In this work, we develop novel single-ion polymer electrolytes by mixing poly(lithium 1- [3-(methacryloyloxy) propylsulfonyl]-1-(trifluoromethanesulfonyl) imide) (PLiMTFSI) and poly(ethylene oxide) (PEO) with different molecular weights. The impact of PLiMTFSI on the crystallization and conductivity of the blends was explored in detail. When PLiMTFSI (an amorphous polymer) is added to PEO, the crystallization ability of PEO decreases. However, blends with high-molecular weight PEO (1000 kg/mol) experience a lower reduction in crystallinity and melting points. As a result, lower conductivity values were obtained in these blends, which is why most of the study was then focused on blends incorporating a lower-molecular weight PEO (100 kg/mol). We show that the melting point, degree of crystallinity, spherulitic growth, and overall crystallization kinetics decrease in the presence of PLiMTFSI, which are all signs of miscibility. Furthermore, the blends show a single glass transition temperature over the whole composition range. Therefore, our results indicate that PEO and PLiMTFSI are miscible, as corroborated by applying the Nishi-Wang equation and obtaining negative chi(12 )values (i.e., the Flory-Huggins interaction parameter) for all blends. Our results show that intermediate molecular weight blends (100 kg/mol PEO and 50 kg/mol PLiMTFSI) showed the highest ionic conductivity value. Interestingly, a value of 2.1 X 10(-4) S/cm was obtained at 70 degrees C, which is one of the highest reported so far for a free-standing film of single-ion conducting polymer electrolytes. Finally, employing dielectric spectroscopy, the contribution of ion density and ion mobility to ionic conductivity could be separated. It was found that ion mobility is the parameter that has a greater weight in the conduction process.