Lychee-like TiO@TiN dual-function composite material for lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries are promising candidates for next generation rechargeable batteries because of their high energy density of 2600 W h kg. However, the insulating nature of sulfur and LiS, the "shuttle effect" of lithium polysulfides (LiPSs), and the volumetric change of sulfur electrodes limit the practical application of Li-S batteries. Here, lychee-like TiO@TiN hollow spheres (LTTHS) have been developed that combine the advantages of high adsorption TiO and high conductivity TiN to achieve smooth adsorption/spread/conversion of LiPSs and use them as a sulfur host material in Li-S batteries for the first time. The cathode exhibits an initial specific capacity of 1254 mA h g and a reversible capacity of 533 mA h g after 500 cycles at 0.2C, which corresponds to an average coulombic efficiency up to 99%. The cell with the LTTHS@S cathode achieved an extended lifespan of over 1000 cycles. Such good performance can be assigned to the good adsorption and catalysis of the dual-function TiO@TiN composite. This work proved that the TiO@TiN composite can be an attractive matrix for sulfur cathodes.