Safety of Aged Li-Ion Cells without Lithium Plating – An ARC-EIS Study

The thermal runaway behavior of commercial high-energy 18650 lithium-ion batteries with Si/graphite anodes and Ni-rich NMC cathodes was investigated by ARC-EIS, accelerating rate calorimetry (ARC) in combination with electrochemical impedance spectroscopy (EIS). The cells were cyclically aged at a rate of 1C and at 45 degrees C without Li plating. Aging was characterized electrochemically by Arrhenius plots of initial aging rates and differential voltage analysis (DVA). The effects of state of health (SoH) and state of charge (SoC) in ARC experiments were investigated regarding the onset of self-heating temperature TSH, venting temperature TVent, onset of thermal runaway temperature TTR, and mass loss. With the aim of early thermal runaway detection without temperature measurement, an ARC-EIS method is proposed. This approach is based on impedance changes during thermal runaway at different SoH and SoC. A correlation between TSH, indicating significant exothermic reactions, and different impedance values (Re(Z), phi(Z), and Nyquist integral) was observed for different SoH and SoC levels.