Processing of Onion-like Carbon for Electrochemical Capacitors

Abstract

Multi-shell fullerenes known as onion-like carbon (OLC) are especially attractive in applications relative to energy storage, such as electrochemical capacitors, due to a near-spherical shape of particles, their nanoscale diameters and high conductivity leading to fast rate performance. Because of this, onion-like carbon can be fabricated into electrodes, used as a conductive additive, and may have potential in composites and additive manufacturing. However due to agglomeration of OLC particles, creating a stable, aqueous dispersion for ink production or formulating composites proves challenging. We explore how attrition milling, acid treatment, and probe sonication can be employed to decrease agglomeration and provide colloidal stability in aqueous media. We also investigate how the electrochemical performance changes with each processing step as well as the treatments in succession. When tested in electrochemical capacitors, the processing increases the capacitance by a factor of three, due to an added pseudocapacitive contribution which is not present in untreated OLC. As a result, the processing of OLC proves to be advantageous for the production of stable, aqueous solutions, which also exhibit improved electrochemical properties suitable for functional inks, conductive additives, and fabrication of composite electrodes. Electrochemical capacitors are widely studied due to their affordable and efficient electrical energy storage which is needed to enable widespread use of renewable energy sources and provide energy security.1 These devices strive to solve energy issues by providing quick charge-discharge (millisecond to second time constants), high power densities and long cycle lives. Mainly due to the mechanism by which charge is stored, these devices, unlike batteries, store energy by physical adsorption of ions leading to the formation of the electric double layer on the electrode. Due to the performance metrics necessary to achieve functioning devices, the electrode is commonly made from highly conductive, thermally and electrically stable, large surface area carbon materials such as activated carbon (AC), and carbide-derived carbon (CDC).1 Carbon black or carbon nanotubes are often added to the activated carbon and other electrode materials to improve their electronic conductivity and performance at high rates.2 Another carbon material, onion-like carbon (OLC) has also shown promise in electrochemical capacitors because of a unique, multishell fullerene structure with nanoscale diameters (5-10 nm).3-8 OLC can be considered as the ultimate carbon black because of its small particle size and high electrical conductivity. These materials have accessible and non-functionalized external surface areas, enabling the quick charging and discharging necessary for electrochemical capacitors. Previously investigated OLC-based microsupercapacitors, fabricated with interdigitated architectures, achieved high-rate performance, delivered stack capacitances four orders of magnitude higher than that of electrolytic capa...

In-Situ Arc Discharge-Derived FeSn2/Onion-Like Carbon Nanocapsules as Improved Stannide-Based Electrocatalytic Anode Materials for Lithium-Ion Batteries

“…It is noted that the initial specific discharge capacity of the FeSn 2 /OLC nanocapsule-based anodes (835 mAh•g −1 ) was higher than the theoretical specific discharge capacity of the FeSn 2 nanoparticle-based anodes (~804 mAh•g −1 ) [21]. This is attributed to the following four possibilities: (1) The theoretical capacity of FeSn 2 is based on the conventional alloying mechanism, in which the reduction reaction of FeSn 2 is assumed to be irreversible [29]; (2) an organic polymeric/gel-like film might had formed at the interface of the core/shell-structured anode, which enhanced their capacity via "pseudo-capacitance" [30]; (3) the hollow structure and large surface area of the OLC shells enabled the storage of Li + ions at the interfaces and pores of the electrocatalytic FeSn 2 /OLC nanocapsule-based anodes [11,19]; and (4) the high electrical conductivity of the OLC shell facilitated electron transfer during lithiation and delithiation process [20,31]. On the other hand, the poor electrocatalytic performance of the FeSn 2 nanoparticle-based anodes is rooted in their electrochemical instability, since the FeSn 2 nanoparticles undergo pulverization and exfoliation during lithiation-delithiation process [2,10,11].…”

“…OLC are nanoparticles with quasi-spherical shape composed of multiple enclosed fullerene-like defective carbon shells with diameters between 5-10 nm [19]. Owing to their surface defective features, they exhibit superior electrical conductivity, structural flexibility, and full accessibility of ion adsorption/desorption on their surface [20].…”

“…Schematic representation of formation of FeSn 2 /OLC nanocapsules during in-situ arc-discharge process[20,26].…”

Selective synthesis of turbostratic polyhedral carbon nano-onions by arc discharge in water

“…In 1992, Ugarte obtained CNOs by strong electron irradiation of carbon soot containing tubular carbon structures and amorphous carbon [5]. CNOs have been evaluated to have strong potential impact in many different fields: tribology [6], lithium-ion batteries [7], fuel cells [8], supercapacitors [9], electromagnetic shielding [10], electro-optics [11]. Among the different methods for the synthesis of CNOs, the more investigated in recent years are the annealing of detonation nanodiamonds [12], and the arc discharge between graphite electrodes in deionized water [13].…”