Designing Prussian blue coated iron electrode with exceptional cyclic and rate performance on potassium-ion storage

The larger size of K+ was a major hurdle that greatly restricted the rapid development of potassium-ion batteries (PIBs). Indiscriminate transplantation of lithium-ion storage materials in PIBs was sure to fail because of unexpected structural collapse caused by huge volume change and sluggish ionic kinetics in electrode. In this work, we designed an open-up core-shell structure, which contained inner iron core and outer Prussian blue (PB) shell. Electrons from external circuit preferred to get into conductive iron core and thereafter transmit to PB shell through large-angle scattering. Meanwhile, K+ ions from electrolyte could readily diffuse into PB lattice cavities and participate in redox reactions along with the scattered electrons. Thereupon, this core-shell structure could boost K-storage capability without sacrificing conductivity. It delivered a capacity of 402 mAh g−1 after 1000 cycles at 0.2 A g−1 and exhibited a capacity of 321 mAh g−1 at 5 A g−1. •PBCI, containing inner iron core and outer PB shell, was successfully synthesized.•PBCI had isolated electron and K+-ion conduction pathways.•PBCI delivered a K-storage capacity of 402 mAh g−1 after 1000 cycles at 0.2 A g−1.•At 5 A g−1, the K-storage capacity of PBCI was as high as 321 mAh g−1.•The K-storage capability of PBCI was dominated by pseudo-capacitance mechanism.