Defect-Free Prussian Blue Analogue as Zero-Strain Cathode Material for High-Energy-Density Potassium-Ion Batteries

Prussian blue analogues (PBAs) have been widely studied as cathodes for potassium-ion batteries (PIBs) due to their three-dimensional framework structure and easily adjustable composition. However, the phase transition behavior and [Fe(CN)(6)](4-) anionic defects severely deteriorate electrochemical performances. Herein, we propose a defect-free potassium iron manganese hexacyanoferrate (K1.47Fe0.5Mn0.5[Fe(CN)(6)]<middle dot>1.26H(2)O, KFMHCF-1/2) as the cathode material for PIBs. The Fe-Mn binary synergistic and defect-free effects can inhibit the cell volume change and octahedral slip during the K-ion insertion/extraction process, so that the phase transformation behavior (monoclinic <-> cubic) is effectively inhibited, achieving a zero-strain solid solution mechanism employing Fe and Mn as dual active-sites. Thus, KFMHCF-1/2 contributes the highest initial capacity of 155.3 mAh<middle dot>g(-1) with an energy density of 599.5 Wh<middle dot>kg(-1) at 10 mA<middle dot>g(-1) among the reported PBA cathodes, superior rate capability, and cyclic stability over 450 cycles. The assembled K-ion full battery using K deposited on graphite (K@G) as anode also delivers high reversible specific capacity of 131.1 mAh<middle dot>g(-1) at 20 mA<middle dot>g(-1) and ultralong lifespans over 1000 cycles at 50 mA<middle dot>g(-1) with the lowest capacity decay rate of 0.044% per cycle. This work will promote the rapid application of high-energy-density PIBs.