Electrical properties of ionic liquid and double perovskite-type metal oxide composites - A new method to tailor grain-boundary impedance of ceramic electrolytes

Huge grain-boundary impedance (GBI) contribution to the total conductivity in solid state (ceramic) polycrystalline and non-crystalline (amorphous) electrolytes, especially at low temperatures, is one of the major concerns in numerous electrochemical solid state ionic devices (SSIDs), including solid oxide fuel cells, gas sensors, gas pumps, and all-solid-state batteries. Decreasing the GBI is anticipated to improve the total conductivity that may enhance the performance by decreasing the ohmic loss in SSIDs. As a proof-of-concept, well-known ceramic proton conducting Ba₃Ca _1.18Nb_1.82O_8.73 (BCN 18) was used to demonstrate a facile method to eliminate/decrease the GBI, which differs from the traditional strategies, including wet chemical methods that seem to rather fail to completely eradicate GBI, especially at low temperatures. The present work shows that BCN 18 treated with fast ion conducting ionic liquids (IL), 1-butyl-3-methylimidazolium tetrafluoroborate (C₈H ₁₅BF₄N₂) (BMImBF₄), exhibits a total (bulk + grain-boundary) conductivity of 10^{- 5} S cm^{- 1} at 23 C in air under ambient condition which is about seven orders of magnitude higher than that of BCN18 and about three orders of magnitude lower than that of pure IL BMImBF₄.