Rational design of the composition and electrochemically favorable structural configuration of electrode materials are highly required to develop high-performance supercapacitors. Here, we report our findings on the design of interconnected NiGa₂O₄ nanosheets as advanced cathode electrodes for supercapacitors. Rietveld refinement analysis demonstrates that the incorporation of Ga into NiO leads to a larger cubic lattice parameter that promotes faster charge-transfer kinetics, enabling significantly improved electrochemical performance. The NiGa₂O₄ electrode delivers a specific capacitance of 1508 F g⁻¹ at a current density of 1 A g⁻¹ with a capacitance retention of 63.7% at 20 A g⁻¹, together with excellent cycling stability after 10 000 charge–discharge cycles (capacitance retention of 102.4%). An asymmetric supercapacitor device was assembled by using NiGa₂O₄ and Fe₂O₃ as cathode and anode electrodes, respectively. The ASC delivers a high energy density of 45.2 W h kg⁻¹ at a power density of 1600 W kg⁻¹ with exceptional cycling stability (94.3% cell capacitance retention after 10 000 cycles). These results suggest that NiGa₂O₄ can serve as a new class cathode material for advanced electrochemical energy storage applications.