Unlocking electrochemical potential: amorphous NaFePO4 as a high-capacity and cycle-stable cathode material for advanced sodium-ion batteries

Abstract

Traditional cathode materials are well-defined high crystalline structures, but the repeated ion insertion/extraction with high lattice stress and volume change during the charge/discharge will cause structural degradation and diminish electrochemical performance. Herein we identify an amorphous iron phosphate electrode, NaFePO₄, which can be rechargeable and show excellent electrochemical properties. The amorphous NaFePO₄ electrode delivers a reversible capacity of 160.5 mAh g⁻¹ at 20 mA g⁻¹, accompanied by remarkable rate capability and cycling stability. Unlike conventional crystalline materials, the excellent electrochemical performance of the amorphous NaFePO₄ electrode stems from the absence of lattice limitation in the amorphous structure, which allows for the accommodation of local stress and volume change during the long-term sodiation/desodiation processes. Further experimental characterizations and theoretical simulation reveal the underlying redox characteristics. This research offers some insights for the development of innovative amorphous electrode materials with low cost and attractive electrochemical properties for wide energy storage applications.