Biological waste-based hard carbon material as well as preparation method and application thereof

Abstract

The invention relates to a biological waste-based hard carbon material as well as a preparation method and application thereof. The preparation method of the biological waste-based hard carbon material comprises the following steps: (1) pretreating biological wastes to obtain pre-carbonized powder; (2) adding polyvinylpyrrolidone and thiourea into the pre-carbonized powder, and crushing; and (3) carrying out high-temperature reaction at 250 DEG C or above to obtain the biological waste-based hard carbon material. According to the technical scheme provided by the invention, the fact that the pyrolysis gas generation characteristic of polyvinylpyrrolidone and the heteroatom doping function of thiourea have the effective treatment characteristic on bio-based carbonization is found for the first time. Because the decomposition temperatures of polyvinylpyrrolidone and thiourea are different, a unique hierarchical pore structure is formed in the material, and meanwhile, a C-S-N bond is formed through a chemical bond to optimize an electron energy band structure of hard carbon, so that the conductivity of the material is remarkably improved, and the sodium storage performance of the hard carbon material is greatly optimized.

Description

Technical Field

[0001] The present invention belongs to the field of ion battery materials, and relates to a bio-waste-based hard carbon material, a preparation method thereof, and an application thereof. Background Art

[0002] Under the trend of accelerating the global layout of sustainable energy and the development of smart grids, sodium-ion batteries have become a research hotspot in the field of electrochemical energy storage due to the advantages of rich sodium resources, low cost, and high safety. However, the performance of its negative electrode materials still faces challenges: traditional graphite cannot effectively embed sodium ions (Na + (radius 0.102nm)) due to its narrow interlayer spacing (about 0.335nm), while hard carbon materials, with disordered carbon layer stacking (interlayer spacing > 0.37nm), rich micropores, and defect structures, have become ideal negative electrode candidate materials for sodium-ion batteries. However, the actual performance of existing hard carbon materials (such as specific capacity, cycle life, rate performance) is still limited by problems such as insufficient specific surface area and low powder conductivity, and technical breakthroughs are urgently needed.

[0003] In recent years, significant progress has been made in the research on preparing hard carbon using bio-wastes (such as fruit shells, straw, etc.) as precursors, and the main technical routes include:

[0004] 1. Directional carbonization of fruit shell raw materials

[0005] For example: The hard carbon material disclosed in the Chinese patent with the publication number CN111564630A is prepared by subjecting orange peel to hydrothermal reaction (150 - 180°C) combined with pre-carbonization (200 - 300°C) and high-temperature pyrolysis (in an inert atmosphere) to obtain a hard carbon material with uniform particle size.

[0006] 2. Development of a general process for multi-source biomass

[0007] The Chinese patent with the publication number CN119079977A proposes a general method for preparing hard carbon materials. The biomass raw material is treated and soaked in a strong alkali KOH solution to destroy the organic molecules in the biomass raw material to obtain a biomass raw material; the treated biomass raw material is placed in a tubular furnace under a nitrogen atmosphere, heated from room temperature to 200°C, and then preheated at 200°C in an inert atmosphere for 2 hours to dehydrate and soften the material; following the end of preheating and dehydration, the tubular furnace is heated to 1200°C and held for 2 hours, and after the holding ends, it is naturally cooled to obtain the hard carbon material.

[0008] 3. Enzymatic hydrolysis-assisted structure regulation

[0009] The Chinese patent with the publication number CN116477604A proposes a preparation method of hard carbon materials, which includes: (I) enzymatically hydrolyzing a polysaccharide with multiple branched chains under the action of an enzyme, and performing the first sintering and then pulverizing to obtain a precursor; (II) mixing the precursor with an ammonium salt solution, drying, and performing the second sintering to obtain a fired material; (III) carbonizing the fired material.

[0010] Although progress has been made in the research of biomass-based hard carbon materials, there are still significant bottlenecks in the optimization of their mechanical properties under different application scenarios.

[0011] For example: Outdoor portable power supplies need to achieve high energy output under the conditions of light weight and small volume, and at the same time support fast charging and discharging (such as 1-3C rate), which requires the biomass-based hard carbon materials in sodium-ion batteries to balance the active sites and interface stability, and consider the cost and volume problems brought by the introduction of additives.

[0012] Another example: Home energy storage systems need to withstand daily charging and discharging (>5000 cycles) and operate stably in environments such as high temperature (solar energy). The requirements for sodium-ion batteries focus on the inhibition effect of materials on electrolyte decomposition and the interface impedance problem of the external coating layer.

[0013] In addition, the power supply of emergency rescue equipment needs to maintain stable output at extreme temperatures (-20°C to 60°C) and still be able to be used immediately after long-term storage. This requires the biomass-based hard carbon materials in sodium-ion batteries to have temperature sensitivity and maintain the balance of conductivity and self-discharge.

[0014] It can be said that for the optimization of the mechanical properties of biomass-based hard carbon materials, considering the needs of application scenarios and the uncertainty of performance optimization, it is necessary to break away from the R & D path of "maximizing a single performance", and instead focus on the core pain points of application scenarios, and achieve precise parameter matching through the collaborative design of structure-performance-process. For example, outdoor power supplies need to balance specific surface area and conductivity, home energy storage needs to give priority to inhibiting side reactions, and emergency equipment needs to overcome the stability contradiction in a wide temperature range.

[0015] In addition, on the one hand, there are differences in the understanding of those skilled in the art; on the other hand, although the inventor studied a large number of literatures and patents when making this invention, all details and contents are not listed in detail due to space limitations. However, this does not mean that this invention does not have the features of these prior arts. On the contrary, this invention already has all the features of the prior arts, and the applicant reserves the right to add relevant prior arts in the background art. Summary of the Invention

[0016] Based on the above technical problems, the present invention relates to a preparation method of a bio-waste-based hard carbon material, which includes the following steps:

[0017] (1) Pretreatment of biological waste to obtain pre-carbonized powder;

[0018] (2) Add polyvinylpyrrolidone and thiourea to the pre-carbonized powder and pulverize;

[0019] (3) React at a high temperature above 250 °C to obtain a biological waste-based hard carbon material.

[0020] According to a preferred embodiment, the preparation method of the biological waste-based hard carbon material comprises the following steps: Add 1 to 50 parts of polyvinylpyrrolidone and 1 to 50 parts of thiourea to 100 parts of pre-carbonized powder by weight. Preferably, the mass ratio of the pre-carbonized powder to polyvinylpyrrolidone is 100:1 to 50. The mass ratio of the pre-carbonized powder to thiourea is 100:1 to 50.

[0021] Preferably, the weight ratio of the pre-carbonized powder, polyvinylpyrrolidone and thiourea is 10:1:2. The weight ratio of the pre-carbonized powder, polyvinylpyrrolidone and thiourea is 20:1:2. The weight ratio of the pre-carbonized powder, polyvinylpyrrolidone and thiourea is 20:3:6.

[0022] According to a preferred embodiment, the "pretreatment of biological waste" includes the following steps:

[0023] Treat the biological waste at a temperature of ≥600 °C and <1000 °C;

[0024] Pickle and remove impurities at a temperature of ≥80 °C and <100 °C.

[0025] Preferably, the "pretreatment of biological waste" includes the following steps:

[0026] Heat up to 600 °C at a heating rate of 5 °C / min and keep warm for 1 h.

[0027] According to a preferred embodiment, the "pretreatment of biological waste" includes the following steps:

[0028] S1: Perform pre-carbonization treatment on the biological waste, and then pulverize it to obtain refined pre-carbonized powder;

[0029] S2: Perform pickling treatment on the pre-carbonized powder of S1 to remove impurities, and then perform drying.

[0030] Preferably, the pre-carbonization temperature is 500 - 600 °C. The carbonization time is 1 - 2 h. The particle size of the refined pre-carbonized powder is 1 - 5 mm.

[0031] According to a preferred embodiment, the preparation method of the biological waste-based hard carbon material further comprises the following steps:

[0032] Ball-mill the pre-carbonized powder mixed with polyvinylpyrrolidone and thiourea.

[0033] Preferably, the ball milling time is 0.5 to 3 h.

[0034] According to a preferred embodiment, the "high-temperature reaction above 250°C" further includes the following steps:

[0035] Performing carbonization treatment of the high-temperature reaction above 250°C under a protective atmosphere.

[0036] Preferably, the protective atmosphere is one of nitrogen or argon.

[0037] According to a preferred embodiment, the acidic reagent used for "pickling and impurity removal" is selected from one or more of hydrochloric acid, hydrofluoric acid, and sulfuric acid.

[0038] Preferably, "pickling and impurity removal" is carried out using hydrochloric acid. The concentration of hydrochloric acid is 1 to 5 mol / L. The pickling temperature is 60 to 100°C. The pickling time is 3 to 12 h.

[0039] According to a preferred embodiment, the "high-temperature reaction above 250°C" includes the following steps:

[0040] Performing heat preservation treatment at a temperature of ≥250°C and <350°C for 1 to 3 h;

[0041] Performing heat preservation treatment at a temperature of ≥350°C and <1400°C for 1 to 3 h;

[0042] Performing heat preservation treatment at a temperature of ≥1300°C and <1500°C for 1 to 3 h.

[0043] According to a preferred embodiment, the "high-temperature reaction above 250°C" includes the following steps:

[0044] Maintaining the temperature at 250°C for 2 h;

[0045] The heat preservation time at 350°C is 2 h;

[0046] The heat preservation time at 1400°C is 3 h.

[0047] Preferably, the "high-temperature reaction above 250°C" includes the following steps:

[0048] Heating to 250°C at a heating rate of 5°C / min and maintaining the temperature for 1 to 3 h;

[0049] Heating to 350°C at a heating rate of 5°C / min and the heat preservation time is 1 to 3 h;

[0050] Finally, heating to 1300 - 1500°C at a heating rate of 1 - 3°C / min.

[0051] The cooling method is natural cooling.

[0052] More preferably, the "high-temperature reaction above 250°C" includes the following steps:

[0053] Heat up to 250 °C at a heating rate of 5 °C / min and keep the temperature for 2 h;

[0054] Heat up to 350 °C at a heating rate of 5 °C / min and keep the temperature for 2 h;

[0055] Heat up to 1400 °C at a heating rate of 2 °C / min and keep the temperature for 3 h.

[0056] According to a preferred embodiment, the biological waste is selected from one or more of bagasse, straw, wood chips, fruit shells, and rice husks.

[0057] On the other hand, the present invention relates to a hard carbon material prepared based on the preparation method disclosed in the present invention, and its specific surface area and conductivity are selected from the following groups:

[0058] (1) The specific surface area is 16.2 m 2 / g and the conductivity is 28.3 S / cm;

[0059] (2) The specific surface area is 9.8 m 2 / g and the conductivity is 16.5 S / cm.

[0060] According to a preferred embodiment, the carbon layer spacing is 0.372 - 0.379 nm. Preferably, the carbon layer spacing is 0.376 nm.

[0061] On the other hand, the present invention relates to the application of the hard carbon material disclosed in the present invention or the hard carbon material prepared based on the preparation method disclosed in the present invention in a sodium ion battery or the negative electrode of a sodium ion battery.

[0062] The technical solution provided by the present invention first discovers that the pyrolysis gas generation characteristics of polyvinylpyrrolidone and the heteroatom doping function of thiourea have effective treatment characteristics for biobased carbonization. Due to the different decomposition temperatures of polyvinylpyrrolidone and thiourea, a unique hierarchical pore structure is formed inside the material. At the same time, the C-S-N bond is formed through chemical bonds to optimize the electronic energy band structure of the hard carbon, significantly improving the conductivity of the material and greatly optimizing the sodium storage performance of the hard carbon material.

[0063] Specifically, the instantaneous high-pressure gas generated by the decomposition of polyvinylpyrrolidone not only promotes pore formation but also drives the uniform dispersion of the decomposition products of thiourea in the carbon matrix. This dynamic coupling effect breaks through the limitations of traditional static doping. In the prior art, pore formers (such as KOH) and dopants (such as sulfur powder) usually need to be treated step by step, while the molecular-level precursor compatibility of the present invention synchronously completes the triple functions of pore formation, doping, and structural ordering in a single pyrolysis process.

[0064] 1. The technical solution of the present invention adopts the composite combination of polyvinylpyrrolidone and thiourea to achieve the dual-functional coupling of the chemical treatment of bio-carbonized materials. During the gradient pyrolysis process of polyvinylpyrrolidone at 250-1500 °C, the breaking of its molecular chains generates oxidizing gases such as CO and CO2, triggering the micro-etching effect and forming three-dimensional through-pores with pore sizes distributed from 2 to 50 nm; the S and N elements generated by the decomposition of thiourea are embedded in the carbon skeleton in an atomic doping manner to form a C-S-N covalent bond network; the relevant experimental results prove (Examples 1 and 7) that through this atomic doping method, the conductivity of the material can be greatly improved (from 10.2 S / cm to 28.3 S / cm), and the S / N co-doping sites significantly improve the chemical adsorption energy of sodium ions (the adsorption energy is increased from -1.2 eV to -2.5 eV, which is significantly better than the single doping system).

[0065] 2. The stepwise temperature-rising process (250 °C → 350 °C → 1400 °C) innovatively designed in the technical solution of the present invention precisely matches the release rate of the decomposition gas of polyvinylpyrrolidone with the carbon skeleton reconstruction process by regulating the pyrolysis kinetics in stages. Through gradient-assisted pyrolysis, this process condition can induce the graphite microcrystals of the material to be oriented along the ( Figure 1 002) crystal plane in the [], expanding the layer spacing to 0.376 nm, which is significantly improved compared with the conventional carbonization process (0.365 nm), providing an ideal diffusion channel for the rapid insertion of sodium ions.

[0066] 3. Based on the stepwise temperature-rising process and the specific combination of the reaction composition, the dual-mode pore structure of the hard carbon material (micropores provide sodium storage sites, and mesopores construct ion pathways) enables the specific surface area to reach 16.2 m 2 / g while maintaining a closed pore rate of about 25.7% (the relative amount in the pore structure), successfully cracking the negative impact of high specific surface area on the first efficiency. In addition, based on the microscopic phenomenon that the S / N co-doping forms a local polarization electric field and reduces the surface adsorption energy barrier of sodium ions, the sodium-ion battery using this material achieves a high first efficiency of 87.5% and a reversible capacity of 336.4 mAh / g. Description of the Drawings

[0067] Figure 1 XRD pattern of the hard carbon negative electrode material related to Example 1 of the present invention;

[0068] Figure 2 First-cycle charge-discharge performance diagrams of the hard carbon negative electrode materials related to Examples 1 and 7 of the present invention;

[0069] Figure 3 0.1C cycling performance diagrams of the hard carbon negative electrode materials related to Examples 1 and 7 of the present invention. Detailed Description of the Invention

[0070] In the description of the present invention, the terms are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. In the description of the present invention, the meaning of "a plurality" is two or more, unless otherwise specifically defined.

[0071] Example 1

[0072] This example provides a method for preparing a bio-waste-based hard carbon material. The preparation method includes the following steps:

[0073] S1: Place 40 g of fruit shells in a tube furnace, heat them at a heating rate of 5 °C / min to 600 °C, keep them at a constant temperature for 1 h to obtain a pre-carbonized material, and crush the pre-carbonized material to obtain a refined powder;

[0074] S2: Treat the pre-carbonized powder obtained in S1 with 3 mol / L hydrochloric acid at 80 °C for pickling to remove impurities. The pickling time is 6 h, and then put it into an oven for drying;

[0075] S3: Add 2 g of polyvinylpyrrolidone and 4 g of thiourea to 20 g of the pre-carbonized powder after pickling treatment in S2, and then carry out ball milling treatment. The ball-to-material ratio is 5:1, and the ball milling time is 1 h to obtain a mixture;

[0076] S4: Place the mixture after ball milling in S3 in a tube furnace. The protective atmosphere is argon. First, heat it at a heating rate of 5 °C / min to 250 °C and keep it at a constant temperature for 2 h, then heat it at a heating rate of 5 °C / min to 350 °C and keep it at a constant temperature for 2 h, and finally heat it at a heating rate of 2 °C / min to 1400 °C and keep it at a constant temperature for 3 h. The cooling method is natural cooling to obtain a hard carbon material.

[0077] Example 2

[0078] This example provides a method for preparing a bio-waste-based hard carbon material. The preparation method includes the following steps:

[0079] S1: Place 40 g of fruit shells in a tube furnace, heat them at a heating rate of 5 °C / min to 600 °C, keep them at a constant temperature for 1 h to obtain a pre-carbonized material, and crush the pre-carbonized material to obtain a refined powder;

[0080] S2: Treat the pre-carbonized powder obtained in S1 with 3 mol / L hydrochloric acid at 80 °C for pickling to remove impurities. The pickling time is 6 h, and then put it into an oven for drying;

[0081] S3: Add 1 g of polyvinylpyrrolidone and 2 g of thiourea to 20 g of the pre-carbonized powder after pickling treatment in S2, and then carry out ball milling treatment. The ball-to-material ratio is 5:1, and the ball milling time is 1 h to obtain a mixture;

[0082] S4: Place the mixture after ball milling in S3 into a tube furnace. The protective atmosphere is argon. First, heat it to 250 °C at a heating rate of 5 °C / min and hold for 2 h. Then, heat it to 350 °C at a heating rate of 5 °C / min and hold for 2 h. Finally, heat it to 1400 °C at a heating rate of 2 °C / min and hold for 3 h. The cooling method is natural cooling to obtain the hard carbon material.

[0083] Example 3

[0084] This example provides a method for preparing a hard carbon material based on biological waste. The preparation method includes the following steps:

[0085] S1: Place 40 g of fruit shells in a tube furnace and heat it to 600 °C at a heating rate of 5 °C / min. After holding for 1 h, obtain the pre-carbonized material. Crush the pre-carbonized material to obtain a refined powder.

[0086] S2: Perform pickling treatment on the pre-carbonized powder in S1 with 3 mol / L hydrochloric acid at 80 °C to remove impurities. The pickling time is 6 h, and then put it into an oven for drying.

[0087] S3: Add 3 g of polyvinylpyrrolidone and 6 g of thiourea to 20 g of the pre-carbonized powder after pickling treatment in S2, and then perform ball milling. The ball-to-material ratio is 5:1, and the ball milling time is 1 h to obtain a mixture.

[0088] S4: Place the mixture after ball milling in S3 into a tube furnace. The protective atmosphere is argon. First, heat it to 250 °C at a heating rate of 5 °C / min and hold for 2 h. Then, heat it to 350 °C at a heating rate of 5 °C / min and hold for 2 h. Finally, heat it to 1400 °C at a heating rate of 2 °C / min and hold for 3 h. The cooling method is natural cooling to obtain the hard carbon material.

[0089] Example 4

[0090] This example provides a method for preparing a hard carbon material based on biological waste. The preparation method includes the following steps:

[0091] S1: Place 40 g of fruit shells in a tube furnace and heat it to 600 °C at a heating rate of 5 °C / min. After holding for 1 h, obtain the pre-carbonized material. Crush the pre-carbonized material to obtain a refined powder.

[0092] S2: Perform pickling treatment on the pre-carbonized powder in S1 with 3 mol / L hydrochloric acid at 80 °C to remove impurities. The pickling time is 6 h, and then put it into an oven for drying.

[0093] S3: Add 2 g of polyvinylpyrrolidone to 20 g of the pre-carbonized powder after pickling treatment in S2, and then perform ball milling. The ball-to-material ratio is 5:1, and the ball milling time is 1 h to obtain a mixture.

[0094] S4: Place the mixture after ball milling in S3 into a tubular furnace. The protective atmosphere is argon. Heat it to 350 °C at a heating rate of 5 °C / min and hold for 2 h. Finally, heat it to 1400 °C at a heating rate of 2 °C / min and hold for 3 h. The cooling method is natural cooling to obtain the hard carbon material.

[0095] Example 5

[0096] According to the electrolysis steps in Example 2 and using the electrolysis equipment disclosed in Example 3, perform three rounds of electrolysis. This example provides a method for preparing a bio-waste-based hard carbon material. The preparation method includes the following steps:

[0097] S1: Place 40 g of fruit shells in a tubular furnace. Heat it to 600 °C at a heating rate of 5 °C / min. After holding for 1 h, obtain the pre-carbonized material. Crush the pre-carbonized material to obtain a refined powder.

[0098] S2: Perform pickling treatment on the pre-carbonized powder in S1 with 3 mol / L hydrochloric acid at 80 °C to remove impurities. The pickling time is 6 h, and then put it into an oven for drying.

[0099] S3: Add 4 g of thiourea to 20 g of the pre-carbonized powder after pickling treatment in S2, and then perform ball milling. The ball-to-material ratio is 5:1, and the ball milling time is 1 h to obtain a mixture.

[0100] S4: Place the mixture after ball milling in S3 into a tubular furnace. The protective atmosphere is argon. First, heat it to 250 °C at a heating rate of 5 °C / min and hold for 2 h. Finally, heat it to 1400 °C at a heating rate of 2 °C / min and hold for 3 h. The cooling method is natural cooling to obtain the hard carbon material.

[0101] Example 6

[0102] This example provides a method for preparing a bio-waste-based hard carbon material. The preparation method includes the following steps:

[0103] S1: Place 40 g of wood chips in a tubular furnace. Heat it to 600 °C at a heating rate of 5 °C / min. After holding for 1 h, obtain the pre-carbonized material. Crush the pre-carbonized material to obtain a refined powder.

[0104] S2: Perform pickling treatment on the pre-carbonized powder in S1 with 3 mol / L hydrochloric acid at 80 °C to remove impurities. The pickling time is 6 h, and then put it into an oven for drying.

[0105] S3: Add 2 g of polyvinylpyrrolidone and 4 g of thiourea to 20 g of the pre-carbonized powder after pickling treatment in S2, and then perform ball milling. The ball-to-material ratio is 5:1, and the ball milling time is 1 h to obtain a mixture.

[0106] S4: Place the mixture after ball milling in S3 into a tubular furnace. The protective atmosphere is argon. First, heat it to 250 °C at a heating rate of 5 °C / min and hold for 2 h. Then, heat it to 350 °C at a heating rate of 5 °C / min and hold for 2 h. Finally, heat it to 1400 °C at a heating rate of 2 °C / min and hold for 3 h. The cooling method is natural cooling to obtain the hard carbon material.

[0107] Example 7

[0108] This example provides a method for preparing a hard carbon material based on biological waste. The preparation method includes the following steps:

[0109] S1: Place 40 g of fruit shells in a tubular furnace and heat it to 600 °C at a heating rate of 5 °C / min. After holding for 1 h, obtain the pre-carbonized material, and crush the pre-carbonized material to obtain a refined powder;

[0110] S2: Perform pickling treatment on the pre-carbonized powder in S1 with 3 mol / L hydrochloric acid at 80 °C to remove impurities. The pickling time is 6 h, and then put it into an oven for drying;

[0111] S3: Perform ball milling on 20 g of the pre-carbonized powder after pickling treatment in S2. The ball-to-material ratio is 5:1, and the ball milling time is 1 h to obtain the precursor material;

[0112] S4: Place the precursor material after ball milling in S3 into a tubular furnace. The protective atmosphere is argon. Heat it to 1400 °C at a heating rate of 2 °C / min and hold for 3 h. The cooling method is natural cooling to obtain the hard carbon material.

[0113] Example 8

[0114] This example provides a method for preparing a hard carbon material based on biological waste. The preparation method includes the following steps:

[0115] S1: Place 40 g of fruit shells in a tubular furnace and heat it to 600 °C at a heating rate of 5 °C / min. After holding for 1 h, obtain the pre-carbonized material, and crush the pre-carbonized material to obtain a refined powder;

[0116] S2: Perform pickling treatment on the pre-carbonized powder in S1 with 3 mol / L hydrochloric acid at 80 °C to remove impurities. The pickling time is 6 h, and then put it into an oven for drying;

[0117] S3: Add 1 g of polyvinylpyrrolidone and 1 g of thiourea to 20 g of the pre-carbonized powder after pickling treatment in S2, and then perform ball milling. The ball-to-material ratio is 5:1, and the ball milling time is 1 h to obtain a mixture;

[0118] S4: Place the mixture after ball milling in S3 into a tubular furnace. The protective atmosphere is argon. First, heat it to 250 °C at a heating rate of 5 °C / min and hold for 2 h. Then, heat it to 350 °C at a heating rate of 5 °C / min and hold for 2 h. Finally, heat it to 1400 °C at a heating rate of 2 °C / min and hold for 3 h. The cooling method is natural cooling to obtain the hard carbon material.

[0119] Example 9

[0120] This example provides a method for preparing a hard carbon material based on biological waste. The preparation method includes the following steps:

[0121] S1: Place 40 g of fruit shells in a tubular furnace and heat it to 600 °C at a heating rate of 5 °C / min. After holding for 1 h, obtain the pre-carbonized material, and crush the pre-carbonized material to obtain a refined powder.

[0122] S2: Perform pickling treatment on the pre-carbonized powder in S1 with 3 mol / L hydrochloric acid at 80 °C to remove impurities. The pickling time is 6 h, and then put it into an oven for drying.

[0123] S3: Add 6 g of polyvinylpyrrolidone and 2 g of thiourea to 20 g of the pre-carbonized powder after pickling treatment in S2, and then perform ball milling. The ball-to-material ratio is 5:1, and the ball milling time is 1 h to obtain a mixture.

[0124] S4: Place the mixture after ball milling in S3 into a tubular furnace. The protective atmosphere is argon. First, heat it to 250 °C at a heating rate of 5 °C / min and hold for 2 h. Then, heat it to 350 °C at a heating rate of 5 °C / min and hold for 2 h. Finally, heat it to 1400 °C at a heating rate of 2 °C / min and hold for 3 h. The cooling method is natural cooling to obtain the hard carbon material.

[0125] Example 10

[0126] In this example, the hard carbon materials prepared in the previous Examples 1 - 7 will be tested for corresponding parameters based on the following method.

[0127] 1. Preparation of the negative electrode plate of the sodium-ion battery

[0128] Accurately weigh each component by mass percentage: hard carbon active material (93.5%), conductive carbon black (Super P, 2%), sodium carboxymethyl cellulose (CMC, 1.5%), and styrene-butadiene rubber (SBR, 3%). Add deionized water step by step to adjust the solid content to 40%-50%. Use a planetary mixer to disperse at a high speed of 2000 rpm for 30 minutes, and then switch to a low speed of 500 rpm to stir for 2 hours to remove air bubbles, obtaining a uniform and stable viscous slurry. Select 16μm thick aluminum foil as the current collector, and use an automatic coater to uniformly coat the slurry on the surface of the aluminum foil with a wet film thickness of 100μm. Transfer to a blast drying oven for gradient temperature rise treatment: initially dry at 70°C for 4h to remove free water, and then raise the temperature to 110°C and maintain for 8 hours to completely remove bound water. After drying, the electrode sheet is compacted by a pair of rollers to a compaction density (1.0-1.1g / cm 3 ) that can be controlled. Use a precision mold to punch the dried electrode sheet into a standard circular sheet with a diameter of Φ14mm. The electrode sheet is immediately transferred to an argon atmosphere glove box (H2O / O2 <0.1ppm) for storage to avoid moisture absorption side reactions.

[0129] 2. Assembly of Sodium-Ion Batteries

[0130] The battery is assembled inside a glove box filled with an argon atmosphere. Use the prepared hard carbon material electrode sheet as the negative electrode, commercial electrolyte 1.0mol / L NaPF6 / EC:DMC (1:1) (V:V) as the electrolyte, Na metal sheet as the counter electrode, and glass fiber GF / D as the separator to assemble a CR2032 coin cell.

[0131] 3. Electrochemical Performance Testing

[0132] Specifically: in the voltage range of 0.001-2.5V and at a current density of 0.1C (30mAh / g), the first discharge specific capacity (mAh / g) and the first charge specific capacity (mAh / g) are measured, and the first Coulomb efficiency is calculated.

[0133] 4. Measurement of Specific Surface Area and Conductivity

[0134] The specific surface area of the test example is measured in accordance with the national standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-Ion Batteries", and the powder conductivity is measured using a four-probe method.

[0135] Figure 1 The X-ray diffraction (XRD) pattern shows the crystal structure of the hard carbon material prepared in Example 1. According to Figure 1 As shown, by fitting the (002) peak plane, the 002 peak is located at 23.7°, and the layer spacing of the hard carbon is about 0.376nm. This value indicates that the material is more suitable for high-capacity sodium-ion battery applications.

[0136] The parameters of the hard carbon materials prepared in Examples 1 to 7 are shown in Table 1 below, Figure 2 and Figure 3 as shown.

[0137] Table 1

[0138]

[0139] For the hard carbon material prepared in Example 1, the initial charge specific capacity is 336.4 mAh / g, the initial discharge specific capacity reaches 384.4 mAh / g, and the initial Coulombic efficiency is 87.5%. In addition, this material has a relatively large specific surface area, with a value of 16.2 m 2 / g, and at the same time, the powder conductivity is relatively high, being 28.3 S / cm.

[0140] For the hard carbon material in Example 2, the initial charge specific capacity and the initial discharge specific capacity are 321.8 mAh / g and 370.3 mAh / g respectively, and the initial Coulombic efficiency is 86.9%. Its specific surface area is relatively small, being 9.8 m 2 / g, while the powder conductivity is 16.5 S / cm, showing its performance characteristics in different aspects.

[0141] For Example 3, the initial charge specific capacity of this hard carbon material is 329.7 mAh / g, the initial discharge specific capacity reaches 386.5 mAh / g, and the initial Coulombic efficiency is 85.3%. This material has a relatively high specific surface area, with a value of 18.4 m 2 / g, and the powder conductivity is as high as 32.1 S / cm, indicating its high efficiency in electrochemical reactions.

[0142] For the hard carbon material prepared in Example 4, the initial charge specific capacity and the initial discharge specific capacity are 298.6 mAh / g and 342.4 mAh / g respectively, and the initial Coulombic efficiency is 87.2%. The specific surface area of this material is only 8.8 m 2 / g, and the powder conductivity is 16.7 S / cm.

[0143] In Example 5, the initial charge specific capacity of the hard carbon material is 293.7 mAhg -1 , the initial discharge specific capacity is 343.9 mAh / g, and the initial Coulombic efficiency is 85.4%. It should be noted that the specific surface area of this material is the smallest, only 5.3 m 2 / g, while the powder conductivity is 14.3 S / cm.

[0144] For the hard carbon material prepared in Example 6, the initial charge specific capacity and the initial discharge specific capacity are 327.4 mAh / g and 378.1 mAh / g respectively, and the initial Coulombic efficiency is 86.6%. The specific surface area of this material is 17.7 m 2 / g, the powder conductivity is 24.5 S / cm.

[0145] In Example 7, the initial charge specific capacity of the hard carbon material is 287.4 mAh / g, the initial discharge specific capacity is 341.7 mAh / g, and the initial Coulomb efficiency is 84.1%. The specific surface area of this material is 4.2 m 2 / g, which is the lowest among all examples, and the powder conductivity is 10.2 S / cm, revealing its possible limitations under specific conditions.

[0146] The hard carbon material prepared in Example 1 has the best comprehensive performance and the highest powder conductivity (the initial charge / discharge specific capacity reaches 336.4 / 384.4 mAh / g, the initial Coulomb efficiency is 87.5%, and the powder conductivity is 28.3 S / cm). For the battery of emergency rescue lighting equipment, the high conductivity of Example 1 ensures the charge transfer efficiency in low-temperature environments and effectively reduces the energy loss caused by internal resistance. In some natural disasters or emergencies, a low-temperature environment may be faced, such as in snowy areas and alpine regions. The sodium battery prepared by it can provide stable lighting during rescue. Based on this, the present invention provides a battery for emergency rescue lighting equipment, and its preparation method is the preparation method shown in Example 1.

[0147] The present invention provides a battery for a home energy storage system, and its preparation method is the preparation method shown in Example 6. The hard carbon material prepared in Example 6 uses wood chips to replace the fruit shell, reducing the cost of the precursor. As a by-product of wood processing, the annual output of wood chips can reach hundreds of millions of tons, having the advantage of large-scale supply. At the same time, although the conductivity of this material is slightly lower than that of Example 1 (24.5 S / cm), its specific capacity of 327.4 / 378.1 mAh / g and Coulomb efficiency of 86.6% still meet the home energy storage requirements, and the relatively high specific surface area of 17.7 m 2 / g enhances the ion adsorption ability and has more advantages in continuous charge and discharge scenarios.

[0148] It should be noted that the above specific embodiments are exemplary. Those skilled in the art can come up with various solutions inspired by the disclosed content of the present invention, and these solutions also belong to the disclosure scope of the present invention and fall within the protection scope of the present invention. Those skilled in the art should understand that the description and drawings of the present invention are illustrative and do not constitute a limitation to the claims. The protection scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing a biowaste-based hard carbon material, characterized in that: The following steps are involved: (1) Pretreatment of biological waste to obtain pre-carbonized powder; (2) adding polyvinyl pyrrolidone and thiourea to the pre-carbonized powder and crushing the powder; (3) High temperature reaction above 250°C to obtain biowaste-based hard carbon materials.

2. The preparation method according to claim 1, characterized in that: It includes the following steps: To 100 parts by weight of the pre-carbonized powder are added 1 to 50 parts by weight of polyvinyl pyrrolidone and 1 to 50 parts by weight of thiourea.

3. The preparation method according to claim 1 or 2, characterized in that: The "pretreatment of biological waste" comprises the following steps: Treating biological waste at a temperature of ≥600°C and <1000°C; Pickling and impurity removal at a temperature ≥80℃ and <100℃.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The acidic reagent used in the "pickling and impurity removal" is selected from one or more of hydrochloric acid, hydrofluoric acid and sulfuric acid.

5. The preparation method according to any one of claims 1 to 3, characterized in that: The "high temperature reaction above 250°C" comprises the following steps: Heat preservation treatment at a temperature of ≥250℃ and <350℃ for 1 to 3 hours; Heat preservation treatment at a temperature of ≥350℃ and <1400℃ for 1 to 3 hours; Heat preservation treatment at a temperature of ≥1300℃ and <1500℃ for 1 to 3 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The "high temperature reaction above 250°C" comprises the following steps: Keep at 250℃ for 2h; The holding time at 350℃ is 2h; The holding time at 1400℃ is 3h.

7. The preparation method according to claim 6, characterized in that: The biological waste is selected from one or more of bagasse, straw, wood chips, fruit shells and rice shells.

8. The hard carbon material according to any one of claims 1 to 7, characterized in that: The specific surface area and electrical conductivity of the hard carbon material are selected from the following group: (1) Specific surface area is 16.2m 2 / g, conductivity is 28.3S / cm; (2) Specific surface area is 9.8m 2 / g, and the electrical conductivity is 16.5S / cm.

9. The hard carbon material according to claim 8, characterized in that The carbon layer spacing is 0.372-0.379 nm.

10. Use of the hard carbon material according to any one of claims 1 to 7 or the hard carbon material prepared by the preparation method according to any one of claims 8 to 9, characterized in that: The application is to prepare a sodium ion battery or a negative electrode of a sodium ion battery.

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