based hard carbon material, acetylene black, and sodium carboxymethyl cellulose aqueous solution (mass concentration of 2%) in a mass ratio of 92:3:5. The slurry was then coated, dried, and cut to obtain an electrode sheet. A sodium metal counter electrode was used, and a 1.0 mol / L NaPF6 solution (solvent consisting of diethyl carbonate and ethylene carbonate in a volume ratio of 1:1) was used as the electrolyte to assemble a sodium-ion button battery.

[0068] Electrochemical performance tests were conducted on the sodium-ion button battery at a temperature of 25°C, a current density of 20 mA / g, and a voltage range of 0.001–2.5 V. Table 1 shows that the sodium-ion button battery assembled in this embodiment has a first-charge specific capacity of 353.4 mAh / g and an initial coulombic efficiency of 85.2%.

[0069] Example 3

[0070] 10g of corn starch was dried in an electric heating oven at 65℃ for 10h to obtain a carbon precursor. 2.1g of polyether F-127 and 70g of potassium chloride were mixed and added to 300mL of deionized water, then frozen into a solid at -40℃. The solid was pre-cooled to -40℃ in a vacuum freeze dryer and treated for 12h, followed by sieving through a 500-mesh standard sieve.

[0071] The carbon precursor was blended with a pre-treated heat-conducting medium. Under tumbling conditions, a trace amount of deionized water was continuously added (5 mL every 30 min) for pre-oxidation treatment. The temperature was increased to 190℃ at a rate of 10℃ / min and held for 1 h. Then, the temperature was increased to 210℃ at a rate of 10℃ / min and held for 1 h. Finally, the temperature was increased to 250℃ at a rate of 10℃ / min and held for 3 h. After pre-oxidation, the temperature was naturally cooled to room temperature.

[0072] The heat-conducting medium and oxidation products were dissolved in deionized water, and the precipitate was collected to obtain the oxidation products. The solution was dried to obtain a reusable heat-conducting medium. The oxidation products were carbonized under an argon atmosphere, with the temperature increased to 700℃ at a rate of 4℃ / min, and then increased to 1300℃ at a rate of 1℃ / min, and held at 1300℃ for 8 hours. After cooling to room temperature, the materials were acid-washed with a 1% sulfuric acid solution to obtain starch-based hard carbon material.

[0073] A slurry was prepared by mixing starch-based hard carbon material, acetylene black, and sodium carboxymethyl cellulose aqueous solution (mass concentration of 2%) in a mass ratio of 92:3:5. The slurry was then coated, dried, and cut to obtain an electrode sheet. A sodium metal counter electrode was used, and a 1.0 mol / L NaPF6 solution (solvent consisting of diethyl carbonate and ethylene carbonate in a volume ratio of 1:1) was used as the electrolyte to assemble a sodium-ion button battery.

[0074] Electrochemical performance tests were conducted on the sodium-ion button battery at a temperature of 25°C, a current density of 20 mA / g, and a voltage range of 0.001–2.5 V. Table 1 shows that the sodium-ion button battery assembled in this embodiment has a first-charge specific capacity of 362.9 mAh / g and an initial coulombic efficiency of 82.6%.

[0075] Example 4

[0076] 10g of corn starch was dried in an electric heating oven at 70℃ for 6h to obtain a carbon precursor; 60g of magnesium chloride was ball-milled at 200r / min for 16h and then sieved through a 400-mesh standard sieve.

[0077] The carbon precursor was blended with a pre-treated heat-conducting medium. Under tumbling conditions, a trace amount of deionized water was continuously added (5 mL every 30 min) for pre-oxidation treatment. The temperature was increased to 210℃ at a rate of 6℃ / min and held for 1.5 h. Then, the temperature was increased to 250℃ at a rate of 6℃ / min and held for 1.5 h. Finally, the temperature was increased to 290℃ at a rate of 6℃ / min and held for 6 h. After pre-oxidation, the temperature was allowed to cool naturally to room temperature.

[0078] The heat-conducting medium and oxidation products were dissolved in deionized water, and the precipitate was collected to obtain the oxidation products. The solution was dried to obtain a reusable heat-conducting medium. The oxidation products were carbonized under an argon atmosphere, with the temperature increased to 1000℃ at a rate of 3℃ / min, and then increased to 1600℃ at a rate of 3℃ / min, and held at 1600℃ for 4 hours. After cooling to room temperature, the materials were acid-washed with a 3% (w / w) sulfuric acid solution to obtain a starch-based hard carbon material.

[0079] A slurry was prepared by mixing starch-based hard carbon material, acetylene black, and sodium carboxymethyl cellulose aqueous solution (mass concentration of 2%) in a mass ratio of 92:3:5. The slurry was then coated, dried, and cut to obtain an electrode sheet. A sodium metal counter electrode was used, and a 1.0 mol / L NaPF6 solution (solvent consisting of diethyl carbonate and ethylene carbonate in a volume ratio of 1:1) was used as the electrolyte to assemble a sodium-ion button battery.

[0080] Electrochemical performance tests were conducted on the sodium-ion button battery at a temperature of 25°C, a current density of 20 mA / g, and a voltage range of 0.001–2.5 V. Table 1 shows that the sodium-ion button battery assembled in this embodiment has a first-charge specific capacity of 342.2 mAh / g and an initial coulombic efficiency of 87.7%.

[0081] Comparative Example 1

[0082] No pre-oxidation treatment was used; the carbonization was carried out directly, and other conditions were the same as in Example 1.

[0083] Comparative Example 2

[0084] No heat-conducting medium was added, and all other conditions were the same as in Example 1.

[0085] Comparative Example 3

[0086] The tumbling process was not used, and all other conditions were the same as in Example 1.

[0087] Comparative Example 4

[0088] The mass of the heat transfer medium was changed to 20g, and other conditions were the same as in Example 1.

[0089] The reversible capacity and initial coulombic efficiency of the assembled sodium-ion button cells in the examples and comparative examples are shown in Table 1.

[0090] Table 1. Reversible capacity and initial coulombic efficiency of assembled sodium-ion coin cells in the examples and comparative examples.

[0091] Reversible capacity (mAh / g) First coulombic efficiency / % Example 1 366.7 83.9 Example 2 353.4 85.2 Example 3 362.9 82.6 Example 4 342.2 87.7 Comparative Example 1 185.3 60.5 Comparative Example 2 216.4 63.8 Comparative Example 3 247.4 71.3 Comparative Example 4 234.6 68.9

[0092] As can be seen from Example 1 and Comparative Example 1, the pre-oxidation treatment before carbonization is beneficial to the stabilization of starch particles. The prepared hard carbon material retains the original spherical morphology of the carbon precursor, providing a large number of active sites for the insertion and extraction of sodium ions, which is beneficial to improving reversible capacity and first coulombic efficiency.

[0093] As can be seen from Example 1 and Comparative Example 2, adding a heat-conducting medium can effectively physically isolate starch particles, uniformly conduct heat, and avoid melting and foaming caused by excessively high local temperatures.

[0094] As can be seen from Example 1 and Comparative Example 3, the tumbling process can make the starch granules heat evenly during the pre-oxidation process, which is beneficial to increase the contact between starch and oxygen and improve the oxidation efficiency.

[0095] As can be seen from Example 1 and Comparative Example 4, a smaller amount of thermally conductive medium will affect the heat conduction effect, thereby affecting the spherical morphology and final electrochemical performance of the hard carbon material.

[0096] Furthermore, as can be seen from Examples 1 to 4, parameters such as the type of carbon precursor, the pre-oxidation heating rate, the pre-oxidation temperature and holding time, the number of pre-oxidations, the carbonization heating rate, the carbonization temperature and holding time, and the type and concentration of acid washing can also affect the electrochemical performance of the assembled sodium-ion battery.

[0097] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a starch-based hard carbon material based on a thermally conductive medium, characterized in that, It includes the following steps: 1) The starch is dried to obtain a carbon precursor; The heat-conducting medium is ball-milled or freeze-dried to obtain a pretreated heat-conducting medium. 2) After mixing the carbon precursor and the pretreated heat-conducting medium, the mixture is pre-oxidized under tumbling conditions, and then the heat-conducting medium and oxidation products are separated. 3) The oxidation products are sequentially carbonized and acid-washed under a protective atmosphere to obtain starch-based hard carbon material; Step 1) The heat-conducting medium is a water-soluble salt; Step 2) The mass ratio of the carbon precursor to the pretreated heat-conducting medium is 1:1~20; In step 2), under the condition of tumbling treatment, water is continuously added for pre-oxidation treatment, with 4-6 mL of water added every 25-35 minutes. Step 2) The separation involves dissolving the heat-conducting medium and the oxidation product in deionized water, taking the precipitate to obtain the oxidation product, and drying the solution to obtain a reusable heat-conducting medium. The temperature of the pre-oxidation treatment is 150~400℃, the heating rate is 2~20℃ / min, the pre-oxidation treatment time is 1~24h, and the number of pre-oxidation treatments is 2~6.

2. The preparation method according to claim 1, characterized in that, The starch is potato starch, cassava starch, pea starch, wheat starch, sorghum starch, rice starch, or corn starch.

3. The preparation method according to claim 2, characterized in that, Step 1) The drying temperature is 30~90℃, and the drying time is 2~36h; The heat-conducting medium is sodium chloride, potassium chloride, magnesium chloride, sodium carbonate, potassium carbonate, or potassium sulfate.

4. The preparation method according to claim 3, characterized in that, Step 1) The ball milling speed is 100~800 r / min, the ball milling time is 1~24 h, and the ball milling is sieved after ball milling with a mesh size of 100~500 mesh.

5. The preparation method according to claim 3, characterized in that, In step 1), a surfactant is added during the freeze-drying process. The surfactant is polyether, and the mass ratio of polyether to the heat-conducting medium is 0.015~0.05:

1. The freeze-drying temperature is -50~-40℃, and the freeze-drying time is 6~24h. After freeze-drying, the sample is sieved with a mesh size of 100~600 mesh.

6. The preparation method according to claim 5, characterized in that, Step 3) The protective atmosphere is argon or nitrogen, the carbonization temperature is 1100~2600℃, the carbonization time is 1~10h, and the heating rate to the carbonization temperature is 0.5~20℃ / min.

7. The starch-based hard carbon material based on a thermally conductive medium prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the starch-based hard carbon material based on a thermally conductive medium as described in claim 7 in sodium-ion batteries.

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