Crystallographic-orientation dependent Li ion migration and reactions in layered MoSe2

The lithium ion migration dynamics and the fast lithiation pathways in electrode materials are quite critical for the rate capability of lithium ion batteries (LIBs). To reveal the relationship between lithiation behavior and crystallographic orientations in layered MoSe2, its dynamic electrochemical reactions are investigated with in situ microscopy technique. We report the crystallographic-orientation dependent lithium ion migration and reaction in MoSe2, where the preferential lithium-ion migration is observed along the < 1 0 (1) over bar 0 > orientations. These oriented-lithiation tips further assisted the surface to interior lithiation of layered MoSe2. Meanwhile, a phase transition from pristine 2H-MoSe2 to 1T-LixMoSe2 and the following conversion reaction with the formation of Li2Se and Mo are observed during the first lithiation process. The lithiation induced stress and orientation-dependent interfacial reaction rate might be the main factor leading to the orientation-dependent lithiation behavior. The experimentally revealed crystallographic-orientation dependent lithium ion migration and reaction in layered MoSe2 will provide intuitive understanding of the structural evolution during the discharge/charge cycling process, give guidance for the design of anode materials and can broaden the promising application of MoSe2 in solid electrochemical devices.