A severe level of pollution by materials has started to change our climate, significantly affecting our earth, including our living bodies. Therefore, researchers are looking for sustainable and ecological materials for manufacturing and industrial applications. A solid-state rechargeable battery is an electrochemical cell that stores and generates electric energy. A fast ion-conducting solid electrolyte is a crucial component that acts as a separator between the positive and negative electrodes of a cell. In the paper, we have reviewed the electrical conductivity of sodium-ion conducting solid electrolytes. The sodium compounds are non-toxic and ecological materials available globally and cheaply. Additionally, batteries with sodium ions are similar to those with lithium ions in cell configuration and energy density; however, they are more sustainable and ecological. We have also discussed the electrical transport properties of poly(ethylene oxide)x–disodium terephthalate solid polymer electrolyte, where an organic salt, disodium terephthalate, contains two sodium ions per molecule for transport. The composition, x, varied from infinity to 8 in mole ratio to optimize the electrical conductivity of the electrolyte.