Controllable Heterojunctions with a Semicoherent Phase Boundary Boosting the Potassium Storage of CoSe2/FeSe2

Heterostructure construction is an efficient method for reinforcing K+ storage of transition metal selenides. The spontaneously developed internal electric fields give a strong boost to charge transport and significantly reduce the activation energy. Nevertheless, perfection of the interfacial region based on the energy level gradient and lattice matching degree is still a great challenge. Herein, rich vacancies and ultrafine CoSe2–FeSe2 heterojunctions with semicoherent phase boundary are simultaneously obtained, which possess unique electronic structures and abundant active sites. When employed as anodes for potassium‐ion batteries (PIBs), CoSe2–FeSe2@C composites display a reversible potassium storage of 401.1 mAh g−1 at 100 mA g−1 and even 275 mAh g−1 at 2 A g−1. Theoretical calculation also reveals that the potassium‐ion diffusion can be dramatically promoted by the controllable CoSe2–FeSe2 heterojunction.