High frequency impedance characteristics of cylindrical lithium-ion cells: Physical-based modeling of cell state and cell design dependencies

Abstract

High frequency (HF) properties of lithium-ion (Li-ion) batteries receive growing attention, as an increasing number of highly dynamic loads are present in today's hybrid or battery electric vehicles (HEV, BEV). In this paper, we address the need for a better understanding of the HF characteristics of cylindrical Li-ion cells. First in literature, the impact of cell design, ambient temperature and state of charge (SOC) is investigated in a uniquely wide frequency range from 1 kHz to 300 MHz. Impedance measurements performed on eight different 18650 Li-ion cells show a strong correlation with the cell geometry including cell design (high power, high energy cell) and tab positioning along the current collectors. Moreover, the impedance response of the cells varies with temperature above 1 MHz indicating an increasing contribution of ionic current flow as the inductive reactance of the jelly roll becomes larger. SOC variations indicate only slight impedance changes below 1 MHz, most likely due to electrode volume change. The results are summarized in a physical-based HF battery model, which can be used for simulating highly dynamic battery applications such as battery power line communications (PLC) and impulsive noise investigations on the automotive high voltage (HV) power train.