Polyacrylonitrile (PAN) is one of the alternative candidate polymer hosts to form solid polymer electrolytes (SPEs) besides the widely used poly(ethylene oxide). However, over 3 orders of magnitude of discrepancy in ionic conductivity has been reported in PAN-based SPEs, in both the low salt concentration and the high salt concentration regimes. This discrepancy originates from different film processing conditions. In this study, we rigorously examine how processing conditions, including solution mixing, casting, and drying conditions affect the morphology, ion transport, solvation structure, Li and oxidative stability of PAN based electrolytes. It is found that the ion transport, lithium stability and the oxidative stability of PAN-based SPEs are critically dependent on the residual dimethylformamide (DMF) solvent content. We systematically study four different drying conditions and the resulting residual solvent is quantified by infrared spectroscopy. We demonstrate that conductivity variation across 5 orders of magnitude can be obtained depending on the drying conditions. Furthermore, the effects of residual DMF solvent on the ion transport mechanism, stability against lithium and the oxidative stability are elucidated. This thorough study lays the groundwork for future development of PAN based electrolytes.