A comparison of the different broadband impedance measurement techniques for lithium-ion batteries

Electrochemical impedance spectroscopy (EIS) is a well-known technique that has been employed on various electrochemical cells in order to obtain their impedance spectra. Lithium-ion cells are some of these cells to which it has been applied. The impedance spectra obtained from EIS can be used to estimate various battery state of health (SOH) and state of charge (SOC) characteristics. The lengthy acquisition time associated with standard EIS makes it unsuitable for rapid on-line impedance measurements. Alternative methods that take a shorter time have therefore been proposed. This paper compares the spectra obtained by Harmonic Compensated Synchronous Detection (HCSD) broadband signal technique with EIS and a custom Broadband Impedance Spectroscopy (BIS) technique at different DC bias currents which mimic a real time load. The test cells are industry standard Nickel-Cobalt and Manganese Oxide (NCM) lithium-ion cells. The BIS technique is similar to HSCD in the selection of frequencies however the amplitude of the excitation broadband signal is varied to match the impedance magnitude response of the cell. Also, parameter extraction is performed on both EIS and BIS for fault detection purposes.