Ultra-High Energy Density Hybrid Supercapacitors Using MnO2/Reduced Graphene Oxide Hybrid Nanoscrolls

Abstract

Manganese oxide (MnO2) is a promising material for supercapacitor applications, with a theoretical ultra-high energy density of 308 Wh/kg. However, such ultra-high energy density has not been achieved experimentally in MnO2-based supercapacitors because of several practical issues, such as low electrical conductivity of MnO2, incomplete utilization of MnO2, and dissolution of MnO2. The present study investigates the potential of MnO2/reduced graphene oxide (rGO) hybrid nanoscroll (GMS) structures as electrode material for overcoming the difficulties and for developing ultra-high-energy storage systems. A hybrid supercapacitor, comprising MnO2/rGO nanoscrolls as anode material and activated carbon (AC) as a cathode, is fabricated. The GMS/AC hybrid supercapacitor exhibited enhanced energy density, superior rate performance, and promising Li storage capability that bridged the energy–density gap between conventional Li-ion batteries (LIBs) and supercapacitors. The fabricated GMS/AC hybrid supercapacitor demonstrates an ultra-high lithium discharge capacity of 2040 mAh/g. The GMS/AC cell delivered a maximum energy density of 105.3 Wh/kg and a corresponding power density of 308.1 W/kg. It also delivered an energy density of 42.77 Wh/kg at a power density as high as 30,800 W/kg. Our GMS/AC cell’s energy density values are very high compared with those of other reported values of graphene-based hybrid structures. The GMS structures offer significant potential as an electrode material for energy-storage systems and can also enhance the performance of the other electrode materials for LIBs and hybrid supercapacitors.

N-Dopant-Mediated Growth of Metal Oxide Nanoparticles on Carbon Nanotubes

“…Interestingly, the MnO x nanoparticles directly synthesized on the N-doped graphitic surface have a spherical shape with a highly uniform diameter of less than 10 nm ( Figure 2 F). They are distinct from flake-like or rod-like MnO x nanoparticles, generally synthesized on pristine CNTs, as reported in many previous studies [ 28 , 29 , 30 ]. The conformal and uniform formation of MnO x nanoparticles on NCNTs can be elucidated with the even distribution of N dopants over the whole surface and the well-aligned separated structures of the grown NCNTs, which prevent non-uniform nucleation or hidden surfaces resulting from agglomeration.…”

Transition Metal Oxide Electrode Materials for Supercapacitors: A Review of Recent Developments

“…Owing to its rich natural content, no environmental pollution, and high theoretical specific capacitance (1380 F g −1 ), MnO 2 has been widely studied as the most competitive transition metal oxide [ 103 , 104 , 105 ]. However, its application in supercapacitors is seriously affected because of its poor conductivity and slow ion transport rate [ 106 , 107 , 108 ].…”

Construction of α-MnO2 on Carbon Fibers Modified with Carbon Nanotubes for Ultrafast Flexible Supercapacitors in Ionic Liquid Electrolytes with Wide Voltage Windows

“…The total mass loading of α-MnO 2 on CNTs/CC is about 0.73 mg cm −2 and the discharging time at different current densities are used to calculate the energy and power densities. At a power density of 833.35 W kg −1 , the device has an energy density of 57.29 W h kg −1 , and even at 9999.99 W kg −1 , the energy density is still 46.95 Wh kg −1 , which is better than those of M-MnO 2 /rGO//AC (36.4 W h kg −1 at 212.5 W kg −1 ) [53], rMnCo 2 O 4 @rMnO 2 -2 h//AC (32.4 W h kg −1 at 904.9 W kg −1 ) [54], K-MnO 2 //AC (56 W h kg −1 at 550 W kg −1 ) [55], and GMS//AC (42.77 W h kg −1 at 30,800 W kg −1 ) [56].…”

“…Comparison of the electrochemical properties of MnO 2 -based supercapacitors. References [47,[49][50][51][52][53][54][55][56]62] are cited in the supplementary materials. Institutional Review Board Statement: Not applicable.…”