Using potentiometric detection of lithium ions with a rotating ring disc electrode (RRDE), we report for the first time the simultaneous direct measurement of lithium ion fluxes for two experiments: a) O-2 reduction in LiPF6 DMSO electrolyte and b) insertion and release of Li+ into and from LiMn2O4 spinel structure in contact with aqueous Li+ ion solution. The theory of potentiometric RRDE developed for local pH measurement (Albery, Calvo, 1983) could be applied to obtain quantitative description of lithium surface concentration which differs from the analytical concentration under current flow. The new potentiometric technique can detect mismatch of electron and lithium ion fluxes. (C) 2018 Elsevier Ltd. All rights reserved.