What characteristics define a good rechargeable battery? Although properties such as rate capability, cost, cycle life and temperature tolerance must be taken into consideration in any evaluation of a rechargeable battery 1,2 , it is the improvement in energy density that has primarily driven the overall technological progress over the past 150 years -from lead-acid cells in the 1850s, nickelcadmium cells in the 1890s and nickel metal hydride cells in the 1960s to, finally, lithium-ion batteries (LIBs) in the present day.In the current era of LIBs, there is an ever-growing demand for even higher energy densities to power mobile IT devices with increased power consumption and to extend the driving range of electric vehicles. The growth of the global electric vehicle market has been slower than initially predicted about 5 years ago 3 , which reflects the challenge that the battery industry faces: customers react very sensitively to the driving range (and thus the energy density) and price of electric vehicles. Because the energy density of a rechargeable battery is determined mainly by the specific capacities and operating voltages of the anode and the cathode, active materials have been the main focus of research in recent years. Other cell components, including separators, binders, outer cases and, to some extent, the major components of the electrolyte solution (that is, solvent and salt), have little room for further improvement. In other words, a dramatic increase in the energy density requires new redox chemistries between charge-carrier ions and host materials beyond the conventional 'intercalation' mechanisms 4 . Intercalationbased materials have a relatively small number of crystallographic sites for storing charge-carrier ions, leading to limited energy densities. For this reason, the electrodes that operate on the basis of distinct solid-state reactions, such as alloying and conversion, or that use gas-phase reactants have encountered growing interest owing to the likelihood that they will surpass the energy densities of intercalation-based electrodes.New chemistries for charge-carrier ion storage serve as the basis for 'beyond intercalation' or so-called postLIBs 5-7 . The systems governed by these new chemistries offer higher theoretical energy densities, and this benefit is usually translated to, at least, the initial cycles in experimental testing. It is becoming increasingly evident that the short lifetime is a serious problem of post-LIB systems. Indeed, the main technological challenge associated with these systems is overcoming their inferior reversibility. The main factors responsible for the low reversibility are instabilities during the phase transition of active materials and/or uncontrolled reactions at the electrode/electrolyte interface 8 ; this implies that the electrode structures and electrolyte solutions should be developed and optimized as integrated systems to enable the realization of post-LIBs.In this Review, we discuss a wide range of promising post-LIBs, focusing on their advant...

Although the performance of lithium ion-batteries continues to improve, their energy density and cycle life remain insufficient for applications in consumer electronics, transport and large-scale renewable energy storage. Silicon has a large charge storage capacity and this makes it an attractive anode material, but pulverization during cycling and an unstable solid-electrolyte interphase has limited the cycle life of silicon anodes to hundreds of cycles. Here, we show that anodes consisting of an active silicon nanotube surrounded by an ion-permeable silicon oxide shell can cycle over 6,000 times in half cells while retaining more than 85% of their initial capacity. The outer surface of the silicon nanotube is prevented from expansion by the oxide shell, and the expanding inner surface is not exposed to the electrolyte, resulting in a stable solid-electrolyte interphase. Batteries containing these double-walled silicon nanotube anodes exhibit charge capacities approximately eight times larger than conventional carbon anodes and charging rates of up to 20C (a rate of 1C corresponds to complete charge or discharge in one hour).

Recently there is strong interest in lightweight, flexible, and wearable electronics to meet the technological demands of modern society. Integrated energy storage devices of this type are a key area that is still significantly underdeveloped. Here, we describe wearable power devices using everyday textiles as the platform. With an extremely simple "dipping and drying" process using single-walled carbon nanotube (SWNT) ink, we produced highly conductive textiles with conductivity of 125 S cm(-1) and sheet resistance less than 1 Omega/sq. Such conductive textiles show outstanding flexibility and stretchability and demonstrate strong adhesion between the SWNTs and the textiles of interest. Supercapacitors made from these conductive textiles show high areal capacitance, up to 0.48F/cm(2), and high specific energy. We demonstrate the loading of pseudocapacitor materials into these conductive textiles that leads to a 24-fold increase of the areal capacitance of the device. These highly conductive textiles can provide new design opportunities for wearable electronics and energy storage applications.

A bottom-up approach was the key to the successful fabrication of this memory. This approach both minimized the number of processing steps following deposition of the molecular monolayer, as well as protected the molecules from remaining processing steps. In the following paragraphs, we briefly describe the nanofabrication procedures utilized to construct the memory circuit. A full paper describing these procedures in more detail will be submitted for publication in the near future. form an array of top Ti NW electrodes, and the crossbar structure is complete.