Mixed Ionic–Electronic Conductor of Perovskite LixLayMO3−δ toward Carbon‐Free Cathode for Reversible Lithium–Air Batteries

Abstract Mixed ionic–electronic conductors (MIECs) can play a pivotal role in achieving high energies and power densities in rechargeable batteries owing to their ability to simultaneously conduct ions and electrons. Herein, a new strategy is proposed wherein late 3d transition metals (TMs) are substituted into a perovskite Li‐ion conductor to transform it into a Li‐containing MIEC. First‐principles calculations show that perovskite Li x La y MO 3 with late 3d TMs have a low oxygen vacancy formation energy, implying high electron carrier concentrations corresponding to high electronic conductivity. The activation barriers for Li diffusion in Li x La y MO 3 (M = Ti, Cr, Mn, Fe, and Co) are below 0.411 eV, resulting in high Li‐ion conductivity. The designed perovskites of Li 0.34 La 0.55 MnO 3− δ experimentally prove to have high electronic (2.04 × 10 −3 S cm −1 ) and Li‐ion (8.53 × 10 −5 S cm −1 ) conductivities, and when applied in a carbon‐free cathode of a Li–air cell, they deliver superior reversibility at 0.21 mAh cm −2 over 100 charge/discharge cycles while avoiding the degradation associated with carbonaceous materials. This strategy enables the effective design of Li‐conducting MIEC and reversible Li–air batteries.