期刊
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
卷 19, 期 2, 页码 1441-1448出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c6cp06889h
关键词
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资金
- Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under the Batteries for Advanced Transportation Technologies [DE-AC02-05CH11231]
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
- Office of Science of the U.S. Dpartment of Energy, [DE-AC02-05CH11231]
An understanding of the complex solution phase chemistry of dissolved lithium polysulfides is critical to approaches aimed at improving the cyclability and commercial viability of lithium sulfur batteries. Experimental measurements are frustrated by the versatile sulfur-sulfur bond, with spontaneous disproportionation and interconversion leading to unknown equilibrium distributions of polysulfides with varying lengths and charge states. Here, the solubility of isolated lithium polysulfides is calculated from first-principles molecular dynamics simulations. We explore the associated changes in the dissolution free energy, enthalpy and entropy in two regimes: liquid-phase monodentate solvation in dimethylformamide (DMF) and polymer-like chelation in bis(2-methoxyethyl) ether (diglyme). In both of these technologically relevant solvents, we show that the competition between enthalpy and entropy, related to specific interfacial atomic interactions, conspires to increase the relative stability of long chain dianionic species, which exist as Li+-LiSx- contact-ion-pairs. Further, we propose a mechanism of radical polysulfide stabilization in simple solvents through the reorientation of the 1st shell solvent molecules to screen electrostatic fields emanating from the solute and explain nonmonotonicity of the dissolution entropy with polysulfide length in terms of a three-shell solvation model. Our analysis provides statistical dynamics insights into polylsulfide stability, useful to understand or predict the relevant chemical species present in the solvent at low concentrations.
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