Takeshi Kakibe

In recent years, secondary lithium-ion batteries (LIBs) have become critical components for portable devices and large power source systems such as electric vehicles (EVs) and hybrid EVs (HEVs).^[1],[2] However, conventional LIBs typically use flammable nonaqueous liquid electrolytes, posing a serious safety risk. Our previous study^[3] demonstrated that one promising approach for safe LIBs involves using electrolytes based on a series of ionic liquids (ILs) with branched alkyl imidazolium cations. The introduction of bulky branched alkyl groups enhances charge delocalization in imidazolium cations, thereby improving the electrochemical reduction stability. Herein, we evaluated the compatibility and electrochemical performance of two types of ILs: branched alkyl functional and electrochemically polymerizable ILs. Moreover, binary mixture–based electrolytes based on their ILs were investigated for use in LIBs. We synthesized two types of ILs: reduction-stable and polymerizable ILs (Fig. 1). An IL-based electrolyte was mixed with various compositions of reduction-stable and polymerizable ILs, with LiFSA (LiFSA molal concentration: ca. 1.5 mol/kg) serving as the Li ion source. The characteristics of the involved battery were examined using a graphite electrode | IL–LiFSA mixture–based electrolyte | Li metal half-cell configuration. The graphite electrode sheets comprised NMC powder (86 wt%) as the active material, acetylene black (7 wt%) as an electrically conductive additive, and poly(vinylidene fluoride) (7 wt%) as a binder. The graphite electrode sheet, separator, IL–LiFSA mixture–based electrolyte, and Li were assembled into a battery cell. Performance tests for charge–discharge rates were conducted at 303 K, with the involved rates varying from 0.1 to 0.5 C. Fig. 2 shows the first charge–discharge profiles of the graphite | Li half-cells with [EP_isoIm][FSA]–, [AP_isoIm][FSA]–, and [EP_isoIm]_0.8[AP_isoIm]_0.2[FSA]–based electrolytes. During the first charge with the [AP_isoIm][FSA]– and [EP_isoIm]_0.8[AP_isoIm]_0.2[FSA]–based electrolytes, a plateau was observed at approximately 0.5 V, attributed to the reduction decomposition and polymerization of [AP_isoIm] cations on graphite. The presence of [AP_isoIm] cations enabled the formation of a stable solid electrolyte interface, an electron-insulating, lithium-ion-conducting film. [1] M. Wakihara, “Recent developments in lithium ion batteries”, Mater. Sci. Eng., R, 33, 109 (2001). [2] D. D. Lecce, R. Verrelli, and J. Hassoun, “Lithium-ion batteries for sustainable energy storage: recent advances towards new cell configurations”, Green Chem., 19, 3442 (2017). Figure 1

All-solid-state lithium-ion batteries (ASSLBs) have become a good candidate for energy storage devices with safety and long-life time. It is essential to apply an appropriate solid electrolyte, because it is quite important to build the electrode/electrolyte interface with good chemical, electrochemical and mechanical properties ^{[1, 2]}. The previous studies reported that LISICON compound Li_3.5Ge_0.5V_0.5O₄ (LGVO) solid electrolyte has good compatibility with layered rock salt cathode oxides ^[3]. However, the LGVO solid electrolyte phase is easily reductive-decomposed in contact with lithium metal anode. In order to avoid direct contact between LGVO electrolyte and Li metal anode, it is useful to construct intermediate polymer electrolyte layer with high Li⁺ ionic conductivity between them. In this paper, the preparation conditions of polyethylene oxide based polymer electrolyte (PEO-based SPE) film by wet method were discussed. In addition, the polymer film was prepared on the LGVO solid electrolyte layer, and the LGVO/PEO interfacial properties were also studied. PEO-based SPE slurry was prepared by dissolving PEO and different concentrations of Lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) with/without Al₂O₃ nanoparticle in acetonitrile. PEO-based SPE slurry was uniformly coated on the LGVO membrane and dried in a vacuum to obtain LGVO/PEO laminated electrolytes. X-ray diffraction patterns of the several PEO-based SPE are shown in Fig. 1. Low Li⁺ concentrated PEO-based SPE (with Li⁺ : EO ratio = 1:20) exhibited typical PEO diffraction peaks at 15°, 19° and 23°. On the other hand, the crystallinity degree of PEO in high Li⁺ concentrated PEO-based SPE (with Li⁺ : EO ratio = 1:10) decreased dramatically. Especially, there are no diffraction peaks in high Li⁺ concentrated PEO-based SPE (with Li⁺ : EO ratio 1:10) with Al₂O₃ nanoparticle addition. Fig. 2 shows temperature dependence on the ionic conductivities of the PEO-based SPE (with Li⁺ : EO ratio 1:10) with Al₂O₃ nanoparticle in temperature range from 10 to 80 °C. The ionic conductivity of the PEO-based SPE showed a sufficiently higher ionic conductivity (4.25 × 10^-3 Scm^-1) at 60 °C. This study was supported in part by the JST GteX (grant number JPMJGX23S2). [1] E. Quartarone, P. Mustarelli, “Electrolytes for solid-state lithium rechargeable batteries: recent advances and perspectives”, Chem. Soc. Rev., 40, 2525-2540, (2011). [2] R. Chen, Q. Li, X. Yu, L. Chen, H. Li, “Approaching Practically Accessible Solid-State Batteries: Stability Issues Related to Solid Electrolytes and Interfaces”, Chem. Rev., 120, 6820-6877 (2020). [3] T. Okumura, T. Takeuchi, H. Kobayashi, “All-Solid-State Batteries with LiCoO₂-type electrodes: realization of an impurity free interface by utilizing a co-sinterable Li_3.5Ge_0.5V_0.5O₄ electrolyte”, Appl. Energy Mater. 4, 30-34 (2021). Figure 1

In this study, we describe the synthesis of a cholesterol-linked cyanostilobazole salt dye and the tuning of its luminescence by physical stimuli such as electricity and grinding. The dyes exhibited liquid-crystalline properties at temperatures above 170 °C. Some of the solutions were transformed into orange luminescent gels upon the addition of poor solvents. When the solvent was evaporated, the resulting solid xerogel exhibited mechanochromism, its color changed, and its luminescent color changed from orange to red. Furthermore, we investigated the construction of functional gels (mechanochromic gels) that can respond to two stimuli, damage detection by abrasive responsiveness, and electrical response using ionic liquid complexes of polymers as dispersing media. This study provides a new strategy for tuning and switching luminescence using non-chemical stimuli in a single-component system using aggregation.

The γ‐ray resistance of epoxy network polymers was evaluated. Bisphenol A diglycidyl ether (DGEBA) was used as an epoxy oligomer, and 4,4′‐diaminodiphenylmethane (DDM), hexahydrophthalic anhydride (HHPA), and phenolic novolac (PN) were used as curing agents. The thermally crosslinked polymers were irradiated with 0–10 MGy of γ‐rays. The crosslink density as well as the glass‐transition temperature (T_g) for the DDM‐cured and PN‐cured DGEBA resins decreased upon γ‐ray irradiation; however, the elastic modulus at room temperature and the density of the resins increased. By contrast, the T_g for the HHPA‐cured DGEBA resin increased slightly and the crosslink density decreased markedly when the specimen was irradiated with γ‐rays. Among the three cured systems, the HHPA‐cured DGEBA resin exhibited the greatest amount of gas generation during irradiation. Infrared absorption spectra revealed a decrease in the number of ester bonds and an increase in the number of aliphatic and aromatic ether bonds, suggesting that new crosslinking occurred concurrently with chain scission. Overall, among the three cured systems, the PN‐cured DGEBA resin was the most stable in terms of chemical structure and physical properties under γ‐ray irradiation.

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A review on the use of “task-specific” ionic liquids for designing of the structures of ions. Ionic liquids （ILs）entirely consist of ions. In recent years, functionalized ILs, called “task-specific” ILs （TSILs）, are finding anincreasing number of applications in synthesis, separation, catalysis, and electrochemistry.

Etherification of cellulose was performed using a mixture of ionic liquids (ILs) playing roles in both cellulose dissolution and catalysis. We investigated the effects of the reaction time and the ratio of these ILs in the mixture. Cellulose etherification was performed in these IL mixtures. The proportion of propoxy cellulose exceeded 2.5 after 24 h.