The processes of ionic transport in passivating layers on the surface of the lithium electrode in solutions based on thionyl chloride, propylene carbonate and y-butyrolactone have been studied by means of pulse electrochemical methods. The data obtained are quantitatively described by a model which takes into account transport of both the intrinsic mobile lithium ions of the passivating layer and lithium ions injected into the passivating layer from the electrode or from the electrolyte solution under anodic or cathodic current directions, respectively. The values of mobility and concentration of mobile lithium ions in passivating layers formed on lithium in various solutions under open-circuit conditions have been determined. Introdmction On the surface of lithium in electrolytes used in Li batteries, passivating layers (PL) are formed which, in a first approximation, may be considered as thin nonporous films of Li-conducting solid electrolytes [l]. Kinetics of electrode processes at the Li/ nonaqueous-solution interface which was denominated by Peled [l, 23 as 'solid-electrolyte interphase' (SEI) is determined by peculiarities of the ionic transport in PL [l-4]. However, until recently the question concerning a model which would quantitatively describe the transport of ionic carriers in PL on Li for a wide range of variations of current densities and electrode polarizations remained open. In the present work, studies of the ionic transport through SEI were performed using the method of single galvanostatic pulses. Polarization j-E curves on Li and its low-melting alloys were measured after ageing (storing) the electrode being studied in a solution under open-circuit conditions. The Li alloys had been obtained by the method of cathodic intrusion. A thin Li wire placed in the vicinity of the working electrode surface served as a reference electrode. The following solutions were used: 1 M LiiCI, in thionyl chloride (TC), 1 M LiClO, in propylene carbonate (PC) and in PC mixtures with dimethoxyethane (DME),