Prussian
blue (PB) and its analogues have been widely investigated
as promising cathode materials for potassium ion batteries (PIBs)
on account of their 3D open framework, which makes the intercalation/deintercalation
of K+ ions easy and quick. However, the PB materials usually
exhibit limited rate capacity and poor cycling performance, preventing
their development and practical application. In this work, PB doped
with nickel ions via a modified coprecipitation method was explored
to improve the rate capacity and cycling performance of PIBs, and
the effect of Ni doping on the materials’ performance was systematically
studied. The optimal sample, 5% Ni-doped PB, delivered an enhanced
discharge capacity of up to 135 mAh g–1, compared
to 120 mAh g–1 with nondoped PB. Our optimal sample
also displayed excellent cycling performance with 83.1% capacity retention
after 300 cycles (0.1 A g–1) and declining just
0.0059% per cycle from 150 to 300 cycles. The discharge capacity at
the high-voltage plateau increased from ∼40 up to 53 mAh g–1, offering a higher energy density for PIBs. On the
basis of the characterization results, we ascribe the improved performance
to the activation of nickel ions during the Fe2+C6/Fe3+C6 redox reaction.
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 -CN-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.
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