Abstract
For Li–air batteries, dissolved gas can cross over from the air electrode to the Li metal anode and affect the solid-electrolyte interphase (SEI) formation, a phenomenon that has not been fully characterized. In this work, the impact of atmospheric gases on the SEI properties is studied using electrochemical methods and ex situ characterization techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The presence of O2 significantly improved the lithium cyclability; less lithium is consumed to form the SEI or is lost because of electrical disconnects. However, the SEI resistivity and plating overpotentials increased. Lithium cycled in an “air-like” mixed O2/N2 environment also demonstrated improved cycling efficiency, suggesting that dissolved O2 participates in electrolyte reduction, forming a homogeneous SEI, even at low concentrations. The impact of gas environments on Li metal plating and SEI formation represents an additional parameter in designing future Li-metal batteries.
Highlights
Properties is studied using electrochemical methods and ex situ characterization techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy
To test the hypothesis that the LiOH-rich solid-electrolyte interphase (SEI) formed in O2 promotes more uniform Li nucleation, we explored a pretreatment method whereby the cell was first cycled in O2 for 5 cycles before purging and continuing to cycle in Ar
The X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and FTIR results all suggest that the SEI formed in Ar and N2 contains multiple inorganic products from LiTFSI reduction
Summary
The XPS, XRD, and FTIR results all suggest that the SEI formed in Ar and N2 contains multiple inorganic products from LiTFSI reduction. Oxygen and nitrogen can chemically react with lithium metal; this appears to be a minor effect compared to electrochemical SEI formation as shown in EDX measurments of Li metal exposed to gas environments under OCV conditions (Table S2).[27,28,39,60]. Water contamination is another potential source for LiOH,[19,20] and efforts were made in order to minimize this in our study
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