Impact of Lithium-Ion Battery Separators on Gas Evolution during Temperature Abuse

Separators in lithium-ion batteries are considered to be (electro-)chemically inert to typical operating conditions. Yet, temperature abuse tests at elevated temperatures of ca. 60 to 132 °C show that the choice of separator material has a decisive influence on battery behavior and degradation. Using online electrochemical mass spectrometry, we analyzed the evolution of cell voltage and gas products during and after thermal abuse for different separators. Polypropylene and polytetrafluoroethylene seem stable, whereas glass fiber and polyethylene terephthalate separators were reactive and caused additional gas release. Polyethylene terephthalate produced significantly more gas, and the separator failed mechanically, causing unreproducible and drastic performance losses. The CO2 content of polyethylene terephthalate separator is four times higher than that of glass fiber. Yet, a five times higher amount of POF3 was detected for glass fiber. The evolved gas amounts of CO2 or POF3 were modest for polypropylene and polytetrafluoroethylene.