Switchable resistance conducting-polymer layer for Li-ion battery overcharge protection

Abstract Overcharge of Li-ion cells is one of the causes of severe safety problems. Despite many efforts to prevent development of adverse processes at overcharge conditions by using Battery Management Systems, chemical protection remains the most fail-safe solution. In the present work we describe novel approach to overcharge protection of Li-ion cells, which is provided by use of electrically conductive polymer that change electrical conductivity from conductive to insulating stage. The layer of such polymer, deposited between the LiFePO4 -based cathode material and current collector, increase the electrode resistance in more than 20 times when the cell voltage exceeds 4.2 V, acting as a chemical circuit breaker. At 5 V overcharge it allows reversible charge-discharge of the cell without developing of adverse process, while at 6 V overcharge it terminates the cell operation before electrolyte decomposition starts, reducing amount of evolved gases in 4 times compared to non-protected cell.