New Insights into Electrochemical Lithiation/Delithiation Mechanism of α‑MoO₃ Nanobelt by in Situ Transmission Electron Microscopy

The α-MoO₃ nanobelt has great potential for application as anode of lithium ion batteries (LIBs) because of its high capacity and unique one-dimensional layer structure. However, its fundmental electrochemical failure mechanism during first lithiation/delithiation process is still unclear. Here, we constructed an electrochemical setup within α-MoO₃ nanobelt anode inside a transmission electron microscope to observe in situ the mircostructure evolution during cycles. Upon first lithiation, the α-MoO₃ nanobelt converted into numerous Mo nanograins within the Li₂O matrix, with an obvious size expansion. Interestingly, α-MoO₃ nanobelt was found to undergo a two-stage delithiation process. Mo nanograins were first transformed into crystalline Li_1.66Mo_0.66O₂ along with the disappearance of Li₂O and size shrink, followed by the conversion to amorphous Li₂MoO₃. This irreversible phase conversion should be responsible for the large capacity loss in first cycle. In addition, a fully reversile phase conversion between crystalline Mo and amorphous Li₂MoO₃ was revealed accompanying the formation and disapperance of the Li₂O layer during the subsequent cycles. Our experiments provide direct evidence to deeply understand the distinctive electrochemical lithiation/delithiation behaviors of α-MoO₃ nanobelt, shedding light onto the development of α-MoO₃ anode for LIBs.