An Ab Initio Study Of Conjugated Carbon Materials Interaction With Lithium Or/and Hydrogen

At present, resources are insufficient in most courtries, so that great attentions arealways focused on functional materials, such as electrode materials and hydrogen storagematerials. On the basis of our/previous experimental results and theoretical investigations, wecarried out series of theoretical calculations on the interactions of conjugated carbon materialswith lithium or/and hydrogen. The thesis provided theoretical supports for anode materialmodification of lithium ion battery and gave improved suggestions for the hydrogen storagemechamism of carbon materials. The contents and innovations are summaried as follow:1. The interactions of metal atoms(Li, Ca, Al)with aromatic hydrocarbon systems(C₆H₆,C₁₀H₈, C₁₃H₉)show a number of distinctive features. Li, Ca, and Al interact only weakly withbenzene and naphthalene, indicating physisorptions, whereas these metal atoms form a strongcovalent M-C bond with perinaphthene, showing chemisorptions, as revealed in calculations ofthe FMO distribution, M?C distance, binding energies, and charge on metal atoms using MP2with a 6-31G(d, p) basis set. The nature of the interactions relates to the valence orbital type ofmetal and the electron distribution of the conjugated systems of the aromatic hydrocarbons. Dueto the spindly-shaped 3p valence orbital, an Al atom favors the adsorption at the edge of theC₁₃H₉, whereas for a Li and a Ca atom, their ball-shaped 2s/4s valence orbitals overlap with theLUMO+1 of C₁₃H₉, which has a distinctive electron cloud on the central C atom. MP2 hasfurther been shown to reasonably account for weak interactions, whereas HF and B3LYP areboth unsuitable to describe the weak interaction of metal with benzene and naphthalene due totheir poor energetic and geometric results.2. As for the reason why C60 doping into PAS anode material could improve the performanceof lithium ion battery, we could make a summary by one sentence that the improvement is ownto the perfect spherical structure and high symmetry of C₆₀. During the charge or dischargeprocess, Li+ is inclined to form exohedral complexes above the hexagon center of PAS, and thehexagon and pentagon center of C-(60). The interaction between lithium and the anode materials(PAS doped with C₆₀) is weak ionic. The order of BE(C₆₀Li+(H)) < BE(C₆₀Li+(P)) 60 occurs more easily than that on PAS,which facilities the Li+ transportation in battery. By comparison with their precursors, the energygap (E_g) of these complexes are all decreased more or less. The order of ⊿E_g(C₆₀(H)) <⊿E_g(C₆₀(P)) < ⊿E_g(PAS) exhibits that PAS be influenced obviously by the intercalation anddeintercalation reactions, while C₆₀ could keep its structure and undergo many times of cycle soas to effectively increase the cycle lifetime of the battery. To testify the surface property of C₆₀, itis proved that the binding energies of C₆₀ with SEI film (about 13.5eV) are large enough toprotect the anode material from eroding in comparison with the physical constants of C60. Theclosely equal Eg of the composites C60SEI and PASSEI further ensure that they could safeguardthe security of inside anode material together.3. In this work, a systematic study of lithium adsorbed on the surface of (n, n) armchair (n=5-10)and (n, 0) zigzag (n=7-12) SWNTs has been performed by means of first-principle densityfunctional theory. The exterior surface of SWNTs, especially small radius (large curvature) (n, 0)zigzag SWNTs, presents strong attraction to lithium. The existence of a "Ï€-bond defect" on thehexagon center, entitles (n, 0) SWNTs effective reactivity in comparison with (n, n) SWNTs.Lithium can be absorbed on the surface of (7, 0) SWNT with the largest bind energy of 2.66eV.Hence (n, 0) SWNTs with the large curvature (small radius) are promising to be the candidatematerial for storage hydrogen and adsorbing the lithium atom.4. Simulations of H2 and Li interacting at different sites on three aromatic compounds C6H6,C10H8 and C13H9 usi...