PNNL

Abstract

The effects of nonaqueous electrolytes on the performance of primary Li-air batteries operated in dry air environment have been investigated. Organic solvents with low volatility and low moisture absorption are necessary to minimize the change of electrolyte compositions and the reaction between Li anode and water during the discharge process. The polarity of aprotic solvents outweighs the viscosity, ion conductivity and oxygen solubility on the performance of Li-air batteries once these latter properties attain certain reasonable level, because the solvent polarity significantly affects the number of tri-phase regions formed by oxygen, electrolyte, and active carbons (with catalyst) in the air electrode. The most feasible electrolyte formulation is the system of LiTFSI in PC/EC mixtures, whose performance is relatively insensitive to PC/EC ratio and salt concentration. The quantity of such electrolyte added to a Li-air cell has notably effects on the discharge performance of the Li-air battery as well, and a maximum in capacity is observed as a function of electrolyte amount. The coordination effect from the additives or co-solvents [tris(pentafluorophenyl)borane and crown ethers in this study] also greatly affects the discharge performance of a Li-air battery.