First-Principles Study on the Chemisorption of Sodium Ions on the Surface of Carbon Nanotubes

This study systematically investigates the adsorption behavior of sodium atoms on zigzag (7,0) and armchair (7,7) carbon nanotubes (CNTs) using first-principles calculations, focusing on their effects on the electronic structure and optical properties. Three adsorption configurations—inner, outer, and double-sided—were analyzed to clarify the mechanisms of charge transfer and orbital hybridization. The results indicate that internal adsorption in zigzag (7,0) CNTs (−9.43 eV) and external adsorption in armchair (7,7) CNTs (−8.16 eV) achieve a favorable balance between adsorption stability and desorption reversibility, with adsorption energies and diffusion barriers that are more consistent with practical requirements. Optical analyses show typical Drude-type conductive behavior and pronounced polarization in both systems, with the double-sided structure displaying the strongest dielectric and optical conductivity responses. These findings provide valuable theoretical guidance for the design and optimization of carbon-based sodium-ion battery electrodes.