The mechanism of in‐homogeneous mass transfer process of separators in lithium‐ion batteries

Abstract The liquid‐phase mass transport is the key factor affecting battery stability. The influencing mechanism of liquid‐phase mass transport in the separators is still not clear, the internal environment being a complex multi‐field during the service life of lithium‐ion batteries. The liquid‐phase mass transport in the separators is related to the microstructure of the separator and the physicochemical properties of electrolytes. Here, in‐situ local electrochemical impedance spectra were developed to investigate local inhomogeneities in the mass transfer process of lithium‐ion batteries. The geometric microstructure of the separator significantly impacts the mass transfer process, with a reduction in porosity leading to increased overpotentials. A competitive relationship among porosity, tortuosity, and membrane thickness in the geometric parameters of the separator were established, resulting in a peak of polarization. The resistance of the liquid‐phase mass transfer process is positively correlated with the viscosity of the electrolyte, hindering ion migration due to high viscosity. Polarization is closely related to the electrochemical performance, so a phase diagram of battery performance and inhomogeneous mass transfer was developed to guide the design of the battery. This study provides a foundation for the development of high stability lithium‐ion batteries.