Single-ion conducting polymer electrolytes (SICPEs) is a competitive type within polymer-based electrolytes, showing extremely high ion transference number. Theoretically, ion transference number of near unity suggests no dendrites forming during the battery cycling, ensuring the safety of application in batteries intrinsically. However, their low ionic conductivity (IC) hinders practical applications, and its safety related performance has received comparatively little attention. In this thesis, the molecular mechanisms responsible for the related properties of polyethylene terephthalate (PET) and its modified structure (mPET), grafting two side groups -(CF₂)₂O(CF₂)₂SO₂NLiSO₂CF₃ (LiPBTFSI), were studied using computational simulation techniques. Specifically, simultaneous thermal analyser-Fourier transform infrared spectroscopy experiments and density functional theory calculations were used to identify thermally stable grafting sites in PET. Results show that the benzene ring remains intact during degradation, enabling grafting of two LiPBTFSI at the para position to form mPET. Equilibrium molecular dynamics simulations reveal that ethylene carbonate (EC) enhances IC by promoting EC diffusion and Li⁺ coordination with oxygen atoms. The effects of different plasticizers (EC, fluoroethylene carbonate, propylene carbonate) and their concentrations indicate that IC depends on electron distribution of the plasticizer and the resulted polymer flexibility at various concentrations. Non-equilibrium molecular dynamics simulations identify an optimal EC content of 50 wt%, balancing ionic and thermal conductivity. Ab initio and reactive force field based molecular dynamics simulations further show that a solid electrolyte interface (SEI) layer (~2.9 nm, increasing to ~3.25 nm under electric field) forms on lithium slab, mainly composed of LiF, Li₂O, Li₂S, and organic species, clarifying the reduction mechanism and SEI formation process. The reliability of all above results are quantitively or qualitatively proved by comparing with experimental results. These results contribute to the understanding of the molecular-level behaviour affecting the macro properties in SICPEs, inspiring the potential application of mPET based SICPEs in next-generation batteries.