Simulation of ion transport through poly(ethylene oxide) loaded with lithium perchlorate

A hierarchical approach is used to simulate lithium ion motion through poly(ethylene oxide) loaded with lithium perchlorate, alone and with a tungsten oxide (WO3) interface to model an electrochromic smart window assembly. The structure of the polymer is simulated using commercial software. Relaxation of the polymer is allowed on a lattice on which the lithium ions move as a lattice gas. Polarization and van der Waals energy changes are calculated for an added lithium ion at each lattice point. The structure and energy are also calculated in the presence of the WO3 interface. Ion transport is simulated in a kinetic Monte Carlo method, with and without an electric field. During runs at 300 K without the WO3 interface, with a field the lithium ions move 35 angstrom along it and 3-7 angstrom across it but without a field they move 2-5 angstrom; these distances vary with temperature as expected for activated hopping. Ions explore their immediate neighbourhood, occasionally jumping to an adjacent neighbourhood along, across or sometimes against the field, thus circumventing regions where transport is hindered. With the WO3, the lithium ions tend to accumulate at the interface, producing a repulsive potential that reduces ion movement