Preparation method of Ni / Co-LDHs / BC electrode material

Abstract

The application relates to a preparation method of a Ni / Co-LDHs / BC electrode material, and belongs to the technical field of electrode materials. The Ni / Co-LDHs / BC-3 has a high specific capacitance of 1332 F / g under a current density of 1 A / g. After 5000 cycles of cyclic charging and discharging under a current density of 10 A / g, the initial capacitance is retained by 77.82%, and the Ni / Co-LDHs / BC-3 has excellent cycle performance. The method is as follows: reed stalks are pretreated, then carbonized and activated by using a tube furnace, the obtained sample is added into alcohol together with nickel nitrate and cobalt nitrate, and then subjected to hydrothermal reaction and vacuum drying to obtain the Ni / Co-LDHs / BC. The preparation process is simple, the obtained product has the advantages of high specific capacitance, excellent cycle performance and the like, and has a good application prospect.

Description

Technical Field

[0001] This invention relates to a method for preparing Ni / Co-LDHs / BC electrode material, belonging to the field of electrode material technology. Background Technology

[0002] Against the backdrop of rapid technological advancements, developing efficient and stable energy storage technologies has become a crucial research direction. Supercapacitors, with their excellent power characteristics, rapid charge-discharge capabilities, and ultra-long cycle life, occupy a vital position in novel energy storage systems. Electrode materials are a critical component in the structure of supercapacitors, and the relatively low energy density exhibited by supercapacitors still falls short of meeting practical application requirements. This is because the electrochemical performance of the electrode materials almost entirely dominates the energy storage performance of the entire device; therefore, exploring and synthesizing electrode materials with superior electrochemical performance is essential. Although traditional carbon materials and metal oxides have been extensively studied, they each have inherent limitations: carbon-based materials have relatively limited specific capacitance, while metal oxides generally suffer from poor cycle stability, making it difficult to meet the practical demands of high-performance energy storage.

[0003] Hydrotalcite, with its high specific capacitance, abundant redox activity, and precisely tunable structure and composition, is an ideal candidate for enhancing pseudocapacitive behavior in supercapacitors (SCs), showing great potential in catalysis, energy storage, and other fields. We fabricated a Ni / Co binary layered double hydroxide (LDH), exhibiting a typical three-dimensional flower-like hierarchical structure composed of numerous ultrathin two-dimensional nanosheets radially interleaved and stacked. The nanosheet edges show obvious wrinkles and curling features, and the interlayer cross-links form a loose and porous network structure, which not only significantly increases the specific surface area of ​​the material but also provides ample channels for the rapid diffusion of electrolyte ions. From a crystal structure perspective, positively charged [Ni(OH)6] and [Co(OH)6] octahedral units share edges to form the main layers, and the interlayer regions are filled with anions such as CO3²⁻ and water of crystallization to balance the charge, forming a typical layered intercalation structure that provides abundant active sites for reversible Faraday reactions. Meanwhile, the loose, flower-shaped morphology can effectively buffer volume changes during charging and discharging, maintain long-term structural stability, and thus achieve a long cycle life, demonstrating a comprehensive advantage of high specific capacitance, high rate performance and excellent cycle stability in the field of supercapacitors.

[0004] Biochar possesses abundant pore structures and surface functional groups, exhibiting high specific surface area, well-developed porosity, and good chemical stability, demonstrating unique structural advantages and application potential when used as an electrode material for supercapacitors. Structurally, it forms a three-dimensional continuous porous network through the pyrolysis of biomass precursors. The overlapping of layers / particles creates abundant and interconnected channels, with pore sizes ranging from micropores and mesopores to macropores. This structure endows it with a high specific surface area, providing ample active sites for charge storage and effectively improving specific capacitance performance. The well-developed pore system facilitates rapid penetration and diffusion of electrolyte ions, shortening ion transport paths and accelerating charge-discharge kinetics. Simultaneously, biochar itself possesses a certain degree of conductivity, ensuring efficient electron transfer, reducing electrode internal resistance, and improving rate performance. Furthermore, it is widely available, inexpensive, and possesses good chemical and thermal stability, maintaining structural stability during long-term charge-discharge cycles and extending device lifespan. With its excellent electrochemical performance and cost advantages, this biochar material shows significant application prospects in high-performance supercapacitors and energy storage composite electrodes.

[0005] Combining Ni / Co binary layered bimetallic hydroxides (LDHs) with biochar in supercapacitors holds promise for fully leveraging their synergistic advantages and overcoming the limitations of single materials in electrochemical performance and structural stability. Ni / Co binary LDHs provide abundant redox active sites and high pseudocapacitance, significantly enhancing the specific capacitance of the electrode material. Biochar, on the other hand, constructs a three-dimensional continuous porous network, providing efficient channels for the rapid transport of electrons and ions, while simultaneously enhancing the mechanical stability and structural integrity of the electrode. However, current research on the application of LDHs and biochar in supercapacitors is still in its early stages, with challenges such as weak interfacial bonding, low utilization of active sites, and insufficient cycle stability. Further optimization of the preparation process and control of microstructure and interfacial interactions are needed to fully unleash their synergistic energy storage effect and promote their large-scale application in high-performance supercapacitors. Summary of the Invention

[0006] This invention aims to develop a Ni / Co-LDHs / BC composite material for electrode materials. By optimizing the material properties, it achieves high conductivity to promote rapid electron transport while reducing resistance and energy loss. The study explores whether high cycling stability can be maintained while significantly improving the specific capacity of the electrode material. This provides an innovative preparation route for hydrotalcite and biochar composite materials, enabling the fabrication of electrode materials that better meet the requirements of high-performance supercapacitors and other electrochemical energy storage devices.

[0007] This invention uses biochar as the matrix and hydrotalcite as the active component to prepare a hydrotalcite-biochar composite material using a hydrothermal method. The method includes the following steps: Step 1: Biochar Preparation Reed stalks were crushed, dried, and pretreated with a FeCl3-H2O2 system. The mixture was then dried in an oven at 60℃ for 12 h, followed by pre-carbonization in a nitrogen atmosphere to obtain the final precursor. 1 g of carbon was mixed with KOH and placed in 50 mL of distilled water, then ultrasonically dispersed for 24 h to obtain a mixture. This mixture was dried in an oven at 100℃ for 24 h, thoroughly ground, activated in a nitrogen atmosphere, and naturally cooled. The resulting product was collected, KOH residue was removed with a solution, and the mixture was washed with deionized water until neutral. Finally, it was dried in an oven at 60℃ for 24 h to obtain the final sample.

[0008] Step 2: Preparation of Ni / Co-LDHs / BC composite material Ni(NO3)2·6H2O, Co(NO3)2·6H2O, CO(NH2)2, and biochar were added to 60 mL of anhydrous ethanol. The mixture was magnetically stirred for 30 minutes, followed by sonication for 30 minutes to ensure complete dissolution. The mixture was then heated to 120°C in a reaction vessel and reacted for 12 h to prepare the desired sample. The sample was then centrifuged with ethanol and deionized water, respectively. The resulting sample was dried in a vacuum drying oven at 60°C for 24 h.

[0009] Step 3: Electrode material preparation: The obtained Ni / Co-LDHs / BC composite material was mixed and ground uniformly with conductive carbon black and polyvinylidene fluoride, respectively. Then, N-methylpyrrolidone was added dropwise to the mixed powder. A piece of nickel foam was then weighed, and the resulting black mixture was uniformly coated onto a clean, dry nickel foam sheet. The nickel foam with electrode material was then dried in an oven at 60°C for 24 h, and then pressed under a pressure of 10 MPa.

[0010] Preferably, the carbonization temperature under nitrogen atmosphere in step one is 600°C, and the carbonization time is 2 h.

[0011] More preferably, the oven described in step one should be a vacuum oven.

[0012] Preferably, the activation temperature under nitrogen atmosphere in step one is 600°C, and the activation time is 2 h.

[0013] Preferably, the KOH solution in step one should be 1 mol / L.

[0014] Preferably, the centrifugation process in step two should be performed at 8000 rpm for 10 minutes.

[0015] Preferably, the mass ratio of the hydrotalcite / biochar composite material to conductive carbon black and polyvinylidene fluoride described in step three is 8:1:1.

[0016] Preferably, the amount of N-methylpyrrolidone added in step three is 50 μL.

[0017] The beneficial effects of this invention are: The Ni / Co-LDHs / BC prepared in this invention can achieve synergistic coupling of pseudocapacitance and double-layer capacitance. LDHs provide the basis for pseudocapacitive energy storage, while biochar provides support for double-layer energy storage. The heterogeneous interface formed by the two can optimize charge distribution, reduce charge transfer energy barrier, strengthen the synergistic effect of the two energy storage mechanisms, break through the energy storage limit of single materials, and improve the comprehensive energy storage performance of electrode materials.

[0018] The Ni / Co-LDHs / BC composite material prepared by this invention exhibits a typical core-shell encapsulation structure: biochar serves as a rigid core framework, existing in a sheet-like form; two-dimensional LDHs nanosheets are uniformly grown on the surface of the biochar sheets, forming a tightly encapsulated shell structure. The overall morphology is loose and cross-linked in an orderly manner, with abundant hierarchical pore channels retained between the sheets, and no obvious agglomeration or stacking phenomenon is observed, thus achieving efficient interfacial bonding between the two components.

[0019] The Ni / Co-LDHs / BC prepared in this invention exhibits good cycling stability. The three-dimensional porous framework of biochar possesses excellent mechanical strength and toughness, serving as a supporting template to restrict the stacking and aggregation of LDH layers, buffering their volume deformation during energy storage and preventing the collapse of the layered structure. The interfacial coordination between the two enhances the binding force, inhibiting the shedding of active components from LDHs. Simultaneously, the porous structure optimizes ion transport, mitigating performance degradation during cycling and significantly improving the structural stability and cycling performance of the electrode material. Attached Figure Description

[0020] Figure 1 Scanning electron microscope image of Ni / Co-LDHs; Figure 2 Scanning electron microscope image of Ni / Co-LDHs / BC-3 composite material; Figure 3 X-ray diffraction pattern of Ni / Co-LDHs / BC-3 composite material; Figure 4 shows the discharge curve of the Ni / Co-LDHs / BC-X composite electrode material at a current density of 1 A / g. Figure 5 shows the electrochemical performance of the Ni / Co-LDHs / BC-3 composite material; Detailed Implementation Example

[0021] Step 1: Preparation of Biochar Wash, crush, and dry the reed stalks. Weigh 2 g of reed powder for later use. Weigh 2.7029 g of FeCl3 block and place it in 50 mL of deionized water. Stir with a magnetic stirrer for 30 minutes until fully dissolved. Add the weighed reed powder to the solution and soak for 2 h. Filter the water and dry in a 60℃ oven for 12 h. Soak the dried sample again in 50 mL of 5% H2O2 for 2 h and dry in a 60℃ oven for 12 h. Pre-carbonize the dried sample at 600℃ for 2 h in a nitrogen atmosphere to obtain the finished precursor. Mix 1 g of biochar with KOH and place in 50 mL of distilled water. Disperse ultrasonically for 24 h to obtain a mixture. The mixture was dried at 100℃ for 24 h, thoroughly ground, and then activated at 600℃ for 2 h in a nitrogen atmosphere. After natural cooling, the product was collected, KOH residue was removed with 1M HCl solution, washed with deionized water until neutral, and dried at 60℃ for 24 h to obtain the final sample.

[0022] Step 2: Preparation of Ni / Co-LDHs / BC 1.745 g Ni(NO3)2·6H2O, 1.746 g Co(NO3)2·6H2O, 1.44 g CO(NH2)2, and 0.0135 g biochar were added to 60 mL of anhydrous ethanol. The mixture was magnetically stirred for 30 minutes, followed by sonication for 30 minutes to ensure complete dissolution. The mixture was then heated to 120°C in a reaction vessel and reacted for 12 h to prepare the desired sample. The sample was then centrifuged three times, each time with ethanol and deionized water. The resulting sample was dried in a vacuum drying oven at 60°C for 24 h and named Ni / Co-LDHs / BC-1.

[0023] Step 3: Electrode material preparation The obtained Ni / Co-LDHs / BC-1 was mixed and ground uniformly with conductive carbon black and polyvinylidene fluoride, respectively. Then, N-methylpyrrolidone was added dropwise to the mixed powder. A piece of nickel foam was then weighed, and the resulting black mixture was uniformly coated onto a clean, dry nickel foam sheet. The nickel foam with electrode material was dried in an oven at 60°C for 24 h, and then pressed under a pressure of 10 MPa. Example

[0024] Step 1: Preparation of Biochar Wash, crush, and dry the reed stalks. Weigh 2 g of reed powder for later use. Weigh 2.7029 g of FeCl3 block and place it in 50 mL of deionized water. Stir with a magnetic stirrer for 30 minutes until fully dissolved. Add the weighed reed powder to the solution and soak for 2 h. Filter the water and dry in a 60℃ oven for 12 h. Soak the dried sample again in 50 mL of 5% H2O2 for 2 h and dry in a 60℃ oven for 12 h. Pre-carbonize the dried sample at 600℃ for 2 h in a nitrogen atmosphere to obtain the finished precursor. Mix 1 g of biochar with KOH and place in 50 mL of distilled water. Disperse ultrasonically for 24 h to obtain a mixture. The mixture was dried at 100℃ for 24 h, thoroughly ground, and then activated at 600℃ for 2 h in a nitrogen atmosphere. After natural cooling, the product was collected, KOH residue was removed with 1M HCl solution, washed with deionized water until neutral, and dried at 60℃ for 24 h to obtain the final sample.

[0025] Step 2: Preparation of Ni / Co-LDHs / BC 1.745 g Ni(NO3)2·6H2O, 1.746 g Co(NO3)2·6H2O, 1.44 g CO(NH2)2, and 0.0153 g biochar were added to 60 mL of anhydrous ethanol. The mixture was magnetically stirred for 30 minutes, followed by sonication for 30 minutes to ensure complete dissolution. The mixture was then heated to 120°C in a reaction vessel and reacted for 12 h to prepare the desired sample. The sample was then centrifuged three times, each time with ethanol and deionized water. The resulting sample was dried in a vacuum drying oven at 60°C for 24 h and named Ni / Co-LDHs / BC-2.

[0026] Step 3: Electrode material preparation The obtained Ni / Co-LDHs / BC-2 was mixed and ground uniformly with conductive carbon black and polyvinylidene fluoride, respectively. Then, N-methylpyrrolidone was added dropwise to the mixed powder. A piece of nickel foam was then weighed, and the resulting black mixture was uniformly coated onto a clean, dry nickel foam sheet. The nickel foam with electrode material was dried in an oven at 60°C for 24 h, and then pressed under a pressure of 10 MPa. Example

[0027] Step 1: Preparation of Biochar Wash, crush, and dry the reed stalks. Weigh 2 g of reed powder for later use. Weigh 2.7029 g of FeCl3 block and place it in 50 mL of deionized water. Stir with a magnetic stirrer for 30 minutes until fully dissolved. Add the weighed reed powder to the solution and soak for 2 h. Filter the water and dry in a 60℃ oven for 12 h. Soak the dried sample again in 50 mL of 5% H2O2 for 2 h and dry in a 60℃ oven for 12 h. Pre-carbonize the dried sample at 600℃ for 2 h in a nitrogen atmosphere to obtain the finished precursor. Mix 1 g of biochar with KOH and place in 50 mL of distilled water. Disperse ultrasonically for 24 h to obtain a mixture. The mixture was dried at 100℃ for 24 h, thoroughly ground, and then activated at 600℃ for 2 h in a nitrogen atmosphere. After natural cooling, the product was collected, KOH residue was removed with 1M HCl solution, washed with deionized water until neutral, and dried at 60℃ for 24 h to obtain the final sample.

[0028] Step 2: Preparation of Ni / Co-LDHs / BC 1.745 g Ni(NO3)2·6H2O, 1.746 g Co(NO3)2·6H2O, 1.44 g CO(NH2)2, and 0.0174 g biochar were added to 60 mL of anhydrous ethanol. The mixture was magnetically stirred for 30 minutes, followed by sonication for 30 minutes to ensure complete dissolution. The mixture was then heated to 120°C in a reaction vessel and reacted for 12 h to prepare the desired sample. The sample was then centrifuged three times, each time with ethanol and deionized water. The resulting sample was dried in a vacuum drying oven at 60°C for 24 h and named Ni / Co-LDHs / BC-3.

[0029] Step 3: Electrode material preparation The obtained Ni / Co-LDHs / BC-3 was mixed and ground uniformly with conductive carbon black and polyvinylidene fluoride, respectively. Then, N-methylpyrrolidone was added dropwise to the mixed powder. A piece of nickel foam was then weighed, and the resulting black mixture was uniformly coated onto a clean, dry nickel foam sheet. The nickel foam with electrode material was then dried in an oven at 60°C for 24 h, and then pressed under a pressure of 10 MPa. Example

[0030] Step 1: Preparation of Biochar Wash, crush, and dry the reed stalks. Weigh 2 g of reed powder for later use. Weigh 2.7029 g of FeCl3 block and place it in 50 mL of deionized water. Stir with a magnetic stirrer for 30 minutes until fully dissolved. Add the weighed reed powder to the solution and soak for 2 h. Filter the water and dry in a 60℃ oven for 12 h. Soak the dried sample again in 50 mL of 5% H2O2 for 2 h and dry in a 60℃ oven for 12 h. Pre-carbonize the dried sample at 600℃ for 2 h in a nitrogen atmosphere to obtain the finished precursor. Mix 1 g of biochar with KOH and place in 50 mL of distilled water. Disperse ultrasonically for 24 h to obtain a mixture. The mixture was dried at 100℃ for 24 h, thoroughly ground, and then activated at 600℃ for 2 h in a nitrogen atmosphere. After natural cooling, the product was collected, KOH residue was removed with 1M HCl solution, washed with deionized water until neutral, and dried at 60℃ for 24 h to obtain the final sample.

[0031] Step 2: Preparation of Ni / Co-LDHs / BC 1.745 g Ni(NO3)2·6H2O, 1.746 g Co(NO3)2·6H2O, 1.44 g CO(NH2)2, and 0.0195 g biochar were added to 60 mL of anhydrous ethanol. The mixture was magnetically stirred for 30 minutes, followed by sonication for 30 minutes to ensure complete dissolution. The mixture was heated to 120°C in a reaction vessel and reacted for 12 h to prepare the desired sample. The sample was then centrifuged three times, each time with ethanol and deionized water. The resulting sample was dried in a vacuum drying oven at 60°C for 24 h and named Ni / Co-LDHs / BC-4.

[0032] Step 3: Electrode material preparation The obtained Ni / Co-LDHs / BC-4 was mixed and ground uniformly with conductive carbon black and polyvinylidene fluoride, respectively. Then, N-methylpyrrolidone was added dropwise to the mixed powder. A piece of nickel foam was then weighed, and the resulting black mixture was uniformly coated onto a clean, dry nickel foam sheet. The nickel foam with electrode material was then dried in an oven at 60°C for 24 h, and then pressed under a pressure of 10 MPa. Attached Figure

[0033] Depend on Figure 1As shown in the SEM images, Ni / Co-LDHs exhibit a three-dimensional cross-linked nanosheet layered structure. The layers interlock to form abundant pores and channels, presenting an overall loose and porous network morphology with uniform layer thickness. This unique layered porous structure significantly increases the specific surface area and the number of active sites, providing ample reaction sites for redox reactions. Simultaneously, it constructs continuous ion transport channels, shortens ion diffusion paths, accelerates ion insertion and extraction in the electrolyte, and effectively improves the electrode's specific capacitance and rate performance. Furthermore, the cross-linked nanosheet structure possesses good structural toughness, which can buffer volume deformation during charge and discharge, inhibiting the collapse of the layered structure and the shedding of active components. Combined with the synergistic electronic effect of the nickel-cobalt bimetal, this further enhances the electrode's structural stability and cycle life, allowing it to maintain a high capacitance retention rate even after long-term cycling, demonstrating excellent comprehensive electrochemical performance.

[0034] Depend on Figure 2 Scanning electron microscopy (SEM) results show that the prepared Ni / Co-LDHs / BC-3 composite material exhibits a typical core-shell encapsulated structure: biochar serves as a rigid core framework, existing in a sheet-like morphology; two-dimensional LDHs nanosheets are uniformly grown on the surface of the biochar sheets, forming a tightly encapsulated shell structure. The overall morphology is loose and orderly cross-linked, with abundant hierarchical pore channels between the sheets, and no obvious agglomeration or stacking is observed, achieving efficient interfacial bonding between the two components. Compared with single biochar and single LDHs, this composite structure exhibits significant synergistic advantages. The high conductivity of biochar provides a continuous electron transport path for LDHs, effectively compensating for the poor intrinsic conductivity of single LDHs. Meanwhile, the abundant redox active sites of LDHs significantly enhance the pseudocapacitive contribution of the composite material, breaking through the energy storage limit of the double-layer capacitance of single biochar and achieving higher specific capacitance and energy density. In summary, this "carbon core-hydrotalcite shell" coating structure effectively avoids the inherent defects of single materials through interfacial synergy and functional complementarity between components, exhibiting significant advantages in electrochemical performance and providing an efficient strategy for the design and development of high-performance supercapacitor electrode materials.

[0035] The figure shows the X-ray diffraction (XRD) pattern of the NiCo-LDHs / BC-3 composite material. The diffraction peaks can be clearly attributed to the typical layered double hydroxide (LDHs) crystal structure. The strongest diffraction peak at 2θ ≈ 11° corresponds to the (003) crystal plane of LDHs, reflecting the highly ordered stacking of the layers along the c-axis, which is a hallmark feature of the layered structure of LDHs. The diffraction peak of the (006) crystal plane at 2θ ≈ 23° is a second-order diffraction of the (003) crystal plane, which further confirms the periodic stacking of the layers. The broadening of its peak shape indicates that the LDHs grain size is small or that there is a certain degree of disorder in the stacking of the layers. Furthermore, the (012) and (015) diffraction peaks at 2θ ≈ 33° and 38° correspond to the three-dimensional ordered arrangement of metal-oxygen octahedra inside the LDHs layer, while the (110) diffraction peak at 2θ ≈ 60° reflects the uniform arrangement of metal atoms within the ab plane of the layer. These characteristic peaks are highly consistent with the standard NiCo-LDHs card, confirming that the LDHs phase in the composite material has good crystallinity and high purity, with no obvious impurity phase formation. No sharp diffraction peaks (2θ ≈ 26°) of the graphite carbon (002) crystal plane were observed in the spectrum; only broadened diffuse bulges appeared in the 20°-30° range, indicating that the carbon component exists in an amorphous or low-crystallinity form, consistent with the typical XRD characteristics of biochar or porous carbon. In summary, this NiCo-LDHs / BC composite material retains the complete layered crystal structure and abundant electrochemical active sites of LDHs, while introducing amorphous carbon components to construct an efficient electron transport network, laying a solid structural foundation for its excellent electrochemical performance in energy storage fields such as supercapacitors.

[0036] As shown in Figure 4, the specific capacitances of Ni / Co-LDHs / BC-1 to Ni / Co-LDHs / BC-4 and BC can be calculated from the discharge curves to be 1248, 1318, 1332, 1210, and 263 F / g, respectively. With increasing biochar mass, the specific capacitance of the samples first increases and then decreases. When the biochar mass is 0.174 g, Ni / Co-LDHs / BC-3 has the highest specific capacitance (1332 F / g). Comparing the specific capacitance values ​​of Ni / Co-LDHs / BC-1, Ni / Co-LDHs / BC-2, and BC, it can be seen that the incorporation of BC can effectively improve the specific capacitance of the material. However, as the mass of BC continues to increase, the specific capacitance of the material gradually decreases again.

[0037] As shown in Figure 5, Figure 5(a) shows the cyclic voltammetry curves of the material at different scan rates in this experiment, with a potential window of 0-0.5 V. The curves exhibit typical pseudocapacitive characteristics, with obvious redox peaks appearing in both positive and negative scans, corresponding to the reversible redox reaction of the metal cations in the LDHs layer. As the scan rate increases from 10 mV s⁻¹ to 100 mV s⁻¹, the curve shape remains basically intact, with only slight shifts in the redox peaks, indicating that the material possesses excellent rate performance and fast charge transfer kinetics, effectively utilizing active sites even at high scan rates. Figure 5(b) shows the constant current charge-discharge curves of the material at different current densities in this experiment. The curves exhibit typical pseudocapacitive charge-discharge characteristics, with nonlinear potential-time responses in both the charging and discharging segments, corresponding to the reversible redox process of the metal cations in the LDHs layer, which is highly consistent with the redox peak behavior of the cyclic voltammetry curves. As the current density gradually increases from 1 A / g to 10 A / g, the charge-discharge time shortens significantly, consistent with the basic law that capacitance is inversely proportional to current density. The longest charge-discharge time is observed at a current density of 1 A / g, indicating that the material can fully utilize active sites for efficient charge storage. Calculations show that the specific capacitance at a current density of 1 A / g is 1332 F / g. Figure 5(c) shows the electrochemical impedance spectroscopy (EIS) of the electrode material in this embodiment at frequencies ranging from 0.01 to 1,000,000 Hz. The curve shows only a very small semicircle in the high-frequency region, followed by an approximately linear upward trend in the mid-to-low frequency region. This characteristic directly reflects the excellent electrochemical interface properties and ion transport kinetics of the material. Figure 5(d) shows the cycling diagram of the electrode material in this embodiment at a current density of 10 A / g. Calculations show that the capacity retention rate of the material is 77.82% after 5000 cycles.

[0038] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite material using hydrotalcite and biochar, characterized in that... By using reed stalk biochar as the matrix of composite materials, and taking advantage of its high specific surface area, excellent electrochemical conductivity, and good electrochemical stability, materials with good electrochemical performance are obtained.

2. Using hydrotalcite as the active component has two advantages: firstly, hydrotalcite can provide abundant redox active sites, thereby improving the specific capacitance of the electrode material; secondly, the unique layered structure of hydrotalcite gives it excellent ion transport channels. During charging and discharging, these channels can promote the rapid migration and diffusion of ions, greatly enhancing the kinetic performance of the electrode reaction.

3. The key feature of this invention is the use of a pyrolysis carbonization method to prepare biochar, a simple and easy-to-operate method. The composite material is prepared using a hydrothermal method at relatively low temperatures and pressures, preventing excessive pyrolysis and collapse of the biochar, preserving intact pores, and facilitating the direct nucleation and growth of metal ions on the biochar surface, forming a strong interfacial bond that is not easily detached or agglomerated. After freeze-drying, the composite material, conductive carbon black, and polyvinylidene fluoride are mixed, with N-methylpyrrolidone as a dispersant, and uniformly coated onto nickel foam. After drying, it is pressed under 10 MPa pressure to obtain the electrode material.

4. When preparing hydrotalcite as described in claim 2, the hydrotalcite is prepared by a hydrothermal method.

5. When preparing the hydrotalcite / biochar composite material as described in claim 3, the key point is that the composite system of hydrotalcite and biochar must be ultrasonically treated, the purpose of which is to ensure that the biochar is uniformly dispersed in the system.

6. When preparing the hydrotalcite / biochar composite material as described in claim 3, the firing temperature is 120°C and the firing time is 12 h.

7. When preparing the hydrotalcite / biochar composite material as described in claim 3, the composite material is vacuum dried at 60°C for 24 hours.

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