Tungsten Disulfide/Carbon Nanotubes Network For High Capacity And Long Life Lithium-sulfur Batteries

The target of carbon emissions peak and carbon neutrality propels us to develop and utilize energy efficiently.The development of energy storage technology is crucial to realize new energy application.Lithium-sulfur battery(LSB),as a new type of secondary battery using sulfur cathode and lithium anode,is considered as a promising new energy storage device due to its high theoretical specific capacity(1675mAhg^-1)and energy density(2600Whkg^-1).However,the commercialization of lithium-sulfur batteries is hindered by several problems,especially the“shuttle effect”of soluble lithium polysulfides(Li PS)and the sluggish redox kinetics.To date,many strategies were developed from the cathode,anode,electrolyte,and separator-side,etc,to tackle these obstacles.Two-dimensional materials such as graphene and transition metal sulfides have beenwidely used in the field of electrochemical energy storage due to their excellent electrical,optical,and catalytic properties.As a typical two-dimensional transition metal sulfide,WS₂ shows good electronic and ionic conductance and abundant active edge sites,which can chemically adsorb Li PS and catalytically accelerate Li PS conversion.CNTs is a type of one-dimensional carbon materials with outstanding electrical conductivity and mechanical property.Hybridization of 2D WS₂ with 1D CNTs could achieve the advantages of both simultaneously.Herein,a 3D WS₂/CNTs architecture simply built via one-step hydrothermal method was introduced into Li-S battery system serving as functional cathode additive and separator coating layer.From cathode-side and separator surface,such 3D WS₂/CNTs network with abundant active edge sites,large active surface,fast electron pathway twice performs functions of“block-adsorption-catalysis”towards Li PS,thus achieving efficient utilization of sulfur and suppression of shuttle effect.The main conclusions are as follows:(1)3D WS₂/CNTs network was fabricated by directly growing 2D WS₂ onto outer walls of 1D CNTs via one-step hydrothermal method.1D CNTs and 2D WS₂ nanosheets intertwine to form a 3D network structure,contributing to abundant pores and high specific surface(167.4m²g^-1)together with abundant active edge-sites.Adsorption test and XPS analysis before and after Li PS adsorption show that WS₂/CNTs could not only adsorb polysulfides via chemical bonding,but also reversibly react with polysulfides to form thiosulfate and polythionate,thereby retarding polysulfide dissolution and migration.(2)The WS₂/CNTs functional separator was fabricated by vacuum-filtrating WS₂/CNTs dispersion over the commercial PP separator.Visual penetration test shows that compared with pristine PP and CNTs separator,WS₂/CNTs separator demonstrates prominent blocking effect towards polysulfides diffusion.From separator surface,such3D WS₂/CNTs performs functions of“block-adsorption-catalysis”towards Li PS,thus achieving efficient utilization of sulfur and suppression of shuttle effect.Thus,Li-S battery using WS₂/CNTs separator shows impressive electrochemical performances in terms of capacity,cyclability,and rate capability(an initial capacity of 1045.6mAhg^-1 at 1C with an ultralow decay rate of 0.049% over 1000 cycles and 703.5mAhg^-1 at 5C.(3)Furthermore,WS₂/CNTs composite was introduced into Li-S battery systemserving as cathode additive and separator coating simultaneously.From cathode-side and separator surface,3D WS₂/CNTs twice performs functions of mitigating the polysulfide diffusion via physical barrier or chemical interactions and accelerating Li PS conversion kinetics.As a result,compared with Li-S battery using WS₂/CNTs merely as separator coating layer,such Li-S battery configuration using WS₂/CNTs simultaneously as functional cathode additive and separator coating layer demonstrates superior performances in terms of capacity,rate,cycling stability:an initial capacity of 1068.5mAhg^-1 at 1C with an ultralow decay rate of 0.035% from 400^th to 1000^th cycle,753.9mAhg^-1 at 5C.Besides,such cell also shows excellent cycle stability at a high sulfur loading of 2.7mgcm^-2 or high rate of 2C,and self-discharge and anode corrosion was also remarkably mitigated as well.