A preparation method and application of B-NiCo2O4@NiCo-MOF composite material

Abstract

The application belongs to the technical field of composite material preparation, and particularly relates to a preparation method and application of a B-NiCo2O4@NiCo-MOF composite material. Boron-modified nickel cobaltate is prepared, and is used as a precursor to prepare the B-NiCo2O4@NiCo-MOF composite material through a hydrothermal method. The electronic structure of the NiCo2O4 is regulated through B, which effectively improves the conductivity and active site exposure of the material. In combination with the porous characteristics of the NiCo-MOF, the composite material with a hierarchical structure is formed, the synergistic optimization of electronic transmission and mass diffusion is realized, and the composite material is applied to the preparation of a supercapacitor positive electrode, so that the specific capacity and rate response performance of the electrode material are improved, and the supercapacitor has high energy density and super-long service life.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation technology, specifically relating to a preparation method and application of B-NiCo2O4@NiCo-MOF composite material. Background Technology

[0002] Supercapacitors are a novel type of energy storage device that combines the high power characteristics of traditional capacitors with the high energy characteristics of secondary batteries. Their typical structure consists of three parts: high specific surface area electrode materials, electrolyte, and separator. With advantages such as millisecond-level charge / discharge speeds and ultra-long cycle life, they play an irreplaceable role in regenerative braking energy recovery, smart grid frequency regulation, and emergency power supplies. As a core element determining device performance, electrode materials must simultaneously meet requirements such as high conductivity, abundant active sites, and stable structure. This makes the design and development of high-performance electrode materials a current research focus. Transition metal oxides typically possess characteristics such as high theoretical specific capacity and abundant redox activity; however, their poor conductivity and structural collapse due to volume expansion during cycling severely limit their practical performance.

[0003] Metal-organic frameworks (MOFs) are a class of porous crystalline materials formed by the self-assembly of metal ions or metal clusters with organic ligands through coordination bonds. Due to their highly ordered pore structure, ultra-high specific surface area, and tunable chemical composition, MOFs have shown great potential in the field of supercapacitors. Chinese patent CN109166733A discloses a hydrothermal method for preparing Ni / Co-based MOF materials. By adjusting the Ni / Co ratio and introducing carbon nanotubes (CNTs) or graphene oxide (GO), the conductivity and specific surface area of ​​the material are improved, thereby enhancing its electrochemical performance. However, this type of MOF material still suffers from the following problems: structural collapse easily occurs during charge and discharge, leading to insufficient cycle stability; although the introduction of CNTs or GO improves this somewhat, the conductivity of the MOF itself is still not ideal; and MOF particles are prone to aggregation, limiting the full exposure of active sites and effective electrolyte penetration.

[0004] Layered bimetallic hydroxides (LDHs) have attracted widespread attention in the field of supercapacitors due to their unique layered structure and tunable metal composition. For example, Chinese patent CN117912864A discloses a method for preparing NiCo-LDH@Ni(BO2)2 electrode material. This method uses NiCo-MOF as a precursor, converting it to NiCo-LDH through alkaline co-precipitation, and then reacting it with sodium borohydride solution to form Ni(BO2)2 on the surface. This material achieves a yield of 0.5 A·g... -1 The specific capacitance can reach 1373 F·g -1 It also exhibits good cyclic stability.

[0005] However, LDH materials are prone to lamination or structural collapse during long-term cycling, resulting in loss of active sites and blockage of ion diffusion channels. Although the Ni(BO2)2 formed on the surface can improve local conductivity, it is difficult to construct a three-dimensional conductive network that runs through the whole, and the conductivity needs to be improved.

[0006] Therefore, developing highly conductive supercapacitor electrode materials with more continuous conductive networks remains a pressing technical problem to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a B-NiCo2O4@NiCo-MOF composite material, its preparation method, and its application. Boron-modified nickel cobalt oxide is prepared and used as a precursor to obtain the B-NiCo2O4@NiCo-MOF composite material via a hydrothermal method. The composite material is then applied to the preparation of the positive electrode of a supercapacitor.

[0008] The solution to the technical problem of this invention is: The first aspect of this invention provides a method for preparing B-NiCo2O4@NiCo-MOF composite material, comprising the following steps: (1) Preparation of B-NiCo(OH)2: Ni(NO3)2·6H2O and Co(NO3)2·6H2O are mixed evenly in deionized water, and then NaBH4 solution is added. After stirring for 1-2 hours, the mixture is aged for 10-14 hours, centrifuged, and the precipitate is obtained. After washing and drying, a black powder is obtained, which is B-NiCo(OH)2. (2) Preparation of B-NiCo2O4: The B-NiCo(OH)2 was placed in a muffle furnace for calcination, and then washed and dried to obtain a black powder, which is B-NiCo2O4; (3) Preparation of B-NiCo2O4@NiCo-MOF: Dissolve the B-NiCo2O4 in N,N dimethylformamide solution, and disperse it by ultrasonication until uniform to obtain a mixed solution. Then, add Ni(NO3)2·6H2O, Co(NO3)2·6H2O and terephthalic acid to the mixed solution in sequence, stir magnetically until uniform, and heat at 140-160℃ for 6-10h. Centrifuge to obtain precipitate, wash and dry to obtain black powder, which is B-NiCo2O4@NiCo-MOF.

[0009] Preferably, the ratio of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, deionized water and NaBH4 solution is 0.3-0.6g:0.3-0.6g:20-30mL:15-25mL, and more preferably 0.4g:0.4g:25mL:20mL.

[0010] Preferably, the drying process in step (1) is carried out at a temperature of 50-60°C for 12-24 hours.

[0011] Preferably, centrifuge at 5000-8000 r / min for 2 min.

[0012] Preferably, the concentration of the NaBH4 solution is 0.225 mol / L. The strong reducing property of NaBH4 forces the reaction to promote O by controlling the metal valence state. V The generation of [a specific chemical process]. Simultaneously, the doping of B atoms, as a near-metallic element, into metal oxides can optimize wettability and improve electronic conductivity, thereby enhancing the electrochemical performance of the cathode material.

[0013] Preferably, the calcination method is as follows: temperature 400-450℃, calcination time 2h, heating rate 2℃ / min.

[0014] Preferably, the washing method in step (2) is as follows: wash with water and anhydrous ethanol 2-3 times respectively; the drying time is 12-24 hours and the temperature is 60-70℃.

[0015] Preferably, the ratio of B-NiCo2O4, N,N-dimethylformamide, Ni(NO3)2·6H2O, Co(NO3)2·6H2O and terephthalic acid in step (3) is 0.1-0.2g : 40-60 mL : 0.4-0.7g : 0.1-0.4g : 0.1-0.4g, and more preferably 0.1g : 50 mL : 0.5g : 0.3g : 0.2g.

[0016] Preferably, the washing method is as follows: washing 2-3 times with N,N-dimethylformamide and anhydrous ethanol respectively; drying time is 12-24 hours and temperature is 60-70℃.

[0017] The second aspect of this invention discloses a B-NiCo2O4@NiCo-MOF composite material, which is prepared using the aforementioned preparation method.

[0018] The third aspect of this invention discloses the application of the B-NiCo2O4@NiCo-MOF composite material in the preparation of positive electrode materials for supercapacitors.

[0019] This invention uses B-NiCo2O4 as a precursor or substrate and employs a hydrothermal / solvothermal method to grow NiCo-MOF composite materials on its surface. The advantages of this method are: B doping first optimizes the electronic structure of NiCo2O4, making it a highly conductive substrate, resulting in more efficient charge transport during subsequent MOF growth (the "conductive bridge" effect). B on the NiCo2O4 surface participates in the MOF growth process, forming bonds such as BOC with organic ligands, strengthening the heterojunction and reducing contact resistance. When the MOF grows on pre-doped NiCo2O4, its porosity is less likely to be destroyed (if MOF is grown first and then boronized, the MOF structure collapses at high temperatures).

[0020] B-NiCo2O4 exhibits abundant redox activity, but its nanoparticles tend to aggregate, reducing the exposure of active sites and leading to rapid capacity decay at high current densities. The porous structure of MOFs provides numerous active sites, facilitating electrolyte penetration and ion transport. Using B-NiCo2O4 as a precursor to grow MOFs increases the exposure of active sites, prevents aggregation, and improves conductivity and ion transport. By optimizing the electronic structure of NiCo2O4 through boron doping, B-NiCo2O4 provides conductive pathways, reducing internal resistance. Simultaneously, the porous framework of MOFs mitigates volume effects and accelerates electrolyte diffusion, synergistically enhancing the electrochemical activity and stability of the material.

[0021] Compared with the prior art, the present invention has the following advantages: 1. This invention first uses B to regulate the electronic structure of NiCo2O4, which effectively improves the conductivity and active site exposure of the material. Combined with the porous characteristics of NiCo-MOF, a composite material with a hierarchical structure is formed, realizing the synergistic optimization of electron transport and mass diffusion.

[0022] 2. The B-NiCo2O4@NiCo-MOF composite material prepared by the technical solution of this invention exhibits superior performance with high specific capacity. The microporous / mesoporous structure of NiCo-MOF encapsulates B-NiCo2O4, providing a high specific surface area and abundant mass transfer channels, which is beneficial for the rapid penetration of reactants / electrolytes. Applying it to the preparation of supercapacitor cathode materials improves and enhances the specific capacity and rate response performance of the electrode material, resulting in supercapacitors with high energy density and ultra-long service life. Attached Figure Description

[0023] Figure 1 The XRD pattern of the B-NiCo2O4@NiCo-MOF composite material prepared in Example 1 of this invention; Figure 2The electrode material prepared from the B-NiCo2O4@NiCo-MOF composite material prepared in Example 1 of this invention operates within a voltage range of 0-0.45V and a scan rate of 10mV·s. -1 20mV·s -1 30mV·s -1 50mV·s -1 and 80mV·s -1 The following is a cyclic voltammetry chart; Figure 3 The graph shows the relationship between time and voltage when the B-NiCo2O4@NiCo-MOF composite material prepared in Example 1 of this invention is charged and discharged under constant current.

[0024] Figure 4 The image shows the XRD pattern of the B-NiCo2O4 composite material prepared in Comparative Example 1 of this invention. Figure 5 The electrode material prepared from the B-NiCo2O4 composite material prepared in Comparative Example 1 of this invention operates within a voltage range of 0-0.45V and a scan rate of 10mV·s. -1 Cyclic voltammetry; Figure 6 The graph shows the relationship between time and voltage when the B-NiCo2O4 composite material prepared in Comparative Example 1 of this invention is charged and discharged under a constant current. Detailed Implementation

[0025] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0026] Example 1 A method for preparing B-NiCo2O4@NiCo-MOF composite material includes the following steps: S1. Preparation of B-NiCo(OH)2: Mix 0.4g of Ni(NO3)2·6H2O and 0.4g of Co(NO3)2·6H2O in 25mL of deionized water to obtain solution a. Add 20mL of 0.225mol / L NaBH4 solution, stir for 1h and then age for 12h to obtain solution b. Centrifuge at 8000r / min for 2min to remove the supernatant and obtain the precipitate. Wash three times with anhydrous ethanol and dry at 60℃ for 24h to obtain a black powder, which is B-NiCo(OH)2. S2. Preparation of B-NiCo2O4: The 0.3g of B-NiCo(OH)2 mentioned in S1 is evenly spread in a porcelain boat and placed in a muffle furnace and calcined at 450℃ for 2h with a heating rate of 2℃ / min to obtain a black powdery substance, which is B-NiCo2O4. S3. Preparation of B-NiCo2O4@NiCo-MOF: Dissolve 0.1g of B-NiCo2O4 from S2 in 50mL of N,N-dimethylformamide solution and ultrasonically disperse until uniform to obtain solution c. Add 0.5g of Ni(NO3)2·6H2O, 0.3g of Co(NO3)2·6H2O and 0.2g of terephthalic acid to solution c in sequence and stir magnetically until dissolved to obtain solution d. Heat at 160℃ for 6h in a reaction vessel to obtain solution e. Centrifuge at 8000 r / min for 2 min to remove the supernatant and obtain the precipitate. Wash three times with anhydrous ethanol and dry at 60℃ for 24h to obtain a black powder, which is B-NiCo2O4@NiCo-MOF.

[0027] Figure 1 The XRD pattern and corresponding standard card of the B-NiCo2O4@NiCo-MOF composite material prepared in Example 1 are shown below. Figure 1 As shown, the peak positions of B-NiCo2O4 are basically consistent with those of the standard card (JCPDS:20-0781, NiCo2O4), with typical peaks located at 2θ=18.9° (111), 31.2° (220), 36.8° (311), 44.8° (400), and 59.3° (511). The diffraction peaks at 2θ=9.3°, 14.7°, and 18.5° can be attributed to the characteristic diffraction peaks of the (020), (110), and (040) crystal planes, which are characteristic diffraction peaks of NiCo-MOF. Furthermore, an additional peak appears in the low-angle region at 2θ=16.4°, further proving that the B-NiCo2O4@NiCo-MOF material prepared in this embodiment contains B-NiCo2O4 and NiCo-MOF materials.

[0028] Figure 2 When the B-NiCo2O4@NiCo-MOF composite material prepared in Example 1 is used in the positive electrode material, the cyclic voltammetry (CV) curves of the prepared electrode material at different scan rates are obtained. The voltage range is 0-0.45V, and the scan rate is 10mV·s. -1、 20mV·s -1 30mV·s -1 50mV·s -1 and 80mV·s -1The CV curves show that the prepared electrode material has obvious redox peaks, indicating that the B-NiCo2O4@NiCo-MOF composite material is a typical pseudocapacitive material. The paired redox peaks in the curves demonstrate the pseudocapacitive characteristics of the B-NiCo2O4@NiCo-MOF composite material. Furthermore, the peak current of the redox peaks increases significantly with increasing scan rate, indicating that the redox rate on the electrode material accelerates. The faster the redox rate, the better the synergistic optimization performance of interfacial charge transport and ion diffusion in the electrode material.

[0029] Example 2 A method for preparing B-NiCo2O4@NiCo-MOF composite material, the only difference from embodiment 1 is that step (3) is heated at 150°C for 8 hours in a reaction vessel.

[0030] Example 3 A method for preparing a B-NiCo2O4@NiCo-MOF composite material, the only difference from embodiment 1 is that step (3) is heated at 140°C for 10 hours in a reaction vessel.

[0031] Comparative Example 1 (MOF first, then boronization) A method for preparing a composite material includes the following steps: S1. Preparation of NiCo-MOF: Dissolve 0.5g of Ni(NO3)2·6H2O, 0.3g of Co(NO3)2·6H2O and 0.2g of terephthalic acid in 50mL of N,N-dimethylformamide solution, sonicate until uniformly dispersed, add 20mL of 0.23mol / L NaBH4 solution, stir magnetically for 30min, heat in a reaction vessel at 160℃ for 6h, centrifuge at 8000 r / min for 2min, remove the supernatant, obtain the precipitate, wash 3 times with anhydrous ethanol, dry at 60℃ for 24h, and obtain a green powdery substance, which is NiCo-MOF.

[0032] S2. Preparation of B-NiCo2O4: 0.3g of NiCo-MOF described in S1 is evenly spread in a porcelain boat and calcined in a muffle furnace at 450℃ for 2h with a heating rate of 2℃ / min, yielding a black powdery substance, which is B-NiCo2O4. 4。

[0033] Comparative Example 2 A method for preparing a B-NiCo2O4@NiCo-MOF composite material differs from Embodiment 1 only in that step (3) is heated at 135°C for 6 hours in a reaction vessel.

[0034] Comparative Example 3 A method for preparing B-NiCo2O4@NiCo-MOF composite material, which differs from Example 1 only in that step (3) is heated at 165°C for 6 hours in a reaction vessel.

[0035] The composite materials prepared in the examples and comparative examples were used in the positive electrode material. The working electrode was prepared by mixing the active electrode material, acetylene black, and polytetrafluoroethylene (PTFE) (80 wt%:10 wt%:10 wt%). The slurry was then pressed onto nickel foam (NF, 1×1 cm⁻¹) at a pressure of 12 MPa. -2 The sample was vacuum dried overnight at 60°C, with an active substance loading of 4 mg.

[0036] The composite material was subjected to constant current charge-discharge at different current densities. The specific capacitance could be calculated using the formula C = IΔt / mΔV, where I(A), Δt(s), m(g), and ΔV(V) represent the discharge current, discharge time, mass of the active material on the electrode, and potential window, respectively. At 1 A·g -1 3A·g -1 5A·g -1 8A·g -1 The specific capacitance values ​​under different current densities are shown in Table 1.

[0037] Table 1 (Specific capacitance of the examples and comparative examples at different current densities)

[0038] Analysis based on the data in Table 1 and the attached figures: Figure 3 The figures show the galvanostatic charge-discharge curves of the B-NiCo2O4@NiCo-MOF composite material prepared in Example 1 at different current densities. As can be seen from the figures, the galvanostatic charge-discharge curve first rises and then falls with the charging and discharging of the composite material. This indicates that the capacitance of the material is mainly caused by the Faraday redox reaction, suggesting that the electrode material is a pseudocapacitive material. Specifically, at 1 A·g... -1 3A·g -1 5A·g -1 8A·g -1 Calculations show that the specific capacitance values ​​are 911 F·g under different current densities. -1 740 F·g -1 623 F·g -1 588 F·g -1 This indicates that the prepared B-NiCo2O4@NiCo-MOF composite material has a high specific capacitance; when the current density is 8 A·g -1 At that time, the specific capacitance of the composite material can be maintained at 8 A∙g -1The initial specific capacitance at the current density is 64%, indicating that the prepared B-NiCo2O4@NiCo-MOF composite material has good rate performance.

[0039] Comparative Example 1, which involved MOF followed by boronizing, exhibited poor performance. This is due to the limitations of boron modification after NiCo-MOF: the MOF has poor thermal stability, and subsequent boronizing requires high-temperature treatment, which can easily lead to framework collapse and a decrease in specific surface area. Boron (B) may mainly be distributed on the MOF surface, making it difficult to uniformly dope into the entire structure, resulting in limited improvement in conductivity. In contrast, in Example 1, the doping of B in the NiCo2O4 lattice can achieve uniform bulk doping through high-temperature calcination, significantly improving bulk conductivity. B acts as an active site, guiding the orderly growth of the MOF. In Comparative Example 1, post-boronizing is typically limited to the MOF surface or localized areas, making it difficult for B to penetrate deep into the MOF interior (due to the obstruction of organic ligands), resulting in a discontinuous conductive network.

[0040] Figure 4 This is the XRD pattern of Comparative Example 1. For example... Figure 4 As shown, the diffraction peaks appearing near 2θ = 31°, 37°, 45°, 59°, and 65° correspond to the (220), (311), (400), (511), and (440) crystal planes of the spinel structure NiCo2O4, respectively. The broadening of the diffraction peaks indicates that the material has a small grain size or low crystallinity, which is usually related to the porous or nanostructure retained in metal-organic framework-derived materials. No obvious impurity peaks were observed, indicating that the precursor was completely converted into pure spinel oxide during calcination.

[0041] Figure 5 The cyclic voltammetry (CV) curves of the B-NiCo2O4 composite material prepared for Comparative Example 1 when applied as a positive electrode material are shown. The voltage range is 0-0.45V, and the scan rate is 10mV·s. -1 The narrow curve range in the figure indicates weak charge storage capacity and extremely low utilization of active sites. This is mainly attributed to structural defects caused by the synthesis route: during the subsequent high-temperature borosilicate treatment, the inherent porous framework of the MOF precursor is prone to collapse, resulting in a significant decrease in specific surface area and porosity; at the same time, borosilicate treatment may generate amorphous or insulating phases covering the active surface, hindering electron transport and ion diffusion. Compared with the previous high-performance route of "first constructing a B-NiCo2O4 conductive core, and then epitaxially growing a NiCo-MOF porous shell", this route reverses the order, causing the structural advantages of MOF to be lost during high-temperature treatment, and failing to form an effective core-shell synergistic conductive network. Ultimately, this results in the material exhibiting high internal resistance and low active area, manifested as a small CV curve response current and a shape deviating from ideal capacitance behavior.

[0042] Figure 6The graph shows the relationship between time and voltage when the B-NiCo2O4 composite material prepared in Comparative Example 1 of this invention is charged and discharged under a constant current. The charge-discharge curves in the graph exhibit excessively short discharge times within the set voltage window (0.0-0.5V), directly corresponding to extremely low actual specific capacitance. Furthermore, the charge-discharge curves deviate from the symmetrical triangular shape, further indicating that the charge storage process is not an ideal double-layer mechanism. The supposedly significant pseudocapacitive redox plateau is also not clearly presented, meaning that the reaction kinetics of the active sites are slow and the utilization rate is low. These phenomena are consistent with the previous CV analysis conclusions. The fundamental reason lies in the following synthetic route: after high-temperature borylation treatment of the MOF precursor, its fine porous structure collapses, leading to a severe loss of specific surface area and ion transport channels. Simultaneously, the borylation process fails to effectively construct a highly conductive network and may instead introduce interfacial impedance, ultimately resulting in high electrode material resistance, small active area, and sluggish reaction kinetics. This is manifested in the low capacitance, high polarization, and disappearance of the plateau characteristics in the GCD curve.

[0043] In Comparative Example 2, the excessively low heating temperature in the reactor led to a decrease in the specific capacitance of B-NiCo2O4@NiCo-MOF. This was primarily because the lower temperature significantly affected the material's crystallinity, microstructure, and interfacial properties. At 160℃, the hydrothermal reaction energy was sufficient, facilitating the full coordination of terephthalic acid with nickel and cobalt ions. This promoted the formation of an ideal framework for NiCo-MOF with high crystallinity, ordered structure, and well-developed pores. Simultaneously, a uniform and dense coating layer formed on the surface of B-NiCo2O4. This structure provides abundant electrochemical active sites and facilitates rapid electron transport and efficient diffusion of electrolyte ions. However, when the temperature dropped to 135℃, the reaction system energy decreased, resulting in insufficient nucleation and growth of MOF crystals, decreased crystallinity, and increased structural defects. This limited the material's specific surface area and porosity development. Furthermore, the bonding between the MOF and the substrate may be weaker, leading to decreased coating uniformity. These structural defects collectively resulted in a reduction in effective active sites, an increase in charge transfer resistance, and a slowdown in ion diffusion rates, thereby reducing its pseudocapacitive storage capacity, manifested as a significant decrease in specific capacitance.

[0044] In Comparative Example 3, the excessively high heating temperature in the reactor disrupted the optimal microstructure formation process of the material. Increased temperature intensified the reactivity of the metal ions with the organic ligands, leading to excessively rapid growth of NiCo-MOF on the B-NiCo2O4 substrate surface. This potentially resulted in a thicker shell and a denser structure, consequently reducing the material's porosity and specific surface area, decreasing electrochemical active sites, and hindering efficient ion transport in the electrolyte. Simultaneously, higher crystallization temperatures may cause excessive crystallinity, reducing the number of active defect sites available for pseudocapacitive reactions on the surface, and potentially introducing interfacial stress or by-reaction products, increasing charge transfer resistance.

[0045] The composite materials prepared in the examples and comparative examples were used as cathode materials for cycle performance testing at a current density of 8 A∙g⁻¹. -1 Under the condition of continuous charge and discharge for 2000 cycles, its capacity retention rate was recorded, and the cycle stability is shown in Table 2.

[0046] Table 2

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a B-NiCo2O4@NiCo-MOF composite material, characterized in that, The steps are as follows: (1) Preparation of B-NiCo(OH)2: Ni(NO3)2·6H2O and Co(NO3)2·6H2O are mixed evenly in deionized water, and then NaBH4 solution is added. After stirring for 1-2 hours, the mixture is aged for 10-14 hours, centrifuged, and the precipitate is obtained. The precipitate is washed and dried to obtain B-NiCo(OH)2. The ratio of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, deionized water and NaBH4 solution is 0.3-0.6g : 0.3-0.6g : 20-30mL : 15-25mL. (2) Preparation of B-NiCo2O4: The B-NiCo(OH)2 was calcined in a muffle furnace, washed and dried to obtain B-NiCo2O4; (3) Preparation of B-NiCo2O4@NiCo-MOF: The B-NiCo2O4 was dissolved in N,N-dimethylformamide solution and ultrasonically dispersed until uniform to obtain a mixed solution. Ni(NO3)2·6H2O, Co(NO3)2·6H2O and terephthalic acid were added to the mixed solution in sequence. After magnetic stirring until uniform, the mixture was heated at 140-160℃ for 6-10 h. The precipitate was obtained by centrifugation, washed and dried to obtain B-NiCo2O4@NiCo-MOF. The ratio of B-NiCo2O4, N,N-dimethylformamide, Ni(NO3)2·6H2O, Co(NO3)2·6H2O and terephthalic acid was 0.1-0.2 g: 40-60 mL: 0.4-0.7 g: 0.1-0.4 g: 0.1-0.4g, wherein the B-NiCo2O4 serves as a precursor or substrate, and the B on its surface participates in the NiCo-MOF growth process, forming BOC bonds with terephthalic acid to strengthen the heterogeneous interface bonding between B-NiCo2O4 and NiCo-MOF and reduce contact resistance. The porous structure of the NiCo-MOF and the B-NiCo2O4 as a highly conductive substrate together optimize electron transport and mass diffusion. At the same time, the growth of NiCo-MOF with B-NiCo2O4 as a precursor can prevent the aggregation of B-NiCo2O4 nanoparticles and increase the exposure of active sites.

2. The preparation method of the B-NiCo2O4@NiCo-MOF composite material according to claim 1, characterized in that, The drying process in step (1) is carried out at a temperature of 50-60℃ for 12-24 hours.

3. The preparation method of the B-NiCo2O4@NiCo-MOF composite material according to claim 1, characterized in that, The calcination method is as follows: calcination temperature 400-450℃, calcination time 1.5-3h, heating rate 2℃ / min.

4. The preparation method of the B-NiCo2O4@NiCo-MOF composite material according to claim 1, characterized in that, The washing method described in step (2) is as follows: wash with water and anhydrous ethanol 2-3 times respectively; the drying time is 12-24 hours and the temperature is 60-70℃.

5. The method for preparing the B-NiCo2O4@NiCo-MOF composite material according to claim 1, characterized in that, The washing method described in step (3) is as follows: wash with N,N dimethylformamide and anhydrous ethanol 2-3 times respectively; the drying time is 12-24h and the temperature is 60-70℃.

6. A B-NiCo2O4@NiCo-MOF composite material, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.

7. The application of the B-NiCo2O4@NiCo-MOF composite material as described in claim 6 in the preparation of positive electrode materials for supercapacitors.

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