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Engineering of nanostructured electrodes for enhancing their electrochemical performance is a critical issue to further development in energy storage systems. In the present study, we have developed a facile template-free method to engineer 3D hierarchical ravine-like electrode based on MnCo 2 S 4 nanosheet arrays as an efficient material for high-performance electrochemical capacitors. The physico-chemical characteristics of ravine-like structure of MnCo 2 S 4 nanosheets are investigated by different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). The as-prepared MnCo 2 S 4 electrode exhibits an ultrahigh specific capacity of 834 C g−1 (231 mAh g−1) at the current density of 1 A g−1, excellent rate capability and good cycle performance. Thiospinel nature of the MnCo 2 S 4 electrode and its ravine-like nanosheet structure with effective spatial confinement for the electrolyte ions and charge transportation are responsible for this remarkable performance. Furthermore, the assembled MnCo 2 S 4 //AC asymmetric device shows the maximum energy density of 57 W h kg−1 and the highest power density of 20.8 kW kg−1. A template-free method has been developed to engineer 3D ravine-like interconnected MnCo 2 S 4 nanosheet arrays as a positive electrode material for asymmetric electrochemical capacitors. Image 1 • Engineering 3D hierarchical ravine-like interconnected MnCo 2 S 4 nanosheet arrays. • Developing a facile template free method to grow ravine-like nanostructures. • Achieving an ultrahigh specific capacity of 834 C g−1 for the MnCo 2 S 4 electrode. • Delivering remarkable energy density and cycling stability from the MnCo 2 S 4 //AC asymmetric device. [ABSTRACT FROM AUTHOR]