Low-Charge-Carrier-Scattering Three-Dimensional α-MnO₂/β-MnO₂ Networks for Ultra-High-Rate Asymmetrical Supercapacitors

Abstract

The excessive concern over the energy density of supercapacitors is changing their applied direction while the power density is always overlooked. Supercapacitors should be considered as a high-power energy device rather than a neither fish nor fowl energy device. Herein, an ultrafine α-MnO2 needle was formed on β-MnO2 networks, not distributed randomly, but standing on the surface of β-MnO2 vertically forming an array structure with low-charge-carrier scattering. These novel structures possess a rational arrangement of the needles resulting in high capacitance (278.2 F g–1 for α-MnO2/β-MnO2 networks) and excellent rate capability (41.0% remaining with the specific current increased from 0.25 to 64.0 A g–1). Asymmetrical supercapacitors fabricated by reduced graphene oxide (RGO) as the anode and as-prepared structures as the cathode deliver excellent electrochemical performance. Specifically, the devices give a favorable specific energy (29.8 W h kg–1) considering the weight of α-MnO2/β-MnO2 and reduced graphene oxide (RGO) as well as ultrahigh specific power (64.0 kW kg–1) and excellent cyclic stability (>95% of initial capacitance remained after 10 000 cycles). This work opens new avenues for promoting high-power asymmetrical supercapacitors.