Extraordinary lithium storage capacity and lithiation mechanism of partially amorphous molybdenum sulfide on chemically exfoliated graphene

Abstract

Molybdenum sulfides have been researched actively for application in electrochemical energy storages and conversions. For molybdenum sulfides, modifications in stoichiometry and crystal structure can lead to enhancements in their electro-chemical properties. However, even though performance of crystalline molybdenum disulfide-based lithium ion battery (LIB) anodes have been investigated extensively, amorphous molybdenum sulfide-based anodes still need to be researched. Herein we report specific capacity as high as 1872 mAh/g observed from non-stoichiometric partially amorphous molybdenum sulfide formed on chemically exfoliated graphene (MoSx-rGO) as a LIB anode. According to our analysis, amorphous part consisting [Mo3S13]2- building blocks contains an excess amount of sulfur as bridging, shared, or terminal S22−, which contribute significantly in enhancing the capacity of the anode. In depth electrochemical investigations and analysis suggest that MoSx-rGO undergoes a different lithiation mechanism from crystalline MoS2, and consequently exhibits such high capacity with excellent stability at least up to 200 cycles and a decreased c-rate dependence.