Promoting polysulfide redox kinetics by tuning the non-metallic p-band of Mo-based compounds

Abstract

In spite of their high energy density, the application of Li–S batteries is still held back by the sluggish sulfur redox kinetics. Herein, we load a series of Mo-based compounds (i.e., MoO₂, MoS₂, MoN and MoP) on mesoporous carbon nanosheets to modify the separator of Li–S batteries, and systematically study the kinetic behaviors of polysulfides on these separators. We demonstrate that the battery using the MoP-modified separator exhibits the best electrochemical performance because of the narrower energy gap between the metal 3d- and anion 2p-band centers than other compounds. Both experiments and calculations confirm that the narrow energy gap can efficiently lower the decomposition barriers of Li₂S. Accordingly, the battery with the MoP-modified separator exhibits a high rate and long life. In particular, owing to the improved kinetics, this battery can be cycled at −40 °C with a high capacity (391.0 mA h g⁻¹) and a promising stability (capacity retention of 89.6% over 100 cycles).