Synthesis of Ni-Doped TiO2 Microtubes as Cathode Catalyst for Rechargeable Li-O2 Batteries

Abstract

Rechargeable nonaqueous Li-O2 batteries are considered as one of the most promising energy storage systems due to their super-high theoretical energy density. However, some technical obstacles, such as high overpotential and poor cycle stability, need to be overcome urgently, so that it is possible to make Li-O2 batteries commercially viable. The key is to develop effective bifunctional cathode catalysts. Herein, Ni-doped TiO2 (Ni-TiO[Formula: see text] with microtubule structure was prepared by hydrothermal method and used as the cathode catalyst of Li-O2 batteries. At a current density of 100[Formula: see text]mA[Formula: see text]g[Formula: see text], Li-O2 batteries with Ni-TiO2 catalysts showed an initial discharge capacity of 5100[Formula: see text]mAh g[Formula: see text] and can maintain 52 stable cycles at 100[Formula: see text]mA[Formula: see text]g[Formula: see text] with a fixed capacity of 500[Formula: see text]mAh[Formula: see text]g[Formula: see text]. The microtubule structure composed of nanosheets not only facilitates the diffusion of O2 and electrolyte, but also provides abundant catalytic sites for oxygen reduction reactions and oxygen evolution reactions (ORR/OER). In addition, the Ni doping into the structure of TiO2 can significantly enhance the catalytic activity of ORR/OER, resulting in a reduced discharge/charge overpotential and enhanced discharge-specific capacity.