(597d) Molecular Dynamics Simulation of Inorganic Ions in Peo Aqueous Solution Using on Quantum-Chemistry-Based Force Field

Solid polymer electrolytes (SPE), inorganic salts dissolved in the polymer matrix that are known to have high ionic conductivities, are the basic components of polymer batteries [1]. These materials are becoming the subject of intense study. One of the most promising polymer hosts for these polymer/salt systems is polyethylene oxide (PEO), - (CH2 - CH2 - O) n-, which has been shown to have the ability to solvate inorganic salts well [1]. Previous experiments and computer simulations mainly focused on the properties of PEO and salt mixture forming the basis of the PEO/salt batteries and proved that the polarization effects have an important influence on the structure, conformations, and dynamics of PEO, especially in its aqueous solutions [2, 3]. Recently, ternary mixtures composed of PEO/salts in aqueous solution have been shown to display more attractive properties than binary SPE mixtures. Numerous experiments have found a dramatically changed environment for the cations and increased ionic conductivity of polymer/salts electrolytes for increased relative humidity, suggesting that the coupling between polymer chains and cations may be weakened due to the existence of water molecules [4]. Here, we report a molecular dynamics study of inorganic ions in PEO aqueous solution and the competitive solvation of ions between water and polymer oxygen. In order to accurately compute the intermolecular interactions, we take into account polarizabilty via the dynamic shell model and develop a polarizable force field using quantum chemistry calculations [5]. We used earlier published polarizable forcefield for 1, 2-dimethoxyethane (DME)-the simplest PEO polymer molecule [6], the RPOL water model, and their interactions with ions [7]. To obtain force field parameters for interactions between the polarizable water and polymer, we performed ab initio calculations of a DME-water complex in two predominant configurations, and varied distances between the two molecules. The calculated energy profiles were then used to fit non-Coulombic parameters of the forcefield. The developed force field was tested against experimental thermodynamic data and consequently used to study structure and dynamics of PEO/water/salt ternary mixtures. The structure was compared to neutron diffraction experiments and dynamics to conductivity measurements. Complexation of Li+ ions was studied in detail and related to the mechanism of their diffusion [8].