Interface-Tailored NaCrO2@Na2FePO4F/C Heterostructure Cathode Synchronizing High-Rate Capability and Stability for Sodium-Ion Batteries

Abstract

NaCrO2 is a highly promising cathode material for sodium-ion batteries (SIBs) due to its simple synthesis, excellent thermal stability, and the abundance of raw materials. However, as the charge depth increases, the material undergoes a series of phase transitions, leading to significant degradation in structural stability, severely affecting its rate capability and cycle life. Herein, a simple and effective heterostructure design strategy is employed to synthesize NaCrO2@ Na2FePO4F/C bi-phase material, which exhibits excellent rate performance and cycling stability at operating voltages above 3.6 V. A heterostructure with fast Na+ ion transport is constructed on the surface of NaCrO2 aligning Na2FePO4F/C, effectively enhancing the transport kinetics of both Na+ and electrons while improving the material's interfacial stability. The optimized NaCrO2@5% Na2FePO4F/C composite achieves an ultra-high discharge specific capacity of 105.3 mAh·g-1 at 40C, which is 83.6% of its capacity at 0.1C. Furthermore, the material shows remarkable capacity retention of 85.93% for 400 cycles at 5C (2.3–3.7 V), significantly outperforming the pristine NaCrO2, with only 34.88%. This bi-phase heterostructure modification strategy provides a promising pathway for the design of high stability SIBs.