Modulating visible-near-infrared reflectivity in ultrathin graphite by reversible Li-ion intercalation

Two-dimensional materials with optical turnability have wide prospect in related applications such as electrochromic coating and thermal camouflage. Here we report a Li-intercalated ultrathin graphite device with tunable visible-near-infrared reflectivity. After Li-ion intercalation, the Fermi surface of ultrathin graphite will move to a higher level, which prevents the interband optical transitions below it. Therefore, it is possible to change the absorptivity or emissivity of ultrathin graphite through reversible Li-ion intercalation, which accomplishes the modification to reflectivity indirectly. In our experiment, the strong fluorescence background and Peak shifts in Raman spectra, as well as the enlarged layer spacing in XRD spectra, together confirmed that Li-ions were successfully intercalated into the graphite layers. The relative reflectivity of ultrathin graphite increased sharply in a wide range from 460 nm to 1500 nm after complete Li-ion intercalation. At a typical near-infrared wavelength 1500 nm for instance, the relative reflectivity is 0.28 for pristine graphite while 0.70 for fully lithiated graphite. Such reversible intercalated modulation in visible-near-infrared reflectivity of ultrathin graphite might provide a new way to design electrochromic coating, thermal camouflage or radar stealth systems, which also promotes further understanding and optical applications of graphene and other 2D materials.