Mesoporous MnCo2S4 nanosheet arrays as an efficient catalyst for Li–O2 batteries

Abstract

Ternary metal sulfides and ternary metal oxides have received much attention as potential electrodes for high performance rechargeable batteries. Herein, MnCo₂S₄ nanosheets are grown on carbon paper (MCS/CP) via facile electrodeposition followed by low temperature vulcanization for application in Li–O₂ batteries for the first time. The electrochemical performance of freestanding, binder-free MCS/CP oxygen electrodes is compared with those prepared from MnCo₂O₄ nanosheets on CP (MCO/CP). The MCS/CP electrode delivers an extremely high initial specific capacity of 10 760 mA h g⁻¹, twice that of MCO/CP. The former electrode sustains 96 cycles at an upper limit capacity of 500 mA h g⁻¹ at 200 mA g⁻¹, whereas the latter counterpart survives only a few cycles with a poor round trip efficiency. The superior performance of MCS/CP is in part proven by the four times higher electrical conductivity and 250% higher lithium diffusion coefficient than MCO/CP. In addition, the 3D interconnected web of 2D MCS nanosheets offers a few micrometer open voids to accommodate discharge products and a large surface area with internal mesopores providing abundant active sites. The density functional theory calculations reveal a lower adsorption energy for LiO₂ on the surface of MCS than on MCO, which is responsible for the lower OER overpotential and the higher catalytic ability of MCS/CP. The predicted density of states signifies metallic properties of MCS in agreement with the high electrical conductivity of MCS/CP.