A Low‐Cost Durable Na‐FeCl2 Battery with Ultrahigh Rate Capability

Abstract Na‐based batteries have long been regarded as an inexpensive, sustainable candidate for large‐scale stationary energy storage applications. Unfortunately, the market penetration of conventional Na‐NiCl 2 batteries is approaching its limit for several reasons, including limited rate capability and high Ni cost. Herein, a Na‐FeCl 2 battery operating at 190 °C is reported that allows a capacity output of 116 mAh g −1 at an extremely high current density of 33.3 mA cm −2 (≈0.6C). The superior rate performance is rooted in the intrinsically fast kinetics of the Fe/Fe 2+ redox reaction. Furthermore, it is demonstrated that a small amount of Ni additive (10 mol%) effectively mitigates capacity fading of the Fe/NaCl cathode caused by Fe particle pulverization during long‐term cycling. The modified Fe/Ni cathode exhibits excellent cycling stability, maintaining a discharge energy density of over 295 Wh kg −1 for 200 cycles at 10 mA cm −2 (≈ C /5).