Nanosheet-shaped NiCo2O4@PPy composite materials, their preparation methods and applications

Abstract

The application discloses a preparation method of a nanosheet spherical NiCo2O4@PPy composite material. The method comprises the following steps: firstly, preparing a NiCo-CD intermediate product in a spherical structure assembled by nanosheets through a two-step hydrothermal method; the intermediate product has higher surface roughness and richer surface structure levels; then, the intermediate product is converted into NiCo2O4 with a stable spinel structure through high-temperature calcination; finally, in-situ compounding of polypyrrole on the surface of the NiCo2O4 is realized through an oxidation polymerization reaction under low-temperature conditions, so as to construct a closely coupled interface structure. The preparation method is simple, and the obtained material has conductivity and interface charge transport capacity, and can be used for supercapacitors.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor technology, specifically relating to nanosheet spherical NiCo2O4@PPy composite materials, their preparation methods, and applications. Background Technology

[0002] With the miniaturization and portability of new energy technologies and electronic devices, the demand for high-performance energy storage devices is constantly increasing. Supercapacitors, as an energy storage device situated between traditional capacitors and secondary batteries, possess advantages such as high power density, fast charge / discharge speed, long cycle life, and excellent safety performance, making them promising for applications in electric vehicles, portable electronic devices, backup power supplies, and smart grids. However, compared to energy storage devices such as lithium-ion batteries, traditional supercapacitors still suffer from lower energy density. Therefore, developing electrode materials with high specific capacitance, high rate performance, and excellent cycle stability has become an important direction in current supercapacitor research.

[0003] Currently, supercapacitor electrode materials mainly include carbon-based materials, transition metal oxides, and conductive polymers. Among these, carbon-based materials possess good conductivity and structural stability, but their energy storage mechanism primarily relies on the electric double-layer capacitance, resulting in a relatively low theoretical specific capacitance. Conductive polymers exhibit high pseudocapacitance, but are prone to structural expansion and contraction during long-term cycling, leading to poor cycling stability. In contrast, transition metal oxides have attracted widespread attention in the field of supercapacitors due to their multivalent redox reactions and high theoretical specific capacitance.

[0004] NiCo2O4 is a typical spinel-structured transition metal oxide containing both Ni and Co transition metals in its crystal structure. Compared to single metal oxides (such as NiO or Co3O4), NiCo2O4 exhibits higher electrochemical activity and better electronic conductivity, thus being considered a promising electrode material for supercapacitors. Furthermore, NiCo2O4 undergoes a reversible redox reaction in alkaline electrolytes, providing high pseudocapacitance. However, NiCo2O4 still has some shortcomings in practical applications. For example, its intrinsic conductivity remains limited, resulting in low electron transport efficiency under high current density conditions and a decrease in rate performance. Simultaneously, during repeated charge-discharge cycles, the NiCo2O4 structure may experience volume expansion and structural damage, leading to the shedding of active material and affecting cycle stability.

[0005] To improve the electrochemical performance of NiCo2O4, researchers have proposed various modification strategies, such as constructing hierarchical structures, introducing conductive carbon materials, and compositing with conductive polymers. Among these, compositing with conductive polymers is considered an effective modification method. Conductive polymers possess excellent electronic conductivity and pseudocapacitive properties, with polypyrrole (PPy) attracting widespread attention due to its simple preparation method, good environmental stability, excellent conductivity, and high electrochemical activity. When PPy is composited with metal oxides, it not only improves the overall conductivity of the material but also provides additional pseudocapacitive contributions during charge and discharge, thereby significantly enhancing the specific capacitance of the electrode material. Simultaneously, the flexible structure of PPy can buffer the volume changes of metal oxides during charge and discharge to a certain extent, which is beneficial for improving the cycling stability of the material.

[0006] However, existing technologies for composite NiCo2O4 and PPy still have some shortcomings. For example, in some preparation methods, PPy may exhibit localized thickening, uneven deposition, or enhanced aggregation tendency on the NiCo2O4 surface, thus affecting the structural stability and conductive network construction of the material. Furthermore, if the PPy content is not properly controlled, excessive polymer may cover the electrochemically active sites on the NiCo2O4 surface, thereby reducing the material's electrochemical activity. Meanwhile, some composite methods are complex and difficult to implement on a large scale. Therefore, how to construct a uniform and stable PPy coating structure on the NiCo2O4 surface using a simple and controllable method, and achieve a synergistic effect between the two to improve the material's electrochemical performance, remains a pressing technical problem to be solved in this field.

[0007] Therefore, it is necessary to develop a method for preparing NiCo2O4@PPy composite materials with stable structure, tight interfacial bonding, and reasonable conductive network construction, so as to further improve the electrochemical performance and cycle stability of supercapacitor electrode materials. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing nanosheet-shaped NiCo2O4@PPy composite material and the nanosheet-shaped NiCo2O4@PPy composite material prepared by the above method, so as to solve the technical problems of complex preparation methods of NiCo2O4@PPy and low electrochemical activity of the prepared materials in the prior art.

[0009] According to a first aspect of the present invention, a method for preparing nanosheet-like spherical NiCo2O4@PPy composite material is provided, comprising the following steps: S1. Dissolve Ni(NO3)2·6H2O and Co(NO3)2·4H2O in isopropanol to obtain a mixed solution. Add glycerol to the mixed solution, stir, and transfer the resulting mixed solution to a reaction vessel. React at 170-190℃ for 5-7 h to obtain the precursor. S2. Add the precursor to a mixed solution of N,N-dimethylformamide and N-methylpyrrolidone, and react at 150-165℃ for 50-60 min to obtain the intermediate product. S3. The intermediate product is first calcined at 150°C, and then calcined at 300°C for a second time. After cooling, NiCo2O4 is obtained. S4. Disperse NiCo2O4 in water, add surfactant to obtain solution A, set aside; disperse pyrrole in water to obtain solution B; then add solution B dropwise to solution A under stirring at 4-6℃, and then add oxidant dropwise to solution A. React for 6-8 h to obtain the final product.

[0010] This invention first prepares a NiCo-CD intermediate product with a spherical structure assembled from nanosheets using a two-step hydrothermal method. The intermediate product has higher surface roughness and richer surface structure layers. Then, it is converted into NiCo2O4 with a stable spinel structure by two high-temperature calcinations. Finally, under low-temperature conditions, in-situ composite of polypyrrole on the surface of NiCo2O4 is achieved by oxidative polymerization reaction to construct a tightly coupled interface structure.

[0011] In this step, DMF and NMP mainly serve as high-boiling-point mixed solvents and morphology control media to disperse precursors, promote mild reconstruction, and regulate the formation of nanosheet sphere morphology.

[0012] The first calcination primarily aims to remove adsorbed water, water of crystallization, and some organic residues from the intermediate product, while simultaneously causing gentle desorption and preliminary solidification of the precursor. This prevents structural collapse, particle agglomeration, or surface cracking caused by the instantaneous large-scale escape of moisture and organic components during subsequent direct high-temperature processing, thus preserving the original spherical structure of the precursor. The second calcination primarily aims to promote further decomposition of the precursor and drive the transformation of Ni and Co-related components into the spinel phase NiCo2O4, improving the crystallinity and phase purity of the product. Performing a second calcination after the pre-removal and structural stabilization steps are completed further facilitates the formation of a uniform and stable oxide framework.

[0013] In some embodiments, the molar ratio of Ni(NO3)2·6H2O to Co(NO3)2·4H2O is 1:2.

[0014] In some embodiments, in step S1, the reaction is carried out at 180°C for 6 h.

[0015] In some embodiments, the volume ratio of N,N-dimethylformamide to N-methylpyrrolidone is (4-5):1.

[0016] In some embodiments, in step S2, the reaction is carried out at 160°C for 55 min. Controlling the temperature at 160°C provides sufficient energy for the precursor to transform into nanosheets, allowing for structural rearrangement and localized solvothermal conversion, while preventing excessively high temperatures that could lead to rapid particle collapse, over-sintering, or morphological damage. A reaction time of 55 min allows for a more complete structural evolution process; if the time is too short, the precursor conversion will be insufficient, making it difficult to obtain a uniform nanosheet morphology after subsequent calcination; if the time is too long, it may lead to excessive layering, particle agglomeration, or structural densification, which is detrimental to improving the specific surface area and electrochemical performance of the subsequent material. Under the DMF and NMP mixed solvent and solvothermal conditions of 160°C in step S2, the NiCo-Gly precursor undergoes structural rearrangement and localized dissolution-reorganization, beginning its evolution into sheet-like or wrinkled units, forming a nanosheet sphere structure.

[0017] In some embodiments, in step S3, the temperature is 2°C·min -1 Heating rate increased to 150℃; at 1℃·min -1 The temperature is increased to 300℃ at a heating rate of [missing information]. Below 150℃, step S3 mainly involves the removal of moisture, residual solvent, and a small amount of low-temperature organic components. This stage has little impact on crystal phase formation, therefore a relatively fast heating rate can be used, at 2℃·min [missing information]. -1 A higher heating rate improves processing efficiency. However, when the temperature is increased from 150℃ to 300℃, the precursor undergoes deeper organic decomposition, skeletal shrinkage, and inorganic crystalline phase formation. If the temperature rises too quickly during this stage, the sudden increase in internal stress and rapid gas escape can easily lead to: nanosheet structure collapse; sintering and agglomeration of the sphere surface; reduced porosity; and uneven crystalline phase transformation. Therefore, a slower heating rate is beneficial for the precursor to gradually complete its structural transformation and better maintain the hierarchical morphology of the nanosheet spheres.

[0018] In some implementations, in step S3, the first calcination time is 30 min and the second calcination time is 2 h.

[0019] In some embodiments, the oxidant is a ferric chloride hexahydrate solution with a mass concentration of 3.75-12.5 g / L. Preferably, the oxidant is a ferric chloride hexahydrate solution with a mass concentration of 7.5 g / L. The oxidant concentration determines the polymerization rate and nucleation density of the pyrrole monomer. When the oxidant concentration is low, the polymerization rate is slow, and polypyrrole mainly deposits locally at the defect sites and edges of the sheets, having little impact on the sheet thickness. As the oxidant concentration increases, the polymerization rate and nucleation density increase, and polypyrrole grows continuously along the entire nanosheet surface of the NiCo2O4 material, causing the sheets to gradually thicken. When the oxidant concentration is further increased, the polymerization reaction rate is too fast, leading to disordered accumulation of polypyrrole on the sheet surface, accompanied by enhanced homogeneous polymerization in the solution, thereby causing structural agglomeration and pore blockage, which is detrimental to electrolyte ion transport.

[0020] In some embodiments, the surfactant is sodium dodecylbenzenesulfonate. By introducing the surfactant, the dispersibility of NiCo2O4 in solution is improved, and pyrrole monomers are preferentially adsorbed onto the matrix surface through electrostatic interactions and interfacial adsorption, thereby inducing the directional deposition of polypyrrole on the NiCo2O4 surface and preventing spontaneous aggregation of the polymer in solution.

[0021] In some embodiments, the mass ratio of surfactant to NiCo2O4 is (3-4):20.

[0022] In some embodiments, the reaction temperature in step S4 is 5°C. Conducting the polymerization reaction at a low temperature helps suppress the homogeneous polymerization of pyrrole in solution, allowing it to preferentially undergo heterogeneous nucleation and growth on the NiCo2O4 surface, thereby improving the uniformity and density of the shell. Extending the reaction time can further promote shell growth and enhance interfacial bonding.

[0023] In some embodiments, the concentration of pyrrole in solution B is 0.2-1.8 mmol / 5 mL.

[0024] In some implementations, 15-120 mL of pyrrole is added for every 100 g of NiCo2O4.

[0025] In some embodiments, 60 mL of pyrrole is added for every 100 g of NiCo2O4. By selecting the appropriate ratio of pyrrole to NiCo2O4, the resulting nanosheet-like NiCo2O4@PPy composite material exhibits higher coulombic efficiency and specific capacitance, resulting in better energy storage performance.

[0026] In some embodiments, in step S4, the rate of adding solution B is 0.02-0.05 mL / s, and the rate of adding the oxidant is 0.01-0.03 mL / s. By controlling the local concentration changes of pyrrole monomer and oxidant through the dropping rates of solution B and oxidant, the polymerization process becomes more controllable, thereby obtaining a continuous, dense, and adjustable-thickness polypyrrole shell.

[0027] In some implementations, in step S4, the dispersion is followed by ultrasonication.

[0028] In some embodiments, step S4 further includes a purification step. The purification method is as follows: after the reaction has proceeded for 6-8 hours, the resulting product is centrifuged and the lower solid layer is retained. The solid is then washed with water and anhydrous ethanol and dried to obtain the final product.

[0029] According to a second aspect of the present invention, a method for preparing the above-mentioned nanosheet spherical NiCo2O4@PPy composite material is provided to obtain the nanosheet spherical NiCo2O4@PPy composite material.

[0030] The nanosheet-like spherical NiCo2O4@PPy composite material of this invention achieves control over the thickness and uniformity of the polypyrrole shell on the NiCo2O4 surface through synergistic regulation of oxidant concentration, reaction temperature and time, surfactant, dispersion, and feeding method in the preparation process. This constructs a stable core-shell structure composite material, which can regulate the electronic structure and oxidative environment of the NiCo2O4 surface, promote the formation of defect-related oxygen species, and thus enhance the charge transport capacity and electrochemical reactivity of the material. The nanosheet-like spherical NiCo2O4@PPy composite material of this invention has an integrated core-shell nanosheet-like spherical structure, in which NiCo2O4 serves as the core and PPy serves as the outer coating shell.

[0031] According to a third aspect of the invention, the application of nanosheet spherical NiCo2O4@PPy composite material in supercapacitors is provided.

[0032] Nanosheet-shaped NiCo2O4@PPy composite materials can be used as positive electrodes to assemble supercapacitors.

[0033] The beneficial effects of this invention are as follows: (1) The method for preparing the nanosheet spherical NiCo2O4@PPy composite material of the present invention is simple. A uniform and stable PPy coating structure is constructed on the surface of the nanosheet spherical NiCo2O4. The nanosheet spherical NiCo2O4@PPy composite material with stable structure, tight interface bonding and reasonable conductive network construction is successfully prepared by this method.

[0034] (2) By adding the precursor to a mixed solution of DMF and NMP and reacting it, the surface of the intermediate product (NiCo-ND) formed more micro- and nano-scale wrinkles, lamellar edges and staggered stacked regions, which transformed the surface from a relatively flat and dense one to a rough interface with obvious undulations and multiple structural units coexisting. This made the precursor surface rougher, which is beneficial to improve the exposure of active sites of subsequent materials, improve electrolyte wetting performance, and provide more attachment sites for the uniform deposition and stable binding of pyrrole on the material surface.

[0035] (3) This invention optimizes the ratio of pyrrole monomer to NiCo2O4 to control the deposition degree and coating thickness of polypyrrole on the surface of NiCo2O4 nanosheets. This allows the resulting composite material to form an effective surface conductive layer while avoiding interfacial discontinuity caused by insufficient polypyrrole coating, and excessive thickness and density of the sheets due to excessive PPy coating, which would also result in some active sites being masked by PPy coating. The prepared nanosheet-shaped NiCo2O4@PPy composite material achieves a balance between enhanced conductivity and ion transport efficiency, thereby obtaining superior energy storage performance. Attached Figure Description

[0036] Figure 1 This is a SEM image of the NiCo-Gly precursor material of this invention; Figure 2 This is a SEM image of the NiCo2O4 material of this invention; Figure 3 This is a SEM image of NiCo2O4@PPy-60 of the present invention; Figure 4 This is a SEM image of NiCo2O4@PPy-15 of the present invention; Figure 5 This is a SEM image of NiCo2O4@PPy-30 of the present invention; Figure 6 This is a SEM image of NiCo2O4@PPy-120 of the present invention; Figure 7 The images show the Raman spectra of the nanosheet-spherical NiCo2O4@PPy composite material, NiCo2O4 material, and polypyrrole of this invention. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials and reagents involved in the following embodiments are all commercially available.

[0038] Example 1 This embodiment provides a method for preparing nanosheet-shaped NiCo2O4@PPy composite materials, including the following steps: (1) Preparation of NiCo-Gly material: 1 mmol of Ni(NO3)2·6H2O and 2 mmol of Co(NO3)2·4H2O were dissolved in 40 mL of isopropanol and stirred to form a uniform pink solution; then 8 mL of glycerol was added to the above solution and stirred until homogeneous. The resulting mixed solution was transferred to a reaction vessel and subjected to hydrothermal reaction at 180 °C for 6 h. After the reaction was completed, the obtained product was washed three times with anhydrous ethanol and then dried at 60 °C for 24 h to obtain NiCo-Gly precursor material.

[0039] (2) Preparation of NiCo-ND material: Weigh 0.25 g of the NiCo-Gly precursor obtained in step (1), add it to 35 mL of N,N-dimethylformamide (DMF) and 8 mL of N-methylpyrrolidone (NMP), and stir thoroughly to form a uniform pale yellow solution. Transfer the solution to a reaction vessel and react at 160 °C for 55 min. After the reaction is completed, wash and dry to obtain NiCo-ND material.

[0040] (3) Preparation of NiCo2O4 material: The NiCo-ND material obtained in step (2) was calcined in air. First, it was calcined at 2℃·min. -1 The temperature was increased to 150℃ at a heating rate and held for 30 min; then increased at a rate of 1℃·min. -1 The temperature was increased to 300℃ and held for 2 hours. After natural cooling to room temperature, NiCo2O4 material was obtained.

[0041] (4) Preparation of nanosheet spherical NiCo2O4@PPy material: Weigh 200 mg of NiCo2O4 material obtained in step (3), add it to 10 mL of deionized water (DI), and disperse it by ultrasonication for 5-10 min. Then add 0.03 g of sodium dodecylbenzenesulfonate (SDBS) and stir for 30 min to obtain solution A. Take another 5 mL of deionized water, add 60 μL of pyrrole monomer, and sonicate for 10 min to obtain solution B. Cool solutions A and B to about 5°C. Under stirring conditions, slowly add solution B to solution A at a rate of 0.03 mL / s. After the addition is complete, continue stirring for 30 min. Then, dissolve 0.3 g of ferric chloride hexahydrate (FeCl3·6H2O) in 40 mL of deionized water as an oxidant solution. Under low temperature (about 5°C) conditions, add the oxidant solution dropwise to the above mixture at a rate of 0.02 mL / s and continue stirring for 8 h. After the reaction was completed, the product was centrifuged at 6500 rpm and the solid was retained. The solid was then washed three times with deionized water and anhydrous ethanol. Finally, the obtained solid was dried under vacuum to obtain nanosheet spherical NiCo2O4@PPy composite material, denoted as NiCo2O4@PPy-60.

[0042] Example 2 This embodiment provides a method for preparing nanosheet-shaped NiCo2O4@PPy composite materials, including the following steps: (1) Preparation of NiCo-Gly material: 1 mmol of Ni(NO3)2·6H2O and 2 mmol of Co(NO3)2·4H2O were dissolved in 40 mL of isopropanol and stirred to form a uniform pink solution; then 8 mL of glycerol was added to the above solution and stirred until homogeneous. The resulting mixed solution was transferred to a reaction vessel and subjected to hydrothermal reaction at 180 °C for 6 h. After the reaction was completed, the obtained product was washed three times with anhydrous ethanol and then dried at 60 °C for 24 h to obtain NiCo-Gly precursor material.

[0043] (2) Preparation of NiCo-ND material: Weigh 0.25 g of the NiCo-Gly precursor obtained in step (1), add it to 35 mL of N,N-dimethylformamide (DMF) and 8 mL of N-methylpyrrolidone (NMP), and stir thoroughly to form a uniform pale yellow solution. Transfer the solution to a reaction vessel and react at 160 °C for 55 min. After the reaction is completed, wash and dry to obtain NiCo-ND material.

[0044] (3) Preparation of NiCo2O4 material: The NiCo-ND material obtained in step (2) was calcined in air. First, it was calcined at 2℃·min. -1The temperature was increased to 150℃ at a heating rate and held for 30 min; then increased at a rate of 1℃·min. -1 The temperature was increased to 300℃ and held for 2 hours. After natural cooling to room temperature, NiCo2O4 material was obtained.

[0045] (4) Preparation of nanosheet spherical NiCo2O4@PPy material: Weigh 200 mg of NiCo2O4 material obtained in step (3), add it to 10 mL of deionized water (DI), and disperse it by ultrasonication for 5-10 min. Then add 0.03 g of sodium dodecylbenzenesulfonate (SDBS) and stir for 30 min to obtain solution A. Take another 5 mL of deionized water, add 15 μL of pyrrole monomer, and sonicate for 10 min to obtain solution B. Cool solutions A and B to about 5°C. Under stirring conditions, slowly add solution B to solution A at a rate of about 10 s / drop. After the addition is completed, continue stirring for 30 min. Then, dissolve 0.15 g of ferric chloride hexahydrate (FeCl3·6H2O) in 40 mL of deionized water as an oxidant solution. Add the oxidant solution dropwise to the above mixture under low temperature (about 5°C) conditions and continue stirring for 8 h. After the reaction was completed, the product was centrifuged at 6500 rpm and the solid was retained. The solid was then washed three times with deionized water and anhydrous ethanol. Finally, the obtained solid was dried under vacuum to obtain the nanosheet spherical NiCo2O4@PPy composite material, denoted as NiCo2O4@PPy-15.

[0046] Example 3 This embodiment provides a method for preparing nanosheet-shaped NiCo2O4@PPy composite materials, including the following steps: (1) Preparation of NiCo-Gly material: 1 mmol of Ni(NO3)2·6H2O and 2 mmol of Co(NO3)2·4H2O were dissolved in 40 mL of isopropanol and stirred to form a uniform pink solution; then 8 mL of glycerol was added to the above solution and stirred until homogeneous. The resulting mixed solution was transferred to a reaction vessel and subjected to hydrothermal reaction at 180 °C for 6 h. After the reaction was completed, the obtained product was washed several times with anhydrous ethanol and dried at 60 °C for 24 h to obtain NiCo-Gly precursor material.

[0047] (2) Preparation of NiCo-ND material: Weigh 0.25 g of the NiCo-Gly precursor obtained in step (1), add it to 35 mL of N,N-dimethylformamide (DMF) and 8 mL of N-methylpyrrolidone (NMP), and stir thoroughly to form a uniform pale yellow solution. Transfer the solution to a reaction vessel and react at 160 °C for 55 min. After the reaction is completed, wash and dry to obtain NiCo-ND material.

[0048] (3) Preparation of NiCo2O4 material: The NiCo-ND material obtained in step (2) was calcined in air. First, it was calcined at 2℃·min. -1 The temperature was increased to 150℃ at a heating rate and held for 30 min; then increased at a rate of 1℃·min. -1 The temperature was increased to 300℃ and held for 2 hours. After natural cooling to room temperature, NiCo2O4 material was obtained.

[0049] (4) Preparation of nanosheet spherical NiCo2O4@PPy material: Weigh 200 mg of NiCo2O4 material obtained in step (3), add it to 10 mL of deionized water (DI), and disperse it by ultrasonication for 5-10 min. Then add 0.03 g of sodium dodecylbenzenesulfonate (SDBS) and stir for 30 min to obtain solution A. Take another 5 mL of deionized water, add 30 μL of pyrrole monomer, and sonicate for 10 min to obtain solution B. Cool solutions A and B to about 5°C. Under stirring conditions, slowly add solution B to solution A at a rate of about 10 s / drop. After the addition is completed, continue stirring for 30 min. Then, dissolve 0.20 g of ferric chloride hexahydrate (FeCl3·6H2O) in 40 mL of deionized water as an oxidant solution. Add the oxidant solution dropwise to the above mixture under low temperature (about 5°C) conditions and continue stirring for 8 h. After the reaction was completed, the product was separated by centrifugation and washed multiple times with deionized water and anhydrous ethanol. Finally, the obtained solid was dried under vacuum to obtain nanosheet spherical NiCo2O4@PPy composite material, denoted as NiCo2O4@PPy-30.

[0050] Example 4 This embodiment provides a method for preparing nanosheet-shaped NiCo2O4@PPy composite materials, including the following steps: (1) Preparation of NiCo-Gly material: 1 mmol of Ni(NO3)2·6H2O and 2 mmol of Co(NO3)2·4H2O were dissolved in 40 mL of isopropanol and stirred to form a uniform pink solution; then 8 mL of glycerol was added to the above solution and stirred until homogeneous. The resulting mixed solution was transferred to a reaction vessel and subjected to hydrothermal reaction at 180 °C for 6 h. After the reaction was completed, the obtained product was washed several times with anhydrous ethanol and dried at 60 °C for 24 h to obtain NiCo-Gly precursor material.

[0051] (2) Preparation of NiCo-ND material: Weigh 0.25 g of the NiCo-Gly precursor obtained in step (1), add it to 35 mL of N,N-dimethylformamide (DMF) and 8 mL of N-methylpyrrolidone (NMP), and stir thoroughly to form a uniform pale yellow solution. Transfer the solution to a reaction vessel and react at 160 °C for 55 min. After the reaction is completed, wash and dry to obtain NiCo-ND material.

[0052] (3) Preparation of NiCo2O4 material: The NiCo-ND material obtained in step (2) was calcined in air. First, it was calcined at 2℃·min. -1 The temperature was increased to 150℃ at a heating rate and held for 30 min; then increased at a rate of 1℃·min. -1 The temperature was increased to 300℃ and held for 2 hours. After natural cooling to room temperature, NiCo2O4 material was obtained.

[0053] (4) Preparation of nanosheet spherical NiCo2O4@PPy material: Weigh 200 mg of NiCo2O4 material obtained in step (3), add it to 10 mL of deionized water (DI), and disperse it by ultrasonication for 5-10 min. Then add 0.03 g of sodium dodecylbenzenesulfonate (SDBS) and stir for 30 min to obtain solution A. Take another 5 mL of deionized water, add 120 μL of pyrrole monomer, and sonicate for 10 min to obtain solution B. Cool solutions A and B to about 5°C. Under stirring conditions, slowly add solution B to solution A at a rate of about 10 s / drop. After the addition is completed, continue stirring for 30 min. Then, dissolve 0.50 g of ferric chloride hexahydrate (FeCl3·6H2O) in 40 mL of deionized water as an oxidant solution. Add the oxidant solution dropwise to the above mixture under low temperature (about 5°C) conditions and continue stirring for 8 h. After the reaction was completed, the product was separated by centrifugation and washed multiple times with deionized water and anhydrous ethanol. Finally, the obtained solid was dried under vacuum to obtain nanosheet spherical NiCo2O4@PPy composite material, denoted as NiCo2O4@PPy-120.

[0054] Comparative Example 1 This comparative example provides a method for preparing NiCo2O4 material, including the following steps: (1) Preparation of NiCo-Gly material: 1 mmol of Ni(NO3)2·6H2O and 2 mmol of Co(NO3)2·4H2O were dissolved in 40 mL of isopropanol and stirred to form a uniform pink solution; then 8 mL of glycerol was added to the above solution and stirred until homogeneous. The resulting mixed solution was transferred to a reaction vessel and subjected to hydrothermal reaction at 180 °C for 6 h. After the reaction was completed, the obtained product was washed several times with anhydrous ethanol and dried at 60 °C for 24 h to obtain NiCo-Gly precursor material.

[0055] (2) Preparation of NiCo-ND material: Weigh 0.25 g of the NiCo-Gly precursor obtained in step (1), add it to 35 mL of N,N-dimethylformamide (DMF) and 8 mL of N-methylpyrrolidone (NMP), and stir thoroughly to form a uniform pale yellow solution. Transfer the solution to a reaction vessel and react at 160 °C for 55 min. After the reaction is completed, wash and dry to obtain NiCo-ND material.

[0056] (3) Preparation of NiCo2O4 material: The NiCo-ND material obtained in step (2) was calcined in air. First, it was calcined at 2℃·min. -1 The temperature was increased to 150℃ at a heating rate and held for 30 min; then increased at a rate of 1℃·min. -1 The temperature was increased to 300℃ and held for 2 hours. After natural cooling to room temperature, NiCo2O4 material was obtained.

[0057] The NiCo-Gly precursor material, NiCo2O4 material, NiCo2O4@PPy-60, NiCo2O4@PPy-15, NiCo2O4@PPy-30 and NiCo2O4@PPy-120 were characterized by SEM, and the results are as follows: Figures 1-6 As shown. From Figure 1 It can be seen that the NiCo-Gly precursor material obtained in step (1) is spherical. The SEM image of the NiCo2O4 material is shown below. Figure 2 As shown, comparison Figure 1 and Figure 2It can be observed that, compared to the spherical precursor of NiCo-Gly, the NiCo2O4 material maintains the overall spherical morphology while forming a wrinkled micro-nano structure on the surface, thus transforming the morphology into a nanosheet spherical structure. Compared to the NiCo-Gly precursor material with a smooth and dense surface obtained in step (1), the intermediate product (NiCo-ND) obtained in step (2) by adding the precursor to DMF and NMP and then reacting it has a higher surface roughness and a richer surface structure hierarchy. That is, by adding the precursor to DMF and NMP and then reacting it in step (2), the surface of the intermediate product (NiCo-ND) forms more micro-nano scale wrinkles, sheet edges and interlaced stacked regions, so that the surface changes from a relatively smooth and dense surface to a rough interface with obvious undulations and multiple structural units coexisting. This provides more surface sites for the subsequent adhesion and uniform deposition of PPy, which is beneficial to improve the exposure of active sites of the subsequent material, improve the electrolyte wetting performance, and provide more adhesion sites for the uniform deposition and stable bonding of conductive polymer (PPy) on the material surface. Therefore, step (2) plays an important role in constructing high-performance NiCo2O4@PPy composite materials. Figures 3-6 SEM images of the nanosheet-like spherical NiCo2O4@PPy composites obtained with different PPy contents show that the NiCo2O4@PPy composites maintain the nanosheet-assembled spherical structure after the introduction of PPy. Comparison reveals that as the PPy content increases, the nanosheets on the sphere surface gradually thicken, indicating that polypyrrole grows continuously along the entire nanosheet surface, resulting in a gradual increase in the thickness of the sheets.

[0058] Raman spectroscopy characterization was performed on the nanosheet-like spherical NiCo2O4@PPy composite material prepared in Example 1, the NiCo2O4 material prepared in Comparative Example 1, and polypyrrole (PPy). The results are as follows: Figure 7 As shown. From Figure 7 It can be seen that pure NiCo2O4 at 663 cm⁻¹ -1 Characteristic Raman peaks of spinel-structured metal-oxygen bonds are found nearby; pure PPy shows a peak at 1565 cm⁻¹. -1 and 1368 cm -1 The vicinity exhibits characteristic Raman peaks of a polypyrrole molecular framework. In contrast, the nanosheet-like spherical NiCo2O4@PPy composite material obtained in this embodiment of the invention shows a peak at 652 cm⁻¹. -1 1372 cm -1 and 1556 cm -1Characteristic peaks appear simultaneously, corresponding to the characteristic vibrational signals of NiCo2O4 and PPy, respectively. The simultaneous presence of characteristic peaks from both inorganic oxides and conductive polymers in the composite material indicates that PPy has been successfully composited onto the surface or interface region of NiCo2O4, forming the target composite material. Furthermore, the characteristic peaks in the composite material show a certain shift compared to the pure components, indicating an interfacial interaction between PPy and NiCo2O4, which is beneficial for forming a tighter bond between the two phases, thereby improving the structural stability and charge transport synergy of the composite system. This demonstrates the successful preparation of the nanosheet-like spherical NiCo2O4@PPy composite material.

[0059] The performance of NiCo2O4 materials, NiCo2O4@PPy-60, NiCo2O4@PPy-15, NiCo2O4@PPy-30 and NiCo2O4@PPy-120 are then tested.

[0060] Weigh 0.008 g of the product from Examples 1-4 or Comparative Example 1, 0.001 g of acetylene black, and 0.001 g of polytetrafluoroethylene micro powder, place them in a small agate mortar, add 0.5 mL of ethanol, and grind. Press the ground sample with a 1 mm thick nickel foam current collector under a pressure of 10 kPa, dry it in air at room temperature, cut it into 2 cm × 2 cm pieces to prepare supercapacitor electrodes, and immerse them in a 2 M KOH solution. A mercury oxide electrode and a platinum electrode are used as the reference electrode and counter electrode, respectively. The equivalent series resistance R is obtained by testing in a three-electrode system. s (Ω), charge transfer resistance R t Data on (Ω), specific capacitance (F / g), and coulombic efficiency (%).

[0061] The electrochemical performance test results of different materials are shown in Table 1. As can be seen from Table 1, compared with NiCo2O4, the nanosheet-spherical NiCo2O4@PPy composite material has lower equivalent series resistance and charge transfer resistance, indicating that the charge / discharge rate and interfacial charge transfer speed of the supercapacitor assembled from the nanosheet-spherical NiCo2O4@PPy composite material are faster. The specific capacitance and coulombic efficiency of the nanosheet-spherical NiCo2O4@PPy composite material are higher than those of NiCo2O4, indicating that the nanosheet-spherical NiCo2O4@PPy composite material has better energy storage capacity per unit mass and a longer cycle life. This may be because an appropriate amount of PPy coating can form a continuous conductive layer on the NiCo2O4 surface, improving electron transport capability, reducing interfacial charge transfer resistance, while maintaining good pore structure and electrolyte wettability, which is beneficial for OH... -Rapid diffusion to active sites enhances the specific capacitance of the material. The specific capacitance and coulombic efficiency of NiCo2O4@PPy-60 are significantly higher than other nanosheet-like spherical NiCo2O4@PPy composites, and R... s The value is even lower, possibly because when the PPy coating concentration is too low, the conductivity enhancement effect is limited; when the PPy coating concentration is too high, it leads to excessively thickened sheets and a denser structure, which masks some active sites and hinders ion diffusion, thus being detrimental to improving electrochemical performance. Therefore, by controlling the PPy coating concentration, a balance can be achieved between enhanced conductivity and ion transport efficiency, thereby obtaining better energy storage performance. Among them, NiCo2O4@PPy-60 exhibits the best electrochemical performance.

[0062] Table 1 Electrochemical properties of different materials

[0063] To better apply the nanosheet-shaped NiCo2O4@PPy composite material to practical applications, an asymmetric supercapacitor was assembled using NiCo2O4@PPy-60 prepared in Example 1 and NiCo2O4 material prepared in Comparative Example 1 as the positive electrode and commercial activated carbon (AC) for supercapacitors as the negative electrode. A two-electrode test was conducted at a current density of 1 A and a voltage window of 0-1.6 V to obtain the energy density and power density of the supercapacitor. Furthermore, the cycle retention rate of the supercapacitor was obtained under a two-electrode system with a current density of 10 A and 5000 charge-discharge cycles to study its cycle life. The cycle retention rate was calculated using the following formula: Cycle retention rate = Specific capacitance after 5000 charge-discharge cycles / Specific capacitance after the first charge-discharge cycle × 100%.

[0064] Table 2 shows the dual-electrode test results of the nanosheet-spherical NiCo2O4@PPy composite material and NiCo2O4 material. As can be seen from Table 2, compared with Comparative Example 1, the NiCo2O4@PPy-60 prepared in Example 1 exhibits superior energy storage performance. Under similar power density conditions, the energy density of NiCo2O4@PPy-60 is 35.9 Wh kg higher than that of NiCo2O4. -1 Increased to 43.6 Wh kg -1 Power density is 824W kg -1 Increased to 832W kg -1Furthermore, the cycle retention rate increased from 76% to 92%. This indicates that PPy coating of NiCo2O4 not only enhances the material's conductivity and interfacial charge transport capability but also improves structural stability and active site utilization, thereby significantly improving the device's energy storage capacity and cycle durability. The above results demonstrate that the NiCo2O4@PPy composite structure constructed in this invention exhibits significantly superior technical performance compared to single NiCo2O4.

[0065] Table 2. Test results of two electrodes for different materials

[0066] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing nanosheet-shaped spherical NiCo2O4@PPy composite material, characterized in that, Includes the following steps: S1. Dissolve Ni(NO3)2·6H2O and Co(NO3)2·4H2O in isopropanol to obtain a mixed solution. Add glycerol to the mixed solution, stir, and transfer the resulting mixed solution to a reaction vessel. React at 170-190℃ for 5-7 h to obtain the precursor. S2. Add the precursor to a mixed solution of N,N-dimethylformamide and N-methylpyrrolidone, and react at 150-165℃ for 50-60 min to obtain the intermediate product. S3. The intermediate product is first calcined at 150°C, and then calcined at 300°C for a second time. After cooling, NiCo2O4 is obtained. S4. Disperse NiCo2O4 in water, add surfactant to obtain solution A, set aside; disperse pyrrole in water to obtain solution B; then add solution B dropwise to solution A under stirring at 4-6℃, and then add oxidant dropwise to solution A. React for 6-8 h to obtain the final product.

2. The method for preparing the nanosheet-spherical NiCo2O4@PPy composite material according to claim 1, characterized in that, The molar ratio of Ni(NO3)2·6H2O to Co(NO3)2·4H2O is 1:2; the volume ratio of N,N-dimethylformamide to N-methylpyrrolidone is (4-5):

1.

3. The method for preparing the nanosheet-spherical NiCo2O4@PPy composite material according to claim 1, characterized in that, In step S1, the reaction is carried out at 180°C for 6 h; in step S2, the reaction is carried out at 160°C for 55 min.

4. The method for preparing the nanosheet-spherical NiCo2O4@PPy composite material according to claim 1, characterized in that, In step S3, at 2℃·min -1 Heating rate increased to 150℃; at 1℃·min -1 The heating rate is increased to 300℃.

5. The method for preparing the nanosheet-spherical NiCo2O4@PPy composite material according to claim 1, characterized in that, The oxidant is a ferric chloride hexahydrate solution with a mass concentration of 3.75-12.5 g / L.

6. The method for preparing the nanosheet-like spherical NiCo2O4@PPy composite material according to claim 1, characterized in that, The surfactant is sodium dodecylbenzenesulfonate; the mass ratio of surfactant to NiCo2O4 is (3-4):

20.

7. The method for preparing the nanosheet-spherical NiCo2O4@PPy composite material according to claim 1, characterized in that, Add 15-120 mL of pyrrole per 100 g NiCo2O4.

8. The method for preparing the nanosheet-spherical NiCo2O4@PPy composite material according to claim 1, characterized in that, In step S4, the rate at which solution B is added is 0.02-0.05 mL / s, and the rate at which the oxidant is added is 0.01-0.03 mL / s.

9. A nanosheet-shaped spherical NiCo2O4@PPy composite material, characterized in that, The nanosheet spherical NiCo2O4@PPy composite material was prepared by any one of claims 1 to 8.

10. The application of the nanosheet spherical NiCo2O4@PPy composite material according to claim 9 in supercapacitors.

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