A composite polymer membrane with reversible overcharge protection mechanism for lithium ion batteries

A composite electroactive polymer membrane capable of providing a reversible self-activating current shunt for overcharge protection of lithium ion batteries is described. The membrane is composed of p-polyphenyl (PPP) and polyaniline (PAn), and can be p-doped at high oxidation potentials 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-LiMn2O4 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. (c) 2005 Elsevier B.V. All rights reserved.