This work comprises the manufacture and characterization of solid polymer lithium ion conducting electrolytes for structural batteries. In the study, polymer films are produced in situ via a rapid versatile UV irradiation polymerization route, in which ethylene oxide methacrylates are polymerized into thermoset networks. In the first part of the study, the simplicity and efficiency of this manufacturing route is emphasized. Polymer electrolytes are pro-duced with an ionic conductivity ranging from 5.8×10^-10 S cm^-1 up to 1.5×10^-6 S cm^-1, and a storage modulus of up to 2 GPa at 20°C. In the sec-ond part, the effect of the lithium salt content is studied, both for tightly crosslinked systems with a glass transition temperature (T_g) above room temperature but also for sparsely crosslinked system with a T_g below. It is shown that for these systems, there is a threshold amount of 4% lithium salt by weight, above which the ion conducting ability is not affected to a larger extent when the salt content is increased further. It is also shown that the influence of the salt content on the ionic conductivity is similar within both systems. However, the Tg is more affected by the addition of lithium salt for the loosely crosslinked system, and since the Tg is the main affecting parame-ter of the conductivity, the salt content plays a larger role here. In the third part of the study, a thiol functional compound is added via thiol-ene chemistry to create thio-ether segments in the polymer network. This is done in order to expand the toolbox of possible building blocks usable in the design of structural electrolytes. It is shown that solid polymer electrolytes of more homogeneous networks with a narrower glass transition region can be produced this way, and that they have the ability to function as an electrolyte. Finally, the abilities of reinforcing the electrolytes by nano fibrilar cellulose are investigated, by means to improve the mechanical properties without decreasing the ionic conductivity at any larger extent. These composites show conductivity values close to 10^-4 S cm^-1 and a storage modulus around 400 MPa at 25 °C.