Photoelectron spectroscopy (PES) was used for depth-profile characterization of the interface formed on carbon-treated LiFePO4 particles in the cathode of a lithium-ion battery after electrochemical cycling at 23 and 40degreesC in a 1 M LiPF6 mixture of ethylene carbonate and diethyl carbonate. Products from solvent reactions (such as polycarbonates) were not detected at the carbon-treated LiFePO4 surface, contrary to findings for other cathode materials. Salt-based products like LiF, LiPF6, LixPF(y)- and LixPFyOz-type compounds were found on the cathode surface after cycling. Larger amounts of these compounds were detected on the surfaces of electrodes cycled at 40degreesC. (C) 2003 The Electrochemical Society.