Mechanistic insight into high-efficiency sodium storage based on N/O/P-functionalized ultrathin carbon nanosheet

Abstract

Heteroatom functionalized carbon materials are considered as the most promising candidate for SIBs, which display excellent Na+ storage performance. However, the relationship between the structure and electronic properties and sodium storage isn't completely revealed for heteroatom-functionalized carbon, including the effect of heteroatom on conductivity and charge distribution of carbon, the possible stable adsorption model for Na+ ion, and the diffusion characteristic of Na+ ion between heteroatom-functionalized carbon layers. Herein, we synthesize N/O/P-functionalized ultrathin carbon nanosheet aerogels (NOP–CNSAs) via a simple thermal treatment method. The prepared NOP–CNSAs possess ultrahigh specific surface area (SSA) and ultrathin thickness of ~1 nm. The density functional theory (DFT) calculations find that the N/O/P-functionalization in the carbon nanosheets can boost the electronic conductivity of carbon and increase the charge accumulation region around the heteroatoms functionalized bilayer carbon. This results in an increase adsorption energy (−2.64 eV) of Na+, and a decrease in barrier energy values of Na+ diffusion (0.13 eV) in N/O/P-functionalized carbon. When evaluating NOP–CNSAs as anode materials for SIBs, the specific capacity of the sample is 317 mA h g−1 at 100 mA g−1, and the cycling stability is outstanding (182 mA h g−1 at 1000 mA g−1 over 3000 cycles).