Study of structural and phase behaviour of a polymer electrolyte using molecular simulation

There is a growing demand for high energy density, long-durable, highly stable and environmentally sustainable batteries. Polymer electrolyte-based batteries have the potential to meet these demands due to their ability to combine the solid-like stability of polymers with the high ion conductivity of ionic liquids[1]. However, the realization of commercially viable polymer electrolytes requires addressing fundamental polymer science problems. First, the conductivity of ions is appeared to be intimately coupled with the segmental dynamics of polymers. Second, both ion conductivity and mechanical properties of ionic liquids are strongly related to the glass-forming behaviour of polymers. These factors lead to an inverse correlation between ion conductivity and mechanical properties of polymer electrolytes. Therefore, designing polymer electrolytes with high ion conductivity and high mechanical property is an outstanding challenge[2]. Understanding how conductivity and stability of the materials are connected to the exact location of ionic moiety in a polymer architecture, spacer length, and ion pair volume, hierarchical architecture such as block copolymer and telechelic polymers are vital to address this problem. Here we use coarse-

grained molecular simulation[3] of a phenomenological model to understand how the composition of a polymer matrix is correlated to its conductivity. In this model system, a polymer is represented as a Kremer-Grest FENE chain. Ions are modelled as spherical LJ particles with varying size. All the calculations are done in the LJ unit. Particularly, we have systematically analysed ion distribution in a polymer matrix. Ion distribution, which is strongly connected to the material’s conductivity, is shown to beimpacted by the medium's ion-pair size ratio and dielectric constant[4]. We have proposed a phase diagram [5] from the simulated results based on Fractal dimensions which shows variations in three regions from dispersion , Percolated and complete phase seperation of ions in a polymermatrix as a function of ion pair size ratio and dielectric constant.