Due to the abundant and low‐cost K resources, the exploration of suitable materials for potassium‐ion batteries (KIBs) is advancing as a promising alternative to lithium‐ion batteries. However, the large‐sized and sluggish‐kinetic K ions cause poor battery behavior. This work reports a metallic octahedral CoSe2 threaded by N‐doped carbon nanotubes as a flexible framework for a high‐performance KIBs anode. The metallic property of CoSe2 together with the highly conductive N‐doped carbon nanotubes greatly accelerates the electron transfer and improves the rate performance. The carbon nanotube framework serves as a backbone to inhibit the agglomeration, anchor the active materials, and stabilize the integral structure. Every octahedral CoSe2 particle arranges along the carbon nanotubes in sequence, and the zigzag void space can accommodate the volume expansion during cycling, therefore boosting the cycling stability. Density functional theory is also employed to study the K‐ion intercalation/deintercalation process. This unique structure delivers a high capacity (253 mAh g−1 at 0.2 A g−1 over 100 cycles) and enhanced rate performance (173 mAh g−1 at 2.0 A g−1 over 600 cycles) as an advanced anode material for KIBs.

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HIGHLIGHTS • Metallic cobalt selenide quantum dots encapsulated in mesoporous carbon matrix were prepared via a direct hydrothermal method. • The cobalt selenide/carbon composite (Co 0.85 Se-QDs/C) possesses tertiary hierarchical structure, which is the primary quantum dots, the secondary petals flake, and the tertiary hollow micropolyhedron framework. • Benefiting from this tertiary hierarchical structure, the Co 0.85 Se-QDs/C electrode as potassium-ion batteries anode shows an outstanding K-storage performance.

A facile chemical bubbling strategy to generate FexO@NFLG-240 as a performance-enhanced anode material for potassium-ion batteries.