Metal-Ion Coupled Electron Transfer Kinetics in Intercalation-Based Transition Metal Oxides

Electrochemical metal-ion intercalation systems are acknowledged to be a critical energy storage technology. The kinetics of the intercalation processes in transition-metal based oxides determine the practical characteristics of metal-ion batteries, such as the energy density, power, and cyclability. With the emergence of post lithium-ion batteries, such as sodium-ion and potassium-ion batteries, which function predominately in nonaqueous electrolytes of special formulation and exhibit quite varied material stability with regard to their surface chemistries and reactivity with electrolytes, the practical routes for the optimization of metal-ion battery performance become essential. Electrochemical methods offer a variety of means to quantitatively study the diffusional, charge transfer, and phase transformation rates in complex systems, which are, however, rather rarely fully adopted by the metal-ion battery community, which slows down the progress in rationalizing the rate-controlling factors in complex intercalation systems. Herein, several practical approaches for diagnosing the origin of the rate limitations in intercalation materials based on phenomenological models are summarized, focusing on the specifics of charge transfer, diffusion, and nucleation phenomena in redox-active solid electrodes. It is demonstrated that information regarding rate-determining factors can be deduced from relatively simple analysis of experimental methods including cyclic voltammetry, chronoamperometry, and impedance spectroscopy.