National Nanomanufacturing Network

Researchers achieve 'holy grail' of battery design: A stable lithium anode

National Nanomanufacturing Network - July 30, 2014 - 3:31am
The development could lead to smaller, cheaper and more efficient rechargeable batteries. Engineers across the globe have been racing to design smaller, cheaper and more efficient rechargeable batteries to meet the power storage needs of everything from handheld gadgets to electric cars. In a paper (http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2014.152.html) published today in the journal Nature Nanotechnology, researchers at Stanford University report that they have taken a big step toward accomplishing what battery designers have been trying to do for decades – design a pure lithium anode. All batteries have three basic components: an electrolyte to provide electrons, an anode to discharge those electrons and a cathode to receive them. Today, we say we have lithium batteries, but that is only partly true. What we have are lithium ion batteries. The lithium is in the electrolyte but not in the anode. An anode of pure lithium would be a huge boost to battery efficiency. “Of all the materials that one might use in an anode, lithium has the greatest potential. Some call it the Holy Grail,” said Yi Cui (http://profiles.stanford.edu/yi-cui), a professor of Materials Science and Engineering (http://mse.stanford.edu/) and leader of the research team. “It is very lightweight, and it has the highest energy density. You get more power per volume and weight, leading to lighter, smaller batteries with more power.” But engineers have long tried and failed to reach this Holy Grail. “Lithium has major challenges that have made its use in anodes difficult. Many engineers had given up the search, but we found a way to protect the lithium from the problems that have plagued it for so long,” said Guangyuan Zheng, a doctoral candidate in Cui’s lab and first author of the paper. In addition to Cui and Zheng, the research team includes Steven Chu (http://physics.stanford.edu/people/faculty/steven-chu), the former U.S. Secretary of Energy and Nobel Laureate who recently resumed his professorship at Stanford. “In practical terms, if we can triple the energy density and simultaneously decrease the cost four-fold, that would be very exciting. We would have a cell phone with triple the battery life and an electric vehicle with a 300 mile range that cost $25,000 – and with better performance than an internal combustion engine car getting 40 mpg,” Chu said. The engineering challenge In the paper, the authors explain how they are overcoming the problems posed by lithium. Most lithium ion batteries, like those you might find in your smart phone or hybrid car, work similarly. The key components include an anode, the negative pole from which electrons flow out and into a power-hungry device, and the cathode, where the electrons re-enter the battery once they have traveled through the circuit. Separating them is an electrolyte, a solid or liquid loaded with positively charged lithium ions that travel between the anode and cathode. During charging, the positively charged lithium ions in the electrolyte are attracted to the negatively charged anode, and the lithium accumulates on the anode. Today, the anode in a lithium ion battery is actually made of graphite or silicon.Engineers would like to use lithium for the anode, but so far they have been unable to do so. That’s because the lithium ions expand as they gather on the anode during charging. All anode materials, including graphite and silicon, expand somewhat during charging, but not like lithium. Researchers say that lithium’s expansion during charging is “virtually infinite” relative to the other materials. Its expansion is also uneven, causing pits and cracks to form in the outer surface, like paint on the exterior of a balloon that is being inflated. The resulting fissures on the surface of the anode allow the precious lithium ions to escape, forming hair-like or mossy growths, called dendrites. Dendrites, in turn, short circuit the battery and shorten its life. Preventing this buildup is the first challenge of using lithium for the battery’s anode. The second engineering challenge involves finding a way to deal with the fact that lithium anodes are highly chemically reactive with the electrolyte. It uses up the electrolyte and reduces battery life. An additional problem is that the anode and electrolyte produce heat when they come into contact. Lithium batteries, including those in use today, can overheat to the point of fire, or even explosion. They are, therefore, a serious safety concern. The recent battery fires in Tesla cars and on Boeing’s Dreamliner are prominent examples of the challenges of lithium ion batteries. Building the nanospheres To solve these problems the Stanford researchers built a protective layer of interconnected carbon domes on top of their lithium anode. This layer is what the team has called nanospheres. The Stanford team’s nanosphere layer resembles a honeycomb: it creates a flexible, uniform and non-reactive film that protects the unstable lithium from the drawbacks that have made it such a challenge. The carbon nanosphere wall is just 20 nanometers thick. It would take about 5,000 layers stacked one atop another to equal the width of single human hair. “The ideal protective layer for a lithium metal anode needs to be chemically stable to protect against the chemical reactions with the electrolyte and mechanically strong to withstand the expansion of the lithium during charge,” said Cui, who is a member of the Stanford Institute for Materials and Energy Sciences at SLAC National Accelerator Laboratory. The Stanford nanosphere layer is just that. It is made of amorphous carbon, which is chemically stable, yet strong and flexible so as to move freely up and down with the lithium as it expands and contracts during the battery’s normal charge-discharge cycle. Ideal within reach In technical terms, the nanospheres improve the coulombic efficiency of the battery – a ratio of the amount of lithium that can be extracted from the anode when the battery is in use compared with the amount put in during charging. A single round of this give-and-take process is called a cycle. Generally, to be commercially viable, a battery must have a coulombic efficiency of 99.9 percent or more, ideally over as many cycles as possible. Previous anodes of unprotected lithium metal achieved approximately 96 percent efficiency, which dropped to less than 50 percent in just 100 cycles—not nearly good enough. The Stanford team’s new lithium metal anode achieves 99 percent efficiency even at 150 cycles. “The difference between 99 percent and 96 percent, in battery terms, is huge. So, while we’re not quite to that 99.9 percent threshold, where we need to be, we’re close. And this is a significant improvement over any previous design,” Cui said. “With some additional engineering and new electrolytes, we believe we can realize a practical and stable lithium metal anode that could power the next generation of rechargeable batteries.”Source: Stanford School of Engineering (https://engineering.stanford.edu/news/stanford-team-achieves-holy-grail-battery-design-stable-lithium-anode)Image reprinted with permission from Interconnected hollow carbon nanospheres for stable lithium metal anodes ; Guangyuan Zheng, Seok Woo Lee, Zheng Liang, Hyun-Wook Lee, Kai Yan, Hongbin Yao; Nature Nanotechnology 2014.

Progress Review on the Coordinated Implementation of the National Nanotechnology Initiative ...

National Nanomanufacturing Network - July 24, 2014 - 3:53am
The National Nanotechnology Coordination Office (NNCO), on behalf of the Nanoscale Science, Engineering, and Technology (NSET) Subcommittee of the Committee on Technology, National Science and Technology Council (NSTC), will hold a public webinar on Thursday, July 31, 2014 from 12 pm to 1 pm EDT. The purpose of this webinar is to provide a forum to answer questions related to the Federal Government's “Progress Review on the Coordinated Implementation of the National Nanotechnology Initiative (NNI) 2011 Environmental, Health, and Safety Research Strategy.” Discussion during the webinar will focus on the research activities undertaken by NNI agencies to advance the current state of the science as highlighted in the progress review. Representative research activities as provided in the Progress Review will be discussed in the context of the 2011 NNI EHS Research Strategy's six core research areas: Nanomaterial Measurement Infrastructure, Human Exposure Assessment, Human Health, the Environment, Risk Assessment and Risk Management Methods, and Informatics and Modeling. A moderator will identify relevant questions and pose them to the panel of NNI agency representatives during the live webinar. Due to time constraints, not all questions may be addressed. The moderator reserves the right to group similar questions and to skip questions, as appropriate. Please send your questions to webinar@nnco.nano.gov. (mailto:webinar@nnco.nano.gov%3cmailto:webinar@nnco.nano.gov) Details: Thursday, July 31, 2014, 12 pm – 1 pm EDTLog in information and event details at http://www.nano.gov/2014webinar (http://www.nano.gov/2014webinar).A public copy of the “Progress Review on the Coordinated Implementation of the National Nanotechnology Initiative 2011 Environmental, Health, and Safety Research Strategy” can be accessed at www.nano.gov/2014EHSProgressReview (http://www.nano.gov/2014EHSProgressReview). The 2011 NNI EHS Research Strategy can be accessed at www.nano.gov/node/681 (http://www.nano.gov/node/681).Source: Federal Register (https://www.federalregister.gov/articles/2014/07/22/2014-17189/national-nanotechnology-coordination-office)

Nano-sized silicon oxide electrode for the next generation lithium ion batteries

National Nanomanufacturing Network - July 17, 2014 - 3:15am
The lithium ion battery market has been growing steadily and has been seeking an approach to increase battery capacity while retaining its capacity for long recharging process. Structuring materials for electrode at the nanometre-length scale has been known to be an effective way to meet this demand; however, such nanomaterials would essentially need to be produced by high throughput processing in order to transfer these technologies to industry.This article published in the Science and Technology of Advanced Materials ("High throughput production of nanocomposite SiO x powders by plasma spray physical vapor deposition for negative electrode of lithium ion batteries" (http://dx.doi.org/doi:10.1088/1468-6996/15/2/025006)) reports an approach which potentially has an industrially compatible high throughputs to produce nano-sized composite silicon-based powders as a strong candidate for the negative electrode of the next generation high density lithium ion batteries. The authors have successfully produced nanocomposite SiO powders by plasma spray physical vapor deposition using low cost metallurgical grade powders at high throughputs. Using this method, they demonstrated an explicit improvement in the battery capacity cycle performance with these powders as electrode.The uniqueness of this processing method is that nanosized SiO composites are produced instantaneously through the evaporation and subsequent co-condensation of the powder feedstock. The approach is called plasma spray physical vapor deposition (PS-PVD). In Fig. 1, raw SiO and PS-PVD SiO composites are shown.The composites are 20 nm particles, which are composed of a crystalline Si core and SiOx shell. Furthermore, the addition of methane (CH4) promotes the reduction of SiO and results in the decreased SiO-shell thickness as shown in Fig. 2. The core-shell structure is formed in a single-step continuous processing.As a result, the irreversible capacity was effectively decreased, and half-cell batteries made of PS-PVD powders have exhibited improved initial efficiency and maintenance of capacity as high as 1000 mAhg-1 after 100 cycles at the same time.Source: National Institute for Materials Science

Carbodeon enables 20 percent increase in polymer thermal filler conductivity with 0.03 wt. ...

National Nanomanufacturing Network - July 9, 2014 - 6:58am
Vantaa, Finland – 9th July 2014: Carbodeon, a Finnish-based producer of functionalised nanodiamond materials, can now achieve a 20 percent increase in polymer thermal performance by using as little as 0.03 wt.% nanodiamond material at 45 percent thermal filler loading, enabling increased performance at a lower cost than with traditional fillers. Last October, Carbodeon published its data on thermal fillers showing that the conductivity of polyamide 66 (PA66) based thermal compound could be increased by 25 percent by replacing 0.1 wt.% of the typically maximum effective level of boron nitride filler (45 wt.%) with the company’s application fine-tuned nanodiamond material. The latest refinements in nanodiamond materials and compound manufacturing allow similar level performance improvements but with 70 percent less nanodiamond consumption and thus, greatly reduced cost. The samples were manufactured at the VTT Technical Research Centre in Finland and their thermal performance was analyzed by ESK (3M) in Germany. “The performance improvements achieved are derived from the extremely high thermal conductivity of diamond, our ability to optimise the nanodiamond filler affinity to applied polymers and other thermal fillers and finally, Carbodeon’s improvements in nanodiamond filler agglomeration control,” said Carbodeon CTO Vesa Myllymäki. “With the ability to control all these parameters, the nanotechnology key paradigm of ‘less gives more’ can truly be realised.” The active surface chemistry inherent in detonation-synthesised nanodiamonds has historically presented difficulties in utilising the potential benefits of the 4-6nm particles, making them prone to agglomeration. Carbodeon optimises this surface chemistry so that the particles are driven to disperse and to become consistently integrated throughout parent materials, especially polymers. The much-promised properties of diamond can thus be imparted to other materials with very low, and hence economic, concentrations. For more demanding requirements, conductivity increases of as much as 100 percent can be achieved using 1.5 percent nanodiamond materials at 20 percent thermal filler loadings. “This increase in thermal conductivity is achieved without affecting the electrical insulation or other mechanical properties of the material and with no or very low tool wear, making it an ideal choice for a wide range of electronics and LED applications,” said Vesa Myllymäki. “We know we have not yet uncovered all the benefits that Carbodeon nanodiamonds can deliver and continue our focused application development on both polymer thermal compounds, and on metal finishing and industrial polymer coatings,” Myllymäki added. “Recently we were granted a patent on nanodiamond-containing thermoplastic thermal composites and we see great future opportunities for these materials.” About Carbodeon Ltd Carbodeon supplies super hard materials for applications where toughness is at a premium. Its patented technologies offer superior opportunities to several fields of business. Its grades of Ultra-Dispersed Diamonds -– also known as NanoDiamonds – possess the desired properties fine-tuned for a growing number of dedicated applications. These grades are sold under the name uDiamond®. Similarly, the company’s Nicanite® graphitic carbon nitride can be converted to carbon nitride thin-film coatings with unique properties. http://www.carbodeon.com (http://www.carbodeon.com) Contact: Camille Closs +44 (0)20 8286 0654 Watch PR camille@watchpr.com (mailto:camille@watchpr.com)

Improved Method of Device Area Scale-up for SWNT/Silicon Hybrid Solar Cells Using Silver Nanowires

National Nanomanufacturing Network - July 2, 2014 - 5:57am
While research on silicon solar cells has progressed the development of all organic, inorganic, and hybrid materials systems to simultaneously address the diverse set of design criteria for optimal photovoltaic (PV) performance, incorporation of hybrid materials systems has proven to be an effective method to improve some of these issues. With crystalline silicon representing the standard for high efficiency in solar cell designs, cell cost and production capacity remain concerns for the growing emphasis on broad implementation of renewable energy strategies on a global basis, with solar PV being a leading competitor. With recent studies demonstrating that the approach incorporating p-type nano-Carbon with n-type silicon in a hybrid film approach provides excellent diode junction rectification properties, improved collection and transport efficiencies due to the enhanced conductivity of the nano-C film, and superior semiconductor barrier properties at the nano-C/silicon junction. While this has proven effective for small cell design of a few square millimeters, scaling the cell area has proven challenging due to the increase in sheet resistance (Rs) of the nano-C layer as area increases resulting in a reduction in cell efficiency. Recently, Li, et.al, from the Taylor group in the Chemical and Environmental Engineering Department at Yale University, reported on a approach to significantly improve the performance for scaling up cell area for hybrid single walled carbon nanotubes (SWNT)/Silicon solar cells. In this work, the authors utilized p-type SWNTs cast onto n-type silicon as a dense film approximately 15 nm in thickness. For small cell areas on the order of 1-2 mm2, cell performance was significantly improved in comparison to other hybrid approaches due to the low Rs of the SWNT film. For larger cell areas, the Rs increased substantially to kilo-ohm/square, resulting in decreased cell efficiency. While increasing the SWNT film thickness could potentially lower Rs, the trade-off would be a reduction in optical transparency for the film, which would still reduce cell efficiency during scale-up. Patterning of metal conductor traces over the SWNT film was considered as a means to reduce Rs, but the evaporation of metal over the SWNT film resulted in cell shorting as some of the metal penetrated the pores in the film to the silicon junction. Instead, a strategy of casting silver nanowires (AgNWs) from solution at medium densities was investigated as a means to lower Rs while maintaining reasonable optical transparency during cell area scale-up. Reported results showed that casting of the AgNW films over the SWNT film reduced Rs for the scaled cell structures, and that even with the slight increase in optical absorption with the additive bilayer film, the overall performance of the scaled cells was significantly improved in comparison to the SWNT/Silicon hybrid cell design. The cells exhibited improved fill-factors which were most predominant in enhancing the efficiency, even with slight reductions in open circuit voltage and short circuit current observed for the scaled cell areas. To further improve the optical absorption for the cell, the authors cast titania (TiO2) nanoparticles over the AgNW/SWNT surfaces to reduce reflection and increase forward scattering of incident solar radiation, resulting in a marginal improvement which was further increased via post process steps. This work has developed a solution-based approach to mitigate the total resistive power loss that typically hinders the area scale-up of hybrid nano-C/Si solar cells. A nearly twofold increase of photovoltaic efficiency is observed upon the coating of AgNWs onto SWNT/Si junctions, resulting from the significant reduction in the Rs enabled by the AgNW/SWNT bilayer. The SWNT thin film with high optical transparency and extremely small thickness also allows for the direct solution deposition of antireflective TiO2 nanoparticles. A final efficiency of >10% was realized in 49 mm2 cells, with implications for complete solution processed solar cell manufacturing and ultimately cell cost reduction. The work further illustrates the role and versatility that additive nanostructured films can contribute to performance improvements for cell area scale-up. References: Device Area Scale-Up and Improvement of SWNT/Si Solar Cells Using Silver Nanowires (http://onlinelibrary.wiley.com/doi/10.1002/aenm.201400186/pdf). Xiaokai Li, Yeonwoong Jung, Jin-Shun Huang, Tenghooi Goh, and André D. Taylor; Advanced Energy Materials 2014. DOI: 10.1002/aenm.201400186 (http://dx.doi.org/10.1002/aenm.201400186) Images reprinted with permission from John Wiley and Sons; Advanced Energy Materials; Device Area Scale-Up and Improvement of SWNT/Si Solar Cells Using Silver Nanowires; © 2014 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim; Xiaokai Li,Yeonwoong Jung,Jing-Shun Huang,Tenghooi Goh,André D. Taylor.