Low Melting Alkali-Based Inorganic Molten Salts as Battery Electrolytes

Lithium metal batteries (LMBs) promise high energy densities for electrified transport. Liquid electrolytes are currently state-of-the-art, but they are highly volatile and flammable and exacerbate safety concerns. Solid state batteries promise to address the safety concerns plaguing liquids but suffer from highly resistive electrode/electrolyte interfaces. In our work, we explore the use of low melting inorganic molten salts as electrolytes for LMBs. These electrolytes do not contain organic moieties and are not susceptible to the reactions that plague organic moieties in conventional ionic liquids and small molecule electrolytes. Furthermore, they are non-volatile and nonflammable, retaining the promise of solid-state systems. We show these electrolytes have high ionic conductivities at ~80°C, enable smooth lithium deposits, support high Coulombic efficiencies, and can support battery cycling. These inorganic molten salts with accessible melting temperatures open a new class of electrolyte media for both conventional and next generation battery chemistries.