As a new energy-storage device, a supercapacitor has attracted great attention, but its low power density limits its wide application. The key to develop high-performance supercapacitors is to find high-performance electrode materials and design reasonable structures. Here, based on the strategy of structure construction and flexible self-growth, a simple one-step hydrothermal method was used to prepare marshmallow-like MnO2/CC electrode material. The electrochemical properties of the composite in different electrolytes (neutral and alkaline electrolyte) were investigated. This electrode material has excellent electrochemical characteristics in a Na2SO4 electrolyte, with a specific areal capacitance of MnO2/CC of 624 mF cm(-2) and an excellent cycle performance (97.7% after 2000 cycles). As a comparison, the electrode displays higher specific capacitance (1092 mF cm(-2)) and poor cycle performance (49.5%) in KOH. An asymmetric coin cell supercapacitor (ACC) device was assembled using MnO2/CC as a positive electrode, active carbon as a negative electrode, and Na2SO4 as the electrolyte. The device shows good specific capacitance (67.8 F g(-1)) and stable cycle stability (97.3%), superior to many reported supercapacitors.