Dynamic Electrochemical Impedance Spectroscopy Measurement for Operando State Monitoring of Lithium-Ion Batteries

Electrochemical impedance spectroscopy (EIS) is a powerful technique for characterizing physical and chemical processes occurring in lithium-ion batteries (LIBs) to monitor their operational states. However, the traditional EIS measurement approach has three drawbacks: the need for professional test equipment, slow measurement speed, and the requirement to ensure that the LIB maintains a quasi-steady state during testing. These limitations make it impossible to monitor the states of the LIBs under operating conditions through EIS, thereby restricting its practical application. To overcome the above drawbacks, this article injects wideband disturbances into the LIB via a bidirectional dc/dc converter. Moreover, a fast dynamic EIS (DEIS) measurement approach is proposed, which can obtain credible test results in the frequency range of 1 Hz–2 kHz within one disturbance period when the LIB is charging or discharging. The residuals obtained by the Kramers–Kronig (K–K) test are unbiased and within 0.5% over the entire frequency range, indicating the high quality of the DEIS measurement results. Subsequently, the relationship between DEIS and the state of LIBs is explored by experiments and electrochemical theoretical analysis. It is found that the high-frequency part of DEIS can be used to estimate the internal temperature, while the low-frequency part is suitable for reflecting the lithium plating onset. The experimental results show that using the measured DEIS can accurately estimate both the state of charge (SOC) when lithium plating occurs in LIBs and the internal temperature.