In Situ Raman Study of Voltage Tolerance Up to 2.2 V of Ionic Liquid Analogue Supercapacitor Electrolytes Immune to Water Adsorption Conferred by Amphoteric Imidazole Additives

Abstract

Ionic liquid analogues (ILAs) are promising electrolytes for supercapacitors due to their low cost and considerable voltage (>2.0 V). However, the voltage is <1.1 V for water-adsorbed ILAs. Herein for the first time, an amphoteric imidazole (IMZ) additive is reported to address this concern by reconfiguring the solvent shell of ILAs. Addition of only 2 wt % IMZ increases the voltage from 1.1 to 2.2 V, with an increase in capacitance from 178 to 211 F g–1 and an increase in energy density from 6.8 to 32.6 Wh kg–1. In situ Raman reveals that the strong H-bonds formed by IMZ with completive ligands 1,3-propanediol and water induce a reversal of the polarity of the solvent shells, suppressing absorbed water electrochemical activity and thus increasing the voltage. This study solves the problem of low voltage for water-adsorbed ILAs and reduces the equipment cost of ILA-based supercapacitor assembly (e.g., assembly in air without a glovebox).

Competition-Induced Macroscopic Superlubricity of Ionic Liquid Analogues by Hydroxyl Ligands Revealed by in Situ Raman

“…Raman spectra revealed that the components’ characteristic peaks of C–N (at ∼724 cm –1 ) and C–H (at 2800–3100 cm –1 ) in ChCl and C–O (at 800–960 cm –1 and ∼1050 cm –1 ) and O–H (at 3100–3600 cm –1 ) in TEOA coexist in ILA 1:2 , ILA 1:5 , ILA 1:10 , and ILA 1:20 (Figure b), demonstrating the formation of ILAs due to the weak interactions between H-bond donors and H-bond acceptors, such as O–H···O, O–H···Cl, and O–H···N, as well as the additional Coulombic action between ions . The corresponding Raman spectra focusing on the part of H-bonding interactions are magnified in Figure c; in contrast to the predominantly strong H-bonding interactions in ChCl, the H-bonding interactions in TEOA can be divided into the three components of strong (at ∼3255 cm –1 ), weak (at ∼3382 cm –1 ), and non-H-bonds (at ∼3478 cm –1 ) . The H-bonding interactions of ILA 1:2 , ILA 1:5 , ILA 1:10 , and ILA 1:20 mainly consist of strong and weak H-bond components.…”

“…Their morphologies and element contents were analyzed by scanning electron microscopy (SEM, FEI Scios 2 HiVac, 31 The corresponding Raman spectra focusing on the part of H-bonding interactions are magnified in Figure 1c; in contrast to the predominantly strong H-bonding interactions in ChCl, the H-bonding interactions in TEOA can be divided into the three components of strong (at ∼3255 cm −1 ), weak (at ∼3382 cm −1 ), and non-H-bonds (at ∼3478 cm −1 ). 27 The H-bonding interactions of ILA 1:2 , ILA 1:5 , ILA 1:10 , and ILA 1:20 mainly consist of strong and weak H-bond components. With the increase of TEOA content, the ratio of strong H-bonds to total H-bonds (A s /A t ) in ILAs decreases from 0.68 to 0.42, and the FTIR spectra of the ILAs also show the existence of H-bond peaks at 3100−3600 cm −1 in the ILAs (Figure S1).…”

“…32 These results indicate that the H-bonding interactions between Cl − and TEOA are strong H-bonding interactions. 27,33 The chemical shift at 4.36 ppm is considered to be the H response signal in its −OH based on the 1 H NMR data of TEOA (Figure 1d); however, as the proportion of TEOA in ILAs increases (i.e., from ILA 1:2 to ILA 1:20 ), the chemical shift shifts from 4.47 to 4.39 ppm (i.e., Δ δ = 0.081, Figure 1e), gradually approaching that of TEOA, 28 and the viscosity decreases from 0.41 to 0.34 Pa•s (Figure S2). This suggests that the weak interactions between components in ILAs, especially H-bonding interactions, are directly related to the content of TEOA, and they may affect the viscosity of the involved ILAs.…”

“…ILAs are usually formed as a result of strong interactions between H-bond donors and H-bond acceptors, which leads to the formation of a rich H-bond network between microscopic liquid phase species. The H-bonding network usually endows ILAs with high viscosity, which is favorable for increasing the load-bearing capacity but unfavorable for shear resistance reduction at the sliding interface. , For water, the H-bond interactions usually could be divided into three components; i.e., a strong H-bonds resulting from electron transfer, a weak H-bonds without electron transfer, and a non-H-bonds of free water molecules. , Recent advances have revealed that the addition of small amounts of water to ILAs formed by choline chloride (ChCl) and MgCl 2 ·6H 2 O ligands can achieve superlubricity at higher loads (∼160 MPa) on different types of friction pairs; the formation of their low shear resistance interfaces is mainly dependent on the attenuation of strong H-bonds due to the low-viscosity water; and their load-bearing capacity is derived from the high-viscosity contribution of localized strong H-bonding, which both ensures a good adsorption due to the strong H-bonds and prevents the lubricant from being extruded. However, the direct addition of water to the Ch-based ILAs leads to a significant reduction in the proportion of strong H-bonds (i.e., a large viscosity reduction), which restricts their ability to combine superlubricity and high load-bearing performance.…”

Non‐Faraday Electrolyte Additives for Capacitance Boosting by Compression of Dielectric Layer Thickness: Organic Ferroelectric Salts

“…[6][7][8] Traditional attempts to boost E often begin by increasing the specific capacitance (C) of porous carbon (e.g., by increasing specific surface area, SSA) or the voltage window of electrolytes (e.g., by introducing novel electrolyte components). [9][10][11][12][13][14] Theoretically, C is proportional to SSA, but if SSA exceeds a certain threshold (e.g., 1200 m 2 g −1 ), the rise in C slows down and approaches its limit (i.e., even a considerable increase in SSA does not increase C proportionally). [15] It implies that in electrode-electrolyte systems, C should be connected to parameters other than SSA.…”