Combined ab initio quantum mechanics and classical molecular dynamics studies of polyphosphazene polymer electrolytes:: Competitive solvation of Li+ and LiCF3SO3Academic Article
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Ab initio quantum mechanics (QM) and classical molecular dynamics (MD) simulations are employed to model an electrolyte composed of a polyphosphazene (PP), lithium triflate (LiCF 3SO 3), and water. Structures and energetics are systematically studied by QM for binary complexes of Li +, CF 3SO 3-, and Li +CF 3SO 3- with water or PP fragments, and for ternary combinations of Li +CF 3SO 3-, 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 LiCF 3SO 3 and (EO) 6 are also examined. Both Li + and LiCF 3SO 3 coordinate preferentially with neighboring N atoms and a methoxy oxygen near the PP backbone. Classical MD simulations qualitatively reproduce the results of QM calculations, and provide details about the Li + distribution in a larger system. Results of the QM and classical MD calculations suggest a model for the microstructure of the polyelectrolyte.
