A polytriphenylamine (PTPAn)-modified separator was prepared simply by impregnating triphenylamine monomers into a commercial Celgard separator and in situ polymerizing the monomers into electroactive phase by oxidant ozone. This type of electroactive separator can transform from an insulating state to a conductive state at overcharged voltage of similar to 3.7 V (vs. Li+/Li) and act as a self-actuating potential-switchable separator for overcharge protection of LiFePO4/C Li-ion batteries. The experimental results demonstrated that this electroactive separator can reversibly control the cell's voltage at the safe value less than 4.15 V at high rate overcharge of 2C current without obvious negative impact on the normal charge-discharge performances of the commercial LiFePO4/C batteries even at prolonged overcharge cycling, showing a potential application in 3.6 V-class lithium-ion batteries. (C) 2008 Elsevier B.V. All rights reserved.