Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Ongoing technological advances in diverse fields including portable electronics, transportation, and green energy are often hindered by the insufficient capability of energy-storage devices By taking advantage of two different electrode materials, asymmetric supercapacitors can extend their operating voltage window beyond the thermodynamic decomposition voltage of electrolytes while enabling a solution to the energy storage limitations of symmetric supercapacitors This review provides comprehensive knowledge to this field We first look at the essential energy-storage mechanisms and performance evaluation criteria for asymmetric supercapacitors to understand the wide-ranging research conducted in this area Then we move to the recent progress made for the design and fabrication of electrode materials and the overall structure of asymmetric supercapacitors in different categories We also highlight several key scientific challenges and present our perspectives on enhancing the electrochemical performance of future asymmetric supercapacitors

Design and Mechanisms of Asymmetric Supercapacitors.

Flexible solid-state supercapacitors (FSSCs) are frontrunners in energy storage device technology and have attracted extensive attention owing to recent significant breakthroughs in modern wearable electronics In this study, we review the state-of-the-art advancements in FSSCs to provide new insights on mechanisms, emerging electrode materials, flexible gel electrolytes and novel cell designs The review begins with a brief introduction on the fundamental understanding of charge storage mechanisms based on the structural properties of electrode materials The next sections briefly summarise the latest progress in flexible electrodes (ie, freestanding and substrate-supported, including textile, paper, metal foil/wire and polymer-based substrates) and flexible gel electrolytes (ie, aqueous, organic, ionic liquids and redox-active gels) Subsequently, a comprehensive summary of FSSC cell designs introduces some emerging electrode materials, including MXenes, metal nitrides, metal–organic frameworks (MOFs), polyoxometalates (POMs) and black phosphorus Some potential practical applications, such as the development of piezoelectric, photo-, shape-memory, self-healing, electrochromic and integrated sensor-supercapacitors are also discussed The final section highlights current challenges and future perspectives on research in this thriving field

Towards flexible solid-state supercapacitors for smart and wearable electronics

Recent advancements in supercapacitor technology

Supercapacitors have gained a lot of attention due to their unique features like high power, long cycle life and environment-friendly nature. They act as a link for energy-power difference between a traditional capacitor (having high power) and fuel cells/batteries (having high energy storage). In this perspective, a worldwide research has been reported to address this and rapid progress has been achieved in the advancement of fundamental as well as the applied aspects of supercapacitors. Here, a concise description of technologies and working principles of different materials utilized for supercapacitors has been provided. The main focus has been on materials like carbon-based nanomaterials, metal oxides, conducting polymers and their nanocomposites along with some novel materials like metal-organic frameworks, MXenes, metal nitrides, covalent organic frameworks and black phosphorus. The performance of nanocomposites has been analysed by parameters like energy, capacitance, power, cyclic performance and rate capability. Some of the latest supercapacitors such as electrochromic supercapacitor, battery-supercapacitor hybrid device, electrochemical flow capacitor, alternating current line filtering capacitor, micro-supercapacitor, photo-supercapacitor, thermally chargeable supercapacitor, self-healing supercapacitor, piezoelectric and shape memory supercapacitor have also been discussed. This review covers the up-to-date progress achieved in novel materials for supercapacitor electrodes. The latest fabricated symmetric/asymmetric supercapacitors have also been reported.

Review of supercapacitors: Materials and devices

Notably, many significant breakthroughs for a new generation of supercapacitors have been reported in recent years, related to theoretical understanding, material synthesis and device designs. Herein, we summarize the state-of-the-art progress toward mechanisms, new materials, and novel device designs for supercapacitors. Firstly, fundamental understanding of the mechanism is mainly focused on the relationship between the structural properties of electrode materials and their electrochemical performances based on some in situ characterization techniques and simulations. Secondly, some emerging electrode materials are discussed, including metal–organic frameworks (MOFs), covalent organic frameworks (COFs), MXenes, metal nitrides, black phosphorus, LaMnO3, and RbAg4I5/graphite. Thirdly, the device innovations for the next generation of supercapacitors are provided successively, mainly emphasizing flow supercapacitors, alternating current (AC) line-filtering supercapacitors, redox electrolyte enhanced supercapacitors, metal ion hybrid supercapacitors, micro-supercapacitors (fiber, plane and three-dimensional) and multifunctional supercapacitors including electrochromic supercapacitors, self-healing supercapacitors, piezoelectric supercapacitors, shape-memory supercapacitors, thermal self-protective supercapacitors, thermal self-charging supercapacitors, and photo self-charging supercapacitors. Finally, the future developments and key technical challenges are highlighted regarding further research in this thriving field.

Latest advances in supercapacitors: from new electrode materials to novel device designs.

Ion exchange membranes play a crucial role in flow batteries. Such batteries comprise an electrochemical cell in which oxidation and reduction processes can store and release electrons during charge and discharge operations. The electrical energy is stored in a liquid in large reservoirs. Vanadium redox flow batteries are considered here in particular. This chapter reviews (a) principles of electrochemical energy storage and (b) the properties of polymeric and hybrid membrane materials that are suitable for redox flow batteries.

https://www.degruyter.com/downloadpdf/j/pac.2014.86.issue-5/pac-2014-0101/pac-2014-0101.xml

Ion exchange membranes for vanadium redox flow batteries

Anode materials with high capacity for aqueous rechargeable lithium batteries (ARLBs) are very rarely reported. Here we found that a dual core–shell structured MWCNTs@S@PPy nanocomposite prepared by us shows excellent electrochemical performance. Its initial discharge capacity in a saturated LiAc aqueous electrolyte is very high, which is up to 481 mA h g−1 based on the weight of the composite and 879 mA h g−1 based on the sulfur content. It shows excellent rate capability. When nanotube LiMn2O4 is used as a cathode, the assembled ARLB can deliver an energy density of 110 Wh kg−1 based on two electrodes and show excellent cycling. These results show great promise for the practical application of ARLBs.

A high-capacity dual core–shell structured MWCNTs@S@PPy nanocomposite anode for advanced aqueous rechargeable lithium batteries

In this paper, a flow frame with multi-distribution channels is designed. The electrolyte flow distribution in the graphite felt electrode is simulated to be uniform at some degree with the tool of a commercial computational fluid dynamics (CFD) package of Star-CCM+. A 5 kW-class vanadium redox flow battery (VRB) stack composed of 40 single cells is assembled. The electrochemical performance of the VRB stack is investigated. Under the applied current density of 60 mA cm−2 during the charge and discharge processes, the current and energy efficiencies are delivered to be 93.9 and 80.8 %, respectively. A higher average output power of 7.2 kW can be achieved at the current density of 80 mA cm−2 with a lower energy efficiency of 78.4 %. The studies of kW-class VRB stack can be beneficial to the development of large-scale energy storage.

Electrochemical performance of 5 kW all-vanadium redox flow battery stack with a flow frame of multi-distribution channels

The invention relates to a preparation method of an electrode material and an electrode material prepared by the method. The method comprises the following steps: soaking a carbon electrode into a fluorine-containing salt solution, performing high-temperature activation, pickling, deionized water washing, drying and the like, thereby obtaining the electrode material. Compared with a non-treated electrode material, the electrode material disclosed by the invention has lots of defective active sites on the surface, the adsorption capacity of vanadium ions is greatly enhanced, and migration of the vanadium ion to the electrode surface is promoted; meanwhile, more reactive active sites are provided, the charge transfer rate of the electrode/electrolyte is improved, and energy loss and voltageloss of the vanadium cell in the charging and discharging process are reduced, so that the energy efficiency and voltage efficiency of an all-vanadium redox flow battery in the charging and discharging process are improved.

Qingming Zhou

Papers

Latest advances in supercapacitors: from new electrode materials to novel device designs.

Ion exchange membranes for vanadium redox flow batteries

A high-capacity dual core–shell structured MWCNTs@S@PPy nanocomposite anode for advanced aqueous rechargeable lithium batteries

Electrochemical performance of 5 kW all-vanadium redox flow battery stack with a flow frame of multi-distribution channels

Preparation method of multifunctional electrode material for fluorine-containing salt modified vanadium cell