Direct operand visualization of Li-metal plating and stripping inside pressed, closed battery cells using optically transmitting ultra-thin electrode

Abstract

Although the electrochemical reactions inside battery cells form the foundation of various energy storage and conversion processes, they are invisible because the electrodes facing the separator are pressed and closed in the cell. In this study, an optically transmitting ultra-thin Cu electrode was developed and the Li-metal plating/stripping behaviors inside cells, where a pressed planar interface existed between the electrodes and the electrolyte-soaked separator, were observed. Gas evolution at the pressed interface strongly disturbed the Li-metal plating, leading to a porous Li-metal plating morphology and unstable cycling with low Coulombic efficiency. Visual inspection of the pressed interface reveals certain underlying mechanisms of Li-metal plating including the influence of gas evolution, which are not readily captured by indirect approaches, while offering a general framework applicable to various other devices based on closed-cell configurations.