New Materials and New Configurations for Advanced Electrochemical Capacitors

Today, electrochemical capacitors (ECs) have the potential to emerge as a promising energy storage technology. The weakness of EC systems is certainly the limited energy density, which restricts applications to power delivery over only few seconds. As a consequence, many research efforts are focused on designing new materials to improve energy and power densities. These are reviewed below

True Performance Metrics in Electrochemical Energy Storage

A dramatic expansion of research in the area of electrochemical energy storage (EES) during the past decade has been driven by the demand for EES in handheld electronic devices, transportation, and storage of renewable energy for the power grid (1–3). However, the outstanding properties reported for new electrode materials may not necessarily be applicable to performance of electrochemical capacitors (ECs). These devices, also called supercapacitors or ultra-capacitors (4), store charge with ions from solution at charged porous electrodes. Unlike batteries, which store large amounts of energy but deliver it slowly, ECs can deliver energy faster (develop high power), but only for a short time. However, recent work has claimed energy densities for ECs approaching (5) or even exceeding that of batteries. We show that even when some metrics seem to support these claims, actual device performance may be rather mediocre. We will focus here on ECs, but these considerations also apply to lithium (Li)—ion batteries

Electrochemical capacitors for energy management

Rapid storage and efficient delivery of electrical energy in heavy-duty applications are being enabled by electrochemical capacitors

Two-Dimensional MXene with Controlled Interlayer Spacing for Electrochemical Energy Storage

In this issue of ACS Nano, Luo et al. report the preparation of pillared two-dimensional (2D) Ti3C2 MXenes with controllable interlayer spacings between 1 and 2.708 nm. These materials were further intercalated by ion exchange with Sn(+IV) ions. The results show improved electrochemical performance due to improved ion accessibility into the 2D structure as well as the confinement effect, which limits volume expansion during the Li-alloying reaction. Beyond this specific example, the demonstration that the interlayer spacings of MXenes can be fine-tuned by creating pillared structures based on the spontaneous intercalation of surfactants opens new perspectives in the field of electrochemical energy storage

Two-Dimensional MXene with Controlled Interlayer Spacing for Electrochemical Energy Storage

In this issue of ACS Nano, Luo et al. report the preparation of pillared two-dimensional (2D) Ti3C2 MXenes with controllable interlayer spacings between 1 and 2.708 nm. These materials were further intercalated by ion exchange with Sn(+IV) ions. The results show improved electrochemical performance due to improved ion accessibility into the 2D structure as well as the confinement effect, which limits volume expansion during the Li-alloying reaction. Beyond this specific example, the demonstration that the interlayer spacings of MXenes can be fine-tuned by creating pillared structures based on the spontaneous intercalation of surfactants opens new perspectives in the field of electrochemical energy storage

Spark plasma sintered carbon electrodes for electrical double layer capacitor applications

The spark plasma sintering (SPS) is an emerging process for shaping any type of materials (metals, ceramic, polymers and their composites). The advantage of such a process is to prepare densified ceramic materials in a very short time, while keeping the materials internal porosity. In the present work, we have used the SPS technique to prepare activated carbon-based electrodes for Electrochemical Double Layer Capacitor applications (EDLC). Self-supported 600 and 300µm-thick electrodes were prepared and characterized using of Electrochemical Impedance Spectroscopy and galvanostatic cycling in a non-aqueous 1.5MNEt4BF4 in acetonitrile electrolyte. Electrochemical performance of these sintered electrodes were found to be in the same range – or even slightly better – than the conventional tape-casted activated carbon electrodes. Although organic liquid electrolyte was used to characterize the electrochemical performance of the sintered electrodes, these results demonstrate that the SPS technique could be worth of interest in the ultimate goal of designing solid-state supercapacitors

The dynamics of iterated transportation simulations

Iterating between a router and a traffic micro-simulation is an increasibly accepted method for doing traffic assignment. This paper, after pointing out that the analytical theory of simulation-based assignment to-date is insufficient for some practical cases, presents results of simulation studies from a real world study. Specifically, we look into the issues of uniqueness, variability, and robustness and validation. Regarding uniqueness, despite some cautionary notes from a theoretical point of view, we find no indication of ``meta-stable'' states for the iterations. Variability however is considerable. By variability we mean the variation of the simulation of a given plan set by just changing the random seed. We show then results from three different micro-simulations under the same iteration scenario in order to test for the robustness of the results under different implementations. We find the results encouraging, also when comparing to reality and with a traditional assignment result. Keywords: dynamic traffic assignment (DTA); traffic micro-simulation; TRANSIMS; large-scale simulations; urban planningComment: 24 pages, 7 figure

On the origin of the extra capacity at low potential in materials for Li batteries reacting through conversion reaction

The possibility of interfacial storage at low potential for electrode materials reacting through conversion reactions was evaluated. The amount of charge that could be stored through the proposed interfacial mechanism was estimated for a range of different materials and found to be much lower than those observed experimentally. Moreover, the slope of the potential decay and the influence of the current in the extent of stored capacity for experiments carried out in composite electrodes containing Co3O4 are not consistent with a capacitive-like mechanism. In summary, no evidence for capacitive storage could be found, our results being in agreement with the process taking place at low potential being solely related to electrolyte decomposition

Monolithic Carbide-Derived Carbon Films for Micro-Supercapacitors

Microbatteries with dimensions of tens to hundreds of micrometers that are produced by common microfabrication techniques are poised to provide integration of power sources onto electronic devices, but they still suffer from poor cycle lifetime, as well as power and temperature range of operation issues that are alleviated with the use of supercapacitors. There have been a few reports on thin-film and other micro-supercapacitors, but they are either too thin to provide sufficient energy or the technology is not scalable. By etching supercapacitor electrodes into conductive titanium carbide substrates, we demonstrate that monolithic carbon films lead to a volumetric capacity exceeding that of micro- and macroscale supercapacitors reported thus far, by a factor of 2. This study also provides the framework for integration of high-performance micro-supercapacitors onto a variety of devices

Monolithic Carbide-Derived Carbon Films for Micro-Supercapacitors

Microbatteries with dimensions of tens to hundreds of micrometers that are produced by common microfabrication techniques are poised to provide integration of power sources onto electronic devices, but they still suffer from poor cycle lifetime, as well as power and temperature range of operation issues that are alleviated with the use of supercapacitors. There have been a few reports on thin-film and other micro-supercapacitors, but they are either too thin to provide sufficient energy or the technology is not scalable. By etching supercapacitor electrodes into conductive titanium carbide substrates, we demonstrate that monolithic carbon films lead to a volumetric capacity exceeding that of micro- and macroscale supercapacitors reported thus far, by a factor of 2. This study also provides the framework for integration of high-performance micro-supercapacitors onto a variety of devices