Crosslink-Defined Microstructure and Dynamics in Polymer Electrolytes

Solid polymer electrolytes (SPEs) - polymer melts with added salts - exhibit ion conduction and high mechanical properties, and are thus promising materials for future energy storage devices. The ion conductivity in a solid polymer electrolyte (SPE) is intricately connected to the distribution of salt ions within the polymer matrix, though the molecular mechanisms behind this relationship remain poorly understood. Here, we conduct large scale coarse-grained molecular dynamics simulations and establish correlations between ion distribution and transport for a phenomenological SPE model. We show discreate ion aggregates, percolating ion aggregates and macrophase separation in SPEs as a function of ion pair size ratio and dielectric constant of the medium. Furthermore, we show that ion percolations can be finely controlled by crosslinking polymers and the ion diffusion exhibit a strong correlation with the ion distribution in the polymer matrix. These findings implicate that the crosslink as a key variable in SPEs, one that can be used to facilely tune their mechanical property and ion conductivity.