Construction Of NiCo₂O₄-based Composite Nanostructures And The Research Of Their Capacitance Performances

With the rapid development of wearable and portable electronic products,the research and development of flexible energy storage materials have attracted the attention of the majority of scholars.Carbon materials have excellent electrical conductivity and high specific surface area,good corrosion resistance and low density,which have played an irreplaceable role in the development of supercapacitors.The transition metal oxides have great theoretical specific capacity,excellent reversibility,and high reliability.Therefore,some cheap metal oxides began to attract the attention of the majority of researchers,such as NiO,Co₃O₄ and NiCo₂O₄ etc.In particular,the spinel NiCo₂O₄ has the energy storage capacity of their individual monometallic oxides of both NiO and Co₃O₄,thereby it can be improves the electrochemical performance of supercapacitor to further extent due to their synergetic contribution.In this paper,sulfate and chlorate are used as the parent salt first,and NiCo₂O₄/CFC composites are prepared by hydrothermal method.Among them,The NiCo₂O₄/CFC composites obtained with chlorate as the parent salt,reaction temperature of 120°C and reaction time of 3 h have exhibited the best overall specific capacitance of 9.86 F/g.However,after calcination,the stability of the material deteriorates,In order to obtain a stable NiCo₂O₄/C,a carbon film substrate material is prepared using carbon nanotubes as a raw material,carbon fiber is used as a reinforcing material.A CNT/CF film?CC?was used as a substrate material to prepare a NiCo₂O₄/CC composite.When the reaction temperature is 120°C,NiCo₂O₄/CC composites prepared by hydrothermal method exhibited an overall specific capacitance of 13.60 F/g and good cycling stability,and the active material NiCo₂O₄ exhibited a specific capacitance of 128.96 F/g.The NiCo₂O₄/CC material prepared using the NaOH-treated carbon nanotubes exhibited a higher overall specific capacitance of 69.6 F/g,and the active material exhibited a specific capacitance of 249.69 F/g,however,the flexibility of the material deteriorates and the cycle stability decreases.This part uses carbon material as the substrate material and NiCo₂O₄ material combined to achieve a combination of electric double layer capacitance and tantalum capacitance,the material exhibits good flexibility and electrochemical performance,suitable for the preparation of flexible wearable electrochemical devices.In order to prepare NiCo₂O₄ Composites with good electrochemical performance,NiCo₂O₄ was prepared on the surface of foamed nickel?NF?by hydrothermal method with sulfate,chlorate and nitrate as the parent salt.NiCo₂O₄/NF composites were obtained with specific capacitance values of 438.8,331.4 and 1068.3 F/g.In order to obtain the best performance of NiCo₂O₄/NF,nitrate was used as the parent salt and ammonium fluoride was used as the dispersant.The NiCo₂O₄/NF composite material obtained by adding 3 mmol of ammonium fluoride have the best morphology and the best performance,its specific capacitance is 1636.36 F/g,and the material exhibits good cycle stability.At the same time,NiCo₂O₄/NF composites were prepared by electrodeposition,however,the NiCo₂O₄ material does not grow well on the surface of the foamed nickel and has poor electrochemical performance.NiCo₂O₄-based three-dimensional composite material were prepared on the surface of two-dimensional NiCo₂O₄/NF composite by chemical bath deposition,electrodeposition and hydrothermal methods,respectively.Among them,the NiCo₂DHs/NiCo₂O₄/NF Multi-level structural composite obtained by chemical bath deposition method,have exhibited the best electrochemical performance,and the specific capacitance value was 864.5 F/g.After calcination process,NiCo₂O₄/NiCo₂O₄/NF composites exhibited the best electrochemical performance and high specific capacitance value of 2068.52 F/g,and the specific capacitance retention ratio was 43.54%,after 5000 cycles at a current density of 8A/g.NiCo₂DHs/NiCo₂O₄/NF composites were prepared by electrodeposition at deposition times of300s,600s and 900s,respectively,showing good specific capacitances of 392.11,501.45 and510.76 F/g,respectively.NiCo₂DHs/NiCo₂O₄/NF composites showing good specific capacitances of 383.33,416.44 and 380.15 F/g.Using hydrothermal method,set the ion concentration ratios of n(Co²⁺+Ni²⁺):n?urea?were 3:20 and 3:40,respectively,the prepared NiCo₂DHs/NiCo₂O₄/NF and NiCo₂O₄/NiCo₂O₄/NF composites all exhibited good specific capacitances of 484.12,356.55 F/g and 1028.25,848.09 F/g,respectively.And the specific capacitance retention ratio was 55.84%and 54.17%after 4000 cycles at a current density of5 A/g.The NiCo₂O₄/NiCo₂O₄/NF was cycled 5000 times at a current density of 10 A/g,the specific capacitance retention rates were 73.04%and 74.06%,respectively.