Realizing Reversible Conversion‐Alloying of Sb(V) in Polyantimonic Acid for Fast and Durable Lithium‐ and Potassium‐Ion Storage

Abstract Finding suitable electrode materials for alkali‐metal‐ion storage is vital to the next‐generation energy‐storage technologies. Polyantimonic acid (PAA, H₂Sb₂O₆ · nH₂O), having pentavalent antimony species and an interconnected tunnel‐like pyrochlore crystal framework, is a promising high‐capacity energy‐storage material. Fabricating electrochemically reversible PAA electrode materials for alkali‐metal‐ion storage is a challenge and has never been reported due to the extremely poor intrinsic electronic conductivity of PAA associated with the highest oxidation state Sb(V). Combining nanostructure engineering with a conductive‐network construction strategy, here is reported a facile one‐pot synthesis protocol for crafting uniform internal‐void‐containing PAA nano‐octahedra in a composite with nitrogen‐doped reduced graphene oxide nanosheets (PAA⊂N‐RGO), and for the first time, realizing the reversible storage of both Li⁺ and K⁺ ions in PAA⊂N‐RGO. Such an architecture, as validated by theoretical calculations and ex/in situ experiments, not only fully takes advantage of the large‐sized tunnel transport pathways (0.37 nm²) of PAA for fast solid‐phase ionic diffusion but also leads to exponentially increased electrical conductivity (3.3 S cm⁻¹ in PAA⊂N‐RGO vs 4.8 × 10⁻¹⁰ S cm⁻¹ in bare‐PAA) and yields an inside‐out buffer function for accommodating volume expansion. Compared to electrochemically irreversible bare‐PAA, PAA⊂N‐RGO manifests reversible conversion‐alloying of Sb(V) toward fast and durable Li⁺‐ and K⁺‐ion storage.