Co-Construction of Selenium Vacancy and Heterogeneous Structure in FeSe₂/NiSe₂ to Induce Fast Ion Diffusion Kinetics...

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.