Electrochromism of Nanographenes in the Near-Infrared Region.

Nanographene (NG) is a potential candidate for organic EC materials because of its large π-conjugated system, chemical stability, absorption band covering the visible region, and tunable optical properties by postsynthetic modification. We show that NGs carrying redox-active triphenylamine (TPA) units covalently linked to the NG edge function as EC materials in the NIR region. The hybrid materials can be obtained by the installation of TPA units onto the NG edge and display changes in the absorption spectrum in the NIR region extending to a wavelength of over 2000 nm upon one-electron oxidation and reduction at low potentials (<1.1 V). Time-dependent unrestricted density functional theory calculation of a model NG at the UB3LYP/6-31G(d,p) level of theory suggests that a narrow energy gap between the basal plane and the oxidized TPA unit is responsible for the observed EC function in the NIR region.

Sulfur-inserted polymer-anchored edge exfoliated graphite for durable positive electrodes for lithium-sulfur batteries.

Lithium-sulfur batteries hold promising potential for next-generation high-energy-density energy storage. One of their major technical problems is the sulfur active material loss and significant volume change during the charge-discharge process, resulting in rapid capacity fading. Here, we propose sulfur-inserted polymer-anchored edge exfoliated graphite as a positive electrode to accommodate the conflicting requirement of physically restraining sulfur dissolution while maintaining structural flexibility to cope with the volume expansion. The introduction of sulfur between the flexible polymer-anchored graphene layers is achieved by a simple chemical reaction at ambient temperature. The obtained sulfur-carbon composite demonstrates superior sulfur efficiency and cyclability compared to mesoporous carbon-based counterparts. The strong interfacial attraction between sulfur and highly-conductive graphene sheets at the confined interlayer space enables rapid charge transfer and effectively inhibits the polysulfide dissolution, resulting in improved redox reaction reversibility and sulfur efficiency. More importantly, the structural flexibility of layered structure, derived from polymer-anchor, guarantees the stable cycling by accommodating the significant volume expansion of sulfur active materials. Our work provides a simple, proof-of-concept strategy for improving the overall performance of carbon-based positive electrode for Li-S batteries.