Surface films of lithium: an overview of electrochemical studies

There is considerable ambiguity in the literature about the importance of lithium surface film on the electrochemical reaction at the lithium/electrolyte interface. Some studies attribute the measured interfacial properties to the surface film on lithium alone and other studies consider the measured properties due entirely to electron-transfer reaction; while a few studies provide due recognition to both the surface film as well as the charge-transfer reaction. Literature on DC polarization and AC impedance spectroscopic studies of Li/non-aqueous liquid and solid polymer electrolyte interface is reviewed. Our electrochemical impedance spectroscopic studies of lithium/solid polymer electrolyte interface are analyzed using simple equivalent circuit models. The models include both the surface film properties as well as the electron-transfer reaction. The experimental results and reviewed literature support that both the surface film on lithium and the electron-transfer reaction are equally important interfacial phenomena, and should be considered simultaneously during an investigation.