Redox active KI solid-state electrolyte for battery-like electrochemical capacitive energy storage based on MgCo₂O₄ nanoneedles on porous β-polytype silicon carbide

MgCo₂O₄ nanoneedles were introduced on the surface of micro and mesoporous silicon carbide flakes (SiCF) to synthesize a supercapacitor with high capacitive performance, made of hybrid electrode materials. Based on the synergistic effect between electric double layer capacitive contributions of SiCF and faradic reaction of MgCo₂O₄, the SiCF/MgCo₂O₄ electrode shows outstanding energy storage performance, exhibiting a 310.02 C g⁻¹ of specific stored charge capacity at 5 mV s⁻¹ with high capacity retention ratio over wide range of scan rates (83.2% at 500 mV s⁻¹). Furthermore, in conjunction with a capacitive SiCF negative electrode in a quasi-solid-state PVA-KOH–KI gel electrolyte, it resulted in a unique redox-active flexible solid-state asymmetric supercapacitor device. It delivers outstanding capacitive performance (specific stored charge capacity of 185.88 C g⁻¹ at 5 mV s⁻¹), with maximum energy density of 41.308 Wh kg⁻¹ at 464.72 W kg⁻¹ of power density, surpassing many recently reported flexible supercapacitors. Moreover, the ability to operate 3-V green light-emitting diodes (LED) at bending state also indicates its possibility for practical application. Therefore, these novel electrode materials with unique redox-active solid state electrolyte may find promising applications in flexible energy storage devices in future.