Hierarchical core–shell heterostructure of porous carbon nanofiber@ZnCo2O4 nanoneedle arrays: advanced binder-free electrodes for all-solid-state supercapacitors

Abstract

Hierarchical ZnCo₂O₄ nanoneedle arrays are vertically grown on porous carbon nanofibers (PCFs) to form a core–shell heterostructure through a facile hydrothermal method followed by thermal treatment. Such a unique configuration makes full use of the synergistic effects from both excellent electrical conductivity of PCFs and high specific capacitance of ZnCo₂O₄, endowing the hybrid to be an excellent electrode for flexible supercapacitors. Benefiting from their intriguing structural features, the PCF@ZnCo₂O₄ hybrid possesses fascinating electrochemical performance as an integrated binder-free electrode for supercapacitors. Remarkably, this PCF@ZnCo₂O₄ electrode could achieve a high capacitance of 1384 F g⁻¹ at a scan rate of 2 mV s⁻¹. Moreover, an all-solid-state asymmetric supercapacitor fabricated with the as-prepared PCF@ZnCo₂O₄ hybrid as the positive electrode and PCFs as the negative electrode achieves a high energy density of 49.5 W h kg⁻¹ (based on the total mass of the material on the two electrodes) at a power density of 222.7 W kg⁻¹. Furthermore, the all-solid-state asymmetric supercapacitor device exhibits remarkable cycling stability with 90% specific capacitance retention after 3000 cycles. Therefore, these fascinating electrochemical performances make this material hold great promise for next-generation high-energy supercapacitor applications.