Estudo teórico da adsorção de átomos, íons e clusters de Li em nanoestruturas de carbono: um potencial modelo para aplicações eletroquímicas

• Ano de defesa: 2021
• Autor(a) principal: Gabriel Monteiro de Castro
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais
• Palavras-chave em Português: Físico-química; Eletroquímica; Baterias de lítio; Funcionais de densidade; Adsorção; Grafeno; Energia - Armazenamento; Nanotecnologia
• Link de acesso: https://hdl.handle.net/1843/36019

The present work has dealt with the DFT and ab initio methodologies applied for studying the adsorption of atoms, ions and clusters of Lithium (Lin0/+, n = 1 → 4) on different regions of hydrogenated pristine graphene (PG) structures and with the Stone-Wales (SWG) defect. Different combinations of density functionals and basis sets were used for calculating the electronic structure of Li clusters. Among the levels of theory employed, the level B97-D/6-31G(d,p) demonstrated the best results compared with data available from recent literature. The functionals B3LYP and SVWN failed considerably to represent the thermodynamic and electronic parameters of some studied Li clusters. A Li+ ion adsorption mapping process was carried out on one of the PG and SWG models with the focus on simulating the operation of Lithium-Ion Batteries (BIL). As previously observed in the literature, the mappings showed that the Li+ ion is more stable adsorbed on the edges of both PG and SWG structures through an electrostatic interaction. The ChelpG charge distribution calculations, analysis of the boundary orbitals, and the simulated Raman and UV-Vis spectra indicated interference of the metallic and electronic character of the isolated graphenes after the adsorption of the Li0/+ species. The calculated Raman and UV-Vis spectra revealed variations in intensity and displacements of the absorption bands that are typically observed on graphene systems. These variations may contribute to propose new experiments for spectroscopic characterization of Li0/+-Graphenes systems. The results of the mapping carried out with the Li0/+ species were used as a starting point for the adsorption of the Lin0/+ clusters (n = 2 → 4) on the graphene models’ surfaces. The presence of the clusters in the nanostructures revealed a reduction in the values of HOMO-LUMO gap, adiabatic and vertical ionization potentials (PiA e PiV, respectively) and work function (Φ) for all systems. However, a considerable decrease in the electrical voltage values of the theoretical BIL (VBIL) for the systems containing the Stone-Wales defect seems to suggest a great disadvantage when using defective nanostructures in the design of anodic materials for BIL applications. The presence of the Stone-Wales defect provides the systems with greater reactivities to the point of obtaining Li0/+-SWG systems thermodynamically more stable than Li0/+-PG systems. Thus, the working process of BIL can be compromised by using only SWG systems in the construction of the anodic material.