Synthesized From FeVO₄ Precursor and Al₂O₃ Modified Cathode Material Na₄FeV(PO₄)₃ for Sodium Ion Batteries

The NASICON-type cathode Na₄FeV(PO₄)₃ (NFVP) has attracted interest for its open framework and high theoretical capacity. However, current synthesis methods often introduce impurity phases, degrading electrochemical performance. Moreover, the highly oxidizing V⁵⁺ tends to react with the electrolyte at high voltages, causing structural distortion and irreversibility of the V⁴⁺/V⁵⁺ redox couple. Therefore, suppressing impurity formation and the side reactions between V⁵⁺ and the electrolyte is key to improving high-voltage performance. To address these issues, this study proposes a precursor-based synthesis approach to obtain high-purity NFVP with excellent electrochemical performance, combined with an Al₂O₃ protective layer on the NFVP surface. The Al₂O₃ coating minimizes direct contact between the active material and the electrolyte, effectively suppressing side reactions while enhancing structural stability. As a result, the modified cathode shows greatly improved cycling stability and rate capability in the 2.0-4.3 V range. Specifically, after 200 cycles at 1 C, capacity retention increases from 46.4% to 70%, and the specific discharge capacity at 20 C improves from 17.4 to 53.9 mAh g^-1. This work offers a feasible strategy to enhance the high-voltage performance of NASICON-type cathodes for sodium-ion batteries.