STUDY ON THE REDUCTION SPECIES OF SULFUR BY ALKALI-METALS IN NONAQUEOUS SOLVENTS

Rechargeable cells with a sulfur cathode, a lithium anode and a nonaqu eous electrolyte operating at ambient temperature have been extensivel y 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 y et been clarified. In this report, sulfur is reduced in tetrahydrofura n (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-s]/[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(radi cal anion), 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 ad dition of solvents such as crown ether on the behavior of the chemical species formed are examined by ultraviolet (uv)-visual electronic spe ctra, electron spin resonance (ESR) spectra and Raman spectra measurem ents. In addition, gamma-irradiation with Co-60 was carried out to red uce sulfur in glassy solid 2-methyl-THF at -196 degrees C. Furthermore , the reaction between the yellow solution and aliphatic bromide is in vestigated. As a result, it is revealed that the yellow species is S-4 (2-), the blue species is S-3(radical anion) and several polysulfide d ianions and radial anions are in a state of equilibrium. Copyright (C) 1997 Elsevier Science Ltd.