Formation Of Li2S Research Articles

Self-discharge of lithium–sulfur cells using stainless-steel current-collectors

The self-discharge behaviour of Li–S cell, is investigated through changes in the open-circuit voltage (OCV) and discharge capacity with storage time. A fresh Li–S cell experiences 72% sulfur utilization during the first discharge, as based on the theoretical capacity for the formation of Li 2S. After 30 days of storage, the OCV has fallen from 2.48 to 2.16 V and the discharge capacity has decreased from 1206 to 924 mAh g −1 (based on sulfur). Analysis of the self-discharged sample by a variety of techniques shows the formation of lithium polysulfides, such as Li 2S n ( n ≥ 1) from the reaction of lithium and sulfur, which is related to the corrosion of the stainless current-collector. Stainless steel is not the most appropriate current-collector material for Li–S cells. The extent of self-discharge can be decreased by using a gold-coated current-collector that offers protection against corrosion.

In situ — High Temperature Mössbauer Spectroscopy of Iron Nitrides and Nitridoferrates

AbstractThe stoichiometric iron nitrides γ′‐Fe4N, ε‐Fe3N and ζ‐Fe2N were characterized by Mössbauer spectroscopy. The thermal decomposition of ε‐Fe3N was studied in‐situ by means of a specially developed Mössbauer furnace. We found ε‐Fe3N to γ′‐Fe4N and ε‐Fe3Nx (x ≥ 1.3) as decomposition products and determined the border of γ′/ε transformation at T ≅ 930 K. Mössbauer spectroscopy was applied to study in‐situ the thermal decomposition of the nitridometalate Li3[FeIIIN2] and the formation of Li2[(Li1‐xFeIx)N], the compound with the largest local magnetic field ever observed in an iron containing material. The kinetics of formation and the stability of Li2[(Li1‐xFeIx)N] was of particular interest in the present study.

Übergangsmetallkomplexe mit Schwefelliganden, LXXXV. / Transition-Metal Complexes with Sulfur Ligands, LXXXV.

Ni(II) salts and the tetradentate thioether-thiolate ligand ′S4-C2′2- (= 1,2-bis(2-mercaptophenylthio)ethane(2-)) yield [Ni(′S4-C2′)]x (1), that also forms when Na2[Ni(′S2′ )2] (′S2 2-′ = o-benzenedithiolate(2-)) is alkylated by 1,2-dibromoethane. In boiling pyridine 1 adds two solvent molecules and gives pseudooctahedral [Ni(pyr)2(′S4-C2′ )] (2) which was characterized by X-ray structure determination. Reaction of 1 with PMe3 yields [Ni(PMe3)(′S4-C2′)] (4). X-ray structure determination of 4 showed that the Ni center is surrounded by one P and four S atoms in a distorted tetragonal pyramid in which the P atom, one thioether S atom and both of the thiolate S atoms form the base while the second thioether S atom occupies the apical position. Reaction of 1 with n-BuLi leads to removal of the C2H4 bridge of the ′S4-C2′2- ligand and formation of Li2[Ni(′S2′)2]. When [Ni(acac)2]3 is reacted with ′buS4-C2′2 (= 1,2-bis(3,5-ditertiarybutyl-2-mercaptophenylthio)ethane(2-)) which is analogous to ′S4-C2′2-, the trinuclear [Ni(′buS4-C2′)]3 (3) forms. 3 · THF was characterized by X-ray structure determination. It contains one tetrahedrally distorted and two planar [NiS4] cores that are connected via the C2H4 groups of the ligands such that a macrocycle forms. PMe3 cleaves 3 to give mononuclear [Ni(PMe3)(′buS4-C2′)] (5). Due to its lability, it was characterized only by spectroscopic methods.

Formation of lithium polysulfides in aprotic media

The formation of Li 2S n in certain aprotic media can be accomplished either by electrochemical reduction of S 8 or by direct in situ reaction of S 8 with Li or Li 2S. Polysulfide solubilities and spectra vary widely in different solvents as a result of solvent-solute interactions. A requirement for high polysulfide concentration is high solvent basicity. In some cases, such as dimethyl sulfoxide and tetrahydrofuran, S solubility (as Li 2S n ) can exceed 10M. The favored order of dissolved polysulfides depends on the dielectric constant of the solvent, lower values favoring the formation of longer chains.