Extended Data Fig. 4: Characterization of Ca metal anode disassembled from Ca-O2 batteries.
From: A rechargeable calcium–oxygen battery that operates at room temperature
a, XRD pattern of the Ca anode disassembled from a charged Ca-O2 battery showing the presence of metallic Ca and CaF2. b, c, TEM images and the corresponding SAED pattern (inset) of the cycled Ca metal anode. Scale bars, 20 nm (b), 3 nm (c). d, Fast Fourier transform (FFT) images of the crystal regions marked in Fig. 3b showing the presence of metallic Ca (cubic Fm3m crystal phase, (200) plane) and randomly dispersed CaF2 nanocrystals (cubic Fm3m crystal phase, (111) plane). e, XPS Ca 2p spectrum (after etching) of pure Ca metal displaying two peaks centered at 349.5 (Ca 2p1/2) and 346.0 eV (Ca 2p3/2). f, XPS C 1 s, F 1 s, and S 2p spectra of the cycled Ca metal anode, revealing a hybrid SEI composed of inorganic CaF2 and organic compounds.
