<p>In this study, cobalt oxide modified bismuth tin oxide (BiSnO) samples were synthesized via a facile microwave-assisted method and their electrochemical features were systematically investigated. XRD and FE-SEM analyses reveal that controlled cobalt oxide incorporation alters the microstructure from compact aggregates to well-dispersed microrod motifs and ensures uniform elemental distribution, thereby enhancing electrode–electrolyte interactions. Among the series, the 2 wt% Co₃O₄ modified BiSnO exhibits substantially improved electrochemical kinetics, with a low charge-transfer resistance of 0.36 Ω. In a three-electrode configuration, the 2 wt% Co₃O₄ modified electrode delivers a high specific capacity of 354 C g⁻¹ at a current density of 10 A g⁻¹ and excellent cycling stability (114% retention after 2500 cycles). When paired with activated carbon in an asymmetric device, it stably operates over a wide 1.4&#xa0;V potential window and delivers a maximum energy density of 33.6 Wh kg⁻¹ at a power density of 625 W kg⁻¹. The device also maintains 90% of its initial capacity over 2500 cycles, highlighting its durability. These findings demonstrate that the structural tuning of BiSnO through the addition of Co₃O₄ can significantly enhance its charge-storage properties.</p>