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The high temperature lithiation behavior of the MoO2 electrode is examined, which is lithiated by one-electron reduction (by addition reaction) at room temperature. At elevated temperatures, this electrode is lithiated with four-electron reduction by addition and continued conversion reaction. As a result of four-electron reduction, the initial crystalline MoO2 phase is decomposed into a nanosized mixture of metallic Mo and Li2O , which is in turn converted to nanosized MoO2 upon forthcoming delithiation. An interesting feature here is that as-generated nanosized MoO2 is now fully lithiated up to four-electron reduction even at room temperature. This phenomenon is named “thermoelectrochemical activation” because the extension from one- to four-electron reduction is achieved by a simple charge–discharge cycling made at elevated temperatures. The thermoelectrochemically activated MoO2 electrode delivers a reversible specific capacity that is close to the theoretical four-electron capacity (838mAhnormalg−1) with an excellent cycle performance at room temperature.

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‐MoO2) exhibits an unexpectedly high Li+ storage capacity (up to four Li per MoO2 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 (Li2O) in the lithiated a‐MoO2 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.

A vanadium pentoxide electrode is prepared in the amorphous form (a-V2O5), and its electrode performances are compared to those for its crystalline counterpart (c-V2O5). The a-V2O5 electrode outperforms c-V2O5 in several ways. First, it is free from irreversible phase transitions and Li trapping, which evolve in c-V2O5, probably due to the lack of interactions between the inserted Li+ ions/electrons and V2O5 matrix. Second, the absence of Li trapping allows a reversible capacity amounting to >600 mA h g–1, which is larger than that given by c-V2O5. Third, it shows an excellent rate property. The notably high reversible capacity and rate capability seem to be due to Li storage at vacant sites that are ill-defined but numerous in a-V2O5, which Li+ ions can easily access. However, irreversible capacity of a-V2O5 is appreciable in the first cycle due to a parasitic Li reaction with surface hydroxyl groups. Treatment with n-butyllithium can suppress the irreversible capacity by removing the surface hydroxyl groups.

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