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(1.66)Mo(0.66)O2 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.