Is “Water in Salt” Electrolytes the Ultimate Solution? Achieving High Stability of Organic Anodes in Diluted Electrolyte Solutions Via a Wise Anions Selection

Abstract

The introduction of the water‐in‐salt (WIS) concept, using highly concentrated electrolyte solutions to prevent water splitting and widen the electrochemical stability window, has greatly influenced modern aqueous batteries. The successful implementation of these electrolyte solutions in many electrochemical systems shifts the focus from diluted to WIS electrolyte solutions. Considering the high costs and the tendency of these nearly saturated solutions to crystallize, this trend can be carefully re‐evaluated. Herein we show that the stability of organic electrodes comprising the active material perylene‐3,4,9,10‐tetracarboxylic dianhydride (PTCDA), is strongly influenced by the solvation character of the anions rather than the concentration of the electrolyte solution. Even though the charging process of PTCDA involves solely insertion of cations (i.e., principal counter‐ions), surprisingly, the dominant factor influencing its electrochemical performance, including long‐term electrode stability, is the type of the co‐ions (i.e., electrolytic anions). Using systematic electrochemical analysis combined with theoretical simulations, we show that the selection of kosmotropic anions results in fast fading of the PTCDA anodes, while a selection of chaotropic anions leads to excellent stability, even at electrolytes concentrations as low as 0.2M. These findings provide a new conceptual approach for designing advanced electrolyte solutions for aqueous batteries.

To what extent do anions affect the electrodeposition of Zn?

“…The ability of the hydrophobic perchlorate anions to push away water molecules from the electrode interface and therefore to increase the relative concentrations of both cations and anions was demonstrated for NaClO 4 electrolyte solutions as well. 31…”