A gamma fluorinated ether as an additive for enhanced oxygen activity in Li-O2 batteriesElectronic supplementary information (ESI) available. See DOI: 10.1039/c5ta03439f

Perfluorocarbons (PFCs) are known for their high O 2 solubility and have been investigated as additives in Li-O 2 cells to enhance the cathode performance. However, the immiscibility of PFCs with organic solvents remains the main issue to be addressed as it hinders PFC practical application in Li-O 2 cells. Furthermore, the effect of PFC additives on the O 2 mass transport properties in the catholyte and their stability has not been thoroughly investigated. In this study, we investigated the properties of 1,1,1,2,2,3,3,4,4-nonafluoro-6-propoxyhexane (TE4), a gamma fluorinated ether, and found it to be miscible with tetraglyme (TEGDME), a solvent commonly used in Li-O 2 cells. The results show that with the TE4 additive up to 4 times higher O 2 solubility and up to 2 times higher O 2 diffusibility can be achieved. With 20 vol% TE4 addition, the discharge capacity increased about 10 times at a high discharge rate of 400 mA g C −1 , corresponding to about 0.4 mA cm −2 . The chemical stability of TE4 after Li-O 2 cell discharge is investigated using 1 H and 19 F NMR, and the TE4 signal is retained after discharge. FTIR and XPS measurements indicate the presence of Li 2 O 2 as a discharged product, together with side products from the parasitic reactions of LiTFSI salt and TEGDME. A fluorinated additive with good stability toward O 2 − for enhanced O 2 solubility that increases discharge capacity at high discharge rates.