From granules to nanosheets: Unlocking the energy potential of CoFe₂O₄ for highly-efficient asymmetric energy storage applications

With the growing demand, asymmetric supercapacitors have emerged as a vital solution to bridge the gap between high-energy/power demands in modern sustainable energy technologies, offering enhanced operating voltages and energy densities over their symmetric counterparts. Herein, we systematically design and investigate the impact of solvent-mediated morphology engineering on the electrochemical performance of CoFe₂O₄. Among these, the CoFe₂O₄ having nanosheet morphology (CFO-NS) demonstrates superior charge storage behavior, delivering a high specific capacitance of 1397 F/g and maintaining ~996 F/g when current shifts from 1 to 10 A/g, outperforming CoFe₂O₄-compact granular (CFO-CG; 933 → 495 F/g) and CoFe₂O₄-nanobelt-like (CFO-NB; 1275 → 753 F/g) across the same current range. This performance is complemented by exceptional cycling stability (95 % retention after 10,000 cycles). Furthermore, the CFO-NS also exhibits remarkable energy densities of ~112 Wh/kg and a maximum power output of 7.20 kW/kg, significantly exceeding those of its CFO-CG and CFO-NB counterparts. To further validate the potential of CFO-NS in practical configurations, an asymmetric device (CFO-NS//AC) was fabricated, which delivers a high specific capacitance of 180 F/g at 1 A/g with robust retention (97 %, ~91 %, and 87 % at 1, 5, and 10 A/g after 10,000 cycle), and impressive energy-power characteristics (~ 90.03 Wh/kg at 1.80 kW/kg). This study highlights the significance of morphologically-tuned CoFe₂O₄ nanostructures as promising candidates for next-generation high-performance supercapacitor applications.