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

V St-Onge and S Rochon and JC Daigle and A Soldera and JP Claverie, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 60, 25897-25904 (2021).

DOI: 10.1002/anie.202109709

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(-1) at 25 degrees C), thus paving the way for the design of all-solid-state PEO-based sodium batteries operational at room temperature.

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