Review—Operando Optical Spectroscopy Studies of Batteries

The application of in situ optical spectroscopy in battery research has rapidly grown in popularity in the past few decades, yielding considerable new understanding of battery electrochemistry. Most recently, researchers have focused on developing opticallyaccessible battery cells and spectroscopic techniques suitable for studying batteries under commercially-relevant conditions. These “operando” spectroscopic studies have led to better understanding of the complex electrochemical mechanisms and transport behaviors that are critical to improve battery performance and develop new battery chemistries. The growth in popularity and sophistication as well as the multidisciplinary nature of these studies motivates this comprehensive summary of operando optical battery research, including recent advances upon which to build further investigation. In that interest, this review covers the development of operando optical spectroscopy, the spectroscopic methods used, the various approaches to building opticallyaccessible cells, recent technical advances, and their application to specific battery phenomena, including: solid electrolyte interphases, polysulfide shuttling, lithium intercalation, plating and transport, electrode structure, electrode surface reactions, and electrolyte decomposition. The review concludes by surveying emerging techniques and identifying promising areas for further development.