Using Light to Enhance Charge Transfer in Battery Materials: Increasing Charging Rates in LiNi _0.5 Mn _1.5 O ₄

Electrochemical, spectroscopic, and computational studies on the interplay between light perturbation and coupled electron and Li-ion transfer in LiNi0.5Mn1.5O4 (LNMO) cathodes identify that photon perturbation moves the system out of equilibrium, increases entropy, lowers the impedance of the battery, and increases the charging capacity by at least 15% during fast charging by promoting the oxidation of Ni3+ to Ni4+. The correlation with density functional theory calculations points out that oxidation of Ni3+ faces a 30% higher barrier compared with the oxidation of Ni2+ and hence exhibits greater responses to the energy transferred from photons. Structural analysis elucidates that photon energy also assists the transition of LNMO from the Jahn–Teller distorted asymmetric lattice with Ni3+ to the nondistorted Ni4+. Synergistically, photons energize the removal of electrons from Ni3+ and create photoinduced Ni4+ intermediates, followed by the removal of Li+ with almost two times faster diffusion rates.