Functional Complementation of Sn/La Diatomic Sites Over V 2 O 5 Cathodes Resolves the Capacity–Stability Trade‐Off of Aqueous Potassium Ion Battery

ABSTRACT The intrinsic trade‐off between high specific capacity and structural stability severely limits the development of high‐capacity K + cathodes. Herein, we address this limitation through a strategic pairing of f / p ‐block elements for constructing isolated heteronuclear diatomic sites (La/Sn) on carbon substrate. This pairing drives the reconstruction of V 2 O 5 into hydrated layered phase, forming a dual‐function interface where La acts as a structural anchor and Sn as a kinetics promoter. The strongly Lewis acidic La center stabilizes the host framework by suppressing vanadium dissolution, whereas Sn, with energetically accessible p ‐orbitals, facilitates interfacial charge transfer. The resulting interface couples K + intercalation with interfacial proton storage, forming a highly reversible hybrid reaction pathway that reconciles capacity and stability. As a result, C/Sn/La‐V 2 O 5 electrode achieves a high specific capacity of 350 mAh g −1 , exceptional rate capability, and outstanding cycling stability (95.5% retention after 10 000 cycles). Operando spectroscopic analyses support the existence of this dual‐ion coupling pathway governs the reversible charge‐storage process, with the exceptional electrochemical performance originating from the functional complementarity of the Sn/La dual‐atomic sites. This work establishes f / p ‐block element pairing as a promising design strategy for engineering atomic interfaces that integrate complementary charge‐storage mechanisms, with preliminary generality supported by additional element pairs.