Biomass hard carbon material, preparation method and application thereof

Abstract

This invention provides biomass hard carbon materials, their preparation methods, and applications. The biomass hard carbon material includes a biomass hard carbon material matrix and a carbon coating layer present on the surface of the biomass hard carbon material matrix. The biomass hard carbon material matrix includes closed-cell structures, and the biomass hard carbon material satisfies formula 1: T HC ×V closed ×d 002 / SSA≥0.3Equation 1, where T HC V represents the thickness of the carbon coating layer, in nm; closed The volume of the closed aperture is in cm. 3 / g;d 002 The interlayer spacing of the diffraction peaks corresponding to the (002) crystal plane of the biomass hard carbon material is nm; SSA is the specific surface area of ​​the biomass hard carbon material, m². 2 / g. The biomass hard carbon material provided by this invention can improve the specific capacity, initial coulombic efficiency, and rate performance of batteries.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to biomass hard carbon materials, their preparation methods, and applications. Background Technology

[0002] Sodium-ion batteries, due to their abundant sodium resources and low cost, have become an ideal alternative for large-scale energy storage systems (such as grid energy storage, low-speed electric vehicles, and data center backup power). In the electrochemical system of sodium-ion batteries, the performance of the anode material directly determines the battery's energy density, cycle life, and safety. Hard carbon materials, due to their low sodium storage voltage platform, high theoretical specific capacity, and structural stability, have become the preferred anode material for sodium-ion batteries.

[0003] However, the microstructural defects and insufficient surface functional group regulation of traditional hard carbon materials result in low specific capacity, initial coulombic efficiency, and rate performance when applied to sodium-ion batteries, limiting their practical application. Summary of the Invention

[0004] The main objective of this invention is to provide a biomass hard carbon material that can improve the specific capacity, initial coulombic efficiency, and rate performance of batteries.

[0005] The present invention also provides a method for preparing biomass hard carbon material, which can prepare the above-mentioned biomass hard carbon material, and the process is simple and low in cost.

[0006] The present invention also provides a negative electrode sheet comprising the above-mentioned biomass hard carbon material, thereby improving the specific capacity, initial coulombic efficiency and rate performance of the battery.

[0007] The present invention also provides a battery comprising the above-mentioned negative electrode, thereby the battery having excellent specific capacity, initial coulombic efficiency and rate performance.

[0008] In a first aspect, the present invention provides a hard material, comprising a biomass hard carbon material matrix and a carbon coating layer present on the surface of the biomass hard carbon material matrix, wherein the biomass hard carbon material matrix comprises closed pores, and the biomass hard carbon material satisfies Formula 1:

[0009] T HC ×V closed ×d 002 / SSA≥0.3 Equation 1,

[0010] Among them, T HC V represents the thickness of the carbon coating layer, in nm; closed The volume of the closed aperture is in cm. 3 / g;d 002The interlayer spacing of the diffraction peaks corresponding to the (002) crystal plane of the biomass hard carbon material is nm; SSA is the specific surface area of ​​the biomass hard carbon material, m². 2 / g.

[0011] As mentioned above, for biomass hard carbon materials, 0.3≤T HC ×V closed ×d 002 / SSA≤1.0;

[0012] And / or, in the Raman spectrum of the biomass hard carbon material, the intensity ratio of the D peak to the G peak is I. D / I G 1.70≤I D / I G ≤1.85;

[0013] And / or, the closed-cell content of the biomass hard carbon material by volume A is ≥ 45%; preferably, 45% ≤ A ≤ 55%.

[0014] As mentioned above, for biomass hard carbon materials, 35nm≤T HC ≤60nm;

[0015] And / or, 0.23cm 3 / g≤V closed ≤0.3cm 3 / g;

[0016] And / or, 0.374nm≤d 002 ≤0.382nm;

[0017] And / or, 5.0m 2 / g≤SSA≤15.0m 2 / g.

[0018] Secondly, the present invention provides a method for preparing the biomass hard carbon material as described above, comprising the following steps:

[0019] A carbon skeleton material is obtained by spray drying a raw material system including a pre-oxidized first carbon source, phosphate, and metal salt, followed by a first sintering treatment.

[0020] The carbon skeleton material is subjected to a second sintering treatment in the presence of metal salts to obtain a biomass hard carbon material precursor.

[0021] The biomass hard carbon material precursor is subjected to carbon coating treatment to obtain the biomass hard carbon material.

[0022] In the preparation method described above, the temperature of the first sintering treatment is 300~400℃ and the time is 1~2h;

[0023] And / or, the temperature of the second sintering treatment is 600~700℃, and the time is 2~4h.

[0024] The preparation method described above, wherein the pre-oxidation treatment process includes: subjecting the first carbon source to pre-oxidation treatment in air at 200~250℃ for 2~4 hours and / or subjecting it to pre-oxidation treatment under hydrothermal conditions at 180~220℃ for 2~4 hours;

[0025] And / or, the molar concentration of the metal salt in the raw material system is 0.01~0.03 mol / L.

[0026] As described above, the process of carbon coating the biomass hard carbon material precursor includes: performing a third sintering treatment on the biomass hard carbon material precursor in the presence of a second carbon source to obtain the biomass hard carbon material.

[0027] Preferably, the temperature of the third sintering treatment is 800~1000℃ and the time is 1~3h.

[0028] In the preparation method described above, the mass ratio of the first carbon source, phosphate, and metal salt is 1:(1~3):(1~2);

[0029] And / or, the first carbon source includes lignin or lignin-containing biomass raw materials, preferably, the biomass raw materials include at least one of corn cob residue, wheat straw, straw, eucalyptus wood, pine wood, and corn cob;

[0030] And / or, the phosphate includes at least one of disodium hydrogen phosphate, sodium dihydrogen phosphate, and phosphoric acid;

[0031] And / or, the metal salt includes at least one of FeCl3·6H2O, CoCl2·6H2O, and NiCl2·6H2O.

[0032] Thirdly, the present invention provides a negative electrode sheet comprising the biomass hard carbon material as described above or the biomass hard carbon material prepared according to the preparation method described above.

[0033] Fourthly, the present invention provides a battery comprising the negative electrode sheet as described above.

[0034] The biomass hard carbon material provided by this invention, by limiting the relationship between the thickness of the carbon coating layer, the volume of the closed pores, the interlayer spacing of the diffraction peaks corresponding to the (002) crystal plane of the biomass hard carbon material, and the specific surface area of ​​the biomass hard carbon material, can improve the specific capacity, first coulombic efficiency and rate performance of the battery when applied to it. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 SEM image of the biomass hard carbon material of Example 1 provided by the present invention;

[0037] Figure 2 SEM image of the biomass hard carbon material of Comparative Example 5 provided by the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0039] Sodium-ion batteries, as an emerging electrochemical energy storage technology, have shown great application potential in large-scale energy storage due to the abundant, widely distributed, and low-cost nature of sodium resources. They are particularly suitable for grid-scale energy storage, low-speed electric vehicles, and data center backup power. In the electrochemical system of sodium-ion batteries, the anode material is one of the key factors determining the overall performance of the battery, directly affecting its energy density, cycle life, and safety and reliability. Among various anode materials, hard carbon materials are considered one of the most promising anode materials for sodium-ion batteries due to their layered or graphite-like microcrystalline structure suitable for sodium ion insertion / extraction, low and stable sodium storage voltage platform, high theoretical specific capacity, and good structural stability.

[0040] However, traditional hard carbon materials still face a series of challenges in practical applications. First, their microstructure often suffers from uneven defect distribution and unreasonable pore structure, leading to slow sodium ion diffusion kinetics and limiting the material's rate performance. Second, the active groups, such as oxygen-containing functional groups, on the hard carbon surface are poorly regulated, making them prone to side reactions with the electrolyte, forming an unstable solid electrolyte interface film. This results in irreversible consumption of active sodium ions, significantly reducing the battery's initial coulombic efficiency. Furthermore, the sodium storage mechanism of some hard carbon materials remains unclear. The storage sites for sodium ions in hard carbon (such as micropore filling, defect adsorption, and interlayer embedding) and their contribution ratio are difficult to control precisely, hindering further increases in specific capacity. These factors collectively restrict the practical application performance of hard carbon anodes in sodium-ion batteries.

[0041] In the prior art, the above problems are solved by heteroatom doping or chemical vapor deposition (CVD) pore-closed modification.

[0042] Heteroatom doping: By introducing heteroatoms such as nitrogen (N), oxygen (O), and sulfur (S), the electronic structure of hard carbon is modulated to improve its sodium storage capacity. For example, doping hard carbon precursors with nitrogen can introduce defect sites, enhancing the adsorption capacity of sodium ions. However, heteroatom doping usually leads to an increase in the defect density on the hard carbon surface, triggering electrolyte decomposition side reactions, thus significantly reducing the initial coulombic efficiency. Chemical vapor deposition (CVD) pore-closure modification: Using methane (CH4) as a carbon source, a carbon layer is deposited on the surface of a porous carbon substrate to close the pores, reducing the specific surface area and reducing side reactions in sodium ion storage. Although this method can improve the pore closure rate, it has the following problems: Low deposition efficiency: CVD processes require high temperatures (>800℃) and long reaction times, resulting in high energy consumption and increased production costs. Complex process: Additional pore-forming agents (such as ZnO, MgO) and acid washing post-treatment steps are required, leading to a cumbersome process flow and limited improvement in pore closure rate. Insufficient performance balance: Excessive pore closure may hinder the diffusion kinetics of sodium ions, leading to a decrease in rate performance.

[0043] The inventors of this application have discovered through research that by limiting the relationship between the thickness of the carbon coating layer, the volume of the closed pores, the interlayer spacing of the diffraction peaks corresponding to the (002) crystal plane, and the specific surface area of ​​the biomass hard carbon material, the specific capacity, first coulombic efficiency, and rate performance of the battery can be significantly improved.

[0044] Based on this, in a first aspect, the present invention provides a biomass hard carbon material, comprising a biomass hard carbon material matrix and a carbon coating layer present on the surface of the biomass hard carbon material matrix, wherein the biomass hard carbon material matrix comprises closed pores, and the biomass hard carbon material satisfies Formula 1:

[0045] T HC ×V closed ×d 002 / SSA≥0.3 Equation 1,

[0046] Among them, T HC V represents the thickness of the carbon coating layer, in nm; closed The volume of the closed pore is expressed in cm. 3 / g;d 002 SSA represents the interlayer spacing of the diffraction peaks corresponding to the (002) crystal plane of the biomass hard carbon material, in nm; SSA represents the specific surface area of ​​the biomass hard carbon material, in m². 2 / g.

[0047] For example, T HC ×V closed ×d 002 / SSA can be a range consisting of 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 or any two of them.

[0048] The biomass hard carbon material provided by this invention significantly improves the specific capacity, initial coulombic efficiency, and rate performance of batteries by limiting the relationship between the thickness of the carbon coating layer, the volume of the closed pores, the interlayer spacing of the diffraction peaks corresponding to the (002) crystal plane, and the specific surface area. This is because the closed pores in the biomass hard carbon material matrix can, on the one hand, serve as additional sodium storage sites, accommodating sodium ions for fill-in storage; on the other hand, the closed-pore structure can suppress the volume expansion of the biomass hard carbon material during charge and discharge, maintaining the integrity of the matrix structure and preventing the active sites from failing due to structural collapse. Where V... closed The higher the proportion of sodium in biomass hard carbon materials, the more additional capacity they can contribute. The sodium storage mechanisms of biomass hard carbon materials include interlayer embedding and pore filling. 002 Increased spacing means wider interlayer spacing of graphitized microcrystals, making it easier for sodium ions to embed into the interlayer structure and accommodating more sodium ions, thus improving the interlayer sodium storage capacity. Combined with Vclosed pore sodium storage, a dual-site sodium storage of "interlayer + pore" is achieved, significantly improving the overall specific capacity.

[0049] Furthermore, the carbon coating layer on the surface of the biomass hard carbon material matrix is ​​a dense, conductive, and inert layer, which can be directly used as an artificial SEI film substrate. This avoids direct contact between the electrolyte and the biomass hard carbon material matrix, reducing irreversible capacity loss caused by electrolyte decomposition and excessive growth of the solid electrolyte interphase (SEI) film. Where T... HC A reasonable value for SSA can ensure interface stability while avoiding excessive coating thickness that hinders sodium ion transport. A smaller SSA results in a smaller contact area between the biomass hard carbon material and the electrolyte, fewer active sites for side reactions, and less sodium ions and electrolyte consumed during the initial charge-discharge process. In the formula, SSA acts as the denominator; its reduction significantly improves the overall parameter value, synergistically reducing irreversible capacity with the carbon coating, thereby improving the initial coulombic efficiency.

[0050] Meanwhile, the carbon coating layer possesses excellent electronic conductivity, enabling the formation of a continuous electron transport network on the surface of biomass hard carbon materials. This reduces the charge transfer impedance of the electrodes, ensuring rapid electron migration during high-current charging and discharging. The closed-pore structure forms nanochannels that serve as rapid sodium ion transport channels, shortening the diffusion path of sodium ions from the electrolyte to the active sites. The broadened d... 002 This reduces the migration resistance of sodium ions between layers, allowing them to rapidly insert or extract even under high current. The constraints of Equation 1 ensure sufficient sodium storage sites and electronic conductivity while avoiding increased impedance due to excessively large specific surface area or excessively thick coating layers that hinder sodium ion transport, ultimately achieving improved rate performance.

[0051] Therefore, the biomass hard carbon material provided by the present invention can significantly improve the specific capacity, first coulombic efficiency and rate performance of the battery by limiting the relationship between the thickness of the carbon coating layer, the volume of the closed pores, the interlayer spacing of the diffraction peaks corresponding to the (002) crystal plane and the specific surface area.

[0052] In some embodiments of the present invention, 0.3 ≤ T HC ×V closed ×d 002 / SSA ≤ 1.0, for example, can be a range consisting of any two of 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0. This can further improve the battery's specific capacity, initial coulombic efficiency, and rate performance.

[0053] In some embodiments, the intensity ratio of the D peak to the G peak in the Raman spectrum of biomass hard carbon materials is I. D / I G 1.70≤I D / I G ≤1.85, for example, can be a range consisting of 1.70, 1.72, 1.75, 1.80, 1.82, 1.85 or any two of them.

[0054] It is understandable that the G peak (~1580 cm⁻¹) in the Raman spectrum of biomass hard carbon materials... -1 ) Corresponding to sp in graphite microcrystals 2 The in-plane stretching vibrations of hybrid carbon reflect the proportion of ordered graphitized structures in biomass hard carbon materials. A higher G peak intensity indicates a higher degree of graphitization and better electronic conductivity. The D peak (~1350 cm⁻¹)... -1 The vibrations of defects, disordered structures, and edge carbons in biomass hard carbon materials correspond to the following: A higher D peak intensity indicates a greater number of defect sites and nanopores, and a richer abundance of sodium-storing active sites in the biomass hard carbon material. D / I GThe ratio directly characterizes the relative relationship between the disorder and graphitization degree of biomass hard carbon materials. The larger the ratio, the more disordered the structure and defects; the smaller the ratio, the higher the degree of graphitization and the more regular the structure.

[0055] I D / I G Within the aforementioned range, sufficient defect sites and closed pores are preserved to achieve a dual sodium storage mechanism of "interlayer embedding + pore filling," while maintaining continuous sp... 2 The carbon network ensures rapid electron transport, improving specific capacity and thus enhancing the battery's specific capacity, initial coulombic efficiency, and rate performance.

[0056] In some embodiments, the closed-cell content (A) of the biomass hard carbon material by volume is ≥45%, for example, it can be a range of 45%, 46%, 47%, 48%, 49%, 50%, 55%, 60%, 65%, 70%, 80%, or any two of these. Preferably, 45% ≤ A ≤ 55%.

[0057] The amount of closed-cell material effectively reduces the number of exposed defect sites on the surface of biomass hard carbon materials, inhibits electrolyte decomposition reactions on the surface, thereby reducing side reaction activity and improving the first coulombic efficiency. Simultaneously, the closed-cell design optimizes the diffusion path of sodium ions within the material, reduces interfacial impedance, and improves rate performance.

[0058] In some embodiments of the present invention, 35nm≤T HC ≤60nm, for example, can be a range of 35nm, 37nm, 40nm, 42nm, 45nm, 50nm, 55nm, 60nm or any two of them.

[0059] The thickness of the aforementioned carbon coating layer can both suppress side reactions and ensure rapid electron and ion transport, thereby improving the rate performance of the battery.

[0060] In some embodiments, 0.23cm 3 / g≤V closed ≤0.3cm 3 / g, for example, can be 0.23cm 3 / g, 0.24cm 3 / g, 0.25cm 3 / g, 0.26cm 3 / g, 0.27cm 3 / g, 0.28cm 3 / g, 0.29cm 3 / g, 0.3cm 3 / g or a range consisting of any two of them.

[0061] The aforementioned closed-pore volume can reduce the side reaction activity of biomass hard carbon materials, ensuring sufficient pore sodium storage contribution while maintaining the structural rigidity of the biomass hard carbon material matrix and preventing structural collapse.

[0062] In some embodiments, 0.374nm≤d 002 ≤0.382nm, for example, can be a range of 0.374nm, 0.375nm, 0.376nm, 0.378nm, 0.38nm, 0.382nm or any combination thereof.

[0063] The interlayer spacing of the (002) crystal plane can accommodate more sodium ions and ensure the relative stability of the layer structure, thereby improving the rate performance and structural stability of the battery.

[0064] In some embodiments, 5.0m 2 / g≤SSA≤15.0m 2 / g, for example, can be 5.0m 2 / g, 6.0m 2 / g, 8.0m 2 / g, 10.0m 2 / g, 12.0m 2 / g, 15.0m 2 / g or a range consisting of any two of them.

[0065] The specific surface area of ​​the aforementioned biomass hard carbon material can reduce side reactions and facilitate the rapid adsorption and transport of sodium ions, thereby improving the battery's initial coulombic efficiency and rate performance.

[0066] Secondly, the present invention provides a method for preparing the biomass hard carbon material as described above, comprising the following steps:

[0067] A carbon skeleton material is obtained by spray drying a raw material system including a pre-oxidized first carbon source, phosphate, and metal salt, followed by a first sintering treatment.

[0068] The carbon skeleton material is subjected to a second sintering treatment in the presence of metal salts to obtain a biomass hard carbon material precursor.

[0069] Biomass hard carbon material precursors are subjected to carbon coating treatment to obtain biomass hard carbon materials.

[0070] A raw material system including a pre-oxidized first carbon source, phosphate, metal salt and solvent can be spray-dried. Spray drying can effectively mix phosphate and metal salt in the first carbon source.

[0071] Specifically, the first carbon source can be pre-oxidized and then added to a mixed solution of ethanol and water. After the phosphate and metal salt are fully mixed in a certain mass ratio, they are spray-dried to obtain an oxidized carbon source co-solventized with phosphate.

[0072] Spray drying evaporates the solvent at high temperature, allowing phosphate and metal salt to be uniformly coated on the surface of the first carbon source, forming a homogeneous precursor. Co-solventization treatment can enhance the cross-linking activity between phosphate and the first carbon source, providing a chemical basis for subsequent pore-expanding treatment.

[0073] During the first sintering process, the first carbon source and phosphate form a CO-PO3 structure, which catalytically dehydrates and enhances the stability of the carbon skeleton, resulting in a carbon skeleton material.

[0074] The first sintering process can be carried out in an inert atmosphere, and the inert gas can be at least one of nitrogen, helium, and argon.

[0075] The carbon skeleton material undergoes a second sintering treatment in the presence of metal salts. During the second sintering treatment, phosphates decompose to increase microporosity, and metal salts decompose to generate gas, which expands the pores of the carbon skeleton material to form mesopores. Metal elements are deposited on the surface of the carbon skeleton material to obtain a biomass hard carbon material precursor.

[0076] The second sintering process can be carried out in an inert atmosphere, and the inert gas can be at least one of nitrogen, helium, and argon.

[0077] Carbon coating treatment is applied to the precursor of biomass hard carbon material to form a carbon coating layer on the surface of the biomass hard carbon material matrix, thereby obtaining biomass hard carbon material.

[0078] The preparation method of biomass hard carbon material provided by the present invention can prepare the above-mentioned biomass hard carbon material, and the biomass hard carbon material can improve the specific capacity, initial coulombic efficiency and rate performance of the battery.

[0079] In some embodiments of the present invention, the temperature of the first sintering treatment is 300~400°C, for example, it can be a range of 300°C, 320°C, 350°C, 370°C, 400°C or any two of them; the time is 1~2h, for example, it can be a range of 1h, 1.2h, 1.5h, 1.7h, 2h or any two of them.

[0080] Phosphate can catalyze dehydration under the temperature and time of the first sintering treatment, further enhancing the stability of the carbon skeleton material.

[0081] In some embodiments, the temperature of the second sintering treatment is 600~700°C, for example, it can be a range of 600°C, 620°C, 650°C, 670°C, 700°C or any two of them; the time is 2~4h, for example, it can be a range of 2h, 2.5h, 3h, 3.5h, 4h or any two of them.

[0082] The temperature and time of the second sintering process can further promote the decomposition of metal salts to generate gases, thereby expanding the pores of the carbon skeleton material, forming mesopores, and obtaining a hierarchical porous structure, which is beneficial for the subsequent deposition of carbon coating layers.

[0083] In some embodiments of the present invention, the pre-oxidation process includes: subjecting the first carbon source to pre-oxidation treatment in air at 200-250°C (e.g., a range of 200°C, 210°C, 220°C, 230°C, 240°C, 250°C or any two thereof) for 2-4 hours (e.g., a range of 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours or any two thereof) and / or to pre-oxidation treatment under hydrothermal conditions at 180-220°C (e.g., a range of 180°C, 190°C, 200°C, 210°C, 220°C or any two thereof) for 2-4 hours (e.g., a range of 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours or any two thereof).

[0084] Pre-oxidation of the first carbon source using air or hydrothermal treatment can fragment its structure, enrich carboxyl groups, and improve its hydrophilicity.

[0085] Introducing oxygen-containing functional groups enhances the hydrophilicity and reactivity of the first carbon source, providing a structural basis for the uniform mixing of subsequent phosphates and metal salts. At the same time, fragmentation treatment can increase the specific surface area of ​​the first carbon source, creating conditions for pore structure regulation.

[0086] Preferably, the molar concentration of the metal salt in the raw material system is 0.01~0.03 mol / L, for example, it can be within the range of 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, or any combination thereof. This effectively allows the metal salt to generate gas during the second sintering process, thereby expanding the pores of the carbon framework material, forming mesopores, and obtaining a hierarchical porous structure, which is beneficial for the subsequent deposition of the carbon coating layer.

[0087] In some embodiments of the present invention, the process of carbon coating treatment of biomass hard carbon material precursor includes: performing a third sintering treatment on biomass hard carbon material precursor in the presence of a second carbon source to obtain biomass hard carbon material.

[0088] Preferably, the temperature of the third sintering treatment is 800~1000℃, for example, it can be a range of 800℃, 820℃, 850℃, 880℃, 900℃, 950℃, 1000℃ or any two of them; the time is 1~3h, for example, it can be a range of 1h, 1.5h, 2h, 2.5h, 3h or any two of them.

[0089] In one embodiment, the second carbon source includes methane gas. During the third sintering process at the specified temperature and time, the methane gas is introduced. The metal elements deposited on the surface of the carbon skeleton material act as catalysts, which can reduce the decomposition energy barrier of methane and effectively improve the decomposition efficiency of methane. This achieves efficient carbon deposition, promotes the rearrangement of the microstructure of pyrolytic carbon, expands the graphite domain and reduces surface defects, and reduces electronic conductivity and ion diffusion energy barriers, thereby forming a carbon coating layer.

[0090] In some embodiments of the present invention, the mass ratio of the first carbon source, phosphate, and metal salt is 1:(1~3):(1~2), for example, it can be a range of 1:1:1, 1:2:1, 1:3:1, 1:1:2, 1:2:2, 1:3:2 or any two of them.

[0091] At this ratio, phosphates can effectively induce the formation of moderately ordered graphite microcrystalline regions in the carbon framework, and can also form initial channels through thermal decomposition and gas generation, providing a basis for subsequent pore expansion with metal salts. The degree of pore expansion can be precisely controlled with metal salts, ensuring that the amount of gas generated by the decomposition of metal salts matches the pore capacity of the carbon framework.

[0092] In some embodiments, the first carbon source includes lignin or lignin-containing biomass raw materials. Preferably, the biomass raw materials include at least one of corn cob residue, wheat straw, straw, eucalyptus wood, pine wood, and corn cob.

[0093] Lignin is a natural aromatic polymer compound with a large number of benzene ring structures and cross-linking sites in its molecular chain. After carbonization, it easily forms porous carbon with a rigid skeleton, and the pores are mostly in a semi-closed state. After subsequent pore expansion with metal salts, it can be efficiently converted into a closed-cell structure. Compared with other primary carbon sources, lignin-based carbon skeletons have a higher closed-cell formation rate, and lignin is inexpensive and widely available.

[0094] In some embodiments, the phosphate includes at least one of disodium hydrogen phosphate, sodium dihydrogen phosphate, and phosphoric acid.

[0095] The aforementioned phosphates have a moderate decomposition temperature. The H3PO4 vapor released during thermal decomposition can slowly etch the molecular chains of the first carbon source, inducing the formation of graphite microcrystals with moderate order, without destroying the carbon framework structure due to violent reactions. In addition, these water-soluble phosphates are more easily and uniformly dispersed in the first carbon source, resulting in a more uniform mineralization effect.

[0096] In some embodiments, the metal salt includes at least one of FeCl3·6H2O, CoCl2·6H2O, and NiCl2·6H2O.

[0097] The aforementioned metal salts can undergo thermal decomposition at the second sintering temperature to generate Cl2. The Fe, Co, and Ni metal particles produced by the decomposition can serve as catalytic sites, reducing the decomposition energy barrier of the second carbon source and effectively improving the decomposition efficiency of the second carbon source, thereby achieving efficient carbon deposition.

[0098] Thirdly, the present invention provides a negative electrode sheet comprising the biomass hard carbon material as described above or the biomass hard carbon material prepared according to the preparation method described above.

[0099] The negative electrode sheet of the present invention can be prepared using conventional techniques in the art. Specifically, the above-mentioned biomass hard carbon material, conductive agent, and binder can be uniformly dispersed in a solvent to obtain a negative electrode active slurry. Then, the negative electrode active slurry is coated on at least one functional surface of the negative electrode current collector, and after drying, the negative electrode sheet of the present invention can be obtained.

[0100] This invention does not specifically limit the types of conductive agents and adhesives. The conductive agents, adhesives and other components can all be conventional substances in the field. For example, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite and graphene, and the adhesive can be selected from one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber and styrene-acrylic rubber.

[0101] The present invention does not specifically limit the coating method, and any coating method such as gravure coating, extrusion coating, spraying, screen printing, etc. can be used to achieve the coating of the positive electrode active layer slurry.

[0102] The negative electrode provided by the present invention includes the above-mentioned biomass hard carbon material. Therefore, the negative electrode can improve the specific capacity, initial coulombic efficiency and rate performance of the battery.

[0103] Fourthly, the present invention provides a battery comprising the negative electrode sheet as described above, which has advantages corresponding to the aforementioned negative electrode sheet, and will not be elaborated further.

[0104] In addition to the negative electrode, the battery of the present invention also includes a separator, a positive electrode, and an electrolyte. The composition of the positive electrode can refer to conventional negative electrode materials in the art, and the separator can also be a commonly used separator in the art, such as a PP film or a PE film.

[0105] The battery of the present invention can be prepared using conventional methods in the art. Specifically, the positive electrode, separator and negative electrode can be stacked in sequence, and the cell can be obtained by stacking or winding. Then, the battery can be obtained by baking, liquid injection, formation and packaging.

[0106] The battery of the present invention can be a single cell, a battery pack, a battery stack, or a cylindrical cell formed by connecting single cells. These cells can be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a hybrid connection including these connection methods, etc., without particular limitation.

[0107] In some embodiments of the present invention, the battery includes a sodium-ion battery, wherein the specific capacity, initial coulombic efficiency and rate performance of the sodium-ion battery are further improved.

[0108] Fifthly, the present invention provides an electrical device including the battery as described above, which has advantages corresponding to the negative electrode plate described above, and will not be elaborated further.

[0109] The electrical equipment of the present invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles), electronic equipment (e.g., computers, mobile phones, digital cameras, printers, fax machines, etc.), wearable devices (e.g., watches, wristbands, VR glasses, etc.), and home appliances (e.g., air conditioners, refrigerators, washing machines, microwave ovens, etc.), etc., and there are no particular limitations.

[0110] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0111] Example 1

[0112] The preparation method of biomass hard carbon material in this embodiment includes the following steps:

[0113] 1) Lignin was pre-oxidized in air at 250℃ for 2 hours to obtain pre-oxidized lignin. The pre-oxidized lignin, phosphate (including NaH2PO4 and H3PO4 in a 1:1 mass ratio), and FeCl3·6H2O were thoroughly mixed in a mixed solution of ethanol and water in a 1:2:1 mass ratio to obtain the raw material system. The raw material system was then spray-dried to obtain the treated raw material system. The molar concentration of FeCl3·6H2O in the raw material system was 1.0 mol / L.

[0114] 2) The treated raw material system was placed in a nitrogen atmosphere and subjected to a first sintering treatment at 300℃ for 2 hours to obtain a carbon skeleton material. While maintaining the nitrogen atmosphere, the temperature was raised to 600℃, and the carbon skeleton material was subjected to a second sintering treatment in the presence of FeCl3·6H2O for 3 hours. During the second sintering treatment, FeCl3·6H2O generated Cl2 to expand the pores of the carbon skeleton material, resulting in a biomass hard carbon material precursor. The temperature was raised to 900℃, and CH4 was introduced into the biomass hard carbon material precursor for a third sintering treatment of 1.5 hours to obtain the biomass hard carbon material.

[0115] Biomass hard carbon materials include a biomass hard carbon material matrix and a carbon coating layer present on the surface of the biomass hard carbon material matrix. The biomass hard carbon material matrix includes closed-cell structures.

[0116] Example 2

[0117] The preparation method of biomass hard carbon material in this embodiment includes the following steps:

[0118] 1) Lignin was pre-oxidized in air at 250℃ for 2 hours to obtain pre-oxidized lignin. The pre-oxidized lignin, phosphate (including Na₂HPO₄ and H₃PO₄ in a 1:1 mass ratio), and FeCl₃·6H₂O were thoroughly mixed in a mixed solution of ethanol and water in a 1:2:1 mass ratio to obtain the raw material system. The raw material system was then spray-dried to obtain the treated raw material system. The molar concentration of FeCl₃·6H₂O in the raw material system was 1.0 mol / L.

[0119] 2) The treated raw material system was placed in a nitrogen atmosphere and subjected to a first sintering treatment at 400℃ for 1.5h to obtain a carbon skeleton material; while maintaining the nitrogen atmosphere, the temperature was raised to 650℃, and the carbon skeleton material was subjected to a second sintering treatment in the presence of FeCl3·6H2O for 2h. During the second sintering treatment, FeCl3·6H2O generated Cl2 to expand the pores of the carbon skeleton material, thus obtaining a biomass hard carbon material precursor; the temperature was raised to 950℃, and CH4 was introduced into the biomass hard carbon material precursor for a third sintering treatment for 3h to obtain the biomass hard carbon material.

[0120] Biomass hard carbon materials include a biomass hard carbon material matrix and a carbon coating layer present on the surface of the biomass hard carbon material matrix. The biomass hard carbon material matrix includes closed-cell structures.

[0121] Example 3

[0122] The preparation method of biomass hard carbon material in this embodiment includes the following steps:

[0123] 1) Lignin was pre-oxidized by hydrothermal treatment at 220℃ for 2 hours to obtain pre-oxidized lignin. The pre-oxidized lignin, phosphate (including NaH2PO4 and H3PO4 in a mass ratio of 1:1), and FeCl3·6H2O were thoroughly mixed in a mixed solution of ethanol and water in a mass ratio of 1:2:2 to obtain the raw material system. The raw material system was then spray-dried to obtain the treated raw material system. The molar concentration of FeCl3·6H2O in the raw material system was 1.0 mol / L.

[0124] 2) The treated raw material system was placed in a nitrogen atmosphere and subjected to a first sintering treatment at 300℃ for 2 hours to obtain a carbon skeleton material. While maintaining the nitrogen atmosphere, the temperature was raised to 650℃, and the carbon skeleton material was subjected to a second sintering treatment in the presence of FeCl3·6H2O for 2 hours. During the second sintering treatment, FeCl3·6H2O generated Cl2 to expand the pores of the carbon skeleton material, thus obtaining a biomass hard carbon material precursor. The temperature was raised to 1000℃, and CH4 was introduced into the biomass hard carbon material precursor for a third sintering treatment for 2 hours to obtain the biomass hard carbon material.

[0125] Biomass hard carbon materials include a biomass hard carbon material matrix and a carbon coating layer present on the surface of the biomass hard carbon material matrix. The biomass hard carbon material matrix includes closed-cell structures.

[0126] Example 4

[0127] The preparation method of biomass hard carbon material in this embodiment includes the following steps:

[0128] 1) Lignin was pre-oxidized in air at 250℃ for 2 hours to obtain pre-oxidized lignin. The pre-oxidized lignin, phosphate (including NaH2PO4 and H3PO4 in a mass ratio of 1:2), and FeCl3·6H2O were thoroughly mixed in a mixed solution of ethanol and water in a mass ratio of 1:3:1 to obtain the raw material system. The raw material system was then spray-dried to obtain the treated raw material system. The molar concentration of FeCl3·6H2O in the raw material system was 1.0 mol / L.

[0129] 2) The treated raw material system was placed in a nitrogen atmosphere and subjected to a first sintering treatment at 300℃ for 2 hours to obtain a carbon skeleton material. While maintaining the nitrogen atmosphere, the temperature was raised to 650℃, and the carbon skeleton material was subjected to a second sintering treatment in the presence of FeCl3·6H2O for 2 hours. During the second sintering treatment, FeCl3·6H2O generated Cl2 to expand the pores of the carbon skeleton material, thus obtaining a biomass hard carbon material precursor. The temperature was raised to 950℃, and CH4 was introduced into the biomass hard carbon material precursor for a third sintering treatment for 2 hours to obtain the biomass hard carbon material.

[0130] Biomass hard carbon materials include a biomass hard carbon material matrix and a carbon coating layer present on the surface of the biomass hard carbon material matrix. The biomass hard carbon material matrix includes closed-cell structures.

[0131] Example 5

[0132] The preparation method of the biomass hard carbon material in this embodiment is basically the same as that in Example 4, except that the pre-oxidized lignin, phosphate (including NaH2PO4 and H3PO4 in a mass ratio of 1:1), and FeCl3·6H2O are mixed in a mass ratio of 1:2:2.

[0133] Example 6

[0134] The preparation method of the biomass hard carbon material in this embodiment is basically the same as that in Example 5, except that the temperature of the first sintering treatment is 350°C.

[0135] Comparative Example 1

[0136] The preparation method of this comparative example is basically the same as that of the biomass hard carbon material in Example 1, except that the lignin was not pre-oxidized.

[0137] Comparative Example 2

[0138] The preparation method of this comparative example is basically the same as that of the biomass hard carbon material in Example 1, except that the raw material system was not spray-dried and liquid phase impregnation was used instead.

[0139] Comparative Example 3

[0140] The preparation method of this comparative example is basically the same as that of the biomass hard carbon material in Example 1, except that no phosphate (including NaH2PO4 and H3PO4) was added.

[0141] Comparative Example 4

[0142] The preparation method of this comparative example is basically the same as that of the biomass hard carbon material in Example 1, except that the metal salt FeCl3·6H2O was not added.

[0143] Comparative Example 5

[0144] The preparation method of the biomass hard carbon material in this comparative example is basically the same as that in Example 1. The difference is that the three-stage heating is not carried out, but a one-stage heating is used, that is, the temperature of the first sintering treatment, the second sintering treatment and the third sintering treatment are all 950°C.

[0145] Experimental example:

[0146] 1. Thickness of carbon coating: The thickness of the carbon coating was measured using HRTEM.

[0147] 2. Specific Surface Area: The specific surface area of ​​biomass hard carbon materials is tested using the BET static method. First, the biomass hard carbon material is placed in a sample tube of a specialized adsorbent apparatus and pretreated at high temperature (200℃, nitrogen blowing, 2 hours) to remove surface impurities and moisture. Subsequently, an inert gas (usually nitrogen or other adsorbent) is brought into contact with the biomass hard carbon material under a series of known relative pressures until adsorption equilibrium is reached. The instrument measures the adsorption amount at different relative pressures, and the specific surface area is calculated based on these data using BET theory.

[0148] 3. Closed-cell volume: The density is determined using the helium density method, and the closed-cell volume is calculated using the following formula:

[0149] .

[0150] 4. d 002 Testing: X-ray diffractometer was used to test the biomass hard carbon material, according to Bragg's law 2d 002 sinθ=nλ, the interlayer spacing d is calculated. 002 Where λ is the X-ray wavelength; θ is the incident angle; and n is the diffraction order.

[0151] 5. Closed-pore volume content: The closed-pore volume content was fitted using small-angle X-ray scattering (SAXS).

[0152] 6. I D / I G Raman spectroscopy was used to test the biomass hard carbon material, and the intensities of the D and G peaks were obtained. D and I G I D / I G This gives the intensity ratio of peak D to peak G.

[0153] 7. Specific capacity and initial coulomb efficiency:

[0154] A method for preparing a button-type sodium-ion battery includes the following steps:

[0155] Biomass hard carbon material, SP, CMC, and SBR in a mass ratio of 92:2:2:4 were weighed and uniformly mixed in deionized water to prepare a negative electrode slurry. The negative electrode slurry was coated on both the upper and lower surfaces of an aluminum foil current collector and dried in an oven at 80℃ for 1 hour. After drying, it was removed and cooled to room temperature. The roller spacing was adjusted to roll the electrode sheet. The rolled electrode sheet was cut into small round pieces with a diameter of 14 mm and weighed as m1. Similarly, the aluminum foil current collector was cut into aluminum foil round pieces with a diameter of 14 mm and weighed as m2. Wherein, (m1-m2)×0.94 is the mass of the active material, denoted as m3. The weighed small round pieces were then placed in an oven at 80℃ and vacuum dried for 12 hours.

[0156] The vacuum-dried small discs were transferred to a glove box, and a button-type sodium-ion battery was assembled in a glove box with sodium discs as the counter electrode and auxiliary electrode, 1M NaPF6 electrolyte, EC:DMC:DEC=2:2:1, and a glass fiber diaphragm as the separator.

[0157] The assembled button-type sodium-ion battery was left to stand for 12 hours. The electrochemical performance of the standing button-type sodium-ion battery was then tested under constant current using the Wuhan Landian Battery Testing System.

[0158] Charge the battery at a constant current rate of 0.1C to 4.5V, then charge it at a constant voltage rate of 4.5V until the current equals 0.05C. Record this charging capacity as the first-cycle charging specific capacity. After resting for 5 minutes, discharge the battery at a constant current rate of 0.1C until the voltage reaches 2.5V. Record this discharge capacity as the first-cycle discharging specific capacity. Divide the first-cycle discharging specific capacity by the first-cycle charging specific capacity to obtain the initial coulombic efficiency.

[0159] 8. Rate Performance: The biomass hard carbon material is coated into a negative electrode according to the method in the coin capacity test. The positive electrode uses a sodium sheet, along with a glass fiber separator and an electrolyte (1M). A full cell composed of LiPF6 (solvent volume ratio EC:DMC:DEC=2:2:1) was charged at a constant current rate of 0.1C to a voltage of 4.5V, then charged at a constant voltage of 4.5V to a current of 0.05C. After resting for 5 minutes, it was discharged at a constant current rate of 0.1C to a voltage of 2.5V. The capacity at this point was recorded as the discharge capacity at the 0.1C rate. After resting for 10 minutes, it was charged at a constant current rate of 1C to a voltage of 4.5V, then charged at a constant voltage of 4.5V to a current of 0.05C. After resting for 5 minutes, it was discharged at a constant current rate of 1C to a voltage of 2.5V. The capacity at this point was recorded as the discharge capacity at the 1C rate. The discharge capacity at the 1C rate divided by the discharge capacity at the 0.1C rate is the 1C rate performance.

[0160] Figure 1 SEM image of the biomass hard carbon material of Example 1 provided by the present invention.

[0161] from Figure 1 As can be seen, the biomass hard carbon material of Example 1 has no obvious pore structure on its surface and its surface is smooth.

[0162] Figure 2 SEM image of the biomass hard carbon material of Comparative Example 5 provided by the present invention.

[0163] from Figure 2 It can be seen that the biomass hard carbon material in Comparative Example 5 has obvious large pores on its surface. Due to the one-stage heating, the activation degree is uneven, and the carbon deposited on the surface cannot completely cover the pore structure on the surface.

[0164] Table 1

[0165]

[0166] As shown in Table 1, compared with the comparative example, the biomass hard carbon material provided by the present invention, by limiting the relationship between the thickness of the carbon coating layer, the volume of the closed pores, the interlayer spacing of the diffraction peaks corresponding to the (002) crystal plane of the biomass hard carbon material, and the specific surface area of ​​the biomass hard carbon material, can improve the specific capacity, first coulombic efficiency and rate performance of the battery when applied to the battery.

[0167] Compared to Comparative Example 2, Example 1, using pre-oxidized lignin, effectively improves hydrophilicity, allowing phosphates and metal salts to adhere uniformly to the lignin surface during subsequent spray drying. In contrast, Comparative Example 2, employing liquid-phase impregnation, results in poor uniformity of phosphate and metal salt distribution, leading to insufficient activation and unevenness during the subsequent high-temperature process.

[0168] Compared with Comparative Example 3, Example 1 uses a mixture of phosphate and phosphoric acid, which can form a rich porous structure. With the subsequent deposition of methane, the electrochemical performance of the biomass hard carbon material itself is greatly improved.

[0169] Compared with Comparative Example 4, Example 1 uses metal salts, which have a greater impact on subsequent methane deposition. The uniform distribution of metal salts and the acceleration of methane deposition by metal elements can make the thickness of the methane deposition layer more uniform, resulting in a higher initial coulombic efficiency of the biomass hard carbon material.

[0170] Compared with Comparative Example 5, Example 1 uses a three-stage heating process, which can generate a sufficient amount of pore structure in the pore expansion stage, which has a greater impact on the subsequent methane deposition, thereby improving the battery's specific capacity, initial coulombic efficiency and rate performance.

[0171] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A biomass hard carbon material, characterized in that, The material includes a biomass hard carbon matrix and a carbon coating layer on the surface of the biomass hard carbon matrix. The biomass hard carbon matrix has closed pores, and the biomass hard carbon material satisfies Equation 1: T HC ×V closed ×d 002 / SSA≥0.3 Equation 1, Among them, T HC V represents the thickness of the carbon coating layer, in nm; closed The volume of the closed aperture is in cm. 3 / g;d 002 The interlayer spacing of the diffraction peaks corresponding to the (002) crystal plane of the biomass hard carbon material is nm; SSA is the specific surface area of ​​the biomass hard carbon material, m². 2 / g.

2. The biomass hard carbon material according to claim 1, characterized in that, 0.3≤T HC ×V closed ×d 002 / SSA≤1.0; And / or, in the Raman spectrum of the biomass hard carbon material, the intensity ratio of the D peak to the G peak is I. D / I G 1.70≤I D / I G ≤1.85; And / or, the closed-cell content of the biomass hard carbon material by volume A is ≥ 45%; preferably, 45% ≤ A ≤ 55%.

3. The biomass hard carbon material according to claim 1 or 2, characterized in that, 35nm≤T HC ≤60nm; And / or, 0.23cm 3 / g≤V closed ≤0.3cm 3 / g; And / or, 0.374nm≤d 002 ≤0.382nm; And / or, 5.0m 2 / g≤SSA≤15.0m 2 / g.

4. A method for preparing biomass hard carbon material as described in any one of claims 1-3, characterized in that, Includes the following steps: The raw material system, including a pre-oxidized first carbon source, phosphate, and metal salt, is spray-dried and then subjected to a first sintering treatment to obtain a carbon skeleton material. The carbon skeleton material is subjected to a second sintering treatment in the presence of metal salts to obtain a biomass hard carbon material precursor. The biomass hard carbon material precursor is subjected to carbon coating treatment to obtain the biomass hard carbon material.

5. The preparation method according to claim 4, characterized in that, The temperature of the first sintering treatment is 300~400℃, and the time is 1~2h; And / or, the temperature of the second sintering treatment is 600~700℃, and the time is 2~4h.

6. The preparation method according to claim 4 or 5, characterized in that, The pre-oxidation process includes: pre-oxidizing the first carbon source in air at 200-250°C for 2-4 hours and / or pre-oxidizing it under hydrothermal conditions at 180-220°C for 2-4 hours; And / or, the molar concentration of the metal salt in the raw material system is 0.01~0.03 mol / L.

7. The preparation method according to any one of claims 4-6, characterized in that, The process of carbon coating the biomass hard carbon material precursor includes: performing a third sintering treatment on the biomass hard carbon material precursor in the presence of a second carbon source to obtain the biomass hard carbon material. Preferably, the temperature of the third sintering treatment is 800~1000℃ and the time is 1~3h.

8. The preparation method according to any one of claims 4-7, characterized in that, The mass ratio of the first carbon source, phosphate, and metal salt is 1:(1~3):(1~2); And / or, the first carbon source includes lignin or lignin-containing biomass raw materials, preferably, the biomass raw materials include at least one of corn cob residue, wheat straw, straw, eucalyptus wood, pine wood, and corn cob; And / or, the phosphate includes at least one of disodium hydrogen phosphate, sodium dihydrogen phosphate, and phosphoric acid; And / or, the metal salt includes at least one of FeCl3·6H2O, CoCl2·6H2O, and NiCl2·6H2O.

9. A negative electrode sheet, characterized in that, This includes the biomass hard carbon material as described in any one of claims 1-3 or the biomass hard carbon material prepared according to the preparation method described in any one of claims 4-8.

10. A battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

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