Unusual overcharge tolerance behavior in gelled polymer lithium ion cells

Unusual overcharge tolerance behavior was observed in Electrochem’s polymer lithium ion cells. The cells could be overcharged up to several times 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 an oxidation–reduction shuttle mechanism. A correlation between the apparent overcharge tolerance capability and anode to cathode capacity ratio was found. This observation suggested that the observed overcharge tolerance behavior was caused by non-dendritic lithium deposition on the carbon anode surface during overcharge. It was hypothesized that this lithium deposition created some weak electronic conducting paths through which part of the overcharge current was bypassed. Results of surface analyses on both fully charged and overcharged anodes were consistent with the above hypothesis.