Overcharge Protection for 4 V Lithium Batteries at High Rates and Low Temperatures

Overcharge protection for 4 V Li_1.05Mn_1.95O₄/lithium cells at charging rates in excess of 1 mA/cm² (3C) and at temperatures of as low as −20°C was achieved using a bilayer separator coated with two electroactive polymers. High rate and low temperature overcharge protection and discharge performance were improved by employing a design in which the polymer-coated portion of the separator is in parallel with the cell rather than between the electrodes. The effects of different membrane supports for the electroactive polymers were also examined.