Rocksalt-type metal sulfide anodes for high-rate sodium storage

Abstract

The low electrical conductivity of α-MnS generally impedes its use as an electrode material for sodium-ion batteries. However, in this study, an unprecedentedly high capacity and long-term cyclability were achieved for an α-MnS electrode at moderate and high rates by introducing electro-conductive carbon surfaces. A capacity of 302 mA h g⁻¹ was delivered in the first cycle with 85% capacity retention after 200 cycles at 100 mA g⁻¹. Furthermore, the cycling performance at 10C (6.1 A g⁻¹) demonstrated the feasibility of high-rate sodium storage using this anode, with 78% retention of the initial capacity after 200 cycles. This performance was reproduced in a NaCrO₂/α-MnS full cell as well. X-ray diffraction, X-ray photoelectron spectroscopy, and time-of-flight secondary-ion mass spectroscopy were used to unveil the reaction mechanism, and the results provided possible explanations for the good electrode performance and rapid sodium storage capabilities.