Fast-cure ionogel electrolytes with improved ion transport kinetics at room temperature

Abstract

Fast-cure 1-ethyl-3-methylimidazolium trifluoromethanesulfonate based ionogels have been realised for the first time. The influence of curing temperature on the structure of ionogels and their performance as the electrolyte for electric doublelayer capacitors (EDLCs) has been investigated. Hybrid ionogels were synthesised via a non-hydrolytic sol-gel route and were fully gelled post heat-treating at 125, 150, 175 and 200 °C for 60 min with minimal shrinkage. Charge-transfer resistance (a rate-limiting parameter in cell kinetics during charge/discharge cycles) was reduced by ∼80% by increasing the heat-treatment temperature; this was partially attributed to the interlocking effect facilitated by high curing temperature. We report a maximum areal capacitance of 95 mF cm −2. Due to ∼40% increase in the penetrability coefficient of the ionic liquid, the electrode 'full' wetting time dropped from 48 to 5 h when the curing temperature was increased above 150 °C. These results were supported by SEM and Raman spectroscopy to characterise the effect of high temperature heat-treatment on the electrode-ionogel interface and the degree of electrode wetting by the ionic liquid. The fast-cure fabrication process for ionogels removes one of the major hurdles in their industrial application while the improved room temperature ion transport kinetics expands the potential application of ionic liquid-based electrochemical systems.

Sol-gel synthesis pathway and electrochemical performance of ionogels: A deeper look into the importance of alkoxysilane precursor

“…As shown in Figure 9b -f, with the exception of the EDLCs with pristine IL and TMOS ionogel (where charge transfer remains unaltered) Rct is reduced by 30-60% after the CV cycling. Previously, we have shown that the Rct variations over time are assigned to the continuous increase in electrode wetted area by the electrolyte at the interf ace and the depth of the activated carbon 63 . The charging step of the CV cycles effectively increases the surf ace area between AC and ionic liquid, reducing the resistance (R) as per the following relationship 64,65 :…”

“…It is important to note that the nature of Rct in EDLCs with porous electrodes 56,62 is different f rom that in psuedocapacitors which are mainly associated with the Faradaic processes taking place in the cell 60 . Based on our previous work with a similar ionogel system 63 , Rct is postulated to comprise of the ionic impedance components at: (i) the electrode-electrolyte interf ace and (ii) within the textural pores (i.e. inter-particle pores) of the AC electrodes.…”