Electrolyte with Low Polysulfide Solubility for Li-S Batteries

Li-S battery is one of the most promising next-generation rechargeable battery technologies because of its high theoretical energy density and low material cost. However, its success is impeded by the low energy efficiency and fast capacity fade primarily caused by the discharge intermediates, Li-polysulfides (PS), dissolution in the electrolyte. Mitigation of PS dissolution in electrolyte involves the search for a new electrolyte solvent system that exhibits poor solvation to the PS while still having good solvation ability to the electrolyte salt for high ionic conductivity. Applying cosolvents with reduced solvating power but compatible with the state of the art Li-S battery's ether-based electrolyte is one of the most promising concepts. This route is also advantageous of having a low scale-up cost. With the aid of quantum chemical calculation, we have identified high carbon-to-oxygen (C/O) ratio ethers as cosolvent in the new electrolytes that effectively impede PS dissolution while still maintaining high ionic conductivity. Significantly improved cycle life and cycling Coulombic efficiency are observed for Li-S cells using the new composite electrolytes. Anode analysis with different methods also demonstrate that reducing electrolyte's PS solubility results in less sulfur total amount on the lithium anode surface and lower ratio of the longer-chain PS, which is probably a sign of suppressed side reactions between the anode and PS in the electrolyte.