High nitrogen-content carbon nanosheets formed using the Schiff-base reaction in a molten salt medium as efficient anode materials for lithium-ion batteries

Abstract

A series of porous carbon nanosheet materials with high nitrogen content have been prepared using melamine and terephthalaldehyde as carbon precursors through the Schiff-base reaction in a molten salt medium. The molten salt medium is responsible for the formation of sheet morphology and allows efficient immobilization of nitrogen atoms in the carbon framework during thermal pyrolysis, resulting in high-nitrogen-content carbons. XPS results demonstrate that, different from other reported carbons, the carbon nanosheets largely contain pyrrolic and pyridinic groups, both of which are very suitable for Li storage. When the carbon nanosheets are used as anode materials for lithium ion batteries (LIBs), they exhibit a high initial coulombic efficiency of ca. 63.1%, and a high and constant reversible capacity of 605 mA h g⁻¹ at a current density of 100 mA g⁻¹ even after 100 cycles. Moreover, they show a high-rate capability, e.g., a high capacity of 199 mA h g⁻¹ was obtained at 3000 mA g⁻¹ (full charge within 4 min). In contrast, commercial graphite has a value less than 20 mA h g⁻¹ at 3000 mA g⁻¹, showing one-tenth the capacity of the carbon nanosheet material. Such superior electrochemical performance is due to its high porosity, high nitrogen content of ca. 30 wt% and a unique two-dimensional (2D) structure. Thus, the proposed synthesis can be an alternative means for the preparation of high-nitrogen-content porous carbon with specific nitrogen species for energy storage applications.