A universal strategy towards high–energy aqueous multivalent–ion batteries

Rechargeable multivalent metal (e.g., Ca, Mg or, Al) batteries are ideal candidates for large–scale electrochemical energy storage due to their intrinsic low cost. However, their practical application is hampered by the low electrochemical reversibility, dendrite growth at the metal anodes, sluggish multivalent–ion kinetics in metal oxide cathodes and, poor electrode compatibility with non–aqueous organic–based electrolytes. To circumvent these issues, here we report various aqueous multivalent–ion batteries comprising of concentrated aqueous gel electrolytes, sulfur–containing anodes and, high-voltage metal oxide cathodes as alternative systems to the non–aqueous multivalent metal batteries. This rationally designed aqueous battery chemistry enables satisfactory specific energy, favorable reversibility and improved safety. As a demonstration model, we report a room–temperature calcium-ion/sulfur| |metal oxide full cell with a specific energy of 110 Wh kg–1 and remarkable cycling stability. Molecular dynamics modeling and experimental investigations reveal that the side reactions could be significantly restrained through the suppressed water activity and formation of a protective inorganic solid electrolyte interphase. The unique redox chemistry of the multivalent–ion system is also demonstrated for aqueous magnesium–ion/sulfur||metal oxide and aluminum–ion/sulfur||metal oxide full cells.