Rational Design of Solid Polymer Electrolyte Based on Ionic Liquid Monomer for Supercapacitor Applications via Molecular Dynamics Study

The safety concern arising from flammable liquid electrolytes used in batteries and supercapacitors drives technological advances in solid polymer electrolytes (SPEs) in which flammable organic solvents are absent. However, there is always a trade-off between the ionic conductivity and mechanical properties of SPEs due to the lack of interaction between the ionic liquid and polymer resin. The inadequate understanding of SPEs also limits their future exploitation and applications. Herein, we provide a complete approach to develop a new SPE, consisting of a cation (monomer), anion and hardener from ions-monomers using molecular dynamics (MD) simulations. The results show that the strong solid-liquid interactions between the SPE and graphene electrode lead to a very small gap of similar to 5.5 angstrom between the components of SPE and electrode, resulting in a structured solid-to-liquid interface, which can potentially improve energy storage performance. The results also indicated the critical role of the mobility of free-standing anions in the SPE network to achieve high ionic conductivity for applications requiring fast charge/discharge. In addition, the formations of hardener-depleted regions and cation-anion-poor/rich regions near the uncharged/charged electrode surfaces were observed at the molecular level, providing insights for rationally designing the SPEs to overcome the boundaries for further breakthroughs in energy storage technology.