An 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 the NaCrO₂@Na₂FePO₄F/C bi-phase material, which exhibits excellent rate performance and cycling stability at operating voltages above 3.6 V. A heterostructure composite of NaCrO₂@Na₂FePO₄F/C with fast Na⁺ ion transport capability was constructed. The optimized NaCrO₂@5% Na₂FePO₄F/C composite achieves an ultra-high discharge specific capacity of 105.3 mA h g⁻¹ at 40C, which is 83.6% of its capacity at 0.1C. Furthermore, the material shows a remarkable capacity retention of 85.93% for 400 cycles at 5C (2.3–3.7 V), significantly outperforming pristine NaCrO₂, with only 34.88%. This bi-phase heterostructure modification strategy provides a promising pathway for the design of high stability SIBs.