Inhibiting structural degeneration of MoSe2 anode with dual-layer protection for highly robust Na-ion battery

Abstract

MoSe2 with substantial redox sites and large interlayer space (0.64 nm) has been regarded as an attractive alternative for sodium-ion storage. However, the reversible capacity of the MoSe2 electrode quickly decays due to the degeneration of the layered structure. Herein, dual-layer coated MoSe2 nanosheets (MoSe2@C@MoOx) produced by the hydrothermal reaction and atomic layer deposition are proposed to enhance the entire structural durability. In this design, the middle coating layer of carbon with physically elastic and electronically conductive features can buffer volume expansion in the reaction process, enhance the electronic conductivity of MoSe2 and MoOx, and boost the reaction kinetics. The outer coating layer of MoOx as a solid-state electrolyte can enhance cyclic stability. Meanwhile, MoOx participates in the Na + storage process, which enhances the reversible capacity of the entire electrode. The MoSe2@C@MoOx electrode demonstrates highly initial discharge capacity (645 mA h g−1) and outstanding cyclic stability (520 mA h g−1 after 200 cycles) compared with uncoated or carbon-coated MoSe2 electrode. Additionally, the Na+ storage mechanism confirmed by ex-situ X-ray diffraction suggested that the Se element is formed after charging instead of the MoSe2 component. This design may provide a new paradigm of other nanomaterials for energy storage.