Abstract
Poly(ethylene oxide) (PEO)-based polymers are common hosts in solid polymer electrolytes (SPEs) for high-power energy devices. Molecular simulations have provided valuable molecular insights into structures and ion transport mechanisms of PEO-based SPEs. The calculation of thermodynamic and kinetic properties rely crucially on the dependability of the molecular force fields describing inter- and intra-molecular interactions with the target system. In this work, we reparametrized atomic partial charges for the widely applied optimized potentials for liquid simulations (OPLS) force field of PEO. The revised OPLS force field, OPLSR, improves the calculations of density, thermal expansion coefficient, and the phase transition of the PEO system. In particular, OPLSR greatly enhances the accuracy of the calculated dielectric constant of PEO, which is critical for simulating polymer electrolytes. The reparameterization method was further applied to SPE system of PEO/LiTFSI with O:Li ratio of 16:1. Based on the reparametrized partial charges, we applied separate charge-scaling factors for PEO and Li salts. The charge-rescaled OPLSR model significantly improves the resulting kinetics of Li+ transport while maintaining the accurate description of coordination structures within PEO-based SPE. The proposed OPLSR force field can benefit the future simulation studies of SPE systems.
Highlights
Solid polymer electrolytes (SPEs) have attracted wide attention due to their high safety, low leakage issue and good mechanical strength compared with conventional liquid electrolytes [1,2]
The optimized potentials for liquid simulations (OPLS) model revised with restrained electrostatic potential (RESP) charges, OPLSR, for Poly(ethylene oxide) (PEO) was derived as described in the Methods section
Series of Molecular dynamics (MD) simulations were conducted to validate the OPLSR force field in predicting PEO melt properties compared with original OPLS model, the model developed by Barbosa et al [26], and the experimental data
Summary
Solid polymer electrolytes (SPEs) have attracted wide attention due to their high safety, low leakage issue and good mechanical strength compared with conventional liquid electrolytes [1,2]. Among various SPEs, poly(ethylene oxide) PEO, or poly(ethylene glycol) PEG, is one of the most common polymer hosts for its low toxicity, good electrochemical stability, and the excellent ability to dissolve various lithium salts [5,6]. Short chained PEODME, referred as glyme, has less interaction with anions due to lack of terminal hydroxyl groups [9,10]. Glyme has been commonly applied in room temperature ionic liquids or as plasticizers for SPE to enhance the ion conductivity [11,12,13,14]. Please note that at high molecular weight, PEODME and PEO show similar physico-chemical characteristics as polymer electrolyte for the minimal effects of terminal groups in long-chain polymeric systems [15,16,17]
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