Ultra-stable all-solid-state sodium-metal batteries enabled by perfluoropolyether-based electrolytes

Abstract Rechargeable batteries paired with sodium (Na)-metal anodes are considered as one of the most promising high energy and low-cost energy storage systems. However, the use of highly reactive Na metal and the formation of Na dendrites during battery operation have caused significant safety concerns, especially when highly flammable liquid electrolytes are used. Herein, we design and develop a solvent-free solid polymer electrolytes (SPEs) based on a perfluoropolyether (PFPE) terminated polyethylene glycol (PEG)-based block copolymer for safe and stable all-solid-state Na-metal batteries. Compared with traditional poly(ethylene oxide) (PEO) or PEG SPEs, our results suggest that block copolymer design allows for the formation of self-assembled microstructures leading to high storage modulus at elevated temperatures with the PEG domains providing transport channels even at high salt concentration (EO/Na+ = 8:2). Moreover, it is demonstrated that the incorporation of PFPE segments enhances the Na+ transference number of the electrolyte to 0.46 at 80 oC. Finally, the proposed SPE exhibits highly stable symmetric cell cycling performance with high current density (0.5 mA cm-2 and 1.0 mAh cm-2, up to 1300 hours). The assembled all-solid-state Na-metal batteries with Na3V2(PO4)3 cathode demonstrate outstanding rate performance, high capacity retention and long-term charge/discharge stability (CE = 99.91%) after more than 900 cycles.