Biomass-based hard carbon material and preparation method and use thereof

Abstract

The application provides a biomass-based hard carbon material and a preparation method and application thereof. The preparation method comprises sequentially performing anaerobic baking, impurity removal, oxidation modification and high-temperature carbonization on a biomass raw material to obtain the biomass-based hard carbon material. By sequentially performing anaerobic baking and impurity removal, lignin and cellulose in the biomass raw material are destroyed, pores and defects are left in the interior, the material is in a metastable state structure, impurities are exposed, and then impurity removal can be realized at room temperature, and the impurity removal effect is excellent. The obtained biomass-based hard carbon has low impurity content, the ash content can be reduced to below 0.5 wt%, and has a disordered interlayer structure, which is beneficial to the embedding / extraction of sodium ions, and can exhibit high reversible capacity and initial efficiency performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, such as a biomass-based hard carbon material and its preparation method and uses. Background Technology

[0002] Sodium-ion batteries, as rechargeable batteries, have an electrochemical mechanism similar to that of lithium batteries. However, compared with lithium-ion batteries, sodium-ion batteries have the following advantages: abundant and inexpensive raw materials; the ability to discharge to 0V; and a battery energy density greater than 100Wh / kg, comparable to lithium iron phosphate batteries. It is evident that their cost advantage is significant.

[0003] As a negative electrode material for sodium-ion batteries, hard carbon has a more prominent capacity and stability compared to graphite, which is commonly used in lithium batteries. This is because the radius of sodium ions (0.103 nm) is much larger than that of lithium ions (0.071 nm). The small interlayer spacing of graphite is not conducive to the insertion and extraction of sodium ions, while the long-range disorder of hard carbon structure, with many defects and micropores, helps the adsorption and storage of sodium ions.

[0004] The raw materials for hard carbon are mainly divided into biomass-based, resin-based, and coal-based. Among them, resin-based hard carbon has good performance but higher cost; coal-based hard carbon has difficulty in increasing capacity and relies on coal mining for raw materials; in comparison, biomass-based hard carbon has more advantages in development and application due to its wide availability of raw materials, easy structure control, and lower cost.

[0005] CN115259136A discloses a method for mass-producing biomass-based hard carbon materials using waste biomass. The method involves extracting lignin from biomass by using a specific pretreatment solution to break down the biomass, pre-carbonizing and high-temperature carbonizing the obtained lignin, and then drying it after acid washing at 40-80°C to obtain the target hard carbon material.

[0006] CN113044827A discloses a method for preparing a nano-carbon composite biomass hard carbon electrode material. The method involves cleaning and crushing the biomass raw material, heating it with an alkaline solution, cleaning and drying it, heating and stirring it in a 1-5 mol / L alkaline solution at 90-120°C, then adding it to a 1-5 mol / L acid solution and heating and stirring it at 90-120°C, followed by microwave hydrothermal reaction, pre-carbonization and high-temperature treatment to obtain the target hard carbon material.

[0007] Currently, the methods for preparing hard carbon using biomass raw materials are quite cumbersome, and the disadvantage of preparing hard carbon from biomass raw materials is the excessive amount of impurities. Therefore, the commonly used impurity removal methods in industry are high-temperature alkaline washing and acid washing, as described above. However, this method has high processing costs and requires sophisticated equipment. Therefore, there is a need to develop a new manufacturing scheme for biomass-based hard carbon materials. Summary of the Invention

[0008] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0009] This application provides a biomass-based hard carbon material, its preparation method, and its uses. The preparation method involves sequentially subjecting biomass raw materials to anaerobic baking, impurity removal, oxidative modification, and high-temperature carbonization to obtain the biomass-based hard carbon material. This application first performs anaerobic baking and impurity removal sequentially, which destroys lignin and cellulose in the biomass raw materials, leaving pores and defects inside, thus placing the material in a metastable structure to expose impurities. Impurity removal can then be achieved at room temperature with excellent results. The resulting biomass-based hard carbon has low impurity content, with ash content reduced to below 0.5 wt%, and possesses a disordered interlayer structure, which is beneficial for sodium ion insertion / extraction, exhibiting high reversible capacity and first-efficiency performance.

[0010] In a first aspect, embodiments of this application provide a method for preparing a biomass-based hard carbon material, the method comprising the following steps:

[0011] Biomass raw materials are subjected to anaerobic baking, impurity removal, oxidative modification and high-temperature carbonization in sequence to obtain biomass-based hard carbon materials.

[0012] This application first performs anaerobic baking and impurity removal sequentially, which destroys lignin and cellulose in the biomass raw materials, leaving pores and defects inside, so that the material is in a metastable structure to expose impurities. Then, impurity removal can be achieved at room temperature with excellent impurity removal effect. The resulting biomass-based hard carbon has low impurity content, and the ash content can be reduced to below 0.5 wt%. It also has a disordered interlayer structure, which is conducive to the insertion / extraction of sodium ions, and can exhibit high reversible capacity and first-efficiency performance.

[0013] Specifically, in terms of raw material composition, the main components contributing to hard carbon in biomass raw materials are lignin and some cellulose. Biomass raw materials, especially fibrous biomass raw materials, are composed of hemicellulose, cellulose, lignin, and various impurities. These impurities are all present in the structure of hemicellulose, cellulose, and lignin. To remove these impurities, it is necessary to disrupt the stable bonds between hemicellulose, cellulose, and lignin. Therefore, this application first performs anaerobic baking, which causes hemicellulose, cellulose, and lignin to decompose under certain temperature conditions, exposing the impurities. Therefore, subsequent impurity removal can be carried out under ambient temperature conditions. Furthermore, the main impurities in the biomass can be analyzed by elemental analysis, making the subsequent impurity removal more targeted.

[0014] Since biomass raw materials are mainly composed of three major components: hemicellulose, cellulose, and lignin, with cellulose as the skeleton and lignin and hemicellulose tightly wrapped around the skeleton, it is difficult to break the stable structure of biomass raw materials by directly removing impurities and oxidizing without anaerobic baking. Since the decomposition temperature of hemicellulose, cellulose, and lignin increases in that order, hemicellulose and some cellulose can be decomposed at relatively low temperatures. Therefore, anaerobic baking can provide natural pore sites for organic carbon sources and can also destroy the original stable structure of biomass, which is beneficial for subsequent removal of impurities and oxidizing.

[0015] After anaerobic baking, the impurity removal and oxidation modification processes can be carried out at room temperature because the material is in a metastable state and some impurities are exposed. The hard carbon precursor after impurity removal is mainly composed of C, H and O segment structures and is still in an organic state. In this state, oxidation modification directly introduces oxygen-containing functional groups as connecting bonds between organic segments. The strength of these bonds is higher than that of hydrogen bonds, which is beneficial for subsequent aromatic cyclization rearrangement.

[0016] In summary, the preparation method described in this application can be used to produce normalized hard carbon materials from different biomass raw materials. Normalization refers to the process of processing essentially different materials to obtain materials with similar structures and properties. As mentioned above, the components of biomass raw materials are hemicellulose, cellulose, lignin, and impurities. The differences between different biomass raw materials lie in the composition of impurities and the content of the three major components. The biomass-based hard carbon obtained by the preparation method described in this application has similar structures and minimal differences in performance.

[0017] The following are preferred technical solutions of this application, but are not intended to limit the technical solutions provided in this application. The technical objectives and beneficial effects of this application can be better achieved through the following technical solutions.

[0018] As a preferred technical solution of this application, the biomass raw materials include any one or a combination of at least two of the following: poplar wood chips, pine wood chips, lychee wood chips, coconut shells, bamboo chips, cotton, or wheat straw.

[0019] As a preferred technical solution of this application, the anaerobic baking is carried out under an inert atmosphere with an oxygen concentration of <1000ppm, such as 990ppm, 900ppm, 800ppm, 700ppm, 600ppm, 500ppm, 400ppm, 300ppm, 200ppm, 100ppm, 50ppm, 10ppm or 0ppm, where 0ppm is an anaerobic atmosphere, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0020] Preferably, the inert atmosphere includes any one or a combination of at least two of nitrogen, argon, or helium, with typical but non-limiting examples of such combinations including combinations of nitrogen and argon, nitrogen and helium, or argon and helium.

[0021] Preferably, the temperature of the anaerobic baking is 200-1000℃, such as 200℃, 300℃, 400℃, 500℃, 600℃, 700℃, 800℃, 900℃ or 1000℃, and the time is 15-48h, such as 15h, 18h, 21h, 24h, 27h, 30h, 33h, 36h, 39h, 42h, 45h or 48h, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0022] Preferably, after the anaerobic baking and before the impurity removal, the material is cooled to <50°C, discharged, and subjected to first crushing to obtain first precursor particles, and then the first precursor particles are subjected to impurity removal.

[0023] Preferably, the median particle size of the first precursor particles is 0.5 to 1 mm, such as 0.5 mm, 0.55 mm, 0.6 mm, 0.65 mm, 0.7 mm, 0.75 mm, 0.8 mm, 0.85 mm, 0.9 mm, 0.95 mm or 1 mm, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0024] As a preferred technical solution of this application, the impurity removal is liquid phase impurity removal, in which the biomass raw material after anaerobic baking is treated in a solution containing an impurity removal agent.

[0025] Preferably, the impurity remover comprises any one or a combination of at least two of sodium hydroxide, potassium hydroxide, sulfuric acid, hydrochloric acid, phosphoric acid, or hydrofluoric acid. Typical but non-limiting examples of such combinations include combinations of sodium hydroxide and potassium hydroxide, sulfuric acid and hydrochloric acid, hydrochloric acid and phosphoric acid, hydrochloric acid and hydrofluoric acid, phosphoric acid and hydrofluoric acid, or sulfuric acid and hydrofluoric acid.

[0026] Preferably, the solution containing the impurity remover also contains additives.

[0027] Preferably, the additive comprises any one or a combination of at least two of thiourea, urea, disodium ethylenediaminetetraacetate, citric acid, ammonia, or sodium gluconate. Typical but non-limiting examples of such combinations include combinations of thiourea and urea, thiourea and disodium ethylenediaminetetraacetate, citric acid and disodium ethylenediaminetetraacetate, ammonia and urea, or sodium gluconate and citric acid.

[0028] This application preferably uses a combination of impurity remover and additives to produce a synergistic effect, which allows the pretreated precursor to decompose further at room temperature. After further decomposition, abundant pores and defects are left inside the material. At this time, the material is in a metastable structure, and a displacement reaction occurs between the impurities and the impurity remover. The impurities are in a free state and dissolved in the aqueous solution, thereby further improving the impurity removal effect at room temperature.

[0029] It should be noted that the role of the additive is to open up the chain segment structure of the hard carbon precursor, thereby promoting the impurity removal effect of the impurity remover. The impurity remover is determined according to the type of impurity element in the material. Impurity elements can be divided into alkaline metal / non-metal elements and acidic metal / non-metal elements. The types of impurity metal / non-metal elements with higher content are identified through testing, and then the impurity remover is used in a targeted manner.

[0030] Preferably, the liquid phase impurity removal is performed at a rotation speed of 100 to 500 rpm, such as 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, or 500 rpm, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0031] Preferably, the liquid phase impurity removal process takes 3 to 24 hours, such as 3 hours, 6 hours, 9 hours, 12 hours, 15 hours, 18 hours, 21 hours, or 24 hours, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0032] Preferably, after the impurity removal and before the oxidation modification, the material is first washed until pH=7, dried, and then subjected to a second crushing.

[0033] Preferably, the drying temperature is 80-120°C, such as 80°C, 90°C, 100°C, 110°C or 120°C, and the drying time is 8-12 hours, such as 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0034] Preferably, the second crushing yields second precursor particles, which are then subjected to oxidative modification. The median particle size of the second precursor particles is 4–10 μm, such as 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, or 10 μm, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0035] This application preferably involves coarse crushing (first crushing) after anaerobic baking, followed by fine crushing (second crushing) after impurity removal. By reducing the particle size and combining it with structural solidification (oxidative modification), the pores and defects can be exposed to the greatest extent. Oxidative modification introduces oxygen-containing functional groups into the material structure as connecting bonds between chain segments, which have a higher strength than hydrogen bonds and are beneficial for subsequent aromatic cyclization rearrangement. In the subsequent high-temperature carbonization process, as the temperature slowly increases, the material itself experiences tensile stress, causing it to continuously shrink, achieving a "self-repair" effect and "repairing" the surface pores, thereby forming a closed-cell structure.

[0036] As a preferred technical solution of this application, the oxidation modification method includes oxygen-containing sintering and / or liquid-phase oxidation.

[0037] One of the purposes of the oxidation modification in this application is to introduce oxygen-containing functional groups. When the reaction is complete, some oxygen molecules react with carbon to form oxygen-containing functional groups as active sites, while other oxygen reacts with some carbon to generate CO and / or CO2, which further forms pores on the surface and inside of the material. These pores help to store sodium ions, thereby improving the electrochemical performance of the material.

[0038] Preferably, the oxygen concentration of the oxygen-containing sintering is 10% to 15%, such as 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, or 15%, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0039] Preferably, the oxygen-containing sintering temperature is 400–600°C, such as 400°C, 420°C, 440°C, 460°C, 480°C, 500°C, 520°C, 540°C, 560°C, 580°C, or 600°C, and the time is 1–5 hours, such as 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0040] Preferably, the liquid-phase oxidation process involves treating the purified biomass raw material in a solution containing an oxidant.

[0041] Preferably, the liquid phase oxidation treatment time is 6 to 12 hours, such as 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, or 12 hours, and the treatment temperature is -3 to 5 degrees Celsius, such as -3 degrees Celsius, -2 degrees Celsius, -1 degrees Celsius, 0 degrees Celsius, 1 degree Celsius, 2 degrees Celsius, 3 degrees Celsius, 4 degrees Celsius, or 5 degrees Celsius, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0042] As a preferred technical solution of this application, the high-temperature carbonization temperature is 1600-1800℃, such as 1600℃, 1620℃, 1640℃, 1660℃, 1680℃, 1700℃, 1720℃, 1740℃, 1760℃, 1780℃ or 1800℃, and the time is 3-20h, such as 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h or 20h, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0043] Preferably, the heating rate of the high-temperature carbonization is 0.5 to 3℃ / min, for example, 0.5℃ / min, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min or 3℃ / min, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0044] Preferably, the high-temperature carbonization is carried out under an inert atmosphere.

[0045] As a preferred technical solution of this application, the preparation method includes the following steps:

[0046] (1) Place the biomass raw material in an inert atmosphere, with no oxygen or oxygen concentration <1000ppm in the system, and bake it at 200-1000℃ for 15-48h. When cooled to <50℃, discharge the material and perform the first crushing to obtain millimeter-sized first precursor particles with a median particle size of 0.5-1mm.

[0047] (2) The first precursor particles are mixed with an aqueous solution containing a purifying agent and additives, stirred at 100-500 rpm for 3-24 h for liquid phase purifying, washed with water until pH=7, dried at 80-120℃ for 8-12 h, and then crushed to obtain micron-sized second precursor particles with a median particle size of 4-10 μm.

[0048] (3) The second precursor particles are placed in an inert atmosphere with an oxygen concentration of 10% to 15% in the system and sintered at 400 to 600°C for 15 to 48 hours. After cooling to room temperature, the third precursor particles are obtained.

[0049] Alternatively, the second precursor particles are mixed with an aqueous solution containing an oxidant, stirred at -3 to 5°C for 6 to 12 hours, and dried to obtain the third precursor particles;

[0050] (4) Under the protection of inert gas, the third precursor particles are heated at a rate of 0.5 to 3 °C / min and carbonized at 1600 to 1800 °C for 3 to 20 hours. After cooling to room temperature, biomass-based hard carbon material is obtained.

[0051] Secondly, embodiments of this application provide a biomass-based hard carbon material, obtained using the preparation method described in the first aspect.

[0052] Preferably, the ash content of the hard carbon material is <0.5wt%, such as 0.45wt%, 0.40wt%, 0.35wt%, 0.30wt%, 0.25wt%, 0.20wt%, 0.15wt%, 0.10wt%, 0.05wt%, or 0.01wt%, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0053] Preferably, the pore size of the hard carbon material is 0.5 to 20 nm, such as 0.5 nm, 1 nm, 3 nm, 5 nm, 7 nm, 9 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm or 20 nm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0054] Preferably, the true density of the hard carbon material is 1.3–2.0 g / cm³. 3 For example, 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 Or 2.0g / cm 3 This applies to, but is not limited to, the listed values; other unlisted values ​​within the above range also apply.

[0055] Preferably, the specific surface area of ​​the hard carbon material is <5 g / m². 2 For example, 4.8g / m 2 4.5g / m 2 4g / m 2 3.5g / m 2 3g / m 2 2.5g / m 2 2g / m 2 1.5g / m 2 1g / m 2 0.5g / m 2 or 0.1g / m 2This applies to, but is not limited to, the listed values; other unlisted values ​​within the above range also apply.

[0056] Thirdly, embodiments of this application provide a negative electrode sheet containing the biomass-based hard carbon material described in the second aspect.

[0057] Fourthly, embodiments of this application provide a battery containing the negative electrode sheet described in the third aspect.

[0058] Compared with related technical solutions, the embodiments of this application have at least the following beneficial effects:

[0059] (1) In this embodiment, the lignin and cellulose in the biomass raw material are destroyed by first performing anaerobic baking and impurity removal in sequence, leaving pores and defects inside, so that the material is in a metastable structure to expose impurities. Then, impurity removal can be achieved at room temperature, and the impurity removal effect is excellent. The resulting biomass-based hard carbon has low impurity content, and the ash content can be reduced to below 0.5wt%. It also has a disordered interlayer structure, which is conducive to the insertion / extraction of sodium ions and can exhibit high reversible capacity and first-efficiency performance.

[0060] (2) In the embodiments of this application, the impurity remover and the additive work together to produce a synergistic effect, so that the pretreated precursor is further decomposed at room temperature. After further decomposition, rich pores and defects are left inside the material. At this time, the material is in a metastable structure. The impurities and the impurity remover undergo a displacement reaction. The impurities are in a free state and dissolved in the aqueous solution, thereby further improving the impurity removal effect at room temperature.

[0061] (3) In this embodiment, coarse crushing (first crushing) is performed after anaerobic baking, and fine crushing (second crushing) is performed after impurity removal. By reducing the particle size and solidifying the structure, the pores and defects can be exposed to the greatest extent. In the subsequent high-temperature carbonization process, as the temperature slowly rises, the material shrinks continuously due to the tension stress of the material itself, achieving a "self-repair" effect and "repairing" the pores on the surface, thereby forming a closed-cell structure.

[0062] (4) In this application embodiment, oxygen-containing functional groups are introduced through oxidation modification. When the reaction is complete, some oxygen molecules react with carbon to form oxygen-containing functional groups as active sites, while other oxygen reacts with some carbon to generate CO and / or CO2, which further forms pores on the surface and inside of the material. These pores help to store sodium ions, thereby improving the electrochemical performance of the material.

[0063] (5) The preparation method described in the embodiments of this application is widely applicable to biomass raw materials, has low cost, and has practical significance for the industrial application of hard carbon anode materials.

[0064] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0065] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0066] Figure 1 This is a SEM image of the first precursor particles obtained in Example 1;

[0067] Figure 2 This is a SEM image of the biomass-based hard carbon material obtained in Example 1;

[0068] Figure 3 This is a charge-discharge curve of the biomass-based hard carbon material obtained in Example 1;

[0069] Figure 4 This is the XRD pattern of the biomass-based hard carbon material obtained in Example 1. Detailed Implementation

[0070] The technical solution of this application will be further described below through specific implementation methods.

[0071] Those skilled in the art should understand that the embodiments described are merely illustrative of this application and should not be construed as specific limitations on this application.

[0072] Example 1

[0073] This embodiment provides a biomass-based hard carbon material, which is prepared by the following method:

[0074] (1) Place 1 kg of bamboo chips in a nitrogen atmosphere with an oxygen concentration of less than 200 ppm, heat to 400°C, treat for 12 h, cool to below 50°C and discharge, and crush to a median particle size of 1 mm using a jaw crusher to obtain the first precursor particles.

[0075] (2) The first precursor particles obtained in step (1) are placed in a stirred tank, and sodium hydroxide, sodium gluconate and water are added in sequence in a mass ratio of 22:4:74. The mixture is stirred at room temperature for 3 hours, washed until neutral, dried, and crushed to a median particle size of 5 μm using an air jet mill to obtain the second precursor particles.

[0076] (3) The second precursor particles from step (2) are placed in a nitrogen atmosphere with an oxygen concentration controlled at 8%, and the temperature is rapidly increased to 800℃ at a rate of 5℃ / min for 6 hours to introduce oxygen-containing functional groups and obtain the third precursor particles.

[0077] (4) Under argon conditions, the third precursor particles obtained in step (3) are subjected to high-temperature closed-pore treatment, heated to 1700℃ at 2℃ / min, kept at the temperature for 8h, and cooled to room temperature to obtain biomass-based hard carbon material with internal pore structure.

[0078] Figure 1 and Figure 2 The images are SEM images of the first precursor particles obtained in Example 1 and the biomass-based hard carbon material obtained after high-temperature sintering. As can be seen from the images, the surface of the first precursor particles contains a large number of particulate impurities. The surface of the biomass-based hard carbon material obtained after impurity removal and carbonization is smooth, and the particle size is significantly reduced after carbonization. Figure 3 This is the charge-discharge curve of the biomass-based hard carbon material obtained in Example 1. The graph shows the electrochemical performance of the biomass-based hard carbon: initial charge 334.43 mAh / g, initial charge 88.65%. Figure 4 The image shows the XRD pattern of the biomass-based hard carbon material obtained in Example 1. As can be seen from the image, the hard carbon material is free of impurities, and the lattice spacing is calculated to be around 3.8 nm.

[0079] Example 2

[0080] This embodiment provides a biomass-based hard carbon material, which is prepared by the following method:

[0081] (1) Place 1 kg of pine wood chips in a nitrogen atmosphere with an oxygen concentration of less than 200 ppm, heat to 250°C, treat for 48 h, cool to below 50°C and discharge, and crush to a median particle size of 1 mm using a jaw crusher to obtain the first precursor particles.

[0082] (2) The first precursor particles obtained in step (1) are placed in a stirred tank, and sodium hydroxide, thiourea and water are added in sequence in a mass ratio of 12:7:81. The mixture is stirred at room temperature for 3 hours, washed until neutral, dried, and crushed to a median particle size of 5 μm using an air jet mill to obtain the second precursor particles.

[0083] (3) The second precursor particles from step (2) are placed in a nitrogen atmosphere with an oxygen concentration controlled at 8%, and the temperature is rapidly increased to 800℃ at a rate of 5℃ / min for 6 hours to introduce oxygen-containing functional groups and obtain the third precursor particles.

[0084] (4) Under argon conditions, the third precursor particles obtained in step (3) are subjected to high-temperature closed-pore treatment, heated to 1700℃ at 2℃ / min, kept at the temperature for 8h, and cooled to room temperature to obtain biomass-based hard carbon material with internal pore structure.

[0085] Example 3

[0086] This embodiment provides a biomass-based hard carbon material, which is prepared by the following method:

[0087] (1) Place 1 kg of poplar wood chips in a nitrogen atmosphere with an oxygen concentration of less than 200 ppm, heat to 600 ℃, treat for 28 h, cool to below 50 ℃ and discharge, and crush to a median particle size of 1 mm using a jaw crusher to obtain the first precursor particles.

[0088] (2) The first precursor particles obtained in step (1) are placed in a stirred tank containing 20% ​​HF, stirred at room temperature for 3 hours, washed until neutral, dried, and crushed to a median particle size of 5 μm using an air jet mill to obtain the second precursor particles.

[0089] (3) Place the second precursor particles from step (2) in 500 mL of a mixed solution of phosphoric acid and sulfuric acid with a molar ratio of 3:1. Stir with a stirrer at 0-3℃. Add 3 g of potassium permanganate every two minutes, and add a total of 60 g in batches. Stir for 6 h. Finally, add 100 mL of hydrogen peroxide and stir for 12 h. Wash until neutral, introduce oxygen-containing functional groups, and dry to obtain the third precursor particles.

[0090] (4) Under argon conditions, the third precursor particles obtained in step (3) are subjected to high-temperature closed-pore treatment, heated to 1600℃ at 2℃ / min, kept at the temperature for 8h, and cooled to room temperature to obtain biomass-based hard carbon material with internal pore structure.

[0091] Example 4

[0092] This embodiment provides a biomass-based hard carbon material, and step (3) of the preparation method of the biomass-based hard carbon material is as follows:

[0093] The second precursor particles from step (2) were placed in 500 mL of a mixed solution of phosphoric acid and sulfuric acid with a molar ratio of 3:1. The mixture was stirred with a stirrer at a temperature of 0-3℃. 3 g of potassium permanganate was added every two minutes, and a total of 60 g was added in batches. The mixture was stirred for 6 hours. Finally, 100 mL of hydrogen peroxide was added and the mixture was stirred for 12 hours. The mixture was washed until neutral, oxygen-containing functional groups were introduced, and the mixture was dried to obtain the third precursor particles.

[0094] Apart from this, all other conditions are exactly the same as in Example 2.

[0095] Example 5

[0096] This embodiment provides a biomass-based hard carbon material. In step (2) of the preparation method of the biomass-based hard carbon material, urea is used to replace thiourea. Apart from this, the other conditions are exactly the same as in Example 2.

[0097] Example 6

[0098] This embodiment provides a biomass-based hard carbon material. In step (2) of the preparation method of the biomass-based hard carbon material, disodium ethylenediaminetetraacetate is used to replace thiourea. Apart from this, the other conditions are exactly the same as in Example 2.

[0099] Example 7

[0100] This embodiment provides a biomass-based hard carbon material. In step (2) of the preparation method of the biomass-based hard carbon material, ammonia water is used to replace thiourea. Apart from this, the other conditions are exactly the same as in Example 2.

[0101] Example 8

[0102] This embodiment provides a biomass-based hard carbon material. In step (2) of the preparation method of the biomass-based hard carbon material, sodium gluconate is used instead of thiourea. Otherwise, the other conditions are exactly the same as in Example 2.

[0103] Comparative Example 1

[0104] This comparative example provides a biomass-based hard carbon material, which is prepared by the following method:

[0105] (1) Place 1 kg of bamboo chips in an argon atmosphere with an oxygen concentration of less than 200 ppm, heat to 1600 ℃ at 5 ℃ / min, keep warm for 10 h, cool down to room temperature, and discharge the material after cooling to below 50 ℃.

[0106] (2) The median particle size of the sample obtained in step (1) is reduced to 5 μm by air jet milling to obtain biomass-based hard carbon material.

[0107] Comparative Example 2

[0108] This comparative example provides a biomass-based hard carbon material. The preparation method of the biomass-based hard carbon material does not perform step (2), but directly uses the first precursor particles obtained in step (1) to perform step (3). Apart from this, the other conditions are exactly the same as those in Example 2.

[0109] Comparative Example 3

[0110] This comparative example provides a biomass-based hard carbon material. The preparation method of the biomass-based hard carbon material does not perform step (3), but directly uses the second precursor particles obtained in step (2) to perform step (4). Apart from this, the other conditions are exactly the same as those in Example 2.

[0111] Comparative Example 4

[0112] This comparative example provides a biomass-based hard carbon material. The difference between the preparation method of this biomass hard carbon material and that of Example 2 is that it sequentially undergoes anaerobic baking, oxidative modification, impurity removal, and high-temperature carbonization. The preparation method is as follows:

[0113] (1) Place 1 kg of coconut shell under a nitrogen atmosphere with an oxygen concentration of less than 200 ppm, heat to 250°C, treat for 48 h, cool to below 50°C and discharge, and crush to a median particle size of 1 mm using a jaw crusher to obtain the first precursor particles.

[0114] (2) The first precursor particles obtained in step (1) are placed in a nitrogen atmosphere, with the oxygen concentration controlled at 8%, and the temperature is rapidly increased to 800℃ at 5℃ / min. After treatment for 6 hours, oxygen-containing functional groups are introduced, and the particles are crushed to a median particle size of 5μm using an air jet mill to obtain the second precursor particles.

[0115] (3) Place the second precursor particles from step (2) in a stirred tank, add sodium hydroxide, thiourea and water in a mass ratio of 12:7:81, stir at room temperature for 3 hours, wash until neutral, dry, and obtain the third precursor particles.

[0116] (4) Under argon conditions, the third precursor particles obtained in step (3) are subjected to high-temperature closed-cell treatment, heated to 1700℃ at 2℃ / min, kept at the temperature for 8h, and cooled to room temperature to obtain biomass-based hard carbon material.

[0117] Comparative Example 5

[0118] This comparative example provides a biomass-based hard carbon material. The difference between the preparation method of this biomass hard carbon material and that of Example 2 is that it sequentially undergoes anaerobic baking, oxidative modification, high-temperature carbonization, and impurity removal. The preparation method is as follows:

[0119] (1) Place 1 kg of coconut shell under a nitrogen atmosphere with an oxygen concentration of less than 200 ppm, heat to 250°C, treat for 48 h, cool to below 50°C and discharge, and crush to a median particle size of 1 mm using a jaw crusher to obtain the first precursor particles.

[0120] (2) The first precursor particles obtained in step (1) are placed in a nitrogen atmosphere, with the oxygen concentration controlled at 8%, and the temperature is rapidly increased to 800℃ at 5℃ / min. After treatment for 6 hours, oxygen-containing functional groups are introduced, and the particles are crushed to a median particle size of 5μm using an air jet mill to obtain the second precursor particles.

[0121] (3) Under argon conditions, the second precursor particles from step (2) were subjected to high-temperature closed-pore treatment, heated to 1700℃ at 2℃ / min, kept at the temperature for 8h, and cooled to room temperature to obtain the third precursor particles.

[0122] (4) Place the third precursor particles obtained in step (3) in a stirred tank, add sodium hydroxide, thiourea and water in sequence at a mass ratio of 12:7:81, stir at room temperature for 3 hours, wash until neutral, and dry to obtain biomass-based hard carbon material.

[0123] The ash content of the hard carbon materials obtained in the examples and comparative examples was tested according to the national standard method GB / T 17664-1999, and the results are recorded in Table 1.

[0124] The hard carbon materials obtained in the examples and comparative examples were mixed with sodium carboxymethyl cellulose, super P conductive agent, and polymer binder in a ratio of 95:2:1:2 in deionized water to form a slurry. This slurry was then coated onto copper foil, and the electrode was dried in a drying oven at 80°C for 4–10 hours to obtain a hard carbon negative electrode. Finally, coin cells were assembled in a glove box filled with argon atmosphere. The electrolyte used was NaClO4 dissolved in ethylene carbonate and propylene carbonate in a volume ratio of 1:1. Sodium metal foil was used as the counter electrode and reference electrode. The electrochemical performance was tested using an electrochemical workstation and other equipment, and the results are recorded in Table 1.

[0125] Table 1

[0126]

[0127] As shown in Table 1:

[0128] The specific surface area of ​​the biomass-based hard carbon sample prepared in the examples is smaller than that of Comparative Example 1. The specific surface area of ​​the sample after medium-temperature treatment in the examples is larger than that after high-temperature carbonization. This is because the temperature is rapidly increased to the medium-temperature stage, causing the structure in the material to rearrange rapidly. Due to the rapid temperature change, the molecular weight moves faster and faster, making the connections between structures gradually disordered, and exposing a large number of pores and defects. As the temperature is further slowly increased, and with the presence of catalytic gas, impurity elements are removed. Due to the temperature change, the tensile stress of the material itself exists, causing the material to continuously shrink, achieving a "self-repair" effect, "repairing" the surface pores without affecting the formation of the internal pore structure, thus reducing the specific surface area.

[0129] The electrochemical performance of the hard carbon product prepared in the examples is better than that of Comparative Example 1. This is because, during the high-temperature catalytic carbonization process, on the one hand, the impurities contained in the material are catalytically volatilized, and on the other hand, the material undergoes structural rearrangement, which can repair the surface defects on its own, forming closed pores, reducing the specific surface area, and reducing the sodium ions forming SEI, thereby improving the capacity and first efficiency of the material.

[0130] The electrochemical performance of Example 2 is better than that of Example 4. This is because the liquid-phase oxidation of Example 4 is carried out in solution. In addition to the effect of the oxidant on the material, the aqueous solution also affects the structure of the material under the action of a strong oxidant, resulting in an excessively large specific surface area and abundant internal pores. This makes it impossible for the material to close the pores through its own tension, resulting in a difference in performance compared to Example 2.

[0131] The electrochemical performance of Example 2 is better than that of Comparative Examples 2 and 3. Since the material in Comparative Example 2 was not purified, it has a great impact on the material's capacity and first-efficiency performance. The presence of impurities leads to a low carbon content in the material. Untreated impurities such as Si react with carbon to form SiC, causing changes in the material structure and making it difficult to achieve excellent energy storage performance. The material in Comparative Example 3 has been purified, and its performance is relatively excellent. However, since the pores in Comparative Example 3 are all natural pores, its energy storage is limited, and its capacity is significantly different from that of Example 2.

[0132] The electrochemical performance of Example 2 is better than that of Comparative Examples 4 and 5. The comparative examples adjusted the process sequence so that the material could not achieve the effect of impurity removal. The presence of impurities resulted in a low carbon content in the material. Untreated impurities such as Si reacted with carbon to form SiC, causing changes in the material structure and making it difficult to achieve excellent energy storage performance.

[0133] This application illustrates its detailed structural features through the above embodiments, but it is not limited to these detailed structural features, meaning that this application does not necessarily rely on them for implementation. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of selected components, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this application.

[0134] The preferred embodiments of this application have been described in detail above. However, this application is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this application, various simple modifications can be made to the technical solution of this application, and these simple modifications all fall within the protection scope of this application.

[0135] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this application will not describe the various possible combinations separately.

[0136] Furthermore, various different implementations of this application can be combined in any way, as long as they do not violate the spirit of this application, they should also be regarded as the content disclosed in this application.

Claims

1. A method for preparing a biomass-based hard carbon material, comprising the following steps: an oxygen-free roasting, a removal of impurities, an oxidative modification, and a high-temperature carbonization of a biomass raw material in sequence to obtain a biomass-based hard carbon material, wherein the removal of impurities removes alkaline / non-metallic elements and acidic metallic / non-metallic elements, and the ash content of the biomass-based hard carbon material is less than 0.5 wt. %; the biomass raw material is any one or a combination of at least two of white poplar sawdust, pine sawdust, lychee sawdust, coconut shell, bamboo sawdust, or wheat straw; the temperature of the oxygen-free roasting is 200-1000 ℃, and the time is 15-48 h; the method for the oxidative modification comprises oxygen-containing sintering and / or liquid-phase oxidation, wherein the temperature of the oxygen-containing sintering is 420-600 ℃, the oxygen concentration is 10-15 %, and the time is 1-5 h; and the liquid-phase oxidation treats the biomass raw material after the removal of impurities in a solution containing an oxidizing agent.

2. The production method according to claim 1, wherein, the oxygen-free roasting is performed in an inert atmosphere, and the oxygen concentration is less than 1000 ppm.

3. The production method according to claim 2, wherein, the inert atmosphere comprises any one or a combination of at least two of nitrogen, argon, or helium.

4. The production method according to claim 1, wherein after the oxygen-free roasting, the biomass raw material is cooled to less than 50 ℃ before the removal of impurities, discharged, and first crushed to obtain first precursor particles, and the first precursor particles are subjected to the removal of impurities.

5. The production method according to claim 4, wherein the median particle size of the first precursor particles is 0.5-1 mm.

6. The production method according to claim 1, wherein the removal of impurities is liquid-phase removal of impurities, which treats the biomass raw material after the oxygen-free roasting in a solution containing a removal agent.

7. The production method according to claim 6, wherein the removal agent comprises any one or a combination of at least two of sodium hydroxide, potassium hydroxide, sulfuric acid, hydrochloric acid, phosphoric acid, or hydrofluoric acid.

8. The production method according to claim 6, wherein the solution containing the removal agent also contains an additive.

9. The production method according to claim 8, wherein the additive comprises any one or a combination of at least two of thiourea, urea, disodium ethylenediaminetetraacetate, citric acid, ammonia, or sodium gluconate.

10. The production method according to claim 6, wherein the liquid-phase removal of impurities is performed at a rotation speed of 100-500 rpm.

11. The production method according to claim 6, wherein the treatment time of the liquid-phase removal of impurities is 3-24 h.

12. The method of producing according to claim 1, wherein, after the removal of impurities, the biomass raw material is washed until the pH is 7 before the oxidative modification, dried, and then second crushed.

13. The method of making according to claim 12, wherein, the temperature of the drying is 80-120 ℃, and the time is 8-12 h.

14. The method of making according to claim 12, wherein, the second crushing obtains second precursor particles, and the second precursor particles are subjected to the oxidative modification, wherein the median particle size of the second precursor particles is 4-10 μm.

15. The method of producing according to claim 1, wherein, the treatment time of the liquid-phase oxidation is 6-12 h, and the treatment temperature is -3-5 ℃.

16. The method of producing according to claim 1, wherein, the temperature of the high-temperature carbonization is 1600-1800 ℃, and the time is 3-20 h.

17. The method of producing according to claim 1, wherein, the heating rate of the high-temperature carbonization is 0.5-3 ℃ / min.

18. The method of producing according to claim 1, wherein, the high-temperature carbonization is performed in an inert atmosphere. 19.The method according to claim 1, comprising the following steps: (1) placing a biomass raw material in an inert atmosphere, wherein the oxygen concentration in the system is less than 1000 ppm, and performing oxygen-free roasting at 200-1000 ℃ for 15-48 h, and then discharging and first crushing when the temperature is less than 50 ℃ to obtain first precursor particles with a median particle size of 0.5-1 mm. (2) mixing the first precursor particles with an aqueous solution containing a decontaminating agent and an additive, stirring at 100-500 rpm for 3-24 h to perform liquid-phase decontamination, washing with water until pH=7, drying at 80-120℃ for 8-12 h, performing secondary crushing to obtain micron-sized second precursor particles with a median particle size of 4-10 μm; (3) placing the second precursor particles in an inert atmosphere with an oxygen concentration of 10%-15% in the system, performing oxygen-containing sintering at 420-600℃ for 15-48 h, and cooling to room temperature to obtain third precursor particles; or, mixing the second precursor particles with an aqueous solution containing an oxidizing agent, stirring at -3-5℃ for 6-12 h, and drying to obtain third precursor particles; (4) under the protection of an inert gas, heating the third precursor particles at a rate of 0.5-3℃ / min, and performing high-temperature carbonization at 1600-1800℃ for 3-20 h, and cooling to room temperature to obtain a biomass-based hard carbon material.

20. A biomass-based hard carbon material obtained using the preparation method of any one of claims 1-19, wherein the ash content of the biomass-based hard carbon material is <0.5 wt%.

21. The biomass-based hard carbon material of claim 20, wherein, The pore size of the biomass-based hard carbon material is 0.5-20 nm.

22. The biomass-based hard carbon material of claim 20, wherein, The true density of the biomass-based hard carbon material is 1.3-2.0 g / cm 3 .

23. The biomass-based hard carbon material of claim 20, wherein, The specific surface area of the biomass-based hard carbon material is < 5 g / m 2 .

24. A negative electrode sheet containing the biomass-based hard carbon material of any one of claims 20-23.

25. A battery containing the negative electrode sheet of claim 24.

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