Amount of free liquid electrolyte in commercial large format prismatic Li-ion battery cells

Abstract

The amount of free liquid electrolyte contained in commercial large format prismatic Li-ion battery cells was measured for both fresh and aged cells. Results show that cells can contain free liquid electrolyte in significant amounts - maximum average amount reaching ca. 18 g (> 15 ml) in fresh cells of some well-established manufacturers and ca. 39 g (ca. 35 ml) in fresh cells of less-well established manufacturers. Cycle-aged cells were found to contain significantly lower amount of free electrolyte at the end of their life in an electric vehicle (EV) compared to the fresh cells of the same type. Preliminary results suggest that calendar ageing does not seem to noticeably reduce the amount of free liquid electrolyte in Li-ion battery cells. Comparing our findings to the previously published quantitative evaluation of the toxicity of Li-ion battery electrolytes [5], it can be concluded that an accidental release of the free liquid electrolyte from a single large format Li-ion battery cell can be sufficient for the formation of potentially toxic atmosphere in enclosed spaces.