Transition metal-free graphene framework based on disulfide bridges as a Li host material

Abstract

A graphene sulfide framework (GSF) is designed and synthesized via a hybridization of graphene and organic compounds for use in electrodes for high-performance Li-ion batteries (LIB). This electrode material is devoid of transition metal and features a layered framework structure that is constructed by the formation of covalent disulfide bonds between organic linker molecules and graphene sheets. This structure capitalizes on the advantageous properties of each of the components in an electrochemical reaction. The structures of GSFs are characterized by Cs-corrected transmission electron microscopy (Cs-TEM), field emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XRD). Depending on current density, the GSF electrodes exhibit two different types of electrochemical behavior during Li incorporation/extraction process, indicating the involvement of multiple Li-incorporation mechanisms. Various types of dithiol organics as linker components are incorporated in the GSF to evaluate the effect of length or structure on the electrochemical properties. The linker-dependent Li storage mechanism is explained based on the results of differential capacity analyses and electrochemical impedance spectroscopy (EIS). The GSF proposed in this study shows promise as an electrode material for a high-performance energy-storage system that is inexpensive and free of transition metals.