Surface modification of hollow capsule by Dawson-type polyoxometalate as sulfur hosts for ultralong-life lithium-sulfur batteries

摘要

Reasonable construction of sulfur host with high conductivity,large sulfur storage gap,strong chemical adsorption,and fast oxidation–reduction kinetics of polysulfide is very significant for its practical use in lithium-sulfur batteries(LSBs).In this paper,the surface modification of MIL-88A(Fe)is carried out by Dawson-type polyoxometalate(POM),and a hollow capsule shell material with P_(2)W_(18),Fe_(3)O_(4),and C components is synthesized by the subsequent carbonization process.When applied as the sulfur host,the hollow capsule shell material can efficiently improve the conductivity of sulfur electrode and restrain the volumetric change of active sulfur while charging and discharging.On this foundation,electrochemical analysis and density functional theory(DFT)calculation show that the P_(2)W_(18)on the outer layer of the capsule shell have effective electrocatalytic activity and potent chemical bond on the lithium polysulfides(LiPSs),which is helpful to block the shuttle effect.Therefore,the as-assembled LSBs display the outstanding specific capacity and prominent cycle stability.Specifically,it delivers an excellent reversible capacity of 1063 mAh/g after 100 cycles of charge–discharge at a rate of 0.5 C,accounting for a preservation by 96%in comparison to that of the initial cycle.Moreover,even after 2000 cycles at 1 C,the reversible specific capacity of 585 mAh/g can still be maintained with an average decay rate of only 0.021%.