AbstractMagnesium Ion based Solid State Batteries (MIBs) are subject of intensive studies due to abundance of magnesium, its advantages in volumetric capacity, and the reduced dendrite growth. Here we report on a true solid polymer electrolyte system without liquid additives or plasticizers that reaches conductivities above 10−5 S cm−1 at room temperature and above 10−4 S cm−1 at 50 °C. An electrospun polymer electrolyte membrane fabricated from a polymer electrolyte featuring a composition of PEO : Mg(TFSI)2 36 : 1 [where PEO stands for poly(ethyleneoxide) and Mg(TFSI)2 for magnesium bis(trifluoromethanesulfonyl) imide] was identified as the best performing system. Magnesium transport was substantiated by different methods, and the electrochemical properties including solid electrolyte interface (SEI) formation were investigated. Electrospinning as a preparation method has been identified as a powerful tool to enhance the electrochemical properties beyond conventional polymer membrane fabrication techniques.