Controllable Heterojunctions with a Semicoherent Phase Boundary Boosting the Potassium Storage of CoSe 2 /FeSe 2

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 CoSe 2 –FeSe 2 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), CoSe 2 –FeSe 2 @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 CoSe 2 –FeSe 2 heterojunction.