Atomic scale modeling of PEO based solid polymer electrolytes for solid state rechargeable batteries

Abstract

Direct observation of migration pathways of ions and a quantitative dissection of their energetics in solid polymer electrolytes (SPEs) are essential to understand the molecular origins of barriers limiting the conductivity of these novel materials. The principal driving forces controlling the degree of conductivity of SPEs including the nature of macromolecular packing, ion-polymer interactions, ion coordination structure, conformational order and mobility of polymers are significantly different among the SPEs. However, the precise correlations between these molecular factors and the ion transport in SPEs are not well established. It remains unclear whether disordered amorphous or ordered crystalline structures promote conduction of ions in SPEs. The other important challenges that remain in SPE-related research are the identification of low-energy ion conduction pathways, characterization of the free energy profiles and the structural and dynamical contributions to the favorable (stable energy wells) and unfavorable (activation energy barriers) ion sites along these conduction pathways. newline newlineDetailed molecular studies are needed to establish a precise correlation between the nature of polymer packing, dynamics, energetics, and ion conduction for rational design of SPE-based fast ion conductors. In this regard, molecular dynamics (MD) simulations and enhanced sampling free energy methods play an important role in elucidating the atomistic details of ion transport and the critical ion-ion and ion-polymer interactions in SPEs. In the present thesis, we have employed molecular dynamics (MD) simulation, enhanced sampling methods (for example, the adaptive biasing force (ABF) method, well-tempered metadynamics (WTmetaD) simulation, and nudged elastic band (NEB) method) and normal mode analysis (NMA) to investigate the structure, dynamics and energetics of crystalline and amorphous phases of poly(ethylene oxide) (PEO) and PEO-based SPEs.