Study on the reduction species of sulfur by alkali metals in nonaqueous solvents

• Published in: Electrochimica acta Vol. 42; no. 6; pp. 1019 - 1029
• Main Authors: Tobishima, Shin-Ichi, Yamamoto, Hideo, Matsuda, Minoru
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 1997; Elsevier
• Subjects: alkali metal; Applied sciences; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Exact sciences and technology; lithium battery; nonaqueous solvent; polysulfide; sulfur; sulfur; polysulfide; alkali metal; lithium battery; nonaqueous solvent; Lithium Ions; EPR spectrometry; Hexamethylphosphorotriamide; Secondary cell; Electrode material; Tetrahydrofurane; Chemical reduction; Organic solvent; Medium effect; N,N-Dimethylformamide; Battery; Reaction mechanism; Alkali metal Ions; Raman spectrometry; Electrochemical reaction; Sulfur; DME; Non aqueous solvent; Ultraviolet visible spectrometry
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/S0013-4686(96)00281-2

Rechargeable cells with a sulfur cathode, a lithium anode and a nonaqueous electrolyte operating at ambient temperature have been extensively studied as a possible application of sulfur combined with nonaqueous solvent. However, the behavior of the chemical species formed by the reduction of sulfur with alkali metals in nonaqueous solvent has not yet been clarified. In this report, sulfur is reduced in tetrahydrofuran (THF) by alkali metals (M: Na, K, Li and Cs), by anthracene radical anions or by diphenylethylene dimer dianions with alkali metal counter cations mainly under the experimental condition of [S 8] [M] > 0.25 . The system produced by the reduction is the yellow solution consisting of polysulfide dianions ( S m 2−, m > 1) and radical anions ( S n −, n > 1) which changes into a blue solution by the addition of hexamethylphosphoric triamide with a much higher polarity than THF. The influence of the kind of alkali metal, the temperature and the addition of solvents such as crown ether on the behavior of the chemical species formed are examined by ultraviolet ( uv)-visual electronic spectra, electron spin resonance (ESR) spectra and Raman spectra measurements. In addition, γ-irradiation with 60Co was carried out to reduce sulfur in glassy solid 2-methyl-THF at — 196 °C. Furthermore, the reaction between the yellow solution and aliphatic bromide is investigated. As a result, it is revealed that the yellow species is S 4 2−, the blue species is S 3 − and several polysulfide dianions and radial anions are in a state of equilibrium.