Spatially dual-confined metallic selenide double active centers for boosting potassium ion storage

Potassium-ion batteries (PIBs) have received increased attention for grid-scale energy storage applications; however, their practical development is still hindered by the lack of advanced anode materials to overcome the slow kinetics and huge volume expansion. Herein, a multi-interface engineered iron-nickel bimetallic selenide (NiSe2/FeSe2, NFS) space-confined in a dual-carbon structure is designed as an efficient anode for PIBs. The NFS heterostructure with different band structures endows a built-in electric field, which facilitates fast interfacial electron transport and reduced ionic diffusion resistance. Moreover, the NC@C matrix further accelerates the charge carrier transport dynamics of NFS while suppressing the huge volume change to ensure good cycling performance. Consequently, the as-prepared NFS@NC@C exhibits a high initial specific capacity of 349.6 mA h g-1 at 0.1 A/g, good rate capability, and ultra-low capacity degradation rate of 0.021 % per cycle after 1200 cycles at 5 A/g. Further ex/in-situ investigations and theoretical calculations unveil the K+ storage mechanism of NFS@NC@C, which involves a phase conversion reaction for K+-ions migration with a low diffusion energy barrier. This work heralds the prospect of space-confined multi-heterointerface design for high-performance PIBs electrode materials.