Impedance Modeling and Analysis of Solid/Liquid Hybrid Electrolyte Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have been widely used in electric vehicles and energy storage applications. However, conventional LIB is mainly composed of flammable liquid electrolytes, which has significant potential safety hazards and thermal runaway risks. Reducing the liquid electrolyte content helps to improve the intrinsic safety of batteries. A solid/liquid hybrid electrolyte lithium-ion battery (SLE-LIB) with less electrolyte (i.e., quasi-solid-state LIB) has been chosen as a transition from liquid electrolyte LIBs to all-solid-state LIBs, and it has achieved commercial application. Although electrochemical impedance is a powerful technique for condition monitoring and degradation analysis of batteries, the impedance model considering solid/liquid hybrid electrolytes has not yet been well established. To fill this gap, this paper investigates the impedance variation of a commercial SLE-LIB under different aging cycles, temperatures, and state-of-charge conditions. An equivalent circuit model (ECM) of the impedance spectrum is established to analyze its features further. The analysis results identify the available impedance features and corresponding internal changes in SLE-LIBs for condition monitoring, e.g., the imaginary-part impedance, ECM parameters for temperature monitoring. Furthermore, three case studies are introduced based on the obtained impedance feature parameters. The results illustrate that the estimation errors of temperature and health state are less than 4%, and the proposed impedance features can be used for degradation analysis. The research results can provide references for condition monitoring and degradation analysis of SLE-LIBs.