To further illustrate the Li + coordination environment in the PiHCIL-SPEs, solid-state MAS NMR experiments were performed. Analysis of the asymmetric 7 Li signals (Figure ) shows two Li + environments (Figure and). Consistent with Greenbaum's work, the right peak (45% of total integral) in SPE20:1:1 is assigned to the Li + ions closely bound to the EO units which can be considered as solvated Li + . The left peak (55% of total integral) represents Li + ions that have weakened Li + -EO interactions which are less restricted and behave more as in ionic states. As HCIL concentration increases, SPE8:1:1 shows 81% weakly coordinated Li + and only 19% strongly bonded Li + , indicating more Li + ions escape from strong Li + -EO interactions to the disordered environment where they possess a higher degree of freedom. Thus, the addition of HCIL can mitigate the affinity between EO and Li + interaction which is consistent with the FTIR results. Previous research has shown that Li + ions are more mobile in disordered environments, promoting faster ion transport. This is consistent with our EIS analysis where SPE8:1:1 shows the highest ionic conductivity. The close interactions between Li + and FSI -anions are established in the 19 F- Li HETCOR spectrum shown in Figure , where F shows strong cross peaks with the 7 Li signal. Taken together, solid-state NMR results confirm the important role of Li + environment to the overall ionic conductivity. The favorable Li + ion environment of SPE8:1:1 promotes its superior room temperature ionic conductivity among the prepared PiHCIL-SPEs. As Li + conduction in SPEs mainly relies on chain segmental motion within the polymer's amorphous regions, high salt concentration that leads to increased amorphous domains therefore facilitates faster ion transport, owing to its plasticizing effect. However, this increase in ion conductivity often comes at the expense of mechanical robustness due to reduced crystallinity and increased segmental motion. This dynamic shifts with our PiHCIL-SPEs, where membrane robustness is not solely reliant on the crystalline domains. The electrochemical stability window (ESW) of the PiHCIL-SPEs was obtained by LSV measurement of a Li||SS cell, scanning from open-circuit voltage to 6 V against Li/Li + at a rate of 0.1 mV s -1 as shown in Figure . Apart from SPE8:1:1, all the other SPEs experienced oxidative degradation below 4 V which is commonly seen in PEO-based SPEs, 9 whereas SPE8:1:1 showed high electrochemical stability of 5.1 V (5 µA cm -2 current density was used as the cut-off current 47 ), indicating its excellent oxidation stability and potential to work with high-voltage materials. The excellent electrochemical stability of SPE8:1:1 can be attributed to a high concentration of HCIL, promoting the polymer chains to strongly interact with Li + ions and FSI -anion clusters. The coordinated ions and surrounded ion clusters act like a shield, protecting EO from oxidation and reducing the highest occupied molecular orbital level of the PiHCIL-SPE, all of which contribute to its improved oxidation stability. Thereby the SPE8:1:1 has been chosen as the best candidate among others and will be investigated for the advanced electrochemical testing that will be discussed below.