Biochar material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of battery materials, and discloses a biochar material as well as a preparation method and application thereof. The biochar material comprises hard carbon microspheres and a soft carbon layer wrapping the outer sides of the hard carbon microspheres, the ratio of the thickness of the soft carbon layer to the radius of the hard carbon microspheres is 1: (250-930), the specific surface area of the biochar material is smaller than or equal to 5.5 m < 2 > / g, the median diameter D50 is 3.5-9 microns, the interlayer spacing d002 is 0.37-0.39 nm, and the eccentricity rate is smaller than 0.3. The biochar material has relatively high rate capability and cycle performance when being applied to a battery.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a biochar material. Furthermore, this invention also relates to a method for preparing the biochar material and its applications. Background Technology

[0002] In the field of energy storage, lithium-ion batteries, sodium-ion batteries, lead-carbon batteries, and lead-lithium batteries have become core energy storage devices in portable electronic devices, electric vehicles, and large-scale energy storage systems due to their high energy density and stable cycle performance. Among these, the anode material, as a key component of the battery, directly affects the battery's capacity, cycle life, rate performance, and safety. Therefore, the development of high-performance anode materials has always been a research hotspot in the field of energy materials.

[0003] Hard carbon materials, with their unique disordered carbon structure, high theoretical specific capacity, excellent cycle stability, and good reversible insertion / extraction of alkali metal ions (such as lithium ions and sodium ions), are considered highly promising anode materials for various types of batteries. Compared to graphite-based anode materials, hard carbon materials perform better in meeting high capacity requirements and wide temperature adaptability scenarios, especially in the field of sodium-ion batteries. Due to the large radius of sodium ions, the interlayer spacing of graphite is insufficient to meet the insertion requirements of sodium ions, while the disordered structure and abundant porosity of hard carbon materials provide more storage sites for sodium ions, making it one of the preferred materials for sodium-ion battery anodes.

[0004] However, there are still many problems to be solved in the preparation of hard carbon anode materials. First, existing preparation methods mostly use precursors such as biomass, resin, and polymers to obtain them through high-temperature carbonization. Due to the non-uniformity of the precursor composition and the complexity of the pyrolysis reaction during carbonization, the resulting hard carbon materials have low bulk density and uneven performance, which means that their initial coulombic efficiency, rate performance, and cycle performance need to be further improved. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of low packing density and uneven performance of existing hard carbon materials, which result in the need for further improvement in initial coulombic efficiency, rate performance and cycle performance. This invention provides a biochar material, its preparation method and application, which exhibits high rate performance and cycle performance when applied to batteries.

[0006] To achieve the above objectives, a first aspect of the present invention provides a biochar material comprising hard carbon microspheres and a soft carbon layer surrounding the hard carbon microspheres, wherein the ratio of the thickness of the soft carbon layer to the radius of the hard carbon microspheres is 1:250-930, and the specific surface area of ​​the biochar material is ≤5.5 m². 2 / g, median particle size D50 is 3.5-9μm, interlayer spacing d 002 The wavelength is 0.37-0.39 nm and the eccentricity is less than 0.3.

[0007] Preferably, the ratio of the thickness of the soft carbon layer to the radius of the hard carbon microspheres is 1:600-750, and the specific surface area of ​​the biochar material is 4.5-5.5 m². 2 / g, eccentricity rate is 0.27-0.29.

[0008] Preferably, the carbon content in the hard carbon microspheres is ≥99.2wt% and the ash content is ≤1.0wt%.

[0009] Preferably, the tap density of the biochar material is ≥0.85 g / cm³. 3 .

[0010] A second aspect of the present invention provides a method for preparing the biochar material provided in the first aspect above, the method comprising the following steps: S1. The biomass raw material is pre-oxidized and then carbonized to obtain intermediate carbon material; S2. The intermediate carbon material is crushed and then ball-milled and washed to obtain intermediate product I. S3. Mix the intermediate product I with the additive and granulate to obtain intermediate product II; The additive is selected from at least one of phenolic resin, polyvinyl alcohol, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, molasses, tall oil fatty acids, and starch; S4. The intermediate product is subjected to carbonization treatment II to obtain intermediate product III; The carbonization treatment II includes a first carbonization treatment and a second carbonization treatment. The conditions for the first carbonization treatment include: a temperature of 500-700℃ and a time of 3-6 hours; The conditions for the second carbonization treatment include: a temperature of 1300-1800℃ and a time of 1-6 hours; S5. The solution containing the encapsulating material and the intermediate product III are mixed, dried, and then subjected to carbonization treatment III, followed by spheroidizing and shaping treatment. The mass ratio of the packaging material to the intermediate product III is 1:9.5-16.

[0011] Preferably, the biomass raw material is selected from at least one of macadamia nut shells, palm shells, eucalyptus wood, bamboo, and sugarcane bagasse.

[0012] More preferably, the biomass raw material is selected from at least one of palm fruit shells, eucalyptus wood, and sugarcane bagasse.

[0013] Preferably, step S1 further includes: crushing, washing and drying the biomass raw material before carbonizing it.

[0014] More preferably, the washing includes acid washing and water washing, wherein the acid used in the acid washing is selected from at least one of sulfuric acid, hydrochloric acid and nitric acid.

[0015] Preferably, in step S1, the pre-oxidation conditions include: a temperature of 250-450°C and a time of 0.5-2 hours; The conditions for the carbonization treatment I include: a temperature of 550-750℃ and a time of 2-8h.

[0016] More preferably, the pre-oxidation conditions include: a temperature of 300-400°C and a time of 0.5-1 h; The conditions for the carbonization treatment I include: a temperature of 600-700℃ and a time of 4-6 hours.

[0017] Preferably, in step S2, the particle size of the particles obtained after crushing is ≤74μm; Preferably, in step S2, the ball milling conditions include: a rotation speed of 250-400 rpm and a time of 2-6 hours.

[0018] Preferably, in step S2, the washing includes acid washing and water washing, wherein the acid used for acid washing is selected from at least two of hydrofluoric acid, sulfuric acid, hydrochloric acid and nitric acid.

[0019] Preferably, in step S3, the amount of the additive is 0.03-0.1g relative to 1g of the intermediate product I.

[0020] Preferably, in step S3, the additive is molasses and / or tall oil fatty acid.

[0021] Preferably, step S4 further includes: acid washing, drying, crushing and demagnetizing the product obtained from carbonization treatment II.

[0022] More preferably, in step S4, the acid used for pickling is selected from at least one of sulfuric acid, hydrochloric acid, and nitric acid.

[0023] Preferably, in step S5, the conditions for carbonization treatment III include: a temperature of 650-850℃ and a time of 2-4h.

[0024] In step S5, the spheroidizing process is carried out in a particle spheroidizing device for 5-10 minutes.

[0025] A third aspect of the present invention provides the application of the above-described biochar material or the biochar material prepared by the above-described preparation method in sodium batteries, lead-carbon batteries or lead-lithium batteries.

[0026] Through the above technical solution, the biochar material provided by this invention is defined as comprising hard carbon microspheres and a soft carbon layer coating the outside of the hard carbon microspheres. The ratio of the thickness of the soft carbon layer to the radius of the hard carbon microspheres is also limited. Simultaneously, the specific surface area, median particle size, interlayer spacing, and eccentricity of the biochar material are also limited, resulting in a more regular morphology, effectively increasing the packing density, achieving uniform coating of battery electrodes during electrode preparation, and effectively reducing polarization during battery charging and discharging, thus improving rate performance. Furthermore, it can prevent excessive decomposition of the electrolyte on the material surface, increasing ion transport rate, and further improving rate performance while enhancing the initial coulombic efficiency and cycle stability of the battery. In addition, the biochar material provided by this invention can reduce performance differences between battery batches in large-scale applications, which is beneficial for quality control in industrial production and can be widely promoted and applied in various types of batteries. Attached Figure Description

[0027] Figure 1 The XRD pattern of the biochar material prepared in Example 1 is shown below. Figure 2 The charge-discharge curves of the biochar material prepared in Example 1 are shown. Figure 3 The charge-discharge curves of the biochar material prepared in Example 2 are shown below. Figure 4 The charge-discharge curves of the biochar material prepared in Example 5 are shown below. Figure 5 TEM image of the biochar material prepared in Example 6; Figure 6 The charge-discharge curves of the biochar material prepared in Example 10 are shown below. Figure 7 The charge-discharge curves of the biochar material prepared in Example 12 are shown. Detailed Implementation

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] Low material packing density on the electrode sheet can affect the energy density of the battery. Moreover, morphological differences can lead to uneven contact resistance of material particles, exacerbating polarization during battery charging and discharging, and reducing rate performance and coulombic efficiency. It may also cause excessive decomposition of electrolyte on the material surface, forming a thick solid electrolyte interphase (SEI) film. This not only consumes a large amount of active lithium / sodium and reduces the initial coulombic efficiency, but may also cause battery cycle performance degradation due to repeated rupture and repair of the SEI film.

[0030] As previously stated, a first aspect of this invention provides a biochar material comprising hard carbon microspheres and a soft carbon layer surrounding the hard carbon microspheres. The ratio of the thickness of the soft carbon layer to the radius of the hard carbon microspheres is 1:250-930, and the specific surface area of ​​the biochar material is ≤5.5 m². 2 / g, median particle size D50 is 3.5-9μm, interlayer spacing d 002 The wavelength is 0.37-0.39 nm and the eccentricity is less than 0.3.

[0031] During their research, the inventors discovered that by defining the biochar material as comprising hard carbon microspheres and a soft carbon layer encapsulating the hard carbon microspheres, and by limiting the ratio of the soft carbon layer thickness to the radius of the hard carbon microspheres, as well as the specific surface area, median particle size, interlayer spacing, and eccentricity of the biochar material, the material achieves a more regular morphology, effectively increasing its packing density. This enables uniform coating of battery electrodes during preparation and effectively reduces polarization during battery charging and discharging, improving coulombic efficiency and rate performance. Furthermore, it prevents excessive decomposition of the electrolyte on the material surface, increasing ion transport rate and further enhancing rate performance while improving initial coulombic efficiency and cycle stability. In addition, the biochar material provided by this invention can reduce performance differences between battery batches in large-scale applications, facilitating quality control in industrial production and enabling large-scale application in various types of batteries.

[0032] According to the present invention, the ratio of the thickness of the soft carbon layer to the radius of the hard carbon microspheres can be 1:250, 1:350, 1:450, 1:550, 1:650, 1:750, 1:850, 1:930, or any value within any two of the above ranges; the specific surface area of ​​the biochar material can be 0.5 m². 2 / g, 1.5m 2 / g, 2.5m 2 / g, 3.5m 2 / g, 4.5m 2 / g, 5.5m 2 / g, or any value within the range of any two of the above values; the median particle size D50 can be 3.5μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, or any value within the range of any two of the above values; interlayer spacing d 002 The values ​​can be 0.37nm, 0.375nm, 0.38nm, 0.385nm, 0.388nm, 0.39nm, or any value within the range formed by any two of the above values; the eccentricity can be 0.01, 0.1, 0.15, 0.2, 0.25, 0.29, or any value within the range formed by any two of the above values.

[0033] To further improve the specific capacity, initial coulombic efficiency, and cycle stability of the material, preferably, the ratio of the thickness of the soft carbon layer to the radius of the hard carbon microspheres is 1:600-750, and the specific surface area of ​​the biochar material is 4.5-5.5 m². 2 / g, eccentricity rate is 0.27-0.29.

[0034] In order to further improve the specific capacity, initial coulombic efficiency, rate performance and cycle stability of the material, preferably, the carbon content of the hard carbon microspheres is ≥99.2wt% and the ash content is ≤1.0wt%.

[0035] Preferably, the tap density of the biochar material is ≥0.85 g / cm³. 3 Studies have found that controlling the tap density of the material within the aforementioned range can further improve its initial coulombic efficiency, rate performance, and cycle stability. From the perspective of further improving the initial coulombic efficiency, rate performance, and cycle stability, it is further preferred that the tap density of the biochar material is 0.85-1.1 g / cm³. 3 Preferably, the porosity of the biochar material is ≤37%.

[0036] A second aspect of the present invention provides a method for preparing biochar material, the method comprising the following steps: S1. The biomass raw material is pre-oxidized and then carbonized to obtain intermediate carbon material; S2. The intermediate carbon material is crushed and then ball-milled and washed to obtain intermediate product I. S3. Mix the intermediate product I with the additive and granulate to obtain intermediate product II; The additive is selected from at least one of phenolic resin, polyvinyl alcohol, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, molasses, tall oil fatty acids, and starch; S4. The intermediate product is subjected to carbonization treatment II to obtain intermediate product III; The carbonization treatment II includes a first carbonization treatment and a second carbonization treatment. The conditions for the first carbonization treatment include: a temperature of 500-700℃, which can be 500℃, 550℃, 600℃, 650℃, 700℃, or any value within any two of the above values; and a time of 3-6h, which can be 3h, 4h, 5h, 6h, or any value within any two of the above values. The conditions for the second carbonization treatment include: a temperature of 1300-1800℃, which can be 1300℃, 1400℃, 1500℃, 1600℃, 1700℃, 1800℃, or any value within any two of the above values; and a time of 1-6h, which can be 1h, 2h, 3h, 4h, 5h, 6h, or any value within any two of the above values. S5. The solution containing the encapsulating material and the intermediate product III are mixed, dried, and then subjected to carbonization treatment III, followed by spheroidizing and shaping treatment to obtain biochar material. The mass ratio of the encapsulating material to intermediate product III is 1:9.5-16; the biochar material comprises hard carbon microspheres and a soft carbon layer encapsulating the outside of the hard carbon microspheres, the ratio of the thickness of the soft carbon layer to the radius of the hard carbon microspheres is 1:250-930, and the specific surface area of ​​the biochar material is ≤5.5 m². 2 / g, median particle size D50 is 3.5-9μm, interlayer spacing d 002 The wavelength is 0.37-0.39 nm and the eccentricity is less than 0.3.

[0037] During their research, the inventors discovered that the biochar material prepared by the above-mentioned method comprises hard carbon microspheres and a soft carbon layer coating the outside of the hard carbon microspheres. Simultaneously, the ratio of the thickness of the soft carbon layer to the radius of the hard carbon microspheres, the specific surface area of ​​the biochar material, the median particle size, the interlayer spacing, and the eccentricity are controlled within specific ranges. This results in a relatively regular morphology, effectively increasing the packing density and achieving uniform coating of the battery electrode during electrode preparation. Furthermore, it effectively reduces polarization during battery charging and discharging, improving coulombic efficiency and rate performance. Moreover, it prevents excessive decomposition of the electrolyte on the material surface, increasing ion transport rate and further improving rate performance while enhancing initial coulombic efficiency and cycle stability. In addition, the biochar material provided by this invention can reduce performance differences between battery batches in large-scale applications, facilitating quality control in industrial production and enabling large-scale application in various types of batteries.

[0038] The purpose of pre-oxidation is to remove some volatile components from biomass raw materials, introduce oxygen-containing functional groups, increase the active sites for subsequent low-temperature carbonization, and increase specific surface area and porosity, thereby increasing carbon yield and improving the surface physicochemical properties of the material.

[0039] In step S4, the first carbonization treatment can carbonize the additive into carbon material, and the second carbonization treatment can react the carbon material into hard carbon material, achieving precise positioning of carbon interlayer spacing, microcrystal size, and voids, obtaining a highly disordered hard carbon material with a large number of nano-sized closed pores and appropriate interlayer spacing, thereby further improving the reversible capacity, initial coulombic efficiency, and cycle stability of the subsequently obtained biochar material, and also exhibiting a significant low voltage plateau.

[0040] Preferably, the biomass raw material is selected from at least one of macadamia nut shells, palm shells, eucalyptus wood, bamboo, and sugarcane bagasse. Biochar materials made from the above-mentioned biomass raw materials exhibit higher initial coulombic efficiency, rate performance, and cycle stability. Further preferably, considering the potential to further improve the initial coulombic efficiency and cycle stability of the material, the biomass raw material is selected from at least one of palm shells, eucalyptus wood, and sugarcane bagasse.

[0041] Preferably, step S1 further includes: crushing, washing, and drying the biomass raw material before carbonization. Crushing the raw material before washing improves its flowability, increases its specific surface area, or provides more contactable reaction sites for subsequent acid or carbonization processes, which is beneficial for acid washing and carbonization. More preferably, the washing includes acid washing and water washing, wherein the acid used in the acid washing is selected from at least one of sulfuric acid, hydrochloric acid, and nitric acid. Using the above-mentioned acids in acid washing can remove ash (impurities such as metal ions, silicates, and carbonates) from the biomass raw material, providing high-quality raw materials for the preparation of biomass materials.

[0042] According to the present invention, the crushing in step S1 can be carried out by mechanical crushing, and the mechanical crushing can be carried out by a pulverizer. Drying can be carried out by any drying method, such as baking or air drying.

[0043] Preferably, the acid solution used in the pickling process has a molar concentration of 0.5-7 mol / L, and the solid-liquid ratio of the biomass raw material to the acid solution is 1:2-5 (g / mL).

[0044] Preferably, in step S1, the carbonization treatment I includes pre-oxidation followed by carbonization. More preferably, the pre-oxidation conditions include: a temperature of 250-450℃, which can be 250℃, 300℃, 350℃, 400℃, 450℃, or any value within any two of the above ranges; and a time of 0.5-2h, which can be 0.5h, 1h, 1.5h, 2h, or any value within any two of the above ranges. The carbonization treatment I conditions include: a temperature of 550-750℃, which can be 550℃, 600℃, 650℃, 700℃, 750℃, or any value within any two of the above ranges; and a time of 2-8h, which can be 2h, 4h, 6h, 8h, or any value within any two of the above ranges. During the low-temperature carbonization process, the oxygen-containing functional groups (such as carboxyl and carbonyl groups) introduced by pre-oxidation undergo cross-linking and aromatization reactions upon heating, forming stable "bridge bonds" at lower temperatures and constructing a robust network framework. Simultaneously, lignin, cellulose, hemicellulose, and oxygen-containing functional groups in the biomass material decompose and escape as small molecules such as CO, CO2, and H2O, "etching" numerous micropores and mesopores into the carbon framework, constructing a well-developed porous structure in the carbon material. This also allows for precise control of the heteroatom doping content of the carbon material, increasing its carbon content and further improving the specific capacity, initial coulombic efficiency, rate performance, and cycle stability of the subsequently prepared biomass material. More preferably, the pre-oxidation conditions include a temperature of 300-400℃ and a time of 0.5-1 h; the carbonization treatment I conditions include a temperature of 600-700℃ and a time of 4-6 h. This can reduce production costs while ensuring the stretching ratio of the biomass material.

[0045] According to the present invention, the pre-oxidation is carried out in an oxygen-containing atmosphere. Preferably, the heating rate to the pre-oxidation temperature is 1-5°C / min, and the heating rate to the carbonization temperature is 2-10°C / min.

[0046] Preferably, in step S2, the particle size of the particles obtained after crushing is ≤74μm. This can reduce agglomeration in subsequent processing and further improve the initial coulombic efficiency, rate performance, and cycle stability of the subsequently produced activated carbon material.

[0047] According to the present invention, the crushing in step S2 can be mechanical crushing and / or air jet crushing, as long as the particle size of the crushed particles is less than or equal to 74 μm. Preferably, the crushing step includes: mechanically crushing the intermediate carbon material to obtain particles with a particle size ≤ 1 mm, and then subjecting the particles to air jet crushing to obtain particles with a particle size ≤ 74 μm. Using the above method can reduce the proportion of long rod-shaped, block-shaped, or flaky particles, resulting in particles with a uniform particle size distribution and a more regular shape; it can also obtain micron-sized ultrafine powder with concentrated particle size distribution, good dispersibility, and minimal agglomeration.

[0048] Preferably, in step S2, the ball milling conditions include: a rotational speed of 250-400 rpm, which can be 250 rpm, 300 rpm, 350 rpm, 400 rpm, or any value within any two of the above ranges; and a time of 2-6 hours, which can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any value within any two of the above ranges. Under these conditions, the particle size of the carbon material can be further reduced, the sharp edges of irregular carbon particles can be smoothed, the particle shape gradually tends towards a spherical shape, and the disorder of the carbon particles can be increased while reducing the degree of graphitization, thereby improving energy storage characteristics.

[0049] Preferably, in step S2, the washing includes acid washing and water washing. The acid used for acid washing is selected from at least two of hydrofluoric acid, sulfuric acid, hydrochloric acid, and nitric acid. Acid washing with the above-mentioned acids can further remove residual inorganic antifouling impurities and metallic iron impurities introduced during processing from the carbon material. Water washing after acid washing can further rinse away soluble reaction products and also wash away residual acid.

[0050] Preferably, the acid solution used in step S2 has a molar concentration of 1-8 mol / L, and the solid-liquid ratio of the intermediate carbon material to the acid solution is 1:3-6 (g / mL).

[0051] Preferably, in step S3, the amount of the additive relative to 1g of the intermediate product I is 0.03-0.1g, which can be 0.03g, 0.04g, 0.05g, 0.06g, 0.07g, 0.08g, 0.09g, 0.1g, or any value within any two of the above ranges. Controlling the amount of additive within the above range can further improve the tensile properties and cycle stability of the subsequently obtained biomass material.

[0052] Preferably, in step S3, the additive is molasses and / or tall oil fatty acids. Biochar materials prepared by mixing molasses and / or tall oil fatty acids with char materials exhibit better tensile properties and cycle stability.

[0053] Preferably, in step S3, the mixing is carried out in a high-efficiency mixer for 3-10 minutes. This can overcome the segregation phenomenon that may occur due to the different densities and particle sizes of carbon powder and additives, ensure that the rheological behavior of the mixture is highly consistent, the material flowability is stable, and the stability of the subsequent granulation process is guaranteed. At the same time, the amount of additives is optimized and the cost is reduced.

[0054] Preferably, the granulation conditions include a pressure of 7.5-10 MPa, which can be 7.5 MPa, 8 MPa, 8.5 MPa, 9 MPa, 9.5 MPa, or 10 MPa. High-pressure molding ensures close contact between carbon powder particles, and through the action of additives, the macropores of the carbon material are compressed and filled, while simultaneously enhancing the micropore connectivity within the particles, optimizing the pore structure, balancing particle size and specific surface area, and improving the tap density.

[0055] Preferably, the particle size of the granulated particles is 1-3 mm, which provides an ideal precursor for subsequent high-temperature hard carbonization, simplifies the operation, and facilitates continuous production.

[0056] Preferably, the carbonization process II is carried out under vacuum or a protective gas.

[0057] Preferably, step S4 further includes: acid washing, drying, crushing, and demagnetizing the product obtained from carbonization treatment II. Acid washing can further remove impurities from the carbon material and reduce its ash content. Crushing ensures that the particle size and distribution of the carbon material meet the requirements for use. Demagnetization can be performed using commonly used demagnetization methods in the prior art to remove magnetic substances from the carbon material. Specifically, demagnetization is performed on an electromagnetic demagnetizer. More preferably, step S4 further includes: mixing the demagnetized product for 2-5 minutes to ensure uniform mixing and eliminate differences between carbon material particles through homogenization, thereby ensuring high consistency and reliability of the final product performance. More preferably, in step S4, the acid used for acid washing is selected from at least one of sulfuric acid, hydrochloric acid, and nitric acid.

[0058] Preferably, the crushing includes coarse crushing, fine crushing and air jet milling, and after crushing, the powder obtained after crushing is further subjected to sieving treatment. The sieving treatment is carried out on an ultrasonic vibrating screen with a screen mesh size of 500-1500 mesh.

[0059] Preferably, in step S5, the wrapping material can be asphalt and / or polyester.

[0060] Preferably, in step S5, the drying can be spray drying.

[0061] More preferably, in step S5, the conditions for carbonization treatment III include: a temperature of 650-850℃, which can be 650℃, 700℃, 750℃, 800℃, 850℃, or any value within any two of the above ranges; and a time of 2-4h, which can be 2h, 3h, 4h, or any value within any two of the above ranges. At this temperature, the surface-coated material can be transformed into a nanoscale amorphous carbon layer (soft carbon layer), achieving surface modification of the hard carbon material and forming a biochar anode material with a core-shell structure. Furthermore, the biochar material prepared by this method can provide a stable voltage plateau, exhibiting high specific capacity and high initial efficiency; it also possesses more active sites, providing rapid surface adsorption capacity, thereby improving the slope region capacity of the biochar material. The outer soft carbon layer can improve the conductivity of the biochar material and enhance its rate performance. The outer soft carbon layer forms a relatively uniform and dense surface, mitigating volume changes in the hard carbon core and reducing direct corrosion of the hard carbon core by the electrolyte. It also makes the SEI film formed on the material surface more uniform and stable, further improving the initial coulombic efficiency and long-cycle stability of the biochar material. Furthermore, although the soft carbon layer slightly increases the specific surface area of ​​the material, it fills the pores of the hard carbon material, especially mesopores and macropores, significantly reducing the specific surface area of ​​the hard carbon material. This ensures that additional capacity and rapid kinetics are provided without sacrificing the initial coulombic efficiency. It also contains more oxygen-containing functional groups, which helps improve the dispersibility of the electrode slurry, allowing the biochar material, conductive agent, and additives to bind more tightly, thereby reducing the electrode interfacial impedance.

[0062] Preferably, the heating rate of carbonization treatment III is 2-5℃ / min.

[0063] In step S5, the spheroidization process is carried out in a particle spheroidization device for a time of 5-10 minutes, which can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, or any value within any two of the above ranges. This process removes the irregular edges of the amorphous carbon layer, gradually making the particle shape more spherical, reducing the specific surface area and porosity, and obtaining spherical powder with a narrower and more uniform particle size distribution, thereby improving the rate performance and long-cycle stability of the material.

[0064] A third aspect of this invention provides the application of the above-described biochar material or the biochar material prepared by the above-described preparation method in sodium batteries, lead-carbon batteries, or lead-lithium batteries. The above-described biochar material exhibits good rate performance and long-cycle stability when applied to sodium batteries, lead-carbon batteries, or lead-lithium batteries.

[0065] The present invention will be described in detail below through examples. In the following examples, the phenolic resin and hydroxymethyl cellulose raw materials are commercially available products from Aladdin Company.

[0066] Example 1 (1) Using macadamia nut shells as raw materials, they are mechanically crushed, then acid washed (0.5 mol / L hydrochloric acid solution), washed with pure water and dried. They are then pre-oxidized at 3℃ / min to 300℃ for 2 hours to obtain intermediate pre-oxidized products. Then they are carbonized at 5℃ / min to 600℃ for 4 hours to obtain intermediate carbon materials. (2) After mechanically crushing the intermediate carbon material, particles with a particle size ≤1mm are obtained. Then, air jet milling is carried out to obtain particles with a particle size ≤74μm. The particles are ball-milled at 350rpm for 4h, and then acid-washed (a mixed solution of hydrofluoric acid, hydrochloric acid and nitric acid, with a volume ratio of concentrated hydrofluoric acid, concentrated hydrochloric acid, concentrated nitric acid and water of 6:40:1:500), washed with pure water and dried to obtain intermediate product I; (3) Mix 1 kg of intermediate product with 50 g of hydroxymethyl cellulose in a high-efficiency mixer for 6 min, granulate, and obtain intermediate product II.

[0067] (4) Heat intermediate product II to 700℃ at 5℃ / min and hold for 6 hours, then heat to 1400℃ and hold for 3 hours to obtain intermediate product III.

[0068] (5) Dissolve 80g of asphalt in 300mL of DMF solution, add 950g of intermediate product III and 3000mL of ethanol, and spray dry to obtain asphalt-coated carbon material. Then, heat the material to 750℃ at a heating rate of 5℃ / min and carbonize it for 3 hours to obtain carbon material. Finally, spheroidize and shape the material using a pelletizing device for 10 minutes to obtain biochar material. See the XRD pattern for details. Figure 1 .

[0069] Example 2 Biochar material was prepared according to the method of Example 1, except that in step (4), intermediate product III was heated to 700°C at 5°C / min and kept at 700°C for 6 hours, and then heated to 1500°C and kept at 1500°C for 2 hours.

[0070] Example 3 Biochar material was prepared according to the method of Example 1, except that macadamia nut shells were replaced with palm shells.

[0071] Example 4 Biochar materials were prepared according to the method of Example 1, except that macadamia nut shells were replaced with bamboo.

[0072] Example 5 Biochar materials were prepared according to the method of Example 1, except that macadamia nut shells were replaced with eucalyptus wood.

[0073] Example 6 Biochar material was prepared according to the method in Example 1, except that macadamia nut shells were replaced with sugarcane bagasse and pitch was replaced with phenolic resin. TEM images of the prepared biochar are shown below. Figure 5 As shown.

[0074] Example 7 Biochar material was prepared according to the method of Example 1, except that in step (4), intermediate product III was heated to 500°C at 5°C / min and kept at 5°C for 6 hours, and then heated to 1800°C and kept at 1 hour.

[0075] Example 8 Biochar materials were prepared according to the method of Example 1, except that hydroxymethyl cellulose was replaced with phenolic resin.

[0076] Example 9 Biochar materials were prepared according to the method of Example 1, except that hydroxymethyl cellulose was replaced with molasses.

[0077] Example 10 Biochar materials were prepared according to the method of Example 1, except that hydroxymethyl cellulose was replaced with tall oil fatty acids.

[0078] Example 11 Biochar was prepared according to the method of Example 1, except that in step (3), the amount of hydroxymethyl cellulose used was 30g; In step (5), the amount of asphalt used is 60g.

[0079] Example 12 Biochar was prepared according to the method of Example 1, except that in step (3), the amount of hydroxymethyl cellulose used was 100g; In step (5), the amount of asphalt used is 100g.

[0080] Comparative Example 1 Biochar material was prepared according to the method of Example 1, except that in step (4), intermediate product II was heated to 700°C at 5°C / min and kept at that temperature for 6 hours, and then heated to 1200°C and kept at that temperature for 4 hours.

[0081] Comparative Example 2 Biochar materials were prepared according to the method of Example 1, except that the biomass materials were not pre-oxidized in step (1).

[0082] Comparative Example 3 Biochar materials were prepared according to the method of Example 1, except that step (3) was not included.

[0083] Comparative Example 4 Biochar materials were prepared according to the method of Example 1, except that in step (5), spheroidizing and shaping treatment was not performed.

[0084] Comparative Example 5 Biochar was prepared according to the method of Example 1, except that ball milling was not performed in step (2).

[0085] Comparative Example 6 Biochar was prepared according to the method of Example 1, except that in step (4), intermediate product II was heated to 1300°C at 5°C / min and held for 6 hours.

[0086] Comparative Example 7 Biochar materials were prepared according to the method of Example 1, except that in step (5), intermediate product III was directly subjected to spheroidization and shaping treatment.

[0087] Test Example 1 XRD technology was used to analyze and calculate the interlayer spacing. d 002 Transmission electron microscopy was used to determine the thickness of the soft carbon layer and the radius of the hard carbon particles. Ten hard carbon particles (the largest, middle, and smallest) were selected, and their average value was used to calculate the particle radius. The thickness of the soft carbon layer was calculated by averaging the thicknesses of the largest, middle, and smallest hard carbon particles. Scanning electron microscopy was used to determine the radius of spherical or near-spherical hard carbon particles (the major semi-axis a and the minor semi-axis b) using the formula... Calculate the eccentricity and take its average value. The particle size distribution and median particle size D50 of the biochar were determined by laser diffraction, the specific surface area of ​​the biochar was determined by gas adsorption BET method, and the carbon content of the biochar was determined by combustion method. The mass of the biochar before ignition (m1) and the mass of the residue after ignition (m2) were weighed by high-temperature ignition. The ash content was calculated. The tap density of the biochar was determined using a tap density meter. All parameters are recorded in Table 1.

[0088] Using the biochar material prepared in the above examples or comparative examples as the negative electrode, and sodium sheet as the positive electrode, a sodium-ion button battery was assembled. The metallic sodium sheet was used as the counter electrode, Celgard 2400 polypropylene-based three-layer membrane was used as the battery separator, and 1 mol / L NaPF6 DME solution was used as the electrolyte. The sodium-ion battery was assembled in a glove box filled with argon gas and with strict control of the water vapor index.

[0089] After the assembled sodium-ion batteries were left to stand for 24 hours, charge-discharge tests were conducted using a LAND battery tester. The charge-discharge test voltage for the battery made from biochar material in Example 1 was 0-1.5V, and the current density was 30mA / g (0.1C), 300mA / g (1C), and 500mA / g (1.67C). The initial discharge specific capacity was calculated as initial discharge capacity / mass of biochar material, the initial charge specific capacity was calculated as initial charge capacity / mass of biochar material, and the initial coulombic efficiency was calculated as initial charge specific capacity / initial discharge specific capacity × 100%. The initial sodium storage specific capacity, initial coulombic efficiency, and cycle performance are recorded in Table 2. The charge-discharge curves of the battery made from biochar material in Example 1 are shown below. Figure 2 As shown, the charge-discharge curves of the battery made from the biochar material in Example 2 are as follows. Figure 3 As shown, the charge-discharge curves of the battery made from the biochar material in Example 5 are as follows. Figure 4 As shown, the charge-discharge curves of the battery made from the biochar material in Example 10 are as follows. Figure 6 As shown, the charge-discharge curves of the battery made from the biochar material in Example 12 are as follows. Figure 7 As shown.

[0090] Table 1

[0091] Table 2

[0092] The results in Tables 1 and 2 show that the ratio of the thickness of the soft carbon layer to the radius of the hard carbon microspheres in the examples is within the range of 1:250-930, and the specific surface area of ​​the biochar material is ≤5.5m². 2 / g, median particle size D50 is 3.5-9μm, interlayer spacing d 002 With a wavelength of 0.37-0.39 nm and an eccentricity of less than 0.3, the initial sodium storage capacity of the embodiment is higher than that of Comparative Examples 1 and 2, and the initial coulombic efficiency and cycle efficiency are both better than those of Comparative Examples 1 to 7. This indicates that the biochar material provided by the present invention has high sphericity, initial sodium storage capacity, high initial coulombic efficiency, excellent rate performance and cycle stability.

[0093] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A biochar material, characterized in that, The biochar material comprises hard carbon microspheres and a soft carbon layer surrounding the hard carbon microspheres. The ratio of the thickness of the soft carbon layer to the radius of the hard carbon microspheres is 1:250-930, and the specific surface area of ​​the biochar material is ≤5.5 m². 2 / g, median particle size D50 is 3.5-9μm, interlayer spacing d 002 The wavelength is 0.37-0.39 nm and the eccentricity is less than 0.

3.

2. The biochar material according to claim 1, characterized in that, The ratio of the thickness of the soft carbon layer to the radius of the hard carbon microspheres is 1:600-750, and the specific surface area of ​​the biochar material is 4.5-5.5 m². 2 / g, eccentricity rate is 0.27-0.29; Preferably, the carbon content of the hard carbon microspheres is ≥99.2 wt%, and the ash content is ≤1.0 wt%. Preferably, the tap density of the biochar material is ≥0.85 g / cm³. 3 .

3. A method for preparing biochar material as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: S1. The biomass raw material is pre-oxidized and then carbonized to obtain intermediate carbon material; S2. The intermediate carbon material is crushed and then ball-milled and washed to obtain intermediate product I. S3. Mix the intermediate product I with the additive and granulate to obtain intermediate product II; The additive is selected from at least one of phenolic resin, polyvinyl alcohol, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, molasses, tall oil fatty acids, and starch; S4. The intermediate product is subjected to carbonization treatment II to obtain intermediate product III; The carbonization treatment II includes a first carbonization treatment and a second carbonization treatment. The conditions for the first carbonization treatment include: a temperature of 500-700℃ and a time of 3-6 hours; The conditions for the second carbonization treatment include: a temperature of 1300-1800℃ and a time of 1-6 hours; S5. The solution containing the encapsulating material and the intermediate product III are mixed, dried, and then subjected to carbonization treatment III, followed by spheroidizing and shaping treatment. The mass ratio of the packaging material to the intermediate product III is 1:9.5-16.

4. The preparation method according to claim 3, characterized in that, The biomass raw material is selected from at least one of macadamia nut shells, palm shells, eucalyptus wood, bamboo, and sugarcane bagasse, preferably at least one of palm shells, eucalyptus wood, and sugarcane bagasse; and / or, Step S1 further includes: before carbonizing the biomass raw material, crushing, washing and drying the biomass raw material; Preferably, the washing includes acid washing and water washing; The acid used in the pickling is selected from at least one of sulfuric acid, hydrochloric acid, and nitric acid.

5. The preparation method according to claim 3, characterized in that, In step S1, the pre-oxidation conditions include: a temperature of 250-450℃ and a time of 0.5-2h; The conditions for the carbonization treatment I include: a temperature of 550-750℃ and a time of 2-8h; Preferably, the pre-oxidation conditions include: a temperature of 300-400℃ and a time of 0.5-1h; The conditions for the carbonization treatment I include: a temperature of 600-700℃ and a time of 4-6 hours.

6. The preparation method according to claim 3, characterized in that, In step S2, the particle size of the particles obtained after crushing is ≤74μm; Preferably, the ball milling conditions include: a rotational speed of 250-400 rpm and a time of 2-6 hours; and / or, The washing process includes acid washing and water washing, wherein the acid used for acid washing is selected from at least two of hydrofluoric acid, sulfuric acid, hydrochloric acid and nitric acid.

7. The preparation method according to any one of claims 3 to 6, characterized in that, In step S3, the amount of the additive is 0.03-0.1g relative to 1g of the intermediate product I; and / or, The additive is molasses and / or tall oil fatty acids.

8. The preparation method according to any one of claims 3 to 6, characterized in that, Step S4 also includes: acid washing, drying, crushing and demagnetizing the product obtained from carbonization treatment II; Preferably, the acid used in the pickling is selected from at least one of sulfuric acid, hydrochloric acid, and nitric acid.

9. The preparation method according to any one of claims 3 to 6, characterized in that, In step S5, the conditions for carbonization treatment III include: a temperature of 650-850℃ and a time of 2-4 hours; and / or, The spheroidizing process is carried out in a particle spheroidizing device for 5-10 minutes.

10. The application of the biochar material according to any one of claims 1-2 or the biochar material prepared by the preparation method according to any one of claims 3 to 9 in sodium batteries, lead-carbon batteries or lead-lithium batteries.

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