Bimetallic CoNi2Se4 nanostructures on nickel-foam substrates were fabricated by a potentiostatic deposition method by adjusting the deposition solution pH, and used as electrode materials in battery-type supercapacitors. The electrodeposition solution pH had an important role in the fabrication of the desirable CoNi2Se4 nanostructures. At a deposition solution pH of 2.0, the synthesized product contained CoNi2Se4 nanoparticles. In contrast, a partially converted flake-like morphology was obtained at pH = 2.5. The appropriate flake-like morphology was formed by increasing the deposition solution pH to 3.0. The robust flake-like structure facilitated the electron transport during redox reactions, providing an excellent electrochemical behavior in terms of specific capacity, rate capability, and cyclic stability. A battery-type supercapacitor based on the flake-like CoNi2Se4 structure exhibited a maximum specific capacity of 632.5 C g−1 at a current density of 1 A g−1 and excellent rate performance (capacity retention of 91%) in the range of 1 to 40 A g−1. The material retained 83.31% of its initial capacity after 3000 cycles of charging/discharging at a current density of 40 A g−1, which suggests a high long-term cycling stability. The excellent electrochemical performance of the CoNi2Se4 electrode material make it very promising for application in supercapacitors.