K-doped Na3Fe2(PO4)3 cathode materials with high-stable structure for sodium-ion stored energy battery

A novel NASICON-type K0.24Na2.76Fe2(PO4)3 (K0.24NFP) is synthesized via a simple solid-state reaction method. K-doped method can enlarge lattice distance and restrain the structure dilapidation from Na3Fe2(PO4)3 to Na5Fe2(PO4)3. Comparison with undoped-Na3Fe2(PO4)3 (NFP) sample (82.1 mAh g−1), K0.24NFP electrode shows a 101.3 mAh g−1 discharge capacity at 10 mA g−1, which up to 97% of theoretical capacity. As for rate capability performance, a high reversible capacity of 73.6 mAh g−1 at 1000 mA g−1. The cycle stability performance measurement results indicate that the discharge capacity of K0.24NFP electrode is up to 93.7 mAh g−1 after 500 cycles at 100 mA g−1. The excellent electrochemical performance is attributed to the improvement of structural stability and the highest intercalation-deintercalation kinetic of sodium-ions (DNa+ = 3.98 × 10−11) due to K-doped. Hence, the K-doped iron-based phosphate (K0.24Na2.76Fe2(PO4)3) should be a potential cathode material in sodium-ions batteries for scale energy storage.