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

Abstract A novel NASICON-type K 0.24 Na 2.76 Fe 2 (PO 4 ) 3 (K 0.24 NFP) is synthesized via a simple solid-state reaction method. K-doped method can enlarge lattice distance and restrain the structure dilapidation from Na 3 Fe 2 (PO 4 ) 3 to Na 5 Fe 2 (PO 4 ) 3 . Comparison with undoped-Na 3 Fe 2 (PO 4 ) 3 (NFP) sample (82.1 mAh g −1 ), K 0.24 NFP 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 K 0.24 NFP 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 (D Na +  = 3.98 × 10 −11 ) due to K-doped. Hence, the K-doped iron-based phosphate (K 0.24 Na 2.76 Fe 2 (PO 4 ) 3 ) should be a potential cathode material in sodium-ions batteries for scale energy storage.