There is strong recent interest in ultrathin, flexible, safe energy storage devices to meet the various design and power needs of modern gadgets. To build such fully flexible and robust electrochemical devices, multiple components with specific electrochemical and interfacial properties need to be integrated into single units. Here we show that these basic components, the electrode, separator, and electrolyte, can all be integrated into single contiguous nanocomposite units that can serve as building blocks for a variety of thin mechanically flexible energy storage devices. Nanoporous cellulose paper embedded with aligned carbon nanotube electrode and electrolyte constitutes the basic unit. The units are used to build various flexible supercapacitor, battery, hybrid, and dual-storage battery-in-supercapacitor devices. The thin freestanding nanocomposite paper devices offer complete mechanical flexibility during operation. The supercapacitors operate with electrolytes including aqueous solvents, room temperature ionic liquids, and bioelectrolytes and over record temperature ranges. These easy-to-assemble integrated nanocomposite energy-storage systems could provide unprecedented design ingenuity for a variety of devices operating over a wide range of temperature and environmental conditions. batteries ͉ carbon nanotubes ͉ supercapacitor T here has been recent interest in flexible safe energy devices, based on supercapacitors and batteries, to meet the various requirements of modern gadgets (1-3). Electrochemical energy can be stored in two fundamentally different ways. In a battery, the charge storage is achieved by electron transfer that produces a redox reaction in the electroactive materials (3). In an electric double-layer capacitor, namely the supercapacitor, the chargestorage process is nonFaradic, that is, ideally no electron transfer takes place across the electrode interface, and the storage of electric charge and energy is electrostatic. Because the charging and discharging of such supercapacitors involve no chemical phase and composition changes, such capacitors have a high degree of cyclability. However, in certain supercapacitors based on pseudocapacitance, the essential process can be Faradic, similar to that in a battery. However, an essential fundamental difference from battery behavior arises because, in such systems, the chemical and associated electrode potentials are a continuous function of degree of charge, unlike the thermodynamic behavior of single-phase battery reactants (3). Now, with the demand for efficient power devices to meet the high-power and -energy applications, there seems to be the possibility of an ideal compromise, which combines some of the storage capabilities of batteries and some of the power-discharge characteristics of capacitors in devices capable of storing useful quantities of electricity that can be discharged very quickly. We address here this need to develop new integrated hybrid devices with adaptability in various thin-film as well as bulk applications by using...

Coaxial manganese oxide/carbon nanotube (CNT) arrays deposited inside porous alumina templates were used as cathodes in a lithium battery. Excellent cyclic stability and capacity of MnO2/CNT coaxial nanotube electrodes resulted from the hybrid nature of the electrodes with improved electronic conductivity and dual mechanism of lithium storage. The reversible capacity of the battery was increased by an order compared to template grown MnO2 nanotubes, making them suitable electrodes for advanced Li ion batteries.

We report the synthesis of heterodimensional nanostructures of MoS2 quantum dots interspersed in few-layered sheets of MoS2, using a liquid exfoliation technique in organic solvents. This unique hybrid morphology results from the optimized experimental conditions involving bath sonication followed by ultrasound probe sonication. We show that such heterodimensional hybrid materials could easily be extracted from the solvent as precipitates when post-treated with less polar volatile solvents such as chloroform. Such tailored MoS2 nanostructures, when directly used as electrodes for hydrogen evolution reaction, showed excellent electrocatalytic activity with low overpotential. Hence, we believe this could lead to large-scale synthesis of liquid-exfoliated layered nanostructures for their potential applications.

There are several advantages of growing carbon nanotubes (CNTs) directly on bulk metals, for example in the formation of robust CNT-metal contacts during growth. Usually, aligned CNTs are grown either by using thin catalyst layers predeposited on substrates or through vapour-phase catalyst delivery. The latter method, although flexible, is unsuitable for growing CNTs directly on metallic substrates. Here we report on the growth of aligned multiwalled CNTs on a metallic alloy, Inconel 600 (Inconel), using vapour-phase catalyst delivery. The CNTs are well anchored to the substrate and show excellent electrical contact with it. These CNT-metal structures were then used to fabricate double-layer capacitors and field-emitter devices, which demonstrated improved performance over previously designed CNT structures. Inconel coatings can also be used to grow CNTs on other metallic substrates. This finding overcomes the substrate limitation for nanotube growth which should assist the development of future CNT-related technologies.

Materials engineering plays a key role in the field of energy storage. In particular, engineering materials at the nanoscale offers unique properties resulting in high performance electrodes and electrolytes in various energy storage devices. Consequently, considerable efforts have been made in recent years to fulfill the future requirements of electrochemical energy storage using these advanced materials. Various multi‐functional hybrid nanostructured materials are currently being studied to improve energy and power densities of next generation storage devices. This review describes some of the recent progress in the synthesis of different types of hybrid nanostructures using template assisted and non‐template based methods. The potential applications and recent research efforts to utilize these hybrid nanostructures to enhance the electrochemical energy storage properties of Li‐ion battery and supercapacitor are discussed. This review also briefly outlines some of the recent progress and new approaches being explored in the techniques of fabrication of 3D battery structures using hybrid nanoarchitectures.