Pseudo-solid-state electrolytes utilizing the ionic liquid family for rechargeable batteries

The advent of solid-state electrolytes has unearthed a new paradigm of next-generation batteries endowed with improved electrochemical properties and exceptional safety. Amongst them, Li-stuffed garnet type oxides, sulfides, and NASICON type solid-state electrolytes have emerged with fascinating ionic conductivity, electrochemical stability, and high safety standards, besides creating an avenue for using metal anodes to maximize energy density. However, the actual performance of solid-state electrolytes is heavily encumbered by unexpected metal dendrite formation and typically manifests high resistances between the metal electrodes/solid-state electrolytes or grain boundaries, thereby restricting their practical applications. Recent studies have reported several novel approaches, such as modifying solid-state electrolytes using ionic liquids to form the so-called "pseudo-solid-state electrolytes". This class of electrolytes encompassing materials such as ionogel using ionic liquids and ionic plastic crystals has been gaining rekindled interest for their unique properties that promise great strides in battery performance and diversified utility. This minireview paper summarizes recent progress in pseudo-solid-state electrolytes utilizing ionic liquids, highlighting their fundamental properties while elaborating expedient design strategies. The realistic prospects and future challenges associated with developing pseudo-solid-state electrolyte materials present an insight into their properties to inspire far-reaching exploration into their material characteristics and functionalities.