Partially nitrogenized mesoporous Co3O4 nanoflakes as a binder-free positive electrode for high-performance flexible solid-state asymmetric supercapacitors

Highlights: • Partially nitrogenized Co₃O₄ nanoflakes were directly deposited on carbon fabric. • The introduction of N element cause the increase of conductivity and active sites. • The N-Co₃O₄@CF electrode exhibited a high specific capacity of 473.3 C g⁻¹. • The assembled FSASC exhibited an excellent electrochemical performance. • A 100-bending-cycle test (only 5% loss in capacitance) indicated a good flexibility. -- Abstract: Flexible energy storage and conversion devices have drawn intensive attention in wearable electronics. Herein, partially nitrogenized mesoporous Co₃O₄ nanoflakes were deposited on hydrophilic conductive carbon fabric (N-Co₃O₄@CF) through a simple two-step preparation method, involving the electrodeposition of the precursor and subsequent thermal annealing under controlled conditions. The binder-free N-Co₃O₄@CF material was designed to be and innovative positive electrode with a greatly enhanced capacity of 473.3 C g⁻¹ owing to the changes in the electrical conductivity and electrochemical active sites caused by nitrogen introduction. Moreover, a flexible solid-state asymmetric supercapacitor (FSASC) combined with N-Co₃O₄@CF as the positive electrode and 3D interconnected Fe₂O₃ nanosheet networks (Fe₂O₃@CF) materials as the negative electrode was assembled. The fabricated FSASC achieved a high specific capacitance of 111.6 F g⁻¹ and excellent cycling stability (93.8% capacitance retention after 10,000 cycles). In addition, the device exhibited exceptional flexibility and excellent mechanical stability after flexibility tests, including bending the FSASC at various bending angles (no significant change of the CV and GCD curves after bending 180°) and a 100-bending-cycle durability test (only 5% loss in capacitance after continuous bending). Finally, the FSASC device delivered a competitive energy density of 39.7 Wh kg⁻¹ with the low-cost, lightweight and easy fabrication features, which may open up a promising opportunity for wearable energy storage device.