Combined ab Initio Quantum Mechanics and Classical Molecular Dynamics Studies of Polyphosphazene Polymer Electrolytes: Competitive Solvation of Li+ and LiCF3SO3

Abstract

Ab initio quantum mechanics (QM) and classical molecular dynamics (MD) simulations are employed to model an electrolyte composed of a polyphosphazene (PP), lithium triflate (LiCF3SO3), and water. Structures and energetics are systematically studied by QM for binary complexes of Li+, CF3SO3-, and Li+CF3SO3- with water or PP fragments, and for ternary combinations of Li+CF3SO3-, PP fragments, and water. Li+ interacts most strongly with the backbone nitrogen of PP, somewhat more weakly (and comparably) with ether oxygens on PP side chains and with water oxygens. This indicates that Li+−N interactions should significantly affect migration of Li+ in PP polymer electrolytes. Calculated coordination patterns of Li+ with the poly(ethylene oxide) model (ethylene oxide)6 [(EO)6] agree with experimental results in which Li+ is strongly coordinated with five oxygens in PEO. Binary aggregates of LiCF3SO3 and (EO)6 are also examined. Both Li+ and LiCF3SO3 coordinate preferentially with neighboring N atoms and a methoxy...