Extended Data Fig. 2: XPS spectrum of interwoven carbon fibers.

a, Pristine, (b) after exposure to IL+AlCl3 electrolyte, (c) after exposure to dimethyl carbonate as a negative control. Peak assignments: 284.8 eV (C-C, C-H), 286 eV (C-O), 287.5–288 eV (C=O, O-C-O), 289 eV (O=C-O). The intensities at 286 and 287.5 ~ 288 eV suggest that the exposure to IL+AlCl3 notably increases the level of oxygen enrichment on carbon fibers.