Synergistic Effect of Binary Electrolyte on Enhancement of the Energy Density in Li-O2 Batteries.

Enhancement of the discharge capacity of lithium-oxygen batteries (LOBs) while maintaining a high cell voltage is an important challenge to overcome to achieve an ideal energy density. Both the cell voltage and discharge capacity of an LOB could be controlled by employing a binary solvent electrolyte composed of dimethyl sulfoxide (DMSO) and acetonitrile (MeCN), whereby an energy density 3.2 times higher than that of the 100 vol % DMSO electrolyte was obtained with an electrolyte containing 50 vol % of DMSO. The difference in the solvent species that preferentially solvates Li+ and that which controls the adsorption-desorption equilibrium of the discharge reaction intermediate, LiO2, on the cathode/electrolyte interface provides these unique properties of the binary solvent electrolyte. Combined spectroscopic and electrochemical analysis have revealed that the solvated complex of Li+ and the environment of the cathode/electrolyte interface were the determinants of the cell voltage and discharge capacity, respectively.