Preparation And Electrochemical Properties Of Metal Selenides And Their Composites

Developing new battery systems with superior energy/power density,long life and low cost has been very significance owing to growing demands for electric vehicle and large-scale energy storage devices.Lithium-ion battery has been commercialized successfully in the past few decades,but its limited theoretical specific capacity(～300mAh g^-1)can not meet the increasing demand for high energy density storage.Lithium-sulfur battery has attracted wide interest of researchers in recent years because of its extremely high theoretical capacity(1675 mAh g^-1).However,the insulation of sulfur and the shuttle effect of polysulfides lead to the rapid decay of lithium-sulfur battery capacity.In order to solve the above problems,from the point of view of the structure design and modification of lithium-ion battery anode materials and lithium-sulfur battery cathode materials,two kinds of molybdenum diselenide/molybdenum dioxide composites（MoSe₂@MoO₂ and MoSe₂/MoO₂）were synthesized by heat treatment and water steam etch,respectively,and their electrochemical properties were studied,which provides an important reference for the application of lithium-ion battery and lithium-sulfur battery.（1）A flower MoSe₂@MoO₂ composite for lithium ion battery with high performance was prepared by simple heat treatment.MoSe₂ can lead to the rapid migration of Li⁺due to its large layer spacing.Meanwhile,MoO₂ can protect the lamellar structure of MoSe₂ from being damaged during the charge/discharge process,so as to ensure the active area required for full contact with the electrolyte.In addition,the flower structure of MoSe₂@MoO₂composite can effectively alleviate the huge volume change during the charge/discharge process,thus showing excellent electrochemical performance.（2）The MoSe₂,MoSe₂/MoO₂ and MoO₃ were prepared by water steam etching and changing the etching time.The microstructure,specific surface area and electrochemical properties of the three materials were characterized and analyzed.Meanwhile,S/MoSe₂,MoSe₂/MoO₂ and MoO₃ were obtained by mixing the three materials with sulfur by hydrothermal method and investigated the effects of different cathode materials on electrochemical properties.The results show that the S/MoSe₂/MoO₂ composite can achieve high utilization rate of active materials when the etching time is 5 min,and the rate and long cycle performance of the composite are excellent.