In the quest to make better batteries, researchers at Sandia performed extensive, atomistic molecular dynamics (MD) simulations of a set of ionomer melts. Ionomers are polymers that typically have a neutral backbone with a small number of charged moieties that are covalently bound to the polymer backbone. Ionomer melts, liquids containing just ionomer olecules and their oppositely charged ions, show promise as safe, solvent-free, lightweight, single-ion-conducting battery electrolytes if

their conductivity can be made high enough. However, without a solvent, ions aggregate and their dynamics slow, leading to conductivity too low for battery applications. Sandia researchers have used molecular dynamics simulations to better understand the ionic aggregates formed in ionomer melts and also the effects of these aggregates on ion dynamics. Recent atomistic simulations have focused on the effects of different ionomer backbone designs and different cations on structures resulting from ionic aggregation. Atomistic molecular dynamics simulations are computationally expensive, making Red Sky invaluable for some of these simulations. The simulations revealed that ionomers have a rich variety of ionic aggregate morphologies, often including long, “stringy” aggregates. This result contrasts the assumption in interpreting experimental

scattering data; that of spherical aggregates with liquid-like order. These unsuspected morphologies nevertheless fit experimental X-ray data well. Simulations on Red Sky showed that an applied electric field can induce alignment of the aggregates, and also revealed a relaxation mechanism involving ions moving along the aggregate network. This enhanced understanding is important for designing ionomers with better ion conduction properties.

Contact: Amalie Frischknecht |


Snapshot of MD simulation showing “stringy” ionic aggregates consisting of lithium ions (yellow) and oxygen atoms (red). The rest of the ionomer is not shown for clarity.