Free-Standing Three-Dimensional CuCo2S4 Nanosheet Array with High Catalytic Activity as an Efficient Oxygen Electrode for Lithium-Oxygen Batteries.

In this work, a novel free-standing CuCo2S4 nanosheet cathode (CuCo2S4@Ni) with high catalytic activity is fabricated for aprotic lithium-oxygen (Li-O2) battery. This deliberately designed oxygen electrode is found to yield lower overpotential (0.82 V), improved specific capacity (9673 mA h g-1 at 100 mA g-1), and enhanced cycle life (164 cycles) as compared to the traditional carbonaceous electrode. The improved performance can be ascribed to the superb spinel structure of CuCo2S4, in which both Cu and Co exhibit more abundant redox properties, improving oxygen reduction reaction and oxygen evolution reaction kinetics effectively and boosting the electrochemical reactions. Furthermore, the well-designed architecture also plays a critical role in the improved performance. Encouraged by the excellent catalytic activity of this free-standing cathode, large-scale pouch-type Li-O2 cell based on CuCo2S4@Ni cathode is fabricated and can work under different bending and twisting conditions. This free-standing electrode provides a new strategy for developing Li-O2 batteries with excellent performance and flexible wearable devices.