A novel type of additives for improving cathode cyclability has been developed. Three electrolyte additives, biphenyl (BP), o-terphenyl (OT), and m-terphenyl (MT) have been investigated for improving the cyclability of cathode materials like LiCoO2 and LiMn2O4. The effect of these additives is correlated to the properties of the surface film on the cathode electrode, which comes from the decomposition of the additives at high potentials. (C) 2004 The Electrochemical Society.