The Analysis And Application Of First-principles On The Design Of Several Low-dimension Energy Materials

Experiment, computation, and theory are indispensable for the materials analysis and design. Material modeling stretches over computation and theory, which makes its importance self-explanatory. With respect to computation, the development of computational materials has pushed density functional theory and its computation methodologies to high technique application area, of which materials analysis and design is an active research concern of domain. With respect to theory, in the framework of density functional theory and without the consideration of high energy radiation correction, to describe various kinds of properties of a many-particle system, the only things we should know involve the electromagnetism theory, Schrodinger equation, and/or Dirac equation plus seven parameters (the mass and charge of electron/atoms, Bohr radii, Planck constant, fine-structure constant) which have no relationship with specific materials. Based on this, concretely, this thesis tries to perform first principles analysis and design to the low dimension materials, which have been applied in the areas of dye-sensitized solar cell, hydrogen storage, and rechargeable Li ion battery. This includes,(1) In the framework of density functional theory/time-dependent density functional theory, we investigate geometry properties, excitations and electronic structures of triarylamine-based dyes before and after binding to titanium, and compare the effects of two different anchor groups on the system photoelectrochemical properties. The results show that, compared with rhodanine-3-acetic acid anchor, cyanoacrylic acid anchor can provide larger open circuit potentials and more favorable conjugation with titanium. This result is expected to shed light on the design of metal-free organic dyes for Dye-sensitized Solar Cells.(2) We investigate the geometries, electronic structure, thermodynamics, and hydrogen storage properties of magnesium (Mg)/magnesium-hydrogen (Mg-H) nanowires with the diameter of several nanometers. The results show that magnesium(Mg)/magnesium-hydrogen(Mg-H) nanowires within this scale possess the same hydrogen content as its bulk phase, but only half of the hydrogen desorption enthalpy of its bulk phase, which means this system can absorption/desorption hydrogen at room temperature. Further research exhibits that system stability and its Mg-H interaction can be controlled by hydrogen content and size, which is essentially led by the competition of the mechanisum of Mg-H interaction.(3) We demonstrate Li transport process in the silicon thin film anode of rechargeable Li-ion batteries. We find that Li surface intercalation is the rate-limiting step during the process, due to its high energy barrier, Li transport will be very slow in this step and will affect the whole Li transport, and finally, silicon anode will not reach high-rate capability. We further investigate the effect of surface doping by group III/V elements on the energy barrier of rate-limiting step. The results show that subsurface/surface Al doping or surface P doping is promising for the design of silicon anode materials applied in Li-ion batteries with high-rate charge/discharge capability.