Sodium Adsorption and Intercalation in Bilayer Graphene Doped with B, N, Si and P: A First-Principles Study

Abstract

Heteroatom-doped graphene is a potential anode material in sodium-ion batteries (SIBs). However, understanding the mechanisms of Na adsorption on the surface and intercalation in the interlayer remains a critical challenge to develop a suitable heteroatom-doped graphene anode. In this work, the structural and electronic influences in B-, N-, Si- and P-doped bilayer graphene (BLG) have been investigated by first-principles calculations. Pyridinic N, graphitic B and Si-doped BLG have preferential adsorption for Na with stronger surface binding than intercalation. The undoped carbon layer of B-doped BLG can be converted into n-type doping state by inserting Na, and the doped layer remains p-type mainly caused by the different electrons transfer to carbon layers from Na. Additionally, the electronic conductivity and Na diffusions on surfaces and in interlayers during sodiation are improved by doping heteroatoms. However, pyridinic N, graphitic Si and P doping promote the Na storage on surfaces and in interlayers of BLG due to the structural influence of carbon vacancy, which leads to high activation barriers during desodiation. The graphitic N-doped BLG is unsuitable and reduces the numbers of storage sites for Na in/on it. Therefore, B-doped and pyridinic N-doped BLG are promising anodes for SIBs because of stronger attraction and better kinetics of the electronic and cationic transport.