Combined physical confinement and chemical adsorption on co-doped hollow TiO2 for long-term cycle lithium-sulfur batteries.

Abstract

Lithium-sulfur (Li-S) batteries have long been expected to be promising high-energy-density secondary batteries because of their high theoretical specific capacity and element abundances. Yet, their poor cyclability and low rate-capacity strongly limited their practical application. Herein, a nitrogen and sulfur dual doped hollow TiO2 sphere is designed and synthesized for the sulfur host. The dual doped hollow TiO2 can enhance the adsorption ability of soluble lithium polysulfides, which effectively promote the conversion reaction of lithium polysulfides from high-order to low-order in Li-S batteries. What is more, the hollow spherical TiO2 host provides a deposition space for lithium polysulfides and blocks polysulfide migration from the cathode to the electrolyte. Both theoretical calculations and experimental studies confirmed that the electrochemical properties of the sulfur electrode are significantly improved by the dual doped hollow TiO2 sphere. The typical as-prepared dual doped hollow TiO2 cathode coated sulfur has a capacity of 1258 mA h g-1 for the first discharge and a capacity decay as low as 0.0648% per cycle during 500 cycles with a sulfur loading of 3.8 mg cm-2.