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, NaClO 4 (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 behaviour. 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 at 25°C), thus paving the way for the design of all-solid-state PEO-based sodium batteries operational at room temperature.