The full potential of wireless devices remains unattainable due to limitations in battery performance. It is the thesis of the guest editors and contributing authors of this issue of MRS Bulletin that there is much room for improvement, that we are still far from the practical limits of the technology, and that materials research has the capability to pave the way for a new generation of rechargeable batteries that will offer a dramatic improvement in power delivery over anything available today. The basics of battery operation, including the relevant electrochemistry, are reviewed, unsolved problems are enumerated, and prospective solutions are indicated.

Recent developments in polymer electrolyte materials for lithium batteries are reviewed in this article. Four general classifications are recognized: (1) solvent-containing systems in which a liquid electrolyte solution either is fully miscible with a single-phase swollen polymer matrix (gel) or is a two-phase system in which “free” liquid occupies micropores within a swollen polymer network (hybrid), and conductivity (≥∼1 mS cm-1 at ambient temperature) is essentially independent of the polymer segmental motion (the thermal motion of segments of atoms along the backbone of a flexible polymer chain); (2) solvent-free, ion-coupled systems (typically polyether–Li salt complexes) in which both anions and cations are mobile within an amorphous, rubbery phase (conductivity ≤0.1 mS cm-1 at ambient temperature); (3) “single-ion” systems with anions fixed to the polymer backbone or systems with anion mobilities reduced by incorporation within larger molecules or by associations with the chain (conductivity ∼10-5 Scm-1 at ambient temperature); and (4) decoupled systems in which ionic mobility through channeled structures involves minimal local segmental displacements (conductivity 0.1–1 mS cm-1 at ambient temperature).

Template synthesis is a versatile nanomaterial fabrication method used to make monodisperse nanoparticles of a variety of materials including metals, semiconductors, carbons, and polymers. We have used the template method to prepare nanostructured lithium-ion battery electrodes in which nanofibers or nanotubes of the electrode material protrude from an underlying current-collector surface like the bristles of a brush. Nanostructured electrodes of this type composed of carbon, LiMn2O4, V2O5, tin, TiO2, and TiS2 have been prepared. In all cases, the nanostructured electrode showed dramatically improved rate capabilities relative to thin-film control electrodes composed of the same material. The rate capabilities are improved because the distance that Li+ must diffuse in the solid state (the current- and power-limiting step in Li-ion battery electrodes) is significantly smaller in the nanostructured electrode. For example, in a nanofiber-based electrode, the distance that Li+ must diffuse is restricted to the radius of the fiber, which may be as small as 50 nm. Recent developments in template-prepared nanostructured electrodes are reviewed.

Compared with LiCoO2, the dominant cathode material in today's lithium batteries, lithium nickel oxide derivatives [Li(Ni, M)O2, where M – Co, Fe, Al, Mg] offer a higher specific energy at a lower cost. The synthesis and structure of these materials are described. The electrochemical performances of the pure nickel compound and a number of multicomponent systems are assessed. The goals of these fundamental studies are to optimize the synthesis conditions and material composition to achieve good electrochemical reversibility, decrease capacity loss upon cycling, and enhance thermal stability in the deintercalated state in order to improve cell safety.

Solid-state nuclear magnetic resonance (NMR) spectroscopy has been employed to characterize a variety of phenomena that are central to the functioning of lithium and lithium-ion batteries. These include Li insertion and de-insertion mechanisms in carbonaceous and other anode materials and in transition-metal oxide cathodes, and ion-transport mechanisms in polymer and gel electrolytes. Investigations carried out over the last several years by the authors and other groups are reviewed in this article. Results for lithium manganese oxide spinel cathodes, carbon-based and SnO anodes, and polymer and gel electrolytes are discussed.

Computational modeling is playing an increasingly important role in materials research and design. At the system level, the impact of cell design, electrode thickness, electrode morphology, new packaging techniques, and numerous other factors on battery performance can be predicted with battery simulators based on complex electrochemical transport equations. Such simulation tools have allowed the battery industry to optimize the power and energy density that can be achieved with a given set of electrode and electrolyte materials. At the materials level, first-principles calculations, which can be used to predict properties of previously unknown materials ab initio, have now made it possible to design materials for higher capacity and better stability. The state of the art in computational modeling of rechargeable batteries is reviewed.

Lithium batteries have been successfully used in implantable biomedical devices for the last 30 years, and in some cases the use of lithium power sources has significantly contributed to the viability of the device. These battery systems fall into two major categories: primary, or single-use, cells containing lithium-metal anodes; and secondary, or rechargeable, systems utilizing lithium-ion chemistry. Primary lithium batteries have been used for implantable devices such as cardiac pacemakers, drug pumps, neurostimulators, and cardiac defibrillators. Rechargeable batteries have been used with left ventricular assist devices and total artificial hearts. All of these cells share the characteristics of high safety, reliability, energy density, and predictability of performance. Additionally, state-of-charge indication and low self-discharge are important features, along with charging safety and high cycle life for rechargeable cells.

The key to market success for electric vehicles (EVs) has always been the energy-storage device, which limits driving range and vehicle acceleration. In many respects, rechargeable lithium batteries are the most attractive technology for storing energy and delivering it on demand in an automobile. Past and ongoing efforts to develop electric-based automotive propulsion systems are chronicled in this article.

In 1994, the U.S. National Science Foundation (NSF) established Materials Research Science and Engineering Centers (MRSECs). The goal was to provide support for interdisciplinary materials research and education of the highest quality while addressing fundamental problems in science and engineering that are important to society. The centers are expected to undertake materials research of a scope and complexity that would not be feasible under traditional funding for individual research projects or small groups. Centers are funded for a limited period of time—currently five years—after which they can re-compete against new proposals. In 1994, MRSECs were established at 11 universities throughout the country. Two years later, 13 new centers were established in a second round of funding. Additional competitions were completed in 1998, 2000, and 2002. As of April 2002, there were 29 MRSECs.