Functional Complementation of Sn/La Diatomic Sites Over V2O5 Cathodes Resolves the Capacity-Stability Trade-Off of Aqueous Potassium Ion Battery.

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 V2O5 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-V2O5 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.