Reversible Lithium Storage with High Mobility at Structural Defects in Amorphous Molybdenum Dioxide Electrode

This work demonstrates that structural defects in amorphous metal oxide electrodes can serve as a reversible Li + storage site for lithium secondary batteries. For instance, molybdenum dioxide electrode in amorphous form ( a ‐MoO 2 ) exhibits an unexpectedly high Li + storage capacity (up to four Li per MoO 2 unit), which is larger by a factor of four than that for the crystalline counterpart. The conversion‐type lithiation is discarded for this electrode from the absence of Mo metal and lithium oxide (Li 2 O) in the lithiated a ‐MoO 2 electrode and the retention of local structural framework. The sloping voltage profile in a wide potential range suggests that Li + ions are inserted into the structural defects that are electrochemically nonequivalent. This electrode also shows an excellent cycle stability and rate capability. The latter feature is seemingly due to a rather opened Li + diffusion pathway provided by the structural defects. A high Li + mobility is confirmed from nuclear magnetic resonance study.