“Water-in-salt” electrolyte enhanced high voltage aqueous supercapacitor with all-pseudocapacitive metal-oxide electrodes

The Applications of Water‐in‐Salt Electrolytes in Electrochemical Energy Storage Devices

“…It is worth noting that the redox potentials of redox couples may be removed in various electrolytes, in addition, the exploration of high‐capacity pseudocapacitive materials applying WISEs is significant due to the lack of them currently. [ 24,106 ]…”

“…assembled a pseudocapacitance capacitor using a Fe 3 O 4 as cathode, a MnO 2 as anode and 21 m LiTFSI as the WISE. [ 24 ] The SC reached a working voltage window of 2.2 V, resulting from the wide ESW of WISE and low electrocatalytic activity of Fe 3 O 4 and MnO 2 in WISE. And the SC achieved the maximum specific energy density of 35.5 Wh kg −1 at 151.9 W kg −1 .…”

“…It is worth noting that the redox potentials of redox couples may be removed in various electrolytes, in addition, the exploration of high-capacity pseudocapacitive materials applying WISEs is significant due to the lack of them currently. [24,106] Exploring new mixed electrolyte systems to improve the performances of WISEs. It can be seen from the studies above that the decreased viscosity and increased ionic conductivity will be achieved when a certain amount of organic solvents are added to WISEs.…”

“…Benefiting from these advantages, WISEs have been widely used in batteries and supercapacitors (SCs). [ 2,15,19–24 ] Obviously, there are some disadvantages of WISEs hindering their practical applications compared to traditional aqueous electrolytes and organic electrolytes: 1) The high viscosity and low conductivity compared with the traditional dilute electrolytes will deteriorate the rate performance of the devices employing WISEs; 2) the high cost of WISEs caused by high concentration and ionic liquids commonly used is a key factor limiting their industrial application; 3) the strong corrosivity of some WISEs resulting from the high concentration puts forward higher requirements for the current collectors, diaphragms, and packaging materials; 4) WISEs have poor wettability to the electrodes, which will increase the impedance of the devices, deteriorate the cycling performance and lead to the longer time for the electrolyte injection process; 5) the low temperature application of WISEs is limited by the salting‐out because of the decrease of solubility at lower temperatures. [ 25–30 ] Therefore, the dedicated discussion on some studies focusing on solving these shortcomings of WISEs will be conducted in Section 3.…”

Metal oxide-based supercapacitors: progress and prospectives

“…3a-c . 53 Moreover, Yu et al summarized some key tips on supercapacitors based on "water-in-salt" electrolytes. 54 Although the working potential window of the reported WIS systems has improved dramatically, environmental and economic concerns related to their practical applications still need to be solved.…”