Mixed Ionic–Electronic Conductor of Perovskite Li_xLa_yMO_3−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 Li_xLa_yMO₃ 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_xLa_yMO₃ (M = Ti, Cr, Mn, Fe, and Co) are below 0.411 eV, resulting in high Li-ion conductivity. The designed perovskites of Li_0.34La_0.55MnO_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.