Design and synthesis of macroporous (Mn1/3Co2/3)O-carbon nanotubes composite microspheres as efficient catalysts for rechargeable Li-O2 batteries

Abstract

Unique-structured (Mn1/3Co2/3)O-carbon nanotubes (MnCoO-CNT) composite microspheres synthesized by one-pot spray pyrolysis were studied as air electrode for lithium–oxygen (Li-O2) batteries. The (Mn1/3Co2/3)O nanocrystals were first introduced as efficient electrocatalysts for oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs). In addition, the optimum structure of CNT microspheres was designed as efficient support material for (Mn1/3Co2/3)O nanocatalysts with high electrical conductivity and high accommodation ability for Li2O2 products. The macroporous MnCoO-CNT composite microspheres exhibited excellent bifunctional oxygen catalytic activities in terms of a positive half-wave potential (0.67 V) for ORRs and high limiting diffusion current (35 mA cm−2 at 1.0 V) for OERs. When applied as a cathode material for Li–O2 batteries, the MnCoO–CNT microspheres delivered a high discharge capacity (37142 mA h g−1 at 200 mA g−1), excellent rate capability (4458 mA h g−1 at 2000 mA g−1), and long-term cycle stability (245 cycles at a capacity of 500 mA h g−1 at 200 mA g−1). The synergetic effect of macroporous CNT microspheres with high electrical conductivity and high electrocatalytic activities of the (Mn1/3Co2/3)O nanocatalyst were responsible for the superior performance of MnCoO–CNT composite microspheres as cathode material for Li–O2 batteries.