Graphene-supported polyoxometalate entrapped in a MIL-88A network with highly efficient conversion of polysulfides in Li-S batteries.

Abstract

It has been demonstrated that polyoxometalates (POMs) have strong anchoring abilities with efficient catalysis of lithium polysulfides (LiPSs). However, the severe aggregation that buries the effective active sites of POMs along with poor electrical conductivity limits the practical application of POMs in lithium sulfur batteries (LSBs). In our strategy, we utilized reduced graphene oxide (rGO) to support a POM catalyst entrapped in a MIL-88A(FeCo) network with a hollow shell skeleton as the sulfur host material. H4PW11VO40 (PW11V) with optimal vanadium atom implantation ensures the ruggedness and integrity of the hollow structure, which is conducive to achieving high sulfur loading as well as accommodating the volume change of the sulfur cathode during the charging and discharging process. Importantly, PW11V can capture polysulfides through firm chemical adsorption and accelerate redox reactions of LiPS conversion by effective electrochemical catalysis. Furthermore, the satisfactory electrical conductivity of rGO provides access for electrons to reach the interface of PW11V and polysulfides and trigger Li-S conversion reactions. Thus, the constructed PW11V-based sulfur cathode exhibited a superior specific capacity of 905 mA h g-1 after 100 cycles under 0.2 C and long cycling life with a capacity recession rate of 0.046% for each cycle upon 500 cycles under 3 C. This research reveals the effect of vanadium atom substitution of POMs on the cycling performance of a sulfur cathode and affords insight for developing high-performance LSBs.