The open circuit voltage (OCV) model of the solid polymer electrolyte (SPE)/salt system in lithium batteries is established by combining concentrated solution theory with the modified double lattice–non-random (MDL-NR) model which describes the non-ideal behavior of the salt activity in the polymer electrolyte. The activity parameters are obtained from the phase diagram for the given systems and used to describe the OCV of the corresponding systems with one additional parameter, transport number, t+0. The proposed model agrees very well with the OCV data for various PEO/salt systems.
