LAUSR

Abstract Lithium-FeS2 is an attractive chemistry for rechargeable lithium batteries because of its high theoretical energy density ~1313 Wh kg−1. However, fast capacity fade is generally observed in this system due to the irreversible dissolution of active materials (polysulfide ions, Fe ion etc.) into the electrolyte. This work investigates the effect of ethereal electrolyte solvents’ structure on its solvating power of Li-polysulfides and eventually on the cycling stability of rechargeable Li-FeS2 cells. Methyl t-butyl ether (MTBE), a high carbon/oxygen ratio ether, is studied and compared with the standard 1,2-dimethoxyethane (DME):1,3-dioxolane (DOL) ether couple as electrolyte solvent for Li-FeS2 and similar chemistries. The higher level of non-polar character and the additional steric hindrance in MTBE both endow it with significantly lower solvating capability and lower solubility of Li-polysulfides than DME:DOL. This is predicted by quantum chemical calculation and verified by experiments. In electrochemical test, MTBE solvent helps to significantly improve the cycling stability of the Li-FeS2 cell. Post-cycling material analysis and impedance tests both indicate that this is due to the alleviated active material dissolution and re-deposition on the lithium anode. Similar improvement is also observed in the Li-CuS cell case. Although the ionic conductivity of the electrolyte is also affected by this new solvent and MBTE cannot yet be a satisfactory solution, our study presents important guidance in designing future electrolyte for Li-FeS2 battery.