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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A low-resistance polypyrrole (PPy) film that can achieve high rates (rates of >1C) while suppressing polysulfide dissolution is developed in this study. To achieve high-rate characteristic in a sulfur cathode with high sulfur loading, a three-dimensional (3D) aluminum foam current collector is used and the Li+ concentration of the PPy film is enhanced by a glyme–Li equimolar complex as the polymerization electrolyte. A PPy–sulfur/ketjenblack (S/KB) 3D aluminum foam laminated cell with a sulfur loading of 5 mg cm−2 is prepared. Consequently, a high discharge capacity of 794 mAh g−1-sulfur at 3.0C is achieved using 1 M lithium bis-(trifluoromethylsulfonyl)imide (LiTFSI) with dimethoxyethane (DME) and 1,3-dioxolane (DOL), (DME/DOL = 1/1 vol.) as the electrolyte and Li foil as the anode. In the cycling test, PPy-S/KB 3D Al foam cathode achieved a significant improvement in discharge capacity retention compared to bare S/KB 3D Al foam cathode without PPy coating. Moreover, almost no polysulfide dissolution is confirmed from the ultraviolet–visible spectrum of the electrolyte after the cycle evaluation. Here, we prepare a 3D structure S/KB cathode that can support high rates while suppressing sulfur dissolution by PPy coating, and reveal its potential for lithium–sulfur battery application.

An anionic polymer coating produced by ultraviolet curing and thermosetting to suppress polysulfide dissolution of the sulfur cathode for lithium-sulfur batteries was investigated. An sulfur/Ketjenblack cathode with a high sulfur loading of 10 mg cm−2 was prepared using a three-dimensional foam current collector. From the current rate and cycle characteristics, the cross-linked polymer coating suppressed the polysulfide dissolution, and the discharge capacities were 1031 and 414 mAh g−1-sulfur at 0.1 and 1.0C, respectively. In a long-term cycle test of 300 cycles, a capacity retention rate was 41%. An average coulombic efficiency was 91% throughout the cycles.

[Introduction] In recent years, lithium-sulfur batteries can be expected as a promising candidate for next generation energy storage devices because of its high energy density. Generally, the cathode is fabricated by infiltration of sulfur into Ketjen black (KB) with aluminum foil current collector. However, it is not easy to increase the sulfur loading amounts and maintain the rate performances for electric vehicles which are required more than 3C rate, due to the lack of Li ion and electron paths. To solve this issue, we have reported the new type sulfur electrode prepared using 3D mesh structured Al foam, resulting in increased sulfur loading amounts which are 5 - 10 times or more compared to conventional sulfur cathode fabricated using 2D structured aluminum foil current collector [1], [2], [3]. In this study, we optimized the fabrication method of sulfur cathode for high sulfur loading on 3D mesh structured Al foam for a high energy density Li-S laminated battery. [Experimental] S/KB composite was obtained by mixing sulfur and KB with weight ratio of 6:4, by heating at 155 °C for 12 h under N2 atmosphere. Afterward obtained S/KB composite was dispersed by ball milling for 12h. S/KB cathode was fabricated by S/KB slurry (weight ratio of S/KB (6/4) : Binder = 96.5 : 3.5). The high sulfur loaded cathode (15.3 mg/cm2) was obtained using 3D mesh structured Al foam (1mm in thickness). To assemble the cell, the cathode was pressed (0.4 mm in thickness). 5 Ah class laminated cell (70 x 70 mm) was prepared using the S/KB cathodes (6 stacked), Li anodes (7 stacked), separators (7 stacked), and the electrolyte (LiTFSI: G1(monoglyme)/G3(triglyme): HFE(hydrofluoroether)= 1: 1: 4 (molar ratio)). Electrochemical performances were tested with voltage range between 1.0 V – 3.3 V after activation process. In addition, coin cells were prepared using above materials to evaluate the ionic conductivity by DC polarization method. [Results and Discussion] To design a high energy density cell such as laminated type cell, it is important to optimize the ratio between using amount of electrolyte and solid materials in electrode. Fig. 1 shows the relationship between the calculated E/S ratio (electrolyte amount (µℓ)/sulfur loading amounts (mg)), porosity filling rate of electrolyte (%), and the gravimetric energy density (Wh/kg). It was possible to reduce the electrolyte filling rate to 100% which is corresponding to E/S = 1.7, achieving the 340 Wh/kg theoretically. It is important to secure an ion path in whole electrode to optimize utilization of E/S ratio. In our previous report, we fabricated the S/KB cathode using 3D mesh structured Al foam regardless of the porosity, implying that it has bad ion conductivity. To improve the ion conductivity of S/KB cathode which has high sulfur loading amounts, we prepared a cathode that loaded S/KB very uniformly and retained the high porosity of the 3D mesh structured Al foam. As a result, we confirmed that the S/KB cathode/3D Al mesh which has good porosity shows improved ionic conductivity than control sample fabricated by conventional method. Fig. 2 shows the charge/discharge curve of Li-S laminated battery prepared by a new method with optimized E/S ratio of 2.3 (conventional method requires high E/S ratio of 3.6 or more). High capacity of 5.2 Ah, and energy density (301 Wh/kg and 435 Wh/ℓ, excluding laminate and tab) was achieved with high sulfur loaded laminated cell (sulfur loading amount of 15.4 mg/cm2, 1156 mAh/g-S). References: [1]. H. Mikuriya, T. Yokoshima, Moongook Jeong, H. Nara, T. Momma, and T. Osaka, "High-energy laminated-type Li-S batteries using high-sulfur loading positive electrode on aluminum foam", PRiME, A03-0444 (2016). [2]. H. Nara, T. Yokoshima, H. Mikuriya, S. Tsuda, T. Momma, and T. Osaka, “The potential for the creation of a high areal capacity lithium-sulfur battery using a metal foam current collector”, J. Electrochem. Soc. 164:A5026–A5030 (2017). [3]. H. Mikuriya, A. Shiosaki, S. Ahn, H. Nara, N. Nakamura, and T. Osaka “Research and development of high energy density Li-S battery with high sulfur loading cathode using 3D-Al foam” The 87th ECSJ Spring Meeting 3G15 (2020). Acknowledgement This work was partly supported by Advanced Low Carbon Technology Research, Development Program Special Priority Research Area “Next-Generation Rechargeable Battery” (ALCA-Spring) from the Japan Science and Technology Agency (JST) (Grant Number JPMJAL1301). Figure 1