Effects of overvoltage and temperature on the lithium insertion kinetics of MgMn2O4

The power capability of lithium-ion batteries strongly depends on the reaction kinetics of the lithium insertion material used in the electrodes. Previously, chronoamperometry revealed that the lithium insertion reaction of MgMn₂O₄ differs between static and dynamic processes and that the dynamic process consists of a nucleation–growth process followed by diffusion. Herein, we present the overvoltage and temperature dependence of the reaction rate of MgMn₂O₄ through chronoamperometry results under different applied voltages and temperatures. The rate constant of each process is determined by fitting the measured current profile to a solid-state reaction model. The rate constant of the nucleation-growth process exhibits an Arrhenius relationship with temperature and a Tafel-like relationship with overvoltage, whereas that of diffusion exhibits an Arrhenius relationship with temperature and does not depend on overvoltage. These dependencies are different because nucleation–growth is a reaction process on the particle surface, whereas diffusion is a reaction process occurring inside the particle. Accordingly, the rate-determining step of lithium insertion under various operating conditions is discussed.