Low-Valent CuIO Stabilized by a Layered Vanadium Oxide: Potential Reversal and Physicochemical Iodine-Anchoring for Synergistic Cu/V/I Conversions.

In order to solve the dissolution and shuttle effect of iodine/iodide in Na-I2 batteries, Cu/organic species cointercalated vanadium oxide Cux(org)0.19V2O5 (Cu-org-VO) microsheets decorated with low-valent CuIO nanoparticles (NPs) are designated as iodine hosts. During the hydrothermal synthesis, m-phenylenediamine was converted into an aromatic N-heterocyclic species (org) and inserted into the layered vanadium oxide, improving electron conductivity. The expanded interlayer spacing of Cu-org-VO with variable-valence V can confine I2 physically and activate I-I bonds. Moreover, the V → O → Cu electron transfer in the Cu-org-VO/CuO heterostructure can stabilize low-valent CuIO NPs and inhibit their aggregation. And this heterostructure can be in situ transformed into the Cu-org-VO/CuI heterostructure after iodine loading. Impressively, due to the interactions within the heterostructure and CuI-induced potential reversals, the reactions of Cu0 + 1/2I2 ↔ CuI and Cu2++ Cu0 + 2I- ↔ 2 CuI can occur spontaneously to achieve the synergistic redox of copper and iodine with improved kinetics. And this strategy of "physical confinement", "chemical conversion" and "synergistic redox" can immobilize iodine physicochemically and accomplish multielectron transfer of Cu/I/V, leading to a coupled battery with a high voltage output, but circumventing the generation of unstable high-valent iodine species.