The polarity of a series of ionic liquids (ILs) based on hydroxyethyl-imidazolium moiety with various anions ([PF(6)], [NTf(2)], [ClO(4)], [DCA], [NO(3)], [AC], and [Cl]) and their corresponding nonhydroxyl ILs was investigated by solvatochromic dyes and fluorescence probe molecules. Most of the nonhydroxyl ILs exhibit anion-independent polarity with similar E(T)(30) in the narrow range of 50.7-52.6 kcal/mol, except [EMIm][AC] (49.7 kcal/mol). However, the polarity of the hydroxyl ILs covers a rather wide range (E(T)(30) = 51.2-61.7 kcal/mol) and is strongly anion-dependent. According to their E(T)(30) or E(T)(33) values, the hydroxyl ILs can be further classified into the following three groups: (Iota) acetate-based hydroxyl ILs [HOEMIm][AC] exhibit polarity scale (E(T)(30) = 51.2 kcal/mol) similar to short chain alcohol and fall in the range of the nonhydroxyl ILs; (II) Hydroxyl ILs containing anions [NO(3)], [DCA], and [Cl] exhibit comparable polarity (E(T)(30) = 55.5-56.9 kcal/mol), moderately higher than those of their nonhydroxyl ILs; (III) Hydroxyl ILs containing anions [PF(6)], [NTf(2)], and [ClO(4)] possess unusual "hyperpolarity" (E(T)(30) = 60.3-61.7 kcal/mol) close to protic ILs and water. Kamlet-Taft parameters and density functional theory calculations indicated that the greatly expanded range of polarity of hydroxyl ILs is correlated to an intramolecular synergistic solvent effect of the ionic hydrogen-bonded HBD/HBA complexes generated by intrasolvent HBD/HBA association between the anions and the hydroxyl group on cations, wherein hydroxyl group exhibits a significant differentiating effect on the strength of H-bonding and thus the polarity. Spiropyran-merocyanine equilibrium acted as a model polarity-sensitive reaction indeed shows obviously polarity-dependent solvatochromism, photochromism, and thermal reversion in hydroxyl ILs.

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Polymerized ionic liquids (PILs) have several advantages over ionic liquids, such as easy handling, good electrochemical performance, and chemical compatibility. In this research, a solid-state electrolyte composite membrane was successfully fabricated by using an imidazolium-based polymerized ionic liquid as polymer matrix, a kind of porous fiber cloth as rigid frame, and lithium bis­(trifluoro­methane­sulfonyl)­imide (LiTFSI) as lithium salt. The ionic conductivity of the composite electrolyte with 2.0 mol/kg LiTFSI is 7.78 × 10–5 S cm–1 at 30 °C and reaches 5.92 × 10–4 S cm–1 at 60 °C, which is considered a satisfactory value for potential application in lithium-ion batteries. The specific discharge capacity of the LiFe­PO4/Li cell with as-prepared composite electrolyte is 138.4 mAh g–1, and 90% of the discharge capacity is retained after 250 cycles at 60 °C. In order to further improve the conductivity, Li1.3­Al0.3­Ti1.7­(PO4)3 (LATP) ceramic electrolyte particles are dispersed in a PIL polymer matrix to prepare the PIL-LiTFSI-LATP composite electrolyte. LiFe­PO4/Li cells using PIL-LiTFSI-LATP (10 wt % LATP) as a solid-state electrolyte exhibit excellent rate performance and high capacity retention (close to 97% after 250 cycles at 60 °C). This work may provide a unique way to prepare a new series of electrolytes for high-performance solid-state lithium batteries.

The electric fields of ionic liquids are only slightly higher than those of common molecular solvents, and are strongly structure-dependent; they noticeably decrease with anion size because of increased separation of ions, and slightly decrease as the alkyl chain elongates due to increasing spatial heterogeneity. These were the key results of vibrational Stark effect spectroscopy and molecular dynamics simulations.

Al-doped layered cathode materials Li1.5–x Al x Mn0.675Ni0.1675Co0.1675O2 have been successfully synthesized via a rapid nucleation and post-solvothermal method. The surface morphology and crystal structures of Al-doped Li-rich materials are investigated via scanning electron microscopy, X-ray diffraction, Raman spectra, and X-ray photoelectron spectroscopy. After optimization, the Li1.45Al0.05Mn0.675Ni0.1675Co0.1675O2 (Al = 0.05) sample showed excellent electrochemical performance, and the discharge capacities are 323.7 and 120 mAh g–1 at a rate of 0.1 and 20 C, respectively. These improvements, based on electrochemical performance evaluation and density functional theory calculations, might be ascribed to the increased electron conductivity of layered Li-rich material via Al3+ ions doped into a crystal structure.

In the past 20 years, the concept of ionic liquids (ILs) have been extensively applied in the fields of chemistry, materials, and life sciences. [1] Undoubtedly, the ionic liquids composed of quaternary ammonium cations and anions, such as BF 4 À , PF 6 À , Cl À , and NTf 2 À , have been the backbone of this area since immidazolium cation ionic liquids were synthesized by Zaworotko et al. and were brought into catalysis and synthesis by Seddon, Rogers, Welton, Wasserscheid, and others. [2] Thousands of reactions have been performed in these ionic liquids and many of them exhibited better behavior than organic solvents. [3] Normally, the fine performance of these ionic liquids was attributed to the specific ionic environment of the ionic liquid. Nevertheless, the acidity of the air-and moisture-stable ionic liquids and its effect on catalysis is an interesting topic.As it is well known, a large amount of organic reactions can be catalyzed or promoted by an acid environment. [4] During our investigation of the function of ionic liquids in catalysis, especially air-and moisture-stable ones, we found that these ILs normally exhibit weak acidity in the presence of a small amount of water. That means the interpretations about the function of air-and moisture-stable ionic liquids in catalytic reactions are possibly wrong because the presence of trace amount of water is not avoidable in reality. Herein, we present our results on the study of acidity of air-and moisture-stable ionic liquids and their activity in some known acid-catalyzed reactions. We hope these results could be helpful for researchers in this area to reconsider the influence of the acidity of airand moisture-stable ionic liquids on catalysis and also in other fields. At the initial stage, the acidity of ionic liquids-water with different cations and anions were measured with a pH meter. The concentration of ionic liquid in water was 0.1 m. The operation was performed with methods given in the Annual Book of American Society for Testing and Materials Standards (ASTM) with slight modification. [5] As shown in Figure 1, ionic liquid-water mixtures with BF 4 À anions were all acidic. Interestingly, the acidity of the ionic liquids could be tuned via substituted alkyl variation. The pH value of EMImBF 4 ionic liquid reached 3.44(0.03) but the pH value of BMImBF 4 and HMImBF 4 were 4.27(0.14) and 6.61(0.03) respectively. BMImBF 4 ionic liquids purchased from Merck (lot code: S5204049909) and Sigma-Aldrich (lot code: 0001415814) were also measured for comparison. Under the same condition, their pH values were 4.70(0.05) and 4.30(0.09), respectively, which are exactly the same as the acidity of the ionic liquids that we synthesized. The incorporation of an hydroxyl group would further enhance the acidity of ionic liquids with BF 4 À anion. The pH value reached 3.12(0.01) and 3.11(0.02) with hydroxyethyl or hydroxypropyl groups. The substitution of the C2 position with a methyl group weakens the acidity of this kind of ionic liquid. For the ionic liquid BMMIm...