First-principles study of ionic conductor Li3N

• Main Author: Kow, Yan Siong.
• Other Authors: Dong Zhili
• Format: Final Year Project
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering::Materials::Energy materials
• Online Access: http://hdl.handle.net/10356/48439
• Institution: Nanyang Technological University

Since the 1960s, extensive researches have been done to search for promising materials for batteries in order to meet rising performance requirements of electronic devices. In order to achieve in high quality battery, it needs to have sufficiently high voltage, high durability (long-lasting), thin, easy for portable use and eco-friendly. Among various types of Lithium (Li) based material, Lithium Nitride (Li3N) is a type of fast ionic conductor, which is quite suitable as rechargeable battery material. Therefore, the purpose of this project is to investigate the Li vacancy formation energy of Li3N. There are mainly two phases in Li3N, including the Alpha-phase Lithium Nitride (α -Li3N) and Beta-phase Lithium Nitride (β-Li3N). In this project, the vacancy formation in β-Li3N is focused, based on previous knowledge on α -Li3N. The vacancy formation energy is calculated by solving the Schrödinger equation with first principles calculations. Density Functional Theory (DFT) and Generalized Gradient Approximation (GGA) are also applied along with the first principles calculations. Detailed calculations and material simulations are performed with the help of Vienna Ab-initio Simulation Package (VASP) and Materials Studio 5.5 software at Institute of High Performance (IHPC) under A*STAR Agency. Chemical potential of Li (µLi) is calculated and then compared under two different conditions, the Li rich condition and nitrogen (N2) rich condition. Calculations reveal that µLi is higher under Li rich condition than under N2 rich condition (i.e. Li poor condition). It indicates that Li vacancy formation is probably more favourable under Li rich condition. Moreover, the diffusion mechanism of Li+ ions in α-Li3N and β-Li3N are also diverged. The diffusion are dependent on two factors, including the site to site diffusion length of Li+ ion, and the Li removal energy of respective Li(1)-N and Li(2)-N bond. In α-Li3N, the diffusion is more dominant within the Li(2)2N plane; however, the diffusion is more likely to occur within the Li(1) plane in β-Li3N due to shorter diffusion length and lower Li removal energy (i.e. weaker Li-N bond).