IMPEDANCE SPECTROSCOPY OF LITHIUM ELECTRODES .1. GENERAL BEHAVIOR IN PROPYLENE CARBONATE SOLUTIONS AND THE CORRELATION TO SURFACE-CHEMISTRY AND CYCLING EFFICIENCY

This study involves impedance spectroscopy of Li electrodes in propylene carbonate solutions as a function of solution composition. The influences of the salt used, its concentration and the presence of contaminants such as H2O, O2, CO2 and propylene glycol, on the interfacial properties (as reflected by impedance spectroscopy) was measured. The advantage of this work over previous similar studies is that the electrode surfaces were prepared in situ in the solutions. The interfacial impedances measured in the various solutions were correlated to the previously studied Li surface chemistry and cycling efficiency in the same solutions. The ageing processes of the Li/solution interphase that could be followed by this technique are discussed in light of the Li surface chemistry in solutions. Modeling the electrical properties of the Li/solution interface by equivalent circuits is in agreement with the assumption that the interphase formed on lithium in solutions has a multilayer structure including a porous part on the solution side.