Metallic two-dimensional C3N allotropes with electron and ion channels for high-performance Li-ion battery anode materials

Two-dimensional monolayer C3N has attracted much attention in many fields, owing to its unique mechanical, electrical and thermal properties and diverse structure. However, the physical origin of these properties lacks a systematic and clear understanding. In this work, three dynamically stable metallic C3N allotropes were computationally investigated. The cohesive energy of all these structures is within 0.09 eV/atom of that of the experimentally reported semi-conductive C3N structure. Density-functional theory calculations showed that the metallicity of two-dimensional C3N can be attributed to the continuity of the carbon chains, which form channels for passage of free electrons. Furthermore, additional calculations showed that the C3N allotropes possess excellent mechanical properties, good electronic conductivity and Li migration capability (wherein the C-C chains provide a good migration channel for lithium ions). These properties make C3N a promising candidate for Li-ion battery anode materials. Our findings suggest a physical mechanistic basis for modulating the electrochemical properties of such materials by controlling the arrangement of atoms. The study also provides new ideas for the modulation of the structure and properties of two-dimensional materials and points out a direction for the ongoing development and application of C-N materials and devices.