The structural and ionic conductivity analysis of poly(ethylene oxide)/LiTFSI/MOF-5 nanocomposite electrolytes by using molecular dynamics simulations

In this study, the structure and ionic conductivity behavior of a polymer nanocomposite electrolyte system consisting of poly(ethylene oxide) (PEO), metal-organic framework 5 (MOF-5), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were investigated by using molecular dynamics (MD) simulations. Based on ionic conductivity data from MD simulations, the mobility of Li cations increases in PEO:LiTFSI electrolyte system with the addition of MOF-5. Zn atoms of MOF-5 hold almost three TFSI anions per Zn atom. In addition, when Zn atoms of MOFs and oxygen atoms of PEO interact, four oxygen atoms are saturated per Zn atom. Furthermore, Li cations are stuck among oxygen atoms of PEO as a result of their ionic interactions with O atoms. Positive charges of MOF-5 leads to the separation of Li cations from TFSI anions in PEO:LiTFSI:MOF-5 electrolyte system. In addition, positively charged atoms of MOF-5 interact with oxygen atoms of PEO chains. MOF-5 exhibits acidic surface properties through Zn atoms located close to its surface, and Zn atoms interact with partially negatively charged oxygen atoms of PEO chains and fully negatively charged TFSI anions. Therefore, lithium cations are released. The mobility of Li cations increases due to favorable interactions of MOF-5 with PEO and TFSI anions. The ionic conductivity results verify that nanoparticles like MOF-5 consisting of positively charged atoms can be used to improve the ionic mobility in electrolyte systems which include PEO-like polymers consisting of partially negative charged atoms.