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.