Quasi-solid aqueous electrolytes for low-cost sustainable alkali metal batteries.

Aqueous electrolytes are highly important for batteries due to their sustainability, greenness, and low cost. However, the free water molecules react violently with alkali metals, rendering the high-capacity of alkali metal anodes unusable. Here, we confined water molecules in a carcerand-like network to build quasi-solid aqueous electrolytes (QAEs) with reduced water molecules' freedom and matched them with the low-cost chloride salts. The formed QAEs possess substantially different properties than liquid water molecules, including stable operation with alkali metal anodes without gas evolution. Specifically, the alkali metal anodes could directly cycle in a water-based environment with suppressed dendrites growth, electrode dissolution, and the polysulfide shuttle. The Li metal symmetric cells achieved long-term cycling over 7,000 h (and over 5,000/4,000 h for Na/K symmetric cells), and all Cu-based alkali metal cells exhibited a Coulombic efficiency of over 99%. Full metal batteries, such as Li||S batteries, attained high Coulombic efficiency, long life (over 4,000 cycles), and unprecedented energy density among water-based rechargeable batteries. This article is protected by copyright. All rights reserved.