Lithium polysulphides

Lithium polysulphides-—Fusion of lithium hydroxide with sulphur yields a yellow mass like liver of sulphur, probably consisting of polysulphides of lithium. Berzelius isolated a hydrated disulphide, Li2S2, iH20, by concentrating an aqueous solution of the monosulphide. 

Virtually nothing is known about the lithium polysulphides, Sodiumtetrasulphide is the highest stable sodium poly sulphide, although higher ones may be present in... 

The high ionization potential and the very low density of the metals are promising to make use of them in high-temperature batteries Electrochemical cells using lithium as anode, a solid ceramic electrolyte and lithium polysulphide as cathode may reach a theoretical energy density of 3000 Wh kg- . Problems are caused by the bad compatibility of lithium with ceramic materials. 

Dimethyl-l-propynithallium Lithium Sodium polysulphide Diethylphosphine... 

The monosulphide and polysulphides are formed by burning the metals in sulphur vapour, by the action of sulphur on the metals dissolved in liquid ammonia, and by the action of the molten metals on sulphur dissolved in toluene. Hydrates or alcoholates and, in some cases, the anhydrous compounds may be prepared by dissolving sulphur in hot solutions of the hydrosulphides or monosulphides. Potassium, rubidium and caesium give all the sulphides where = 1, 2, 3, 4, 5, or 6 sodium only up to the pentasulphide, and lithium only those for which x = 1, 2 and 4 (Pearson and Robinson, 1931). All the metals form two polysulphides of relatively outstanding stability one is invariably the disulphide, and the other tetrasulphide in the case of lithium or sodium, and pentasulphide in the case of potassium, rubidium or caesium. The amount of water of crystallisation and the solubility decrease with increase in atomic number of the metal, the gradation being most marked between sodium and potassium. 

A spectroscopic study212 of solutions of alkali-metal polysulphides in DMF has shown the blue coloration to be due to the formation of the trisulphur radical anion S3. This result is contrary to that previously published (W. Giggenbach, J. C. S. Dalton, 1973, 729), which identified the species as the supersulphide ion S2. Further information on the formation of S3 in solutions of elemental sulphur in HMPA was also obtained, and it is now thought that the elemental sulphur is reduced by impurities present in the solvent, probably by dimethylamine. The reaction of piperidyl-lithium with S8 in HMPA was studied in order to determine the stoicheiometry and the nature of the final products. The stoicheiometry of the reaction was found to be ... 

Polysulphides. The reactions of lithium and sodium with sulphur in liquid ammonia have been studied. The thermal behaviour Of the polysulphides was also investigated by means of thermogravimetric and differential thermal analyses. The enthalpies of formation of both the sulphides and polysulphides of lithium and sodium have been determined in 0.1 N-H2SO4 by reaction calorimetry. The crystal structures of two compounds, and both containing... 

JI 11] Jl X., Evers S., Black R., et al, Stabilizing lithium-sulphur cathodes using polysulphide reservoirs , Nature Commun, vol. 2, p. 325, 2011. 

PAN 14] Pang Q., KUNDU D., Cuisinier M., et al, Surface-enhanced redox chemistry of polysulphides on a metallic and polar host for lithium-sulphur batteries , Nature Communications, vol. 5, p. 4759, 2014. 

Lithium aluminium hydride has also been widely used as a probe (Studebaker and Nabors, 1959 Studebaker, 1970). This reagent reacts with disulphides and polysulphides as follows ... 

Schematic diagram of the most conventional Li/S batteries and its t5 cal discharge voltage profile. The circled areas correspond to the progressive formation of the polysulphides during discharge. (Adapted from B. Scrosati, J. Hassoun and Y.-K. Sun, Lithium-ion batteries. A look into the future. Energy Environ. Set. 4, 2011, 3287-3295. Reproduced by permission of The Royal Society of Chemistry.)...

These results consistently contributed to improvements in the technology of lithium/sulphur battery however, some residual issues still remain to prevent full practical application of this high-energy battery system. Most of the recent works rely on conventional liquid organic carbonate solution as the preferred electrolyte although the sulphur and/or the lithium sulphide are shielded into a carbon matrix, either mesoporous [46] or spherical [50], thus in principle preventing the direct contact with the electrolyte, it is not yet fully established whether the solubility of the polysulphides is effectively blocked. Another issue still to be solved is in the relatively modest power capability of these batteries. 

Important progress has been achieved in the recent years on the performance of high-energy batteries. However, further work is essential to assure the practical implementation of lithium-sulphur and lithium-air batteries. While for the former, there is still need to develop the most favourable structure to assure a complete control of the polysulphide solubility, for the latter, much more issues have to be addressed before practical application is viable. Lithium-air is imdoubtedly one of the most promising energy storage... 

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