Electrolyte design is an important enabler for Li-S batteries, which have been actively pursued as one of the next generations of energy storage devices. First, we emphasize the role of electrolyte solvation in changing the thermodynamics of lithiation reaction and the open circuit voltage (OCV). Density functional theory (DFT)-based calculations were used to predict the temperature and solvent dependent OCV. We successfully predicted the two-plateaued OCV with fully solvated Li-polysulfide (Li-PS) and the one-plateaued OCV with non-solvated Li-PS, in agreement with experimental observation in typical Li-S batteries with liquid or solid electrolytes. Furthermore, if Li-PS is only partially solvated, its formation energy increases, leading to a transition from the two-plateaued to the one-plateaued OCV, as the Li-PS changes from fully solvation to partial or no-solvated state. Secondly, we show how the solvation effect changes with the electrolyte concentration. Based on this relationship, a new Li-PS dissolution mitigation strategy is proposed and tested, as the partial solvation can be created with a highly concentrated electrolyte or by varying pore size in the carbon matrix to confine S and limit the number of solvents transported into the pores. Finally, we explore the structure and dynamics of highly concentrated electrolyte and methods to enhance its viscosity. Thus, combining electrolyte and nano-structure design, the performance of Li-S batteries can be improved.

Understanding the electrolyte concentration and the effect of solvation for Li-S batteries

2019 Spring National Meeting

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