Co‐Construction of Selenium Vacancy and Heterogeneous Structure in FeSe ₂ /NiSe ₂ to Induce Fast Ion Diffusion Kinetics for Potassium‐Ion Batteries

Owing to their distinctive architectures and prominent theoretical capacity, transition metal selenides (TMSs) have been recognized as attractive candidates for anode components in potassium-ion batteries (PIBs). However, their commercial application of TMSs has been long hampered by poor structural stability and slow kinetics. Herein, a composite of transition metal selenides embedded within a carbon and MXene network is designed and synthesized, featuring the coexistence of vacancies and heterostructures (FeSe₂/NiSe₂@CM). The FeSe₂/NiSe₂ heterostructure markedly enhances charge transport kinetics through a spontaneously formed built-in electric field, while selenium vacancies increase defect density, exposing a greater number of active sites and further optimizing ion diffusion kinetics. Electrochemical evaluations demonstrate that the material possesses an exceptional rate performance (493 mAh g^-1/0.1 A g^-1 and 166 mAh g^-1/10 A g^-1) and long-term durability (75.4% capacity retention after 2000 cycles at 5 A g^-1). Additionally, in situ and ex situ characterizations imply the FeSe₂/NiSe₂@CM composite stores potassium through a combined intercalation and conversion mechanism. Moreover, potassium-ion hybrid capacitors assembled with this anode exhibit practical potential in delivering simultaneously high energy and power densities. This work proposes an effective heterostructure-vacancies synergistic optimization strategy for the rational conception of excellent performance anode materials for PIBs.