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

Abstract

Porous carbon, which is the most widely used cathode material ever for Li–O₂ 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–O₂ 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–O₂ 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–O₂ 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 O₂ in the environment.