First-principles study of Li adsorption in functionalized carbon nanotubes

According to the increasing inquiry of better electrochemical materials for electrical energy device such as battery of high energy and power density, various types of lithium intercalation materials have been used to promote Li adsorption. To raise the Li adsorption capacity of the carbon-based electrode, the carbon nanotubes (CNTs) have been considered to be one of the promising candidates because of its outstanding electrical and mechanical properties. Therefore, many theoretical and experimental works have been assigned to study the intercalation of Li in single-walled carbon nanotubes (SWCNTs) [۱]. In this study, we investigate the detailed energetic of lithium adsorption on the functionalized SWCNTs. Moreover, electronic properties of functionalized nanotubes before and after lithium doped were investigated.All calculations were carried out using the Quantum-Espresso package in which the DFT methodology is implemented using plane wave expansions and pseudopotentials [۲]. The structures considered here are NH۲/(۸,۰), COOH/(۸,۰) SWCNTs doped with lithium. The cutoff energies for plane waves were chosen to be ۵۰ Ry. Calculations were performed in the supercell approximation. The lattice parameter along the axial direction of the nanotube is ۳ times the unit length of the pristine nanotube. The Brillouin zones were sampled with ۱×۱×۹ Monkhorst–Pack meshes, which represent the convergence of our systems, along the Ƚ-Z direction [۳].Results and Discussion After functionalization of (۸,۰) SWCNT with –NH۲ and –COOH groups, we doped Li in the inside and outside of these nanotubes. The adsorption of Li on different sites of NH۲/(۸,۰), are presented in Figure ۱. The binding energy, (Eb=E(CNT+Li)-E(CNT)-E(Li)), of all Li-doped functionalized nanotubes was calculated and reported in Table۱. Considering the binding energy as a criterion for adsorption tendency, the internal adsorption of Li is more desirable than the external adsorption of Li. As indicated in Table ۱, the binding energy of Li-doped NH۲/(۸,۰) and COOH/(۸,۰) for all sites is more than of Li-doped (۸,۰) SWCNT. Moreover, binding energy of site A for functionalized nanotubes is more than that of all other sites.ConclusionAccording to the first principles calculations, functionalization of (۸,۰) nanotube with –NH۲ and –COOH groups increases the Li adsorption energies. After Li doping functionalized SWCNTs, conduction of functionalized SWCNTs is reduced.

کلیدواژه ها:

Density functional theory ، functionalized SWCNT ، Binding energy ، band structure.