The Origin of Li-O₂Battery Performance Enhancement Using Fluorocarbon Additive

Abstract

Perfluorocarbon compounds (PFC) are known for their high O2 dissolution capability and have been investigated as additives/electrolyte solvents to improve Li-O2 batteries performance. Nevertheless, systematic studies that go beyond the proof of concept that fluorocarbon additives enhance the performance of Li-O2 batteries have not been carried out yet. In this work, we investigate 1-methoxyheptafluoropropane additive (1-PFC), a fluorocarbon with an ether functional group that has been considered as one of the candidates as additives in the Li-O2 battery. Using electrochemical methods and physical characterization of discharge products, we found that the enhancement of the discharge capacity of Li-O2 cells with 1-PFC additive is most likely correlated with instability of the 1-PFC additive against superoxide radicals, rather than the improvement in O2 solubility.

Electrolyte Additives for Lithium Metal Anodes and Rechargeable Lithium Metal Batteries: Progress and Perspectives

“…In addition to improving the stability of Li 0 , polymer‐based additives (PEO, polyvinylidene fluoride (PVdF)) and inorganic additives (Al 2 O 3 , SiO 2 ) have also been identified as good options to enhance the stability of the cathode and thus lead to a higher cell capacity . Interestingly, the enhancement of the discharge capacity in cells with perfluorocarbon as an additive is most probably due to the reaction between the additive and superoxide …”

“…[162][163][164] Interestingly,t he enhancement of the discharge capacity in cells with perfluorocarbon as an additive is most probably due to the reaction between the additive and superoxide. [165,166]…”

Current Challenges and Routes Forward for Nonaqueous Lithium–Air Batteries

“…Unfortunately, those early studies were done in organic carbonate electrolytes (PC and others), which are now known to be unsuitable for Li–O 2 batteries due to poor stability against superoxides. Later work has used more suitable electrolytes, such as tetraglyme, − DME, and DMSO, and significant improvements in capacity were again reported. To increase the miscibility of fluorinated compounds with the other cosolvent, the use of a perfluorinated lithium salt surfactant has been reported (lithium perfluorooctanesulfonate (LiPFOS), see structure in Figure a), which enabled an impressive solubility of >60 wt % of BrC 6 F 13 in tetraglyme.…”

“…(a) Structure of some selected fluorinated compounds. (b) IR-corrected CVs of glassy carbon in 0.15 M TBAPF 6 in DME saturated with either Ar or O 2 with various concentrations of 1-PFC additive (noted in the legend as HFE, hydrofluoroether); scan rate = 100 mV/s . (c) O 2 concentration for various TE4 additive concentrations in TEGDME as a function of O 2 pressure .…”

Fluorinated Graphite (FG)-Modified Li–S Batteries with Superhigh Primary Specific Capacity and Improved Cycle Stability

“…Therefore, all of the F in FG transformed into LiF after sufficient discharge. The Li-CF x primary battery can achieve a high energy density of up to 1560 W h kg –1 . , Herein, the FG additive is introduced into the cathode to improve the performance of Li–S batteries. Figure a shows the schematic illustration discharge process of FG composite cathodes.…”