Carbon black supercapacitors employing thin electrodes

Abstract

Carbon black supercapacitors that employ thin (∼1 μm) electrodes were produced by coating and inkjet printing on a conventional current collector or directly on a separator membrane. The simplicity and diversity of ultrathin electrode fabrication were facilitated by the physical form of carbon black, which can be described as a fine particle of around 100 nm in size. It was established that the performance of carbon black in thin supercapacitor electrodes may be compared with carbon nanotube and graphene materials in those instances where fast frequency response is desired from the supercapacitor. At the same time, the fast response supercapacitors that employ nanotubes and graphenes have presently involved more elaborate fabrication routes. RC time constant of 354 μs and phase angle of −75° at 120 Hz is demonstrated for carbon black supercapacitors that employ SC3 carbon black of 1800 m² g⁻¹ surface area.

Introduction

Supercapacitors, ultracapacitors, or electrochemical double layer capacitors are the synonyms of energy storage devices, whose domain of energy density versus power density cannot be accessed neither by electrolytic or electrostatic capacitors, batteries, or fuel cells [1]. Although still evolving into the area of ever more energy containing and powerful devices, supercapacitors have already been able to address the increasing needs of electronic (cell phones, digital cameras, etc.), industrial (uninterruptible power supplies, grid conditioning, windmills, cranes, etc.) and transportation/automotive (trains, busses, cars) sectors [2]. Being unique, in terms of combination of characteristics including power density, temperature range, life cycle and safety, supercapacitors may also be used complementary to batteries, and, in a few certain cases, supercapacitors can even replace batteries [2]. Recently, supercapacitors were also shown to expand their potential application into the realm of electrolytic capacitors for ac line-filtering [3], showcasing that novel carbons (e.g. graphenes), which together with improved conventional carbons (e.g. activated carbons) [4] as well as high-voltage and high-stability electrolytes [5] may provide a pathway for further adoption and expansion of supercapacitors in various applications.

The most common construction of supercapacitors consists of two carbon electrodes, deposited on current collectors (e.g. aluminum foil), and sandwiched together with a non-electronically conducting separator membrane in the middle [1]. Usually, supercapacitor electrodes are fabricated by coating or extrusion with a thickness of around 100 μm for energy density reasons. Thinner electrodes (∼10 μm) are not uncommon for electronic applications of supercapacitors, as the thickness of electrodes is one of the factors determining the Equivalent Series Resistance (ESR) and the power density of supercapacitors [6], [7]. Furthermore, ultrathin electrodes (∼1 μm) can provide superb power density characteristics and rapid response, and, as demonstrated in this study, supercapacitors containing thin electrodes can be fabricated by employing conventional carbon black materials.

Recent work on supercapacitors that use thin electrodes with good ion transport characteristics has exemplified the potential of graphenes [3] and carbon nanotubes [8] for supercapacitors of high frequency response operation. The supercapacitors based on these materials were shown to outperform the conventional activated carbon supercapacitors at high frequencies, whose sluggishness is governed by the complexity of torturous porous network of activated carbon electrodes, resulting in decay of operation above around 0.1 Hz [3] and, in rare instances, in around 10–20 Hz range [9].

In this work, we have continued the exploration of carbon solutions for high frequency response applications of supercapacitors. We demonstrate that carbon blacks can be employed for thin (∼1 μm) electrodes in supercapacitors, allowing fast frequency response operation facilitated by the short length of pores within the carbon black material. In this respect, we have shown that carbon black can be advantageous alternative to presently more expensive carbon nanotubes [8] and graphenes [3] in fast frequency response supercapacitors, potentially finding application in ac line-filtering in electronic devices and in pulse applications of supercapacitors. We also demonstrate that, in addition to conventional manufacturing routes, such as coating, carbon black electrodes can be produced by printing, such as inkjet printing, and deposited directly on separator membranes for ultrathin and flexible supercapacitor architectures.