Polysiloxane‐Based Single‐Ion Conducting Polymer Electrolyte for Sodium Batteries

Sodium-metal batteries promise higher energy densities than sodium-ion batteries, but the high reactivity of sodium metal remains a great challenge. Herein, we present a novel polysiloxane-based single-ion conducting polymer electrolyte (SIPE). Blended with poly(vinylidene fluoride-co-hexafluoropropylene) and infiltrated with small molecular mass organic carbonates, the resulting electrolyte membranes (NaPSiOM) exhibit a high ionic conductivity of 0.2 and 0.4 mS cm−1 at 20 and 40°C, respectively, as well as a wide electrochemical stability window (>4.4 V). The NaPSiOM membranes enable an exceptionally stable cycling of symmetric Na║Na cells for over 2000 h and excellent long-term cycling stability of Na║Na3V2(PO4)3 (NVP) cells for over 1000 cycles. Remarkably, these very good performance metrics are well preserved also when increasing the active material mass loading to commercially relevant levels of up to about 18 mg cm−2 and when changing the cathode chemistry. In fact, when coupled with a Na4Fe3(PO4)2P2O7 cathode, NaPSiOM enables stable cycling for more than 600 cycles at room temperature in single-layer pouch cells comprising 23 cm2 electrodes, thus, underlining the great potential of NaPSiOM for high-performance sodium batteries.