Enhancing Rate Capability in High-Areal-Capacity Na-NiCl₂ Batteries Using Graphene-Anchoring NiFe Nanoparticles as...

Planar high-temperature sodium-nickel chloride (Na-NiCl₂) batteries represent a promising energy storage technology. However, achieving high areal capacity at large current density remains challenging for Na-NiCl₂ batteries. In this study, nickel-iron nanoparticles anchored on reduced graphene oxide (NiFe@RGO) is synthesized and serves as active metal electrode of Na-NiCl₂ batteries. The superior conductivity of RGO reduces charge transfer resistance, while the incorporation of active Fe minimizes polarization, thereby enhancing rate performance. As a result, the NiFe@RGO electrode (≈10 wt.% Fe) presents an areal capacity of ≈6.7 mAh cm^-2 at 14.67 mA cm^-2 and can run stably over 200 cycles at 11 mA cm^-2 with capacity retention of 98.4%. High-areal-loading (150 mg cm^-2) cathode demonstrates a capacity of 18.7 mAh cm^-2 at 19.25 mA cm^-2, while maintaining extra run of 450 and 500 cycles at 11 and 16.5 mA cm^-2, respectively. In situ electrochemical impedance spectroscopy (EIS) coupled with direct current internal resistance (DCIR) analysis reveals that NiFe@RGO electrode maintains low interfacial impedance and interior resistance during the charge-discharge, correlating with its outstanding rate capability. This work provides guidance for the design of Na-NiCl₂ batteries with high areal capacity and high-rate performance.