Enhancement of lithiation on a graphane monolayer through extended H vacancy pathways: An ab initio study

The increasing interest for the need of large-scale energy-storage systems have led to the development of high-performance energy-storage devices such as lithium-ion batteries (LIBs). Two dimensional (2D) materials are promising candidates for fulfilling this requirement due to their peculiar physical properties. However, it is important to understand the role of multiple Li adatoms on the 2D materials, more especially when defects are involved. In this study, first-principles density functional theory (DFT) calculations were performed to study Li on the H vacancies (VH) following the line and zigzag pathways on a graphane sheet. The results of Li atom on a single H vacancy (VH1) reveal an immediate enhanced interaction based on the improved binding energies, high amount of charge transfer and significantly shortened Li height, as compared to those of pristine graphane counterpart. An increase in the number of H vacancies along the line pathway from one (VH1(L)) to five (VH5(L)) further improves the binding energies ranging from 1.82 eV to 2.91 eV. Considering a simultaneous increase of Li atoms and H vacancies following a line pathway (VH1(L) to five VH5(L)), the binding energies tend to reduce in order. However, it is still higher than the minimum Li standard bulk cohesive energy of 1.63 eV. We show that there is a possibility of uniform dispersion of Li atoms with less clustering on a graphane sheet. A transition from insulator to metallic character was observed from VH1(L) to VH5(L), due to an induced new Li states at the vicinity of the Fermi level, suggesting an enhancement of electronic conductivity in the graphane sheet. At five Li atom VH5(L) configuration along the line pathway, we obtained a relatively high storage capacity of 207.49 mAh/g with its corresponding lithiation potential of 1.48 V, comparable to those of well known two dimensional anode materials.