Technological improvements in rechargeable solid-state batteries are being driven by an ever-increasing demand for portable electronic devices. Lithium-ion batteries are the systems of choice, offering high energy density, flexible and lightweight design, and longer lifespan than comparable battery technologies. We present a brief historical review of the development of lithium-based rechargeable batteries, highlight ongoing research strategies, and discuss the challenges that remain regarding the synthesis, characterization, electrochemical performance and safety of these systems.

Issues and challenges facing rechargeable lithium batteries

The large-scale practical application of fuel cells will be difficult to realize if the expensive platinum-based electrocatalysts for oxygen reduction reactions (ORRs) cannot be replaced by other efficient, low-cost, and stable electrodes. Here, we report that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells. In air-saturated 0.1 molar potassium hydroxide, we observed a steady-state output potential of –80 millivolts and a current density of 4.1 milliamps per square centimeter at –0.22 volts, compared with –85 millivolts and 1.1 milliamps per square centimeter at –0.20 volts for a platinum-carbon electrode. The incorporation of electron-accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four-electron pathway for the ORR on VA-NCNTs with a superb performance.

http://science.sciencemag.org/content/sci/323/5915/760.full.pdf

Nitrogen-doped carbon nanotube arrays with high electrocatalytic activity for oxygen reduction.

Energy storage using batteries offers a solution to the intermittent nature of energy production from renewable sources; however, such technology must be sustainable. This Review discusses battery development from a sustainability perspective, considering the energy and environmental costs of state-of-the-art Li-ion batteries and the design of new systems beyond Li-ion. Images: batteries, car, globe: © iStock/Thinkstock.

Towards greener and more sustainable batteries for electrical energy storage

Fossil fuels currently supply most of the world's energy needs, and however unacceptable their long-term consequences, the supplies are likely to remain adequate for the next few generations. Scientists and policy makers must make use of this period of grace to assess alternative sources of energy and determine what is scientifically possible, environmentally acceptable and technologically promising.

Alternative energy technologies

A fundamental change has been achieved in understanding surface electrochemistry due to the profound knowledge of the nature of electrocatalytic processes accumulated over the past several decades and to the recent technological advances in spectroscopy and high resolution imaging. Nowadays one can preferably design electrocatalysts based on the deep theoretical knowledge of electronic structures, via computer-guided engineering of the surface and (electro)chemical properties of materials, followed by the synthesis of practical materials with high performance for specific reactions. This review provides insights into both theoretical and experimental electrochemistry toward a better understanding of a series of key clean energy conversion reactions including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The emphasis of this review is on the origin of the electrocatalytic activity of nanostructured catalysts toward the aforementioned reactions by correlating the apparent electrode performance with their intrinsic electrochemical properties. Also, a rational design of electrocatalysts is proposed starting from the most fundamental aspects of the electronic structure engineering to a more practical level of nanotechnological fabrication.

Design of electrocatalysts for oxygen- and hydrogen-involving energy conversion reactions

Thin film growth of gadolinia by metal-organic chemical vapour deposition (MOCVD)

Miniature oxygen pump-gauge. I. Leakage considerations

Evaluation of perovskite anodes for the complete oxidation of dry methane in solid oxide fuel cells

Neutron powder diffraction structure and electrical properties of the defect pyrochlores Pb1.5M2O6.5 (M = Nb, Ta)

Aluminum nitride (AlN) is currently under investigation as a potential candidate for replacing aluminum oxide (Al2O3) as a substrate material for electronic circuit packaging. The requirements for such a material are that it can be metallized and joined to produce hermetic enclosures for semiconductor devices. A technique for brazing AlN using a nonactive metal braze has been investigated. The process involves the in situ decomposition of an active metal hydride. This process improves the wetting of the AlN and led to the development of strong bonding between braze and ceramic. The ceramic-braze interface was studied using scanning electron microscopy (SEM). The nature of the interfacial reactions and the reaction products have been identified using x-ray diffraction (XRD). The progress of the reaction has been followed using differential thermal analysis (DTA). The experimental results have been correlated with thermodynamic predictions of the reaction processes. In addition to joining ceramic to ceramic, braze joints of AlN to copper and to a low expansion iron-nickel lead frame alloy were made. Residual stress resulting from a mismatch of thermal expansion coefficients between AlN and copper caused cracking in the ceramic upon cooldown from the brazing temperature. No cracking occurred in the ceramic when joined to the iron-nickel alloy. The results obtained are important for the realization of AlN as a ceramic packaging material for semiconductor devices.

Brian C.H. Steele

Papers

Thin film growth of gadolinia by metal-organic chemical vapour deposition (MOCVD)

Miniature oxygen pump-gauge. I. Leakage considerations

Evaluation of perovskite anodes for the complete oxidation of dry methane in solid oxide fuel cells

Neutron powder diffraction structure and electrical properties of the defect pyrochlores Pb1.5M2O6.5 (M = Nb, Ta)

Brazing of aluminum nitride substrates