Direct Superassemblies of Freestanding Metal–Carbon Frameworks Featuring Reversible Crystalline-Phase Transformation for Electrochemical Sodium Storage

High-power sodium-ion batteries (SIBs) with long-term cycling attract increasing attention for large-scale energy storage. However, traditional SIBs toward practical applications still suffer from low rate capability and poor cycle induced by pulverization and amorphorization of anodes at high rate (over 5 C) during the fast ion insertion/extraction process. The present work demonstrates a robust strategy for a variety of (Sb–C, Bi–C, Sn–C, Ge–C, Sb–Bi–C) freestanding metal–carbon framework thin films via a space-confined superassembly (SCSA) strategy. The sodium-ion battery employing the Sb–C framework exhibits an unprecedented performance with a high specific capacity of 246 mAh g–1, long life cycle (5000 cycles), and superb capacity retention (almost 100%) at a high rate of 7.5 C (3.51A g–1). Further investigation indicates that the unique framework structure enables unusual reversible crystalline-phase transformation, guaranteeing the fast and long-cyclability sodium storage. This study may open an av...