A research team led by Livermore scientist Brandon Wood and Rice University physicist Boris Yakobson has developed a theoretical model that predicts how carbon components will perform as electrodes in lithium-ion batteries. The team’s model could lead to advances in the storage capacity of lithium-ion batteries, thus extending their performance life for applications from cell phones to electric vehicles and aerospace technologies.
Several characteristics of lithium-ion battery performance—capacity, voltage, and energy density—are determined by the binding between lithium ions and the electrode material. Yet subtle changes in the structure, chemistry, and shape of an electrode can affect lithium-ion bond strength. The Livermore–Rice research, which appeared in the July 11, 2014, edition of Physical Review Letters, predicts that the strength of this binding is based on intrinsic characteristics of the carbon materials used as battery anodes.
In this study, the team investigated the interactions of lithium with carbon substrates including pristine, defective, and strained graphene; planar carbon clusters; nanotubes; carbon edges; and multilayer stacks. Wood and Rice University’s Yuanyue Liu looked for a “descriptor” that would capture the essential physics of interactions between lithium and the carbon materials. “Our descriptor predicts the performance of a variety of materials,” Wood says, “and finds combinations in which the underlying physics is similar, even if the materials’ structures, morphologies, or chemistries differ. Our model is a predictive tool that could accelerate design and discovery.” The model also provides guidelines for engineering more effective anodes by modifying the electronic and chemical properties of other candidate materials.
Contact: Brandon Wood (925) 422-8391 (wood37@llnl.gov).
Using the National Ignition Facility (NIF), the world’s most energetic laser, a collaboration involving Lawrence Livermore, the University of California at Berkeley, and Princeton University has experimentally re-created the conditions that exist inside giant planets such as Jupiter and Uranus. (Interior of the NIF target chamber is shown at right.) The team’s study, featured in the July 16, 2014, edition of Nature, focused on carbon, which has an important role in most planets. By re-creating these conditions in a laboratory setting, researchers can measure material properties that control how giant planets evolve over time, which is essential information for understanding how these planets form.
For this study, the team used 176 of NIF’s 192 lasers to produce a pressure wave that compressed a diamond sample under pressure more than 50 million times that of Earth’s atmosphere, which is comparable to the pressure at the center of Jupiter and Saturn. The sample vaporized in less than 10-billionths of a second. Although diamond (a form of carbon) is the least compressible material known, the researchers compressed it to a density greater than that of lead at ambient conditions.
Such pressures have been reached in experiments with shock waves, which create temperatures too high to be realistic for planetary interiors. To meet the technical challenge of keeping temperatures low enough to be relevant, the NIF team carefully tuned the rate at which laser intensity changes with time. “Having the ability to explore matter at atomic-scale pressures provides new constraints for dense matter theories and planetary evolution models,” says Livermore physicist and team member Rip Collins.
The data described in this work are among the first tests for predictions made in quantum mechanics more than 80 years ago. Although the NIF data and early theory agree, the team found important differences, suggesting unknown properties for diamond under extreme compression. Future experiments at NIF will focus on unlocking these mysteries.
Contact: Ray Smith (925) 423-5895 (smith248@llnl.gov).
An international team of researchers has discovered a potential new use for the Lawrence Livermore Microbial Detection Array (LLMDA)—providing a rapid surveillance approach to identify emerging viral diseases. In the team’s paper, published in the June 25, 2014, edition of PLOS ONE, the researchers note that emerging viruses are often difficult to diagnose because their symptoms are similar to those of more common viruses. Quickly identifying the correct virus is crucial for patient treatment and for containing a potential epidemic.
Developed in 2008, LLMDA detects microbes by using a checkerboard pattern of probes in the middle of a 2.5-centimeter-wide, 7.5-centimeter-long glass slide. The instrument occupies a niche role between the polymerase chain reaction (PCR) technique and DNA sequencing. One advantage of LLMDA is that it can perform thousands of tests in parallel within 24 hours. PCR, although a faster approach, can run only dozens of tests at a time. The research team, which included Livermore scientists Shea Gardner and Kevin McLoughlin, found that LLMDA is sensitive to a wide range of emerging viruses. In a study with both clinical and nonclinical samples, the array identified 29 emerging viruses, including Dengue fever and West Nile virus. The current version of LLMDA can identify 4,377 viruses and 5,457 bacteria as well as a combined total of 775 protozoa, fungi, and archaea species.
Emerging viruses are normally endemic to tropical and subtropical regions of the world, but increased global travel helps spread viruses into new regions. “With this study, we are closer to developing the technology so that public health laboratories can use it to screen samples for unexpected viruses in the population,” says McLoughlin.
Contact: Kevin McLoughlin (925) 423-5486 (mcloughlin2@llnl.gov).