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.