A First‐Cycle Coulombic Efficiency Higher than 100 % Observed for a Li 2 MO 3 (M=Mo or Ru) Electrode

The lithiation/de‐lithiation behavior of a ternary oxide (Li 2 MO 3 , where M=Mo or Ru) is examined. In the first lithiation, the metal oxide (MO 2 ) component in Li 2 MO 3 is lithiated by a conversion reaction to generate nano‐sized metal (M) particles and two equivalents of Li 2 O. As a result, one idling Li 2 O equivalent is generated from Li 2 MO 3 . In the de‐lithiation period, three equivalents of Li 2 O react with M to generate MO 3 . The first‐cycle Coulombic efficiency is theoretically 150 % since the initial Li 2 MO 3 takes four Li + ions and four electrons per formula unit, whereas the M component is oxidized to MO 3 by releasing six Li + ions and six electrons. In practice, the first‐cycle Coulombic efficiency is less than 150 % owing to an irreversible charge consumption for electrolyte decomposition. The as‐generated MO 3 is lithiated/de‐lithiated from the second cycle with excellent cycle performance and rate capability.