The chemical and structural changes occurring in a LiMnPO4 composite cathode during electrochemical cycling were investigated by in situ Fourier transform infrared (FTIR) spectroscopy in attenuated total reflectance (ATR) mode. Changes in the IR phosphate vibrational structure at the cathode surface were observed during the cathode charge and discharge. The formation and disappearance of a surface layer of electrolyte oxidation products was detected on the cathode during electrochemical cycling, which was directly linked to the interfacial reactions at LixMnPO4. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.076207jes] All rights reserved.