Climate change, diminishing reserves of fossil fuels, energy security, and consumer demand all depend on alternatives to our current course of energy usage and consumption. A broad consensus concurs that implementing energy efficiency and renewable energy technologies are necessities now rather than luxuries to be deferred to some distant future. Neither effort can effect serious change in our energy patterns without marked improvements in electrical energy storage, with electrochemical energy storage in batteries and electrochemical capacitors serving as key components of any plausible scenario.1,2 Consumer expectations of convenience and long-lived portable power further drive the need to push these old devices onto a new performance curve. This issue of MRS Bulletin addresses the significant advances occurring in research laboratories around the world as old electrode materials and designs are re-envisioned, and abandoned materials of the past are reinvigorated by arranging matter and function on the nanoscale to bring batteries and electrochemical capacitors into the 21st century.

High-energy cathode materials with high working potential and/or high specific capacity are desired for future electrification of vehicles. In this article, we provide a general overview of advanced high-energy cathode materials using different approaches such as core-shell, concentration-gradient materials, and the effects of nanocoatings at the particle level to improve both electrochemical performance and safety. We also summarize the methods used to prepare these materials. Special attention is placed on the co-precipitation process for making dense, spherical particles for the purpose of improving the powder packing density and increasing the electrode energy density.

Reducing our dependence on fossil fuels increases the demand for energy storage. Lithium-ion batteries have transformed portable electronics and will continue to be important but cannot deliver the step change in energy density required in the longer term in markets such as electric vehicles and the storage of electricity from renewables. There are a few alternatives. Here we describe two: Li-air and Li-sulfur batteries. We compare the energy densities of Li-ion, Li-air, and Li-S and discuss their differences and the challenges facing Li-air and Li-S, many of which are materials related.

Ongoing technological advances in such disparate areas as consumer electronics, transportation, and energy generation and distribution are often hindered by the capabilities of current energy storage/conversion systems, thereby driving the search for high-performance power sources that are also economically viable, safe to operate, and have limited environmental impact. Electrochemical capacitors (ECs) are a class of energy-storage devices that fill the gap between the high specific energy of batteries and the high specific power of conventional electrostatic capacitors. The most widely available commercial EC, based on a symmetric configuration of two high-surface-area carbon electrodes and a nonaqueous electrolyte, delivers specific energies of up to ∼6 Whkg–1 with sub-second response times. Specific energy can be enhanced by moving to asymmetric configurations and selecting electrode materials (e.g., transition metal oxides) that store charge via rapid and reversible faradaic reactions. Asymmetric EC designs also circumvent the main limitation of aqueous electrolytes by extending their operating voltage window beyond the thermodynamic 1.2 V limit to operating voltages approaching ∼2 V, resulting in high-performance ECs that will satisfy the challenging power and energy demands of emerging technologies and in a more economically and environmentally friendly form than conventional symmetric ECs and batteries.

Three-dimensional (3D) battery architectures have emerged as a new direction for powering microelectromechanical systems and other small autonomous devices. Although there are few examples to date of fully functioning 3D batteries, these power sources have the potential to achieve high power density and high energy density in a small footprint. This overview highlights the various architectures proposed for 3D batteries, the advances made in the fabrication of components designed for these devices, and the remaining technical challenges. Efforts directed at establishing design rules for 3D architectures and modeling are providing insight concerning the energy density and current uniformity achievable with these architectures. The significant progress made on the fabrication of electrodes and electrolytes designed for 3D batteries is an indication that a number of these battery architectures will be successfully demonstrated within the next few years.

With exceptional carrier mobilities, mechanical strength, and optical transparency, graphene is a leading material for next-generation electronic devices. However, for most applications, graphene will need to be integrated with other materials, which motivates efforts to understand and tune its surface chemistry. In particular, the modification of graphene via organic functionalization holds promise for tuning the electronic properties of graphene, controlling interfaces with other materials, and tailoring surface chemical reactivity. Toward these ends, this article reviews recent work from our laboratory on noncovalent and covalent organic functionalization of graphene. Using ultrahigh vacuum scanning tunneling microscopy (UHV STM), the molecular ordering and electronic properties of organic adlayers on graphene are characterized at the molecular scale. In addition, UHV STM is employed to nanopattern these organic layers with sub-5 nm resolution, thus providing a pathway for producing graphene-based heteromolecular nanostructures.