Study On The Preparation Of Nickel-Cobalt Bimetallic Hydroxide/Oxide Composites And Their Properties Of Supercapacitors

Due to its advantages of rapid charge and discharge,high power density,good cycle stability,safety and environmental protection,supercapacitors have the chance to become new energy storage devices in the future.Electrode materials are the key factor for the performance of supercapacitors.Layered double hydroxide（LDH）has good electrochemical properties because of its unique structure.Compared with the traditional chemical reaction,the electrodeposition technology has the characteristics of simple process,short periodicity and less restriction on the substrate.In this paper,Ni-Co LDH were prepared through two types of electrodeposition methods,and the effects of different carbon fiber substrates and cation ratios on morphology and electrochemical properties were explored.Ni-Co LDH were combined with bimetallic oxide nano-needles to design an excellent core-shell electrode material with comprehensive performance.1.Ni-Co LDH/CFP and Ni-Co LDH/CFC composites were successfully prepared by simple electrodeposition of Ni-Co LDH onto different carbon fiber substrates by constant voltage electrodeposition.The Ni-Co LDH composite material produced by using carbon cloth（CFC）as a substrate material has a pleated layered structure and a large specific surface area,so that it has good electrochemical performance.At a current density of 1 A?g^-1,the specific capacitance can reach 1387.5 F?g^-1.In addition,Ni-Co LDH/CFC is used as the positive electrode material and rGO/NF as the negative electrode material,and the assembled Ni-Co LDH/CFC//rGO/NF asymmetric supercapacitor exhibits good performance.When the current density is 1 A?g^-1,the energy density of ASC is 26.6 Wh?kg^-1 and the power density is 850.4 W?kg^-1.2.In order to enhance the comprehensive performance of Ni-Co LDH/CFC,Ni-Co LDH was prepared on carbon cloth by constant current electrodeposition.The effects of the micro-morphology and electrochemical properties of Ni-Co LDH in different Ni/Co ratios were discussed.It was found that when the ratio of Ni:Co=4:1,the formed Ni-Co LDH is composed of ultra-thin nanosheets similar to scales,which makes it have excellent electrochemical properties.It has a specific capacitance of 1540F?g^-1 at a current density of 1 A?g^-1,and the specific capacitance retention is 83.4%at a current density of 15 A?g^-1,indicating its excellent the rate of magnification.The specific capacitance remains 84.6%after 5000 times circles as well.This kind of material is uesd as the positive electrode and Fe₂O₃/rGO as the negative electrode to make an all-solid asymmetric supercapacitor.The energy density of it is 28.2 Wh?kg^-1at a current density of 1 A?g^-1,and the minimum power density is 850 W?kg^-1.3.Moreover,two different morphologies of NiCo₂O₄ nanomaterials were prepared on carbon cloth by hydrothermal-calcination method,and Ni-Co LDH electrode material were composited on acicular NiCo₂O₄ by constant current electrodeposition.Then the core-shell structure with NiCo₂O₄ as core and Ni-Co LDH as shell was successfully prepared.Such a structure would be more conducive to the synergy of bimetallic hydroxides and oxides so that it exhibits excellent electrochemical performance.The reaserches indicate that the NiCo₂O₄@Ni-Co LDH composite has a specific capacitance of 4901.8 mF?cm^-2 at a current density of 2 mA?cm^-2,and only13.3%of the specific capacitance lost after cycling 5000 times at a current density of20 mA?cm^-2.At the same time,using NiCo₂O₄@Ni-Co LDH/CFC as the positive electrode material and activated carbon（AC）as the negative electrode material,the all-solid flexible asymmetric supercapacitor NiCo₂O₄@Ni-Co LDH/CFC//AC/CFC shows its excellent performance.At a current density of 2 mA?cm^-2,the energy density is as high as 0.859 mWh?cm^-3 and the power density is 51.1 mW?cm^-3.