Résumé
Phenomena occurring in the electrolyte as well as the interfaces with the electrodes, such as Li + solvation/desolvation and solid–electrolyte interphase formation, govern the performance and safety of Li‐ion batteries. In this article, a dedicated, spring‐loaded operando attenuated‐total‐reflectance Fourier‐transform infrared cell is presented, enabling quantitative, time‐resolved probing of the electrode–electrolyte processes under electrochemical examination. The optical design is based on a 45 ∘ incidence diamond waveguide, while the electrochemical setup comprises a gas‐tight stainless steel body. The procedure for preparing the self‐supported electrode and the acquisition protocol are also presented, together with a reproducible analysis workflow for tracking solvated versus free electrolyte solvent species without baseline subtraction. Representative measurements on composite tin electrodes validate the ability of the setup to resolve band shifts and intensity changes linked to Li + coordination and electrolyte reduction. The methodology generalizes to diverse negative‐electrode chemistries and provides molecular‐level insight into battery phenomena under electrochemical operating conditions.