Crystallization regulation and electrochemical optimization of free-standing carbon nanofiber-confined vanadium oxide nanodots for advanced flexible zinc ion batteries.

Aqueous zinc ion batteries (ZIBs) are promising candidates for flexible energy storage. Nevertheless, the absence of appropriate cathodes demonstrating good flexibility and electrochemical performance remains a primary bottleneck. Herein, a novel composite carbon nanofiber cathode (VOH ND@CNFs) with confined hydrated vanadium oxide is engineered through cooperative crystallization regulation during carbonization and crystal structure optimization via electrochemical activation. The precursors synthesized by electrospinning technology first undergo calcination processes until primary ultrasmall crystalline V2O3 nanodots occur in carbon fibers (V2O3 ND@CNFs). In the subsequent electrochemical treatment process, the confined V2O3 nanodots are rapidly self-transformed into structurally stable hydrated vanadium oxides. The electrochemical performance of the primary ultrasmall crystalline state for vanadium oxide confined in CNFs after electrochemical optimization is proven to be much superior to that of the noncrystalline state and the secondary crystalline state of vanadium oxide. Consequently, the flexible structure-optimized VOH ND@CNFs cathode exhibits a high specific capacity of 349 mAh g-1 (total weight) at 0.5 A g-1 and retains 125.7 mAh g-1 under high current density (10 A g-1). Furthermore, it demonstrates excellent long-term cycling stability without significant capacity degradation after 1500 cycles at 10 A g-1. This work presents a synergistic crystal optimization strategy for high-performance flexible ZIBs.