Biomass-derived graphitized porous activated carbon negative electrode for lithium ion battery and preparation method of biomass-derived graphitized porous activated carbon negative electrode

Abstract

The embodiment of the invention provides a biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery and a preparation method of the biomass-derived graphitized porous activated carbon negative electrode, and the biomass-derived graphitized porous activated carbon negative electrode for the lithium ion battery comprises a current collector; the active coating is coated on the current collector; wherein the active coating is prepared from biomass graphitized porous activated carbon, a conductive additive and a binder. According to the biomass-derived graphitized porous activated carbon negative electrode for the lithium ion battery and the preparation method of the biomass-derived graphitized porous activated carbon negative electrode, provided by the embodiment of the invention, the biomass graphitized porous activated carbon is activated by adopting a molten salt method; and the lithium ion battery cathode shows high capacity, long service life and fast charge potential, and is especially suitable for being compounded with a high-capacity material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery and a preparation method thereof. BACKGROUND

[0002] With the rapid development of portable electronic devices, electric vehicles and renewable energy systems, the demand for high-performance lithium ion batteries has significantly increased. In order to meet these changing demands, batteries must provide higher energy density, faster charging capability and longer cycle life. As a key component of lithium ion batteries, the negative electrode material plays a decisive role in determining the battery capacity, rate performance and cycle stability.

[0003] The current standard material graphite has a theoretical specific capacity of only about 372 mAh / g, which limits the energy density of the battery, which is far from enough for high-performance applications such as electric vehicles and high-capacity portable electronic devices. In addition, existing negative electrode materials, including silicon and lithium metal, have significant drawbacks. Silicon, although having a high theoretical capacity of about 4200 mAh / g, will undergo volume expansion during lithiation, resulting in mechanical instability and capacity decay. Lithium metal, although providing a high theoretical capacity of 3860 mAh / g, has safety problems due to dendrite formation leading to short circuits and potential hazards.

[0004] Based on this, the current negative electrode material applied in lithium ion batteries cannot meet the needs of current high-performance application scenarios. SUMMARY

[0005] Therefore, the embodiments of the present application provide a biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery and a preparation method thereof to solve the technical problem that the current negative electrode material applied in lithium ion batteries cannot meet the needs of current high-performance application scenarios.

[0006] In a first aspect, the embodiments of the present application provide a biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery, comprising:

[0007] a current collector;

[0008] an active coating coated on the current collector;

[0009] The preparation material of the active coating comprises biomass graphitized porous activated carbon prepared by a molten salt activation method, a conductive additive and a binder.

[0010] In some embodiments, the mass ratio of the biomass graphitized porous activated carbon, the conductive additive and the binder is (5-10):(0.2-2):(0.2-2).

[0011] In some embodiments, the mass ratio of the biomass graphitized porous activated carbon, the conductive additive, and the binder is 8:1:1.

[0012] In some embodiments, the conductive additive comprises at least one of carbon black, conductive graphite, graphene, vapor grown carbon fiber, carbon nanotube.

[0013] In some embodiments, the binder comprises at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, butadiene styrene rubber, polyacrylic acid, water-based polyurethane, sodium alginate.

[0014] In some embodiments, the current collector comprises one of copper foil, aluminum foil, carbon nanotube film, graphene, two-dimensional metal carbide.

[0015] In a second aspect, the embodiments of the present application provide a preparation method of a biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery, the preparation method being used for preparing the biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery of the first aspect, and the preparation method comprising the following steps:

[0016] mixing and annealing a biomass raw material and a molten salt chemical to form a biomass-derived graphitized porous activated carbon;

[0017] providing the biomass-derived graphitized porous activated carbon, the conductive additive, the binder, and the current collector;

[0018] mixing the biomass-derived graphitized porous activated carbon, the conductive additive, and the binder thoroughly to obtain a slurry;

[0019] coating the slurry on the surface of the current collector, and obtaining the biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery after drying.

[0020] In some embodiments, the step of mixing and annealing the biomass raw material and the molten salt chemical to form the graphitized porous activated carbon comprises the following steps:

[0021] providing a roxburghia as the biomass;

[0022] pre-treating the biomass;

[0023] mixing and performing one-time carbonization and activation treatment on the pre-treated biomass to obtain an intermediate;

[0024] performing annealing treatment on the intermediate to obtain the biomass-derived graphitized porous activated carbon.

[0025] In some embodiments, the pre-processed biomass is mixed with the molten salt and subjected to a one-step carbonization and activation treatment, comprising:

[0026] adding a molten salt to the pre-processed biomass;

[0027] carrying out carbonization and activation at 650-950℃ for 1-5h.

[0028] In some embodiments, the molar ratio of the biomass to the molten salt is 1:(3-7).

[0029] In some embodiments, the molar ratio of the biomass to the molten salt is 1:5.

[0030] In some embodiments, the molten salt comprises one of a deep eutectic solvent, a metal chloride composite molten salt, a nitrate molten salt, a sulfate molten salt.

[0031] In some embodiments, the metal chloride composite molten salt comprises zinc chloride and potassium chloride, copper chloride, iron chloride, sodium chloride.

[0032] The deep eutectic solvent comprises a choline chloride and urea system, a choline chloride and lactic acid system.

[0033] In some embodiments, the pre-treatment comprises: crushing and drying the biomass.

[0034] In some embodiments, after the intermediate is subjected to annealing treatment, further comprising: washing and drying the intermediate after the annealing treatment.

[0035] The biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery and the preparation method thereof provided in the embodiments of the present application are as follows: the biomass graphitized porous activated carbon is adopted, the biomass graphitized porous activated carbon is designed in structure and regulated in surface, and exhibits high capacity, long service life and fast charging potential in the lithium ion battery negative electrode, and is especially suitable for being used in combination with high capacity materials. Specifically, the biomass carbon forms a layered structure similar to graphite, has good electronic conductivity, reduces the electrode internal resistance, and improves the charge transport efficiency. The regular interlayer spacing of the graphitized carbon is close to the lithium ion insertion channel of graphite, is beneficial to the fast insertion / extraction of lithium ions, and improves the rate performance. The synergistic effect of the multi-level pore structure provides a large number of active sites through the surface adsorption mechanism to store lithium ions, and contributes to the additional pseudo-capacitance capacity; the mesopore serves as an electrolyte infiltration channel, shortens the lithium ion diffusion path, and simultaneously relieves the volume change stress in the charging and discharging process; the macropore enhances the mechanical stability of the electrode structure, and prevents the pulverization of the active material in the cycle. When the biomass-derived graphitized porous activated carbon negative electrode provided in the present application is paired with a high energy density positive electrode, the biomass-derived graphitized porous carbon negative electrode provides excellent full battery performance, and is very suitable for electric vehicles, portable electronic devices and energy storage systems and the like applications. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0037] Figure 1 is a flowchart of the preparation method of the biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery provided in the embodiments of the present application;

[0038] Figure 2 is a flowchart of the preparation method of the biomass-derived graphitized porous activated carbon in the biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery provided in the embodiments of the present application;

[0039] Figure 3 is the X-ray diffraction pattern of the biomass-derived graphitized porous activated carbon in the biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery provided in the embodiments of the present application;

[0040] Figure 4 is the high-resolution transmission electron microscope image and the selected area electron diffraction spectrum of the biomass-derived graphitized porous activated carbon in the biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery provided in the embodiments of the present application;

[0041] Figure 5 is nitrogen adsorption-desorption isotherm (left) and pore size distribution curve (right) of the biomass-derived graphitized porous activated carbon in the biomass-derived graphitized porous activated carbon negative electrode for lithium ion batteries provided by the embodiments of the present application;

[0042] Figure 6 is cyclic voltammetry comparison curve of the biomass-derived graphitized porous activated carbon negative electrode and the commercial graphite negative electrode provided by the embodiments of the present application under the half-cell configuration, with the scanning rate of 1 mV*s -1

[0043] Figure 7 is constant current charge-discharge voltage comparison curve of the biomass-derived graphitized porous activated carbon negative electrode and the commercial graphite negative electrode provided by the embodiments of the present application under the half-cell configuration, with the current density of 0.1 A*g -1

[0044] Figure 8 is charge-discharge voltage comparison curve of the biomass-derived graphitized porous activated carbon negative electrode and the commercial graphite negative electrode provided by the embodiments of the present application under the full-cell configuration (paired with NMC811 positive electrode), with the current density of 0.1 A*g -1

[0045] Figure 9 is rate performance of the biomass-derived graphitized porous activated carbon negative electrode provided by the embodiments of the present application under the full-cell configuration, under different current densities (0.1-1.6 A*g -1

[0046] Figure 10 is comparative rate performance of the biomass-derived graphitized porous activated carbon negative electrode and the commercial graphite negative electrode provided by the embodiments of the present application under the full-cell configuration, under different current densities (0.1-1.6 A*g -1

[0047] Figure 11 is long-term cycle performance and coulombic efficiency of the biomass-derived graphitized porous activated carbon negative electrode and the commercial graphite negative electrode provided by the embodiments of the present application under the full-cell configuration, after 500 cycles. DETAILED DESCRIPTION

[0048] In the following description, specific details are set forth, such as particular system configurations, techniques, etc., in order to provide a thorough understanding of the embodiments of the present application. However, persons having ordinary skill in the art will readily appreciate that the embodiments of the present application can be practiced without these specific details. In other instances, well-known structures, devices, circuits, and processes have not been described in detail in order to avoid obscuring the description of the embodiments of the present application.

[0049] ​​​​​It should also be understood that the term "and / or" as used herein refers to a combination of one or more of the associated listed items, and all possible combinations, and includes these combinations.

[0050] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0051] It should be understood that the terms "length", "width", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0052] In addition, in the description of the embodiments of the present application and the appended claims, the terms "first", "second", "third" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0053] In the description of the embodiments of the present application, the reference "some embodiments" or "some embodiments" and the like means that the specific features, structures or characteristics described in connection with the embodiments are included in one or more embodiments of the present application. Therefore, the statements "in some embodiments", "in some embodiments", "in other some embodiments", "in other some embodiments" and the like appearing in different places in the specification are not necessarily all referring to the same embodiments, but mean "one or more but not all embodiments", unless otherwise specifically emphasized. The terms "include", "contain", "have" and their variants mean "include but not limited to", unless otherwise specifically emphasized. "Multiple" means two and more than two.

[0054] The first aspect of the embodiments of the present application provides a biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery, comprising a current collector and an active coating layer coated on the current collector.

[0055] The preparation material of the active coating layer comprises biomass graphitized porous activated carbon prepared by using a molten salt activation method, a conductive additive and a binder.

[0056] The biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery provided by the embodiments of the present application is prepared by using biomass graphitized porous activated carbon. The biomass graphitized porous activated carbon exhibits high capacity, long service life and fast charging potential in the lithium ion battery negative electrode through structural design and surface regulation, and is particularly suitable for being used in combination with high-capacity materials. Specifically, the biomass carbon forms a layered structure similar to graphite, has good electronic conductivity, reduces the internal resistance of the electrode, and improves the charge transport efficiency. The regular interlayer spacing of the graphitized carbon is close to the lithium ion insertion channel of graphite, which is beneficial to the rapid insertion / extraction of lithium ions and improves the rate performance. The synergistic effect of the hierarchical pore structure provides a large number of active sites through the surface adsorption mechanism to store lithium ions and contributes to the additional pseudo-capacitance capacity; the mesopores serve as electrolyte infiltration channels, shorten the lithium ion diffusion path, and at the same time, relieve the volume change stress in the charging and discharging process; the macropores enhance the mechanical stability of the electrode structure and prevent the pulverization of the active material in the cycle. When the biomass-derived graphitized porous activated carbon negative electrode is paired with a high-energy-density positive electrode, the biomass-derived graphitized porous carbon negative electrode provides excellent full-cell performance, making it very suitable for electric vehicles, portable electronic devices and energy storage systems and the like.

[0057] In applications, the biomass graphitized porous activated carbon has the following advantages:

[0058] High specific capacity and capacity retention rate. The theoretical capacity of traditional graphite is 372 mAh / g, while the actual capacity of the biomass graphitized porous activated carbon can reach 400-600 mAh / g due to the surface adsorption and defect lithium storage mechanism. The buffer effect of the porous structure reduces the volume effect, and the stable skeleton of high graphitization degree can achieve a capacity retention rate of more than 90% after 100 cycles (the capacity retention rate of traditional graphite is usually 85%-90%).

[0059] Excellent rate performance. The mesoporous dominant fast ion transport path enables the material to maintain a relatively high capacity at a high rate, which is superior to traditional graphite.

[0060] Low-temperature and high-temperature adaptability. The porous structure reduces the influence of electrolyte viscosity, and the capacity retention rate at -20°C can reach 70% of that at room temperature. The high crystallinity of the graphitized carbon reduces the side reaction with the electrolyte, and the capacity decay rate at 60°C is reduced by 30% compared with hard carbon.

[0061] Environmentally friendly and cost advantage. The raw materials are widely available (such as straw, fruit shells, wood waste), which reduces the dependence on petroleum-based precursors and reduces the production cost.

[0062] In some embodiments, the conductive additive includes at least one of carbon black, conductive graphite, graphene, vapor grown carbon fiber, carbon nanotube. In a preferred embodiment, the conductive additive is graphite, and the model is Super P carbon black. Carbon black is used for lithium ion battery positive electrode conductive agent, which can effectively improve the electron and ion passage.

[0063] In application, the conductive additive can also be superconducting carbon black, which can significantly improve the conductivity and reduce the amount of addition by optimizing the specific surface area and branched structure. Carbon nanotubes form "point-to-line" contact with active materials, build a continuous conductive network, and improve the rate performance and cycle life. The two-dimensional sheet structure of graphene realizes "point-to-plane" contact, greatly reduces the amount of conductive agent, and improves the proportion of active material and battery capacity.

[0064] In some embodiments, the binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, water-based polyurethane, sodium alginate. In a preferred embodiment, the binder is polyvinylidene fluoride, which fixes the biomass graphitized porous activated carbon together and ensures the structural integrity of the electrode during the cycle process. In application, the binder is sodium carboxymethyl cellulose, which is used as a water-soluble polymer, and is used in combination with styrene butadiene rubber, which is low in cost, environmentally friendly, and has good compatibility with silicon-based negative electrodes. Styrene butadiene rubber is an elastic latex material with high flexibility, which can buffer the volume change of electrode materials; it is suitable for high-capacity silicon-based negative electrodes. Polyacrylic acid is a water-based binder containing carboxylic acid groups, which can improve the binding force through strong hydrogen bonding and inhibit the volume expansion of silicon negative electrodes; it has good adhesion with aluminum current collectors.

[0065] In some embodiments, the current collector includes one of copper foil, aluminum foil, carbon nanotube film, graphene, two-dimensional metal carbide. In a preferred embodiment, the current collector is copper foil. In application, copper has extremely low bulk resistivity, which can significantly reduce the internal resistance of the electrode, improve the rate performance of the battery, and ensure fast electron transfer during the charging and discharging process due to its excellent conductivity, especially for high-energy-density negative electrodes. At the working potential of the negative electrode, copper does not alloy with lithium, avoiding the failure of the current collector due to lithium expansion. The surface oxide layer is stable in conventional electrolyte and inhibits side reactions. Copper foil can withstand a pressure greater than 200 MPa without breaking during the electrode rolling process, while maintaining flexibility, which is suitable for winding / stacking process. The surface roughness is controllable, and the surface morphology can be adjusted through electrolytic deposition process to enhance the adhesion with active materials and reduce the powder loss. The production technology of copper foil (electrolytic copper foil, rolled copper foil) is mature, with a yield of more than 98%, and is highly compatible with existing coating and slitting equipment. The surface is easy to modify (such as carbon coating, etching treatment), which can be customized to meet different negative electrode requirements.

[0066] In some embodiments, the mass ratio of the biomass-derived graphitized porous activated carbon, the conductive additive, and the binder is (5-10):(0.2-2):(0.2-2). By maximizing the proportion of active material, optimizing the conductive network, and balancing the bonding strength, a synergy of high capacity, long life, and process feasibility is achieved. In some embodiments, the mass ratio of the biomass graphitized porous activated carbon, the conductive additive, and the binder can be 5:2:2, 7:1.5:1.5, 8:1:1, 9:0.5:0.5, 10:0.2:0.2, or any value within the range of (5-10):(0.2-2):(0.2-2).

[0067] In application, the biomass graphitized porous activated carbon is the energy storage main body, its high specific surface area and graphitized structure provide double lithium storage mechanisms (insertion + surface adsorption), and a high proportion can improve the overall capacity of the electrode. The porous structure needs sufficient volume proportion to maintain pore channels to ensure electrolyte infiltration and fast transmission of lithium ions, while avoiding blockage of pores by conductive agents / binders. The conductive additive is adapted, and the proportion of the conductive agent (such as Super P, carbon nanotubes) needs to cover the surface of the activated carbon particles and form a continuous conductive path. Too little will cause electron transmission to be blocked, and too much will occupy the space of the active material, reducing the energy density. The conductivity of biomass activated carbon is weaker than that of graphite, and an appropriate amount of conductive agent is needed to compensate, but graphitization treatment can reduce the amount. The binder balances the structural stability, and the high specific surface area of the porous activated carbon needs more binder to anchor the particles and prevent them from falling off due to volume changes during cycling. The binder needs to uniformly coat the active material and the conductive agent to form a stable slurry. Too low will cause the electrode sheet to be brittle, and too high will increase the internal resistance and hinder ion transmission.

[0068] In a preferred embodiment, the mass ratio of the biomass graphitized porous activated carbon, carbon black, and polyvinylidene fluoride is 8:1:1. In the above ratio, carbon black can effectively improve the conductivity of the biomass graphitized porous activated carbon, and polyvinylidene fluoride can tightly bond the two together, thereby improving the overall result stability and improving the performance of the negative electrode at high charge and discharge rates.

[0069] The embodiments of the present application also provide a preparation method of a biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery, as shown in Figure 1 The preparation method is used for the biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery of the first aspect, and the preparation method comprises the following steps:

[0070] S10, mixing biomass raw materials and molten salt chemicals and performing annealing to form biomass-derived graphitized porous activated carbon;

[0071] S20, providing biomass-derived graphitized porous activated carbon, a conductive additive, a binder, and a current collector;

[0072] S30, fully mixing the biomass-derived graphitized porous activated carbon, the conductive additive, and the binder to obtain a slurry;

[0073] S40, coating the slurry on the surface of the current collector, and drying to obtain a biomass-derived graphitized porous activated carbon negative electrode for lithium-ion batteries.

[0074] The preparation method of the biomass-derived graphitized porous activated carbon negative electrode for lithium-ion batteries provided in the embodiments of the present application is simple and scalable, highly compatible with existing lithium battery negative electrode production lines, does not require complex equipment modification, and is suitable for large-scale production; the slurry dispersion is controllable, and by optimizing the mixing sequence (such as premixing the conductive agent and the binder first, and then gradually adding the activated carbon), it is ensured that the surface of the porous activated carbon is evenly coated with a conductive network to reduce agglomeration.

[0075] In some embodiments, as Figure 2 As shown, in step S10, the biomass raw material and the molten salt chemical are mixed and annealed to form the biomass-derived graphitized porous activated carbon, which includes the following steps:

[0076] S11. providing Radix Astragali as biomass;

[0077] S12, pre-treating the biomass;

[0078] S13, mixing the pre-treated biomass with molten salt and performing a one-time carbonization activation treatment to obtain an intermediate;

[0079] S14. Annealing the intermediate to obtain biomass-derived graphitized porous activated carbon.

[0080] In step S11, radish is provided as biomass. Radish stems are rich in cellulose and lignin, which readily form a cross-linked carbon skeleton upon carbonization, providing the foundation for a porous structure. Its natural vascular structure is retained as ordered mesopores after carbonization, shortening the lithium ion diffusion path. Radish is widely distributed in my country and can be utilized as a waste biomass resource, resulting in low raw material costs. Its high growth rate ensures the feasibility of large-scale supply.

[0081] In step S12, the biomass is pre-processed, including crushing and drying the biomass.

[0082] Other embodiments also include removing surface sediment and ash to prevent metallic impurities from interfering with graphitization during subsequent activation. Low-temperature drying preserves the biomass microstructure, controlling the moisture content to <5% to prevent structural collapse during carbonization. Mechanical crushing increases the specific surface area and improves subsequent activation efficiency.

[0083] In step S13, carbonization and activation are processed synchronously, heated to 600-900℃ in an inert atmosphere, organic components of the plant are decomposed into amorphous carbon, and molten salt (such as ZnCl2-KCl) penetrates into the carbon skeleton to etch and form pores. Cl- in the molten salt reacts with carbon (C+2ZnCl2→CCl4↑+Zn) to generate micropores (<2nm) and mesopores (2-50nm), and the specific surface area is greatly improved. Carbonization and activation are processed synchronously, avoiding the energy loss of the traditional two-step method (carbonization followed by activation), and the total time is greatly shortened. The molten salt acts as a template and catalyst to promote the growth of graphite crystallites and improve the electrical conductivity.

[0084] In application, in step S13, the pretreated biomass is mixed with molten salt and subjected to one-time carbonization and activation treatment to obtain an intermediate, including:

[0085] S131, adding molten salt to the pretreated biomass;

[0086] S132, carbonization and activation are performed at 650-950℃ for 1-5h. The molten salt-assisted synchronous carbonization-activation process, through the synergistic effect of chemical etching, template guidance, and high-temperature graphitization, endows the biomass activated carbon with high specific surface area, hierarchical pores, and high electrical conductivity, making it have high capacity and fast charging characteristics of lithium battery negative electrode. Specifically, the temperature can be 700℃, 720℃, 740℃, 760℃, 780℃, 800℃, 850℃, 880℃, 900℃, etc., any value within the range of 700-900℃, and the time can be 1h, 2h, 2.2h, 2.4h, 2.5h, 2.6h, 2.8h, 3h, 4h, 5h, etc., any value within the range of 1-5h.

[0087] In the application, this step significantly optimizes the porous structure, graphitization degree and electrochemical performance of the material through the synergistic effect of chemistry and physics. ZnCl2 decomposes into ZnO and Cl2 (ZnCl2→ ZnO + Cl2↑) at high temperature, and Cl2 reacts with carbon to generate volatile substances (C + 2Cl2→ CCl4↑), etching the carbon skeleton to form micropores (<2 nm). The molten salt is in a liquid state at high temperature and penetrates into the interior of the biomass fibers. After carbonization, the molten salt residue is removed by acid washing to form a biomimetic multi-level pore structure (vascular mesoporous + random microporous), and the specific surface area is effectively improved. At 700-900°C, cellulose / lignin in biomass pyrolysis generates amorphous carbon, and the molten salt inhibits the generation of tar byproducts, effectively improving the carbon yield. High temperature promotes the ordered arrangement of carbon six-membered rings, locally forming graphite crystallites to improve electrical conductivity. Among them, the temperature gradient control, 700-800°C: mainly generate micropores, the specific surface area increases rapidly; 800-900°C: mesoporous expansion, pore volume is improved. The time is 2 to 3 hours to ensure that the molten salt penetrates and reacts fully, and to avoid insufficient activation for a short time or pore structure collapse for a long time.

[0088] In some embodiments, the molar ratio of biomass to molten salt is 1:(3-7). In specific embodiments, the molar ratio of biomass to molten salt can be 1:3, 1:4, 1:5, 1:6, 1:7, etc. Any value within the range of 1:(4-6) is possible. In a preferred embodiment, the molar ratio of biomass to molten salt is 1:5. The appropriate ratio of molten salt ensures sufficient activator to generate micropores and mesopores, while avoiding excessive etching leading to structural collapse. Metal ions in the molten salt may promote the graphitization of carbon structure and improve electrical conductivity. Suitable ratios may promote the doping of heteroatoms such as nitrogen, sulfur, etc., enhancing electrochemical activity. The preferred ratio may achieve the best performance while reducing the amount of molten salt used and reducing costs. The molar ratio of biomass to molten salt 1:5 achieves an optimal balance between pore structure, graphitization degree, electrochemical performance and cost, and is an ideal choice that takes into account high capacity, fast charging characteristics and industrial feasibility.

[0089] In step S14, high-temperature annealing (1200-1500°C) converts amorphous carbon into graphite-like structure through thermal-induced rearrangement, and the interlayer spacing approaches graphite, improving lithium ion insertion / extraction kinetics. Eliminate dangling bonds and unstable functional groups in the carbon skeleton, reduce the irreversible capacity loss of the first charge and discharge. Post-processing includes washing and drying, using dilute hydrochloric acid to remove residual molten salt and metal particles, which is beneficial to improve purity. Water washing and drying remove acid washing residues and avoid electrolyte side reactions, with a final water content of <0.1%. In addition, it is also possible to perform graded screening to obtain activated carbon particles with concentrated particle size distribution through airflow grading, improving the uniformity of electrode coating.

[0090] In some embodiments, the molten salt comprises one of a deep eutectic solvent, a metal chloride composite molten salt, a nitrate molten salt, a sulfate molten salt. The deep eutectic solvent comprises a choline chloride and urea system, a choline chloride and lactic acid system. The deep eutectic solvent is composed of a hydrogen bond donor and a hydrogen bond acceptor, has the characteristics of simple preparation and biodegradability, and is widely used in lignocellulose pretreatment and biomass activation. Choline chloride + urea, through the action of hydrogen bond, destroys the lignin-carbohydrate complex, selectively removes lignin and retains the cellulose structure. Choline chloride + lactic acid, the acidic deep eutectic solvent can effectively hydrolyze hemicellulose, improve the yield of fermentable sugar, and at the same time recover high-purity lignin.

[0091] In some embodiments, the metal chloride composite molten salt comprises zinc chloride and potassium chloride, copper chloride, iron chloride, sodium chloride; in a preferred embodiment, the metal chloride comprises zinc chloride and potassium chloride.

[0092] In some embodiments, the pretreatment comprises: crushing and drying the biomass. It is conducive to subsequent activation of the biomass by using the molten salt chemicals. In some embodiments, after the intermediate is subjected to the annealing treatment, the intermediate subjected to the annealing treatment is further subjected to washing and drying. It is conducive to removing excess solution chemicals and obtaining high-purity biomass-derived graphitized porous activated carbon.

[0093] Embodiment

[0094] Embodiment 1

[0095] The embodiment of the present application provides a biomass-derived graphitized porous activated carbon negative electrode for a lithium ion battery and a preparation method thereof, wherein the preparation method comprises the following steps:

[0096] S10, 20 g of Rauvolfia verticillata is mixed with 100 g of mixed salt of zinc chloride and potassium chloride, mixed and subjected to one-step carbonization and activation at 800 DEG C for 2 hours to form biomass-derived graphitized porous activated carbon;

[0097] S20, 80 g of biomass-derived graphitized porous activated carbon, 10 g of Super P carbon black as a conductive additive, 10 g of polyvinylidene fluoride as a binder and a copper foil as a current collector are provided;

[0098] S30, the biomass-derived graphitized porous activated carbon, the Super P carbon black and the polyvinylidene fluoride are uniformly mixed to obtain a slurry;

[0099] S40, the slurry is coated on the surface of the current collector, and dried at 100 DEG C for 12 hours to obtain the biomass-derived graphitized porous activated carbon negative electrode for the lithium ion battery.

[0100] Performance test

[0101] The prepared biomass-derived graphitized porous activated carbon, the prepared biomass-derived graphitized porous activated carbon anode for lithium ion batteries and the commercial graphite anode were applied in batteries and the following tests were conducted.

[0102] 1. Structure and morphology characterization

[0103] The formation of graphitized crystalline domains was confirmed by X-ray diffraction (the (002) peak at 2Θ ~ 26.5°), as shown in Figure 3 , where the abscissa is 2Θ in °; the ordinate is intensity; Graphite is graphite.

[0104] High-resolution transmission electron microscopy and selected area electron diffraction verified the existence of graphitized domains, as shown in Figure 4 , where Graphite region is graphite region, Amorphous region is amorphous region, and Diffraction rings are diffraction rings.

[0105] Nitrogen adsorption-desorption isotherms showed type IV curves with hysteresis loops (mesoporosity), as shown on the left side of Figure 5 , where the abscissa is relative pressure, P / P0; the ordinate is adsorption amount, cm 3 / g, where STP represents the volume of gas adsorbed per gram of material at standard temperature and pressure. The pore size distribution (BJH) of mesoporous materials was calculated based on nitrogen adsorption-desorption isotherms to confirm the pore size, as shown on the right side of Figure 5 , where the abscissa is pore size, nm, and the ordinate is pore volume, cm 3 / g / nm.

[0106] 2. Electrochemical performance evaluation

[0107] The redox behavior and lithium ion intercalation / deintercalation kinetics were tested by cyclic voltammetry, as shown in Figure 6 , where the abscissa is lithium ion intercalation / deintercalation kinetics, and the ordinate is current density, mA / g.

[0108] The specific capacity and voltage curves of MJAC anodes and commercial graphite were determined by galvanostatic charge-discharge tests in half-cell configurations and full-cell configurations, as shown in Figure 7 and Figure 8 , where the abscissa is specific capacity, mAh / g, and the ordinate is potential, V.

[0109] The rate performance test was conducted at different current densities, as shown in Figure 9 , where the abscissa is specific capacity, mAh / g, and the ordinate is potential, V.

[0110] Benchmark comparisons were made with commercial synthetic graphite under the same conditions, e.g. Figure 10 As shown, the horizontal axis in the figure is the number of cycles, and the vertical axis is the specific capacity, with the unit being mAh / g.

[0111] The comparison indicators include specific capacity, rate retention and long-term cycle stability, such as Figure 11 As shown in the figure, the horizontal axis is the number of cycles, the vertical axis on the left is the specific capacity, the unit is mAh / g, and the vertical axis on the right is the coulombic efficiency, the unit is %.

[0112] For the electrochemical tests, a polypropylene separator was used, and the electrolyte consisted of 1 M LiPF6 dissolved in a 1:1 volume ratio mixed solvent of ethylene carbonate and dimethyl carbonate.

[0113] Cell assembly: CR2032 coin cells were assembled in an argon-filled glove box (H2O and O2 levels <1 ppm). For the half-cell configuration, lithium metal foil was used as the counter electrode and reference electrode. For the full-cell test, the MJAC anode was mixed with LiNi 0.8 Co 0.1 Mn 0.1 O2 positive electrode pairing.

[0114] Test results

[0115] 1. Structure and morphology characterization

[0116] like Figure 3 As shown in Figure 2, X-ray diffraction analysis of the prepared biomass-derived graphitized porous activated carbon showed a characteristic peak at 2θ≈26.5°, corresponding to the (002) crystal plane of graphite, confirming the formation of graphitized crystal domains. The material has a mixed structure of crystalline (graphitized) and amorphous carbon phases, reflecting the coexistence of ordered and disordered regions.

[0117] like Figure 4 As shown, high-resolution transmission electron microscopy imaging of the prepared biomass-derived graphitized porous activated carbon revealed the coexistence of graphitized domains and amorphous regions; electron diffraction analysis of the prepared biomass-derived graphitized porous activated carbon showed the characteristic diffraction rings of turbo-layered graphite stacking.

[0118] like Figure 5 As shown, the nitrogen adsorption-desorption isotherm ( Figure 5 , left) shows a type IV curve and a clear hysteresis loop, confirming the formation of mesopores during the carbonization and activation of biomass. BJH pore size distribution ( Figure 5 , right) reveals a dominant pore size centered around 3 to 4 nanometers, which provides an optimal balance between accessible surface area and efficient lithium-ion transport, contributing to improved electrochemical performance in lithium-ion battery applications.

[0119] 2. Electrochemical performance

[0120] 2.1 Half-battery test:

[0121] like Figure 6 As shown, the electrochemical behavior of the MJAC (Metaplexis Japonica-derived Activated Carbon) negative electrode was evaluated by cyclic voltammetry tests, which showed more significant redox peaks and higher current responses compared with commercial graphite, indicating better lithium ion insertion / extraction kinetics.

[0122] like Figure 7 As shown, at 0.1A*g -1 At a current density of 1.5 GHz, the MJAC anode exhibits significantly higher specific capacity and a stable voltage plateau, confirming the improvement of its lithiation / delithiation behavior.

[0123] 2.2 Full battery test:

[0124] like Figure 8 As shown, the full battery test of the negative electrode provided in the embodiment of the present application and the NMC811 positive electrode is shown, and the MJAC is 0.1A*g -1 The results show that the negative electrode material has a stable charge-discharge voltage curve and a higher capacity, which verifies the compatibility and improved electrochemical performance of the negative electrode material.

[0125] like Figure 9 As shown, MJAC is -1 The high specific capacity can be maintained even at high current densities. Notably, the charge-discharge voltage curves at different current densities maintain a consistent shape, indicating stable electrochemical behavior, minimal polarization, and efficient lithium ion transport even at high rate conditions.

[0126] like Figure 10 The rate performance comparison with commercial graphite is shown, which directly compares the rate performance of MJAC and commercial graphite, confirming the superiority of MJAC in high-rate charge and discharge capacity retention.

[0127] 2.3 Long-term cycle stability test:

[0128] like Figure 11 As shown, the MJAC anode exhibits excellent long-term electrochemical stability at 0.1 A*g -1At a current density of 1 A / g, it retains over 90% of the initial capacity after 500 cycles, and the coulombic efficiency is always higher than 99%. In contrast, the commercial graphite electrode shows significant capacity fading during the same cycle period. The excellent cycle durability of MJAC is attributed to its highly stable graphitized porous framework, which can effectively accommodate the volume change during repeated lithiation / delithiation processes, minimizing structural degradation and thus ensuring long-term electrochemical performance.

[0129] Compared with the existing negative electrode material of lithium ion battery, the present application has the following significant advantages:

[0130] 1. Stronger rate capability: The graphitic structure of biomass-derived carbon negative electrode material provides superior electrical conductivity compared to traditional graphite, enabling better performance at high charge and discharge rates.

[0131] 2. Higher specific capacity: Optimized porous structure increases the available surface area for lithium ion storage, improving the specific capacity of the negative electrode, exceeding that of graphite.

[0132] 3. Better cycle stability: Stable graphitic structure and controllable porosity of the material resist mechanical degradation during cycling, ensuring long-term reliability and reducing capacity fading.

[0133] 4. Environmentally friendly and sustainable: Using roxburgh rose as the precursor for the negative electrode material provides a green, sustainable alternative to synthetic graphite, reducing environmental impact associated with traditional graphite mining and manufacturing.

[0134] 5. High initial coulombic efficiency: The material exhibits high initial coulombic efficiency, minimizing capacity loss in the first cycle, a common problem with other negative electrode materials such as silicon.

[0135] 6. Scalability and cost-effectiveness: The synthesis process is designed to be scalable and cost-effective, making it suitable for large-scale industrial production.

[0136] 7. High compatibility: When paired with high-energy-density cathodes such as NMC-811, biomass-derived graphitized porous carbon negative electrodes provide excellent full-cell performance, making them very suitable for applications such as electric vehicles, portable electronic devices, and energy storage systems.

[0137] The negative electrode provided in the present application provides a promising solution to the challenges faced by existing negative electrode materials, providing a negative electrode that combines high energy density, fast charge and discharge capability, long cycle life, and sustainability. It is particularly suitable for high-performance applications such as electric vehicles, high-capacity portable devices, and renewable energy storage.

[0138] In the above embodiments, the description of each embodiment focuses on different aspects, and the parts not described or recorded in a certain embodiment can be referred to the relevant description of other embodiments.

[0139] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit the present application; although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the embodiments of the present application.

Claims

1. A biomass-derived graphitized porous activated carbon negative electrode for lithium-ion batteries, characterized in that: include: current collector; an active coating layer, coated on the current collector; The active coating is prepared using materials including biomass-derived graphitized porous activated carbon prepared using a molten salt activation method, a conductive additive, and a binder.

2. The biomass-derived graphitized porous activated carbon negative electrode for lithium-ion batteries according to claim 1, wherein: The mass ratio of the biomass-derived graphitized porous activated carbon, the conductive additive and the binder is (5-10): (0.2-2): (0.2-2).

3. The biomass-derived graphitized porous activated carbon negative electrode for lithium-ion batteries according to claim 1, wherein: The conductive additive includes at least one of carbon black, conductive graphite, graphene, vapor-grown carbon fiber, and carbon nanotubes; And / or, the binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, water-based polyurethane, and sodium alginate; And / or, the current collector includes one of copper foil, aluminum foil, carbon nanotube film, graphene, and two-dimensional metal carbide.

4. A method for preparing a biomass-derived graphitized porous activated carbon negative electrode for lithium-ion batteries, characterized in that: The preparation method is used to prepare the biomass-derived graphitized porous activated carbon negative electrode for lithium-ion batteries according to any one of claims 1 to 3, and the preparation method comprises the following steps: mixing a biomass feedstock and a molten salt chemical and annealing the mixture to form a biomass-derived graphitized porous activated carbon; Providing the biomass-derived graphitized porous activated carbon, the conductive additive, the binder, and the current collector; Fully mixing the biomass-derived graphitized porous activated carbon, the conductive additive, and the binder to obtain a slurry; The slurry is coated on the surface of the current collector, and after drying, the biomass-derived graphitized porous activated carbon negative electrode for lithium-ion batteries is obtained.

5. The preparation method according to claim 4, wherein The preparation of the biomass-derived graphitized porous activated carbon comprises the following steps: providing radish as biomass; performing pre-treatment on the biomass; The pre-treated biomass molten salt is mixed and subjected to a one-time carbonization and activation treatment to obtain an intermediate; The intermediate is annealed to obtain the biomass-derived graphitized porous activated carbon.

6. The preparation method according to claim 5, wherein The mixing of the pre-treated biomass molten salt and the one-time carbonization and activation treatment include: adding molten salt to the pre-treated biomass; Carbonization and activation are carried out at 650°C to 950°C for 1 to 5 hours.

7. The preparation method according to claim 6, wherein The molar ratio of the biomass to the molten salt is 1:(3-7).

8. The preparation method according to claim 6, wherein The molten salt includes one of a low eutectic solvent, a metal chloride composite molten salt, a nitrate molten salt, and a sulfate molten salt.

9. The preparation method according to claim 8, wherein The metal chloride composite molten salt includes zinc chloride, potassium chloride, copper chloride, ferric chloride and sodium chloride; The deep eutectic solvent includes a choline chloride and urea system, and a choline chloride and lactic acid system.

10. The preparation method according to any one of claims 5 to 9, characterized in that: The pre-treatment includes: crushing and drying the biomass; And / or, after annealing the intermediate, the method further comprises: washing and drying the annealed intermediate.

Images