A first-principles study of the electronic structures and transport properties of energy related materials

Abstract

To improve the efficiency of energy conversion and storage, research on energy-related materials with high performance has attracted significant interest. In modern materials science, ab initio calculations based on density functional theory (DFT) are important methods for materials research. The electronic structures obtained via ab initio calculations can be used to deduce various physical and chemical parameters of materials, providing theoretical guidelines for the experimental investigation and development of materials. In the work presented in this dissertation, the electronic structures and transport properties of energy-related materials were studied by means of DFT, Boltzmann transport theory and density functional perturbation theory (DFPT).

First, ferroelectric engineering of two-dimensional (2D) group IV-VI compounds was carried out in the framework of DFT. Two competing phases were considered, i.e., the rippled phase and the hexagonal phase. The rippled phase is non-centrosymmetric and exhibits spontaneous polarization while the hexagonal phase is centrosymmetric and non-ferroelectric. Their relative stability and ferroelectricity were calculated. Pb doping was applied to stabilize the rippled phases of GeX (X = S, Sn or Te) and SnTe, and equiaxial tension was used to manipulate the ferroelectricity in the rippled phases of PbX.

Second, the electrochemical behaviors of 2D materials in alkali metal ion batteries were investigated. It was found that alkali metal atoms exhibit high adsorption and diffusion performance on the surfaces of Janus TiSSe and VSSe, suggesting that these two transition metal dichalcogenides (TMDs) with novel crystal structures are promising anode materials for alkali metal ion batteries. In addition, the adsorption of alkali metal atoms on 2D group IV-VI compounds was simulated, and the results indicated that these compounds may be used as electrode materials for lithium-ion batteries.

Finally, the electronic structures and transport properties of thermoelectric materials were calculated. To realize thermoelectric conversion, thermoelectric engineering of 2D SnTe was carried out. It was predicted that the power factor of 2D SnTe can be enhanced by strain and that iodine may be an effective n-type dopant in 2D SnTe. Moreover, the effects of impurity elements on the electronic structures of some thermoelectric materials were discussed. These DFT calculations may provide theoretical guidelines for the experimental study of thermoelectric materials.