Investigation of Li /  SO 2 Cell Chemistry and Hazards by Spectroscopy and Accelerating Rate Calorimetry

Accelerating rate calorimetry (ARC) has been used to define the thermal and pressure behavior of cells during overdischarge as a function of cell balance and operating temperature. Lithium‐limited cells are shown to be intrinsically safe while cells containing excess lithium at end of life have been shown to be capable of undergoing thermal runaway through a series of coupled reactions. The most serious thermal hazards occurred upon overdischarge at low temperature. ARC analyses of cell components, in situ FTIR analyses, and mass spectroscopic analyses of discharged cathodes have been used to investigate the chemistry associated with the thermal behavior of cells. As expected, the lithium/acetonitrile reaction and the thermal decomposition of lithium dithionite contribute to the thermal runaway process observed in cells overdischarged at ambient temperature. In addition, however, two other reactions have been identified; one initiating at approximately 140°C involving lithium and the electrolyte solution and another initiating at approximately 190°C which is believed to involve lithium and the decomposition products of lithium dithionite. Further investigations are needed to elucidate the chemistry involved in the low temperature safety problems.