Potassium-ion batteries (KIBs) in organic electrolytes hold great promise as an electrochemical energy storage technology owing to the abundance of potassium, close redox potential to lithium, and similar electrochemistry with lithium system. Although carbon materials have been studied as KIB anodes, investigations on KIB cathodes have been scarcely reported. We for the first time report a comprehensive study on potassium Prussian blue K0.220Fe[Fe(CN)6]0.805·4.01H2O nanoparticles as a potential cathode material. The cathode exhibits a high discharge voltage of 3.1~3.4 V, high reversible capacity of 73.2 mAh g-1 , and great cyclability at both low and high rates with a very small capacity decay rate of ~0.09% per cycle. Electrochemical reaction mechanism analysis identifies the carboncoordinated Fe III /Fe II couple as redox-active site and proves structural stability of the cathode during charge/discharge. Furthermore, for the first time, we present a KIB full-cell by coupling the nanoparticles with commercial carbon materials. The full-cell delivers a capacity of 68.5 mAh g-1 at 100 mA g-1 and retains 93.4% of the capacity after 50 cycles. Considering the low cost and material sustainability as well as the great electrochemical performances, this work may pave the way towards more studies on KIB cathodes and trigger future attention on rechargeable KIBs.

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