Linear ether-based highly concentrated electrolytes for Li-sulfur batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Lithium-sulfur (Li-S) batteries offer high theoretical capacity and cost-effectiveness for next-generation energy storage.
• Sparingly solvating electrolytes are crucial for suppressing polysulfide shuttling, improving coulombic efficiency, and extending cycle life in Li-S batteries.

Purpose of the Study:

• To investigate the solubility of lithium polysulfide (Li₂S₈) in various liquid electrolytes.
• To correlate polysulfide solubility with electrolyte properties, specifically donor number (DN_NMR).
• To evaluate the performance of novel dialkyl ether-based electrolytes in Li-S cells.

Main Methods:

• Measured Li₂S₈ solubility in organic electrolytes, highly concentrated electrolytes, and ionic liquids.
• Estimated electrolyte donor numbers (DN_NMR) using ²³Na-NMR spectroscopy.
• Fabricated and tested Li-S cells using electrolytes based on lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and linear chain dialkyl ethers (MPE, BME, EPE).

Main Results:

• Li₂S₈ solubility correlated inversely with DN_NMR, remaining below 100 mM (elemental sulfur) for DN_NMR < 14.
• Monomethyl ethers (e.g., BME) exhibited stronger Li-ion coordination and higher ionic conductivity compared to longer chain ethers (e.g., EPE).
• Li-S cells with dialkyl ether electrolytes showed superior charge-discharge rate capabilities and achieved >300 W h kg^-1 energy density with a pouch-type cell using [Li(BME)₃][TFSA] under lean electrolyte conditions.

Conclusions:

• Electrolytes with low donor numbers (<14) effectively minimize polysulfide dissolution in Li-S batteries.
• Dialkyl ether-based electrolytes, particularly those with monomethyl ethers, offer excellent Li-ion transport properties for high-performance Li-S cells.
• The developed [Li(BME)₃][TFSA] electrolyte demonstrates significant potential for high energy density Li-S battery applications.