A highly efficient polysulfide mediator for lithium–sulfur batteries

TLDR

Lithium–sulfur batteries promise high energy density at low cost, but their practical use is limited by capacity decay caused by the polysulfide shuttle. The study proposes entrapping polysulfides in the cathode via manganese dioxide nanosheets that react with lithium polysulfides to form surface‑bound intermediates. Manganese dioxide nanosheets serve as a redox shuttle that catenates higher polysulfides, forming surface‑bound intermediates and converting them to insoluble lithium sulfide through disproportionation. The sulfur/manganese dioxide nanosheet composite delivers 1,300 mAh g⁻¹ with a 0.036 %/cycle fade over 2,000 cycles, and the mediator strategy also works with graphene oxide, demonstrating broad applicability.

Abstract

The lithium–sulfur battery is receiving intense interest because its theoretical energy density exceeds that of lithium-ion batteries at much lower cost, but practical applications are still hindered by capacity decay caused by the polysulfide shuttle. Here we report a strategy to entrap polysulfides in the cathode that relies on a chemical process, whereby a host—manganese dioxide nanosheets serve as the prototype—reacts with initially formed lithium polysulfides to form surface-bound intermediates. These function as a redox shuttle to catenate and bind 'higher' polysulfides, and convert them on reduction to insoluble lithium sulfide via disproportionation. The sulfur/manganese dioxide nanosheet composite with 75 wt% sulfur exhibits a reversible capacity of 1,300 mA h g−1 at moderate rates and a fade rate over 2,000 cycles of 0.036%/cycle, among the best reported to date. We furthermore show that this mechanism extends to graphene oxide and suggest it can be employed more widely. The polysulfide shuttle is a major problem leading to capacity decay in lithium–sulfur batteries. Here, the authors show that in-situ-generated thiosulfate species on a manganese oxide nanosheet act as a polysulfide mediator, which effectively prevents polysulfide dissolution, leading to enhanced cyclability.