Easily-prepared, economic and environment-friendly high-performance sodium ion secondary battery negative electrode material

Abstract

The invention relates to the field of sodium ion battery materials, in particular to a high-performance sodium ion secondary battery negative electrode material which is easy to prepare, economical and environmentally friendly. The invention relates to an easy-to-prepare, economic and environment-friendly high-performance sodium ion secondary battery negative electrode material. A preparation method of the hard carbon negative electrode material comprises the following steps: biomass pretreatment: cleaning and screening a biomass material, and mixing the biomass material with alpha-Fe2O3 to obtain a precursor reactant; carrying out hydrothermal pre-oxidation treatment on the obtained precursor sample powder, cleaning, filtering, drying, introducing a protective atmosphere, and carrying out low-temperature cracking to obtain a hard carbon precursor; mixing with an acid solution, pickling and drying; and introducing a hydrocarbon atmosphere, and carrying out high-temperature calcination to obtain the hard carbon negative electrode material. The easy-to-prepare, economic and environment-friendly high-performance sodium ion secondary battery negative electrode material provided by the invention has good sodium storage performance, higher reversible specific capacity, charge-discharge cycle stability and first coulombic efficiency, shows excellent reversible sodium storage capacity, and is extremely low in cost, easy to prepare and beneficial to popularization and application.

Description

Technical Field

[0001] The present application relates to the field of sodium ion battery materials, and more specifically, to a high-performance sodium ion secondary battery negative electrode material that is easy to prepare, economical and environmentally friendly. Background Art

[0002] Nowadays, lithium-ion battery energy storage is 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 sustainable energy storage batteries with similar performance to lithium-ion batteries.

[0003] Batteries based on metal ions such as sodium, calcium, and potassium have been proposed one after another. Among them, sodium-ion batteries have the greatest development potential and prospects: sodium and lithium belong to the same family of metals, have similar physical and chemical properties, and are more abundant and widely distributed than lithium metal; sodium-ion batteries can discharge at close to 0V, so they are safer than lithium-ion batteries and are easier to transport.

[0004] In traditional lithium-ion batteries, graphite is generally used as the negative electrode of the battery. However, due to the weak interaction between sodium ions and graphite, and the narrow interlayer of graphite, it is difficult for sodium ions to enter the interlayer of graphite, resulting in the low charge and discharge capacity of sodium-ion batteries with graphite as the negative electrode. This means that it is necessary to reselect the negative electrode material of sodium-ion batteries, and the timely emergence of hard carbon materials fills this gap. The raw materials of hard carbon materials are cheap, widely available, and simple to prepare, with economic and environmental advantages. However, the low first coulomb efficiency, low capacity, and low efficiency of hard carbon materials have led to a lower energy density of sodium-ion batteries than lithium-ion batteries, which has restricted the development of sodium-ion batteries. At the same time, the precursor processing process of hard carbon negative electrodes has not formed a unified standard, and the cost still rises after multiple treatments. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the present application provides an easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material, which adopts the following technical solution: A high-performance sodium ion secondary battery negative electrode material that is easy to prepare, economical and environmentally friendly, wherein the preparation method of the hard carbon negative electrode material comprises: (1) Biomass pretreatment: The biomass material is washed, sieved, and mixed with α-Fe2O3 to obtain a precursor reactant; (2) Pretreatment of precursor reactants: The precursor sample powder obtained in (1) is subjected to hydrothermal preoxidation treatment, and then washed, filtered, and dried, and then introduced into a protective atmosphere for low-temperature pyrolysis to obtain a precursor mixture; (3) acid washing: mixing the precursor mixture obtained in (2) with an acid solution, acid washing, and drying to obtain a hard carbon precursor; (4) High temperature activation: The hard carbon precursor obtained in (3) is introduced into a hydrocarbon atmosphere and calcined at high temperature to obtain a hard carbon negative electrode material.

[0006] By adopting the above technical scheme, hard carbon materials are prepared with biomass waste as precursors. The biomass impurities are removed and the biomass with a certain range of particle sizes 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. Nano-α-Fe2O3 is added as a template to induce hydrothermal treatment of the biomass material so that the material is converted into a spherical form, which greatly increases the specific surface area of ​​the material and forms abundant nano-scale pores, which is beneficial to increase the platform capacity of the hard carbon negative electrode. Hydrothermal treatment is also beneficial to introduce oxygen-containing functional groups, improve the disorder of the obtained hard carbon material, and increase the reversible sodium storage capacity. After initially inducing the formation of a stable precursor morphology, low-temperature cracking is carried out to remove impurity components in the precursor, optimize and adjust the structure of the precursor, form pores at specific positions, and acid wash and high-temperature calcination to form a pseudo-graphite layer and expand the interlayer spacing to prevent pore collapse, making the hard carbon material more stable. Subsequently, hydrocarbons participate in high-temperature calcination to form an in-situ carbon layer on the surface of the hard carbon material, turning some pores into closed pores, which is beneficial to the storage and reversible adsorption of sodium ions, further improving the structural stability of the hard carbon material, and facilitating the embedding / removal of sodium ions, making the charge and discharge rate performance higher and the cycle stability better. In addition, the hard carbon material has a higher energy density, which enhances the first coulombic efficiency of the hard carbon material.

[0007] In a specific embodiment, the biomass material in (1) is tung oil tree shell.

[0008] The mass ratio of the biomass material to α-Fe2O3 is 1:(2-5).

[0009] By adopting the above technical scheme, the tung oil shell has a simple structural component, rich in fat and glyceride, and is very easy to carbonize, resulting in the breaking of molecular bonds. The pretreatment process makes the material have advantages such as high specific surface area and pore structure, which enhances the basis for sodium ion energy storage; the hydrothermal reaction makes the precursor mixture have a higher oxygen content, forming more sodium storage sites. When biomass materials are used in combination with α-Fe2O3, transition metal element ions can enhance the rearrangement of electrons during graphitization, increase the disorder of hard carbon materials, and induce the formation of spherical hard carbon materials, produce more electronic pores, modify the pore structure, and improve stable sodium storage performance. In the present application, the electrochemical sodium storage and cyclic charge-discharge performances of the materials within the mass ratio range of the biomass material and α-Fe2O3 are better. This may be because the α-Fe2O3 content is too little to fully guide the calcination and provide a stable structure, which is not conducive to the intercalation and embedding of sodium ions and the insufficient cycle stability. The excessive α-Fe2O3 leads to a low degree of graphitization of the material, accompanied by insufficient disorder of the pseudo-graphite microcrystalline domains and the amorphous non-crystalline carbon domains, which affects the modifiable processability and is not conducive to the migration and diffusion of sodium ions.

[0010] In a specific embodiment, the hydrocarbon atmosphere in (4) is gasified toluene.

[0011] The mass ratio of the gasified toluene to the hard carbon precursor is 1:(2-4).

[0012] By adopting the above technical solution, the pore modification is further completed by adding hydrocarbons to participate in high-temperature calcination, and high-temperature cracking forms hydrocarbons containing free radicals, which can be attached to the surface of the hard carbon pseudo-graphite layer for further grafting growth, so that the crystal domain defects are passivated, and the carbon layer generated on the surface can cover part of the open pores to become closed pores, thereby improving the storage and intercalation of sodium ions. Too much gasified toluene may increase the time of high-temperature carbonization, resulting in increased costs, and may also block the pores, causing some pores to collapse, thereby affecting the charge and discharge rate performance and cycle charge and discharge stability.

[0013] In a specific embodiment, the high temperature calcination in (4) is carried out by heating the temperature to 800-900°C at a rate of 4-5°C / min, then heating the temperature to 1200-1300°C at a rate of 1-2°C / min, reacting at the constant temperature for 2-4h, cooling the temperature to 800-900°C at a rate of 1-2°C / min, and then cooling the temperature to room temperature at a rate of 4-5°C / min.

[0014] By adopting the above technical solution, the final temperature range can ensure the degree of graphitization of the hard carbon negative electrode material, form an appropriate pseudo-graphite layer spacing, and improve the hard carbon low-voltage platform capacity and the first coulomb efficiency. If the temperature is too low, the degree of graphitization is small, which is not conducive to the stable embedding of sodium ions, affecting the capacity and the first coulomb efficiency of the hard carbon negative electrode material. Through two stages of programmed cooling and heating, the pore formation rate of the hard carbon material is stabilized, and then the pore structure is stable, and the cycle stability is better.

[0015] In a specific embodiment, the hydrothermal pre-oxidation in (2) is a constant temperature hydrothermal reaction at a temperature of 180-200° C. for 12-18 hours.

[0016] By adopting the above technical scheme, the hydrothermal treatment of the material can transform the material into a spherical form, increase the specific surface area and thus increase the sodium storage space. The hydrothermal treatment is also beneficial to the introduction of oxygen-containing functional groups, increase the disorder of the obtained hard carbon material, and increase the reversible sodium storage capacity.

[0017] In a specific possible implementation scheme, the low-temperature cracking in (2) is as follows: under argon protection, the temperature is increased to 300-400°C at a rate of 4-5°C / min, then increased to 500-600°C at a rate of 0.5-1°C / min, and after constant temperature reaction for 2-4 hours, the temperature is reduced to 300-400°C at a rate of 0.5-1°C / min, and then reduced to room temperature at a rate of 4-5°C / min.

[0018] In summary, this application has the following beneficial effects: 1. Prepare hard carbon materials using biomass waste as precursors. Pre-treat the biomass by removing biomass impurities and screening biomass with a certain range of particle sizes and mixing with nano-α-Fe2O3. First, control the precursor morphology through hydrothermal treatment to avoid volume expansion of the precursor during subsequent pyrolysis. Add nano-α-Fe2O3 as a template to induce hydrothermal treatment of the biomass material so that the material is converted into a spherical form, which greatly increases the specific surface area of ​​the material and forms abundant nano-scale pores, which is beneficial to increase the platform capacity of the hard carbon negative electrode. Hydrothermal treatment is also beneficial to introduce oxygen-containing functional groups, improve the disorder of the obtained hard carbon material, and increase the reversible sodium storage capacity. After initially inducing the formation of a stable precursor morphology, low-temperature cracking is carried out to remove impurity components in the precursor, optimize and adjust the structure of the precursor, form pores at specific positions, and acid wash and high-temperature calcination to form a pseudo-graphite layer and expand the interlayer spacing to prevent pore collapse, making the hard carbon material more stable. Subsequently, hydrocarbons participate in high-temperature calcination to form an in-situ carbon layer on the surface of the hard carbon material, turning some pores into closed pores, which is beneficial to the storage and reversible adsorption of sodium ions, further improving the structural stability of the hard carbon material, and facilitating the embedding / removal of sodium ions, making the charge and discharge rate performance higher and the cycle stability better. In addition, the hard carbon material has a higher energy density, which enhances the first coulombic efficiency of the hard carbon material.

[0019] 2. The tung oil shell has a simple structural composition, rich in fat and glyceride, and is very easy to carbonize, resulting in molecular bond breakage. The pretreatment process gives the material advantages such as high specific surface area and pore structure, which enhances the basis for sodium ion energy storage; the hydrothermal reaction makes the precursor mixture contain more oxygen, forming more sodium storage sites. When biomass materials are used in combination with α-Fe2O3, transition metal element ions can enhance the rearrangement of electrons during graphitization, increase the disorder of hard carbon materials, and induce the formation of spherical hard carbon materials, which can produce more electronic pores, modify the pore structure, and improve stable sodium storage performance. In the present application, the electrochemical sodium storage and cyclic charge-discharge performances of the materials within the mass ratio range of the biomass material and α-Fe2O3 are better. This may be because the α-Fe2O3 content is too little to fully guide the calcination and provide a stable structure, which is not conducive to the intercalation and embedding of sodium ions and the insufficient cycle stability. The excessive α-Fe2O3 leads to a low degree of graphitization of the material, accompanied by insufficient disorder of the pseudo-graphite microcrystalline domains and the amorphous non-crystalline carbon domains, which affects the modifiable processability and is not conducive to the migration and diffusion of sodium ions.

[0020] 3. The pores are further modified by adding hydrocarbons to participate in high-temperature calcination. The high-temperature cracking forms hydrocarbons containing free radicals, which can be attached to the surface of the hard carbon pseudo-graphite layer for further grafting growth, so that the crystal domain defects are passivated. The carbon layer generated on the surface can cover part of the open pores to become closed pores, thereby improving the storage and intercalation of sodium ions. Too much toluene may increase the time of high-temperature carbonization, resulting in increased costs, and may also block the pores, causing some pores to collapse, thereby affecting the charge and discharge rate performance and the cycle charge and discharge stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a scanning electron microscope (SEM) image of the hard carbon negative electrode material in Example 1 of the present invention; Figure 2 The first three charge-discharge curves of the hard carbon negative electrode material in Example 1 of the present invention; Figure 3 The first three charge-discharge curves of the hard carbon negative electrode material in Comparative Example 2 of the present invention; Figure 4 The charge-discharge efficiency and specific capacity curve of the hard carbon negative electrode material in Example 1 of the present invention in the first 50 cycles; Figure 5 1 is the cyclic voltammetric discharge curve of the hard carbon negative electrode material in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] The present application is further described in detail below in conjunction with embodiments.

[0023] The raw materials used in the examples and comparative examples that are not otherwise specified are all conventional products that can be purchased from the market.

[0024] Example 1 A high-performance sodium ion secondary battery negative electrode material that is easy to prepare, economical and environmentally friendly is prepared according to the following steps: a biomass-based sodium ion hard carbon negative electrode material is prepared by washing, drying, crushing and screening tung oil shells and mixing them 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 autoclave, reacted at 180°C for 12h, washed with deionized water for 3 times, filtered, and dried at 60°C in a vacuum; the sample obtained by hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, protective argon gas is introduced, the temperature is raised to 300°C at a heating rate of 5°C / min, and then raised to 600°C at a heating rate of 0.5°C / min. Keep the temperature constant for 2 hours, cool to 300°C at a cooling rate of 0.5°C / min, and then cool to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor powder; wash the hard carbon precursor with 2wt% hydrochloric acid for 3 times, dry in an oven at 60°C for 8 hours, take 40g of the obtained hard carbon precursor, pass 10g of vaporized toluene at a gas flow rate of 40ml / min, and carry out high-temperature calcination, increase the temperature to 900°C at a heating rate of 5°C / min, and then increase the temperature to 1300°C at a heating rate of 1°C / min, keep the temperature constant for 2 hours, cool to 900°C at a cooling rate of 1°C / min, and then cool to room temperature at a cooling rate of 5°C / min to obtain a hard carbon negative electrode material powder.

[0025] Example 2 The invention discloses an easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material. The biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: washing, drying, crushing and screening tung oil shells and mixing them with α-Fe2O3 in a mass ratio of 1:5 to form a precursor reactant; performing hydrothermal preoxidation treatment on the obtained precursor sample powder, placing the sample in a hydrothermal autoclave, reacting at 200°C for 18h, washing with deionized water three times, filtering and vacuum drying at 60°C; performing low-temperature pyrolysis on the sample obtained by hydrothermal preoxidation, introducing protective argon gas, heating to 300°C at a heating rate of 4°C / min, and then heating to 500°C at a heating rate of 1°C / min, and then heating to 400°C at a heating rate of 1°C / min. The hard carbon precursor was washed with 2 wt % hydrochloric acid for 3 times and dried in an oven at 60 ° C for 8 h. 40 g of the obtained hard carbon precursor was introduced into 10 g of vaporized toluene at a gas flow rate of 40 ml / min for high-temperature calcination. The temperature was increased to 800 ° C at a heating rate of 4 ° C / min, and then increased to 1200 ° C at a heating rate of 2 ° C / min. The temperature was kept constant for 4 h, the temperature was decreased to 800 ° C at a cooling rate of 2 ° C / min, and then decreased to room temperature at a cooling rate of 4 ° C / min to obtain a hard carbon negative electrode material powder.

[0026] Example 3 A high-performance sodium ion secondary battery negative electrode material that is easy to prepare, economical and environmentally friendly is prepared according to the following steps: tung oil shells are washed, dried, crushed, sieved, and mixed with α-Fe2O3 in a mass ratio of 1:5 to prepare a precursor reactant; the obtained precursor sample powder is subjected to hydrothermal pre-oxidation treatment, the sample is placed in a hydrothermal autoclave, reacted at 180°C for 12h, washed with deionized water 3 times, filtered, and vacuum dried at 60°C; the sample obtained by hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, and protective argon gas is introduced to The temperature was raised to 600°C at a heating rate of 5°C / min, kept constant for 2h, and then cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor powder; the hard carbon precursor was washed three times with 2wt% hydrochloric acid, dried in an oven at 60°C for 8h, 40g of the obtained hard carbon precursor was taken, 10g of vaporized toluene was introduced at a gas flow rate of 40ml / min, and high-temperature calcination was performed, the temperature was raised to 1300°C at a heating rate of 5°C / min, kept constant for 2h, and then cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon negative electrode material powder.

[0027] Example 4 A high-performance sodium ion secondary battery negative electrode material that is easy to prepare, economical and environmentally friendly is prepared according to the following steps: a biomass-based sodium ion hard carbon negative electrode material is prepared by washing, drying, crushing and screening tung oil shells and mixing them with α-Fe2O3 in a mass ratio of 1:2 to prepare a precursor reactant; the obtained precursor sample powder is subjected to hydrothermal pre-oxidation treatment, the sample is placed in a hydrothermal autoclave, reacted at 180°C for 12h, washed with deionized water three times, filtered, and dried at 60°C in a vacuum; the sample obtained by hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, protective argon gas is introduced, the temperature is raised to 300°C at a heating rate of 5°C / min, and then raised to 600°C at a heating rate of 0.5°C / min, and the temperature is kept at 400°C. The hard carbon precursor was washed with 2 wt % hydrochloric acid for 3 times and dried at 60 ° C for 8 h. 40 g of the hard carbon precursor was taken and 10 g of vaporized toluene was introduced at a gas flow rate of 40 ml / min for high-temperature calcination. The temperature was increased to 900 ° C at a heating rate of 5 ° C / min, and then increased to 1300 ° C at a heating rate of 1 ° C / min. The temperature was kept constant for 2 h, and the temperature was decreased to 900 ° C at a cooling rate of 1 ° C / min, and then decreased to room temperature at a cooling rate of 5 ° C / min to obtain hard carbon negative electrode material powder.

[0028] Example 5 The invention discloses an easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material. The biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: washing, drying, crushing and screening tung oil shells and mixing them with α-Fe2O3 in a mass ratio of 1:1 to prepare a precursor reactant; performing hydrothermal preoxidation treatment on the obtained precursor sample powder, placing the sample in a hydrothermal autoclave, reacting at 180°C for 12h, washing with deionized water three times, filtering and vacuum drying at 60°C; performing low-temperature pyrolysis on the sample obtained by hydrothermal preoxidation, introducing protective argon gas, heating the temperature to 300°C at a heating rate of 5°C / min, and then heating the temperature to 600°C at a heating rate of 0.5°C / min, and then heating the temperature to 400°C at a constant temperature. The hard carbon precursor was washed with 2 wt % hydrochloric acid for 3 times and dried in an oven at 60 ° C for 8 h. 40 g of the hard carbon precursor was introduced into 10 g of vaporized toluene at a gas flow rate of 40 ml / min for high-temperature calcination. The temperature was increased to 900 ° C at a heating rate of 5 ° C / min, and then increased to 1300 ° C at a heating rate of 1 ° C / min. The temperature was kept constant for 2 h, and the temperature was decreased to 900 ° C at a cooling rate of 1 ° C / min, and then decreased to room temperature at a cooling rate of 5 ° C / min to obtain hard carbon negative electrode material powder.

[0029] Example 6 A high-performance sodium ion secondary battery negative electrode material that is easy to prepare, economical and environmentally friendly is prepared according to the following steps: tung oil shells are washed, dried, crushed, sieved, and mixed with α-Fe2O3 in 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 autoclave, reacted at 180°C for 12h, washed with deionized water three times, filtered, and dried at 60°C in a vacuum; the sample obtained by hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, protective argon gas is introduced, the temperature is raised to 300°C at a heating rate of 5°C / min, and then raised to 600°C at a heating rate of 0.5°C / min, and the temperature is kept at 400°C. The hard carbon precursor was washed with 2 wt % hydrochloric acid for 3 times and dried in an oven at 60 ° C for 8 h. 40 g of the hard carbon precursor was introduced into 10 g of vaporized toluene at a gas flow rate of 40 ml / min for high-temperature calcination. The temperature was increased to 900 ° C at a heating rate of 5 ° C / min, and then increased to 1300 ° C at a heating rate of 1 ° C / min. The temperature was kept constant for 2 h, and the temperature was decreased to 900 ° C at a cooling rate of 1 ° C / min, and then decreased to room temperature at a cooling rate of 5 ° C / min to obtain hard carbon negative electrode material powder.

[0030] Example 7 A high-performance sodium ion secondary battery negative electrode material that is easy to prepare, economical and environmentally friendly is prepared according to the following steps: a biomass-based sodium ion hard carbon negative electrode material is prepared by washing, drying, crushing and screening tung oil shells and mixing them with α-Fe2O3 in 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 autoclave, reacted at 180°C for 12h, washed with deionized water three times, filtered, and dried at 60°C in a vacuum; the sample obtained by hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, protective argon gas is introduced, the temperature is raised to 300°C at a heating rate of 5°C / min, and then raised to 600°C at a heating rate of 0.5°C / min, and the temperature is kept at 400°C. The hard carbon precursor was washed with 2 wt % hydrochloric acid for 3 times and dried in an oven at 60 ° C for 8 h. 20 g of the hard carbon precursor was introduced into 10 g of vaporized toluene at a gas flow rate of 40 ml / min for high-temperature calcination. The temperature was increased to 900 ° C at a heating rate of 5 ° C / min, and then increased to 1300 ° C at a heating rate of 1 ° C / min. The temperature was kept constant for 2 h, and the temperature was decreased to 900 ° C at a cooling rate of 1 ° C / min, and then decreased to room temperature at a cooling rate of 5 ° C / min to obtain a hard carbon negative electrode material powder.

[0031] Example 8 A high-performance sodium ion secondary battery negative electrode material that is easy to prepare, economical and environmentally friendly is prepared according to the following steps: a biomass-based sodium ion hard carbon negative electrode material is prepared by washing, drying, crushing and screening tung oil shells and mixing them with α-Fe2O3 in 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 autoclave, reacted at 180°C for 12h, washed with deionized water three times, filtered, and dried at 60°C in a vacuum; the sample obtained by hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, protective argon gas is introduced, the temperature is raised to 300°C at a heating rate of 5°C / min, and then raised to 600°C at a heating rate of 0.5°C / min, and the temperature is kept at 400°C. The hard carbon precursor was washed with 2 wt % hydrochloric acid for 3 times and dried in an oven at 60 ° C for 8 h. 10 g of the obtained hard carbon precursor was introduced into 10 g of vaporized toluene at a gas flow rate of 40 ml / min for high-temperature calcination. The temperature was increased to 900 ° C at a heating rate of 5 ° C / min, and then increased to 1300 ° C at a heating rate of 1 ° C / min. The temperature was kept constant for 2 h, the temperature was decreased to 900 ° C at a cooling rate of 1 ° C / min, and then decreased to room temperature at a cooling rate of 5 ° C / min to obtain hard carbon negative electrode material powder.

[0032] Comparative Example Comparative Example 1 A high-performance sodium ion secondary battery negative electrode material that is easy to prepare, economical and environmentally friendly is prepared according to the following steps: a precursor reactant after washing, drying, crushing and screening tung oil shells; a precursor sample powder obtained is subjected to hydrothermal preoxidation treatment, the sample is placed in a hydrothermal autoclave, reacted at 180°C for 12 hours, washed with deionized water three times, filtered, and dried at 60°C in a vacuum; the sample obtained by hydrothermal preoxidation is subjected to low-temperature pyrolysis, protective argon gas is introduced, the temperature is raised to 300°C at a rate of 5°C / min, and then raised to 600°C at a rate of 0.5°C / min, kept at a constant temperature for 2 hours, and heated to 0.5°C / min. / min cooling rate to 300 ° C, and then cooled to room temperature at a cooling rate of 5 ° C / min to obtain a hard carbon precursor powder; the hard carbon precursor is washed with 2wt% hydrochloric acid for 3 times, dried in an oven at 60 ° C for 8 h, 40g of the obtained hard carbon precursor is taken and 10g of vaporized toluene is passed through at a gas flow rate of 40ml / min for high-temperature calcination, the temperature is increased to 900 ° C at a heating rate of 5 ° C / min, and then increased to 1300 ° C at a heating rate of 1 ° C / min, kept at a constant temperature for 2h, cooled to 900 ° C at a cooling rate of 1 ° C / min, and then cooled to room temperature at a cooling rate of 5 ° C / min to obtain a hard carbon negative electrode material powder.

[0033] Comparative Example 2 The invention discloses an easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material. The biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: washing, drying, crushing and screening tung oil shells and mixing them with α-Fe2O3 in a mass ratio of 1:5 to form a precursor reactant; performing low-temperature pyrolysis, introducing protective argon gas, heating the temperature to 300°C at a heating rate of 5°C / min, then heating the temperature to 600°C at a heating rate of 0.5°C / min, maintaining the temperature for 2h, cooling the temperature to 300°C at a cooling rate of 0.5°C / min, and then cooling the temperature to 500°C at a cooling rate of 5°C / min. The temperature was reduced to room temperature at a rate to obtain a hard carbon precursor powder; the hard carbon precursor was washed three times with 2wt% hydrochloric acid, dried in an oven at 60°C for 8h, 40g of the obtained hard carbon precursor was introduced into 10g of vaporized toluene at a gas flow rate of 40ml / min, and high-temperature calcination was performed, the temperature was increased to 900°C at a heating rate of 5°C / min, and then increased to 1300°C at a heating rate of 1°C / min, kept at a constant temperature for 2h, cooled to 900°C at a cooling rate of 1°C / min, and then cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon negative electrode material powder.

[0034] Comparative Example 3 A high-performance sodium ion secondary battery negative electrode material that is easy to prepare, economical and environmentally friendly is prepared according to the following steps: tung oil shells are washed, dried, crushed, sieved, and mixed with α-Fe2O3 in 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 autoclave, reacted at 180°C for 12h, washed with deionized water three times, filtered, and dried at 60°C in a vacuum; the sample obtained by hydrothermal pre-oxidation is subjected to low-temperature pyrolysis, protective argon gas is introduced, the temperature is raised to 300°C at a heating rate of 5°C / min, and then raised to 600°C at a heating rate of 0.5°C / min. Keep the temperature constant for 2 hours, cool to 300°C at a cooling rate of 0.5°C / min, and then cool to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor powder; wash the hard carbon precursor with 2wt% hydrochloric acid for 3 times, dry in an oven at 60°C for 8 hours, take 40g of the obtained hard carbon precursor, pass 10g of argon gas at a gas flow rate of 40ml / min, carry out high-temperature calcination, increase the temperature to 900°C at a heating rate of 5°C / min, and then increase the temperature to 1300°C at a heating rate of 1°C / min, keep the temperature constant for 2 hours, cool to 900°C at a cooling rate of 1°C / min, and then cool to room temperature at a cooling rate of 5°C / min to obtain a hard carbon negative electrode material powder.

[0035] Performance Testing The physical and chemical performance test technical indicators of an easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material prepared in the embodiment and comparative example are measured using the following method: a. Pore size analysis: The N2 isothermal adsorption-desorption curve was measured using the BEL-SorpMaxII specific surface area and vapor adsorption analyzer produced by MicrotracBEL of Japan. The pore volume of the material was calculated based on the adsorption amount when the relative pressure was about 0.99.

[0036] b. Electrical performance test: The test was conducted by a half-cell test method, specifically: the hard carbon negative electrode material of the above embodiments and comparative examples: sodium alginate: Super-p = 90:5:5 (weight ratio), water was added to adjust the slurry, and coated on aluminum foil to make a negative electrode sheet, the electrolyte used was a 1 mol / L LiPF6 solution, the solvent was a mixture of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1:1, the polypropylene microporous membrane was used as a diaphragm, and the counter electrode was a sodium sheet, and assembled into a battery. A constant current charge and discharge experiment was conducted in the LAND battery test system, and the charge and discharge voltage was limited to 0.01-2.0V. The results are shown in Table 1 below: Table 1 Performance test results As can be seen from Table 1, the easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material obtained in the above embodiment has a large pore size distribution range and porosity, shows a typical round morphology, has good sodium storage performance, higher reversible specific capacity, first coulomb efficiency and good charge and discharge cycle stability, shows excellent reversible sodium storage capacity, and has extremely low cost, is easy to prepare, and is conducive to promotion and application.

[0037] By comparing Example 1 with Examples 4-6 and Comparative Example 1, it can be seen that the easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material obtained in Comparative Example 1 has a lower pore size range, reversible specific capacity, first three charge specific capacity and first coulombic efficiency than Examples 4-6. Comparative analysis shows that the combination of biomass tung oil shell and α-Fe2O3 using transition metal element ions can enhance the rearrangement of electrons during graphitization, increase the disorder of hard carbon materials, and induce the formation of spherical hard carbon materials, which can produce more electronic pores, modify the pore structure, and improve the stable sodium storage performance. In the present application, the electrochemical sodium storage and cyclic charge-discharge performances of the materials within the mass ratio range of the biomass material and α-Fe2O3 are better. This may be because the α-Fe2O3 content is too little to fully guide the calcination and provide a stable structure, which is not conducive to the intercalation and embedding of sodium ions and the insufficient cycle stability. The excessive α-Fe2O3 leads to a low degree of graphitization of the material, accompanied by insufficient disorder of the pseudo-graphite microcrystalline domains and the amorphous non-crystalline carbon domains, which affects the modifiable processability and is not conducive to the migration and diffusion of sodium ions.

[0038] Comparing Example 1 with Examples 7-8 and Comparative Example 3, it can be seen that the pore size range, reversible specific capacity, first three charge specific capacity and first coulomb efficiency of the easily prepared, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode 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 complete the pore modification, high-temperature pyrolysis to form hydrocarbons containing free radicals, which can be attached to the surface of the hard carbon pseudo-graphite layer for further grafting growth, so that the crystal domain defects are passivated, and the carbon layer generated on the surface can cover part of the open pores to become closed pores, thereby improving the storage and intercalation of sodium ions. Excessive toluene may increase the time of high-temperature carbonization, resulting in increased costs, and may also block the pores, causing partial collapse of the pores, thereby affecting the charge and discharge rate performance and the cycle charge and discharge stability.

[0039] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. An easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material, characterized in that: The preparation method of the hard carbon negative electrode material comprises: (1) Biomass pretreatment: The biomass material is washed, screened, and mixed with α-Fe2O3 to obtain a precursor reactant; (2) Pretreatment of precursor reactants: The precursor sample powder obtained in (1) is subjected to hydrothermal pre-oxidation treatment, and then washed, filtered, and dried, and then introduced into a protective atmosphere for low-temperature pyrolysis to obtain a precursor mixture; (3) pickling: mixing the precursor mixture obtained in (2) with an acid solution, pickling, and then drying to obtain a hard carbon precursor; (4) High temperature activation: The hard carbon precursor obtained in (3) is introduced into a hydrocarbon atmosphere and calcined at high temperature to obtain a hard carbon negative electrode material.

2. The easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material according to claim 1, characterized in that: The biomass material in (1) is tung oil tree shell.

3. The easy-to-prepare, economical and environmentally friendly high-performance 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).

4. The easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material according to claim 1, characterized in that: The hydrocarbon atmosphere in (4) is gasified toluene.

5. The easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material according to claim 4, characterized in that: The mass ratio of the gasified toluene to the hard carbon precursor is 1:(2-4).

6. The easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material according to claim 1, characterized in that: The high temperature calcination is carried out at a heating rate of 4-5°C / min to 800-900°C, then at a heating rate of 1-2°C / min to 1200-1300°C, after isothermal reaction for 2-4 hours, the temperature is reduced to 800-900°C at a cooling rate of 1-2°C / min, and then at a cooling rate of 4-5°C / min to room temperature.

7. The easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material according to claim 1, characterized in that: The hydrothermal pre-oxidation in (2) is to carry out a constant temperature hydrothermal reaction at a temperature of 180-200° C. for 12-18 hours.

8. The easy-to-prepare, economical and environmentally friendly high-performance sodium ion secondary battery negative electrode material according to claim 1, characterized in that: The (2) medium-low temperature cracking is to, under argon protection, heat up to 300-400°C at a rate of 4-5°C / min, then heat up to 500-600°C at a rate of 0.5-1°C / min, react at constant temperature for 2-4 hours, then cool down to 300-400°C at a rate of 0.5-1°C / min, and then cool down to room temperature at a rate of 4-5°C / min.

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