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Water-in-Salt Electrolytes for Dual-ion Batteries
Zafar, Zahid Ali ; Červenka, Jiří (advisor) ; Hassouna, Fatima (referee) ; Liu, Wei (referee)
Key Words: water-in-salt electrolytes; dual-ion batteries; anion-intercalation; chaotropic anion Abstract Aqueous electrolytes offer high intrinsic safety, high ionic conductivity, and low costs, which makes them very attractive for electrochemical energy storage systems (EESS). Nevertheless, their biggest bottleneck is the narrow electrochemical stability window (ESW) of water of 1.23V, beyond which water undergoes hydrogen and oxygen evolution reactions. This restricts the choice of electrode materials within the H2 and O2 evolution potentials and limits the achievable energy and power densities of aqueous-based EESS. For instance, aqueous multivalent aluminum- and zinc-based batteries promise high energy density due to the multivalent redox chemistry of metal- ions (Al3+ , Zn2+ ), but they exhibit much lower energy density owing to the small ESW of the aqueous electrolytes, which does not allow using high-voltage cathodes. In this thesis, the issue of the narrow ESW for these multivalent batteries has been addressed by using the concept of "water-in-salt" electrolytes (WiSE). This concept is based on using high concentrations of salts in aqueous electrolytes, which results in strong modifications of the water structure and widening of the ESW by restricting the free water content in WiSE. More...
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