Reversible Aqueous Aluminum Metal Batteries Enabled by a Water-in-Salt Electrolyte

Aluminum (Al), the most abundant metallic element on the earth crust, has been reckoned as a promising battery material for its the highest theoretical volume capacity (8046 mAh cm-3). Being rechargeable in ionic liquid electrolytes, however, the Al anode and battery case suffer from corrosion. On the other hand, Al is irreversible in aqueous electrolyte with severe hydrogen evolution reaction. Here, we demonstrate a water-in-salt aluminum ion electrolyte (WISE) based on Al and lithium salts to tackle the above challenges. In the WISE system, water molecules can be confined within the Li+ solvation structures. This diminished Al3+-H2O interaction essentially eliminates the hydrolysis effect, effectively protecting Al anode from corrosion. Therefore, long-term Al plating/stripping can be realized. Furthermore, two types of high-performance full batteries have been demonstrated using copper hexacyanoferrate (CuHCF, a Prussian Blue Analogues) and LiNi0.8Co0.1Mn0.1O2 (NCM) as cathodes. The reversibility of Al anode laid the foundation for low cost rechargeable batteries suffering for large-scale energy storage.