Mixed Ionic–Electronic Conductor of Perovskite Li<i><sub>x</sub></i>La<i><sub>y</sub></i>MO<sub>3−</sub><i><sub>δ</sub></i> toward Carbon‐Free Cathode for Reversible Lithium–Air Batteries
Sang Bok, Hyuk Jae Kwon, Mokwon Kim, Seong‐Min Bak, Hyunpyo Lee, Steven N. Ehrlich, Jeong‐Ju Cho, Dongmin Im, Dong‐Hwa Seo
Abstract
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.