The kinetic and thermodynamic studies of the intercalation process of lithium ions in the layered structure of niobium disulfide with a 3R-type modification were made. The standard free energy of lithium intercalation into the van der Waals gaps, AG!, was -218 kJ mol-' at 298 K in the range of x = O-l in Li,NbS,. Applying the thermodynamic model by Nagelberg and Worm11 [Nagelberg and Worrell, J. Solid St. Chem. 38, 321 (1981)] the interaction energy between the intercalated lithium ions was estimated as a model parameter. The chemical diffusion coefficients, 6, of lithium in the disulfide were measured as functions of the lithium composition and tern rature by using several kinds of electrolytes and an ac impedance method. The obtained values of fTe based on a geometrical surface area, were dependent on the lithium composition and the kind of electrolytes. The values of d obtained in 1 M LiClO, and 1 M LiAsF, solutions of propylene carbonate were found to be of the order of IO-* cm* s-' at 298 K for 0.2 < x < 0.6 in Li,NbS,, corresponding to a lithium self-diffusion coefficient of 10e9 cm* s-' order, while in the 1 M LiBF, solution a considerably lower values of B, 10-lo-lO-" cm* s-', were obtained for 0.1 < x < 0.5. The activation energies for the diffusion of lithium in the range of 20-30 kJ mol-' in the LiClO, and LiAsF, solutions, and in the range of 80-90 kJ mol-' in the LiBF, solution; the values in the former electrolytes are typical of diffusion in layered insertion materials, whereas in the latter electrolyte the kinetics may be controlled by the surface layer.