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.

Reliable Organic Carbonyl Electrode Materials Enabled by Electrolyte and Interfacial Chemistry Regulation

“…The rate performance of carbonyl electrodes can be influenced by salt concentration, additives, and interfacial chemistry. For example, the PTCDA electrode exhibits capacities of approximately 90, 53, and 17 mAh g –1 at 10 A g –1 in 1, 0.5, and 0.2 M NaClO 4 aqueous electrolytes, respectively (Figure a) . The enhanced rate performance of PTCDA in electrolytes with higher concentrations is attributed to the higher availability of the Na + ions near the electrode surface and the higher conductivity.…”

“…For example, the PTCDA electrode exhibits capacities of approximately 90, 53, and 17 mAh g −1 at 10 A g −1 in 1, 0.5, and 0.2 M NaClO 4 aqueous electrolytes, respectively (Figure 5a). 63 The enhanced rate performance of PTCDA in electrolytes with higher concentrations is attributed to the higher availability of the Na + ions near the electrode surface and the higher conductivity. Of course, considering that the viscosity of the electrolyte increases with the concentration, the higher the concentration of the electrolyte is not the better for the rate performance of electrodes.…”

“…The EIS data and fitted curves for (e) DME and (f) EC/DEC electrolytes after different cycles. (a) Reproduced with permission from ref . Copyright 2023, Wiley-VCH.…”

Status and strategies of electrolyte engineering for low-temperature sodium-ion batteries

“…, the stability of sodium ion embedded in the cathode is not determined by its concentration but by the properties of its anti-ion. 90 Through electrochemical analysis and theoretical calculation, they proved that the anode performance is mainly dominated by the anionic solvation characteristics. Therefore, it is possible to achieve aqueous sodium-ion batteries with excellent performance at low temperatures by selecting the appropriate anions.…”

Electrolyte-Induced Morphology Evolution to Boost Potassium Storage Performance of Perylene-3,4,9,10-tetracarboxylic Dianhydride

“…Electrolytes play an important role in the dissolution of organic electrode materials and the solvation/desolvation of charge carriers. − Electrolyte engineering has been considered an effective strategy to improve the electrochemical performance of organic materials for PIBs. − For example, both Lu’s and Song’s groups demonstrated that the electrochemical performance of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) can be significantly elevated by using a high-concentration electrolyte. Bai et al achieved a superior cycling stability (only a capacity decay of 20 mAh g –1 after 320 cycles) of 3,4,9,10-perylenetetracarboxylic diimide in an ether-based electrolyte .…”