A photohealable ion gel based on the photodimerisation of anthracene as a dynamic covalent bond was developed.

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Introduction Eutectic gallium-indium (Ga-In) has excellent properties, such as low melting point of 15.3 °C, high thermal and electronic conductivity, and metallic luster. Ga-In has promise as a liquid electron-conducting material owing to its low viscosity, negligible vapor pressure and low toxicity.1, 2) On the other hand, ionic liquids are ambient temperature molten salts that have attracted considerable attention because of unique properties such as high ionic conductivity, non-volatility and thermal stability. We proposed that ion gels, composed of macromolecular networks swollen with ionic liquids, exhibit self-standing film-forming ability in addition to the unique properties of ionic liquids. In this study, we prepared composite gel materials containing ionic liquid and Ga-In. This composite gel (metal gel) might have high electronic conductivity based on Ga-In and high ionic conductivity originated from the ionic liquid, as well as good mechanical properties based on the polymer, such as flexibility and strechability. These new materials are applicable to flexible or stretchable devices in wearable and flexible electronics applications. Experimental We chose hydrogen bonding copolymers of N,N-dimethylacrylamide (DMAAm) and acrylic acid (AAc) (P(DMAAm-r-AAc)) as the matrix polymers. This copolymer was combined with a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([C2mim][NTf2]) to form an ion gel.3) In order to improve dispersibility of Ga-In in the composite gel, bulk Ga-In was ultra-sonicated in ethanol and the suspension of Ga-In microdroplets was mixed with P(DMAAm-r-AAc) and [C2mim][NTf2]. The composite gels were prepared by solution casting method either in the air where thin oxide layer is formed on the Ga-In particles4) or under inert atmosphere to examine the effects of preparation conditions on their properties. Results and Discussion In tensile tests, Young’s modulus increased with increasing volume fraction of Ga-In in the composite gels. In rheological measurements, storage modulus was higher than loss modulus, confirming soft solid-like behavior of the composite gels. In both measurements, modulus of composite gels was higher than that of ion gels. We found difference in the temperature dependent rheological properties between the composite gels prepared in air and under inert atmosphere. The presence/absence of the surface oxide layer on the Ga-In particles was likely responsible for the difference in the rheological responses. Electronic conductivity was improved by a factor of 106 for the composite gels prepared under inert atmosphere compared to that of the composite gels prepared in the air. It was found that the oxide layers on the Ga-In particles had a significant impact on the rheological and electronic properties. However, electronic conductivity of the composite gels prepared under inert atmosphere was still low compared to that of bulk Ga-In. To achieve high electronic conductivity comparable to the bulk value, volume fraction of Ga-In microdroplets needs to be increased in the composite gels. In order to improve dispersibility of high-loading Ga-In in the composite gel, Ga-In microdroplets were prepared with dispersants. The results suggested that there is a trade-off between dispersibility of the Ga-In microdroplets and the electronic conductivity: better dispersibility of Ga-In microdroplets resulted in lower electronic conductivity. Acknowledgement This study was supported in part by Core Research for Evolutionary Science and Technology (CREST) of the Japan Science and Technology Agency (JST). References 1) Kazem, N. et al, Adv. Mater., 2017, 29, 1-14. 2) Anderson, T. J. et al, Phase Equilibria, 1991, 12, 64-72. 3) Tamate, R. et al, Adv. Mater, 2018, 30, 1802792 4) Ren, L. et al, Adv. Funct. Mater., 2016, 26, 8111-8118. Figure 1

We report the photocontrollable micelle–cluster transition of an ABC-type triblock copolymer in an ionic liquid (IL). Polystyrene-b-poly(ethylene oxide)-b-poly(4-phenylazobenzyl acrylamide-r-N-isopropylacrylamide) (PSt-b-PEO-b-P(AzoBnAm-r-NIPAm)) was synthesised, where PSt is IL-phobic, PEO is IL-philic, and P(AzoBnAm-r-NIPAm) is photo- and thermoresponsive in the IL. At high temperatures, the triblock copolymer forms micelles with PSt cores; furthermore, at low temperatures, micelles self-assemble into clusters induced by the aggregation of P(AzoBnAm-r-NIPAm). Under UV irradiation, the micelles form clusters at lower temperatures than that in the dark because of the change in the solubility of P(AzoBnAm-r-NIPAm) induced by photoisomerisation of the azobenzene groups, indicating that this triblock copolymer has a photocontrollable micelle–cluster transition temperature.

Li-S batteries have received much attention as the next-generation secondary batteries because of their extremely high theoretical energy density. A roll-to-roll fabrication method based on continuous laminating and winding of the sheet-like electrodes and electrolyte without an electrolyte injecting process would enable a more efficient manufacturing process for mass production of Li-S batteries. In order to realize such batteries, it is necessary to prepare the sheet-type sulfur cathode electrode in which an electrolyte is incorporated. We recently reported that a less volatile, highly concentrated lithium salt electrolyte could serve as a good dispersing media of carbon nanotube (CNT).[1] In this study, the same method was applied not only to CNT but also to other carbonaceous materials to obtain sheet sulfur cathode electrode containing highly concentrated electrolytes that serve as the dispersing media. As a result, we fabricated a Li-S polymer battery by combining the sheet sulfur cathode and the polymer gel electrolyte membrane.[2] This is a trail to realize polymer Li-S battery fabricated by the roll-to-roll process. The cathode slurry was prepared by adding a dispersion solvent, NMP (N-methyl-2-pyrrolidone), to the mixture (sulfur, Ketjen black (KB), polymer, and highly concentrated electrolyte: [Li(SL)2][TFSA] (SL : sulfolane, [TFSA] = [N(SO2CF3)2])[3]). This slurry was coated to an Al foil current collector and dried to obtain the gel cathode. The gel electrolyte was prepared from PVDF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene)) and [Li(SL)2][TFSA] by a solvent casting method. The Li-S polymer battery was then prepared using the gel cathode, electrolyte and Li-anode. Figure 1(a) shows a conceptual scheme of roll-to-roll making process for the Li-S polymer battery. By using the sheet-like cathode and gel electrolyte, a battery can be manufactured simply via laminating them with Li-anode. It is worth mentioning that the subsequent electrolyte injecting step can be omitted here because the gel cathode and electrolyte already contain uniformly distributed electrolytes. Figure 1(b) shows the charge-discharge curves of the Li-S polymer battery. The battery delivered the initial discharge capacity of 850 mAh g−1. After 20 cycles, nearly 700 mAh g−1 of capacity could be retained, which indicated reasonable cycling stability. In our previous research,[1] CNT was used as the carbonaceous material for the S gel cathode. However, in this study, we found the amounts of electrolyte could be greatly reduced by using KB. It is considered that CNT requires more electrolyte to disperse the aggregated bundles and to unbundle them by cation-π interaction. Hence, our results would indicate a great potential on designing the sulfur gel cathode by a very simple method with lower cost materials. The detailed electrochemical behavior of the Li-S polymer batteries will be discussed in the presentation. Further, studies on the effects of composition and thickness of the S gel cathode and gel electrolyte on the electrochemical behavior will be presented. References [1] R. Tamate, A. Saruwatari, et al., Electrochem. Commun., 2019, 109, 106598. [2] T. Michot, A. Nishimoto, M. Watanabe, Electrochim. Acta, 2000, 45, 1347. [3] A. Nakanishi, K. Ueno, et al., J. Phys. Chem. C, 2019, 123, 14229. Figure 1