Improving Potassium-Ion Batteries by Optimizing the Composition of Prussian Blue Cathode

Prussian blue and its analogues are considered as superior cathode materials for nonaqueous potassium-ion batteries because of their three-dimensional open framework structure, high stability, and low cost. In this work, a series of ternary K 2 Ni x Co 1– x Fe(CN) 6 with various Co/Ni ratios are synthesized for potassium-ion batteries. By optimizing the Prussian blue analogue with Ni and Co connected to the N end, the ternary-metal K 2 Ni 0.36 Co 0.64 Fe(CN) 6 exhibits much higher performance as compared with that of the corresponding binary counterparts. Specifically, the ternary K 2 Ni 0.36 Co 0.64 Fe(CN) 6 delivers a high initial capacity of 86 mAh g –1 with a retention of 98% after 50 cycles, which is much higher than that of K 2 NiFe(CN) 6 and K 2 CoFe(CN) 6 . Moreover, the capacity retention remains up to 88% after 300 cycles, indicating the excellent stability of our ternary material. It is revealed by this work that the composition of the transition metal ions connected to the N end of the -C≡N- group could significantly affect the performance of the cathodes of Prussian blue analogues. Furthermore, this work may provide an efficient strategy to improve the electrochemical performance of Prussian blue cathodes for potassium ion batteries.