A confined nanocrystal-in-nanofiber architecture: stabilizing high-entropy oxide nanoparticles in carbon nanofibers for superior lithium storage.

High-entropy oxides (HEOs), characterized by their entropy-stabilized structures and versatile redox capabilities, represent a frontier in high-capacity anode materials for next-generation lithium-ion batteries. Despite exhibiting significant potential in energy storage due to their tunable chemical composition and "cocktail" effect, research into HEOs remains in its infancy, primarily focused on material composition design and preliminary electrochemical validation. HEOs also face bottlenecks including complex synthesis processes, low first-cycle coulombic efficiency, rapid capacity decay at high current densities, and insufficient understanding of their intricate redox mechanisms. These factors severely constrain their practical application. Herein, we present a robust spatial confinement strategy to engineer a "nanocrystal-in-fiber" architecture, featuring ultrafine (CoFeNiCrMn)3O4 spinel nanoparticles in situ encapsulated within interconnected carbon nanofibers via electrospinning and optimized thermal treatment. This integrated design creates a resilient 3D conductive framework that not only accelerates electron/ion transport kinetics but also serves as a mechanical buffer to accommodate lattice strain and prevent active material detachment. Systematic optimization of precursor concentration and calcination temperature reveals that the HEO/C-1.25-300 composite achieves a superior balance between crystallinity and structural integrity. Consequently, the optimized electrode delivers outstanding electrochemical performance, maintaining a high reversible capacity of 653.2 mAh g-1 after 100 cycles at 100 mA g-1 (corresponding to a remarkable 96% retention) and exhibiting excellent rate capability up to 2 A g-1. This work establishes a versatile structural engineering paradigm for mitigating the degradation of entropy-stabilized oxides, paving the way for durable high-energy storage devices.