Biomass-based hard carbon material, preparation method thereof and battery

Abstract

The application provides a biomass-based hard carbon material, a preparation method thereof and a battery. The preparation method comprises the following steps: sequentially performing alkali treatment, acid treatment, crystallization pretreatment and carbonization on a biomass carbon source to obtain the biomass-based hard carbon material. The preparation method provided by the application cooperates the above preparation process and preparation sequence, regulates the pore structure of the hard carbon material, forms a closed pore structure with a large pore volume, and the special closed pore structure improves the reversible sodium storage capacity and cycle stability of the biomass-based hard carbon material.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a biomass-based hard carbon material, its preparation method, and a battery, particularly to a biomass-based hard carbon material more suitable for sodium-ion batteries, its preparation method, and a sodium-ion battery. Background Technology

[0002] With the depletion of traditional fossil fuel reserves and the environmental problems caused by their extraction and utilization, countries are increasing their efforts in the research and development and utilization of new energy technologies, aiming to achieve energy structure transformation and upgrading, and promote sustainable economic and social development. Lithium-ion battery energy storage technology has made significant progress in energy density and technological maturity, and has been widely used in electric vehicles, large-scale energy storage, and other fields. However, lithium-ion batteries have drawbacks such as low abundance and uneven distribution of lithium resources in the Earth's crust, and high battery costs. In contrast, sodium-ion batteries, due to their abundant resources and low cost, have become a potential alternative to lithium-ion batteries. Their research and development have rapidly progressed globally in recent years, demonstrating broad application prospects.

[0003] Anode materials are one of the key materials for the development and application of sodium-ion battery technology. Among them, carbon materials, as the anode of sodium-ion batteries, stand out due to their excellent electrochemical performance, good stability, and low cost. Biomass-based hard carbon, with its unique non-layered structure, can provide more sodium-ion storage sites, exhibiting a high sodium storage capacity and becoming one of the research hotspots for sodium-ion battery anode materials. From the perspective of the sodium storage mechanism of hard carbon anodes, different types of pore structures in hard carbon materials have an important impact on the electrochemical performance of sodium-ion batteries. Hard carbon materials with closed pore structures are more conducive to sodium storage. With the increase of closed pore content, the number of sodium-ion storage sites increases, while the specific surface area of ​​hard carbon decreases accordingly. This structural characteristic can significantly improve the low-voltage plateau capacity, initial coulombic efficiency, and cycle stability of hard carbon anodes.

[0004] Currently, the mainstream technology route for preparing biomass-based hard carbon mainly involves processes such as raw material pretreatment, material purification, pre-carbonization, crushing, and high-temperature carbonization. This route makes it difficult to adjust the pore structure of the hard carbon material, thus hindering the improvement of its reversible sodium storage capacity and cycle stability.

[0005] Therefore, how to adjust the pore structure of biomass-based hard carbon materials to improve their reversible sodium storage capacity and cycle stability is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a biomass-based hard carbon material, its preparation method, and a battery thereof. The preparation method provided by the present invention involves sequentially subjecting a biomass carbon source to alkali treatment, acid treatment, crystallization pretreatment, and carbonization. These processes work synergistically to regulate the pore structure of the hard carbon material, forming a closed-pore structure. This unique closed-pore structure has a large pore volume, improving the reversible sodium storage capacity and cycle stability of the biomass-based hard carbon material.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a biomass-based hard carbon material, the method comprising the following steps:

[0009] The biomass carbon source is subjected to alkali treatment, acid treatment, crystallization pretreatment and carbonization in sequence to obtain the biomass-based hard carbon material.

[0010] It should be noted that the biomass carbon source mentioned in this invention refers to the general term for all biological organisms produced by photosynthesis, including plants, crops, forestry waste, marine products (such as various seaweeds), etc. Any type of material that can be reasonably known by those skilled in the art is applicable to this invention; for example, it can be wheat straw, peanut shells, rapeseed stalks, rice husks, bamboo, coconut shells, corn stalks or pine, etc., which are abundant and inexpensive.

[0011] The preparation method provided by this invention, in which each preparation process and preparation sequence work together, regulates the raw material components of biomass carbon source, cellulose, hemicellulose, and lignin, as well as the crystallinity of cellulose, to obtain a biomass carbon source with high content and high crystallinity. The high content of crystalline cellulose can be transformed into long graphite-like layers in the subsequent low carbonization process, surrounding and shrinking the active sites to form a closed pore structure (i.e., closed-pore structure), thereby realizing the regulation of the pore structure of the hard carbon material obtained by carbonization, and achieving the purpose of improving the reversible sodium storage capacity and cycle stability of biomass-based hard carbon material.

[0012] Biomass carbon sources include cellulose, hemicellulose, and lignin, with high contents of cellulose and hemicellulose. Excessive amorphous hemicellulose and lignin can hinder the movement of cellulose molecular chains during subsequent low-temperature pretreatment, thus affecting cellulose crystallization. Conversely, excessively low amorphous hemicellulose and lignin content can lead to excessive graphitization of the carbon layer during high-temperature carbonization, hindering the formation of nanopores. Therefore, the alkali and acid treatments in this invention serve two purposes: firstly, they remove impurities from the biomass carbon source; secondly, during alkali treatment, some hemicellulose and lignin are dissolved, increasing the cellulose content; and thirdly, acid treatment further regulates the raw material composition of the biomass carbon source. Cellulose, hemicellulose, and lignin also neutralize the alkaline substances produced during the alkali treatment process. Because crystalline regions in the biomass carbon source swell and partially dissolve after alkali and acid treatments, the content of amorphous cellulose increases. Since amorphous cellulose is not conducive to the formation of closed pore structures, crystallization pretreatment controls the glass transition temperature range of cellulose, allowing cellulose molecular chain segments to move and rearrange, thus enabling cellulose to transform from an amorphous to a crystalline state and increasing the crystallinity of cellulose in the biomass carbon source. High crystalline cellulose content facilitates the formation of closed pores in hard carbon after high-temperature carbonization, and the resulting closed-pore structure has a larger pore volume, thereby improving the reversible sodium storage capacity and cycle stability of biomass-based hard carbon materials.

[0013] In this invention, the preparation processes and order of alkali treatment, acid treatment, crystallization pretreatment and carbonization must be coordinated. Without any one of the steps, it is impossible to achieve closed-pore adjustment and obtain a closed-pore structure with a large pore volume.

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0015] Preferably, the present invention first dries and crushes the biomass carbon source, controlling the moisture content to 5% to 10%, such as 5%, 6%, 7%, 8%, 9%, or 10%, and the particle size to 10 to 50 mesh, such as 10 mesh, 20 mesh, 30 mesh, 40 mesh, or 50 mesh, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0016] Preferably, the alkali treatment includes:

[0017] A mixture of biomass carbon source and alkaline solution is subjected to alkali treatment to obtain the alkali-treated product.

[0018] It should be noted that the alkaline substance in the alkaline solution of the present invention is a conventional technical solution, such as including but not limited to at least one of ammonia, potassium hydroxide or sodium hydroxide.

[0019] Preferably, the concentration of the alkaline solution is 0.1 to 5 mol / L, such as 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, or 5 mol / L, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0020] Preferably, the mass ratio of the biomass carbon source to the alkaline solution is 1:(5-10), such as 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9, 1:9.5 or 1:10, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] In this invention, by simultaneously controlling the concentration of the alkaline solution to 0.1–5 mol / L and the mass ratio of the biomass carbon source to the alkaline solution to 1:(5–10), the two work synergistically to better remove impurities while dissolving some hemicellulose and lignin, thereby increasing the cellulose content in the biomass carbon source and thus improving the performance of the material.

[0022] Preferably, the alkali treatment time is 1 to 4 hours, such as 1 hour, 2 hours, 3 hours or 4 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the acid treatment includes:

[0024] The product after alkali treatment is mixed with an acidic solution and then subjected to acid treatment to obtain the product after acid treatment.

[0025] It should be noted that the acidic substance in the acid solution of the present invention is a conventional technical solution, such as including but not limited to at least one of hydrochloric acid, hydrofluoric acid or nitric acid; and after acid treatment, it can be washed with pure water, centrifuged, dried and other processes to obtain the acid-treated product.

[0026] Preferably, the concentration of the acidic solution is 0.1 to 5 mol / L, such as 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, or 5 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, the mass ratio of the biomass carbon source to the acidic solution is 1:(5-10), such as 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9, 1:9.5 or 1:10, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] In this invention, by using an acidic solution with a concentration of 0.1–5 mol / L and a synergistic mass ratio of the biomass carbon source to the acidic solution of 1:(5–10), it is more conducive to the neutralization and impurity removal of biomass after alkali washing.

[0029] Preferably, the acid treatment time is 1 to 4 hours, such as 1 hour, 2 hours, 3 hours or 4 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Furthermore, the present invention adjusts the alkali treatment time to 1-4 hours and / or the acid treatment time to 1-4 hours in order to remove impurities from the biomass carbon source and regulate the cellulose content.

[0031] Preferably, the crystallization pretreatment includes:

[0032] The product after acid treatment is subjected to low-temperature pretreatment.

[0033] Preferably, the heating rate of the low-temperature pretreatment is 1 to 3 °C / min, such as 1 °C / min, 1.5 °C / min, 2 °C / min, 2.5 °C / min or 3 °C / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the holding temperature after the low-temperature pretreatment is 100-180℃, such as 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃ or 180℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] In this invention, the temperature of the low-temperature pretreatment is controlled to be between 100 and 180°C, which is more conducive to controlling the temperature within the glass transition temperature range of cellulose. This allows the cellulose molecular chain segments to move and rearrange, enabling cellulose to complete the transition from an amorphous state to a crystalline state, thereby increasing the crystallinity of cellulose. In the subsequent carbonization process, this helps to form a closed pore structure, improving capacity and cycle performance.

[0036] Preferably, the holding time after the low-temperature pretreatment is 10 to 30 minutes, such as 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] In this invention, the holding time after the low-temperature pretreatment is preferably 10 to 30 minutes, which is beneficial for the full peristaltic rearrangement of cellulose molecular chain segments.

[0038] Preferably, the cooling rate during the cooling process after the low-temperature pretreatment and heat preservation is 15-20℃ / min, such as 15℃ / min, 18℃ / min, 19.5℃ / min or 20℃ / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] In the crystallization pretreatment process, this invention does not use natural cooling to room temperature, but controls the cooling rate to achieve a regular cooling process from the holding temperature to room temperature, which is more conducive to the preservation of the structure of cellulose molecular chain segments after rearrangement and crystallization. The preferred cooling rate is 15-20℃ / min, which helps the molecular chain segments freeze quickly and maintain the integrity of the crystal structure.

[0040] Preferably, the carbonization includes sequential pre-carbonization and high-temperature carbonization.

[0041] In this invention, the purpose of pre-carbonization is to remove moisture, ash and volatile matter from the carbon source to form hard carbon with initial pores distributed on the surface.

[0042] Preferably, the heating rate of the pre-carbonization is 15 to 20 °C / min, such as 15 °C / min, 18 °C / min or 20 °C / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, the holding temperature after pre-carbonization is 450-600℃, such as 450℃, 500℃, 550℃ or 600℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] Preferably, the holding time after the pre-carbonization heating is 2 to 5 hours, such as 2 hours, 3 hours, 4 hours or 5 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] Preferably, the pre-carbonized material is crushed to obtain a product with a median particle size D50 of 5 to 10 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] Preferably, the heating rate of the high-temperature carbonization is 3 to 5 °C / min, such as 3 °C / min, 4 °C / min or 5 °C / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] Preferably, the holding temperature after the high-temperature carbonization is 1000-1500℃, such as 1000℃, 1100℃, 1200℃, 1300℃, 1400℃ or 1500℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] Preferably, the holding time after the high-temperature carbonization is 3 to 5 hours, such as 3 hours, 4 hours or 5 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] Preferably, the atmosphere during the carbonization process of the present invention is a protective atmosphere, which includes a nitrogen atmosphere and / or an inert gas atmosphere, and the inert gas includes, but is not limited to, argon or helium.

[0050] As a preferred technical solution, the preparation method includes the following steps:

[0051] Mix biomass carbon source with an alkaline solution of 0.1–5 mol / L and treat with alkali for 1–4 hours to obtain the alkaline-treated product;

[0052] The product after alkali treatment is mixed with an acidic solution with a concentration of 0.1–5 mol / L and subjected to acid treatment for 1–4 hours to obtain the acid-treated product.

[0053] The product after acid treatment is subjected to crystallization pretreatment, which includes: heating to 100-180℃ at a heating rate of 1-3℃ / min and holding at that temperature for 10-30min, and then cooling at a cooling rate of 15-20℃ / min to obtain the pretreated substance.

[0054] The material after crystallization pretreatment is pre-carbonized at 450-600℃, the pre-carbonized material is crushed, and the crushed product is carbonized at 1000-1500℃ to obtain the biomass-based hard carbon material.

[0055] The mass ratio of the biomass carbon source to the alkaline solution is 1:(5-10), and the mass ratio of the biomass carbon source to the acidic solution is 1:(5-10).

[0056] In a second aspect, the present invention provides a biomass-based hard carbon material, which is prepared by the preparation method described in the first aspect;

[0057] The biomass-based hard carbon material has a closed-cell structure inside.

[0058] The hard carbon material provided by this invention has a closed-cell structure, which is more conducive to sodium storage. As the content of closed-cell structure increases, the number of sodium ion storage sites increases. This structural characteristic can significantly improve the capacity and cycle stability of hard carbon anodes.

[0059] Preferably, the pore volume of the closed-cell structure is 1.4–2.0 cm. 3 / g, for example, 1.4cm 3 / g, 1.5cm 3 / g, 1.6cm 3 / g, 1.7cm 3 / g, 1.8cm 3 / g, 1.81cm 3 / g, 1.82cm 3 / g, 1.83cm 3 / g, 1.84cm 3 / g, 1.85cm 3 / g, 1.86cm 3 / g, 1.87cm 3 / g, 1.88cm 3 / g, 1.89cm 3 / g, 1.9cm 3 / g, 1.93cm 3 / g, 1.95cm 3 / g, 1.98cm 3 / g or 2.0cm 3 / g, etc., preferably 1.8~2.0cm 3 / g, but not limited to the listed values; other unlisted values ​​within this range also apply.

[0060] The closed-cell structure of this invention has a larger pore volume, which is more conducive to sodium storage.

[0061] Thirdly, the present invention also provides a battery comprising the biomass-based hard carbon material as described in the second aspect.

[0062] Preferably, the battery comprises a sodium-ion battery.

[0063] The biomass-based hard carbon material provided by this invention is more suitable for sodium-ion batteries, and when used as a negative electrode active material, it has a more superior effect on improving the performance of sodium-ion batteries. However, in addition to sodium-ion batteries, its use in other types of battery structures, such as lithium-ion batteries, is not excluded. In principle, this invention is applicable to all conventional uses of hard carbon materials.

[0064] Furthermore, the sodium-ion battery provided by this invention, apart from the aforementioned characteristics of the biomass-based hard carbon material, has other conventional technical solutions in terms of structure, raw materials, and preparation process. Those skilled in the art can make adaptive selections and adjustments according to actual needs, and this invention will not elaborate further.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] The preparation method provided by this invention, in which each preparation process and preparation sequence work together, regulates the raw material components of biomass carbon source, namely cellulose, hemicellulose, and lignin, as well as the crystallinity of cellulose, to obtain a biomass carbon source with high content and high crystallinity. The high content of crystalline cellulose can be transformed into long graphite-like layers in the subsequent low carbonization process, surrounding and shrinking the active sites to form a closed-pore structure with a large pore volume. This achieves the regulation of the pore structure of the hard carbon material obtained by carbonization, thereby improving the reversible sodium storage capacity and cycle stability of biomass-based hard carbon material. Attached Figure Description

[0067] Figure 1 The flowchart illustrates the mechanism of the preparation method provided in Example 1. Detailed Implementation

[0068] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0069] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms “comprising” and “having” and any variations thereof in this application are intended to cover non-exclusive inclusion.

[0070] Example 1

[0071] This embodiment provides a biomass-based hard carbon material with an internal closed-cell structure. The preparation method of the biomass-based hard carbon material is as follows:

[0072] like Figure 1 As shown:

[0073] (1) Dry and crush the biomass carbon source rice husk, control its moisture content at 5% and its particle size at 30 mesh;

[0074] (2) The rice husks were treated with a 3 mol / L sodium hydroxide solution for 4 hours. The mass ratio of the sodium hydroxide solution to the rice husks was 8:1. The rice husks were then treated with the alkali.

[0075] (3) The rice husks after alkali treatment were acid-treated with a 3 mol / L hydrochloric acid solution for 4 hours. The mass ratio of the hydrochloric acid solution to the rice husks treated in step (1) was 8:1. The acid-treated material was centrifuged, then washed with pure water until neutral, and then centrifuged and dried to obtain the acid-treated rice husks.

[0076] (4) Place the acid-treated rice husks in a high-low temperature oven, heat them to 140°C at a heating rate of 3°C / min and keep them at that temperature for 20 min, and then cool them to room temperature at a cooling rate of 20°C / min to complete the crystallization pretreatment.

[0077] (5) The material after crystallization pretreatment is heated to 600℃ at a heating rate of 20℃ / min and kept at the temperature for 2h to complete the precarbonization. The precarbonized material is crushed so that the D50 particle size after crushing is 8μm.

[0078] The crushed material was heated to 1500℃ at a heating rate of 5℃ / min for high-temperature carbonization and held at that temperature for 3 hours to obtain the biomass-based hard carbon material.

[0079] Example 2

[0080] This embodiment provides a biomass-based hard carbon material with an internal closed-cell structure. The preparation method of the biomass-based hard carbon material is as follows:

[0081] (1) Dry and crush the biomass carbon source rice husk, control its moisture content at 8% and its particle size at 50 mesh;

[0082] (2) The rice husks were treated with a 5 mol / L sodium hydroxide solution for 1 h. The mass ratio of the sodium hydroxide solution to the rice husks was 5:1. The rice husks were then treated with the alkali.

[0083] (3) The rice husks after alkali treatment are acid-treated with a hydrochloric acid solution with a concentration of 5 mol / L for 1 h. The mass ratio of hydrochloric acid solution to rice husks treated in step (1) is 5:1. The acid-treated material is centrifuged, then washed with pure water until neutral, and then centrifuged and dried to obtain acid-treated rice husks.

[0084] (4) Place the acid-treated rice husks in a high-low temperature oven, heat them to 180°C at a heating rate of 1°C / min and keep them at that temperature for 10 min, and then cool them to room temperature at a cooling rate of 15°C / min to complete the crystallization pretreatment.

[0085] (5) The material after crystallization pretreatment is heated to 450℃ at a heating rate of 15℃ / min and kept at the temperature for 5h to complete the precarbonization. The precarbonized material is crushed so that the D50 particle size after crushing is 10μm.

[0086] The crushed material was heated to 1000℃ at a heating rate of 3℃ / min for high-temperature carbonization and held at that temperature for 5 hours to obtain the biomass-based hard carbon material.

[0087] Example 3

[0088] This embodiment provides a biomass-based hard carbon material with an internal closed-cell structure. The preparation method of the biomass-based hard carbon material is as follows:

[0089] (1) Dry and crush the biomass carbon source rice husk, control its moisture content at 10%, and its particle size at 10 mesh;

[0090] (2) The rice husks were treated with a sodium hydroxide solution with a concentration of 0.1 mol / L for 3 hours. The mass ratio of the sodium hydroxide solution to the rice husks was 10:1. The rice husks were then treated with the alkali.

[0091] (3) The rice husks after alkali treatment were acid-treated with a hydrochloric acid solution with a concentration of 0.1 mol / L for 3 hours. The mass ratio of the hydrochloric acid solution to the rice husks treated in step (1) was 10:1. The acid-treated material was centrifuged, then washed with pure water until neutral, and then centrifuged and dried to obtain the acid-treated rice husks.

[0092] (4) Place the acid-treated rice husks in a high-low temperature oven, heat them to 100℃ at a heating rate of 2℃ / min and keep them at that temperature for 30min, and then cool them to room temperature at a cooling rate of 17.5℃ / min to complete the crystallization pretreatment.

[0093] (5) The material after crystallization pretreatment is heated to 500℃ at a heating rate of 17.5℃ / min and kept at the temperature for 3h to complete the precarbonization. The precarbonized material is crushed so that the D50 particle size after crushing is 5μm.

[0094] The crushed material was heated to 1300℃ at a heating rate of 4℃ / min for high-temperature carbonization and held at that temperature for 4 hours to obtain the biomass-based hard carbon material.

[0095] Example 4

[0096] The difference between this embodiment and embodiment 1 is that the biomass carbon source in this embodiment is bamboo; the alkaline substance in step (2) is ammonia water; and the acidic substance in step (3) is nitric acid.

[0097] The remaining preparation methods and parameters are consistent with those in Example 1.

[0098] Example 5

[0099] The difference between this embodiment and embodiment 1 is that in step (2) of this embodiment, the concentration of sodium hydroxide solution is 6 mol / L.

[0100] The remaining preparation methods and parameters are consistent with those in Example 1.

[0101] Example 6

[0102] The difference between this embodiment and embodiment 1 is that in step (2) of this embodiment, the concentration of hydrochloric acid solution is 6 mol / L.

[0103] The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] Example 7

[0105] The difference between this embodiment and embodiment 1 is that in step (4) of this embodiment, the heat preservation temperature is 80℃.

[0106] The remaining preparation methods and parameters are consistent with those in Example 1.

[0107] Example 8

[0108] The difference between this embodiment and embodiment 1 is that in step (4) of this embodiment, the heat preservation temperature is 200℃.

[0109] The remaining preparation methods and parameters are consistent with those in Example 1.

[0110] Example 9

[0111] The difference between this embodiment and embodiment 1 is that in step (4) of this embodiment, the heat preservation time is 5 minutes.

[0112] The remaining preparation methods and parameters are consistent with those in Example 1.

[0113] Example 10

[0114] The difference between this embodiment and embodiment 1 is that in step (4) of this embodiment, after the heat preservation is completed, the temperature is naturally cooled down to room temperature.

[0115] The remaining preparation methods and parameters are consistent with those in Example 1.

[0116] Comparative Example 1

[0117] The difference between this comparative example and Example 1 is that the alkali treatment in step (2) is not performed in this comparative example.

[0118] The remaining preparation methods and parameters are consistent with those in Example 1.

[0119] Comparative Example 2

[0120] The difference between this comparative example and Example 1 is that the acid treatment in step (3) is not performed in this comparative example.

[0121] The remaining preparation methods and parameters are consistent with those in Example 1.

[0122] Comparative Example 3

[0123] The difference between this comparative example and Example 1 is that the crystallization pretreatment process in step (4) is not performed in this comparative example.

[0124] The remaining preparation methods and parameters are consistent with those in Example 1.

[0125] The pore structure of the biomass-based hard carbon materials obtained in Examples 1-10 and Comparative Examples 1-3 was characterized by gas adsorption, specifically by measuring the closed-pore volume and diameter. The specific test conditions were: the hard carbon anode material was placed at 150℃-300℃ and a pressure <10... -6 Degas for 1-6 hours at a Bar environment; then, introduce nitrogen gas at liquid nitrogen temperature to slowly restore the pressure to atmospheric pressure, followed by another 10 hours of degassing. -6 Bar was used to record data to obtain adsorption-desorption isotherms. The pore size distribution and pore volume of the hard carbon anode material were calculated based on the density functional theory (DFT) model. The test results are shown in Table 1.

[0126] Table 1

[0127] <![CDATA[Closed cell volume (cm 3 / g)]]> Average pore size (nm) Example 1 1.881 1.98 Example 2 1.860 1.94 Example 3 1.839 1.93 Example 4 1.803 1.90 Example 5 1.722 1.91 Example 6 1.663 1.82 Example 7 1.435 1.72 Example 8 1.512 1.79 Example 9 1.410 1.68 Example 10 1.642 1.81 Comparative Example 1 1.280 1.46 Comparative Example 2 0.886 1.03 Comparative Example 3 1.349 1.57

[0128] The biomass-based hard carbon materials provided in Examples 1-10 and Comparative Examples 1-3 were applied to batteries and their performance was tested.

[0129] I. Battery fabrication:

[0130] Biomass-based hard carbon powder, conductive agent SuperP, binder sodium carboxymethyl cellulose, and styrene-butadiene rubber were mixed evenly in a mass ratio of 94.5:1.5:1.5:2.5. A suitable amount of water was added and stirred to form a slurry. The slurry was then evenly coated onto a current collector copper foil. After drying, it was cut into circular electrode sheets with a diameter of 18 mm. Under vacuum conditions, the electrode sheets were dried at 80°C with forced air for approximately 3 hours, followed by vacuum drying at 80°C for 6 hours, and finally rolled to a surface density of 4-7 mg / cm³. 2 Reserved. Then transferred to the glove box for later use. The assembly of the simulated battery was carried out in an Ar atmosphere glove box, using a sodium metal sheet as the counter electrode and 1 mol / L NaPF6 dissolved in ethylene carbonate solution as the electrolyte, to assemble a CR2430 button cell.

[0131] II Performance Testing

[0132] The prepared battery was subjected to electrochemical performance testing. Specifically, a constant current charge-discharge mode was used to conduct charge-discharge tests at a current density of 30 mA / g. The battery cycle charge-discharge performance was tested under the conditions of a discharge cutoff voltage of 0V and a charge cutoff voltage of 2.0V. The test results are shown in Table 2.

[0133] Table 2

[0134]

[0135]

[0136] In summary, the preparation method provided by this invention, through the coordinated operation of various preparation processes and the order of preparation, regulates the raw material components of the biomass carbon source, namely cellulose, hemicellulose, and lignin, as well as the crystallinity of cellulose, resulting in a biomass carbon source with high content and high crystallinity. The high content of crystalline cellulose can be transformed into long graphite-like layers during the subsequent low-carbonization process, surrounding and shrinking the active sites to form a closed-pore structure with a large pore volume. This achieves the regulation of the pore structure of the hard carbon material obtained by carbonization, thereby improving the reversible sodium storage capacity and cycle stability of the biomass-based hard carbon material.

[0137] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a biomass-based hard carbon material, characterized by, The preparation method comprises the following steps: The biomass carbon source is sequentially subjected to alkali treatment, acid treatment, crystallization pretreatment and carbonization to obtain the biomass-based hard carbon material; The crystallization pretreatment comprises: low-temperature pretreatment of the product after acid treatment; The holding temperature after the low-temperature pretreatment is raised is 100-180℃.

2. The production method according to claim 1, characterized by, The alkali treatment comprises: The biomass carbon source is mixed with an alkaline solution to perform alkali treatment to obtain a product after alkali treatment.

3. The preparation method according to claim 2, characterized in that, The concentration of the alkaline solution is 0.1-5 mol / L.

4. The production method according to claim 2, characterized by, The mass ratio of the biomass carbon source to the alkaline solution is 1:(5-10).

5. The preparation method according to claim 1, characterized in that, The alkali treatment time is 1-4 h.

6. The method of claim 1, wherein, The acid treatment comprises: The product after alkali treatment is mixed with an acidic solution to perform acid treatment to obtain a product after acid treatment.

7. The preparation method according to claim 6, characterized in that, The concentration of the acidic solution is 0.1-5 mol / L.

8. The preparation method according to claim 6, characterized in that, The mass ratio of the biomass carbon source to the acidic solution is 1:(5-10).

9. The method of claim 1, wherein, The acid treatment time is 1-4 h.

10. The method of claim 1, wherein, The low-temperature pretreatment has a temperature raising rate of 1-3℃ / min.

11. The method of claim 1, wherein, The holding time after the low-temperature pretreatment is raised is 10-30 min.

12. The method of claim 1, wherein, The temperature lowering rate in the temperature lowering process after the low-temperature pretreatment is raised is 15-20℃ / min.

13. The method of claim 1, wherein, The carbonization comprises sequentially performing pre-carbonization and high-temperature carbonization.

14. The method of claim 13, wherein, The pre-carbonization has a temperature raising rate of 15-20℃ / min, a holding temperature after the pre-carbonization is raised is 450-600℃, and a holding time after the pre-carbonization is raised is 2-5 h.

15. The preparation method according to claim 13, characterized in that, The pre-carbonized product is crushed to obtain a product with a median particle size D50 of 5-10 μm.

16. The method of claim 13, wherein, The high-temperature carbonization has a temperature raising rate of 3-5℃ / min, a holding temperature after the high-temperature carbonization is raised is 1000-1500℃, and a holding time after the high-temperature carbonization is raised is 3-5 h.

17. The method of claim 1, wherein, The preparation method comprises the following steps: The biomass carbon source is mixed with an alkaline solution with a concentration of 0.1-5 mol / L to perform alkali treatment for 1-4 h to obtain a product after alkali treatment; The product after alkali treatment is mixed with an acidic solution with a concentration of 0.1-5 mol / L to perform acid treatment for 1-4 h to obtain a product after acid treatment; The product after acid treatment is subjected to crystallization pretreatment, which comprises: raising the temperature to 100-180℃ at a temperature raising rate of 1-3℃ / min and then holding for 10-30 min, and then lowering the temperature at a temperature lowering rate of 15-20℃ / min to obtain a product after crystallization pretreatment; The product after crystallization pretreatment is subjected to pre-carbonization at 450-600℃, the pre-carbonized product is crushed, and the crushed product is subjected to high-temperature carbonization at 1000-1500℃ to obtain the biomass-based hard carbon material; The mass ratio of the biomass carbon source to the alkaline solution is 1:(5-10), and the mass ratio of the biomass carbon source to the acidic solution is 1:(5-10).

18. A biomass-based hard carbon material, characterized by, The biomass-based hard carbon material is prepared by the preparation method in any one of claims 1-17. The biomass-based hard carbon material has a closed pore structure in the interior.

19. The biomass-based hard carbon material of claim 18, wherein, The pore volume of the closed pore structure is 1.4-2.0 cm3 / g 3 / g.

20. The biomass-based hard carbon material of claim 18, wherein, The pore volume of the closed pore structure is 1.8-2.0 cm3 / g 3 / g.

21. A battery, characterized by The battery comprises the biomass-based hard carbon material in any one of claims 18-20.

22. The battery of claim 21, wherein, The battery includes a sodium-ion battery.

Images