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 Ba3Ca1.18Nb1.82O8.73 (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 (C8H15BF4N2) (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.

► Ceramic proton conductors and ionic liquid composites were prepared by sonication.
► BMImBF4 treated BCN perovskite shows total conductivity of 10− 5 S cm− 1 at 23 °C.
► Total conductivity of composite was found to be stable over the extended period.
► Ionic liquids seem to eliminate the grain-boundary impedance of solid electrolytes.