Dynamic Elucidation of Lithium Insertion Reaction into MgMn2O4 Spinel

Abstract

Since the expansion of Li-ion battery applications from portable electronic devices to electric vehicles and renewable energy storage, high-power capability is becoming increasingly important as a battery performance metric. Elucidation of the reaction mechanism of Li insertion materials is a major task in the battery research field, because it offers crucial insights into both the kinetics of the Li insertion reaction and the development of high-power Li-ion batteries. In this study, the mechanism for Li insertion into MgMn2O4 spinel, across the entire reaction range, was elucidated by fitting the current response during constant-potential discharge reaction using solid-state kinetic reaction (nucleation-growth, diffusion, and contraction) models. The fitting results revealed that the Li insertion reaction in the dynamic (non-equilibrium) process proceeds via nucleation-growth followed by solid-state Li-ion diffusion (single-phase), while Li insertion into MgMn2O4 proceeds through a two-phase coexistence reaction in the equilibrium state, as observed by ex situ XRD analysis. The finding that the reaction mechanisms in the dynamic and equilibrium processes are different indicates that the kinetics of the Li insertion reaction should be considered through a dynamic rather than an equilibrium process viewpoint.