Engineering selenium-doped nitrogen-rich carbon nanosheets as anode materials for enhanced Na-Ion storage

Heteroatom-doping is an effective way to regulate the electronic structure of carbon so as to improve their Na-ion storage capability. In all kinds of heteroatoms, selenium (Se)-doping has rarely been investigated even though Se has unique physicochemical properties. Herein, we report a facile fabrication of Se/N-codoped carbon nanosheets (N/Se-CNs) with 10 at% N and 2 at% Se by an oxidation-selenization process. The synchrotron X-ray photoelectron spectroscopy (XPS) measurements indicate that Se doping can significantly change the electronic structures of carbon nanosheets, because Se can act as stronger electron-withdrawing units for Na storage compared with C and N. Therefore, Se can better play the role of improving the conductivity and wettability of the carbon materials. And Se atoms effectively enlarge the interlayer distance of carbon nanosheets to enhance the Na-ion diffusion kinetics and also generate extra active sites for Na-ion storage. Served as anode materials for SIBs, the N/Se-CNs delivers higher specific capacity and better rate capability compared with only N-doped carbon nanosheets. Therefore, Se-doping is an effective way for improvement of Na-storage capability of carbon materials. Moreover, this work should provide a new pathway for design of carbons doped by heteroatoms with large atomic size towards excellent Na-ion storage.