A Selective Interaction between Cation and Separator Membrane in Lithium Secondary Batteries

The presence of a specific Coulombic interaction between the lithium cation and the separator membrane in lithium secondary batteries was proven in this study, through evaluating the mobilities and microviscosities of the mobile ions in electrolyte solutions outside and within the separator membrane. The magnitude of the interaction depends on the solvation structure of the lithium cation, whose net charge is affected by the type and number of solvating species due to their shielding effect. Lithium cations with larger or more strongly coordinated solvating species are less attracted to the membrane; therefore, they display higher mobility compared to weakly solvated cations that are more strongly attracted to the membrane. We confirmed that the mobility of lithium cations in the separator membrane is controlled by their solvated structure in the electrolyte, as well as by the surface charge of the separator membrane. This knowledge could lead to the systematic design of battery performance appropriate for the battery loading system.