Unraveling insights for ion transport enhancement by metal–organic framework-5 in polyethylene oxide and polyvinylidene fluoride electrolytes: classical molecular dynamics and metadynamics simulations

Abstract

The structural and dynamical properties of simulation systems consisting of metal organic frameworks (MOFs), particularly MOF-5, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, and two well-known polymers, poly(vinylidene fluoride) (PVDF) and poly(ethylene oxide) (PEO), in different compositions were investigated using classical molecular dynamics (cMD) and well-tempered metadynamics (WT-MD) simulations. The cMD simulations revealed that the PEO-based hybrid electrolyte system containing LiTFSI salt and MOF-5 (System D) exhibits the highest diffusion coefficient for Li+ ions and comparatively weaker interactions between Li+ ions and the surrounding TFSI− anions than the other investigated systems. The enhanced ionic mobility is attributed to the favorable local environment generated by the incorporation of MOF-5, which facilitates efficient Li+ ion transport while reducing ion-trapping effects, as evidenced by structural properties in terms of radial distribution functions, structure factors, spatial distribution functions, three-dimensional density distributions, ion pairing, and contact number analysis obtained from cMD. In addition, consistent with the structural properties, the dynamical and thermodynamic properties, evaluated through mean squared displacement and potential of mean force analysis, also indicate a high diffusion coefficient for Li+ ions and favorable free-energy of Li+–PEO interactions in System D. Furthermore, WT-MD simulations demonstrated that System D possesses a relatively lower free-energy barrier for Li+ ion mobility, indicating energetically favorable ion transport pathways. The combined findings from cMD and WT-MD simulations highlight the critical role of MOF-5 in regulating the dynamics and transport behavior of Li+ ions. Therefore, this study provides valuable design guidelines for engineering hybrid MOF–polymer electrolytes with optimized ion transport properties for solid-state battery applications.