In Situ Measurement of Ionic and Electronic Conductivities of Conductive Polymers as a Function of Electrochemical Doping in Battery Electrolytes

Conductive polymers are being studied increasingly as additives in lithium-ion batteries, supercapacitors, and other electrochemical devices due to their ability to conduct electrons and ions and serve as binders. These polymers undergo electrochemical doping during battery cycling along with swelling by the electrolyte solvent, whereupon the ionic and electronic conductivities change by several orders of magnitude. Measuring these large changes as a function of electrochemical doping, in situ, in a relevant electrolyte, has been a challenge thus far. We show that the ionic and electronic conductivity of a range of p-type and n-type conducting polymer thin films can be reliably measured as a function of electrochemical doping in relevant battery electrolytes by impedance spectroscopy on interdigitated electrodes by combining two separate electrode geometries. The results demonstrate the broad applicability of the methodology for gaining insights into the electrical conduction in polymers in relevant environments, particularly for batteries and other electrochemical devices.