Abstract
A Monte Carlo (MC) model to incorporate the effect of Al2O3 with different particle sizes in enhancing the ionic conductivity of composite polymer electrolytes consisting of polyethylene oxide (PEO), lithium trifluoromethanesulfonate (LiCF3SO3), and ethylene carbonate (EC), is proposed. The simulated ionic conductivity in our MC model is validated by the results of electrochemical impedance spectroscopy, which determined the room temperature ionic conductivity of various composite electrolyte samples differing from the size of the Al2O3 prepared via the solution cast method. With the simulated current density and recurrence relation, cation transference numbers, t+si of composite polymer electrolytes were derived using the steady-state current method proposed by Bruce et al. Addition of Al2O3 (≤10 μm) in micron size greatly enhances the ionic conductivity to a magnitude of two orders, i.e., from 2.9025×10-7 S/cm to 2.970×10-5 S/cm and doubles the cation transference number from 0.230 to 0.465. However, the addition of Al2O3 (<50 nm) in nano size decreases both the ionic conductivity and the cation transference number. The smaller size of Al2O3 in the nano range is responsible for the congestion on the conducting pathways that traps some of the Li+ in PEO electrolytes.
