Agricultural waste biomass-based hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of hard carbon materials, in particular to an agricultural waste biomass-based hard carbon negative electrode material and a preparation method and application thereof. According to the preparation method of the agricultural waste biomass-based hard carbon negative electrode material, the agricultural waste is taken as a substrate, and the agricultural waste biomass-based hard carbon negative electrode material is obtained by boiling, softening, drying, powdering by a powdering machine, hot-pressing, densifying and carbonizing. The agricultural waste biomass-based hard carbon negative electrode material disclosed by the invention has a large number of short graphite domain regions and forms a rich closed-pore structure, so that the transmission distance of sodium ions is shortened to realize high-rate performance, and meanwhile, the increased sodium storage sites are beneficial to improving the capacity. According to the invention, excellent rate capability and cycling stability of the hard carbon negative electrode material are realized, so that the cycle life, the rate capability and the first-circle coulombic efficiency of the sodium ion battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of hard carbon materials, and particularly relates to an agricultural waste biomass-based hard carbon anode material, a preparation method thereof, and an application thereof. Background Art

[0002] Sodium-ion batteries (SIBs), as a promising candidate for the next-generation electrochemical energy storage technology, have attracted much attention in recent years due to their abundant sodium resources, low cost, and compatibility with mature lithium-ion battery (LIBs) technology. In the selection of anode materials, since the radius of sodium ions (0.102 nm) is larger than that of lithium ions, it is difficult to directly use traditional graphite anode materials to complete the process of sodium ion deintercalation / insertion. Hard carbon is a material composed of a large number of disordered graphite lattices and amorphous carbon regions. Due to its large interlayer spacing, complex microstructure, and abundant sodium storage sites, it is considered to be the most promising anode material for sodium ion industrialization. The hard carbon prepared from raw materials such as phenolic resin and coal tar pitch has problems such as high cost, low capacity, and poor rate performance, which limit its feasibility in large-scale applications.

[0003] Biomass-based hard carbon materials have become one of the most promising hard carbon precursors due to their high specific capacity, good cycle stability, and relatively low cost. Using biomass-based hard carbon as the anode material of sodium-ion batteries can effectively reduce the battery cost. However, there are many amorphous regions and amorphous areas in biomass, and the hard carbon obtained after carbonization often has uneven pores and a high degree of disorder. During the charge and discharge process, the structure is prone to collapse, thereby reducing the battery life. In addition, the disordered carbon structure has poor conductivity, which also makes the diffusion path of sodium ions in hard carbon complex and irregular, increasing the difficulty of sodium ion diffusion in carbon materials, slowing down the migration speed of sodium ions, and seriously affecting the charge and discharge efficiency of the battery. Therefore, it is crucial to adopt a simple and universal method to improve the crystallinity of the precursor for preparing a hard carbon anode material with high capacity, high rate, and good cycle performance at the same time. Summary of the Invention

[0004] The purpose of the present invention is to propose an agricultural waste biomass-based hard carbon anode material, a preparation method thereof, and an application thereof in view of the above deficiencies of the prior art.

[0005] A preparation method of an agricultural waste biomass-based hard carbon anode material of the present invention uses agricultural waste as a substrate, dries it after boiling and softening treatment, and then performs hot pressing densification treatment after pulverizing treatment by a pulverizer, and carbonizes it to obtain the agricultural waste biomass-based hard carbon anode material.

[0006] Further, the hot pressing temperature is 100-140 °C, the time is 0.5-2 h, and the applied pressure is 200-5000 psi.

[0007] Further, the carbonization atmosphere is nitrogen, argon or a hydrogen-argon mixture, the carbonization temperature is 300 - 1500 °C, the heating rate is 1 - 10 °C / min, and the carbonization time is 0.5 - 10 h.

[0008] Further, pre-carbonization treatment is carried out before the carbonization treatment.

[0009] Further, the pre-carbonization treatment is carried out under an inert gas at 100 - 400 °C for 0.5 - 2 h, and the heating rate is 1 - 10 °C / min.

[0010] Further, the inert gas is nitrogen, argon or a hydrogen-argon mixture.

[0011] Further, the agricultural waste material is straw, wheat straw, corn straw, corn cob, bagasse, bamboo, coconut shell and crop straw of miscellaneous grains.

[0012] Further, hot pressing is carried out using a flat vulcanizer or a hot press.

[0013] An agricultural waste biomass-based hard carbon anode material prepared by the above preparation method.

[0014] An application of the agricultural waste biomass-based hard carbon anode material as described above, as the anode of a sodium-ion battery.

[0015] Through research, the applicant found that for natural biomass, after high-temperature carbonization, due to its complex components, the structure of the obtained hard carbon material is relatively chaotic. Complex macromolecules such as cellulose are prone to form a highly disordered structure after carbonization, and some will also form highly ordered graphite domain regions. Excessive disorder will make the conductivity of the material weak and weaken its rate performance, while excessive order will lead to a reduction in sodium storage sites, thereby reducing its capacity. After hot pressing the biomass material, the internal structure of the biomass can be effectively changed, and its cellulose crystallinity can be improved. Furthermore, more and more effective closed pore structures and short and uniformly distributed graphite domain regions can be constructed after carbonization. In this way, both the electronic conductivity can be effectively improved and the closed pore sodium storage can be enhanced, thereby improving the cycle stability. During the hot pressing process, lignin acts as a cross-linking agent, melting first and then tightly cross-linking components such as cellulose to form a dense structure. In the subsequent carbonization process, a denser carbon structure is formed, reducing its specific surface area and effectively reducing side reactions and improving the first-cycle Coulomb efficiency.

[0016] The biomass-based hard carbon anode material of the present invention has a large number of short graphite domain regions, a rich closed pore structure, and a low specific surface area. After being applied to the anode of a sodium-ion battery, its large number of short graphite domain regions shorten the sodium-ion transmission distance and improve the rate performance. At the same time, the formed rich closed pore structure also increases the sodium storage sites, contributing to the improvement of the capacity. Moreover, the stable closed pore structure can improve the cycle stability, and the low specific surface area can effectively reduce side reactions and improve the first-cycle Coulombic efficiency. Therefore, the present invention realizes the excellent rate performance and cycle stability of the hard carbon anode material, thereby achieving the improvement of the cycle life, rate performance, and first-cycle Coulombic efficiency of the sodium-ion battery.

[0017] The hard carbon material prepared by the present invention also has a high tap density, improving the practicality.

[0018] The biomass precursor used in the present invention has a wide source, is environmentally friendly, does not require any chemical addition, and the preparation method is simple. The used modification method has simple process operations, no pickling and alkali washing steps in the common hard carbon anode preparation process, is environmentally friendly, has low requirements for equipment, and has good application prospects. Brief Description of the Drawings

[0019] Figure 1 XRD spectra before carbonization of Example 1, Example 5, and Comparative Example 1;

[0020] Figure 2 Thermogravimetric analysis diagrams of Example 1 and Comparative Example 1 in an argon atmosphere at a heating rate of 5 °C per minute;

[0021] Figure 3 First-cycle electrochemical curve performance diagrams of Example 1 and Comparative Example 1 at a current density of 30 mA h / g in a half-cell;

[0022] Figure 4 (a) High-magnification transmission diagram of Comparative Example 1, (b) high-magnification transmission diagram of Example 1;

[0023] Figure 5 Long-cycle performance comparison diagrams of Example 1 and Comparative Example 1 at a current density of 900 mA / g;

[0024] Figure 6 Rate performance diagrams of Example 1 and Comparative Example 1 at a current density of 30 - 1500 mA / g;

[0025] Figure 7 Full-cell performance diagram after Example 1 is matched with a sodium vanadium phosphate cathode;

[0026] Figure 8 Long-cycle performance comparison diagrams of Example 2 and Comparative Example 2 at a current density of 300 mA / g;

[0027] Figure 9 Rate performance graphs of Example 2 and Comparative Example 2 at a current density of 20 - 2000 mA / g. Detailed implementation methods

[0028] The following are specific examples of the present invention. In combination with the attached drawings, the technical solutions of the present invention will be further described, but the present invention is not limited to these examples.

[0029] Example 1:

[0030] (1) Wash the corncob with flowing water, boil it in boiling water for 10 min to soften, and then dry it in an oven at 80 °C.

[0031] (2) Put it into a pulverizer to powder, and then pass through a 160 - mesh sieve to obtain a delicate sieved corncob powder.

[0032] (3) Spread the corncob powder on an iron plate to form a 5 cm * 5 cm square area with a thickness of about 1 - 2 mm. Cover the corncob powder with another iron plate, and heat it on a flat vulcanizer at 140 °C under a pressure of 3000 psi for 2 h.

[0033] (4) Under the protection of an argon atmosphere, heat the hot - pressed amber - like translucent corncob chip at a heating rate of 3 °C / min to 300 °C, hold for 2 h, and then heat it at a heating rate of 5 °C / min to 1300 °C and hold for 5 h to obtain corncob carbon.

[0034] (5) After the material is cooled to room temperature, transfer it to a beaker, wash it with distilled water, and dry it.

[0035] Mix it with conductive agent acetylene black and binder polyvinylidene fluoride in a mass ratio of 8:1:1 and load it onto a copper foil to cut into electrode sheets with a diameter of 12 mm, and the loading amount is 1.5 - 2 mg / cm 2 , use a sodium sheet as the counter - electrode, the separator is whatman GF - D glass fiber separator, the electrolyte is 1 M NaPF6 dissolved in DEGDME, assemble a button battery, and test it at a current density of 300 mA / g to test its Coulomb efficiency and cyclic reversible capacity. The battery performance is shown in the appendix Figure 4 .

[0036] Weigh sodium vanadium phosphate, acetylene black, and polyvinylidene fluoride according to a mass ratio of 8:1:1, add an appropriate amount of N - methylpyrrolidone, and grind them evenly in a mortar. Then use a spatula to coat the slurry on a commercial aluminum foil, place it in an oven at 60 °C for vacuum drying, and cut it into circular pieces with a diameter of 10 mm. After matching with the corncob hard - carbon negative electrode, assemble a button sodium - ion battery. The operating temperature of the sodium - ion battery is - 20 - 80 °C, preferably 25 °C, and the battery performance is shown in the appendix Figure 5 .

[0037] The agricultural waste biomass carbon base in this embodiment is corncob. The selected corncob is just one of the common agricultural wastes. If there are requirements for the structure and elemental composition of the biomass itself, the corresponding common agricultural waste biomass can be selected. The flat vulcanizer treatment method described in the present invention is just one of the hot pressing treatment methods. The method of this embodiment can also be used for other agricultural waste biomass. The application field of its products can also be extended to the research and development of devices for other types of secondary batteries and non-energy storage fields that require carbon materials.

[0038] Example 2:

[0039] (1) Wash the bamboo with flowing water, place it in boiling water for 10 minutes to soften after washing, and then dry it in an oven at 80 °C.

[0040] (2) Put it into a powder grinder to powder, and then pass through a 160-mesh sieve to obtain fine sieved bamboo powder.

[0041] (3) Spread the bamboo powder flat on an iron plate, in a 5 cm * 5 cm square area, with a thickness of about 1 - 2 mm. Cover the bamboo powder with another iron plate, and place it on a flat vulcanizer to heat at 140 °C and pressurize at 3000 psi for 2 hours.

[0042] (4) Under the protection of an argon atmosphere, heat the hot-pressed bamboo sheet at a heating rate of 3 °C / min to 300 °C, hold for 2 hours, and then heat at a heating rate of 5 °C / min to 1300 °C, hold for 5 hours to obtain bamboo carbon.

[0043] (5) After the material is cooled to room temperature, transfer it to a beaker, wash it with distilled water, and dry it.

[0044] Mix it with conductive agent acetylene black and binder polyvinylidene fluoride in a mass ratio of 8:1:1 and load it onto a copper foil to cut into electrode sheets with a diameter of 12 mm, and the loading amount is 1.5 - 2 mg / cm 2 , use a sodium sheet as the counter electrode, the separator is whatman GF-D glass fiber separator, the electrolyte is 1M NaPF6 dissolved in DEGDME, assemble a button battery, and test it at a current density of 300 mA / g to test its Coulomb efficiency and cyclic reversible capacity. The electrochemical performance is shown in Table 1 in the appendix.

[0045] Example 3:

[0046] (1) Wash the corncob with flowing water, place it in boiling water for 10 minutes to soften after washing, and then dry it in an oven at 80 °C.

[0047] (2) Put it into a pulverizer to grind it into powder, and then pass it through a 160-mesh sieve to obtain fine sieved corn cob powder.

[0048] (3) Spread the corn cob powder flat on an iron plate to form a 5 cm * 5 cm square area with a thickness of about 1 - 2 mm. Cover the corn cob powder with another iron plate and place it on a flat vulcanizer for heating at 100 °C under a pressure of 3000 psi for 2 h.

[0049] (4) Place the hot-pressed corn chips under the protection of an argon atmosphere, heat them to 300 °C at a heating rate of 3 °C / min, hold for 2 h, then heat them to 1300 °C at a heating rate of 5 °C / min and hold for 5 h to obtain corn cob carbon.

[0050] (5) After the material is cooled to room temperature, transfer it to a beaker, wash it with distilled water, and dry it.

[0051] Mix it with conductive agent acetylene black and binder polyvinylidene fluoride in a mass ratio of 8:1:1 and load it onto a copper foil to cut into electrode sheets with a diameter of 12 mm, and the loading amount is 1.5 - 2 mg / cm 2 , use a sodium sheet as the counter electrode, the separator is whatman GF-D glass fiber separator, the electrolyte is 1 M NaPF6 dissolved in DEGDME, assemble a button battery, and test it at a current density of 300 mA / g to test its Coulomb efficiency and cyclic reversible capacity. The electrochemical performance is shown in Table 1.

[0052] Example 4:

[0053] (1) Wash the corn cob with running water, place it in boiling water for 10 min to soften it after washing, and then dry it in an oven at 80 °C.

[0054] (2) Put it into a pulverizer to grind it into powder, and then pass it through a 160-mesh sieve to obtain fine sieved corn cob powder.

[0055] (3) Spread the corn cob powder flat on an iron plate to form a 5 cm * 5 cm square area with a thickness of about 1 - 2 mm. Cover the corn cob powder with another iron plate and place it on a flat vulcanizer for heating at 140 °C under a pressure of 5000 psi for 2 h.

[0056] (4) Place the hot-pressed corn chips under the protection of an argon atmosphere, heat them to 300 °C at a heating rate of 3 °C / min, hold for 2 h, then heat them to 1300 °C at a heating rate of 5 °C / min and hold for 5 h to obtain corn cob carbon.

[0057] Comparative Example 1:

[0058] (1) Wash the corncob with flowing water, boil it in boiling water for 10 min to soften, and then dry it in an oven at 80 °C.

[0059] (2) Put it into a pulverizer to powder it, and then sieve it through a 160-mesh sieve to obtain fine sieved corncob powder.

[0060] (3) Under the protection of an argon atmosphere, heat the pulverized corncob powder at a heating rate of 3 °C / min to 300 °C, hold for 2 h, and then heat it at a heating rate of 5 °C / min to 1300 °C and hold for 5 h to obtain corncob carbon.

[0061] (4) After the material is cooled to room temperature, transfer it to a beaker, wash it with distilled water, and dry it. Mix it with the conductive agent acetylene black and the binder polyvinylidene fluoride in a mass ratio of 8:1:1, load it onto a copper foil, cut it into electrode sheets with a diameter of 12 mm, and the loading amount is 1.5 - 2 mg / cm 2 , use a sodium sheet as the counter electrode, the separator is whatman GF-D glass fiber separator, the electrolyte is 1 M NaPF6 dissolved in DEGDME, assemble a button battery, and test it at a current density of 300 mA / g to test its Coulomb efficiency and cyclic reversible capacity. The battery performance is shown in the appendix Figure 4 .

[0062] Comparative Example 2:

[0063] (1) Wash the moso bamboo with flowing water, boil it in boiling water for 10 min to soften, and then dry it in an oven at 80 °C.

[0064] (2) Put it into a pulverizer to powder it, and then sieve it through a 160-mesh sieve to obtain fine sieved moso bamboo powder.

[0065] (3) Under the protection of an argon atmosphere, heat the pulverized moso bamboo powder at a heating rate of 3 °C / min to 300 °C, hold for 2 h, and then heat it at a heating rate of 5 °C / min to 1300 °C and hold for 5 h to obtain moso bamboo carbon.

[0066] (4) After the material is cooled to room temperature, transfer it to a beaker, wash it with distilled water, and dry it. Mix it with the conductive agent acetylene black and the binder polyvinylidene fluoride in a mass ratio of 8:1:1, load it onto a copper foil, cut it into electrode sheets with a diameter of 12 mm, and the loading amount is 1.5 - 2 mg / cm 2 , use a sodium sheet as the counter electrode, the separator is whatman GF-D glass fiber separator, the electrolyte is 1 M NaPF6 dissolved in DEGDME, assemble a button battery, and test it at a current density of 300 mA / g to test its Coulomb efficiency and cyclic reversible capacity. The battery performance is shown in the appendix Figure 6 .

[0067] Comparative Example 3:

[0068] (1) The corncobs were cleaned with flowing water, softened by boiling in boiling water for 10 min, and then dried in an oven at 80 °C.

[0069] (2) They were put into a powder mill to be powdered, and then passed through a 160-mesh sieve to obtain fine sieved corncob powder.

[0070] (3) The corncob powder was spread flat on an iron plate, in a 5 cm * 5 cm square area, with a thickness of about 1 - 2 mm. Another iron plate was used to cover the corncob powder, and it was placed on a flat vulcanizer and heated at 180 °C under a pressure of 3000 psi for 2 hours.

[0071] (4) The heat-pressed corncob chips were heated to 300 °C at a heating rate of 3 °C / min under the protection of an argon atmosphere, held for 2 h, and then heated to 1300 °C at a heating rate of 5 °C / min and held for 5 h to obtain corncob carbon.

[0072] Comparative Example 4:

[0073] (1) The corncobs were cleaned with flowing water, softened by boiling in boiling water for 10 min, and then dried in an oven at 80 °C.

[0074] (2) They were put into a powder mill to be powdered, and then passed through a 160-mesh sieve to obtain fine sieved corncob powder.

[0075] (3) The corncob powder was spread flat on an iron plate, in a 5 cm * 5 cm square area, with a thickness of about 1 - 2 mm. Another iron plate was used to cover the corncob powder, and it was placed on a flat vulcanizer and heated at 60 °C under a pressure of 3000 psi for 2 hours.

[0076] (4) The heat-pressed corncob chips were heated to 300 °C at a heating rate of 3 °C / min under the protection of an argon atmosphere, held for 2 h, and then heated to 1300 °C at a heating rate of 5 °C / min and held for 5 h to obtain corncob carbon.

[0077] (5) After the material was cooled to room temperature, it was transferred to a beaker, washed with distilled water, and dried.

[0078] It was mixed with the conductive agent acetylene black and the binder polyvinylidene fluoride in a mass ratio of 8:1:1 and loaded onto a copper foil to be cut into electrode sheets with a diameter of 12 mm, and the loading amount was 1.5 - 2 mg / cm 2, using sodium flakes as the counter electrode, whatman GF-D glass fiber diaphragm as the separator, and 1M NaPF6 dissolved in DEGDME as the electrolyte, a button battery was assembled and tested at a current density of 300 mA / g to measure its Coulombic efficiency and cyclic reversible capacity. The electrochemical performance is shown in Table 1 in the appendix.

[0079] Table 1 Proportion of cellulose crystallinity before and after treatment and corresponding electrochemical performance in the appendix

[0080]

[0081] Table 2 List of electrochemical performance at different current densities

[0082]

[0083] As can be seen from Table 1, the higher the hot pressing temperature, the greater the proportion of cellulose crystallinity, the higher the reversible capacity of the anode material, and the better the capacity retention rate after 100 cycles. However, when the hot pressing temperature continues to rise to 180 °C, the corn chips obtained in Comparative Example 3 can no longer present a transparent amber state, but instead a charred state, and a large amount of dark brown viscous liquid is produced, causing great damage to the structure of the original biomass material. Therefore, after continued carbonization, the anode structure of the sodium-ion battery is unstable and the cycling performance is poor, with the capacity retention rate only being 88.6% after 100 cycles. According to Example 5, changing the pressure has little effect on the electrochemical performance of the prepared material.

[0084] As can be seen from Table 2, when comparing Example 1 with Comparative Example 1 and Example 2 with Comparative Example 2, for the materials after hot pressing treatment, not only is the capacity significantly improved at low current densities, with the capacity increasing by 50 - 100 mA h / g relatively, but the capacity gap is even greater at high current densities, with the capacity after hot pressing increasing by about 200 mA h / g. The hot pressing treatment shows very excellent rate performance.

[0085] Figure 1 XRD patterns before carbonization of Example 1 and Comparative Example 1. From Figure 1 it can be seen that the XRD patterns of Comparative Example 1 and Example 1 have two obvious diffraction peaks, corresponding to the (200) and (040) crystal planes of cellulose respectively. After hot pressing treatment, the proportion of the crystalline peaks of cellulose gradually increases, indicating that higher proportion of crystalline cellulose can be obtained through hot pressing treatment. This higher proportion of crystalline cellulose can induce the formation of more and more stable closed-pore carbon structures.

[0086] Figure 2For the thermogravimetric analysis of Example 1 and Comparative Example 1 under an argon atmosphere at a heating rate of 5 degrees per minute, the treated lignin undergoes vitrification, its molecular structure becomes more compact, and its thermal stability is significantly improved. The pyrolysis of lignin in Comparative Example 1 mainly occurs at 200 - 900 °C, while the pyrolysis temperature range of the lignin in Example 1 shifts towards higher temperatures (such as 250 - 950 °C). The polycondensation reaction of vitrified lignin at high temperatures (>500 °C) is enhanced, generating more polycyclic aromatic hydrocarbons and coke, resulting in a reduced mass loss rate of Example 1 at the high-temperature stage. The final residue is higher than that of Comparative Example 1, and its thermogravimetric curve shows multiple small peaks in the 200 - 500 °C interval (reflecting the complex decomposition of lignin). The peak intensity of the thermogravimetric curve of Example 1 in this interval weakens and is delayed, indicating that the vitrified lignin decomposes more slowly and is concentrated at higher temperatures. After hot pressing treatment, the crystallinity of cellulose is increased, the molecular chain arrangement is more ordered, and higher energy is required to break the hydrogen bond network. The pyrolysis of the original cellulose is concentrated at 300 - 400 °C, while the pyrolysis of cellulose in Example 1 extends to 300 - 500 °C (stepwise decomposition of the crystalline and amorphous regions). The chain breakage of high-crystallinity cellulose requires higher activation energy, resulting in a lower mass loss rate of Example 1 in the 300 - 400 °C interval compared to Comparative Example 1 (such as the height of the main peak of cellulose in the figure decreasing or the peak shape flattening), and a high hard carbon yield, improving production efficiency.

[0087] Figure 3 For the first-cycle electrochemical curve performance diagrams of Example 1 and Comparative Example 1 at a current density of 30 mA / g in a half-cell, it can be observed that the ramp regions of the two basically coincide. However, in the plateau region where the voltage is less than 0.1 V, the plateau capacity of Example 1 after hot pressing treatment has been greatly improved.

[0088] Figure 4 (a) is the high-magnification transmission image of Comparative Example 1. It can be seen that there are many long-chain graphite domain regions in the microstructure, and there are fewer closed-pore regions surrounded by carbon layers. In such a long-range ordered graphite domain region, the ion diffusion barrier for sodium ions is large. Especially during high-rate charge and discharge, it is difficult to efficiently embed and extract, resulting in poor rate performance. While (b) is the high-magnification transmission image of Example 1, showing more short graphite domain regions, which is beneficial to shortening the sodium ion transmission path and improving the rate performance. The number of closed-pore structures surrounded by them also increases accordingly. As the storage region for quasi-metallic sodium, the plateau sodium storage capacity is improved.

[0089] Figure 5 For the long-cycle performance comparison diagram of Example 1 and Comparative Example 1 at a current density of 900 mA / g, using the corn cob material prepared by the present invention, compared with the untreated corn cob material, the capacity of the material after hot pressing treatment is increased by 60 - 80 mAh / g, can be stably cycled more than 500 times, and the capacity retention rate is still above 80%.

[0090] Figure 6 Figure showing the rate performance of Example 1 and Comparative Example 1 at current densities from 30 to 1500 mA / g. In Example 1, even at an ultra-high current density of 1500 mA / g, the capacity is 297 mA h / g, while in Comparative Example 1, the capacity is only 76 mA h / g. After hot pressing treatment, the rate performance of the material is significantly improved. This is attributed to the fact that during the hot pressing process and the pyrolysis of the precursor, highly crystalline cellulose is more stable and less likely to decompose into small molecules or gases. Therefore, it can better maintain its shape and structure at high temperatures. This process helps to form a more uniform carbon structure, creating conditions for the final formation of a closed pore structure. Even at high current densities, the closed pores can stably store sodium ions.

[0091] Figure 7 Figure showing the performance of the full cell after matching Example 1 with a sodium vanadium phosphate cathode. It can stably cycle more than 200 times at a current density of 130 mA / g, and the capacity can still reach above 90 mA h / g.

[0092] Figure 8 Figure comparing the long cycle performance of Example 2 and Comparative Example 2 at a current density of 300 mA / g. Using the bamboo material prepared by the present invention, compared with the bamboo material without hot pressing treatment, the capacity of the treated material is increased by 70 - 80 mA h / g, and it can stably cycle more than 500 times, and the capacity retention rate is still 90%.

[0093] Figure 9 Figure showing the rate performance of Example 2 and Comparative Example 2 at current densities from 20 to 2000 mA / g. In Example 2, even at an ultra-high current density of 2000 mA / g, the capacity is 251 mA h / g, while in Comparative Example 2, the capacity is only 62 mA h / g. After replacing different biomass precursors and hot pressing treatment, the rate performance of the material can also be significantly improved, proving that our method is a universal method.

[0094] The present invention proposes to change the crystallinity of cellulose in biomass by hot pressing, and then use the precursor after high-temperature carbonization in the hard carbon anode of a sodium-ion battery. It can be seen that as the hot pressing treatment temperature increases, the crystallinity of cellulose continuously improves. The precursor with a higher cellulose crystallinity is prone to form a hard carbon material with a more abundant closed pore volume and a smaller graphite domain region after carbonization. Correspondingly, the microstructure of the hard carbon is more stable, and the sodium storage sites are more abundant. Furthermore, while the performance of the sodium-ion battery continuously improves, the capacity retention rate after 100 cycles also increases. This not only endows agricultural waste with extremely high reutilization value but also can well solve the problems of poor conductivity and unstable cycling of the biomass hard carbon anode itself. By this means, increasing the proportion of crystalline cellulose in the agricultural waste biomass material itself can effectively improve the stability of its closed pores and enhance its electrochemical performance.

[0095] Where not covered above, the prior art shall apply.

[0096] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and not for limiting the scope of the present invention. Those skilled in the technical field to which the present invention pertains may make various modifications or supplements to the described specific embodiments or use similar means for substitution, but will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of an agricultural waste biomass-based hard carbon anode material, characterized in that: Using agricultural waste as a substrate, it is softened by boiling, dried, pulverized by a pulverizer, and then hot-pressed and densified, and carbonized to obtain an agricultural waste biomass-based hard carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that: The hot-pressing temperature is 100-140 °C, the time is 0.5-2 h, and the applied pressure is 200-5000 psi.

3. The preparation method according to claim 1, characterized in that: The carbonization atmosphere is nitrogen, argon or a hydrogen-argon mixed gas. The carbonization temperature is 300-1500 °C, the heating rate is 1-10 °C / min, and the carbonization time is 0.5-10 h.

4. The preparation method according to claim 1, wherein: Pre-carbonization treatment is carried out before carbonization treatment.

5. The preparation method according to claim 1, characterized in that: The pre-carbonization treatment is carried out at 100-400 °C for 0.5-2 h under an inert gas, and the heating rate is 1-10 °C / min.

6. The preparation method according to claim 1, wherein: The inert gas is nitrogen, argon or a hydrogen-argon mixed gas.

7. The preparation method according to claim 1, characterized in that: The agricultural waste material is crop straws such as rice straw, wheat straw, corn straw, corn cob, beans, miscellaneous grains, bagasse and peanut shells.

8. The preparation method according to claim 1, characterized in that: Hot pressing is carried out using a flat vulcanizer or a hot press.

9. An agricultural waste biomass-based hard carbon negative electrode material prepared by the preparation method according to any one of claims 1-8.

10. Application of the agricultural waste biomass-based hard carbon negative electrode material as described in claim 9, characterized in that: As the negative electrode of a sodium ion battery.

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