Preparation And Application Of Hollow Graphene Microspheres For Li-S Batteries

Li-S battery is recognized as a promising secondary energy storage battery due to its high theoretical energy density(2600Wh kg-1).However,the inherent problems of poor conductivity,shuttle effect,volume effect,high electrolyte/sulfur ratio and low sulfur loading limit the practical application of Li-S battery.In this paper,the experimental contents of the following three parts were designed for the inherent problems of Li-S battery.(1)Using pure sulfur as the main material of cathode electrode.Hollow graphene spheres separator coating was introduced.Hollow graphene spheres separator coating has obvious adsorption and blocking effect on polysulfide,which can effectively fix polysulfide on the cathode side,prevent polysulfide from shuttling to the anode electrode and react with lithium metal leading to shuttle effect.The discharge capacity of Li-S battery with hollow graphene spheres coated separator is 829.6mAh g"1 after 200 cycles at 0.2C,and the capacity retention rate is 70.76%.The reduction of the shuttle effect can improve the coulombic efficiency and cyclic stability of Li-S battery which can improve the electrochemical performance of Li-S battery.(2)Multifunctional hollow graphene/SnO2 composite spheres were used as sulfur hosts.The hollow spherical structure of the composite material can buffer the volume change of active material in the cathode of Li-S battery and alleviate the volume effect.The hollow structure provides space for the realization of high sulfur loading,and the graphene conductive framework can improve the conductivity of Li-S battery.At the same time,the composite material sulfur host have physical and chemical double adsorption effect on polysulfide,which can effectively fix polysulfide and prevent its dissolution and diffusion to the electrolyte,which can also alleviate the shuttle effect to a certain extent.The discharge capacity of Li-S battery with composite sulfur hosts is 753.61mAh g"1 after 100 cycles at 0.2C,which is 50.79%higher than that of pure sulfur as cathode electrode active material.(3)On the basis of multifunctional hollow graphene/SnO2 composite spheres sulfur hosts,hollow graphene spheres coated separator was also added.Synergistic effect of multifunctional hollow graphene/SnO2 composite spheres sulfur host and hollow graphene spheres separator coating can further inhibit the shuttle effect while improving the conductivity and alleviating the volume effect,thus further improving the electrochemical performance of Li-S batteries.The electrolyte has better wettability for the composite hollow spheres sulfur host and hollow graphene spheres separator coating,which can fix the electrolyte,thereby reducing the amount of electrolyte,which is conducive to improving the overall energy density of L-S battery.The discharge capacity of the Li-S battery with hollow graphene spheres coated separator and multifunctional graphene/SnO2 composite sulfur hosts is 853.97mAh g-1 after 200 cycles,and the initial discharge capacity is still 662.86mAh g-1 under the condition of 5 ?L mg-1 low electrolyte consumption,and the capacity is 73%of the electrolyte consumption of 10 ?L mg-1.