Abstract
In this work we discuss the degradation chemistry on carbon-free electrodes of two ether based electrolytes for Li-O2 batteries, i.e. tetraethylene glycol dimethyl ether (TEGDME) and dimethoxy ethane (DME) with lithium trifluoromethane sulfonate (LiTfO) as salt. To this aim we developed an all-metallic positive electrode by electrodeposition of a gold dendritic film on a nickel foam (Au@Ni). These carbon-free electro-catalytic electrodes have been used to investigate the degradation chemistry of the electrolytes in Li-O2 cells by eliminating the parallel parasitic reactions due to the commonly used carbon electro-catalysts. In particular the composition and morphological evolutions of the Au@Ni electrodes after discharge and cycling have been characterized ex situ by Raman Spectroscopy, X-ray Photoemission Spectroscopy and Scanning Electron Microscopy. We also couple this experimental study with thermodynamic predictions about the onset degradation of the DME molecule based on density functional theory calculations. In summary in both DME/LiTfO and TEGDME/LiTfO electrolytes, the degradation involves the oxidation of the ether solvent to a mixture of carbonates and carboxylates/formate/oxalate. DME is apparently more strongly degraded compared to TEGDME whereas the LiTfO anion is highly stable. Calculations suggest the key role played by the singlet oxygen molecule as initiator of the degradation path.
Highlights
To cite this version: Marco Carboni, Andrea Marrani, Riccardo Spezia, Sergio Brutti
In this work, nanostructured Au films constituted of nano-dendrites have been grown on metallic nickel foams (Au@Ni) through an electrochemical deposition reaction and characterized by X-ray diffraction, X-ray Photoemission Spectroscopy (XPS) and Scanning Electron Microscopy (SEM) and voltammetry
The Au@Ni pristine electrode: preliminary characterization.— The synthesized Au@Ni electrodes have been preliminary characterized by SEM, X-ray photoemission spectroscopy (XPS) and X-ray Diffraction (XRD) before testing in Li-O2 cells as shown in the supplementary information
Summary
To cite this version: Marco Carboni, Andrea Marrani, Riccardo Spezia, Sergio Brutti. Degradation of LiTfO/TEGME and LiTfO/DME Electrolytes in Li-O2 Batteries. Aprotic lithium-oxygen batteries (Li-O2) are a challenging and promising technology for future reversible energy storage.[1,2,3,4,5,6] with a theoretical specific energy of 3305 Wh kg−1, nonaqueous Li-O2 batteries can be considered a valid alternative to the common fossil fuels for transportation. Thanks to these promising figures, Li-O2 batteries have been systematically studied in the last ten years[7] and rewarding performance has been achieved.[8,9,10]. From the fundamental science point of view, recent advancements have been achieved in the comprehension of the basic redox reactions that rules Li-O2 batteries,[11,12,13,14,15,16] in the identification of stable lithium salts[9,17,18] and solvents,[8,19,20] or in the understanding the parasitic reactions.[21,22,23,24,25,26] many important issues must still be tackled in order to develop commercial Li-O2 cells,[27] in particular concerning the long term chemical/electrochemical stability of the cell.[8,21,23,28]
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