Sodium-ion secondary battery negative electrode material

Abstract

The application relates to the field of sodium ion battery materials, and more particularly to a sodium ion secondary battery negative electrode material. A sodium ion secondary battery negative electrode material, a preparation method of the negative electrode material comprises the following steps of biomass pretreatment: biomass material is mixed with alpha-Fe2O3 into a precursor reactant after being cleaned and sieved; the obtained precursor sample powder is subjected to hydrothermal pre-oxidation treatment, cleaned, filtered, dried, and then subjected to low-temperature cracking in a protective atmosphere to obtain a hard carbon precursor; the hard carbon precursor is mixed with an acid solution, subjected to acid pickling, dried, and then subjected to high-temperature calcination in a hydrocarbon atmosphere to obtain a hard carbon negative electrode material. The sodium ion secondary battery negative electrode material has good sodium storage performance, higher reversible specific capacity, charge-discharge cycle stability and initial coulomb efficiency, exhibits excellent reversible sodium storage capacity, and is extremely low in cost, easy to prepare and beneficial to popularization and application.

Description

Technical Field

[0001] This application relates to the field of sodium-ion battery materials, and more specifically, to a sodium-ion secondary battery anode material. Background Technology

[0002] Lithium-ion batteries are now widely used in electronics, communications, transportation and other fields. However, due to the limited reserves and uneven distribution of lithium resources, there is an urgent need to find energy storage batteries with similar performance that can be developed sustainably.

[0003] Based on the successive proposals of metal ion-based batteries such as sodium, calcium, and potassium, sodium-ion batteries have the greatest development potential and prospects: sodium and lithium belong to the same group of metals, have similar physicochemical properties, and sodium is more abundant and widely distributed than lithium metal; sodium-ion batteries can discharge at near 0V, making them safer than lithium-ion batteries and easier to transport.

[0004] In traditional lithium-ion batteries, graphite is generally used as the negative electrode. However, due to the weak interaction between sodium ions and graphite, and the narrow interlayer structure of graphite, sodium ions have difficulty penetrating the graphite layers, resulting in low charge and discharge capacities for sodium-ion batteries using graphite as the negative electrode. This necessitates the selection of a new negative electrode material for sodium-ion batteries, and hard carbon materials have timely emerged to fill this gap. Hard carbon materials are inexpensive, widely available, and simple to prepare, offering economic and environmental advantages. However, the low initial coulombic efficiency, low capacity, and low efficiency of hard carbon materials result in lower energy density for sodium-ion batteries compared to lithium-ion batteries, hindering the development of sodium-ion batteries. Furthermore, the precursor processing of hard carbon negative electrodes lacks a unified standard, leading to increased costs even after multiple processing steps. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this application provides a sodium-ion secondary battery negative electrode material, employing the following technical solution:

[0006] A sodium-ion secondary battery negative electrode material, the preparation method of the negative electrode material includes:

[0007] (1) Biomass pretreatment: The biomass material is washed, sieved and then mixed with α-Fe2O3 to obtain the precursor reactant.

[0008] (2) Pretreatment of precursor reactants: After hydrothermal pre-oxidation treatment of the precursor sample powder obtained in (1), it is washed, filtered and dried, and then pyrolyzed at low temperature under a protective atmosphere to obtain a precursor mixture.

[0009] (3) Acid washing: The precursor mixture obtained in (2) is mixed with an acid solution, acid washed and dried to obtain hard carbon precursor;

[0010] (4) High-temperature activation: The hard carbon precursor obtained in (3) is introduced into a hydrocarbon atmosphere and calcined at high temperature to obtain hard carbon anode material.

[0011] By adopting the above technical solution, hard carbon materials are prepared using biomass waste as a precursor. The biomass is pretreated by removing impurities and sieving a certain range of particle sizes, and then mixed with nano-α-Fe2O3. The precursor morphology is first controlled by hydrothermal treatment to avoid the volume expansion of the precursor during subsequent pyrolysis. Furthermore, by adding nano-α-Fe2O3 as a template to induce hydrothermal treatment of the biomass material, the material is transformed into a spherical shape, which greatly increases the specific surface area of ​​the material and forms abundant nanoscale pores. This is beneficial to increasing the plateau capacity of the hard carbon anode. Hydrothermal treatment also facilitates the introduction of oxygen-containing functional groups, enhancing the disorder of the resulting hard carbon material, increasing reversible sodium storage capacity, and initially inducing the formation of a stable precursor morphology. Low-temperature pyrolysis then removes impurities from the precursor, optimizing its structure and creating pores at specific locations. Acid washing followed by high-temperature calcination forms a pseudo-graphite layer and expands the interlayer spacing, preventing pore collapse and making the hard carbon material more stable. Subsequently, hydrocarbons participate in high-temperature calcination, forming an in-situ carbon layer on the surface of the hard carbon material, turning some pores into closed pores. This facilitates sodium ion storage and reversible adsorption, further improving the structural stability of the hard carbon material and promoting sodium ion insertion / extraction. This results in higher charge / discharge rate performance, better cycle stability, and higher energy density, enhancing the initial coulombic efficiency of the hard carbon material.

[0012] In one specific implementation scheme, the biomass material in (1) is tung oil shell.

[0013] The mass ratio of the biomass material to α-Fe2O3 is 1:(2-5).

[0014] By adopting the above technical solution, the tung oil shell has a simple structure, rich in fats and glycerides, and is easily carbonized, leading to the breakage of molecular bonds. The pretreatment process gives the material advantages such as high specific surface area and pore structure, enhancing the foundation for sodium ion energy storage; the hydrothermal reaction results in a higher oxygen content in the precursor mixture, forming more sodium storage sites. When biomass materials are used in combination with α-Fe2O3, transition metal ions can enhance the electron rearrangement during graphitization, increase the disorder of hard carbon materials, and further induce the formation of spherical hard carbon materials, generating more electron porosity, modifying the pore structure, and improving stable sodium storage performance. In this application, the biomass material and the material within the mass ratio range of α-Fe2O3 exhibit superior electrochemical sodium storage and cyclic charge-discharge performance. This may be because insufficient α-Fe2O3 content cannot adequately guide calcination and provide a stable structure, which is not conducive to the intercalation of sodium ions and results in insufficient cycle stability. On the other hand, excessive α-Fe2O3 leads to a low degree of graphitization in the material, accompanied by insufficient disorder of pseudo-graphite microcrystalline domains and amorphous carbon domains, affecting the modifiability and processability, and hindering the migration and diffusion of sodium ions.

[0015] In one specific implementation, the hydrocarbon atmosphere in (4) is vaporized toluene.

[0016] The mass ratio of vaporized toluene to hard carbon precursor is 1:(2-4).

[0017] By employing the above technical solution, hydrocarbons are added to participate in high-temperature calcination to further modify the pores. High-temperature pyrolysis forms hydrocarbons containing free radicals, which can adhere to the surface of the hard carbon pseudo-graphite layer for further graft growth, passivating crystal domain defects. The carbon layer generated on the surface can cover part of the open pores, turning them into closed pores, thereby improving the storage and intercalation / extraction of sodium ions. Excessive vaporization of toluene may increase the high-temperature carbonization time, leading to increased costs, and may also block the pores, causing some pores to collapse, thus affecting charge / discharge rate performance and cycle charge / discharge stability.

[0018] In one specific implementation scheme, the high-temperature calcination in (4) is to raise the temperature to 800-900℃ at a rate of 4-5℃ / min, then raise it to 1200-1300℃ at a rate of 1-2℃ / min, react at a constant temperature for 2-4 hours, then lower the temperature to 800-900℃ at a rate of 1-2℃ / min, and then lower it to room temperature at a rate of 4-5℃ / min.

[0019] By adopting the above technical solution, the final temperature range can ensure the graphitization degree of the hard carbon anode material, forming an appropriate pseudo-graphite interlayer spacing, improving the low-voltage plateau capacity and initial coulombic efficiency of the hard carbon anode material. If the temperature is too low, the graphitization degree is small, which is not conducive to the stable intercalation of sodium ions, affecting the capacity and initial coulombic efficiency of the hard carbon anode material. Through two-stage programmed cooling and heating, the pore formation rate of the hard carbon material is stabilized, thereby stabilizing the pore structure and improving cycle stability.

[0020] In one specific implementation scheme, the hydrothermal pre-oxidation in (2) is carried out at a constant temperature of 180-200℃ for 12-18 hours.

[0021] By adopting the above technical solutions, hydrothermal treatment of materials can transform them into spherical shapes, increase the specific surface area and thus improve the sodium storage capacity. Hydrothermal treatment is also conducive to introducing oxygen-containing functional groups, improving the disorder of the resulting hard carbon materials, and increasing the reversible sodium storage capacity.

[0022] In one specific implementation scheme, the low-temperature pyrolysis in (2) is carried out under argon protection, with a heating rate of 4-5℃ / min to 300-400℃, then with a heating rate of 0.5-1℃ / min to 500-600℃, and after a constant temperature reaction for 2-4 hours, the temperature is reduced to 300-400℃ at a cooling rate of 0.5-1℃ / min, and then reduced to room temperature at a cooling rate of 4-5℃ / min.

[0023] In summary, this application has the following beneficial effects:

[0024] 1. Hard carbon materials are prepared using biomass waste as a precursor. Biomass impurities are removed and the biomass with a certain particle size is screened and mixed with nano-α-Fe2O3 for pretreatment. The precursor morphology is first controlled by hydrothermal treatment to avoid the volume expansion of the precursor during subsequent pyrolysis. Furthermore, by adding nano-α-Fe2O3 as a template to induce hydrothermal treatment of biomass materials, the materials are transformed into spherical shapes, which greatly increases the specific surface area of ​​the materials and forms abundant nanoscale pores. This is beneficial to increasing the plateau capacity of hard carbon anodes. Hydrothermal treatment also facilitates the introduction of oxygen-containing functional groups, enhancing the disorder of the resulting hard carbon material, increasing reversible sodium storage capacity, and initially inducing the formation of a stable precursor morphology. Low-temperature pyrolysis then removes impurities from the precursor, optimizing its structure and creating pores at specific locations. Acid washing followed by high-temperature calcination forms a pseudo-graphite layer and expands the interlayer spacing, preventing pore collapse and making the hard carbon material more stable. Subsequently, hydrocarbons participate in high-temperature calcination, forming an in-situ carbon layer on the surface of the hard carbon material, turning some pores into closed pores. This facilitates sodium ion storage and reversible adsorption, further improving the structural stability of the hard carbon material and promoting sodium ion insertion / extraction. This results in higher charge / discharge rate performance, better cycle stability, and higher energy density, enhancing the initial coulombic efficiency of the hard carbon material.

[0025] 2. Tung oil shells have a simple structure, rich in fats and glycerides, and are easily carbonized, leading to the breakage of molecular bonds. Pretreatment processes endow the material with advantages such as high specific surface area and porous structure, enhancing the foundation for sodium ion storage. Hydrothermal reactions result in a higher oxygen content in the precursor mixture, forming more sodium storage sites. When biomass materials are used in combination with α-Fe₂O₃, transition metal ions can enhance electron rearrangement during graphitization, increasing the disorder of hard carbon materials and inducing the formation of spherical hard carbon materials. This generates more electron porosity, modifies the pore structure, and improves stable sodium storage performance. In this application, the biomass material and the material within the mass ratio range of α-Fe2O3 exhibit superior electrochemical sodium storage and cyclic charge-discharge performance. This may be because insufficient α-Fe2O3 content cannot adequately guide calcination and provide a stable structure, which is not conducive to the intercalation of sodium ions and results in insufficient cycle stability. On the other hand, excessive α-Fe2O3 leads to a low degree of graphitization in the material, accompanied by insufficient disorder of pseudo-graphite microcrystalline domains and amorphous carbon domains, affecting the modifiability and processability, and hindering the migration and diffusion of sodium ions.

[0026] 3. By adding hydrocarbons to participate in high-temperature calcination, pore modification is further completed. High-temperature pyrolysis forms hydrocarbons containing free radicals, which can adhere to the surface of the hard carbon pseudo-graphite layer for further graft growth, passivating crystal domain defects. The carbon layer generated on the surface can cover part of the open pores, turning them into closed pores, thereby improving the storage and intercalation / extraction of sodium ions. Excessive toluene may increase the high-temperature carbonization time, leading to increased costs, and may also block the pores, causing some pores to collapse, thus affecting charge / discharge rate performance and cycle charge / discharge stability. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope (SEM) image of the hard carbon anode material in Example 1 of the present invention;

[0028] Figure 2 The first three charge-discharge curves of the hard carbon anode material in Example 1 of this invention;

[0029] Figure 3 The first three charge-discharge curves of the hard carbon anode material in Comparative Example 2 of this invention are shown.

[0030] Figure 4 The charge-discharge efficiency and specific capacity curves of the hard carbon anode material in Example 1 of the present invention for the first 50 cycles.

[0031] Figure 5 The cyclic voltammetry discharge curves of the hard carbon anode material in Example 1 of this invention are shown. Detailed Implementation

[0032] The present application will be further described in detail below with reference to the embodiments.

[0033] Unless otherwise specified, all raw materials used in the examples and comparative examples are commercially available products.

[0034] Example 1

[0035] A sodium-ion secondary battery anode material is prepared according to the following steps: Tung oil shells are washed, dried, pulverized, and sieved, then mixed with α-Fe₂O₃ at a mass ratio of 1:5 to form a precursor reactant; the obtained precursor sample powder is subjected to hydrothermal pre-oxidation treatment, the sample is placed in a hydrothermal reactor, reacted at 180℃ for 12 hours, washed three times with deionized water, filtered, and dried under vacuum at 60℃; the sample obtained from hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, with protective argon gas introduced, the temperature is raised to 300℃ at a heating rate of 5℃ / min, then raised to 600℃ at a heating rate of 0.5℃ / min, held at this temperature for 2 hours, and then... The temperature was lowered to 300℃ at a rate of 0.5℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon precursor powder. The hard carbon precursor was washed three times with 2wt% hydrochloric acid and dried in an oven at 60℃ for 8 hours. 40g of the obtained hard carbon precursor was calcined at high temperature by introducing 10g of vaporized toluene at a gas flow rate of 40ml / min. The temperature was increased to 900℃ at a rate of 5℃ / min, then increased to 1300℃ at a rate of 1℃ / min, held at the temperature for 2 hours, and then lowered to 900℃ at a rate of 1℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon anode material powder.

[0036] Example 2

[0037] A sodium-ion secondary battery anode material is prepared according to the following steps: Tung oil shells are washed, dried, pulverized, and sieved, then mixed with α-Fe₂O₃ at a mass ratio of 1:5 to form a precursor reactant; the obtained precursor sample powder is subjected to hydrothermal pre-oxidation treatment, the sample is placed in a hydrothermal reactor, reacted at 200℃ for 18 hours, washed three times with deionized water, filtered, and dried under vacuum at 60℃; the sample obtained from hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, with protective argon gas introduced, the temperature is raised to 300℃ at a rate of 4℃ / min, then raised to 500℃ at a rate of 1℃ / min, held at this temperature for 4 hours, and then further pyrolyzed at a rate of 1℃ / min. The temperature was lowered to 300℃ at a cooling rate of ℃ / min, and then lowered to room temperature at a cooling rate of 4℃ / min to obtain hard carbon precursor powder. The hard carbon precursor was washed three times with 2wt% hydrochloric acid and dried in an oven at 60℃ for 8 hours. 40g of the obtained hard carbon precursor was calcined at high temperature by introducing 10g of vaporized toluene at a gas flow rate of 40ml / min. The temperature was increased to 800℃ at a heating rate of 4℃ / min, then increased to 1200℃ at a heating rate of 2℃ / min, held at the temperature for 4 hours, and then lowered to 800℃ at a cooling rate of 2℃ / min, and then lowered to room temperature at a cooling rate of 4℃ / min to obtain hard carbon anode material powder.

[0038] Example 3

[0039] A sodium-ion secondary battery anode material is prepared according to the following steps: Tung oil shells are washed, dried, pulverized, and sieved, then mixed with α-Fe₂O₃ at a mass ratio of 1:5 to form a precursor reactant; the obtained precursor sample powder is subjected to hydrothermal pre-oxidation treatment, the sample is placed in a hydrothermal reactor, reacted at 180℃ for 12 h, washed three times with deionized water, filtered, and dried under vacuum at 60℃; the sample obtained from hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, with protective argon gas introduced at a rate of 5℃ / min. The temperature was raised to 600℃ at a heating rate, held at that temperature for 2 hours, and then cooled to room temperature at a cooling rate of 5℃ / min to obtain hard carbon precursor powder. The hard carbon precursor was washed three times with 2wt% hydrochloric acid and dried in an oven at 60℃ for 8 hours. 40g of the obtained hard carbon precursor was then calcined at high temperature by introducing 10g of vaporized toluene at a gas flow rate of 40ml / min. The temperature was raised to 1300℃ at a heating rate of 5℃ / min, held at that temperature for 2 hours, and then cooled to room temperature at a cooling rate of 5℃ / min to obtain hard carbon anode material powder.

[0040] Example 4

[0041] A sodium-ion secondary battery anode material is prepared according to the following steps: Tung oil shells are washed, dried, pulverized, and sieved, then mixed with α-Fe₂O₃ at a mass ratio of 1:2 to form a precursor reactant; the obtained precursor sample powder is subjected to hydrothermal pre-oxidation treatment, the sample is placed in a hydrothermal reactor, reacted at 180℃ for 12 h, washed three times with deionized water, filtered, and dried under vacuum at 60℃; the sample obtained from hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, with protective argon gas introduced, the temperature is raised to 300℃ at a heating rate of 5℃ / min, then raised to 600℃ at a heating rate of 0.5℃ / min, held at this temperature for 2 h, and then... The temperature was lowered to 300℃ at a rate of 0.5℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon precursor powder. The hard carbon precursor was washed three times with 2wt% hydrochloric acid and dried in an oven at 60℃ for 8 hours. 40g of the obtained hard carbon precursor was calcined at high temperature by passing 10g of vaporized toluene through it at a gas flow rate of 40ml / min. The temperature was increased to 900℃ at a rate of 5℃ / min, then increased to 1300℃ at a rate of 1℃ / min, held at the temperature for 2 hours, and then lowered to 900℃ at a rate of 1℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon anode material powder.

[0042] Example 5

[0043] A sodium-ion secondary battery anode material is prepared according to the following steps: Tung oil shells are washed, dried, pulverized, and sieved, then mixed with α-Fe₂O₃ at a mass ratio of 1:1 to form a precursor reactant; the obtained precursor sample powder is subjected to hydrothermal pre-oxidation treatment, the sample is placed in a hydrothermal reactor, reacted at 180℃ for 12 hours, washed three times with deionized water, filtered, and dried under vacuum at 60℃; the sample obtained from hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, with protective argon gas introduced, the temperature increased to 300℃ at a heating rate of 5℃ / min, then increased to 600℃ at a heating rate of 0.5℃ / min, held at this temperature for 2 hours, and then... The temperature was lowered to 300℃ at a rate of 0.5℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon precursor powder. The hard carbon precursor was washed three times with 2wt% hydrochloric acid and dried in an oven at 60℃ for 8 hours. 40g of the obtained hard carbon precursor was calcined at high temperature by introducing 10g of vaporized toluene at a gas flow rate of 40ml / min. The temperature was increased to 900℃ at a rate of 5℃ / min, then increased to 1300℃ at a rate of 1℃ / min, held at the temperature for 2 hours, and then lowered to 900℃ at a rate of 1℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon anode material powder.

[0044] Example 6

[0045] A sodium-ion secondary battery anode material is prepared according to the following steps: Tung oil shells are washed, dried, pulverized, and sieved, then mixed with α-Fe₂O₃ at a mass ratio of 1:6 to form a precursor reactant; the obtained precursor sample powder is subjected to hydrothermal pre-oxidation treatment, the sample is placed in a hydrothermal reactor, reacted at 180℃ for 12 h, washed three times with deionized water, filtered, and dried under vacuum at 60℃; the sample obtained from hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, with protective argon gas introduced, the temperature is raised to 300℃ at a rate of 5℃ / min, then raised to 600℃ at a rate of 0.5℃ / min, held at this temperature for 2 h, and then... The temperature was lowered to 300℃ at a rate of 0.5℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon precursor powder. The hard carbon precursor was washed three times with 2wt% hydrochloric acid and dried in an oven at 60℃ for 8 hours. 40g of the obtained hard carbon precursor was calcined at high temperature by introducing 10g of vaporized toluene at a gas flow rate of 40ml / min. The temperature was increased to 900℃ at a rate of 5℃ / min, then increased to 1300℃ at a rate of 1℃ / min, held at the temperature for 2 hours, and then lowered to 900℃ at a rate of 1℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon anode material powder.

[0046] Example 7

[0047] A sodium-ion secondary battery anode material is prepared according to the following steps: Tung oil shells are washed, dried, pulverized, and sieved, then mixed with α-Fe₂O₃ at a mass ratio of 1:5 to form a precursor reactant; the obtained precursor sample powder is subjected to hydrothermal pre-oxidation treatment, the sample is placed in a hydrothermal reactor, reacted at 180℃ for 12 hours, washed three times with deionized water, filtered, and dried under vacuum at 60℃; the sample obtained from hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, with protective argon gas introduced, the temperature is raised to 300℃ at a heating rate of 5℃ / min, then raised to 600℃ at a heating rate of 0.5℃ / min, held at this temperature for 2 hours, and then... The temperature was lowered to 300℃ at a rate of 0.5℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon precursor powder. The hard carbon precursor was washed three times with 2wt% hydrochloric acid and dried in an oven at 60℃ for 8 hours. 20g of the obtained hard carbon precursor was passed through 10g of vaporized toluene at a gas flow rate of 40ml / min for high-temperature calcination. The temperature was increased to 900℃ at a rate of 5℃ / min, then increased to 1300℃ at a rate of 1℃ / min, held at the temperature for 2 hours, and then lowered to 900℃ at a rate of 1℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon anode material powder.

[0048] Example 8

[0049] A sodium-ion secondary battery anode material is prepared according to the following steps: Tung oil shells are washed, dried, pulverized, and sieved, then mixed with α-Fe₂O₃ at a mass ratio of 1:5 to form a precursor reactant; the obtained precursor sample powder is subjected to hydrothermal pre-oxidation treatment, the sample is placed in a hydrothermal reactor, reacted at 180℃ for 12 hours, washed three times with deionized water, filtered, and dried under vacuum at 60℃; the sample obtained from hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, with protective argon gas introduced, the temperature is raised to 300℃ at a heating rate of 5℃ / min, then raised to 600℃ at a heating rate of 0.5℃ / min, held at this temperature for 2 hours, and then... The temperature was lowered to 300℃ at a rate of 0.5℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon precursor powder. The hard carbon precursor was washed three times with 2wt% hydrochloric acid and dried in an oven at 60℃ for 8 hours. 10g of the obtained hard carbon precursor was passed through 10g of vaporized toluene at a gas flow rate of 40ml / min for high-temperature calcination. The temperature was increased to 900℃ at a rate of 5℃ / min, then increased to 1300℃ at a rate of 1℃ / min, held at the temperature for 2 hours, and then lowered to 900℃ at a rate of 1℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon anode material powder.

[0050] Comparative Example

[0051] Comparative Example 1

[0052] A sodium-ion secondary battery anode material is prepared according to the following steps: A precursor reactant, obtained by washing, drying, pulverizing, and sieving tung oil shells, is pre-oxidized using hydrothermal methods. The sample is placed in a hydrothermal reactor and reacted at 180°C for 12 hours. It is then washed three times with deionized water, filtered, and dried under vacuum at 60°C. The pre-oxidized sample is then subjected to low-temperature pyrolysis. Protective argon gas is introduced, and the temperature is increased to 300°C at a rate of 5°C / min, then increased to 600°C at a rate of 0.5°C / min, held at this temperature for 2 hours, and then cooled at a rate of 0.5°C / min. The temperature was lowered to 300℃ at a rate of 5℃ / min, and then lowered to room temperature to obtain hard carbon precursor powder. The hard carbon precursor was washed three times with 2wt% hydrochloric acid and dried in an oven at 60℃ for 8 hours. 40g of the obtained hard carbon precursor was passed through 10g of vaporized toluene at a gas flow rate of 40ml / min for high-temperature calcination. The temperature was increased to 900℃ at a rate of 5℃ / min, then increased to 1300℃ at a rate of 1℃ / min, held at the temperature for 2 hours, and then lowered to 900℃ at a rate of 1℃ / min, and then lowered to room temperature at a rate of 5℃ / min to obtain hard carbon anode material powder.

[0053] Comparative Example 2

[0054] A sodium-ion secondary battery anode material is prepared by the following steps: Tung oil shells are washed, dried, crushed, and sieved, then mixed with α-Fe₂O₃ at a mass ratio of 1:5 to form a precursor reactant; low-temperature pyrolysis is performed, with protective argon gas introduced, and the temperature is increased to 300℃ at a rate of 5℃ / min, then increased to 600℃ at a rate of 0.5℃ / min, held at this temperature for 2 hours, and then decreased to 300℃ at a rate of 0.5℃ / min, followed by a decrease to room temperature at a rate of 5℃ / min. Hard carbon precursor powder was obtained; the hard carbon precursor was washed three times with 2wt% hydrochloric acid and dried in an oven at 60℃ for 8 hours. 40g of the obtained hard carbon precursor was passed through 10g of vaporized toluene at a gas flow rate of 40ml / min and calcined at high temperature. The temperature was increased to 900℃ at a heating rate of 5℃ / min, then increased to 1300℃ at a heating rate of 1℃ / min, held at the temperature for 2 hours, and then cooled to 900℃ at a cooling rate of 1℃ / min, and then cooled to room temperature at a cooling rate of 5℃ / min to obtain hard carbon anode material powder.

[0055] Comparative Example 3

[0056] A sodium-ion secondary battery anode material is prepared according to the following steps: Tung oil shells are washed, dried, pulverized, and sieved, then mixed with α-Fe₂O₃ at a mass ratio of 1:5 to form a precursor reactant; the obtained precursor sample powder is subjected to hydrothermal pre-oxidation treatment, the sample is placed in a hydrothermal reactor, reacted at 180℃ for 12 hours, washed three times with deionized water, filtered, and dried under vacuum at 60℃; the sample obtained from hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, with protective argon gas introduced, the temperature is raised to 300℃ at a rate of 5℃ / min, then raised to 600℃ at a rate of 0.5℃ / min, and held at this temperature for 2 hours. The temperature was lowered to 300℃ at a cooling rate of 0.5℃ / min, and then lowered to room temperature at a cooling rate of 5℃ / min to obtain hard carbon precursor powder. The hard carbon precursor was washed three times with 2wt% hydrochloric acid and dried in an oven at 60℃ for 8 hours. 40g of the obtained hard carbon precursor was calcined at high temperature by introducing 10g of argon gas at a gas flow rate of 40ml / min. The temperature was increased to 900℃ at a heating rate of 5℃ / min, then increased to 1300℃ at a heating rate of 1℃ / min, held at the temperature for 2 hours, and then lowered to 900℃ at a cooling rate of 1℃ / min, and then lowered to room temperature at a cooling rate of 5℃ / min to obtain hard carbon anode material powder.

[0057] Performance testing

[0058] The physicochemical properties of the sodium-ion secondary battery anode material prepared in the examples and comparative examples were tested using the following methods: a. Pore size analysis: The N2 isothermal adsorption-desorption curve was measured using a BEL-SorpMaxII specific surface area and vapor adsorption analyzer manufactured by MicrotracBEL Corporation of Japan. The pore volume of the material was calculated based on the adsorption amount at a relative pressure of approximately 0.99.

[0059] b. Electrical Performance Testing: The electrical performance was tested using a half-cell test method. Specifically, the hard carbon negative electrode material from the above examples and comparative examples was mixed with sodium alginate and Super-p in a weight ratio of 90:5:5 (by weight), and water was added to adjust the slurry. This slurry was then coated onto aluminum foil to form a negative electrode sheet. The electrolyte was a 1 mol / L LiPF6 solution, with a solvent consisting of a 1:1 volume ratio mixture of EC (ethylene carbonate) and DEC (diethyl carbonate). A polypropylene microporous membrane was used as the separator, and a sodium sheet was used as the counter electrode. The battery was then assembled. Constant current charge-discharge experiments were conducted using the LAND battery testing system, with the charge-discharge voltage limited to 0.01-2.0V. The results are shown in Table 1 below.

[0060] Table 1 Performance Test Results

[0061]

[0062]

[0063] As shown in Table 1, the high-performance sodium-ion secondary battery anode material obtained in the above embodiments, which is easy to prepare, economical and environmentally friendly, has a large pore size distribution range and porosity, exhibits a typical spherical morphology, has good sodium storage performance, higher reversible specific capacity, first coulombic efficiency and good charge-discharge cycle stability, and demonstrates excellent reversible sodium storage capacity. Moreover, it is extremely low in cost, easy to prepare, and conducive to widespread application.

[0064] Comparing Example 1 with Examples 4-6 and Comparative Example 1, it can be seen that the pore size range, reversible specific capacity, first three-cycle charging specific capacity, and first coulombic efficiency of the easy-to-prepare, economical, and environmentally friendly high-performance sodium-ion secondary battery anode material prepared in Comparative Example 1 are all lower than those in Examples 4-6. Comparative analysis shows that the combination of biomass tung oil shells and α-Fe2O3 using transition metal element ions can enhance the electron rearrangement during graphitization, increase the disorder of hard carbon materials, and induce the formation of spherical hard carbon materials, which can generate more electron pores, modify the pore structure, and improve the stable sodium storage performance. In this application, the biomass material and the material within the mass ratio range of α-Fe2O3 exhibit superior electrochemical sodium storage and cyclic charge-discharge performance. This may be because insufficient α-Fe2O3 content cannot adequately guide calcination and provide a stable structure, which is not conducive to the intercalation of sodium ions and results in insufficient cycle stability. On the other hand, excessive α-Fe2O3 leads to a low degree of graphitization in the material, accompanied by insufficient disorder of pseudo-graphite microcrystalline domains and amorphous carbon domains, affecting the modifiability and processability, and hindering the migration and diffusion of sodium ions.

[0065] Comparing Examples 1, 7-8, and Comparative Example 3, it is evident that the pore size range, reversible specific capacity, first three-cycle charge specific capacity, and initial coulombic efficiency of the easily prepared, economical, and environmentally friendly high-performance sodium-ion secondary battery anode material obtained in Example 1 are all lower than those in Example 1. The applicant believes that by adding hydrocarbons to participate in high-temperature calcination to further modify the pores, high-temperature pyrolysis forms hydrocarbons containing free radicals, which can adhere to the surface of the hard carbon pseudo-graphite layer for further graft growth, thus passivating crystal domain defects. The carbon layer generated on the surface can cover part of the open pores, turning them into closed pores, thereby improving the storage and intercalation / deintercalation of sodium ions. Excessive toluene may increase the high-temperature carbonization time, leading to increased costs, and may also clog the pores, causing partial pore collapse, thereby affecting charge / discharge rate performance and cycle charge / discharge stability.

[0066] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made to the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A sodium-ion secondary battery anode material, characterized in that: The preparation method of the negative electrode material includes: (1) Biomass pretreatment: after washing and sieving, the biomass material is mixed with α-Fe2O3 to obtain a precursor reactant; (2) Pretreatment of precursor reactant: after hydrothermal pre-oxidation treatment of the precursor sample powder obtained in (1), it is washed, filtered, dried, and then pyrolyzed at low temperature under a protective atmosphere to obtain a precursor mixture; (3) Acid washing: after mixing the precursor mixture obtained in (2) with an acid solution, it is washed and dried to obtain a hard carbon precursor; (4) High temperature activation: after passing the hard carbon precursor obtained in (3) into a hydrocarbon atmosphere, it is calcined at high temperature to obtain a hard carbon negative electrode material; the biomass material in (1) is tung oil shell; the hydrocarbon atmosphere in (4) is vaporized toluene.

2. The sodium-ion secondary battery negative electrode material according to claim 1, characterized in that: The mass ratio of the biomass material to α-Fe2O3 is 1:(2-5).

3. The sodium-ion secondary battery negative electrode material according to claim 1, characterized in that: The mass ratio of vaporized toluene to hard carbon precursor is 1:(2-4).

4. The sodium-ion secondary battery negative electrode material according to claim 1, characterized in that: High-temperature calcination involves raising the temperature to 800-900℃ at a rate of 4-5℃ / min, then raising it to 1200-1300℃ at a rate of 1-2℃ / min, maintaining the temperature for 2-4 hours, then lowering the temperature to 800-900℃ at a rate of 1-2℃ / min, and finally lowering it to room temperature at a rate of 4-5℃ / min.

5. The sodium-ion secondary battery negative electrode material according to claim 1, characterized in that: The hydrothermal pre-oxidation in (2) is carried out at a constant temperature of 180-200℃ for 12-18 hours.

6. The sodium-ion secondary battery negative electrode material according to claim 1, characterized in that: The low-temperature pyrolysis in (2) is carried out under argon protection, with a heating rate of 4-5℃ / min to 300-400℃, then with a heating rate of 0.5-1℃ / min to 500-600℃, and after a constant temperature reaction for 2-4 hours, the temperature is reduced to 300-400℃ at a cooling rate of 0.5-1℃ / min, and then reduced to room temperature at a cooling rate of 4-5℃ / min.

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