The low ionic conductivity across solid-solid interfaces and through the solid electrolyte is a limiting factor for commercial implementation of all solid state batteries. Through the understanding of Li+ ion diffusion by using first-principles molecular dynamics, significant insights in developing new battery materials can be achieved. Previous research has determined the mechanism for the lithium ion diffusion pathway through Li3InBr6 and noted its non-Arrhenius behavior at high temperatures. These results expand on those previous findings by simulating diffusion in Li3InBr6-xClx at temperatures between 700-900K. In particular, we will determine the effects of high temperature and analyze the electronic structure in order to explain variation in the Li+ conductivity in these lithium halides. To simulate lithium ion diffusion and to track bond breaking and formation in Li3InBr6-xClx, ab-initio DFT-MD with ultra-soft (Vanderbilt) pseudo-potentials are used as implemented in the Quantum ESPRESSO PWscf package. Simulations are executed on 2x2x2 Li3InBr6-xClx unit cells for 25 ps with a 1 fs time step at 700 K, 800 K, and 900 K. Maximally Localized Wannier Functions (MLWF), the mean squared displacement (MSD) and diffusion coefficient, radial distribution function (RDF), and plots of bond and Li+ density are used to analyze lithium ion diffusion. It was determined that the exchange of Br anions with Cl anions changes the character of bonds, especially those with polar-covalent interactions. In particular, Br produces more covalent character than Cl, which can be used to explain the experimental difference in conductivity. It was also determined that lithium ion diffusion in Li3InBr6-xClx electrolytes exhibited non-Arrhenius behavior around 900K. This deviation is due to changes in the electronic structure, such as weakening of covalent bonds, as shown through analysis with MLWF.

First-principles molecular dynamics of non-arrhenius Li+ diffusion in solid electrolytes for batteries

253rd National Meeting (2017)

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