A practical guide for separator selection, characterization, and electrochemical evaluation for supercapacitor application

Supercapacitors are widely acknowledged as crucial devices for storing and converting electrical energy, alongside batteries and fuel cells. Their ability to rapidly charge and discharge, typically within seconds or even milliseconds, makes them ideal for high-power applications. This feature provides significant advantages for electric vehicles, such as regenerative braking and hill-climbing, where quick energy transfer is essential. To optimize the power performance of supercapacitor cells, it is essential to focus not only on the active material but also on the inactive components, including binders, conductive agents, and separators. The latter functions as an electronic insulating barrier between the cathode and the anode while facilitating optimal ionic transport across the cell. Therefore, particularly in high-power devices, selecting suitable separators is crucial to ensure fast charging kinetics and minimal cell resistance. Despite significant progress in developing high-power electrode materials, relatively few studies have been dedicated to membranes and their impact on the cell's electrochemical behavior. Herein, we provide a practical guide for choosing appropriate membranes for high-power supercapacitor applications. A comprehensive description of the main characterization methods for reliable evaluation of separators, alongside practical experimental examples, is given below. A special discussion is devoted to the evaluation of membrane impedance by various analytical approaches.