Uncovering giant nanowheels for magnesium ion–based batteries

The giant wheel-shaped Na₁₅{Mo₁₅₄O₄₆₂H₁₄(H₂O)₇₀]_0.5Mo₁₅₂O₄₅₇H₁₄(H₂O)₆₈]_0.5}·ca. 400 H₂O (Mo₁₅₄) is one of the fascinating clusters with the open host framework, which is designed by simple metal-oxygen fragment–linked coordination modes. The generation of structural vacancies (here referred to as defects), the substitution of ligands, and incorporation of heterometallic centers in Mo₁₅₄ could offer several attractive possibilities to achieve good electrochemical performance such as high specific capacity and stability in multivalent batteries. Herein, we have introduced electronically rich giant nanowheel Mo₁₅₄ as a potential cathode material in magnesium-rechargeable batteries (MRBs). The experimental evidence indicates that the Mo₁₅₄ wheels offer a reversible capacity of ～150 mAh g^?1 at 50 mA g^?1 in MRBs, which was retained to about 55 mAh g^?1 after a long cycling life (>500 cycles). Typically, the divalent alkali metals (Mg²⁺) suffer from diffusion and insertion reactions in host materials; however, the stable and high rate performance against cycling with good Coulombic efficiency was achieved for Mo₁₅₄ electrodes. Thus, the work demonstrates that the complex inorganic clusters are promising cathode materials in multivalent ion batteries.