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We examined three sulfone-based electrolyte solutions for use in rechargeable magnesium batteries; i.e., sulfolane (SL), ethyl-i-propyl sulfone (EiPS) and di-n-propyl sulfone (DnPS), in which was dissolved 0.5 mol L −1 magnesium bis(trifluoromethanesulfonyl)amide (Mg(TFSA) 2 ). The specific conductivities of these sulfone-based Mg-electrolyte solutions were 1-2 mS cm −1 at 30 • C. These electrolyte solutions were thermally stable < 250 • C, and electrochemically stable < 2 V vs. Mg reference electrode (Mg wire). In these electrolyte solutions, an organic positive electrode made of 2,5-dimethoxy-1,4-benzoquinone (DMBQ) underwent reversible charge-discharge reactions. The reduction-oxidation current of the metallic Mg negative electrode was observed. A two-electrode cell composed of Mg|Mg(TFSA) 2 /SL|DMBQ endured more than 50 charge-discharge cycles at 30 • Rechargeable magnesium batteries may be an option for replacing the rechargeable lithium batteries because magnesium is much more abundant in the earth's crust and is more widely distributed than lithium. The fact that metallic Mg is less reactive toward ambient water and oxygen than Li may lead to a safer battery. In addition, a volumetric energy density of Mg should be greater than that of metallic Li.To achieve rechargeable magnesium batteries, it is important to consider the combination of the electrolyte and the positive electrode with the Mg negative electrode.1-3 Some solutions of Grignard reagents (RMgX; R = alkyl, X = halogen) are known to function as an electrolyte, in which metallic Mg is electrochemically and reversibly deposited on and dissolved from the negative electrode. 4 However, Grignard reagents are not stable at the high electrochemical potentials required for the positive electrode. 5 Recently, Nakayama et al. 6 revealed that, for Al electrolyte systems, certain sulfones (RR´SO 2 ) can be used as a solvent that endures high potentials. Thus, in the present study, we investigated three sulfones for use as a solvent to dissolve the Mg solute in rechargeable magnesium batteries; viz., sulfolane (SL), ethyl-i-propyl sulfone (EiPS) and di-n-propyl sulfone (DnPS). As the Mg electrolyte, we used magnesium bis(trifluoromethanesulfonyl)amide (Mg(TFSA) 2 ) because it can tolerate a high potential and the large TFSA anion, a soft Lewis base, should facilitate its dissociation from the Mg 2+ cation. In a Mg electrolyte solution, Mg(ClO 4 ) 2 /GBL, in a threeelectrode cell, we previously investigated the potential capability of 2,5-dimethoxy-1,4-benzoquinone (DMBQ), 7 which works as a positive-electrode active material in the lithium system. 8 In Mg(ClO 4 ) 2 /GBL, however, we found that no reversible Mg deposition/dissolution occurred. The objectives of the present study were to determine the fundamental physical properties of these sulfone electrolyte solutions, e.g., the viscosity, conductivity, potential window, etc., and to demonstrate the battery properties of a full-cell, Mg|Mg(TFSA) 2 /sulfone|DMBQ, to shed light on the possibilities and probl...

This study highlights the design concept of a positive electrode material which can accommodate both cations and anions during the charge/discharge process for realizing high energy density rechargeable batteries.

Spinel-type Li 4 Ti 5 O 12 (LTO) is expected as a safe and stable negative electrode material of sodium-ion batteries (SIBs). However, its small lattice volume is not sufficient as the Na + intercalation host. Alternatively, a Nasubstituted spinel titanium oxide phase (Na 3 LiTi 5 O 12 , NTO) with a large lattice volume should be promising. In our previous work, we discovered that such a NTO phase is partially generated in each LTO electrode particle during specific SIB cycling. In the present report, we examined the basic properties of this NTO phase in the NTO/LTO composite electrode. The in-situ XRD measurement of the Na-insertion process revealed that smooth Na + insertion preferentially occurs in the NTO region in the composite electrode because of small lattice expansion in the formation of the Na-inserted NTO phase as well as the smooth Na diffusion in the NTO phase. Thus, the composite electrode containing the NTO phase showed superior rate properties of Na insertion compared to the pristine LTO electrode and showed excellent cycle performance with high efficiency. In addition, the unique stability of the spinel-type NTO phase was examined by the density functional theory calculation, and the effect of the mixed transition-metal (TM)−Li−O network at 16d and 32e sites in lithium−TM oxides was discussed so as to keep the spinel structure for the substitution of 8a-site Li ions by other cationic ions.

Replacing the scarce metal-based positive electrode materials currently used in rechargeable lithium ion batteries with organic compounds helps address environmental issues and might enhance gravimetric electrochemical capacity. The challenge has been to find organic materials with both high capacity and long-cycle life. Here, we study the naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) skeleton as a high capacity candidate electrode for lithium-ion batteries, showing a multielectron-transfer type redox reaction. We also use electron energy-loss spectroscopy to reveal the reaction stoichiometry during charge/discharge processes. While the lithium salt of naphthazarin itself helped deliver a high initial capacity, its cycle-life was not satisfactory. Instead, a newly synthesized naphthazarin-dimer shows a lengthened cycle-life without sacrificing the initial high capacity of 416 mAh g−1 and energy density of 1.1 Wh g−1.