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 ⋅0.49 H 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 superior performance of KNiHCF cathode results from low-strain de-/intercalation mechanism, intrinsic semiconductor property and low potassium diffusion energy barrier. The high power density and long-term stability of KNiHCF//graphite full cell confirmed the feasibility of K-rich KNiHCF cathode in PIBs. This work provides guidance to develop Prussian blue analogues as cathode materials for PIBs.
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