Remark on Conductivity Measurements: The Special Case of Single-Ion Conducting on Blocking Electrodes

Other than dual-ion conducting (DIC) electrolytes, single-ion conducting (SIC) electrolytes do not suffer from concentration polarization at the electrode|electrolyte interface but are compromised by poor overall conductivities. In this work, the battery relevance of an established conductivity measurement method, i.e., impedance spectroscopy, on blocking electrodes (i.e., no ion transfer between an electrode and electrolyte, e.g., stainless steel) is reconsidered. This setup is suitable for DIC electrolytes as the impedance can be solely attributed to intrinsic electrolyte properties, contrary to non-blocking electrodes (ion transfer between an electrode and electrolyte, e.g., Li), where additional/ interfering impedances from interphases would arise. Interestingly, it is the opposite for SIC electrolytes where the total impedance is even higher on blocking electrodes. The required anion movement for charge compensation is simply not possible in SIC electrolytes and leads to an insulating behavior, thus questioning conductivity interpretations. This problem is absent on non blocking electrodes as the charge can be solely compensated by Li+ movement, consequently rendering them more suitable for conductivity measurements of SIC electrolytes. Nevertheless, given the poor Li passivation of the SIC electrolyte, which challenges impedance measurements, cells with more suitable electrodes are finally demonstrated.