The Unusual Conductivity of Na+in PEO‐Based Statistical Copolymer Solid Electrolytes: When Less Means More

Abstract The low conductivity of Na+electrolytes in solid polymer electrolytes (SPEs) curtails the development of Na polymer batteries. In this study, NaClO4(3–24 wt %, 90–9:1 O:Na) is dissolved in statistical copolymers of ethylene oxide (EO) and propylene oxide (PO) (0–20 mol %). Remarkably, the conductivity of these SPEs increases as the concentration of Na+decreases, thus departing from the usual Nernstian behavior. Using a combination of calorimetric measurements and molecular dynamic simulations, this unusual phenomenon is attributed to the presence of physical cross‐links generated by Na+. As a result, polymers containing a low salt concentration (3 wt %) display a drastically enhanced ionic conductivity (up to 0.2 10−4 S cm−1at 25 °C), thus paving the way for the design of all‐solid‐state PEO‐based sodium batteries operational at room temperature.