Low‐Temperature and Fast‐Charge Sodium Metal Batteries

Abstract Low‐temperature operation of sodium metal batteries (SMBs) at the high rate faces challenges of unstable solid electrolyte interphase (SEI), Na dendrite growth, and sluggish Na + transfer kinetics, causing a largely capacity curtailment. Herein, low‐temperature and fast‐charge SMBs are successfully constructed by synergetic design of the electrolyte and electrode. The optimized weak‐solvation dual‐salt electrolyte enables high Na plating/stripping reversibility and the formation of NaF‐rich SEI layer to stabilize sodium metal. Moreover, an integrated copper sulfide electrode is in situ fabricated by directly chemical sulfuration of copper current collector with micro‐sized sulfur particles, which significantly improves the electronic conductivity and Na + diffusion, knocking down the kinetic barriers. Consequently, this SMB achieves the reversible capacity of 202.8 mAh g −1 at −20 °C and 1 C (1 C = 558 mA g −1 ). Even at −40 °C, a high capacity of 230.0 mAh g −1 can still be delivered at 0.2 C. This study is encouraging for further exploration of cryogenic alkali metal batteries, and enriches the electrode material for low‐temperature energy storage.