Great improvement in the safety of lithium ion battery is needed to meet the full requirements of electric vehicles(EV). Among these safety hazards, overcharge has long been recognized as a primary concern because it can lead to dangerous events such as thermal runaway,fire and explosion. The electroactive polymer approach utilizes the unique electronic properties of the polymers to form a reversible resistive shunt between the current collectors and protect the cell from overcharging. The process is self-activated by voltage, and it does not pose interference during normal cell charge and discharge.

In this work, we report the recent progress in cell overcharge protection for high-energy-density lithium ion batteries. By incorporating the reversible electroactive polymers into highly porous membrane separators, we demonstrate that the composites can provide reversible and stable overcharge protection for a variety of cell chemistries. The results for the protection of Li_1.05Mn_1.95O₄ or LiNi_0.8Co_0.15Al_0.05O₂ electrode will be discussed. Both cells were protected at a steady state voltage of 4.5 V for well over 100 cycles.