Dual-salt assisted synergistic synthesis of Prussian white cathode towards high-capacity and long cycle potassium ion battery

Prussian blue analogues(PBAs) are considered as superior cathode materials for potassium-ion batteries(PIBs) because of their three-dimensional open framework structure,high stability,and low cost.However,the intrinsic lattice defects and low potassium content typically results in poor rate and cycling performance,thus limited their practical applications.In this work,high-quality K1.64FeFe(CN)6(PW-HQ)material with less crystalline water(6.21%) and high potassium content(1.64 mol^(-1)) was successfully synthesized by a novel coprecipitation method with potassium citrate(K-CA) and potassium chloride(KCl) addition.Specifically,the electrode delivers a reversible capacity of 113.1 mA h g^(-1)at the current rate of 50 mA g^(-1)with~100% coulombic efficiency.Besides,the electrode retained 90% reversible capacity at 500 mA g^(-1)current density after 1000 cycles,indicating only 0.01% capacity decay per cycle.Moreover,we have revealed that the introduction of K-CA controlled the chelating rate of Fe(Ⅱ) and the addition of KCl increased the K+content,hence improving the capacity and stability of the asprepared electrodes.Structural evolution and potassium storage mechanism were further investigated by detailed ex-situ X-ray diffraction and in-situ Raman measurements,which demonstrated reversible potassiation/depotassiation behavior and negligible volume change during the electrochemical process.In general,this work provides an efficient strategy to eliminate water contents in Prussian blue cathode and improve its electrochemical performance,which plays a key role in promoting the industrialization of potassium ion batteries.