Overcharge tolerance phenomenon in polymer lithium ion cells

An unusual overcharge tolerance phenomenon was observed in Electrochem's polymer lithium ion cells. The cells could be overcharged up to several times of the nominal capacity without a significant increase in cell potential. Experimental studies were carried out to understand this phenomenon. Cyclic voltammograms on gelled solid polymer electrolytes indicated that this phenomenon did not originate from the oxidation-reduction shuttle mechanism. A correlation between the apparent overcharge tolerance capability and anode to cathode capacity ratios was found. This observation suggested that a portion of the overcharge current was bypassed by a weak electronic conducting path associated with nondendritic lithium deposition on carbon anode surfaces during overcharge.