AbstractWe report the ionic conductivity studies of three different Ruddlesden‐Popper layered perovskite (RP‐LP) materials (Li2SrTa2O7, Li2SrNb2O7, and Li2CaTa2O7) in composites with poly (ethylene oxide) (PEO). For the first time, the lithium‐ion conduction pathway in the RP‐LP materials, of n=2 in AnA′BnO3n+1 general crystal structure, have been studied by using bond valence sum mapping. The results show a two‐dimensional lithium‐ion pathway. The temperature dependence of the conductivity is modelled by using a Vogel−Tamman−Fulcher (VTF)‐type relationship for PEO RP‐LP and pure PEO samples. The PEO RP‐LP composites deliver ionic conductivities in the range of 3.32 to 4.09×10−06 σ cm−2 at 80 °C, and their corresponding activation energies range from 6.37 to 7.01 kJ mol−1 at the calculated temperature slope range of 50 to 80 °C. They also deliver appreciable lithium transference numbers in the range of 0.20 to 0.58 at 30 °C and an excellent wide potential window stability of 4 V.