Conducting polymer films grown from mixed solutions of biphenyl (BP) and cyclohexylbenzene (CHB) have been evaluated in 1.0 M LiClO4 in propylene carbonate as an overcharge protecting agent. When the polymer films electrochemically deposited in situ during overcharging processes are overoxidized, the battery cathodes become passivated, lower the current flow, and act as an overcharge inhibitor. Effects of varied compositions of BP and CHB have been examined by monitoring the rate of film growth by potentiodynamic, electrochemical quartz crystal microbalance, and electrochemical impedance spectroscopic measurements. The results indicate that a mixed polymer film prepared from a solution containing 0.05 M BP and 0.15 M CHB provided the best performance in that its passivated form displayed the largest electrical resistance than films grown under other experimental conditions. (C) 2008 The Electrochemical Society.