DFT Molecular Dynamics Simulations of Li+

Abstract

INTRODUCTIONUsing first principle Density Functional Theory (DFT) simulations of both the crystalline and amorphous phases of β-Li3PS4, the cause of high conductivity of Li+ ions in the amorphous phase is explored. β-Li3PS4 and other lithium thiosulphates are promising electrolytes for all solid-state batteries, even in their amorphous phases. However, the high conductivity in the amorphous phase is not understood. This research aims to predict conductivity in amorphous electrolytes by comparing diffusion in the crystalline and amorphous phases of a known conductor. METHODOLOGYThis project uses first principle DFT simulations to simulate diffusion paths in the β-Li3PS4 solid electrolyte and its amorphous analog. These simulations are done using the planewave DFT in the Quantum ESPRESSO[1] package, with a 128 atom supercell for the crystalline phase and a 640 atom amorphous electrolyte. By varying different factors such as, cell volume and temperature and lattice disorder, we were able to compare and understand the diffusion of Li+. RESULTS and DISCUSSIONIn this research, we aim to improve conductivity in amorphous and crystalline electrolytes by simulating the lithium ion diffusion pathways in lithium thiophosphates. The structure of the unit cell is shown in Fig. 1 [2] . The data is analyzed to identify the following effects on lithium ion diffusion: Covalent-type bonding between Li+ and the anion sub-lattice The disorder within the cell, from local disorder to the full amorphous phaseLithium ion motion correlations The results presented will be molecular dynamics of both amorphous and crystalline structures of β-Li3PS4. Comparison of local structure and diffusion pathways in the amorphous and crystalline phase, in particular the effect of covalent bonding and correlated Li+ motion. [1] P. Giannozzi, et al J.Phys.:Condens.Matter, 21, 395502 (2009) http://dx.doi.org/10.1088/0953-8984/21/39/395502 . (BibTeX format). [2] VMD- Visual Molecular Dynamics. Computer software. Theoretical and Computational Biophysics Group. Vers. 1.9.2. Board of Trustees of the University of Illinois, n.d. Web. 13 Apr. 2016. Figure 1