High Li+-Transference Number in Loose Coordinated Poly(tetrahydrofuran): A Molecular Dynamics Study

High Li+-transference number in polymer electrolytes is one of the key targets for the development of high-performance lithium-ion batteries (LIBs). In this work, we investigated the mechanism of lithium-ion transport in poly(tetrahydrofuran) (PTHF), compared with that in poly(ethylene oxide) (PEO), to elucidate the effect of oxygen density through molecular dynamics simulations. The effects of polymer chain properties, ion coordination and ion aggregation on diffusion coefficient and ion-transference number were studied in detail. The results show that the lower oxygen density in PTHF leads to a loose coordination structure of Li+ surrounded by the polymer chains. Meanwhile, Li+ and bis(trifluoromethane) sulfonamide (TFSI–) mainly exist in the form of ion pairs in PTHF, and Li+ moves cooperatively with the drive of TFSI–, which makes Li+ more prone to interchain hopping in PTHF than that in PEO. Under the combined influence of the above two factors, higher transference number of Li+ is obtained in the PTHF electrolyte. Our findings shed light on the effects of oxygen content in polymer substrates on ionic coordination conditions and transport mechanisms, providing valuable insights for the design of polymer electrolytes in high-performance solid-state LIBs.