Composite Electrodes of Activated Carbon and Multiwall Carbon Nanotubes Decorated with Silver Nanoparticles for High Power Energy Storage

Markoulidis Markoulidis,Grilli Grilli,Trapalis Trapalis,Todorova Todorova,Lekakou Lekakou

doi:10.3390/jcs3040097

Abstract

Composite materials in electrodes for energy storage devices can combine different materials of high energy density, in terms of high specific surface area and pseudocapacitance, with materials of high power density, in terms of high electrical conductivity and features lowering the contact resistance between electrode and current collector. The present study investigates composite coatings as electrodes for supercapacitors with organic electrolyte 1.5 M TEABF4 in acetonitrile. The composite coatings contain high surface area activated carbon (AC) with only 0.15 wt% multiwall carbon nanotubes (MWCNTs) which, dispersed to their percolation limit, offer high conductivity. The focus of the investigations is on the decoration of MWCNTs with silver nanoparticles, where smaller Ag crystallites of 16.7 nm grew on carboxylic group-functionalized MWCNTs, MWCNT–COOH, against 27–32 nm Ag crystallites grown on unfunctionalized MWCNTs. All Ag-decorated MWCNTs eliminate the contact resistance between the composite electrode and the current collector that exists when undecorated MWCNTs are used in the composite electrodes. Ag-decorated MWCNT–COOH tripled the power density and Ag-decorated MWCNT additive doubled the power density and increased the maximum energy density by 6%, due to pseudocapacitance of Ag, compared to composite electrodes with undecorated MWCNTs.

Highlights

The theory of composite materials has infiltrated the energy storage devices, in the form of composite supercapacitor [1] and hybrid battery–supercapacitor devices [2,3]
The composite electrodes consisted of graphene as the main provider of high capacitance, carbon black and, in some cases, carbon nanotubes as high electrical conductivity additives, with the latter improving mechanical performance and toughness, and sulfur which was used for crosslinking the graphene nanoplatelets and offered a certain degree of pseudocapacitance contributing to the energy density
Given the high conductivity of silver pastes, the present study explores the decoration of conductive multiwall carbon nanotubes (MWCNTs) with Ag nanoparticles, and the addition of this highly conductive material to activated carbon (AC) coatings to be tried as composite electrodes in electrochemical double layer capacitors (EDLCs), where the high AC surface area provides the capacitance, possibly enhanced by any pseudocapacitance of Ag nanoparticles, while the Ag-decorated MWCNTs aim to raise the electrical conductivity in the EDLC

Summary

Introduction

The theory of composite materials has infiltrated the energy storage devices, in the form of composite supercapacitor [1] and hybrid battery–supercapacitor devices [2,3]. Structural energy storage devices target the structural performance of an assembly of composite materials by including the phase of a solid electrolyte possibly in epoxy matrix combined with a fibrous or coating-type porous electrode and a glass fiber separator [4,5,6,7]. Such devices may be fabricated using traditional composite manufacturing techniques, such as resin transfer molding (RTM) [8,9,10], vacuum-assisted RTM [11] or even structural reaction injection molding (SRIM) [12,13]. The composite electrodes consisted of graphene as the main provider of high capacitance, carbon black and, in some cases, carbon nanotubes as high electrical conductivity additives, with the latter improving mechanical performance and toughness, and sulfur which was used for crosslinking the graphene nanoplatelets and offered a certain degree of pseudocapacitance contributing to the energy density

Methods

Results

Conclusion