The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

Supercapacitors have drawn considerable attention in recent years due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. Nanostructured electrode materials have demonstrated superior electrochemical properties in producing high-performance supercapacitors. In this review article, we describe the recent progress and advances in designing nanostructured supercapacitor electrode materials based on various dimensions ranging from zero to three. We highlight the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability, which may serve as a guideline for the next generation of supercapacitor electrode design.

/pdf/supercapacitor-electrode-materials-nanostructures-from-0-to-3zlm6qeqf5.pdf

Supercapacitor electrode materials: nanostructures from 0 to 3 dimensions

The world is recently witnessing an explosive development of novel electronic and optoelectronic devices that demand more-reliable power sources that combine higher energy density and longer-term durability. Supercapacitors have become one of the most promising energy-storage systems, as they present multifold advantages of high power density, fast charging-discharging, and long cyclic stability. However, the intrinsically low energy density inherent to traditional supercapacitors severely limits their widespread applications, triggering researchers to explore new types of supercapacitors with improved performance. Asymmetric supercapacitors (ASCs) assembled using two dissimilar electrode materials offer a distinct advantage of wide operational voltage window, and thereby significantly enhance the energy density. Recent progress made in the field of ASCs is critically reviewed, with the main focus on an extensive survey of the materials developed for ASC electrodes, as well as covering the progress made in the fabrication of ASC devices over the last few decades. Current challenges and a future outlook of the field of ASCs are also discussed.

Asymmetric Supercapacitor Electrodes and Devices.

Bio-integrated wearable systems can measure a broad range of biophysical, biochemical, and environmental signals to provide critical insights into overall health status and to quantify human performance. Recent advances in material science, chemical analysis techniques, device designs, and assembly methods form the foundations for a uniquely differentiated type of wearable technology, characterized by noninvasive, intimate integration with the soft, curved, time-dynamic surfaces of the body. This review summarizes the latest advances in this emerging field of “bio-integrated” technologies in a comprehensive manner that connects fundamental developments in chemistry, material science, and engineering with sensing technologies that have the potential for widespread deployment and societal benefit in human health care. An introduction to the chemistries and materials for the active components of these systems contextualizes essential design considerations for sensors and associated platforms that appear in f...

Bio-Integrated Wearable Systems: A Comprehensive Review

Over the past decade, electrochemical energy storage (EES) devices have greatly improved, as a wide variety of advanced electrode active materials and new device architectures have been developed. These new materials and devices should be evaluated against clear and rigorous metrics, primarily based on the evidence of real performances. A series of criteria are commonly used to characterize and report performance of EES systems in the literature. However, as advanced EES systems are becoming more and more sophisticated, the methodologies to reliably evaluate the performance of the electrode active materials and EES devices need to be refined to realize the true promise as well as the limitations of these fast-moving technologies, and target areas for further development. In the absence of a commonly accepted core group of metrics, inconsistencies may arise between the values attributed to the materials or devices and their real performances. Herein, we provide an overview of the energy storage devices from conventional capacitors to supercapacitors to hybrid systems and ultimately to batteries. The metrics for evaluation of energy storage systems are described, although the focus is kept on capacitive and hybrid energy storage systems. In addition, we discuss the challenges that still need to be addressed for establishing more sophisticated criteria for evaluating EES systems. We hope this effort will foster ongoing dialog and promote greater understanding of these metrics to develop an international protocol for accurate assessment of EES systems.

Towards establishing standard performance metrics for batteries, supercapacitors and beyond.

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have emerged as promising capacitive materials for supercapacitor devices owing to their intrinsically layered structure and large surface areas. Hierarchically integrating 2D TMDs with other functional nanomaterials has recently been pursued to improve electrochemical performances; however, it often suffers from limited cyclic stabilities and capacitance losses due to the poor structural integrity at the interfaces of randomly assembled materials. Here, we report high-performance core/shell nanowire supercapacitors based on an array of one-dimensional (1D) nanowires seamlessly integrated with conformal 2D TMD layers. The 1D and 2D supercapacitor components possess “one-body” geometry with atomically sharp and structurally robust core/shell interfaces, as they were spontaneously converted from identical metal current collectors via sequential oxidation/sulfurization. These hybrid supercapacitors outperform previously developed any stand-alone 2D...

High-Performance One-Body Core/Shell Nanowire Supercapacitor Enabled by Conformal Growth of Capacitive 2D WS2 Layers.

Flexible materials for harvesting and storing energy are desirable for wearable electronics, but efficiency is still an issue. Here, the authors demonstrate a flexible and weavable ribbon which integrates a solar cell and supercapacitor via a shared electrode for efficient energy harvesting and storage.

https://ro.uow.edu.au/cgi/viewcontent.cgi?article=3571&context=aiimpapers

Wearable energy-smart ribbons for synchronous energy harvest and storage.

We demonstrate the design and fabrication of a Ag/PEDOT:PSS/MnO2 layer by layer structure for high performance flexible supercapacitors (SCs). This is a unique design combining Ag-nanowires and PEDOT:PSS-nanopillars as current collectors in SCs. In this sandwich-like structure, electrons can be easily transferred through a networked structure of Ag-nanowires to PEDOT:PSS-nanopillars and finally to the MnO2 layer and vice versa. This scheme provides excellent specific capacitances of 862 F g−1 (based on MnO2) at a current density of 2.5 A g−1 and robust long-term cycling stability. Moreover, SCs fabricated based on this structure exhibit exceptional flexibility and bendability (less than 2% loss in specific capacitance even after 100 bends) and high energy and power densities. All wet processing methods of fabrication along with superior performance make these SCs very attractive for the next generation flexible energy storage systems.

Flexible, sandwich-like Ag-nanowire/PEDOT:PSS-nanopillar/MnO2 high performance supercapacitors

Developing highly efficient perovskite solar cells in a simple and rapid fashion will open the window for their potential commercialization. Semi-transparent devices are of great interest due to their attractive application in building integrated photovoltaics (BIPVs). In this study, efficient perovskite solar cells with good transparency in the visible wavelength range have been developed by a facile and low-temperature PCBM-assisted perovskite growth method. This method results in the formation of a perovskite-PCBM hybrid material at the grain boundaries which is observed by EELS mapping and confirmed by steady-state photoluminescence (PL) spectroscopy, transient photocurrent (TP) measurements and X-ray photoelectron spectroscopy (XPS). The PCBM-assisted perovskite growth method involves fewer steps and therefore is less expensive and time consuming than other similar methods. The semitransparent solar cells developed using this method exhibited power conversion efficiency (PCE) ranging from 12% to 4% depending on the average visible transmittance (AVT) ranging from 3% to 35%. The as-fabricated semitransparent perovskite solar cell with an active layer thickness of only about 150 nm, which is only less than half the active layer thickness of a typical perovskite solar cell, provided a PCE as high as 9.1% with an AVT of 18% and more than 12% with an AVT of 3%.

Chao Li

Papers

Asymmetric Supercapacitor Electrodes and Devices.

High-Performance One-Body Core/Shell Nanowire Supercapacitor Enabled by Conformal Growth of Capacitive 2D WS2 Layers.

Wearable energy-smart ribbons for synchronous energy harvest and storage.

Flexible, sandwich-like Ag-nanowire/PEDOT:PSS-nanopillar/MnO2 high performance supercapacitors

A PCBM-assisted perovskite growth process to fabricate high efficiency semitransparent solar cells