Ionic Conductivity of Ruddlesden‐Popper Layered Perovskites (Li 2 SrTa 2 O 7 , Li 2 SrNb 2 O 7 , and Li 2 CaTa 2 O 7 ) with Poly (ethylene oxide) as a Composite Solid Electrolyte

We report the ionic conductivity studies of three different Ruddlesden‐Popper layered perovskite (RP‐LP) materials (Li 2 SrTa 2 O 7 , Li 2 SrNb 2 O 7 , and Li 2 CaTa 2 O 7 ) 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 A n A′B n O 3 n +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.