Rechargeable Solid‐State Na‐Metal Battery Operating at −20 °C

Abstract Achieving satisfactory performance for a solid‐state Na‐metal battery (SSNMB) with an inorganic solid electrolyte (SE), especially under freezing temperatures, poses a challenge for stabilizing a Na‐metal anode. Herein, this challenge is addressed by utilizing a Natrium super ionic conductor (NASICON) NASICON‐type solid electrolyte, enabling the operation of a rechargeable SSNMB over a wide temperature range from −20 to 45 °C. The interfacial resistance at the Na metal/SE interface is only 0.4 Ω cm 2 at 45 °C and remains below 110 Ω cm 2 even at −20 °C. Remarkably, long‐term Na‐metal plating/stripping cycles lasting over 2000 h at −20 °C are achieved with minimal polarization voltages at 0.1 mA cm −2 . Further analysis reveals the formation of a uniform Na 3− x Ca x PO 4 interphase layer at the interface, which significantly contributes to the exceptional interfacial performance observed. By employing a Na 3 V 1.5 Al 0.5 (PO 4 ) 3 cathode, the full battery system demonstrates excellent adaptability to low temperatures, exhibiting a capacity of 80 mA h g −1 at −20 °C over 50 cycles and retaining a capacity of 108 mAh g −1 (88.5% of the capacity at 45 °C) at 0 °C over 275 cycles. This research significantly reduces the temperature threshold for SSNMB operation and paves the way toward solid‐state batteries suitable for all‐season applications.