Mechanically Robust, Highly Ionic Conductive Gels Based on Random Copolymers for Bending Durable Electrochemical Devices

Abstract

Mechanically robust, highly ionic conductive gels based on a random copolymer of poly[styrene-ran-1-(4-vinylbenzyl)-3-methylimidazolium hexafluorophosphate] (P[S-r-VBMI][PF 6 ]) and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]) are successfully prepared. The gels with either homo P[VBMI][PF 6 ] or conventional PS-block-poly(methyl methacrylate)-block-PS (SMS) show significant trade-off between ionic conductivity and mechanical resilience. In contrast, the P[S-r-VBMI][PF 6 ]-based gels exhibit both large elastic modulus (≈0.105 MPa) and ionic conductivity (≈1.15 mS cm −1 ) at room temperature. To demonstrate that these materials can be used as solid-state electrolytes, the ion gels are functionalized by incorporating electrochromic (EC) chromophores (ethyl viologen, EV 2+ ) and are applied to EC devices (ECDs). The devices show low-voltage operation, large optical transmittance variation, and good cyclic coloration/bleaching stability. In addition, flexibleECDs are fabricated to take advantage of the mechanical properties of the gels. The ECDs have excellent bending durability under both compressive and tensile strains. The versatile P[S-r-VBMI][PF 6 ]-based gel is anticipated to be of advantage in flexible electrochemical applications, such as batteries and electrochemical displays.

Semitransparent Energy‐Storing Functional Photovoltaics Monolithically Integrated with Electrochromic Supercapacitors

“…EC Fabrication: An ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]), and electrochromic (EC) materials including p-trifluoromethylphenyl viologen bis(hexafluorophosphate) [CF 3 -PV(PF 6 ) 2 ], (3-fluoro-4-triflioromethyl) phenyl viologen bis(hexafluorophosphate) [CF 3 F-PV(PF 6 ) 2 ], and diethyl viologen bis(hexafluorophosphate) [EtV(PF 6 ) 2 ] were synthesized according to previous reports. [19,20,37,38] The other chemicals were purchased from Sigma Aldrich. A homogeneous EC gel solution was prepared by blending poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), ionic liquid ([EMI][TFSI] or 1-butyl-3-methylimidazolium tetrafluoroborate [BMI][BF4]), dimethyl ferrocene (dmFc), CF 3 -PV(PF 6 ) 2 (or CF 3 F-PV(PF 6 ) 2 or EtV(PF 6 ) 2 ), and acetone at a weight ratio of 1:4:0.035 (or 0.04 or 0.05):0.13 (or 0.13 or 0.2):15.…”

“…It is noted that dmFc was also added in the gel as a counter anodic EC material for low-voltage operation. [19,20,[25][26][27] No characteristic peaks were shown up to −0.2 V, except for one broad absorption peak at ≈420 nm arising from the dissolved dmFc. Red color (λ max ≈ 545 nm) appeared at −0.3 V, and the intensity became stronger as the applied voltage was increased (see Figure 3b).…”

“…The coloration transition (≈22 s) was faster than the bleaching response (≈65 s), as observed in other gel-based ECDs. [19,20,26,27] Coloration efficiency (η) is defined as ΔOD/ΔQ, where ΔOD and ΔQ are the changes in optical density and the amount of injected charge, respectively, or log(T b /T c )/ΔQ with transmittance values for bleached (T b ) and colored (T c ) states. [28] The η value (≈88.7 cm 2 C −1 ) of the gel-based ECS was calculated from the slope of a line fit to plots of ΔOD versus ΔQ (Figure 3d).…”

“…These materials were selected due to their outstanding EC characteristics such as large transmittance contrast, high coloration efficiency, and low power consumption. [19,20] Figure 1c shows a schematic illustration of the monolithically integrated energy-storing functional photovoltaics, consisting of two parts: ST Q-OPVs (energy harvesting) and ECS (energy storage). First, we fabricated ST Q-OPVs with the inverted structure of indium tin oxide (ITO)/ poly [(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN)/quaternary blend/MoO 3 /Ag (anode).…”

Super‐tough hydrogels using ionically crosslinked networks

“…Generally, cross‐linkers in both hydrogels and ion gels can be categorized into physical crosslinking and chemical crosslinking. The chemically crosslinking is usually considered as tough jointing that is hard to break, while physically crosslinking including ionic bonds, hydrogen bonds, crystal structure, hydrophobic associations, and agglomeration is reversible, which can be easily disrupted under certain condition …”