Lithium ion battery electrolyte degradation of field-tested electric vehicle battery cells – A comprehensive analytical study

The advancements in lithium ion battery (LIB) research extended its application to the automotive sector. Today, LIBs promise the potential of a greenhouse gas emission-reduced transportation sector to counteract climate change. However, challenging requirements on LIBs regarding fast-charging, energy density, safety and lifetime have to be met for costly battery-powered electric vehicles in order to achieve market implementation. Thus, the study of degradation mechanisms on cell level contributes to the understanding of aging phenomena and will enable improvements for future generations of LIBs. Electrolytes from LIB cells of field-tested electric vehicles of five global original equipment manufacturers were investigated by complementary analytical techniques, giving insights into the feasibility of analysis LIB electrolytes beyond lab-scale. The application of a whole series of established analytical techniques allows to comprehensively analyze LIB electrolytes and to provide reliable conclusions about the LIB cell chemistry. This study interrelates findings through elaboration of the status quo of aged LIB electrolytes after field-tests in terms of degradation and proposed pristine composition (reverse-engineering estimate) of the electrolyte for the first time.