Design And Performance Of New Cathode For Li-s Battery

Li-S battery has been considered as one of the most promising candidates for the next generation energy storage systems for its high theoretical capacity(1675mAh/g)and high theoretical specific energy(2600Wh/Kg),which is about 10 times as much as that of commercial lithium-ion batteries.Besides,sulfur is natural abundant,low cost and environmental friendly,which potentially make Li-S batteries more suitable for commercialization.However,the practical applications of Li-S batteries were significantly hampered by the low electronic/ionic conductivity of sulfur and the discharge products,large volume charge of sulfur during the lithiation/delithiation process,and the shuttling of dissolved lithium polysulfides(Li2Sx,4<x<8)in organic liquid electrolytes.These problems eventually lead to high polarization,serious capacity fading and poor rate stability.In this work,wo designed two new Li-S batteries in order to improve the electrochemical performance of the batteries.The first work is about a novel electrode consists of sulfur microspheres that are homogeneously confined within the conductive composite matrix of graphene and poly(3,4-ethylene-dioxythiophene)-poly(styrenesulfonate)(PEDOT-PSS).The characteristic large surface area and wrinkled surface of graphene sheets allow the formation of a conductive layer on the surface of sulfur to suppress the polysulfidedissolution and accommodate the volumetric expansion of sulfur.The addition of PEDOT-PSS also enhances the adhesion between the sulfur and the graphene surface.the overall conductivity of the electrode,and the charge transportation during the charging and discharging processes.The GO/PEDOT/S composite electrode delivers an initial specific capacity of around 800 mAh/g at 0.1 C and maintains the reversible capacity of 600 mAh/g after 100 cycles.The second work is about a thin TiO2 NTs/GO Hybrid Membrane applied as an interlayer for lithium-sulfur batteries.The TiO2 NTs/GO hybrid membrane was fabricated by a simple filtration method.Coupling TiO2 additives to C-S composite is able to improve the cycle life and the capacity retention,which was contributed to an electrostatic attraction(S-Ti-O)that improved the surface adsorption of polysulfides on the TiO2.Besides,the graphene with its unique 3D interconnected network structure was able to store the shuttling polysulfide intermediates during cycling.As a result,the sulfur cathode with TiO2 NTs/GO hybrid membrane as interlayer exhibits an initial discharge capacity of 1431.5 mA h/g and maintains the reversible capacity of 845.8 mA h/g at 0.1C after 100 cycles.