Theoretical Investigation and Design of Optoelectronic and Battery Materials using Multiscale Simulation Methods

Abstract

Developing new materials for optoelectronic and battery applications has been an important research field since the 20th century and will never be ended as long as we use electric energy in daily life. There are always new challenges to solve or improve for commercialized and researched materials. Our purpose is to understand the properties of existing materials and predict the performance of theoretical materials through multiscale molecular simulations, so that we contribute and accelerate to design new materials. In Chapter 1, we introduce the motivation of our studies on optoelectronic and battery materials. Research progress and challenges of each material are introduced, and the trend of how the researchers conduct theoretical calculations in each field is explained. We also discuss the theory and features about our multiscale simulation techniques including density functional theory (DFT), Monte Carlo (MC), and molecular dynamics (MD). In Chapter 2, we investigated structures and properties of experimentally developed optoelectronic and battery materials. First, the formation of Cu-Fe-S nanocrystal (NC) and the source of its high electrical conductivity were analyzed by DFT calculations. The transition pathway of stacking structure and two different behaviors of following reactions depending on Fe content were revealed. The synergetic effects of Cu vacancies and Fe content on electronic structures of Cu-Fe-S NC induced the high electrical conductivity. Next, we investigated the role of H-enriched Cu surface (i.e., CuH) on room-temperature growth mechanism of single-crystalline graphene (SCG). H atoms in Cu subsurface increased the electrophilicity of Cu surface and the probability of benzene radicals binding near active sites. Aromatic hydrocarbon formations on CuH surface exhibited low reaction barriers enough to proceed at room temperature. Finally, the structures and proeprties of thermally annealed poly(methacrylic acid) (PMAA) was investigated to understand high specific capacity and crystallinity. Anhydride carbonyl groups in annealed methacrylic acid (MAA) showed strong Li+ binding and induced stretched structures of PMAAs, leading to more Li+ binding sites and intermolecular interactions than pristine PMAAs. In Chapter 3, we introduced theoretical design of new materials for H2O2 photosynthesis and electrolyte additives via computational screening. First, DFT-based computatioal screening were performed on metal oxides. The phase stability of 665 bulk structures and adsorption energies of reaction intermediates on 2,500 surface models were calculated to predict catalytic performance. As a result, 32 surfaces were sorted out for promising photocatalysts with stable structure, high activity, and selectivity. Additionally, doping effects of another metal atoms and vacancies on selected surfaces with high performance were estimated whether the doping enhances the catalytic activity or selectivity. Next, we predicted the electrochemical properties of electrolyte additives for electrodes of lthium-ion batteries (LIBs) through DFT-based computational screening. 143 cathodic additives based on heteroarene with cyano groups and 109 anodic additives based on vinylene carbonate were generated by modification of various functional groups which affect the electrochemical properties of molecules. In the screening, seven theoretical descriptors were adopted for additive candidates to estimate the oxidative and reductive reactivities and other additional functions in electrolyte. As a result, 17 promising additives with high oxidative or reductive reactivity compared to solvents and existing additives were sorted out.