Potassium-pillared Na4FeV(PO4)3@C cathode for high-performance sodium-ion batteries

Due to the open 3D framework structure and relative high capacity, the NASICON type Na 3 V 2 (PO 4 ) 3 has aroused enormous attention as the cathode material for sodium-ion batteries. However, it still suffers from the toxicity and high cost of vanadium elements, coupled with low electronic conductivity. In this study, we partially substituted V with the environmentally friendly and cost-effective transition element Fe and doped K into the Na site to fabricate a series of Na 4- x K x FeV(PO 4 ) 3 @C composites using a facile sol-gel method. The structural stability, Na + mobility and electronic conductivity can significant improved by replacing Na + with K + and applying a carbon coating. Consequently, the Na 3.9 K 0.1 FeV(PO 4 ) 3 @C electrode delivers a reversible discharge capacity of 83.85 mAh g −1 at 5C after 3000 cycles, with a capacity retention of 91.7 %. It also exhibits an outstanding rate performance with a specific discharge capacity of 83.88 mAh g −1 even at 20.0C. The kinetic analyses and ex-situ characterizations confirm that a small volume change, the pseudocapacitive- dominated sodium storage behavior and highly reversible redox reaction (Fe 2+ / 3+ and V 3+ / 4+ ) occur during the electrochemical reaction process. Finally, the optimized K-doped NFVP cathode also demonstrates great potential in practical utilization through the evaluation of electrochemical performance for full cells. • Low cost and low toxicity NFVP is prepared by Fe replacement and K doping. • The K + acts as a pillar to stabilize host structure and suppress the volume change. • The larger ionic radius of K + expands Na + diffusion pathways, facilitating kinetics. • The x = 0.1 sample still delivers 83.85 mAh g −1 even after 3000 cycles.