Chromium trioxide is calcined from 350 to 400 °C yielding pure Cr2O5. The electrochemical properties of the resulting chromium oxides have been measured in the potential range 2.0–4.5 V (vs. Li+/Li) when used in lithium batteries. The first discharge process, the intercalation of lithium into Cr2O5, proceeds via two steps. In the following cycles, lithium is found to be reversibly de-lithiated/lithiated via a solid solution process with an un-known single phase Li x Cr2O5 (u-phase) characterized by an X-ray diffractive lattice spacing of about 0.20 nm. The sample that results from chromium trioxide being calcined at 350 °C shows the highest capacity of 273 mAh g−1 (the first discharge at 0.5 C rate) and the sample calcined at 400 °C shows the best cyclability with the capacity retention of 96% after 100 cycles. The energy density of Cr2O5 can reach 819 Wh kg−1 with the energy conversion efficiency of 83%.