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

Janardhanan R Rani,Ranjith Thangavel,Minjae Kim,Jae-Hyung Jang,Yun Sung Lee

doi:10.3390/nano10102049

Janardhanan R Rani, Ranjith Thangavel + Show 3 more

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https://doi.org/10.3390/nano10102049

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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.

Highlights

A high-density energy storage system is highly in demand for electric vehicles and flexible energy systems requiring a portfolio of various distributed energy resources
Extensive research has been considerably expanded over the last few years to develop innovative green energy-storage devices such as batteries and supercapacitors to cope with highly intermittent demand on electric energy storage [1,2,3,4,5]
Hybrid supercapacitors based on pseudocapacitance have high energy density than electric double-layer capacitors (EDLCs)

Summary

Introduction

A high-density energy storage system is highly in demand for electric vehicles and flexible energy systems requiring a portfolio of various distributed energy resources. Most of the energy-storage devices are based on batteries, which still have low power density and safety issues [6,7]. Hybrid supercapacitors based on pseudocapacitance (usually based on transition metal oxides) have high energy density than electric double-layer capacitors (EDLCs). Manganese oxide (MnO2) has drawn considerable interest as one of the most promising electrode materials for hybrid supercapacitors owing to its ultra-high theoretical energy density (308 Wh/kg for a single electron reaction), elemental abundance in the earth’s crust, and environmental friendliness [11]. The low conductivity of MnO2 (10−5–10−6 Scm−1) has limited the energy density of MnO2-based hybrid capacitors at an unsatisfactory level [12,13,14]. To overcome the aforementioned issues, such as low energy density and low electrical conductivity, carbonaceous materials are widely used as the conducting platform on which MnO2 particles are attached

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