Side-View Operando microscopy of Graphite Anodes to Understand Kinetic Hysteresis

Abstract

Operando imaging analysis has emerged as a promising characterization tool for the observation of nanoscale processes; chemical synthesis, electrochemical reaction, and physical interaction of various materials. For past a decade, operando microscopy tools have contributed to understanding the lithiation or sodiation behaviors in battery materials for discovering new electrode materials with high performance and identifying the fundamental failure mechanisms that prevent a prolonged cycle life. Among the candidates, graphite anodes have the most promise to apply for lithium-ion batteries, but also have scientific challenges to retain their kinetics upon repeated charge and discharge cycles. To develop a better design of the electrodes, understanding graphite anodes with direct observation has created a high interest. Although such demands lead to extensive studies about operando imaging techniques, the observation is mostly limited for a single particle or a particular position of the electrodes. In this regard, we have demonstrated side-view operando optical microscopy on graphite anodes by a change of color during electrochemical lithiation. Since the color of graphite changes owing to the different bandgap during lithiation and delithiation processes, operando optical microscopy enables to analyze the kinetics of charge and discharge behaviors. In addition, our cell configuration has the manifold advantages of applying and adjusting liquid electrolytes which is similar to commercial cells as a practical application and offering the investigation of the electrode side view. The side-view observation of an electrode level is found that microscale spatial variations in rate and composition control the insertion and desertion to understand the kinetics through the whole electrode. Our results allow for a better fundamental understanding of kinetics in battery materials.