The Preparation Of Transition Metal Chalcogenides And The Research Of Its Aqueous Electrochemical Energy Storage System

With the deterioration of environmental pollution and the energy crisis,the concept of ecological environment and green development has become more and more popular.Renewable energy sources such as wind,tidal,solar and geothermal energy cannot meet the huge energy demands due to the geographical factors and technological constraints.Therefore,it is of particularly significance to design and manufacture electrochemical energy storage systems with high energy and power density,long cycle life as well.Among which,the aqueous battery-supercapacitor hybrid?BSH?system has received extensive attention and in-depth research for its wide application potential.The BSH energy storage system,depending on batteries and supercapacitors combines the battery-type electrode with high energy performance and capacitive electrode with high-rate capability,then inheriting merits of both.Taken the high electrochemical properties into account,BSH systems exhibit huge application potential in electric vehicles,smart grids,and small electronic/optoelectronic devices.In addition,aqueous electrolyte avoids the drawbacks of being toxic and flammable compared with organic electrolyte,so it is much more safety.What's more,the aqueous BSH system exhibits lots of advantages due to the appropriate structural design,such as high efficiency,low cost,safety and environmental friendly.The electrode is the core of BSH,and the preparation of electrode materials plays a decisive role in the construction of efficient BSH.Transition metal chalcogenides?TMCs?with unique"sandwich"structure,good electrical conductivity,highly theoretical capacity are widely used in energy storage systems.In this paper,several TMC nanomaterials are synthesized and applied to aqueous hybrid energy storage,the main contents are as follows:?1?Due to the characters of non-toxic,low-cost,good stability and high theoretical capacity,zinc sulfide?ZnS?has been considered as the alternative electrode material.N-doped porous carbon nanosheets coated ZnS nanoparticle?ZnS/NMC?composites were prepared by a simple co-pyrolysis process originated from metal-organic frameworks?MOFs?.In the composite interface,ZnS nanoparticles are directly in contact with carbon or hierarchical pore structures,which provides fast electron and ion double-transfer pathway that facilitates rapid electrode reactions.In addition,heteroatom N-doping and carbon-coated ZnS nanoparticles can offer more active sites and stabilize electrode reaction during charge and discharge process.At a current density of 1 A g^-1,the specific capacitance of ZnS/NMC is 160 mAh g^-1.After 1000 cycles at 5 A g^-1,92.9%of the initial capacity can be remained.Besides,when the activated carbon?AC?acted as the anode material,the constructed ZnS/NMC//AC aqueous hybrid system exhibited an energy density up to 45.5 Wh Kg^-1.?2?A nanorod-like Co₉Se₈/CdSe?Co-Cd-Se?composite flexible electrode material was synthesized by the assistance of nickel foamed as both substrate current collector.The nanorod structure can increase the contact area between electrode material and electrolyte effectively,therefore increasing the utilization of active material.Simultanously,it can promote rapid electron transfer.The unique three-dimensional structure and flexible properties of nickel foamed can maintain the stable structure and improve the cycling stability.By matching with carbon-coated iron nanoparticle?Fe-C?composites,the Co-Cd-Se//Fe-C hybrid energy storage system exhibited a high energy density of 57.6 Wh Kg^-1 at a power density of 10.9 kW kg^-1.?3?The 1-T phase VSe₂ and rGO composites?1T-VSe₂/rGO?were synthesized through hydrothermal method by using graphene?rGO?as framework.And the composite is used in aqueous BSH energy storage systems.At a current density of 1 A g^-1,1T-VSe₂/rGO stateded a specific capacitance of 156.8 mAh g^-1.When combined with carbon-coated ferroferric oxide?Fe₃O₄-C?nanoparticles anode,the assembled1T-VSe₂/rGO//Fe₃O₄-C hybrid system showed an energy density of 65.6 Wh Kg^-1 at the power density of 1.3 kW Kg^-1.