Boosted crystalline/amorphous Fe2O3-δ core/shell heterostructure for flexible solid-state pseudocapacitors in large scale

Poor electronic conductivity and sluggish ion diffusion are the two main obstacles that limit the pseudocapacitive performance of Fe2O3. In this work, oxygen-deficient Fe2O3-δ nanorod arrays with a unique crystalline core/amorphous shell heterostructure are prepared via a facile and controllable method. The tunable amorphous layer facilitates the Li+ diffusion while introduced oxygen defects in Fe2O3 can be effectively tuned to improve electronic conductivity. More importantly, the resultant crystalline/amorphous interface greatly increases charge storage sites for improved specific capacitance. Consequently, the crystalline core/amorphous shell Fe2O3-δ integrated on graphene delivers a large capacitance of 701 F g−1 (701 mF cm−2) at 1 A g−1, which is almost double the capacitance of the conventional Fe2O3-δ nanorods without amorphous surface layer on graphene. Besides large capacitance, the electrode also exhibits greatly improved rate capability and cycle performance. To construct asymmetric supercapacitor, similar strategy is implemented to prepare Co3O4-δ nanosheet arrays with superior pseudocapacitive performance compared to its pristine counterpart. Importantly, flexible and large-scale (10 × 10 cm2) asymmetric supercapacitors are fabricated with promising device performance, demonstrating the smart electrode design is promising for practical application.