The urge for electrochemical energy storage devices with high gravimetric and volumetric energy density is imminent and the lithium−sulfur (Li-S) battery has been poised as a major next generation battery concept candidate. While it has a (very) high theoretical energy density, low cost and non-toxicity of starting materials,[1] its practical application has been hampered by several obstacles; the active material(s) elemental sulfur (S₈) and lithium sulfide (Li₂S) are both electronic insulators, polysulfides dissolve into the electrolyte and diffuse between the cathode and anode – generating an active material loss, there are dendrites formed at the lithium metal anode, etc.[2,3]

To address (some of) these problems, the solubility properties of the electrolyte are of utmost importance [4] and here we use semi-solid electrolytes – materials without flow but malleable – to hinder the dissolution of sulfur and possibly also mitigate the creation of lithium dendrites. These electrolytes are composed of matrices of hypervalent molecules i.e. with large internal dipole moments, heavily doped with Li-salts to generate Li⁺ conduction paths via percolation networks.[5] We report on initially assessed physico-chemical properties, basic electrochemical properties such as ion conductivity (Figure 1), before progressing to feasibility tests in Li-S battery cells.

This work was funded by “Batterifondsprogrammet” of the Swedish Energy Agency.

Figure 1. Arrhenius plots of two different hypervalency based electrolytes and the matrix used.

References

[1] Q. Pang, X. Liang, C.Y. Kwok, L.F. Nazar, Nat. Energy 1 (2016) 16132.

[2] X. Judez et al., J. Electrochem. Soc. 165 (2018) A6008–A6016.

[3] J. Scheers, S. Fantini, P. Johansson, J. Power Sources 255 (2014) 204–218.

[4] S. Drvarič Talian, S. Jeschke, A. Vizintin, K. Pirnat, I. Arčon, G. Aquilanti, P. Johansson, R. Dominko, Chem. Mater. 29 (2017) 10037–10044.

[5] T. Mizumo, R. Fujita, H. Ohno, J. Ohshita, Chem. Lett. 40 (2011) 798–800.