A gamma fluorinated ether as an additive for enhanced oxygen activity in Li–O2 batteries?

Journal of Materials Chemistry A Pub Date: 2015-08-25 DOI: 10.1039/C5TA03439F

Abstract

Perfluorocarbons (PFCs) are known for their high O2 solubility and have been investigated as additives in Li–O2 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–O2 cells. Furthermore, the effect of PFC additives on the O2 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–O2 cells. The results show that with the TE4 additive up to 4 times higher O2 solubility and up to 2 times higher O2 diffusibility can be achieved. With 20 vol% TE4 addition, the discharge capacity increased about 10 times at a high discharge rate of 400 mA gC?1, corresponding to about 0.4 mA cm?2. The chemical stability of TE4 after Li–O2 cell discharge is investigated using 1H and 19F NMR, and the TE4 signal is retained after discharge. FTIR and XPS measurements indicate the presence of Li2O2 as a discharged product, together with side products from the parasitic reactions of LiTFSI salt and TEGDME.

Graphical abstract: A gamma fluorinated ether as an additive for enhanced oxygen activity in Li–O2 batteries
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