Soft X-ray spectroscopy of light elements in energy storage materials

Abstract The increasing demand for electrochemical energy storage devices continuously promotes the development of new electrode materials and electrolytes. As a result, understanding their structural and electronic properties affecting electrochemical performance becomes crucial. The role of light elements, which are found in anode and cathode materials, in electrolytes and hence in the solid-electrolyte interphases, requires a special attention. Soft X-ray spectroscopies are particularly relevant to probe selectively light elements in complex environment. Here, the recent advances in the characterization of light elements in energy storage materials by soft X-ray spectroscopy and microscopy techniques are reviewed. After introducing the main X-ray spectroscopic methods and their application to ex situ/in situ/operando characterization of electrochemical processes, the role of light elements in the electrode for supercapacitors and Li/Na-ion storage applications is described. The characterization of electrolytes and related ion solvation is then briefly reviewed before describing how the formation and evolution of solid-electrolyte interphases can be monitored with these methods. Finally, major challenges and future opportunities for soft X-rays spectroscopy in the context of electrochemical energy storage are highlighted.