Insight into the role of interfacial reconstruction of manganese oxides toward enhanced electrochemical capacitors

The pursuit of facile synthetic methods for systematic control over the morphology and crystal phase of nanostructures has attracted a tremendous amount of interest. By utilizing the acid-induced layer-to-tunnel transition method of MnO2, we here for the first time report multi-layered sawtooth-shape MnO2 with relatively high mass loading. The optimized electrode exhibits durable activity with enhanced surface area, electrical conductivity and ionic diffusion. A high areal capacitance of 1781.8 mF/cm2 is obtained and excellent rate performance can be corroborated from capacitance retention of 64.1% when the current density is increased by 45-fold. Our uniquely assembled heterostructure endows a large number of active sites and acts as electron superhighways to facilitate efficient charge transportation. Further coupling with activated graphene/CC anode, a flexible device with a maximum operating voltage of 2.2 V is assembled, delivering a high volumetric energy density of 4.3 mWh/cm3 at a power density of 27.6 mW/cm3 with outstanding cycling performance. The finding promotes the development of highly efficient faradaic electrode materials toward closing the gap between achieved and theoretical capacitance without limiting the mass loading.