Sulfur-rich transition metal polysulfides MS5 (M=Mo, W) are synthesized by a low-temperature solution method from corresponding carbonyls M(CO)6 and elemental sulfur. Extensive characterization reveals that all sulfur atoms are assembled into disulfide ligands (S−S) within the structure of the amorphous spherical particles. Their thermodynamic stabilities are estimated for the first time using density functional theory (DFT) calculations, indicating two stable chain models composed either of binuclear [M2S8] or trinuclear [M3S12] fragments linked through S−S units. Molecular dynamics (MD) DFTB simulation proves that the S−S bridges predetermine the supreme flexibility of the polysulfide chains as primary structures of MS5 and their globular secondary arrangements. Interestingly, this type of structural organization is reminiscent of that for classical polymers. Thus, the reasons for MS5 forming exclusively as amorphous phases are uncovered, which may be extended to many other sulfur-rich polysulfides. The potential of these materials as increased capacity cathodes for lithium-ion batteries is shown.
Bibliographical noteFunding Information:
This work was supported by Russian Foundation for Basic Research (RFBR), research project No. 18-33-20006 and by the bilateral Program ?Russian-German Laboratory at BESSY II? in the part of XPS measurements. E. D. G. would like to thank the President of the Russian Federation for the scholarship awarded (C?-140.2018.1).
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- ab initio calculations
- amorphous materials
- chain structures
- molecular dynamics
- synthesis design