The Electrolyte Problem
Conventional electrolytes get oxidized and break down within minutes as a lithium-air battery inhales and exhales oxygen. DMSO, with its high dielectric constant (46 to 48), was tried as a solution and started a years-long debate.
How DMSO Helps
Donut Growth Mode
On discharge, DMSO readily dissolves reaction intermediates, so solid lithium peroxide does not cake onto the electrode. Instead it grows in the electrolyte as micron-scale particles. The electrode stays clear and discharge capacity increases several-fold.
Oxidation Resistance
DMSO holds up to oxidation better than most ethers, so at the high charging voltages needed to release oxygen it does not break down first.
The Three Problems
Reaction with Intermediates
On discharge, oxygen forms aggressive superoxide intermediates. DMSO can dissolve them, but it does not survive the contact; over time those intermediates decompose the solvent into byproducts.
Self-Discharge on Standing
Studies show that after discharge, lithium peroxide particles react with DMSO within days, converting to lithium hydroxide and dimethyl sulfone. A fully charged cell sitting idle quietly degrades.
Lithium Metal Anode
DMSO corrodes the lithium metal anode. Sharp dendrites grow on the surface and can pierce the separator, shorting the cell.
How Researchers Are Taming It
A protective solid-electrolyte layer on the lithium anode keeps DMSO away from the metal. Mixed-solvent formulations blend DMSO with more stable compounds such as sulfolane to retain the donut effect while raising overall electrolyte stability.
DMSO is not the final answer, but without it researchers would not have mapped out the chemistry inside these cells.