Method for preparing nickel-cobalt bimetal functional complex by secondary hydrothermal method, electrode material using nickel-cobalt bimetal functional complex and supercapacitor using nickel-cobalt bimetal functional complex

Abstract

The invention discloses a method for preparing a nickel-cobalt bimetallic functional complex through a secondary hydrothermal method and an electrode material and a supercapacitor using the complex, and the method comprises the steps: dissolving and mixing lithium hydroxide and 2-mercaptobenzoic acid, adding a nickel salt solution, and carrying out a first hydrothermal reaction to prepare a nickel-based precursor (a solid head product A); then, the precursor and cobalt chloride hexahydrate are subjected to a second hydrothermal reaction in a mixed solvent composed of methanol, deionized water and N, N-dimethylformamide (DMF) according to the mass ratio of 10: 1, and finally the target product Ni / Co10-1 is obtained. The bimetallic node functional complex is successfully constructed through a unique secondary hydrothermal process, and the problems that a monometal MOF material is poor in conductivity and low in specific capacity, and a one-step hydrothermal method is uneven in metal ion doping, poor in process stability and the like are effectively solved. The prepared Ni / Co10-1 material has excellent electrochemical performance and can be used as an ideal electrode material of a high-performance supercapacitor.

Description

Technical Field

[0001] This invention relates to the field of supercapacitor fabrication technology, and more specifically to a method for preparing nickel-cobalt bimetallic functional complexes using a secondary hydrothermal method, as well as electrode materials and supercapacitors using such complexes. Background Technology

[0002] With the rapid development of new energy sources (such as electric vehicles, photovoltaic energy storage, and portable electronic devices), the performance requirements for energy storage devices continue to increase. Supercapacitors, due to their fast charging and discharging speed, long cycle life, and high safety, have become key components for bridging the contradiction between energy density and power density in lithium-ion batteries, playing an irreplaceable role in scenarios such as start-stop power supplies and emergency energy storage.

[0003] However, the low energy density of supercapacitors makes it difficult to meet the application requirements of long-duration and high-capacity applications. Their performance bottleneck mainly depends on the structure and electrochemical activity of the electrode materials. Therefore, developing electrode materials with high specific capacity, excellent conductivity, and stability is the core breakthrough for improving the energy density of supercapacitors. Metal-organic frameworks (MOFs) are widely used in the research and development of supercapacitor electrode materials due to their high specific surface area, controllable pore structure, and abundant active metal sites. Among them, single-metal MOFs (such as Ni-MOFs) have become the mainstream research direction in the early stages due to their relatively simple preparation process, low cost, and certain specific capacity advantages in pseudocapacitive energy storage. However, when used as supercapacitor electrode materials, single-metal MOFs still suffer from problems such as poor conductivity, low specific capacity, and poor cycle stability.

[0004] To address the shortcomings of monometallic MOFs, researchers introduced two different metal ions (such as Co-Ni). On the one hand, by utilizing the synergistic effect between the metals, the coordination of the bimetallic nodes is more stable, which can improve the cycling stability of the material. On the other hand, the difference in electronegativity between the two metal ions can optimize the electronic structure, improve the conductivity of the material, and the abundant bimetallic active sites can enhance the redox reaction activity.

[0005] However, existing methods for preparing bimetallic MOFs (such as the one-step hydrothermal method) still have the following limitations: 1. Uneven metal ion doping: In the one-step hydrothermal method, the reactivity of the two metal ions is very different (such as the coordination rate of Co²⁺ and Ni²⁺ are different), which easily leads to the aggregation or uneven distribution of metal ions in the MOF framework, which cannot give full play to the synergistic effect, and the actual specific capacity is far lower than the theoretical value. 2. Poor controllability of pore structure: Existing methods make it difficult to precisely control the pore size of bimetallic MOFs (which typically have a wide distribution range, such as 2-50 nm), resulting in low electrolyte ion transport efficiency and poor rate performance. 3. Low stability of the preparation process: The one-step method is highly sensitive to reaction temperature and pH value, and the batch reproducibility of the product is poor, making it difficult to prepare on a large scale and limiting practical applications. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and provide a bimetallic functional complex electrode material that can precisely control the distribution of bimetallic ions, optimize the pore structure, and has a stable preparation process. Using nickel and cobalt as bimetallic nodes and 2-mercaptobenzoic acid (mba) as organic ligand, Ni / Co10-1 electrode material is synthesized by hydrothermal reaction under heating and pressure. Electrochemical performance testing shows that the specific capacity and energy density of the prepared Ni / Co10-1 electrode material are greatly improved, and it also has a long cycle life.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing nickel-cobalt bimetallic functional complexes by a secondary hydrothermal method, comprising the following steps: S1. Lithium hydroxide and 2-mercaptobenzoic acid are placed in a reaction vessel at a molar mass ratio of 1:1, and anhydrous ethanol is added to dissolve them to obtain solution A; S2. Dissolve the metal salt nickel sulfate hexahydrate in deionized water to obtain solution B, and then mix solution B with solution A to obtain solution C; wherein, the molar mass ratio of the metal salt nickel sulfate hexahydrate to 2-mercaptobenzoic acid in step S1 is 1:2. S3. The reaction vessel containing solution C is fitted with a metal outer shell and placed in an electrically heated blower dryer for reaction. After the reaction is completed, the product is cooled, scraped, rinsed and dried to obtain solid primary product A. S4. Add the initial solid product A:CoCl2·6H2O into the reaction vessel at a mass ratio of 10:1, and add deionized water, N,N-dimethylformamide and methanol in a volume ratio of 1:1:1 as reaction solvents. After stirring and dissolving, put the reaction vessel into an electric heating blower dryer with a metal outer shell on top. S5. Based on the above steps, target product B is obtained, and target product B is named Ni / Co10-1.

[0008] The present invention is further configured such that: in step S1, 3 mmol of lithium hydroxide and 3 mmol of 2-mercaptobenzoic acid (mba) are weighed, and 10 mL of anhydrous ethanol is added.

[0009] The present invention is further configured such that: in step S1, the reaction vessel is placed on a magnetic stirrer and stirred at a constant temperature for 30 minutes until lithium hydroxide and organic ligands are completely dissolved.

[0010] The present invention is further configured as follows: In step S2, the metal salt nickel sulfate hexahydrate used for coordination and deionized water are placed in a beaker, and ultrasonic cleaning is used to accelerate the dissolution of the material to obtain solution B. After dissolution, the solution is added to the reaction vessel of step S1 and stirred at a constant temperature for 30 minutes to obtain solution C.

[0011] The present invention is further configured such that: in step S2, 1.5 mmol of nickel sulfate hexahydrate is weighed and 5 mL of deionized water is taken.

[0012] The present invention is further configured such that: in step S3, the reaction vessel containing solution C is fitted with a metal outer shell and placed in an electric heating blower dryer at 120°C for 96 hours.

[0013] The present invention is further configured such that, in step S3, the cooling, scraping, rinsing, and drying specifically include: After the reactor has cooled to room temperature, retain about 1 / 5 of the liquid volume in the reaction system and transfer it to a beaker lined with filter paper for filtration. Then, scrape off the solid primary product A adhering to the inner wall of the reactor with a spoon, wash off the scraped product with anhydrous ethanol, and combine the washing liquid onto the filter paper for filtration. The washing process includes rinsing with deionized water and anhydrous ethanol alternately 3-5 times, discarding the filtrate, and then placing the washed solid primary product A in an electric heating blower dryer and drying it at 60°C for 12 hours.

[0014] The present invention is further configured as follows: In step S4, 50 mg of solid initial product A and 5 mg of CoCl2·6H2O are weighed; 5 ml each of deionized water, N,N-dimethylformamide (DMF) and methanol are stirred for 1 h until completely dissolved, and the reaction vessel is covered with a metal shell and placed in a 120°C electric heating blower dryer for 24 h.

[0015] The present invention further provides a supercapacitor electrode material, wherein a slurry of the electrode material is coated onto a current collector and dried to obtain the supercapacitor electrode material; the slurry of the electrode material includes, as described above, a nickel-cobalt bimetallic functional complex, a conductive agent, and a binder.

[0016] The adhesive can be made from commonly used adhesive materials for battery electrodes, such as polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, N-methyl-2-pyrrolidone, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, pump rubber, fluororubber and various copolymers. In one embodiment of the present invention, polytetrafluoroethylene is used as the adhesive.

[0017] The current collector is a material that is conductive but does not cause chemical changes in the battery, such as stainless steel, aluminum, nickel, copper, titanium, calcined carbon, nickel foam, etc. In one embodiment of the present invention, nickel foam is used as the current collector.

[0018] The present invention further provides a supercapacitor, comprising, as at least one component of the above-mentioned nickel-cobalt bimetallic functional complex as a supercapacitor electrode material.

[0019] The beneficial effects of this invention are as follows: This invention provides a method for preparing nickel-cobalt bimetallic functional complexes for superelectric devices using a secondary hydrothermal method. Using nickel MOF precursor and cobalt chloride hexahydrate as secondary doped metal salt as raw materials, a hydrothermal reaction is carried out in a closed system to generate functional complexes with bimetallic nodes. This method improves the problems of poor conductivity, low specific capacity, and poor cycle stability of single metal MOFs, and also improves the shortcomings of uneven metal ion doping and low stability of the preparation process in the primary hydrothermal preparation. Attached Figure Description

[0020] Figure 1 This is a comparison of powder X-ray diffraction patterns of the Ni / Co10-1 functional complex and its precursor prepared in Example 1 of this invention.

[0021] Figure 2 The image shows a comparison of X-ray diffraction (XRD) and single-crystal XRD patterns of the Ni / Co10-1 functional complex powder prepared in Example 1 of this invention.

[0022] Figure 3 This is a schematic diagram of the hexanuclear coordination unit of the Ni / Co10-1 functional complex prepared in Example 1 of the present invention.

[0023] Figure 4 This is an analytical diagram of the coordination unit single crystal of the Ni / Co10-1 functional complex prepared in Example 1 of the present invention.

[0024] Figure 5 This is a schematic diagram of the columnar structure of the Ni-functional complex multilayer columnar three-dimensional structure prepared in Example 1 of the present invention.

[0025] Figure 6 The thermogravimetric curve of the Ni / Co10-1 functional complex prepared in Example 1 of this invention is shown.

[0026] Figure 7 This is an X-ray photoelectron spectroscopy (XPS) analysis diagram of the Ni / Co10-1 functional complex prepared in Example 1 of this invention.

[0027] Figure 8The image shows a scanning electron microscope image of the Ni / Co10-1 functional complex prepared in Example 1 of this invention. In the image, (a), (b) and (c) represent the view scales of 100 μm, 20 μm and 5 μm, respectively.

[0028] Figure 9 The image shows the semi-quantitative elemental analysis spectrum (including total surface spectrum and elemental content table) of the Ni / Co10-1 functional complex prepared in Example 1 of this invention.

[0029] Figure 10 The image shows the cyclic voltammetry curves of the Ni / Co10-1 functional complex prepared in Example 2 of this invention at different scan rates in a three-electrode system.

[0030] Figure 11 The graph shows the constant current charge-discharge curve of the Ni / Co10-1 functional complex prepared in Example 2 of this invention in a three-electrode system.

[0031] Figure 12 The specific capacitance curve of the Ni / Co10-1 functional complex prepared in Example 2 of this invention in a three-electrode system is shown.

[0032] Figure 13 The image shows the cyclic voltammetry curves of the coin cell prepared in Example 3 of this invention at different scan rates.

[0033] Figure 14 The graph shows the constant current charge-discharge curves of the coin cell prepared in Example 3 of the present invention under different current densities.

[0034] Figure 15 This is a specific capacitance curve of the coin cell prepared in Example 3 of the present invention.

[0035] Figure 16 This is a graph showing the energy density-power density of the coin cell prepared in Example 3 of the present invention.

[0036] Figure 17 This is a cycle performance curve of the coin cell prepared in Example 3 of the present invention.

[0037] Figure 18 This is an AC impedance curve of the coin cell prepared in Example 3 of the present invention. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to the accompanying drawings.

[0039] Example 1: Preparation of Ni / Co10-1 electrode material for supercapacitors 1. Weigh 0.07185 g (3 mmol) of lithium hydroxide and 0.4626 g (3 mmol) of 2-mercaptobenzoic acid (mba) and place them in a reaction vessel. Then, measure 10 mL of anhydrous ethanol and pour it in. Place the reaction vessel containing the mixture on a magnetic stirrer and stir at a constant temperature for 30 min until the lithium hydroxide and organic ligands are completely dissolved to obtain solution A. 2. Weigh 0.3942 g (1.5 mmol) of nickel sulfate hexahydrate, a metal salt used for coordination, and place it in a beaker. Then, add 5 mL of deionized water and use an ultrasonic cleaner to accelerate the dissolution of the material by ultrasonic treatment for 7 min to obtain solution B. After dissolution, add the solution to the reaction vessel of step ① and stir at a constant temperature for 30 min to obtain solution C. 3. Place the reactor containing solution C in a 120°C electric heating blower dryer with the reactor metal shell attached and react for 96 hours; 4. After the reaction is complete, allow the reactor to cool naturally to room temperature. Retain about 1 / 5 of the liquid volume in the reaction system and transfer it to a beaker lined with filter paper for filtration. Then, scrape off the solid initial product A adhering to the inner wall of the reactor with a spoon, wash off the scraped product with anhydrous ethanol, and combine the washing liquid onto the filter paper for filtration. 5. The obtained solid primary product A is washed with deionized water and anhydrous ethanol alternately 3-5 times (each alternation includes one wash with deionized water and one wash with anhydrous ethanol), the filtrate is discarded, and then the washed solid primary product A is placed in an electric heating blast dryer and dried at 60°C for 12 hours. 6. Weigh 50 mg of solid primary product A and 5 mg of CoCl2·6H2O according to the mass ratio of solid primary product A: CoCl2·6H2O = 10:1 and transfer them to the reaction vessel. Add 5 ml each of deionized water, N,N-dimethylformamide (DMF) and methanol to the reaction vessel in a solvent volume ratio of 1:1:1. Stir for 1 h until completely dissolved. Cover the reaction vessel with a metal shell and place it in a 120°C electric heating blower dryer for 24 h. The target product B was obtained by referring to the above, and the target product B was named Ni / Co10-1.

[0040] Experimental Example 1: Crystal Structure Analysis X-ray diffraction phase analysis was performed on the Ni / Co10-1 functional complex electrode material synthesized in Example 1 using an X-ray diffractometer, such as... Figure 1 As shown. XRD pattern ( Figure 1 The peaks in (above) are compared with the precursor nickel MOF single crystal data ( Figure 1 The peaks simulated below are consistent. Figure 1 and Figure 2It can also be seen that the single crystal diffraction curve has sharp peaks and the peak positions match the core peaks of the powder diffraction. No other peaks were observed, indicating that the synthesized sample is a pure phase and only the peak intensity has changed. This indicates that cobalt chloride hexahydrate has been incorporated into the nickel MOF without destroying the crystal structure, and it has good crystallinity and structural integrity.

[0041] like Figure 3 As shown, the hexanuclear nickel cluster of this complex consists of Ni1A, Ni2A, Ni1B, Ni2B, Ni1C, and Ni2C. Ni1A and Ni2A, Ni1B and Ni2B, Ni1C and Ni2C are each bridged together by two divalent ortho-mercaptobenzoic acid anions, while Ni1A, Ni1B, and Ni1C are bridged together by two sulfide ions to form a triangular structure.

[0042] like Figure 4 As shown, the complex consists of a hexanuclear nickel cluster (left side), a bridged nickel ion (Ni3), a bridged nickel-cobalt co-occupying ion (Ni4 / Co1, where nickel occupies half and cobalt half), and a bridged lithium ion (Li1) (right side). The bridged nickel ion and the bridged nickel-cobalt co-occupying ion are bridged together by oxygen atoms of three hydroxyl groups (O7A, O7B, O7C). The lithium ion (Li1) and Ni3 are bridged together by a divalent ortho-mercaptobenzoic acid anion bridging Ni1B and Ni2B. Similarly, another divalent ortho-mercaptobenzoic acid anion bridging Ni1B and Ni2B bridges Ni4 / Co1 with the lithium ion (Li1A) in the layer below, forming a complex as shown in the diagram. Figure 5 The columnar structure shown is a three-dimensional columnar structure with multiple layers.

[0043] Experimental Example 2: Thermal Stability Analysis (TGA) The thermal stability of the synthesized Ni / Co10-1 functional complex electrode material was analyzed using thermogravimetric analysis (TGA). Figure 6 As can be seen, the mass loss of the complex is approximately 4.36% when the temperature is between 25℃ and 300℃, mainly due to the release of free water molecules from the complex. There are two main decomposition stages between 300℃ and 500℃. In the first stage, as the temperature rises from 300℃ to 360℃, the rapid decrease in sample weight (approximately 39.31%) indicates the decomposition of the organic ligands and the rapid collapse of the structure. In the second stage, between 360℃ and 500℃, Ni and Mn are oxidized. Due to the carbonization of the organic ligands, the structure collapses into the main phases of NiO and MnO, along with some residues (such as C and S). When the temperature exceeds 500℃, the mass decrease of the sample slows down, due to the release of gases formed from the oxidation of residues such as C and S after ligand carbonization.

[0044] Experimental Example 3: X-ray photoelectron spectroscopy (XPS) To further investigate the chemical elemental composition and valence state of the electrode material, the Ni / Co10-1 functional complex synthesized in Example 1 was characterized by X-ray photoelectron spectroscopy. Figure 7 As shown, the peaks for C 1s, O 1s, S 2p, Ni 2p, and Co 2p can be clearly observed. In the C 1s fine spectrum, the fitted peaks at 284.7 eV, 285.7 eV, 286.4 eV, and 288.5 eV indicate the presence of CC / C=C, CS, CO, and C=O peaks in the material structure, consistent with the single-crystal structure analysis. In the O 1s fine spectrum, fitted peaks at 531.4 eV, 532.3 eV, and 529.2 eV are attributed to O=C, OC, and OM bonds, respectively (where M represents metal). In the S 2p fine spectrum, the peaks at 161.57 eV and 162.81 eV are attributed to the S 2p3 / 2 and S 2p1 / 2 of the Ni-S bond, further indicating that the alkaline solution successfully removed the H from the SH group on the ligand, and that the nickel ion underwent a coordination reaction with thiosalicylic acid, consistent with the crystal structure analysis. The peaks at 163.9 eV and 168.7 eV belong to the SC and SO bonds, respectively. The SO bond may be due to the residue of the raw material NiSO4•6H2O on the material surface; in the fine spectrum of Ni 2p, the two main peaks are Ni 2p3 / 2 and Ni 2p1 / 2 doublets at 856 eV and 873.62 eV respectively, and the corresponding spin-orbit splitting energy is 17.62 eV, which can be attributed to the signal of Ni2+, indicating that Ni exists in the crystal structure in the form of Ni2+. The peaks at bond energies of 861.66 eV and 879.96 eV correspond to two satellite peaks, respectively. In the Co 2p fine spectrum, the peaks at 796.8 eV and 781.8 eV represent Co2+ ions, 790.5 eV and 776 eV represent Co3+ ions, and there are two satellite peaks at 785.8 eV and 802.5 eV. Due to the low lithium content, no Li 1s fine spectrum fitting peaks were obtained, and the Ni / Co10-1 functional complex does not contain Cl. Further semi-quantitative EDS analysis confirmed that the Ni / Co10-1 functional complex does not contain an effective amount of chlorine. In summary, the above results indicate that the Ni / Co10-1 functional complex was successfully prepared.

[0045] Experimental Example 4: Scanning Electron Microscopy (SEM) Analysis To investigate the microstructure of the Ni / Co10-1 functional complex, it was characterized by scanning electron microscopy (SEM). The results are as follows: Figure 8 As shown in (a)~(c).

[0046] As shown in the figure, the material particles are uniformly distributed with no obvious agglomeration. The particles exhibit a regular columnar structure with a relatively uniform size distribution and smooth, flat surfaces free of obvious cracks, pores, or structural defects. This uniform and well-dispersed morphological characteristic not only indicates good crystallinity during the preparation process but also increases the effective specific surface area, exposing more active sites for electrochemical reactions. This facilitates sufficient wetting of the electrolyte and provides a structural prerequisite for the effective electrochemical performance.

[0047] Experimental Example 5: Semi-quantitative Elemental Analysis (EDS) The semi-quantitative EDS analysis results of the Ni / Co10-1 functional complex are as follows: Figure 9 As shown, the spectrum clearly reflects the elemental composition and distribution characteristics of the material. The characteristic peaks of the Ni and Co bimetallic elements are clearly defined in the spectrum, confirming the successful introduction of Co into the material system. The elemental content table shows that Ni has a weight percentage of 11.26 wt% and an atomic percentage of 2.76 at%, while Co has a weight percentage of 0.75 wt% and an atomic percentage of 0.18 at%. The reasonable ratio of bimetallic elements provides a structural basis for the material's electrochemical performance. In addition, C 66.82 wt% (79.92 at%), O 17.02 wt% (15.28 at%), S 4.13 wt% (1.85 at%), and trace amounts of Cl 0.01 wt% (0.00 at%) were also detected in the material. The extremely low Cl content is attributed to background interference, indicating that the material does not actually contain any effective amount of chlorine. The composition and content of other elements are consistent with the material's design expectations, providing a reliable elemental composition basis for subsequent performance analysis.

[0048] Example 2: Electrode fabrication for a three-electrode system of a supercapacitor ① The Ni / Co10-1 functional complex prepared in Example 1 was used as the electrode material. It was added to a mortar with acetylene black and PTFE (polytetrafluoroethylene) in a mass ratio of 8:1:1 and ground until it was completely mixed and formed into a paste to obtain the electrode active material. ② The ground electrode active material is evenly coated onto a square nickel foam with a side length of 1 cm and an area of ​​1 cm2. Then it is dried at 60 ℃ for more than 1 h. Next, it is pressed into tablets for 5 seconds with a pressure of 10 t on a powder tablet press and weighed. The mass of the loaded electrode active material is about 2.5 mg. ③Immerse the electrode sheet obtained in ② in 6M KOH electrolyte for more than 6 hours to obtain the electrode sheet to be tested in the three-electrode system.

[0049] Experimental Example 6: Cyclic Voltammetry (CV) Analysis Using an electrochemical workstation CHI760E, the electrode sheet to be tested prepared in Example 2 was subjected to... Tests were conducted at sweep rates of 5 mV / s, 10 mV / s, 20 mV / s, 30 mV / s, and 50 mV / s, and the results are as follows: Figure 10 The figure shows the cyclic voltammetry curve with pseudocapacitive redox peaks, indicating that the redox reaction on the surface of the electrode material is reversible. As the scan rate increases, the redox peaks gradually polarize and shift, suggesting that the Faraday reaction may be controlled by the ion diffusion process.

[0050] Experimental Example 7: Constant Current Charge-Discharge Test Analysis (GCD) Figure 11 The graphs show the galvanostatic charge-discharge curves of the three-electrode system at different current densities. The longest discharge time is observed at a current density of 1 A / g, indicating the highest capacitor performance. As the current density increases, the discharge time gradually decreases, which may be due to insufficient ideal redox activity at high current densities.

[0051] Experimental Example 8: Specific Capacitance Analysis The specific capacitance of the electrode material can be calculated from the constant current charge-discharge curve using the following formula 1: Figure 12 As shown.

[0052] Formula 1 Cm (unit: F / g) is the specific capacitance of the material, and im (unit: A / g) is the charging and discharging current density. The area of ​​the integral current, (Unit: V) represents the charge / discharge voltage window (Vf is the upper limit of voltage, Vi is the lower limit of voltage).

[0053] Depend on Figure 11 It can be clearly seen that when the current density is 1, 2, 3, 5, 8, 10, 15 and 20 A / g, the specific capacitance is 1428.8, 1351.8, 1299.3, 1235.4, 1156, 1105.9, 998.1 and 904 F / g respectively, and the capacitance retention rate is 63.3%.

[0054] Example 3: Preparation of button cell batteries ① The Ni / Co10-1 functional complex prepared in Example 1 was used as the electrode material. It was added to a mortar with acetylene black and PTFE (polytetrafluoroethylene) in a mass ratio of 8:1:1 and ground until it was completely mixed and formed into a paste to obtain the negative electrode active material. ②Activated carbon powder is used as an electrode material. It is added to a mortar with acetylene black and PTFE (polytetrafluoroethylene) in a mass ratio of 8:1:1. The mixture is ground until it is completely mixed and forms a paste, thus obtaining the positive electrode active material. ③ The ground positive and negative electrode active materials were uniformly coated onto 12mm diameter circular nickel foam, then dried at 60℃ for more than 1 hour, and then pressed into tablets for 5 seconds using a powder tablet press with a pressure of 10t and weighed. The final electrode material loading was about 2.5 mg and the coating area was 1.13 cm2. ④ Using glass fiber as the separator and 6M KOH as the electrolyte, the battery case kit model is CR2032. The positive and negative electrode sheets are assembled into a supercapacitor coin cell at room temperature. After assembly, the battery is held at 7.58 MPa pressure for 10 seconds in a coin cell packaging machine. After packaging, it is tested after standing at room temperature for 1 hour.

[0055] Experimental Example 9: Cyclic Volt-Ampere Analysis of Button Cells Figure 13 The figure shows the CV curves of the Ni / Co10-1 / / AC device at different scan rates within a voltage window of 0-1.6V. The low-voltage region of the CV curve is provided by the double-layer capacitance, and the high-voltage region is provided by the pseudocapacitance. As the scan rate continues to increase, the area enclosed by the CV curve continues to increase, and the overall shape of the curve remains good without significant change. This indicates that the Ni / Co10-1 / / AC asymmetric supercapacitor has good electron transfer capability, charge-discharge performance, and reversibility.

[0056] Experimental Example 10: Constant Current Charge-Discharge Analysis of Button Cells The constant current charge-discharge performance of asymmetric supercapacitors is an important basis for evaluating the electrode materials in practical applications. Figure 14 The GCD curves of the Ni / Co10-1 / / AC device at different current densities show that the charge-discharge curves at different current densities exhibit a basically symmetrical shape and have obvious charge-discharge plateaus, indicating that the Ni / Co10-1 / / AC device has battery-type capacitor characteristics. With the increase of current density, the shape does not change significantly, leading to the same conclusion as the CV curve test results: the assembled Ni / Co10-1 / / AC device has good reversibility and charge transfer capability.

[0057] Experimental Example 11: Specific Capacitance Analysis of Button Cells The specific capacitance of the electrode material can be calculated using Equation 1 from the constant current charge-discharge curve of the Ni / Co10-1 / / AC device. Figure 15The specific capacitance of the Ni / Co10-1 / / AC device was calculated at different current densities. At current densities of 0.5, 1, 2, 3, 5, 8, 10, 15, and 20 A / g, the corresponding specific capacitances were 214.18, 159.5, 142.59, 132.69, 119.02, 103.57, 96.19, 79.97, and 66.63 F / g, respectively, with a specific capacitance retention of 31%, demonstrating good rate performance.

[0058] Experimental Example 12: Energy Density-Power Density Analysis of Button Cells The energy density of the Ni / Co10-1 / / AC device can be calculated from the specific capacitance of the device at different current densities using Formula 2. The power density can be calculated from the energy density and discharge duration using Formula 3. Combining the energy density and power density, the radii of the Ni / Co10-1 / / AC device can be obtained. Figure 15 As shown.

[0059] Formula 2 P= Formula 3 E (unit: Wh / kg) is the energy density of the material, Cm (unit: F / g) is the specific capacitance of the material, (Vf-Vi)2 (unit: V) is the charge / discharge voltage window (Vf is the upper limit of voltage, Vi is the lower limit of voltage), P (unit: W / kg) is the power density of the material, and Td (unit: s) is the discharge duration of the material.

[0060] Energy density and power density are two important indicators of supercapacitors. Figure 16 The energy density of the Ni / Co10-1 / / AC device at different power densities is shown. At a power density of 255.02 W / kg, the energy density reaches 76.15 Wh / kg. Even at a high power density of 14454.3 W / kg, it still has an energy density of 23.69 Wh / kg, demonstrating the excellent volumetric properties of Ni / Co10-1.

[0061] Experimental Example 13: Cycle Performance Analysis of Button Cells Figure 17 This is the cycle life curve of the Ni / Co10-1 / / AC device at 5 A / g. After 10,000 charge-discharge cycles, the capacitance retention rate of the ASC device can still reach 75%, showing that it has good cycle stability, which is very important for practical applications.

[0062] Experimental Example 14: AC Impedance Analysis of Button Cells Using an electrochemical workstation, the material was first activated for half an hour using a constant current charge-discharge testing method. After the electrochemical system stabilized, the AC impedance of the Ni / Co10⁻¹ / / AC device was measured at an open-circuit voltage within a frequency range of 10⁻² Hz to 10⁵ Hz. The results are as follows. Figure 18 As shown in the figure, the AC impedance curve of this electrode material can be divided into two parts: a high-frequency region and a low-frequency region. By fitting the impedance spectrum, the equivalent series impedance of this Ni / Co10-1 / / AC device is 0.9815 Ω, and the charge transfer impedance is 0.86834 Ω.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the design concept of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing nickel-cobalt bimetallic functional complexes via a secondary hydrothermal method, characterized in that: Includes the following steps: S1. Lithium hydroxide and 2-mercaptobenzoic acid are placed in a reaction vessel at a molar mass ratio of 1:1, and anhydrous ethanol is added to dissolve them to obtain solution A; S2. Dissolve the metal salt nickel sulfate hexahydrate in deionized water to obtain solution B, and then mix solution B with solution A to obtain solution C; wherein, the molar mass ratio of the metal salt nickel sulfate hexahydrate to 2-mercaptobenzoic acid in step S1 is 1:

2. S3. The reaction vessel containing solution C is fitted with a metal outer shell and placed in an electrically heated blower dryer for reaction. After the reaction is completed, the product is cooled, scraped, rinsed and dried to obtain solid primary product A. S4. Add the initial solid product A:CoCl2·6H2O into the reaction vessel at a mass ratio of 10:1, and add deionized water, N,N-dimethylformamide and methanol in a volume ratio of 1:1:1 as reaction solvents. After stirring and dissolving, put the reaction vessel into an electric heating blower dryer with a metal outer shell on top. S5. Based on the above steps, target product B is obtained, and target product B is named Ni / Co10-1.

2. The method for preparing nickel-cobalt bimetallic functional complexes by secondary hydrothermal method according to claim 1, characterized in that: In step S1, 3 mmol of lithium hydroxide and 3 mmol of 2-mercaptobenzoic acid (mba) are weighed, and 10 mL of anhydrous ethanol is added.

3. The method for preparing nickel-cobalt bimetallic functional complexes by secondary hydrothermal method according to claim 1 or 2, characterized in that: In step S1, the reaction vessel is placed on a magnetic stirrer and stirred at a constant temperature for 30 minutes until lithium hydroxide and organic ligands are completely dissolved.

4. The method for preparing nickel-cobalt bimetallic functional complexes by secondary hydrothermal method according to claim 1, characterized in that: In step S2, nickel sulfate hexahydrate, a metal salt used for coordination, and deionized water are placed in a beaker. An ultrasonic cleaner is used to assist in the ultrasonic treatment to accelerate the dissolution of the material and obtain solution B. After dissolution, the solution is added to the reaction vessel of step S1 and stirred at a constant temperature for 30 minutes to obtain solution C.

5. The method for preparing nickel-cobalt bimetallic functional complexes by secondary hydrothermal method according to claim 2, characterized in that: In step S2, 1.5 mmol of nickel sulfate hexahydrate and 5 mL of deionized water are weighed.

6. The method for preparing nickel-cobalt bimetallic functional complexes by secondary hydrothermal method according to claim 1, characterized in that: In step S3, the reaction vessel containing solution C is covered with a metal outer shell and placed in an electric heating blower dryer at 120°C for 96 hours.

7. The method for preparing nickel-cobalt bimetallic functional complexes by secondary hydrothermal method according to claim 1, characterized in that: In step S3, the cooling, scraping, rinsing, and drying specifically include: After the reactor has cooled to room temperature, retain about 1 / 5 of the liquid volume in the reaction system and transfer it to a beaker lined with filter paper for filtration. Then, scrape off the solid primary product A adhering to the inner wall of the reactor with a spoon, wash off the scraped product with anhydrous ethanol, and combine the washing liquid onto the filter paper for filtration. The washing process includes rinsing with deionized water and anhydrous ethanol alternately 3-5 times, discarding the filtrate, and then placing the washed solid primary product A in an electric heating blower dryer and drying it at 60°C for 12 hours.

8. The method for preparing nickel-cobalt bimetallic functional complexes by secondary hydrothermal method according to claim 1, characterized in that: In step S4, 50 mg of solid initial product A and 5 mg of CoCl2·6H2O are weighed; 5 ml each of deionized water, N,N-dimethylformamide (DMF) and methanol are added and stirred for 1 hour until completely dissolved. The reaction vessel is then covered with a metal outer shell and placed in a 120°C electric heating blower dryer for 24 hours.

9. A supercapacitor electrode material, characterized in that: The electrode material slurry is coated onto the current collector and dried to obtain the supercapacitor electrode material; the electrode material slurry includes the nickel-cobalt bimetallic functional complex, conductive agent, and binder as described in any one of claims 1-8.

10. A supercapacitor, characterized in that: The supercapacitor electrode material includes at least one component of the nickel-cobalt bimetallic functional complex as described in any one of claims 1-8.

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