In order to solve the problem of polysulfide dissolution into the electrolyte on sulfur-based cathodes, we propose a novel method of modifying the S cathode by coating it with a polypyrrole (PPy) film, which is prepared by oxidative electropolymerization using a solution consisting of, 1-methyl-1-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and pyrrole. The PPy film demonstrates a high Li + transport number. The film

The light harvesting-reaction center (LH1-RC) complex from a new thermophilic purple sulfur bacterium Allochromatium (Alc.) tepidum was isolated and characterized by spectroscopic and thermodynamic analyses. The purified Alc. tepidum LH1-RC complex showed a high thermostability comparable to that of another thermophilic purple sulfur bacterium Thermochromatium tepidum, and spectroscopic characteristics similar to those of a mesophilic bacterium Alc. vinosum. Approximately 4-5 Ca per LH1-RC were detected by inductively coupled plasma atomic emission spectroscopy and isothermal titration calorimetry. Upon removal of Ca, the denaturing temperature of the Alc. tepidum LH1-RC complex dropped accompanied by a blue-shift of the LH1 Q absorption band. The effect of Ca was also observed in the resonance Raman shift of the C3-acetyl νC═O band of bacteriochlorophyll-a, indicating changes in the hydrogen-bonding interactions between the pigment and LH1 polypeptides. Thermodynamic parameters for the Ca-binding to the Alc. tepidum LH1-RC complex indicated that this reaction is predominantly driven by the largely favorable electrostatic interactions that counteract the unfavorable negative entropy change. Our data support a hypothesis that Alc. tepidum may be a transitional organism between mesophilic and thermophilic purple bacteria and that Ca is one of the major keys to the thermostability of LH1-RC complexes in purple bacteria.

A novel polypyrrole (PPy) film was investigated to determine the optimal conditions for operation in a Li/S battery. The PPy film was prepared by oxidative electropolymerization to improve the Li/S battery performance, as reported in our previous paper. In such a system, the PPy film was coated directly on the S/Ketjenblack cathode to solve the problem of polysulfide dissolution. The optimum PPy film preparation conditions to prevent polysulfide dissolution and to promote Li + permeability were determined by varying the PPy polymerization bath composition and polymerization potential. As a result, the inclusion of 1.0 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in the polymerization bath (0.1 M pyrrole in 1-methyl-1-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide) was found to be the most important factor for producing a PPy film with a high Li + transport number (t Li + ≈ 1). A polymerization potential of 4.5 V versus Li/Li + was shown to be optimum for the promotion of Li + permeability. The mechanism by which the PPy film prevents polysulfide dissolution and increases Li + permeability is discussed by analyzing the SEM, CV, XPS, and 13 C solid-state NMR data. Lithium/sulfur (Li/S) batteries have attracted substantial attention as a next-generation battery candidate because their theoretical energy density (∼2500 W h kg −1 ) is much higher than the current C/LiCoO 2 system (387 W h kg −1 ). [1][2][3][4] In addition, sulfur exhibits several impressive characteristics, such as abundance in nature and low toxicity. However, Li/S batteries have several intrinsic problems that affect their practical application. Some of the issues associated with the sulfur cathodes include the low ionic and electronic conductivities of sulfur and Li 2 S, large volume expansion of sulfur upon lithiation (∼80% expansion), and dissolution of intermediate products, namely lithium polysulfides (Li 2 S x , where 4 ≤ x ≤ 8), into the electrolyte. 6,7 This dissolution of polysulfide causes "redox shuttle phenomena," which leads to overcharging (low coulombic efficiency) and rapid capacity fading. 8 Various strategies have been developed to solve these problems. 9Since Nazar's group overcame the low conductivity problem of the sulfur cathode and achieved cycle stability by producing a sulfurordered mesoporous carbon (CMK-3) composite, 10 various carbon materials have been studied as hosts for sulfur. 11-15In order to suppress polysulfide dissolution, ionic-liquidbased electrolytes have been investigated. 16,17 Ionic-liquid-based electrolytes show excellent polysulfide dissolution inhibition, while batteries containing the ionic liquid-based electrolytes show relatively high resistances, owing to the high viscosities of these electrolytes. However, the high cost of ionic liquids hinders their practical application compared with commonly used organic electrolytes. There have been many reports on methods for suppressing dissolution of polysulfides by coating or modifying the surface of an active material with a polymer using c...

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