Universal strategy towards high–energy aqueous multivalent ion batteries

Abstract Non–aqueous rechargeable multivalent metal (Ca, Mg, Al, etc.) batteries are promising for large–scale energy storage due to their low cost. However, their practical applications face formidable challenges owing to low electrochemical reversibility and dendrite growth of multivalent metal anodes, sluggish kinetics of multivalent ion in metal oxide cathodes, and poor electrode compatibility of flammable organic electrolytes. To overcome these intrinsic hurdles, we develop aqueous multivalent ion batteries to replace the prevailing non–aqueous multivalent metal batteries by using wide–window super–concentrated aqueous gel electrolytes, the versatile high–capacity sulfur anodes, and high–voltage metal oxide cathodes. This rationally designed aqueous battery chemistry enables the long–lasting multivalent ion batteries featured with increased high energy density, reversibility and safety. As a demonstration model, a calcium ion−sulfur||metal oxide full cell exhibited a high energy density of 110 Wh kg–1 with outstanding cycling stability. Molecular dynamics modelling and experimental investigations revealed that the side reactions could be significantly restrained through the suppressed water activity and formation of protective inorganic solid electrolyte interphase in the aqueous gel electrolyte. The unique redox chemistry has also been successfully extended to aqueous magnesium ion and aluminum ion−sulfur||metal oxide batteries. This work will boost aqueous multivalent ion batteries for low−cost large–scale energy storage.