Flexible manganese oxide electrodes with fernlike structure have been fabricated by in-situ oxidation of well-aligned dendritic metal Mn blades, which are electrodeposited template-freely on metal wire from aqueous electrolyte. The dendritic Mn blades can serve as both efficient current collector with large specific area and precursor for in-situ oxide formation. Related setup design and electrochemical conditions for dendrites deposition were optimized, while a modified dendrite-growth model was also proposed. The flexible and thin fernlike electrode with a capacitance of 653 mF.cm(-2) @ 2 mA.cm(-2), have exhibited a potential for metal dendrites on promoting the energy density of wearable energy devices, rather than a common hazard in electroplating and battery industries. (c) 2019 The Electrochemical Society.