A core-shell-structured TiO2(B) nanofiber@porous RuO2 composite as a carbon-free catalytic cathode for Li-O2 batteries

Porous carbon, which is the most widely used cathode material ever for Li-O-2 batteries, is found to decompose in the charging process, promote electrolyte decomposition, and react with the discharge product. Carbon-free cathodes thus become critical for Li-O-2 batteries, but generally exhibit low capacity and poor rate because of their high density and insufficient pore characteristic. Herein, we present a simple method to prepare a core-shell-structured TiO2(B) nanofiber@porous RuO2 composite, which is used as a carbon-free catalyst for Li-O-2 batteries. The RuO2 coating layer replicates the structure of TiO2 nanofibers to form a one-dimensional RuO2 shell with a typical hierarchical mesoporous/macroporous structure. Besides the reduced undesired decomposition, the abundant porous structure and inherent high conductivity of the RuO2 coating layer also increase the specific capacity, efficiency, rate ability and cycle life. With a high mass loading of 2.5 mg cm(-2) on the cathode, the Li-O-2 battery shows a performance superior to previous reports, including high capacity (800 mA h g(-1) at a current density of 0.125 mA cm(-2) or 50 mA g(-1)) with a very high energy efficiency of >82.5%, good rate (500 mA h g(-1) at a current density of 0.5 mA cm(-2) or 200 mA g(-1)) and long-life (80 cycles at a fixed capacity of 300 mA h g(-1)). It is also demonstrated that the lithiation/de-lithiation of RuO2 can contribute capacity over the charge/discharge process, indicating that this battery can be operated as a rechargeable RuO2/Li battery without O-2 in the environment.