Tri-functionalized polypropylene separator by rGO/MoO2 composite for high-performance lithium–sulfur batteries

The popularity of lithium–sulfur batteries has been increasing gradually due to their ultrahigh theoretical specific capacity and energy density. Nevertheless, they also have lots of drawbacks to be overcome, such as poor conductivity, severe volume expansion, and serious “shuttle effect”. In this work, reduced graphene oxide/molybdenum dioxide (rGO/MoO2) composite is synthesized and applied to modify polypropylene separator. The modified polypropylene separator introduces synergistic tri-functions of physical adsorption, chemical interaction and catalytic effects, which can inhibit the “shuttle effect” and enhance the electrochemical performances of lithium-sulfur batteries. In the prepared rGO/MoO2 composite, the polar MoO2 chemically adsorbs the intermediate lithium polysulfide, while the rGO with good electrical conductivity not only acts as a physical barrier to prevent diffusion of polysulfide ions, but also improves the conversion efficiency of active material intercepted on the separator. As a consequence, the battery assembled with rGO/MoO2 modified polypropylene separator exhibits a reversible capacity of 757.5 mAh·g−1 after 200 cycles at 0.2C with a negligible capacity decay of 0.207% per cycle, which indicates a good long-period cycling stability. Furthermore, the rate performance and self-discharge suppression are also improved by introducing modified polypropylene separator. It shows that rGO/MoO2 composite is a promising material for separator modification in lithium-sulfur batteries.