Synthesis And Electrochemical Performance Of Ni-Co Double Metal Sulfides And Carbon-coated CdO

With higher consumption rates of fossil fuels,increasing environmental pollutions and energy issues become more and more important.Especially,in recent years,the emergence of extreme weather haze had a great influence on human health and life.It is of significance to develop new energy resources,for example,solar,wind and wave,the development of high energy storage system is the precondition of these new energy be widely used.Supercapacitors and Li-ion batteries have attracted much attention as promising electrochemical devices.Supercapacitors have prominent properties such as high specific power with short charging time,but their cycle life and energy density are poor.Lithium-ion batteries?LIBs?have been receiving tremendous attention for potential applications in electric vehicles and portable electronics,owing to their high working voltage,good environmental friendliness,long cycle life.However,it is still a great challenge to develop excellent electrochemical stability LIBs,especially when used at large current rates.As well known,the electrode material plays an important role in an energy storage device.Therefore,the search for new electrode material and its synthesis method are the key to solve current problems.This article pays attention to the preparation of Ni-Co sulfides and carbon-coated CdO with their electrochemical performances in supercapacitors and LIBs,respectively.The contents of this paper are as following:1.The preparation of Ni-Co metal sulfide and its electrochemical performance as electrode material of supercapacitorsIn this chaper,we present facile syntheses of hollow Ni-Co sulfide nanoboxes by using a low-temperature wet-chemical method.The as-prepared materials have an interesting structure with consistent morphology and uniform dispersion.The nanoparticles are very uniform in size.The morphology of the Ni-Co sulfide are very stable,which should be attributed to the compact assembly of small particles on the surface.This synthesis method are simple,easy,operable,and can be completed at a lower temperature,saving time and cost,greatly.With different molar ratios of Ni/Co?1:2 or 2:1?,we have synthesised NiCo₂S₄ and Ni₂CoS₄,with tunable compositions.The resultant Ni-Co sulfides demonstrate high specific capacitances with enhanced cycling stability and rate capability.The NiCo₂S₄ electrode exhibits a capacitance of 1588 F g-1 at 2 A g-1 and a capacitance retention of 88.2%at 5 A g-1 after 4000 cycles.All the experimental results illustrate nanostructured Ni-Co sulfides to be promising electrode materials for high-performance supercapacitors.2.The preparation of carbon-coated CdO and its electrochemical performance as electrode material of LIBsIn this work,we have developed a facile hydrothermal-assisted method for the controllable synthesis of mesoporous carbon-coated CdO.At frist,we have synthesized CdCO₃ microcubes by the traditional drop reaction.Then,Porous carbon-coated CdO?C-coated CdO?microcubes are successfully synthesized by mixing CdCO₃ microcubes with polyvinylpyrrolidone?PVP?and followed by annealing treatment at 500?in the air.PVP are used as carbon source,as well as the protectant for nanoparticles.The C-coated CdO composite,used as an anode material for LIBs,exhibits a remarkably improved electrochemical performance compared with the pure CdO phase.Benefiting from the unique structure and the synergistic effect of different components in the hybrid architectures,the C-coated CdO electrode material in Li-ion batteries displays a superior reversible capacity of 487.2 mA h g-1 after a 800 cycles at a current density of 200 mA g-1.As compared to the pure CdO phase,the C-coated CdO hybrid material shows enhancement in specific capacity and long-term cyclic stability?800 cycles?.Furthermore,the C-coated CdO composite also shows excellent high-current-density performance,which exhibits reversible capacities of 401.85 and 171.83 mAh g-1 during the 20 th cycle at current densities of 200 and 800 mA g-1,respectively.