Design of a portable electrochemical impedance spectroscopy measurement system based on AD5941 for lithium-ion batteries

Electrochemical impedance spectroscopy (EIS) is an important indicator of state of health (SOH) for Lithium-ion batteries (LIBs), but its measurement relies mainly on electrochemical workstations that are costly and cannot be used for on-site testing. This paper designs a portable EIS measurement system based on the high-precision impedance converter chip AD5941, which utilizes a wide-frequency constant current source as the excitation signal and detects the LIB's response voltage signal to obtain EIS data ranging from 0.1 Hz to 2 kHz. In addition, a software interface based on LabVIEW is developed for real -time graphically displaying the EIS information. EIS measurement experiments are performed on a NCR-18650B LIB at different charge states in both singlefrequency mode and frequency-sweep mode using the newly-designed EIS measurement system. The results show that in single-frequency mode, the impedance measurement error at 1 kHz is below 2.8 % compared with a standard single-frequency electrochemical impedance analyzer. In frequency-sweep mode, the Nyquist plot of the LIB is obtained at different charge states and exhibits good repeatability. Moreover, an effective equivalent circuit analysis of the EIS data was performed, which further substantiates the practical utility of the EIS system in providing valuable insights into the battery's electrochemical behavior. Compared to the traditional EIS measurement systems, the proposed EIS measurement system has the advantages of low cost, easy operation and portability, which exhibits promising prospects for on-site EIS applications.