The chemical and structural changes occurring in a LiMnPO4 composite cathode during electrochemical cycling were investigated by ex situ Raman microscopy. An O-2-plasma etching procedure was used to remove the thick surface carbon coating and expose LiMnPO4 particles for Raman characterization of LixMnPO4 at different states of charge (SOC). Pyrophosphate species, Li4P2O7, emerged at the exposed part of the LiMnPO4 composite cathode after a full charge and discharge cycle, indicating that the charged LixMnPO4 electrode is not chemically stable in standard LiPF6/carbonate-based electrolytes at room temperature. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.018209jes] All rights reserved.