Lithium-sulfur batteries are attractive due to the relative abundance of sulfur and a higher theoretical energy density than lithium-ion batteries. However these batteries suffer from poor cycling performance, primarily due to the dissolving of the polysulfide species in the electrolyte. As a step towards rational design strategies for optimizing battery performance, we employed ab-initio molecular dynamics simulations and a rigorous statistical mechanical formalism to access the free energy of the Li2Sx species in a polymeric solvent at room temperature. Our approach allows for the exact inclusion of entropic and quantum-chemical effects, which are crucial for modeling these systems with high fidelity. These free energies are used to determine the equilibrium concentration of each species in the polymeric electrolyte, from which we calculate the associated sulfur K-edge Near-Edge X-ray Absorption Spectra from first principles using the eXcited electron and Core-Hole (XCH) approach. Our predictions are validated by direct comparison to the sulfur K-edge spectra measured at the Advanced Light Source at LBNL.

Insights in the solution phase chemistries and associated X-ray absorption spectra of lithium sulfur batteries materials from ab-inito MD simulations, the two-phase thermodynamics method and constrained DFT calculations

246th National Meeting (2013)

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