Polycyclic Aromatic Hydrocarbons as Anode Materials in Lithium-Ion Batteries: A DFT Study

The structure and energetics of the interactive behavior of Li⁺ and Li with polycyclic aromatic hydrocarbons (PAHs) have been studied at the wB97XD/6-311G(d,p) level of DFT. The electron distribution in the PAHs, analyzed using the topology of the molecular electrostatic potential (MESP), led to the categorization of their aromatic rings into five types, viz R_s, R_n, R_d, R_b, and R_e. Among the different rings, sextet-type R_s and naphthalene-type R_n rings showed the highest interaction with Li⁺. The change in MESP at the nucleus of Li⁺ (ΔV_Li⁺) due to the formation of the complex Li⁺...PAH is found to be proportional to the adsorption energy (E₁). In Li...PAH, the spin density on Li is close to zero, suggesting the formation of Li⁺...PAH^•- due to the electron transfer from Li to PAH. The adsorption energy (E₂) for Li...PAH does not correlate with the change in MESP at the nucleus of Li, whereas the dissociation energy (E₃) of Li⁺...PAH^•- to yield Li⁺ and PAH^•- correlates well with the MESP data, ΔV_Li. The study confirms that the change in MESP at the nucleus of Li⁺ due to complex formation gives a quantitative measure of the electronic effect of the cation-π binding. The cell potential (V_cell) is predicted for the lithium ion battery (LIB) using the Li⁺...PAH and Li...PAH adsorption energies. On the basis of the V_cell data, "carbon nanoflake"-type systems, viz coronene, circumbiphenyl, C₄₂H₁₆, and C₅₀H₁₈ are suggested as good anode materials for LIBs.

Reinforcing the tetracene-based two-dimensional C48H16 sheet by decorating the Li, Na, and K atoms for hydrogen storage and environmental application -A DFT study

To meet the increasing need of energy resources, hydrogen (H₂) is being considered as a promising candidate for energy carrier that has motivated research into appropriate storage materials among scientists. Thus, in this study for the first time, zig-zag and armchair edged tetracene based porous carbon sheet (C₄₈H₁₆) is investigated for H₂ storage using the density functional theory. To explore the hydrogen storage capacity, the hydrogen molecule is initially positioned parallel to the C₄₈H₁₆ sheet at three different sites, resulting in lower adsorption energies of -0.020, -0.024, and -0.015 eV respectively. The Li, Na, and K atoms are decorated to improve H₂ adsorption on the C₄₈H₁₆ sheet. The Li atom decorated C₄₈H₁₆ sheet has a higher binding energy value of -2.070 eV than the Na and K atom decorated C₄₈H₁₆ sheet. The presence of Li, Na, and K atoms on the C₄₈H₁₆ sheet enhance the H₂ adsorption energy than the H₂ on the pristine C₄₈H₁₆ sheet. The decrease of Mulliken charge in alkali metal atoms (Li, Na, and K atom) on the C₄₈H₁₆ sheet reveal that the electron is transferred from H-σ orbital to s orbital of alkali metal atoms on the C₄₈H₁₆ sheet, leads to the enhancement of H₂ binding. Compared to H₂ adsorption on Na and K atom decorated C₄₈H₁₆ sheet, the H₂ adsorption on Li atom decorated C₄₈H₁₆ sheet has the maximum adsorption energy value of -0.389 eV. The obtained hydrogen storage capacity of Li, Na, and K atoms decorated C₄₈H₁₆ sheets are about 7.49 wt%, 7.31 wt%, and 7.14 wt% respectively for four H₂ molecules, which is greater than the targeted hydrogen storage capacity of the United States Department of Energy (DOE). Thus the obtained results in this work reveal that the decorated C₄₈H₁₆ sheets with Li, Na, and K atom plays the potential role in the H₂ storage.

Arsenene monolayer as an outstanding anode material for (Li/Na/Mg)-ion batteries: density functional theory

Arsenene, a single-layer arsenic nanosheet with a honeycomb structure, has recently attracted increasing attention due to its numerous exceptional properties.