Yolk-shell-structured manganese oxide/nitride composite powders comprising cobalt-nanoparticle-embedded nitrogen-doped carbon nanotubes as cathode catalysts for long-life-cycle lithium-oxygen batteries

Abstract

An air-electrode catalyst material with a hierarchically porous structure and efficient chemical composition can improve the performances of lithium-oxygen (Li-O-2) batteries. In this study, hierarchically yolk-shell structured manganese oxide/manganese nitride composite powders comprising Co-nanoparticle-embedded N-doped carbon nanotubes (yCo-NCNT-Mn) are successfully fabricated as O-2-electrode catalysts for Li-O-2 batteries. The asprepared yCo-NCNT-Mn powders exhibit high electrocatalytic activities toward both oxygen reduction and evolution. The Li-O-2 battery with yCo-NCNT-Mn exhibits a high capacity (22,344 mA h g(-1) at 200 mA g(-1)), low charge overpotential (0.25 V), and long cycling life (227 cycles at 200 mA g(-1) and cut-off capacity of 500 mA h g(-1)). Experimental analyses reveal that the improved electrochemical performance can be attributed to the synergistic advantages of the electrically conductive NCNTs and excellent catalytic activity of the bifunctional catalyst as the composite form of Co, NCNT, MnO, and Mn4N. Moreover, the unique hierarchical yolk-shell structure increases the capacity by providing a sufficient space to accommodate Li2O2.