Sodium vanadium hexacyanoferrate as a high-rate capability and long-life cathode material for Na-ion batteries

Na-ion batteries have gradually begun to be commercialized due to their advantages of lower cost and wide source of raw materials, but more excellent electrochemical performance is required to compete with lithium-ion batteries. In this work, sodium vanadium hexacyanoferrate (NaVHCF) was designed and synthesized as a Na-ion cathode material to exhibit excellent electrochemical performance. The results show that the capacity retention rate of 1000 cycles at 2.5C rate is 72 %, the Coulombic efficiency is 100 %, and the capacity retention rate of 5000 cycles at 25C high rate is 65 %. After activating at a low current density of 2.5C, it still has a capacity of 42 mAh g−1 after 2000 cycles at a high rate of 25C, and the capacity retention rate is 92 %. The analysis shows that the excellent rate and long cycling ability are related to the three-dimensional open structure and microporous structure of NaVHCF. During the long cycle, the diffusion coefficient of sodium ions gradually increases and the charge transfer resistance gradually decreases, which improves the battery lifespan. These results suggest that sodium-ion batteries are one step closer to commercial application.