Combined Computational and Experimental Study of Li Exchange Reaction at the Surface of Spinel LiMn2O4 as a Rechargeable Li-Ion Battery Cathode

Abstract

Lithium manganese oxide (LiMn2O4) is regarded as an attractive positive electrode for rechargeable Li-ion batteries, in particular for the power source of electric vehicles, and there is thus an urgent need to improve its charge–discharge kinetics. In the current paper, the kinetics of a Li-ion exchange reaction at the interface between a LiMn2O4 cathode and nonaqueous liquid electrolytes is studied using experimental and computational techniques. Electrochemical ac impedance measurements showed two semicircles corresponding to the interfacial Li-ion exchange, and they are ascribed to the desolvation and lattice incorporation processes according to the adatom model [Bruce, P. G.; Saidi, M. Y. J. Electroanal. Chem. 1992, 322, 93]. To gain deeper insight into the latter process, delithiation from the electrode surface was simulated using density functional theory (DFT), and the DFT results were compared to the dependence of the ac impedance behavior on potential. We conclude that the chemical potential gradient is formed at the surface of positive electrodes, and the difference of the potential between the surface and the bulk corresponds to the activation energy of lattice incorporation.