Ac impedance analysis of lithium ion battery under temperature control

Ac impedance spectra of electrochemical systems are analyzed by considering adequate equivalent circuits, while the differentiation of responses for each elemental step is sometimes difficult. In this study, enlarged impedances were measured by lowering the temperature of a lithium ion battery (LIB) to make the separation of confusing responses easier. The impedance spectra obtained at the temperatures between -20 °C and 20 °C showed drastic change in sizes with shifting of the characteristic frequency. The analysis of impedance spectra using an equivalent circuit revealed changes in resistance of each component and shifting of the time constant for each elemental step. The frequency domain of impedance response of solid electrolyte interphase (SEI) was found to overlap with that of the inductive component of the outer electric lead at 20 °C in our study. The impedance measurement at the low temperatures is considered to be useful for the detection of the SEI and the accurate evaluation of LIB.