Dilute Aqueous Hybrid Electrolyte with Regulated Core‐Shell‐Solvation Structure Endows Safe and Low‐Cost Potassium‐Ion Energy Storage Devices

Abstract

High‐concentration “water‐in‐salt” (WIS) electrolytes with the wider electrochemical stability window (ESW) can give rise to safe, non‐flammable, and high‐energy aqueous potassium‐ion energy storage devices, thus highlighting the prospect for applications in grid‐scale energy storage. However, WIS electrolytes usually depend on highly concentrated salts, leading to serious concerns about cost and sustainability. Here, an aqueous low‐concentration‐based potassium‐ion hybrid electrolyte is demonstrated with the regulated core‐shell‐solvation structure by using an aprotic solvent, i.e., trimethyl phosphate, to limit the water activity. This aqueous hybrid electrolyte has a low salt concentration (1.6 mol L−1) of potassium trifluoromethanesulfonate but with an expanded ESW up to 3.4 V and the nonflammable property. Based on this dilute aqueous hybrid electrolyte, electrochemical double‐layer capacitors are capable of working within a large voltage range (0–2.4 V) at a wide range of temperatures from −20 to 60 °C. An aqueous potassium‐ion battery consisting of an organic 3,4,9,10‐perylenetetracarboxylic diimide anode, Prussian blue K1.5Mn0.61Fe0.39[Fe(CN)6]0.77·H2O cathode and this dilute aqueous hybrid electrolyte can operate well at rates between 0.2 and 4.0 C and deliver a high energy density of 66.5 Wh kg−1 as well as a durable cycling stability with a capacity retention of 84.5% after 600 cycles at 0.8 C.

Reconstructing Hydrogen Bond Network Enables High Voltage Aqueous Zinc‐Ion Supercapacitors

“…The viscosity and conductivity of the electrolyte were compared, (Figure 1b and 1c) and it was observed that the addition of additives resulted in a decrease in ion conductivity. Aqueous solutions are known to have a higher ion conductivity than other solutions, and the presence of additional solvent molecules may be obstacles on the transmission path, [21] thereby interfering with the rapid transmission of ions. The viscosity test results showed that the presence of DMF did not significantly change the viscosity of the solution, possibly due to its strong solvating ability and water‐miscibility.…”

Progress of Prussian Blue and Its Analogues as Cathode Materials for Potassium Ion Batteries

“…On the other hand, most of the organic-based additives can undermine the safety and environmental friendliness of aqueous batteries. [47] In this context, a new dilute aqueous hybrid electrolyte was developed by Chen et al [47] It has a core-shell solventized structure consisting of a low salt concentration (1.6 M potassium trifluoromethanesulfonate) and broke the interaction between water molecules by using a nonprotonic solvent (trimethyl phosphate) with a wide electrochemical stability window (3.4 V) as well as high safety (Figure 5j). The PIB consisting of a K 1.5 Mn 0.61 Fe 0.39 [Fe-(CN) 6 ] 0.77 • H 2 O cathode and this dilute water mixed electrolyte could work well at 0.2 to 4 C and provided a high energy density of 66.5 Wh g À 1 .…”

“…Copyright (2023), with permission from Elsevier Inc. (j) Electrochemical stability window for various electrolytes and enlarged views of the regions corresponding to the potentials for hydrogen and oxygen evolutions, respectively. Reproduced from ref [47]. Copyright (2023), with permission from Wiley-VCH GmbH.…”

Unveiling Organic Electrode Materials in Aqueous Zinc-Ion Batteries: From Structural Design to Electrochemical Performance

“…Importantly, the ionic conductivity of aqueous electrolytes is two orders of magnitude higher than that of non-aqueous electrolytes [ 6 – 8 ]. So far, various lithium-rich alkali metal cations [ 9 – 12 ] (such as Na + and K + ) [ 13 ] and multivalent charges [ 14 – 18 ] (such as Mg 2+ , Al 3+ , and Zn 2+ ) have been developed. Redox reactions in multivalent ionic systems, which involve multiple electrons, can potentially achieve higher energy densities [ 19 – 21 ].…”