Free-standing TiO2 nanowire-embedded graphene hybrid membrane for advanced Li/dissolved polysulfide batteries

The increasing demand for electric vehicles and large-scale smart grids has aroused great interest in developing high energy density storage devices. Lithium–sulfur (Li–S) battery has attracted much attention owing to its high theoretical energy density and abundance, but many challenges such as rapid capacity fade and low sulfur loading and utilization have impeded its practical use. Here, we present a free-standing TiO2 nanowire/graphene hybrid membrane for Li/dissolved polysulfide batteries with high capacity and long cycling life. Graphene membrane with high electrical conductivity is used as a current collector to effectively reduce the internal resistance in the sulfur cathode and physically immobilize the dissolved lithium polysulfides. The TiO2 nanowires introduced into the graphene membrane offer a hierarchical composite structure, in which the TiO2 nanowires not only have strong chemical binding with the lithium polysulfides, but also show a strong catalytic effect for polysulfide reduction and oxidation, promoting a fast redox reaction kinetics with high capacity and low voltage polarization. This hybrid electrode delivers a high specific capacity of 1327 mA h g−1 at 0.2 C rate, a Coulombic efficiency approaching 100%, high-rate performance of 850 mA h g−1 at 2 C rate, and long cyclic stability with a capacity of 1053 mA h g−1 at 0.2 C rate over 200 cycles, demonstrating great prospect for application in high energy Li–S batteries.