Operando soft x-ray emission spectroscopy of LiMn2O4 thin film involving Li–ion extraction/insertion reaction

Abstract

We developed an electrochemical in situ cell for soft x-ray emission spectroscopy (XES) to accurately investigate the redox reaction and electronic structure of transition metals in the cathode materials for Li–ion battery. The in situ cell consists of a Li–metal counter electrode, an organic electrolyte solution, and a cathode on a membrane window which separates the liquid electrolyte from high vacuum and can pass the incoming and emitted photons. In this study, the Mn 3d electronic structure of LiMn2O4 thin-film electrode was clarified by the operando XES. At the charged state, the XES spectrum changed significantly from the open-circuit-voltage (OCV) state, suggesting oxidation of the Mn3+ component through Li–ion extraction. Upon discharge up to 3.0V vs. Li/Li+, the XES spectrum almost returned to its profile at the OCV state with small difference, indicating the valence change of Mn: Mn3.6+→Mn4+→Mn3.3+ corresponding to the OCV, charged, and discharged states.