Void Space Control in Porous Carbon for High-Density Supercapacitive Charge Storage

Abstract

High-density charge (energy) storage under supercapacitive mode requires an electrode that would deliver larger space for charge accumulation and offer a larger electrochemical potential difference at an electrode–electrolyte interface. Porous carbon has been a preferred electrode for commercial supercapacitors; however, its charge storability is much lower than that of state-of-the-art charge-storage devices such as lithium-ion batteries. We show that one of the primary limiting factors is the voids in porous carbon, which do not contribute to the capacitance because their sizes are much larger than the size of the solvated/unsolvated ions in the electrolyte. We partially activate these voids by filling them with a flower-shaped 3D hierarchical pseudocapacitive material (MnCo2O4) by assuming that flower-shaped fillers would provide an additional easily accessible surface for charge adsorption. Less than 10 wt % MnCo2O4 in the porous carbon from palm kernel shells through simple wet impregnation results in a five-fold increase in the charge storability. Laboratory prototypes of symmetric supercapacitors are fabricated using the MnCo2O4-filled carbon electrodes, which show five times higher specific energy than pure carbon and are cycled over 5000 times with >95% capacitance retention. The present strategy of activating the voids by hierarchical 3D nanostructures could be applied to build high-performance energy-storage devices.

The control of lithium‐ion batteries and supercapacitors in hybrid energy storage systems for electric vehicles: A review

“…In this context, a new type of electrical energy storage element-supercapacitors has been born. 35 The capacity of supercapacitors ranges from a few farads to hundreds of thousands of farads, which is much larger than ordinary capacitors of microfarad level. 36 While retaining the advantages of the fast discharge rate of capacitors, the charge storage capacity is greatly increased.…”

“…In recent years, with the development of solid‐state ion conductor technology, the volume of capacitors has gradually decreased, and the space occupied by a one‐farad capacitor can be reduced to one cubic centimeter. In this context, a new type of electrical energy storage element‐supercapacitors has been born 35 . The capacity of supercapacitors ranges from a few farads to hundreds of thousands of farads, which is much larger than ordinary capacitors of microfarad level 36 .…”

CoMnO2-Decorated Polyimide-Based Carbon Fiber Electrodes for Wire-Type Asymmetric Supercapacitor Applications

“…Here, Pt wire was used as the counter electrode, Ag/AgCl as the reference electrode and the prepared samples as the working electrode, respectively. The CV curves were recorded within the potential window from 0 to 0.6 V (vs. Ag/AgCl) in 1M KOH electrolyte at various scan rates (5,10,20,50, and 100 mV s −1 ). The GCD tests were carried out within the potential range of 0 to 0.5 V in 1M KOH.…”

“…In general, the charge storage mechanism of supercapacitors is divided in two ways, either by forming electrical double layer charge accumulation (electrical double layer capacitors; EDLCs) or by using faradaic reactions (pseudocapacitor) at the interface between the electrode and electrolyte [ 2 , 4 ]. So far, various efforts have been made to meet increasing demand of high energy density and high-rate supercapacitors [ 2 , 5 ]. The development of the transition metal oxides-based pseudocapacitors with high specific capacitance values and excellent cycling stability, which can store and release the charges via the reversible redox reactions of metal oxide’s surface and inner sites [ 4 , 5 ], have practical value because transition metal oxides and hydroxides have higher theoretical specific capacitance and excellent energy density.…”

“…So far, various efforts have been made to meet increasing demand of high energy density and high-rate supercapacitors [ 2 , 5 ]. The development of the transition metal oxides-based pseudocapacitors with high specific capacitance values and excellent cycling stability, which can store and release the charges via the reversible redox reactions of metal oxide’s surface and inner sites [ 4 , 5 ], have practical value because transition metal oxides and hydroxides have higher theoretical specific capacitance and excellent energy density. In order to fulfill the growing energy density demands for next generation high-performance supercapacitors, the energy density (E = 0.5(CV 2 )) of supercapacitors can be improved by increasing the specific capacitance (C) and operation potential window (V).…”