Biomass-based composite electrode material, electrode sheet and hybrid supercapacitor

Abstract

The application provides a biomass-based composite electrode material, an electrode sheet and a hybrid supercapacitor, and belongs to the technical field of electrochemical energy storage. 3 The biomass-based composite electrode material comprises: a biomass-derived porous carbon matrix, pores with multiple pore sizes, the volume of the pores is 0.7-1.7 cm 2 / g; and nickel-cobalt layered double hydroxide nanosheets vertically anchored on the surface of the biomass-derived porous carbon matrix; the specific surface area of the composite electrode material is 900-1400 m 2 / g. The biomass-based composite electrode material of the application significantly improves the ion adsorption and charge storage capacity. In addition, the electrode material is applied in a capacitor, which effectively improves the energy density, electrode conductivity and cycle stability of the supercapacitor.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to a biomass-based composite electrode material, electrode sheet, and hybrid supercapacitor. Background Technology

[0002] With the continued growth of global energy demand and the increasing severity of environmental pollution, the development of efficient and environmentally friendly energy storage devices has become a key research direction. Supercapacitors, based on the double-layer energy storage principle, have demonstrated significant value in the energy storage field due to their advantages such as high power density, rapid charge-discharge characteristics, long cycle life, and wide operating temperature range. However, current conventional supercapacitors still face bottlenecks such as low energy density, limited ion adsorption capacity, and insufficient electrode conductivity.

[0003] To improve performance, researchers are exploring the application of biomass materials in electrode fabrication. Biomass materials are widely available, abundant, and inexpensive, and their pyrolysis-derived porous carbon materials possess good electrical conductivity and chemical stability. However, original biomass porous carbon has significant drawbacks: its specific surface area is generally insufficient, leading to a reduction in effective ion adsorption sites; its pore structure is simple and its pore size distribution is unreasonable, making it difficult to form an efficient hierarchical pore system, thus affecting ion transport kinetics; and its pore volume is low, limiting the electrolyte wetting depth and charge storage capacity. These factors collectively restrict its practical application in high-performance supercapacitors.

[0004] Furthermore, existing preparation processes struggle to synergistically optimize the high specific surface area, rich pore network, and excellent conductivity of porous carbon, leading to an imbalance in the overall material performance. Additionally, the limited proportion of conductive agents in the electrode formulation increases ion migration resistance, further weakening the device's energy conversion efficiency. These issues have hindered progress in improving the overall performance of supercapacitors using biomass-based electrode materials. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a biomass-based composite electrode material, electrode sheet, and hybrid supercapacitor, solving the bottleneck problems of low energy density, limited ion adsorption capacity, and insufficient electrode conductivity in the prior art.

[0006] To address the aforementioned problems, the first aspect of this invention provides a biomass-based composite electrode material, comprising: a biomass-derived porous carbon matrix having pores of varying sizes, wherein the volume of the pores is 0.7–1.7 cm³. 3 / g; and nickel-cobalt layered double hydroxide nanosheets vertically anchored to the surface of the biomass-derived porous carbon matrix; the specific surface area of ​​the composite electrode material is 900–1400 m². 2 / g.

[0007] As one embodiment of the first aspect, the raw material for the biomass-derived porous carbon matrix is ​​agricultural waste, which includes at least one of corn stalks, bamboo, sawdust, and biogas residue.

[0008] As one embodiment of the first aspect, the molar ratio of nickel to cobalt in the nickel-cobalt layered double hydroxide is 1:1 to 2:1.

[0009] As one embodiment of the first aspect, the method for preparing the biomass-derived porous carbon matrix includes:

[0010] The raw materials of the biomass-derived porous carbon matrix are mixed with potassium hydroxide and zinc acetate to prepare a slurry;

[0011] The slurry was dried and then carbonized and activated in an inert atmosphere to obtain the biomass-derived porous carbon matrix.

[0012] As an embodiment of the first aspect, the mass ratio of the raw material of the biomass-derived porous carbon matrix, the potassium hydroxide and the zinc acetate is 1:(0.5–2):1.5.

[0013] In a second aspect, the present invention also provides an electrode sheet comprising a porous carbon electrode layer, wherein the porous carbon electrode layer comprises the biomass-based composite electrode material explained in the first aspect.

[0014] As an embodiment of the second aspect, the raw materials of the porous carbon electrode layer, by mass percentage, include: 87–95% composite electrode material, wherein the composite electrode material is the biomass-based composite electrode material of the first aspect embodiment; 3–8% conductive agent; 1–3% binder; and 1–2% dispersant.

[0015] As an embodiment of the second aspect, the electrode sheet further includes: a ceramic coating disposed on the surface of the porous carbon electrode layer, and a diaphragm layer disposed on the surface of the ceramic coating, wherein the thickness of the porous carbon electrode layer is 60-120 μm, and the thickness of the ceramic coating is 0.2-0.5 μm.

[0016] Thirdly, the present invention also provides a hybrid supercapacitor, comprising a core structure, including: a core structure comprising at least two electric layer composites, wherein the electric layer composites comprise: a positive electrode, a first separator, a negative electrode, and a second separator stacked sequentially from the inside to the outside, wherein the positive electrode comprises the biomass-based composite electrode material as described in any one of claims 1-5 as the active material.

[0017] As an embodiment of the third aspect, a hybrid supercapacitor includes at least two electrical layer composites that are stacked and wound to form the core structure;

[0018] In this configuration, the negative electrode of one of the two adjacent electrical layer complexes is electrically connected to the positive electrode of the other electrical layer complex.

[0019] Due to the above technical solution, the present invention has at least the following beneficial effects:

[0020] The biomass-based composite electrode material according to embodiments of the present invention comprises a biomass-derived porous carbon matrix and has pores of varying sizes, with a pore volume expected to be 0.7–1.7 cm³. 3 The expected values ​​for g and specific surface area are 900–1400 m². 2 / g, and vertically anchored nickel-cobalt layered double hydroxide nanosheets, significantly enhance ion adsorption and charge storage capabilities by optimizing pore structure and strengthening interfacial bonding. Furthermore, electrode sheets prepared from this material are used in double-layer supercapacitors, and these capacitors have a core structure composed of two stacked electric layer composites. This not only reduces the overall volume of the double-layer supercapacitor but also effectively improves the supercapacitor's energy density, electrode conductivity, and cycle stability. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the unfolded structure of the capacitor cell according to an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the capacitor cell structure after winding, according to an embodiment of the present invention.

[0023] Figure 3 This is a flowchart of a method for preparing a capacitor according to an embodiment of the present invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] As described in the background above, traditional supercapacitors have limitations in terms of energy density, ion adsorption capacity, and the proportion of conductive agents added to the electrodes. While biomass porous carbon materials have advantages, their specific surface area and porosity are insufficient, and the interfacial bonding and uniformity are difficult to control when combined with other materials, affecting the conductivity and stability of the composite materials. Existing preparation methods struggle to simultaneously achieve high specific surface area, porous structure, and conductivity, limiting their application in electrochemically efficient supercapacitors.

[0026] To address the aforementioned technical problems, this invention provides a biomass-based composite electrode material, which utilizes a multi-level pore size with a pore volume expected to be 0.7–1.7 cm³. 3 A biomass-derived porous carbon matrix of / g is composited with nickel-cobalt layered double hydroxide nanosheets vertically anchored to the surface of the matrix, and the specific surface area of ​​the composite electrode material is expected to reach 900–1400 m². 2 / g. Specific surface area refers to the total surface area per unit mass of solid (usually measured in m²). 2 / g). Within a certain range, a larger specific surface area means that the material surface can adsorb more ions, store more charge, and thus have a larger capacitance (capacitance). Pore volume refers to the total volume of pores per unit mass of solid material (usually measured in cm³). 3 The large pore volume ( / g) means that there are many voids inside the material, allowing the electrolyte to fully wet the interior. This material overcomes the problems of low specific surface area, insufficient porosity, and poor composite interface bonding in existing biomass porous carbon materials, providing an electrode material for achieving high electrochemical performance in supercapacitors.

[0027] The biomass-based composite electrode material of the present invention will be described below with reference to specific embodiments.

[0028] The biomass-based composite electrode material of this invention includes a biomass-derived porous carbon matrix and nickel-cobalt layered double hydroxide nanosheets vertically anchored to the surface of the matrix.

[0029] The biomass-derived porous carbon matrix has pores with multi-level pore sizes, and the expected pore volume is 0.7–1.7 cm³. 3 / g, for example, 0.8 cm 3 / g, 0.9 cm 3 / g, 1.0 cm 3 / g, 1.1 cm 3 / g, 1.2 cm 3 / g, 1.3 cm 3 / g, 1.4 cm 3 / g, 1.5 cm 3 / g or 1.6 cm 3 / g. Hierarchical pores refer to pore structures with different sizes, including micropores, mesopores, and macropores, coexisting within the carbon matrix. This hierarchical pore structure facilitates rapid ion transport and adsorption in the electrolyte, while also increasing the number of active sites. Furthermore, the combination of a biomass-derived porous carbon matrix with nickel-cobalt layered double hydroxide nanosheets vertically anchored to its surface achieves a composite electrode material with a expected specific surface area of ​​900–1400 m². 2 / g, for example, 1000 m2 / g、1100 m 2 / g、1200 m 2 / g or 1300 m 2 / g etc.

[0030] Therefore, by using the above-mentioned multi-level pore size and pore volume expected to be 0.7–1.7 cm, 3 Composites of a biomass-derived porous carbon matrix with nickel-cobalt layered double hydroxide nanosheets vertically anchored to its surface can synergistically enhance the electrochemical performance of the material. The biomass-derived porous carbon matrix provides conductivity and framework stability, while its hierarchical pore structure facilitates increased ion diffusion and transport rates in the electrolyte. The nickel-cobalt layered double hydroxide nanosheets improve capacitance. The tight bonding and synergistic effect of these two components enable the composite electrode material to achieve capacitance values ​​of 900–1400 μm. 2 The specific surface area of ​​ / g ensures the number of active sites in the material, thereby improving the ion adsorption capacity and charge storage capacity of the electrode material. In the application of supercapacitors, this can provide an increase in ion adsorption sites and improve the efficiency of ion transport channels, thereby enhancing the charge storage capacity and energy density of the electrode. At the same time, the structural stability and conductivity of the material are guaranteed.

[0031] In some embodiments, the raw material for the biomass-derived porous carbon matrix is ​​agricultural waste, including at least one of corn stalks, bamboo, sawdust, and biogas residue. Using agricultural waste allows for the reuse of these crops. Furthermore, these agricultural wastes are abundant carbon sources, inexpensive, and widely available.

[0032] The preparation of biomass-derived porous carbon matrix can be achieved through various methods. For example, biomass raw materials such as corn stalks, bamboo, and sawdust can be pretreated and then carbonized under an inert atmosphere. The carbonized product can be physically activated, such as by steam activation or carbon dioxide activation, or chemically activated, such as by using activators like phosphoric acid or zinc chloride, to introduce a hierarchical pore structure. By adjusting parameters such as carbonization temperature, type and amount of activator, and activation time, the pore structure of the obtained porous carbon matrix can be controlled to achieve a hierarchical pore size, and the pore volume can be adjusted to 0.7–1.7 cm³. 3 The range of / g.

[0033] For example, in some embodiments, biomass porous char can be mixed with nickel salts, cobalt salts, ethylene glycol, hexamethylenetetramine, and water, and subjected to a hydrothermal reaction at 120-180°C for 6-12 hours, causing nickel-cobalt LDH nanosheets to be vertically oriented and anchored on the porous char surface, forming a three-dimensional hierarchical structure. By selecting suitable activators and activation conditions, a char matrix with micropores, mesopores, and macropores can be obtained, thereby providing ion transport channels and adsorption sites for subsequent composite materials.

[0034] In other embodiments, agricultural waste can also be selected from those rich in cellulose, hemicellulose, and lignin, such as rice husks, straw, and peanut shells. These materials readily form porous structures during pyrolysis and carbonization. Alternatively, agricultural waste containing heteroatoms such as nitrogen and sulfur, such as rapeseed husks and soybean meal, can be selected. These heteroatoms can be incorporated into the carbon framework during carbonization, improving the conductivity and electrochemical activity of the porous carbon.

[0035] In some embodiments, the molar ratio of nickel to cobalt in the nickel-cobalt layered double hydroxide (NiCo-LDH) is 1:1 to 2:1.

[0036] Nickel-cobalt layered double hydroxides (NiCo) are important electrode material components, and their electrochemical performance is closely related to the molar ratio of nickel to cobalt. This molar ratio directly affects the crystal structure, electronic properties, and distribution of electrochemically active sites in NiCo layered double hydroxides. For example, in the preparation of NiCo layered double hydroxides, the target molar ratio can be achieved by precisely controlling the initial concentrations of nickel and cobalt salt precursors in co-precipitation or hydrothermal synthesis methods. Furthermore, during the synthesis process, the incorporation ratio of nickel and cobalt in the NiCo layered double hydroxide structure can be further optimized by adjusting parameters such as pH, reaction temperature, and stirring rate to ensure the formation of a stable layered structure with the desired electrochemical performance.

[0037] By controlling the molar ratio of nickel to cobalt within the range of 1:1 to 2:1, the redox activity of cobalt and the structural stability of nickel can be balanced, effectively optimizing the crystal structure and electron transport properties of nickel-cobalt layered double hydroxide nanosheets. This ensures that the nickel-cobalt layered double hydroxide nanosheets can be stably and uniformly anchored vertically on the surface of the biomass-derived porous carbon matrix, significantly improving the interfacial bonding within the composite electrode material and avoiding crystal defects or reduced electrochemical activity caused by ratio imbalance.

[0038] In one embodiment of the present invention, a method for preparing a biomass-derived porous carbon matrix includes:

[0039] 1) The raw materials of biomass-derived porous carbon matrix are mixed with potassium hydroxide and zinc acetate to form a slurry.

[0040] Among them, potassium hydroxide, as a chemical activator, can undergo an oxidation-reduction reaction with carbon materials at high temperatures, etching the carbon skeleton and thus forming abundant micropores and mesopores inside the carbon materials, significantly improving the specific surface area and porosity.

[0041] Zinc acetate acts as a template agent in this preparation process. It decomposes or volatilizes during carbonization and activation, leaving pores corresponding to its own crystal structure, thereby precisely controlling the pore size distribution.

[0042] 2) After drying the slurry, carbonize and activate it in an inert atmosphere to obtain a biomass-derived porous carbon matrix.

[0043] In some embodiments, after the slurry is dried, it can be carbonized and activated in a nitrogen atmosphere at around 800°C for about 2 hours.

[0044] Drying the slurry removes any moisture or solvents it contains. The presence of moisture can cause steam expansion during high-temperature carbonization, leading to uneven material structure or even cracking. It also affects the effective contact and reaction between the activator and the carbon precursor. Carbonization activation in an inert atmosphere prevents oxidation of biomass raw materials with oxygen at high temperatures, thus avoiding combustion loss and structural damage to the carbon material. Commonly used inert atmospheres include nitrogen, argon, or helium. These gases do not chemically react with the carbon material at high temperatures, effectively protecting the integrity of the carbon skeleton and ensuring the smooth progress of the carbonization activation process.

[0045] This method can obtain a biomass-derived porous carbon matrix with micropores and mesopores, and the biomass-derived porous carbon matrix has a high specific surface area, providing an ideal anchoring substrate for vertically anchoring nickel-cobalt layered double hydroxide nanosheets, enhancing the ion transport path, improving the conductivity and ion adsorption capacity of the composite electrode material, thereby significantly improving the overall performance of the composite electrode material, and effectively solving the problem that existing methods are difficult to accurately control pore volume and specific surface area, resulting in insufficient porosity and unstable conductivity of the material.

[0046] In some embodiments, an improper ratio of raw materials to activator may lead to uneven slurry mixing, affecting the carbonization activation effect and thus failing to obtain the ideal pore volume and specific surface area. Therefore, in this embodiment of the invention, the mass ratio of the raw materials, potassium hydroxide, and zinc acetate in the biomass-derived porous carbon matrix is ​​limited to 1:(0.5–2):1.5, for example, 1:1:1.5, 1:1.5:1.5, or 1:2:1.5, etc. This ratio effectively solves the problem of uneven slurry mixing caused by an improper ratio of raw materials to activator. Furthermore, this ratio ensures that the activator and structure-directing agent can act uniformly on the carbon precursor during the carbonization activation process, thereby forming a consistent and controllable porous structure. This precise mass ratio control results in a biomass-derived porous carbon matrix with ideal pore volume and specific surface area, significantly improving its ion adsorption capacity and charge transport efficiency as an electrode material, providing an excellent matrix for subsequent composite nickel-cobalt layered double hydroxide nanosheets, thereby improving the overall electrochemical performance of the composite electrode material.

[0047] This application also proposes an electrode sheet comprising a porous carbon electrode layer, wherein the porous carbon electrode layer contains a biomass-based composite electrode material. This biomass-based composite electrode material has hierarchical pore sizes and pore volumes of 0.7–1.7 cm³. 3 A biomass-derived porous carbon matrix of / g is composited with nickel-cobalt layered double hydroxide nanosheets vertically anchored to the surface of the matrix, thereby achieving a specific surface area of ​​900–1400 m² for the composite electrode material. 2 / g. Effectively improves the ion adsorption capacity and charge transport efficiency of the electrode sheet.

[0048] In some embodiments, the raw materials for the porous carbon electrode layer, by mass percentage, include: 87–95% composite electrode material, wherein the composite electrode material is the aforementioned biomass-based composite electrode material; 3–8% conductive agent; 1–3% binder; and 1–2% dispersant.

[0049] The composite electrode material is the main active material of the electrode layer, primarily responsible for charge storage and release. This composite electrode material consists of a biomass-derived porous carbon matrix and nickel-cobalt layered double hydroxide nanosheets vertically anchored to the surface of the biomass-derived porous carbon matrix. It provides a high specific surface area and abundant electrochemical active sites, which is crucial for achieving high energy density and high power density. The mass percentage of the composite electrode material is limited to the range of 87–95%, ensuring that the electrode layer has sufficient active material to provide high capacity while reserving appropriate space for other auxiliary materials.

[0050] Conductive agents are substances added to electrode materials to improve the overall conductivity of the electrode. Their function is to reduce the internal resistance of the electrode and promote the rapid transport of electrons between active material particles and between the active material and the current collector, thereby improving the power performance and charge / discharge efficiency of the capacitor.

[0051] The conductive agent can be carbon black, such as acetylene black or Ketjen black; or carbon materials such as graphene or carbon nanotubes; or conductive polymers such as polyaniline or polypyrrole. The mass percentage of the conductive agent is limited to the range of 3–8%, which can effectively improve the conductivity of the electrode, reduce internal resistance, and avoid the adverse effects of excessive addition on adhesion and dispersibility.

[0052] Binders are polymeric materials used to bond active material particles, conductive agents, and other components together, ensuring a firm adhesion to the current collector. They impart the necessary mechanical strength and structural stability to the electrode layer, preventing the active material from detaching or pulverizing during electrode fabrication and recycling, thus ensuring the integrity and long-term stability of the electrode. Binders can be selected from polymers such as polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose; or elastomers such as styrene-butadiene rubber and polyacrylonitrile. The mass percentage of the binder is limited to 1–3% to guarantee the mechanical strength and adhesion of the electrode layer, preventing the electrode material from detaching during charging and discharging.

[0053] The mass percentage of the dispersant is limited to 1–2%, which can promote the uniform mixing and dispersion of raw materials and ensure the uniformity of the electrode layer.

[0054] In this embodiment, by precisely defining the mass percentage of each raw material component in the porous carbon electrode layer, including the composite electrode material, conductive agent, binder, and dispersant, problems such as insufficient electrode conductivity, reduced mechanical strength, and uneven component dispersion caused by raw material imbalance are avoided. This allows the prepared electrode layer to maintain high energy density while also possessing good power characteristics and cycle stability, thereby improving the overall performance and reliability of the supercapacitor.

[0055] In some embodiments, the electrode sheet further includes a ceramic coating disposed on the surface of the porous carbon electrode layer, and a diaphragm layer disposed on the surface of the ceramic coating.

[0056] The porous carbon electrode layer has a thickness of 60-120 μm, achieving an optimized balance between energy density, power density, mechanical strength, and ion transport efficiency. This thickness range can be achieved by precisely controlling process parameters such as the coating amount of the electrode slurry, the coating speed, and subsequent rolling density.

[0057] The ceramic coating thickness is 0.2-0.5 μm. The goal is to ensure the ceramic coating provides sufficient mechanical strength and heat resistance while minimizing the volume of inactive material, thus avoiding a significant reduction in the capacitor's energy density.

[0058] In the embodiments of this application, by setting a ceramic coating on the surface of the porous carbon electrode layer, a robust protective layer can be provided for the electrode, significantly enhancing the overall mechanical strength of the electrode and effectively preventing breakage during manufacturing processes such as winding or stacking. Furthermore, by setting a separator layer on the surface of the ceramic coating as an insulating barrier, electrical isolation between the electrodes can be ensured, thereby effectively avoiding the risk of short circuits. Simultaneously, by optimizing the thickness of the porous carbon electrode layer to 60-120 μm and controlling the thickness of the ceramic coating to 0.2-0.5 μm, not only is the energy density and mechanical stability of the electrode optimized, but the coating is also ensured to be thin enough to reduce the volume of inactive materials, while providing sufficient strength to compensate for the insufficient strength of the thin separator. This allows the electrode sheet to maintain excellent stability under extreme conditions such as high temperatures, significantly improving the overall performance and reliability of the capacitor.

[0059] Furthermore, traditional supercapacitors have significant limitations in output voltage and energy density, making them unsuitable for high-voltage applications. To address this issue, this application proposes a double-layer supercapacitor.

[0060] refer to Figure 1 , Figure 1 A schematic diagram of the unfolded cross-section of the cell structure of a hybrid supercapacitor according to an embodiment of the present invention is shown.

[0061] like Figure 1 As shown, the hybrid supercapacitor includes a core structure comprising a first electric layer composite 10 and a second electric layer composite 20. It includes a first positive electrode 11, a first separator 12, a first negative electrode 13, and a second separator 14. The second electric layer composite 20 includes a second positive electrode 21, a third separator 22, a second negative electrode 23, and a fourth separator 24.

[0062] The first positive electrode 11 and the second positive electrode 21 can have the same structure, both including a porous carbon electrode layer, and the material of the porous carbon electrode layer is a biomass-based composite electrode material.

[0063] In some embodiments, such as Figure 2 As shown, the first tab 31 of the first positive electrode 11 and the second tab 32 of the second positive electrode 23 can be arranged in opposite directions, such as... Figure 2Extending above and below, in some embodiments, the two tabs can also be located on the same side. The length of the first tab 31 and the second tab 32 can be 10-30mm, the width can be 3-10mm, and the thickness can be 0.5-2mm. This thickness is simple to manufacture and meets performance requirements.

[0064] By designing the core structure to include at least two electric layer composites, the series connection of these composites was achieved, thus breaking through the voltage limitation of a single cell and enabling the overall output voltage of the supercapacitor to reach more than twice that of a single electric layer composite. The specific stacking order of the electric layer composites ensures effective isolation between the positive and negative electrodes, reducing the risk of internal short circuits and optimizing the ion transport path to reduce internal resistance. Simultaneously, the application of biomass-based composite electrode materials enhances the ion adsorption capacity of the porous carbon electrode layer, improves charge storage capacity, and further increases energy density.

[0065] In some embodiments, such as Figure 1 The first and second electric layer composites shown can be stacked and then wound to obtain the core structure. Furthermore, the negative electrode of the first pad composite is electrically connected to the positive electrode of the second electric layer composite. This achieves both physical compact integration and internal electrical series connection of the electric layer composites. Compared to a structure with two individual core structures connected in series, this structure significantly reduces the length of the core structure in a side-by-side design, thus reducing the overall system volume. Moreover, this stacked and wound structural design allows multiple electric layer composites to be efficiently integrated within a limited space, significantly improving the space utilization and energy density of the core structure.

[0066] In some embodiments, the core structure can be configured with two or more electrical layer composites to flexibly adjust the output voltage level according to actual needs. The porous carbon electrode layer of the positive electrode uses a biomass-based composite electrode material, which combines the high specific surface area of ​​biomass-derived porous carbon with the stability of the composite structure, effectively solving the shortcomings of traditional electrode materials in ion adsorption and conductivity. Through the above technical solution, the supercapacitor achieves a high energy density within a 3V voltage window, meeting the device's requirements for high voltage output and efficient energy storage.

[0067] In some embodiments, reference Figure 3 The flowchart of the capacitor manufacturing method shown is as follows: Figure 3 As shown, the preparation method includes S11-S18.

[0068] S11 involves mixing biomass raw materials with potassium hydroxide and zinc acetate in a certain proportion to form a slurry, drying it, and then carbonizing and activating it at high temperature under nitrogen to obtain porous biomass carbon.

[0069] S12 involves mixing biomass porous carbon with nickel salts, cobalt salts, etc., and then carrying out a hydrothermal reaction to obtain a biomass-derived porous carbon and nickel-cobalt LDH composite.

[0070] S13, the conductive agent, binder, dispersant and the composite are mixed in proportion, and an appropriate amount of solvent is added and stirred evenly to form a slurry.

[0071] S14, the slurry is evenly coated onto the current collector using a coating machine, and then the positive electrode sheet is obtained by rolling and shearing.

[0072] S15: Porous carbon material is mixed with conductive agent, binder and dispersant in proportion, an appropriate amount of solvent is added and stirred into a slurry, which is then coated onto the current collector, and a ceramic coating layer and a separator layer are coated in sequence. The negative electrode sheet is obtained by rolling and shearing.

[0073] S16, the positive electrode sheet and the negative electrode sheet are stacked in a double-layer composite structure, then wound to form a columnar core, and multiple double-layer composites are connected in series as described above, and electrode tabs are welded.

[0074] S17. Place the core with the welded tabs into the capacitor case and weld the cover to the case.

[0075] S18. The assembled semi-finished product is dried, then injected with an optimized multivalent ion electrolyte, and finally encapsulated to obtain a capacitor.

[0076] The electrolyte can be a multivalent ion or organic compound electrolyte. The concentration of the electrolyte is 0.5-1.5 mol / L, and the solvent is one or more of acetonitrile, propylene carbonate, sulfolane, ethyl isopropyl sulfone, and ethyl isobutyl sulfone. The solute is a suitable high-voltage organic compound such as bis(pyrrolidine)spirocyclic ammonium tetrafluoroborate.

[0077] The finished capacitors are subjected to electrical performance tests such as capacitance and internal resistance tests, and high-temperature accelerated aging tests are conducted. The supercapacitor cells are placed in a 65°C high-temperature chamber, and their capacitance and internal resistance are retested at regular intervals to screen out qualified products.

[0078] The preparation process of the biomass-based composite electrode material and capacitor of the present invention will be described in detail below with reference to specific embodiments.

[0079] Example 1

[0080] The biomass raw material used was corn stalks, which were mixed with potassium hydroxide and zinc acetate in a 1:1 mass ratio to form a pulp. After drying, the pulp was carbonized and activated at 800℃ under nitrogen for 2 hours. Potassium hydroxide acted as an activator, etching the carbon framework to create micropores, while zinc acetate acted as a template agent to guide the formation of mesopores and macropores. The resulting porous carbon had a specific surface area of ​​1036 m². 2 / g, pore volume is 1.02cm³3 / g.

[0081] Composite material preparation: The above-mentioned biomass porous carbon was mixed with nickel salt (Ni(NO3)2) and cobalt salt (Co(NO3)2) in a molar ratio of 1:1, and then subjected to a hydrothermal reaction at 140°C for 8 hours with ethylene glycol, hexamethylenetetramine and water, so that nickel cobalt LDH nanosheets were vertically oriented and anchored on the surface of the porous carbon to form a three-dimensional hierarchical structure.

[0082] Electrode preparation: A biomass-derived porous carbon-nickel-cobalt LDH composite (91.5%) was mixed with a conductive agent (acetylene black, 5%), a binder (polyvinylidene fluoride, 2%), and a dispersant (sodium carboxymethyl cellulose, 1.5%) by mass fraction. An appropriate amount of N-methylpyrrolidone solvent was added and stirred until homogeneous to form a slurry. The slurry was uniformly coated onto a current collector aluminum foil, and after drying and pressing, a positive electrode sheet was obtained.

[0083] Negative electrode preparation: The porous carbon electrode layer of the second electrode (negative electrode) is made of commercial activated carbon (specific surface area of ​​1500 m²). 2 / g). A ceramic coating (alumina, 0.3 μm thick) is coated on the current collector surface and then composited on the membrane layer (polyvinylidene fluoride, 15 μm thick).

[0084] Device assembly: The electrolyte used is a 1 mol / L tetrafluoroborate bispyrrolidine spirocyclic quaternary ammonium salt electrolyte, and the solvent is a mixture of acetonitrile and propylene carbonate. The positive and negative electrode sheets are stacked in a double-layer composite structure, wound to form a columnar core, and then the tabs are welded on. After encapsulation, a hybrid supercapacitor is obtained.

[0085] Performance testing:

[0086] The prepared supercapacitor was subjected to electrochemical performance testing. The results showed that the device achieved an energy density of 35 Wh / kg at a power density of 800 W / kg; after 5000 cycles at a current density of 10 A / g, the capacity retention was still above 92%, demonstrating excellent cycle stability.

[0087] Example 2

[0088] The biomass raw material used was bamboo, which was mixed with potassium hydroxide and zinc acetate at a mass ratio of 1.5:1 to form a pulp. After drying, it was carbonized and activated at 850℃ under nitrogen for 2.5 hours. The resulting porous carbon had a specific surface area of ​​1180 m². 2 / g, pore volume is 1.45cm³ 3 / g.

[0089] Composite material preparation: Biomass porous carbon was mixed with nickel salt and cobalt salt in a molar ratio of 1.5:1 and subjected to a hydrothermal reaction at 160°C for 10 hours to prepare the composite material.

[0090] Electrode formulation: by mass fraction, 88.5% biomass-derived porous carbon and nickel-cobalt LDH composite, 6% conductive agent, 2.5% binder, and 2% dispersant.

[0091] Negative electrode structure: The porous carbon electrode layer of the second electrode is made of porous graphene with a thickness of 80 μm. The ceramic coating is a mixture of zirconium oxide and calcium oxide with a thickness of 0.4 μm. The separator layer is made of polyethersulfone with a thickness of 12 μm.

[0092] Device parameters: The electrolyte used is 1.2 mol / L bis(pyrrolidine) spirocyclic ammonium salt tetrafluoroborate (SBPBF4), and the solvent is sulfolane. The double-layer complex has 3 layers, and the tabs are reverse-biased.

[0093] Performance testing:

[0094] The sample was tested and found to have a specific capacitance of 420 F / g at a current density of 0.5 A / g, and it maintained stable performance over a wide temperature range of -20℃ to 60℃, demonstrating that the material has good environmental adaptability.

[0095] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A biomass-based composite electrode material, characterized in that, include: A biomass-derived porous carbon matrix having pores of varying sizes, the pores having a volume of 0.7–1.7 cm³. 3 / g; and, Nickel-cobalt layered double hydroxide nanosheets vertically anchored to the surface of the biomass-derived porous carbon matrix; The specific surface area of ​​the composite electrode material is 900–1400 m². 2 / g.

2. The composite electrode material according to claim 1, characterized in that, The raw material for the biomass-derived porous carbon matrix is ​​agricultural waste, which includes at least one of corn stalks, bamboo, sawdust, and biogas residue.

3. The composite electrode material according to claim 1, characterized in that, The molar ratio of nickel to cobalt in the nickel-cobalt layered double hydroxide is 1:1 to 2:

1.

4. The composite electrode material according to claim 1, characterized in that, The method for preparing the biomass-derived porous carbon matrix includes: The raw materials of the biomass-derived porous carbon matrix are mixed with potassium hydroxide and zinc acetate to prepare a slurry; The slurry is dried and then carbonized and activated in an inert atmosphere to obtain the biomass-derived porous carbon matrix.

5. The composite electrode material according to claim 4, characterized in that, The raw material for the biomass-derived porous carbon matrix, the potassium hydroxide and the zinc acetate, have a mass ratio of 1:(0.5–2):1.

5.

6. An electrode sheet, characterized in that, It includes a porous carbon electrode layer, wherein the porous carbon electrode layer comprises the biomass-based composite electrode material according to any one of claims 1–5.

7. The electrode sheet according to claim 6, characterized in that, The raw materials of the porous carbon electrode layer, by mass percentage, include: - 87–95% composite electrode material, wherein the composite electrode material is the biomass-based composite electrode material according to any one of claims 1-5; 3–8% conductive agent; - 1–3% binder; and 1–2% dispersant.

8. The electrode sheet according to claim 6, characterized in that, Also includes: A ceramic coating is disposed on the surface of the porous carbon electrode layer, and a membrane layer is disposed on the surface of the ceramic coating, wherein the thickness of the porous carbon electrode layer is 60-120 μm, and the thickness of the ceramic coating is 0.2-0.5 μm.

9. A hybrid supercapacitor, characterized in that, include: A core structure comprising at least two electrical layer composites, the electrical layer composites comprising, from the inside out, a positive electrode, a first separator, a negative electrode and a second separator, wherein the positive electrode comprises the biomass-based composite electrode material as described in any one of claims 1-5 as the active material.

10. The hybrid supercapacitor according to claim 9, characterized in that, The core structure is formed by stacking and winding at least two electrical layer composites. In this configuration, the negative electrode of one of the two adjacent electrical layer complexes is electrically connected to the positive electrode of the other electrical layer complex.

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