DFT Study of Diffusion Rate in Solid Electrolytes for Safe Design of Solid State Batteries

Abstract

Lithium ion batteries(LIBs) are in high demand as energy storage media because of their high energy density, outstanding power density, and main feature is deliberate self- discharge rates. In point of fact, LIBs are leading the market of portable devices since their launch in the 1990. However, high emergent demand for large battery packs, especially those to be equipped on electric vehicles, requires severe safety concerns because of incapable electrolytes being more toxic and flammable. Solid state batteries are encouraging substitutions to LIBs and eventual key solution to the safety issues because of non-flammability of solid electrolytes which is the leading feature of solid electrolyte. The compatible potential between SEs and Lithium metal anodes and with high voltage cathode also lead to solid state batteries with higher energy density compared with conventional lithium ion batteries. So, solid-state batteries have been appealing wide attention for next generation energy storage devices due to the probability to realize higher energy density and superior safety performance compared with the state of art the art lithium ion batteries. However, the currently available SSBs have low performance due to slow ionic transport between SE and electrodes which leads to poor cycling stability. There are still many issues to be addressed to meet the industrially scalable solid state batteries. In the present thesis, the main focus is on the calculation of diffusion rate through solid electrolytes in order to get contribution in the research of finding the parameters which are involved in ionic diffusivity through solid electrolytes. Lithium argyrodite superionic conductor of the form Li7GeS5Br has shown great promise as a sulfide based solid state electrolytes due to high energy density and high diffusivity rate. In the present work simulation method is used to calculate the Li ions diffusion coefficient through solid electrolytes. Molecular Dynamics simulation is a powerful tool to study the diffusion coefficient through solid electrolytes. In this project, MD simulation is used to calculate the diffusion coefficient through Li7GeS5Br. With the help of MSD versus time plot the diffusion coefficient is calculated. Firstly, the structure of Li7GeS5Br is optimized. The optimized supercell was used as a benchmark model for subsequent calculations. During simulation process different trajectories of ionic movement have been collected in which lithium ions intra cage and inter cage jumps have been visualized. These detailed diffusion pathways and properties offer a throughout understanding of the diffusion process in solids and provide improved road map to design solid state batteries.