Li-S battery is being considered a candidate as a future power source for electric vehicles since it can potentially provide a very large energy density. Nonetheless, the formation of soluble intermediate species such as polysulfides makes the redox chemistry of sulfur less reversible and therefore restricts the practical use of Li-S battery. While most approaches pursue the confinement of polysulfides in nanostructured conductive networks, this study explores a feasibility of using electron mediators to convert polysulfide species away from the conductive network. A Keggin-type polyoxometalate has been selected as the mediator based on the redox potential calculation using a density functional theory (DFT) method. The DFT study has also shown how the selection of composing elements affects the electronic properties of Keggin compounds. A series of electrochemical cell tests reveal that only a small amount of mediator molecules (10 mM) in nonaqueous electrolyte can significantly improve both the reduction and the oxidation reactions of Li-S chemistry.

Polyoxometalates as electron mediators for better Li-S cell performance

247th National Meeting (2014)

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