(335j) Design of New Electrolytes for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries, when commercialized, are projected to have energy densities of at least 500 Wh/kg, twice the energy density of current lithium-ion batteries. Despite this promise, several challenges are still unresolved. Firstly, once sulfur in the cathode is reduced, the lithium polysulfides that form are soluble in the electrolytes, leading to active sulfur loss and poor cycle life. Secondly, the solvated polysulfides migrate to the lithium anode and are further reduced. To address these concerns, much work has focused on engineering the cathode with microstructures that can trap polysulfides. Researchers focused on the electrolyte have designed additives (such as fluorinated ethers) or increased the salt content in the electrolyte to limit the dissolution of polysulfides. However, all these studies have maintained the use of the conventional electrolyte; a mixture of dioxolane and dimethoxyethane.

In this work, we set out instead to redesign the Li-S electrolyte. We synthesize a variety of new electrolytes and characterize their ionic conductivity and electrochemical properties. We show these electrolytes can support sulfur reduction and oxidation, and when compared to the conventional electrolyte, can better protect the lithium metal anode and prevent polysulfide shuttle. We use these novel electrolytes in lithium-sulfur batteries, and study the discharge/charge performance with cycling, and show they also yield higher coulombic efficiencies.

Knowledge gained from this work can allow for these electrolytes to be explored in other battery systems beyond lithium-sulfur.