“Water-in-ionic liquid” solutions towards wide electrochemical stability windows for aqueous rechargeable batteries

Water in Protic Ionic Liquids: Properties and Use of a New Class of Electrolytes for Energy‐Storage Devices

“…[8] The use of water-in-ILs has been less investigated. [9] Most likely,t his is owing to the factt hat one of the prerequisites for the use of ILs in energy-storage devices is, as for any type of non-aqueous electrolytic solutions, av ery low water content.A samatter of fact, large amountso fw ater might have dramatic effects on the stability and cycle life of electrochemical devices. [10] For this reason,t he ILs used in LIBs and EDLCs typically contain less than 50-100 ppm of water.…”

High‐Voltage and Low‐Temperature Aqueous Supercapacitor Enabled by “Water‐in‐Imidazolium Chloride” Electrolytes

“…Thus,s upercapacitors are promising for rapid response in peak shavinga nd grid stabilization. [15] By adding molecular solvents, such as water or acetonitrile, into ionic liquids, [16][17][18] the viscosity can be greatly reduced and the ion conductivity can be accordingly enhanced with as acrifice in the electrochemical stability window of the electrolytes. Besides the selection and optimization of electrode materials towards high availablesurface areas and porosities, [5][6][7][8][9][10] great efforts have been made to tailor the electrolyte formulation including the selection of types of solvents and electrolyte ions.…”

“…[11][12][13] The amount of stored energy in supercapacitors can be increased by increasing the ion-accessible surfacea rea of the electrode materials. [16,17] It is considered that the fast ion transport rate, broad working voltage window,a nd al arge amount of electrostatically accumulated chargei na queous electrolytes can promote the energy storage performance of as upercapacitor. [14] However,t hey typically have poor ion conductivities, from about af ew mS cm À1 for ionic liquids to tens of mS cm À1 for conventionalo rganic electrolytes at room temperature.…”

“…Water as an atural alternative to the flammable organic solvents or highly viscous room-temperaturei onic liquidsi si deal for use as aw orking medium for electrochemical devices with the merits of intrinsic safety and fast transport for ionic species. [16,17] It is considered that the fast ion transport rate, broad working voltage window,a nd al arge amount of electrostatically accumulated chargei na queous electrolytes can promote the energy storage performance of as upercapacitor. However,i th as been al ongstanding challenge that water has an arrow electrochemical stability window (a sum of the thermodynamic value and kinetic overpotential).…”

“…It has been reported that most aqueous electro-lytes with asymmetric electrodesh ave amaximum energy density of about 30-70 Wh kg À1 . [35] Such ah ighe nergy density of the present electrolytes is associated with the high concentration of the electrolytei ons, high ion conductivity, [17] and high operating voltage. These values are much highert han those of a previously reported concentrated aqueous LiTFSI electrolyte, [23] and also higher than those with ionic liquid ([EMIm][TFSI]) in acetonitrile as electrolyte and porous biomass-derived graphene-based carbon (BGC, with as urface area of 3657 m 2 g À1 ) electrodes.…”