Abstract: One of the most ubiquitous technologies in our modern society is the lithium-ion battery. However, a major issue plaguing current lithium-ion battery technology is the risk of thermal runaway, a series of irreversible exothermic reactions that can result in fire or explosions, endangering the user. One strategy to mitigate this issue, is to replace the flammable liquid electrolyte with a solid fast-ion conductor such as a lithium garnet. However, to achieve performance comparable with current battery technology, the ionic conductivity of this electrolyte material must be improved by about an order of magnitude.
The lithium garnet series Li7-xLa3Zr2-xTaxO12 (x = 0−2) has shown great promise as a solid electrolyte material; however, the room temperature conductivity is currently too low to find wide commercial success. To better understand the mechanisms of ionic diffusion within the crystal, a combined molecular dynamics (MD) and quasi-elastic neutron scattering (QENS) study was performed. QENS experiments allow us to measure the dynamic structure factor S(Q,ω), capturing both the residence time and mean jump distance of lithium directly, while our MD simulations allow for the observation of individual diffusion events. Overall, we saw good agreement between the QENS and simulation work, both predicting a jump-diffusion model in the form described by Singwi and Sjölander. The lithium concentration effects on diffusivity will also be addressed, as well as some best-practice techniques with respect to modeling the garnet series by using DFT and MD.