A new multi‐purpose operando electrochemical cell was designed, constructed and tested on the Swiss–Norwegian Beamlines BM01 and BM31 at the European Synchrotron Radiation Facility. Single‐crystal sapphire X‐ray windows provide a good signal‐to‐noise ratio, excellent electrochemical contact because of the constant pressure between the electrodes, and perfect electrochemical stability at high potentials due to the inert and non‐conductive nature of sapphire. Examination of the phase transformations in the Li1–xFe0.5Mn0.5PO4 positive electrode (cathode) material at C/2 and 10C charge and discharge rates, and a study of the valence state of the Ni cations in the Li1–xNi0.5Mn1.5O4 cathode material for Li‐ion batteries, revealed the applicability of this novel cell design to diffraction and spectroscopic investigations of high‐power/high‐voltage electrodes for metal‐ion batteries.