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 (838 mAh g(-1)) with an excellent cycle performance at room temperature.