A composite electroactive polymer membrane capable of providing a reversible self-activating current shunt for overcharge protection of 4.20 V-class lithium batteries and lithium ion batteries was（described.） The membrane is composed of a p-polyphenyl（PPP） layer and a polyaniline（PAn） layer

and can be p-doped at high oxidation potentials of 4.30 V into conductive phase and de-doped at normal operating voltages into an electronically isolating separator

functioning as a potential-sensitive switch for controlling the battery voltage at charging.The experimental results from the laboratory Li/LiMn

2

O

4

cells demonstrate that this composite membrane can reversibly control the battery voltage at required value at prolonged overcharge and has no negative impact on the battery performances at normal charge-discharge conditions.