A durian shell bio-hard carbon material for sodium ion battery negative electrode and its preparation method

Abstract

The present invention provides a durian shell bio-hard carbon material for a sodium ion battery negative electrode and a preparation method thereof, belonging to the technical field of battery materials. The durian shell bio-hard carbon material of the present invention is obtained by washing fresh durian shells, drying, crushing, alkali soaking, acid soaking, washing to neutrality, and freeze-drying at low temperature, followed by low-temperature pre-oxidation and high-temperature calcination without oxygen using Joule heat. The present invention uses abundant, discarded durian shells as raw materials, has a simple process flow, and greatly improves process efficiency. The durian shell bio-hard carbon negative electrode material prepared by the present invention has good sodium storage capacity. In battery applications, sodium ions can be effectively deintercalated from the negative electrode. The sodium ion battery assembled from the obtained sodium ion battery negative electrode has the advantages of high specific capacity, improved first efficiency, and excellent cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a durian shell bio-hard carbon material for a sodium ion battery negative electrode and a preparation method thereof. Background Art

[0002] While lithium-ion batteries dominate the market and are widely used in various fields, the high dependence on imported lithium resources has prompted the exploration of more diversified energy storage solutions. Sodium-ion batteries, as an emerging force, are beginning to emerge in the market.

[0003] Given the global abundance and cost-effectiveness of sodium resources, as well as the similar working principles of sodium-ion batteries and lithium-ion batteries, the industry is increasingly looking forward to sodium-ion batteries, hoping that they can replace or supplement lithium-ion batteries in certain application scenarios. However, the larger size of sodium ions (about 0.1nm) compared to lithium ions (about 0.06nm) poses a challenge to traditional graphite anode materials, as the interlayer spacing is difficult to effectively accommodate the insertion and extraction of sodium ions, severely limiting the capacity performance of sodium-ion batteries.

[0004] In-depth research has revealed that hard carbon materials show great potential as anode materials for sodium-ion batteries. Unlike the lithium storage mechanism of graphite, the sodium storage mechanism of hard carbon is more complex and diverse, and remains to be fully elucidated. However, generally accepted mechanisms include various reaction types, such as intercalation, alloying, and conversion. The unique structure of hard carbon, characterized by surface defects, interlayer voids, and micropores, provides ample storage space for sodium ions, making it an ideal anode material for sodium-ion batteries. Importantly, hard carbon materials derived from biomass are not only abundant and low-cost, but also environmentally friendly and relatively simple to prepare. These materials have shown positive effects in improving the Coulombic efficiency and conductivity of sodium-ion batteries, meeting the market demand for high-performance, low-cost energy storage materials. Considering cost, environmental performance, and practical application, biomass-derived carbon materials are undoubtedly an ideal choice for sodium-ion battery anode materials. Their structural controllability and performance optimisation offer broad potential for the development of future energy storage technologies.

[0005] Patent No. 202211276795.X proposes a durian shell-based hard carbon anode material and a preparation method thereof. The preparation method comprises the following steps: (1) soaking dried durian shell powder in hot water and acid, filtering, and drying to obtain a precursor powder; (2) pre-carbonizing the precursor powder under an inert atmosphere to obtain an intermediate product; (3) soaking the intermediate product in an alkaline solution, then soaking it in acid, washing it to neutrality, and drying it to obtain a purified product; (4) carbonizing the purified product under an inert atmosphere to obtain a durian shell-based hard carbon anode material. The present invention utilizes biological waste durian shell as raw material, is environmentally friendly, and has low cost. The prepared durian shell-based hard carbon anode material is conducive to ion storage, has a high specific capacity, and has excellent low-temperature performance. This patent utilizes a traditional tubular furnace carbonization process. Scanning electron microscopy images show that the prepared hard carbon material has a relatively small porous structure and the specific surface area needs to be further improved. Summary of the Invention

[0006] To solve the above technical problems, the present invention proposes a durian shell bio-hard carbon material for sodium ion battery negative electrode and a preparation method thereof. The preparation method has a simple process flow, low cost, and is environmentally friendly. The sodium ion battery assembled with the sodium ion battery negative electrode prepared with this material has the advantages of high specific capacity, significantly improved first efficiency, and excellent cycle performance.

[0007] To achieve the above objectives, the present invention provides the following technical solutions:

[0008] One of the technical solutions of the present invention:

[0009] A preparation method of a durian shell bio-hard carbon material comprises the following steps: washing fresh durian shell, drying, crushing, soaking in alkali, soaking in acid, washing until neutral, and freeze-drying the shell; and then sequentially subjecting the shell to low-temperature pre-oxidation and high-temperature calcination without oxygen using a Joule heat method to obtain the durian shell bio-hard carbon material.

[0010] Furthermore, in the preparation method of durian shell biological hard carbon material, the temperature of the low-temperature pre-oxidation is 200-450°C, the time is 4-12 hours, and the Joule heat method oxygen-free low-temperature pre-carbonization process is carried out in a muffle furnace to achieve preliminary sintering and pore formation.

[0011] Furthermore, in the preparation method of durian shell biological hard carbon material, the temperature of the Joule heat method oxygen-free high-temperature calcination is 900-1500°C, the time is 0.5-2h, and the Joule heat method oxygen-free high-temperature calcination process is carried out in a Joule rapid heating furnace.

[0012] Furthermore, in the preparation method of durian shell biological hard carbon material, the acid solution used in the acid soaking includes one or more of sulfuric acid, hydrochloric acid and hydrofluoric acid solutions, and the alkaline solution used in the alkali soaking includes one or more of sodium hydroxide, potassium hydroxide and ammonia solution, and the concentration of the acid solution or the alkaline solution is 0.2-6 mol / L.

[0013] Furthermore, in the preparation method of the durian shell biological hard carbon material, the durian shell accounts for 10-50% of the mass of the alkaline solution or the acid solution.

[0014] Furthermore, in the preparation method of the durian shell bio-hard carbon material, the low-temperature freeze-drying treatment lasts for 12-72 hours at a temperature of -98°C to -50°C. Freeze-drying effectively preserves the biomass material's original carbon structure, avoiding the shortcomings of drying, such as shrinkage of the carbon skeleton and reduced pore size. This increases the specific surface area of ​​the carbon material and improves the sodium storage capacity of the hard carbon.

[0015] The second technical solution of the present invention:

[0016] A durian shell biological hard carbon material is prepared according to the preparation method.

[0017] The third technical solution of the present invention:

[0018] The application of the durian shell biological hard carbon material in preparing a negative electrode sheet of a sodium ion battery.

[0019] The fourth technical solution of the present invention:

[0020] A negative electrode sheet for a sodium ion battery comprises the durian shell bio-hard carbon material. The durian shell bio-hard carbon material is mixed with conductive carbon black and an adhesive, and stirred evenly to obtain an electrode slurry. The electrode slurry is applied on a current collector, dried, and then rolled to obtain the negative electrode sheet.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects:

[0022] (1) The method provided by the present invention uses durian shells, which are abundant in source and environmental waste, as raw materials, has low cost, energy conservation and environmental protection, and can be recycled and reused.

[0023] (2) The process flow of the present invention is short, which greatly improves process efficiency and saves costs, and is conducive to industrialization.

[0024] (3) The durian shell bio-hard carbon negative electrode material prepared by the present invention has good sodium storage capacity. In battery applications, sodium ions can be effectively deintercalated in the negative electrode. The sodium ion battery assembled from the prepared sodium ion battery negative electrode has the advantages of high specific capacity, significant improvement in first efficiency, and excellent cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0026] Figure 1 The figures are SEM images of the durian shell bio-hard carbon materials prepared in Example 1 and Comparative Example 1, wherein A) and B) are SEM images of the durian shell bio-hard carbon materials at different magnifications of Example 1, and C) and D) are SEM images of the durian shell bio-hard carbon materials at different magnifications of Comparative Example 1;

[0027] Figure 2 This is the cycle curve of the sodium ion battery prepared using the durian shell bio-hard carbon material of Example 1 as raw material;

[0028] Figure 3 This is the cycle curve of the sodium ion battery prepared using the durian shell bio-hard carbon material of Comparative Example 1 as raw material;

[0029] Figure 4 The first three charge and discharge results of the sodium ion battery prepared in Example 1 and Comparative Example 1, wherein A)-C) represent the first three charge and discharge results of the sodium ion battery prepared in Example 1, and D)-F) represent the first three charge and discharge results of the sodium ion battery prepared in Comparative Example 1;

[0030] Figure 5 This is the cycle curve of the sodium ion battery prepared using the durian shell bio-hard carbon material of Example 2 as raw material;

[0031] Figure 6 This is the cycle curve of the sodium ion battery prepared using the durian shell bio-hard carbon material of Example 4 as raw material;

[0032] Figure 7 This is the cycle curve of the sodium ion battery prepared using the durian shell bio-hard carbon material of Comparative Example 2 as raw material;

[0033] Figure 8 This is the cycle curve of the sodium ion battery prepared using the durian shell bio-hard carbon material of Comparative Example 3 as raw material;

[0034] Figure 9 This is the cycle curve of the sodium ion battery prepared using the durian shell bio-hard carbon material of Comparative Example 4 as raw material;

[0035] Figure 10 This is the cycle curve of the sodium ion battery prepared using the durian shell bio-hard carbon material of Comparative Example 5 as raw material;

[0036] Figure 11This is the cycle curve of the sodium ion battery prepared using the durian shell bio-hard carbon material of Comparative Example 6 as raw material;

[0037] Figure 12 This is the cycle curve of the sodium ion battery prepared using the durian shell bio-hard carbon material of Example 3 as raw material. DETAILED DESCRIPTION

[0038] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0039] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0040] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0041] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0042] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0043] An embodiment of the present invention provides a method for preparing a durian shell bio-hard carbon material, comprising washing, drying, crushing, soaking in alkali, soaking in acid, washing until neutral, and freeze-drying the shells at low temperature. The shells are then subjected to low-temperature pre-oxidation and high-temperature calcination without oxygen using a Joule heat method to obtain the durian shell bio-hard carbon material.

[0044] In a preferred embodiment of the present invention, the freeze-drying time is 12-72 hours at a temperature of -98°C to -50°C. Freeze-drying can effectively preserve the original carbon structure of the biomass material, thereby avoiding the shortcomings of carbon skeleton shrinkage and pore reduction caused by drying, thereby increasing the specific surface area of ​​the carbon material and improving the sodium storage capacity of the hard carbon.

[0045] In a preferred embodiment of the present invention, the temperature of the low-temperature pre-oxidation is 200-450°C, and the time is 4-12 hours. For example, the temperature of the low-temperature pre-oxidation can be 200°C, 250°C, 300°C, 350°C, 400°C or 450°C, and the time can be 4 hours, 6 hours, 8 hours, 10 hours or 12 hours. Within the above temperature and time ranges, the release of volatile substances in the biomass raw materials can be reduced, so that more carbon elements are retained in the solid product. At the same time, the hydrogen bonds of cellulose, hemicellulose and lignin in the biomass material are broken, and some functional group oxidation gases escape, forming a rich pore structure, thereby increasing the yield and purity of hard carbon and its electrochemical performance.

[0046] The low-temperature pre-oxidation process using Joule heating is performed in a muffle furnace to achieve initial sintering and pore formation. The appropriate temperature can improve the carbonization efficiency of the material, improve the microstructure, increase the porosity, increase the specific surface area, and enhance the stability of the hard carbon.

[0047] In a preferred embodiment of the present invention, the Joule heat method oxygen-free high-temperature calcination temperature is 900-1500°C, and the time is 0.5-2 hours. The Joule heat method oxygen-free high-temperature calcination process is carried out in a Joule rapid heating furnace. For example, the Joule heat method oxygen-free high-temperature calcination temperature can be 900°C, 1000°C, 1100°C, 1200°C, 1400°C, or 1500°C, and the time can be 0.5 hours, 1 hour, 1.5 hours, 1.8 hours, or 2 hours. Preliminary sintering and forming holes can be achieved within the above oxygen-free high-temperature calcination temperature and time ranges.

[0048] The Joule heating method, a secondary calcination process involving oxygen-free high-temperature calcination, effectively fixes carbon, making the negative electrode material more stable during charge and discharge cycles. Furthermore, it further increases the pore structure of the carbon material, thereby improving battery capacity. Using Joule heating accelerates this process and allows for better carbon fixation, increasing yield and surface area, thereby enhancing the performance of sodium-ion batteries assembled from these negative electrode materials.

[0049] In a preferred embodiment of the present invention, the acid solution used in the acid soaking includes one or more of sulfuric acid, hydrochloric acid and hydrofluoric acid solutions, and the alkaline solution used in the alkali soaking includes one or more of sodium hydroxide, potassium hydroxide and ammonia solution, and the concentration of the acid solution or the alkaline solution is 0.2-6 mol / L.

[0050] In a preferred embodiment of the present invention, the mass proportion of the durian shell in the alkaline solution or the acid solution is 10-50%, and there is no particular limitation, as long as the durian shell is immersed.

[0051] The embodiment of the present invention also provides a durian shell biological hard carbon material prepared according to the above preparation method, which is prepared according to the above preparation method.

[0052] All raw materials used in the examples of the present invention were purchased from the market.

[0053] The technical solution of the present invention is further illustrated by the following examples.

[0054] Example 1

[0055] (1) washing the durian shell with deionized water, cutting it into small pieces (1 cm to 3 cm in diameter), and shaking it in an ultrasonic machine for 30 min. Then, rinsing it with deionized water and drying it at 60° C. were performed using a wall-breaking machine to obtain a durian shell powdered raw material (particle size <13 μm);

[0056] (2) The above-mentioned durian shell powdered raw material is placed in a 500 mL beaker, deionized water is added to cover the sample, and the sample is placed in an 80 ° C oil bath for 2 hours, and then transferred to a 2 mol / L NaOH solution, stirred and soaked at 60 ° C for 2 hours, and then washed to neutrality, and then transferred to a 2 mol / L HCl solution, stirred and soaked at 60 ° C for 2 hours, and then washed to neutrality. After freezing in a refrigerator, it is placed in a -98 ° C freeze dryer for low-temperature freeze-drying for 36 hours. After freeze-drying the water, a durian shell powder precursor is obtained;

[0057] (3) The obtained durian shell powder precursor was transferred into a muffle furnace, heated to 300°C in an air atmosphere and kept at this temperature for 10 h to obtain pre-pyrolyzed carbon;

[0058] (4) grinding the obtained pre-pyrolyzed carbon into powder and passing it through a 1000-mesh sieve to obtain an intermediate;

[0059] (5) The obtained intermediate was transferred into a Joule rapid heating furnace with nitrogen, and the temperature was rapidly raised to 1300 °C and kept at this temperature for 2 h to obtain the durian shell bio-hard carbon material.

[0060] Example 2

[0061] (1) washing the durian shell with deionized water, cutting it into small pieces (1 cm to 3 cm in diameter), and shaking it in an ultrasonic machine for 30 min. Then, rinsing it with deionized water and drying it at 60° C. were performed using a wall-breaking machine to obtain a durian shell powdered raw material (particle size <13 μm);

[0062] (2) The above-mentioned durian shell powdered raw material is placed in a 500 mL beaker, deionized water is added to cover the sample, and the sample is placed in an 80 ° C oil bath for 2 hours. Then, it is transferred to a 2 mol / L KOH solution, stirred and soaked at 60 ° C for 2 hours, and then washed until neutral. It is transferred to a 2 mol / L H2SO4 solution, stirred and soaked at 60 ° C for 2 hours, and then washed until neutral. After freezing in a refrigerator, it is placed in a -98 ° C freeze dryer for low-temperature freeze-drying for 48 hours. After freeze-drying the water, a durian shell powder precursor is obtained;

[0063] (3) The obtained durian shell powder precursor was transferred into a muffle furnace, heated to 400°C in an air atmosphere and kept at this temperature for 12 hours to obtain pre-pyrolysis carbon;

[0064] (4) grinding the obtained pre-pyrolyzed carbon into powder and passing it through a 1000-mesh sieve to obtain an intermediate;

[0065] (5) The obtained intermediate was transferred into a Joule rapid heating furnace with nitrogen, and the temperature was rapidly raised to 900 °C and kept at this temperature for 2 h to obtain the durian shell bio-hard carbon material.

[0066] Example 3

[0067] (1) washing the durian shell with deionized water, cutting it into small pieces (1 cm to 3 cm in diameter), and shaking it in an ultrasonic machine for 30 min. Then, rinsing it with deionized water and drying it at 60° C. were performed using a wall-breaking machine to obtain a durian shell powdered raw material (particle size <13 μm);

[0068] (2) The above-mentioned durian shell powdered raw material is placed in a 500 mL beaker, deionized water is added to cover the sample, and the sample is placed in an 80 ° C oil bath for 2 hours, and then transferred to 2 mol / L NaOH, stirred and soaked at 60 ° C for 2 hours, and then washed to neutrality, and then transferred to 2 mol / L HCL solution, stirred and soaked at 60 ° C for 2 hours, and then washed to neutrality. After freezing in a refrigerator, it is placed in a -98 ° C freeze dryer for low-temperature freeze-drying for 60 hours. After freeze-drying the water, a durian shell powder precursor is obtained;

[0069] (3) The obtained durian shell powder precursor was transferred into a muffle furnace, heated to 450°C in an air atmosphere and kept at this temperature for 2 h to obtain pre-pyrolyzed carbon;

[0070] (4) grinding the obtained pre-pyrolyzed carbon into powder and passing it through a 1000-mesh sieve to obtain an intermediate;

[0071] (5) The obtained intermediate was transferred into a Joule rapid heating furnace with nitrogen, and the temperature was rapidly raised to 1500°C and kept at this temperature for 0.5 h to obtain the durian shell bio-hard carbon material.

[0072] Example 4

[0073] (1) washing the durian shell with deionized water, cutting it into small pieces (1 cm to 3 cm in diameter), and shaking it in an ultrasonic machine for 30 min. Then, rinsing it with deionized water and drying it at 60° C. were performed using a wall-breaking machine to obtain a durian shell powdered raw material (particle size <13 μm);

[0074] (2) The above-mentioned durian shell powdered raw material is placed in a 500 mL beaker, deionized water is added to cover the sample, and the sample is placed in an 80 ° C oil bath for 2 hours, and then transferred to 4 mol / L NaOH, stirred and soaked at 60 ° C for 2 hours, and then washed to neutrality, and then transferred to 4 mol / L HCL solution, stirred and soaked at 60 ° C for 2 hours, and then washed to neutrality. After freezing in a refrigerator, it is placed in a -98 ° C freeze dryer for low-temperature freeze-drying for 72 hours. After freeze-drying the water, a durian shell powder precursor is obtained;

[0075] (3) The obtained durian shell powder precursor was transferred into a muffle furnace, heated to 250°C in an air atmosphere and kept at this temperature for 6 hours to obtain pre-pyrolysis carbon;

[0076] (4) grinding the obtained pre-pyrolyzed carbon into powder and passing it through a 1000-mesh sieve to obtain an intermediate;

[0077] (5) The obtained intermediate was transferred into a Joule rapid heating furnace with nitrogen, and the temperature was rapidly raised to 1100°C and kept at this temperature for 1.5 h to obtain the durian shell bio-hard carbon material.

[0078] Comparative Example 1

[0079] (1) washing the durian shell with deionized water, cutting it into small pieces (1 cm to 3 cm in diameter), and shaking it in an ultrasonic machine for 30 min. Then, rinsing it with deionized water and drying it at 60° C. were performed using a wall-breaking machine to obtain a durian shell powdered raw material (particle size <13 μm);

[0080] (2) The above-mentioned durian shell powdered raw material was placed in a 500 mL beaker, deionized water was added to cover the sample, and the sample was placed in an 80 ° C oil bath for 2 hours. Then, it was transferred to a 2 mol / L NaOH solution, stirred and soaked at 60 ° C for 2 hours, and then washed until neutral. After freezing in a refrigerator, it was placed in a -98 ° C freeze dryer for low-temperature freeze-drying for 24 hours. After freeze-drying the water, a durian shell powder precursor was obtained;

[0081] (3) The obtained durian shell powder precursor was transferred into a muffle furnace, heated to 300°C in an air atmosphere and kept at this temperature for 8 hours to obtain pre-pyrolysis carbon;

[0082] (4) The obtained pre-pyrolyzed carbon is ball-milled into powder and passed through a 1000-mesh sieve to obtain the durian shell bio-hard carbon material.

[0083] Comparative Example 2

[0084] (1) washing the durian shell with deionized water, cutting it into small pieces (1 cm to 3 cm in diameter), and shaking it in an ultrasonic machine for 30 min. Then, rinsing it with deionized water and drying it at 60° C. were performed using a wall-breaking machine to obtain a durian shell powdered raw material (particle size <13 μm);

[0085] (2) The above-mentioned durian shell powdered raw material is placed in a 500 mL beaker, deionized water is added to cover the sample, and the sample is placed in an 80 ° C oil bath for 2 hours, and then transferred to 2 mol / L NaOH, stirred and soaked at 60 ° C for 2 hours, and then washed to neutrality, and then transferred to 2 mol / L HCL solution, stirred and soaked at 60 ° C for 2 hours, and then washed to neutrality. After freezing in a refrigerator, it is placed in a -98 ° C freeze dryer for low-temperature freeze-drying for 12 hours. After freeze-drying the water, a durian shell powder precursor is obtained;

[0086] (3) ball-milling the obtained durian shell powder precursor into powder, and passing it through a 1000-mesh sieve to obtain an intermediate;

[0087] (4) The obtained intermediate was transferred into a Joule rapid heating furnace with nitrogen, and the temperature was rapidly raised to 1300°C and kept at this temperature for 2 hours to obtain the durian shell bio-hard carbon material.

[0088] Comparative Example 3

[0089] The same as Example 1, except that in step (3), the obtained durian shell powder precursor is transferred into a muffle furnace, heated to 500° C. and kept at this temperature for 2 h to obtain pre-pyrolysis carbon.

[0090] Comparative Example 4

[0091] The same as Example 1, except that in step (3), the obtained durian shell powder precursor is transferred into a muffle furnace, heated to 150° C. and kept warm for 3 h to obtain pre-pyrolysis carbon.

[0092] Comparative Example 5

[0093] The same as Example 1, except that in step (5), the intermediate obtained is transferred into a Joule rapid heating furnace filled with nitrogen, heated to 2500° C. and kept warm for 0.5 h to obtain the durian shell bio-hard carbon material.

[0094] Comparative Example 6

[0095] The same as Example 1, except that in step (5), the intermediate obtained is transferred into a Joule rapid heating furnace filled with nitrogen, heated to 800° C. and kept warm for 2 h to obtain the durian shell bio-hard carbon material.

[0096] Performance Testing

[0097] The SEM images of the durian shell bio-hard carbon materials prepared in Example 1 and Comparative Example 1 are shown in FIG. Figure 1Figures A) and B) are SEM images of the durian shell bio-hard carbon material at different magnifications of Example 1, and Figures C) and D) are SEM images of the durian shell bio-hard carbon material at different magnifications of Comparative Example 1. It can be seen that the durian shell bio-hard carbon material prepared in Example 1 has a large number of obvious honeycomb network structures, which is more conducive to the storage of sodium ions. However, the durian shell bio-hard carbon material prepared in Comparative Example 1 has a smaller specific surface area, a more closed pore structure, and fewer surface active sites, which means that the performance of the battery prepared using this as raw material will be lower than that of Example 1.

[0098] The durian shell bio-hard carbon material prepared in the embodiment or comparative example is mixed with conductive carbon black (Ketjen black) and an adhesive (PVDF, i.e. polyvinylidene fluoride) in a mass ratio of 8:1:1, and stirred evenly to obtain an electrode slurry; the obtained electrode slurry is applied to a current collector, dried, and then rolled to obtain a negative electrode sheet for a sodium ion battery, which is further prepared into a sodium ion battery.

[0099] The prepared sodium ion battery was charged and discharged at a current density of 0.2 A / g. The cycle curve of the sodium ion battery prepared with the durian shell bio-hard carbon material of Example 1 as the raw material is shown in FIG. Figure 2 ,from Figure 2 It can be seen from the graph that the battery negative electrode sheet has good cycle stability and has a high capacity at a current density of 0.2A / g. The cycle curve of the sodium ion battery prepared with the durian shell bio-hard carbon material of Comparative Example 1 is shown in FIG. Figure 3 ,from Figure 3 It can be seen that the cycle stability of the negative electrode sheet of the battery is general, the first efficiency is much lower than that of Example 1, and the capacity is low at a current density of 0.2 A / g.

[0100] The first three charge and discharge results of the sodium ion battery prepared in Example 1 are shown in FIG. Figure 4 A)-C) in the figure, the first three charge and discharge results of the sodium ion battery prepared in Comparative Example 1 are shown in FIG. Figure 4 D)-F) in represents comparative example 1, by Figure 4 It can be seen that, apart from the formation of an SEI film in the first cycle, the curves of Example 1 in the second and third cycles are essentially consistent, indicating good stability. Furthermore, the inclusion of the rapid heating furnace increases the number of material defects and enriches the pores, resulting in significant capacity gains in both the plateau and ramp regions. In contrast, Comparative Example 1 exhibits significant capacity loss in the second and third cycles.

[0101] Using the same method, the sodium ion batteries prepared in Examples 2-4 and Comparative Examples 2-6 were subjected to charge and discharge tests at a current density of 0.2 A / g. The results are as follows:

[0102] The cycle curve of the sodium ion battery prepared with the durian shell biological hard carbon material of Example 2 as raw material is shown in FIG. Figure 5 ,Depend on Figure 5 It can be seen that the secondary pyrolysis temperature of Example 2 is reduced, and the alkali treatment step is replaced with a more alkaline potassium hydroxide solution, so the capacity of the prepared battery is reduced. However, due to the high heating rate of the Joule fast reaction furnace, the pore structure is rich and the stability is acceptable.

[0103] The cycle curve of the sodium ion battery prepared with the durian shell biological hard carbon material of Example 4 as raw material is shown in FIG. Figure 6 ,Depend on Figure 6 It can be seen that Example 4 increases the concentration of acid and alkali, making the surface active sites of the etched hard carbon negative electrode rich and the sodium storage capacity strong, but the temperature decreases, resulting in a decrease in the pore structure and average cycle performance.

[0104] The cycle curve of the sodium ion battery prepared with the durian shell bio-hard carbon material of Comparative Example 2 as raw material is shown in FIG. Figure 7 ,Depend on Figure 7 It can be seen that Example 4 adopts a one-step firing method and only performs high-temperature pre-firing, so the pore richness is far from enough. Although the cycle stability is acceptable, the capacity decreases significantly.

[0105] The cycle curve of the sodium ion battery prepared with the durian shell bio-hard carbon material of Comparative Example 3 as raw material is shown in FIG. Figure 8 ,Depend on Figure 8 It can be seen that Comparative Example 3 greatly increases the pre-oxidation temperature, which wastes a lot of energy. In addition, the high pre-oxidation temperature may lead to more carbon loss and poor capacity, but the cycle is relatively stable.

[0106] The cycle curve of the sodium ion battery prepared with the durian shell bio-hard carbon material of Comparative Example 4 as raw material is shown in FIG. Figure 9 ,Depend on Figure 9 It can be seen that Comparative Example 4 greatly reduces the pre-oxidation temperature. 150°C may just evaporate the moisture of the material, and its support and influence on the pore structure are negligible, so the battery capacity performance is poor.

[0107] The cycle curve of the sodium ion battery prepared with the durian shell bio-hard carbon material of Comparative Example 5 as raw material is shown in FIG. Figure 10 ,Depend on Figure 10 It can be seen that Comparative Example 5 greatly improves the secondary high-temperature pyrolysis temperature, and the battery cycle performance is also improved to a reasonable extent. However, the ultra-high temperature may lead to severe graphitization, resulting in poor battery stability. Moreover, the conditions are too harsh for mass production, and there is a large waste of resources.

[0108] The cycle curve of the sodium ion battery prepared with the durian shell bio-hard carbon material of Comparative Example 6 as raw material is shown in FIG. Figure 11 ,Depend on Figure 11It can be seen that in Comparative Example 6, the secondary high-temperature calcination temperature was lowered to 800°C, resulting in insufficient carbon fixation. As a result, the battery performance was poor, and the cycle and cycle stability were low, and even dropped significantly after 25 cycles.

[0109] The cycle curve of the sodium ion battery prepared with the durian shell bio-hard carbon material of Example 3 as raw material is shown in FIG. Figure 12 , slightly increasing the secondary calcination temperature, the capacity is better and the stability is also better.

[0110] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for preparing a durian shell biological hard carbon material, characterized in that: The durian shell bio-hard carbon material is obtained by washing, drying, crushing, soaking in alkali, soaking in acid, washing until neutral, and freeze-drying the fresh durian shell, and then performing low-temperature pre-oxidation and high-temperature calcination in an oxygen-free manner using Joule heat. The temperature of the low-temperature pre-oxidation is 200-450°C and the time is 4-12 hours; The temperature of the oxygen-free high-temperature calcination by Joule heat method is 900-1500°C and the time is 0.5-2h; The concentrations of the acid solution used in the acid soaking and the alkaline solution used in the alkaline soaking are 0.2-6 mol / L.

2. The method for preparing a durian shell biological hard carbon material according to claim 1, wherein The acid solution used in the acid soaking includes one or more of sulfuric acid, hydrochloric acid and hydrofluoric acid solutions, and the alkaline solution used in the alkaline soaking includes one or more of sodium hydroxide, potassium hydroxide and ammonia solution.

3. The preparation method of durian shell biological hard carbon material according to claim 1, wherein The low-temperature freeze-drying treatment takes 12-72 hours at a temperature of -98°C to -50°C.

4. A durian shell biological hard carbon material, characterized in that Prepared according to the preparation method according to any one of claims 1 to 3.

5. Application of the durian shell biological hard carbon material as claimed in claim 4 in preparing a battery negative electrode sheet for a sodium ion battery.

6. A negative electrode sheet for a sodium ion battery, characterized in that: The invention comprises the durian shell biological hard carbon material according to claim 4.

7. The negative electrode sheet for sodium ion battery according to claim 6, characterized in that: The durian shell biological hard carbon material is mixed with conductive carbon black and an adhesive, and stirred evenly to obtain an electrode slurry; the electrode slurry is applied on a current collector, dried, and then rolled to obtain the battery negative electrode sheet for the sodium ion battery.

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