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

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 LixLayMO3 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 LixLayMO3 (M = Ti, Cr, Mn, Fe, and Co) are below 0.411 eV, resulting in high Li‐ion conductivity. The designed perovskites of Li0.34La0.55MnO3−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. A new class of mixed ionic–electronic conductors (MIECs) is designed for a carbon‐free cathode of a Li–air cell. The oxygen vacancy formation energies and Li diffusion barriers of the perovskites are calculated to estimate the electronic and Li‐ion conductivities, respectively. The Li–air cell with an MIEC cathode delivers superior reversibility due to its high electronic and Li‐ion conductivities.