Improved Li-Metal Cycling Performance in High Concentrated Electrolytes for Li-O-2 Batteries

Since the carbonate-solvents used in Li-ion batteries were incompatible for Li-O-2 electrochemistry, alternatives have been investigated recently. Dimethyl sulfoxide (DMSO) stands among the best solvents for the Li-O-2 system owing to its comparative stability against the superoxide and peroxide species formed during cell discharge. However, it has a drawback of instability towards metallic lithium. Recent reports suggest the use of concentrated electrolytes that prevent solvent decomposition via shielding from lithium-metal. Herein, LiTFSI/DMSO is chosen as salt/solvent configuration with 3 salt concentrations. The solution properties, namely ionic conductivity, Li-transference number, and viscosity are studied along with electrochemical properties such as Li-stripping/plating coulombic efficiency and symmetrical long-term cycling. It is shown that concentrated electrolytes (>1 M) exhibit superior cycling stability and coulombic efficiency. Post cycling analysis on electrodes confirms solvent decomposition only in low concentrated electrolyte. Moreover, the presence of oxygen in concentrated solutions yields an even better cycling stability than oxygen free electrolyte.