Encapsulating sulfur into mesoporous TiO2 host as a high performance cathode for lithium-sulfur battery

The commercialization of lithium-sulfur (Li-S) battery has so far hindered by the low electrochemical utilization and rapid capacity fading of sulfur cathode, which is induced by low electric/ionic conductivity, high dissolution of intermediate polysulfides and the volume expansion of sulfur. Herein, we describe an on-site adsorption strategy toward superior stability of sulfur electrode by encapsulating elemental sulfur into mesoporous TiO2 host. Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) measurements obviously indicate that elemental sulfur (S) occupy the mesopores of the TiO2 host, forming a core-shell liked nanostructure. The TiO2/S composite exhibits a superior cycling stability and high Coulombic efficiency during the charge/discharge process. Even at a high current rate of 1 C, the TiO2/S composite shows an initial specific capacity of 650 mAh g−1 and a specific retention of 89% after 100 cycles. The excellent electrochemical performances are critical related to the significant roles TiO2 host played during the electrochemical reaction. Firstly, the nano-sized TiO2 (∼5 nm) traps the polysulfides via chemical bonding interaction to prevent their dissolution and minimize the “shuttle effect”. More importantly, the in situ formed LixTiO2, acting as a mixed electric/ionic conductor, facilitates easier Li+/e− transport. The unique functions of the TiO2 plus its easy availability make the current study conceptually provides new opportunities to reach long-term cycling stability of sulfur cathode using carbon-free hosts.