A Low‐Strain Potassium‐Rich Prussian Blue Analogue Cathode for High Power Potassium‐Ion Batteries

Most of the cathode materials for potassium ion batteries (PIBs) suffer from poor structural stability due to the large ionic radius of K + , resulting in poor cycling stability. Here we report a low-strain potassium-rich K 1.84 Ni[Fe(CN) 6 ] 0.88 ∙0.49H 2 O (KNiHCF) as a cathode material for PIBs. The as-prepared KNiHCF cathode can deliver reversible discharge capacity of 62.8 mAh g -1 at 100 mA·g -1 , with a high discharge voltage of 3.82 V. It can also achieve a superior rate performance of 45.8 mAh g -1 at 5000 mA g -1 , with a capacity retention of 88.6% after 100 cycles. The combination of in situ characterizations and theoretical calculations unveils that the superior performance of KNiHCF cathode results from low-strain de-/intercalation mechanism, intrinsic semiconductor property and low potassium diffusion energy barrier. In addition, the high power density and long term stability of KNiHCF//graphite full cell have further proved the feasibility of K-rich KNiHCF cathode in PIBs. This work is expected to provide meaningful guidance to develop Prussian blue analogues as cathode materials for high-performance PIBs.