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

Finding suitable electrode materials for alkali-metal-ion storage is vital to the next-generation energy-storage technologies. Polyantimonic acid (PAA, H2Sb2O6 center dot nH(2)O), 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 subset of N-RGO), and for the first time, realizing the reversible storage of both Li+ and K+ ions in PAA subset of 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 nm(2)) of PAA for fast solid-phase ionic diffusion but also leads to exponentially increased electrical conductivity (3.3 S cm(-1) in PAA subset of N-RGO vs 4.8 x 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 subset of N-RGO manifests reversible conversion-alloying of Sb(V) toward fast and durable Li+- and K+-ion storage.