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

Rechargeable multivalent metal (e.g., Ca, Mg, Al) batteries are promising for large-scale energy storage due to low cost but face poor reversibility, dendrite growth at metal anodes, sluggish multivalent-ion kinetics in metal oxide cathodes, and incompatibility with non-aqueous electrolytes. This work reports aqueous multivalent-ion batteries that pair concentrated aqueous gel electrolytes with sulfur-containing anodes and high-voltage metal oxide cathodes as alternatives to non-aqueous systems. The designed aqueous chemistry provides satisfactory specific energy, favorable reversibility, and improved safety. A room-temperature aqueous calcium-ion/sulfur|metal oxide full cell achieves 110 Wh kg−1 specific energy with remarkable cycling stability. Molecular dynamics and experiments reveal suppressed side reactions via reduced water activity and formation of a protective inorganic solid electrolyte interphase. The unique redox chemistry is further demonstrated in aqueous magnesium-ion/sulfur||metal oxide and aluminum-ion/sulfur||metal oxide full cells.