The sensitive aspects of modelling polymer-ceramic composite solid-state electrolytes using molecular dynamics...

Solid-state composite electrolytes have arisen as one of the most promising materials classes for next-generation Li-ion battery technology. These composites mix ceramic and solid-polymer ion conductors with the aim of combining the advantages of each material. The ion-transport mechanisms within such materials, however, remain elusive. This knowledge gap can to a large part be attributed to difficulties in studying processes at the ceramic-polymer interface, which are expected to play a major role in the overall ion transport through the electrolyte. Computational efforts have the potential of providing significant insight into these processes. One of the main challenges to overcome is then to understand how a sufficiently robust model can be constructed in order to provide reliable results. To this end, a series of molecular dynamics simulations are here carried out with a variation of certain structural (surface termination and polymer length) and pair potential (van der Waals parameters and partial charges) models of the Li₇La₃Zr₂O₁₂ (LLZO) poly(ethylene oxide) (PEO) system, in order to test how sensitive the outcome is to each variation. The study shows that the static and dynamic properties of Li-ion are significantly affected by van der Waals parameters as well as the surface terminations, while the thickness of the interfacial region - where the structure-dynamic properties are different as compared to the bulk-like regime - is the same irrespective of the simulation setup.