Preparation And Study On Electrochemical Properties Of Nickel And Cobalt Transition Metal Compounds

Supercapacitors as a sort of energy storage system are the most promising reserve force compared to Li ion battery and NI-MH batteries on the basis of their high power density,short charging-discharging time and long lifespan.The properties of supercapacitors usually depend on electrode materials.Therefore,many researchers try hard to exploit new electrode material which possess the optimal electrochemical performance.In this paper,we prepared 3D hierarchical structures Ni_xCo_9-xS₈,different morphologies NiCo₂S₄ and amorphous nickel-cobalt-borons electrode material which possess the optimal electrochemical performance.The morphology and the structure of the samples were characterized by TEM,XRD,SEM,FTIR,XPS.The electrochemical properties of materials were evaluated by using a standard three-electrode and two-electrode system in a 6.0 M KOH aqueous solution.The details and results are summarized as follows:1.A novel 3D flowerlike NixCo9-x S8 nanosheets with polyvinyl pyrrolidone as morphology agent have been synthesized via one-step solvothermal synthesis procedure.This 3D NixCo9-x S8 nanosheets achieve high specific surface area and outstanding electrochemical performance.When as for electrode materials,it demonstrates excellent specific capacitance of 1319.76 F/g at 1 A/g,and wonderful rate performance of 1040.4F/g at 20 A/g.Also,it achieves remarkable cycling stability that still retains 90% of max capacity after 1500 cycles.An asymmetric supercapacitor was assembled with Ni_xCo_9-xS₈ as a positive electrode and activated carbon?AC?as a negative electrode,it emerges high energy density 43.80 Wh/kg.2.In order to explore the affect of different morphology to NiCo₂S₄ electrode materials,we synthesized different morphology NiCo₂S₄ via one-step solvothermal synthesis procedure with ethylenediamine and water as mixed solvent and different sulfur source as morphology agent.Due to different microstructures of materials with different specific active sites,therefore,the materials of Ni Co₂S₄ 3D flower ball perform to the bestof the electrochemical performance.When as for electrode materials,it demonstrates excellent specific capacitance of 1363.68 F/g at 1 A/g,and wonderful rate performance of958.32 F/g at 20 A/g.3.Nickel-cobalt-borons are synthesized through facile and cost-effective reduction method.The effects of Ni/Co molar ratios and crystallinity on its supercapacitive performance are systematically investigated.It was found that nickel-cobalt-borons with the Ni/Co ratio being 2:1 and amorphous structure manifest the optimum specific capacitance of 2226.96 F/g at a current density of 1 A /g and still remain 1879.2 F/g at a high discharge current density of 20 A/g.An asymmetric supercapacitor device has been fabricated with nickel-cobalt-borons as the positive electrode and commercial activated carbon as the negative electrode material.The device delivers an ultrahigh energy density of 66.40 Wh/kg.This device remains at 85.76% of its initial capacitance even after 5000charge-discharge cycles.