Welcome to Boston, America’s college town! With over 150,000 college students, almost 25% of the city is still attending and learning at some of the best universities in the world. Join us tonight at the student mixer to meet and connect with your peers from around the globe! (Food and drink provided).
Student Mixer
Monday, November 30
7:30–8:30 p.m.
Sheraton Boston Hotel, 3rd Floor, Commonwealth
Yi Cui, Stanford University
Nanomaterials Design for Energy and Environment
Written by Ashley A. White
Sustainable energy generation, efficiency, and environmental protection are the defining goals for the research of Yi Cui, who is celebrating his 10th year as a professor at Stanford University. His tools for simultaneously meeting these aims are nanomaterials.
Cui began his talk with an overview of progress in nanomaterial-based solutions to energy and environmental problems. Over the last 30 years, scientists have developed a wide range of nano- and microscale structures, and now have the ability to control size, shape, and pore distribution, composition, chemical function, heterostructure, assembly, and an array of properties. Cui cited these achievements as the foundations for tackling energy and environmental challenges—a toolkit which he uses and has developed further, looking first to the technology to identify a critical capability gap, then determining whether a materials solution can address it.
Cui focused his talk on his advancements in high-energy batteries through nanomaterial design. Next-generation batteries will need high energy density, long cycle and calendar life, good safety, fast charging rates, and low cost. For Cui, high energy density is the most critical parameter, as it can serve as a gateway to addressing the other aspects.
When Cui began his work in batteries, he determined that a fundamental paradigm shift in battery material design was needed to significantly increase energy density, and he believed the answer lay in silicon. Silicon anodes offer 11 times the specific capacity of the graphite used today, but taking advantage of that capacity means accommodating a 400% volume change as the battery charges and discharges. To successfully use silicon, he would need to understand the mechanisms of volume expansion, avoid fracturing the electrode crystal, build a stable solid-electrolyte interphase (SEI), and enable stability at the whole electrode level. Cui walked the audience through what he called the 10 generations of silicon anode design that have addressed those challenges and defined his research for nearly a decade.
Cui’s earliest approaches focused on growing silicon nanowires, which allowed electrons to travel efficiently and prevented fracturing due to the small diameter of the wires, which enable easy strain relaxation. He also used the nanowires to study the anisotropic expansion properties of crystalline silicon. Generation-four approaches employed a double-walled hollow structure composed of a silicon nanotube surrounded by an ion-permeable silicon oxide shell to improve the stability of the SEI and minimize degradation of the mechanical integrity of the silicon electrode as it expands and contracts through repeated cycling. Cui’s research showed that this structure could survive over 6,000 charge-discharge cycles while retaining 85% of its initial capacity.
Generation-eight earned Cui and his colleagues a Nature Nanotechnology cover in 2014 for what he calls “pomegranate-like” anode structures. These architectures are composed of single silicon nanoparticles encapsulated by a conductive carbon layer that leaves enough room to accommodate volume changes. An ensemble of the coated nanoparticles is then blanketed by a thicker carbon layer that acts as an electrolyte barrier, resulting in a stable SEI and superior cyclability.
One of the most interesting aspects of Cui’s talk was his work on sourcing silicon. Oftentimes materials scientists focus on optimizing devices for performance, leaving aspects like material sourcing and cost to someone else to sort out. Cui, however, has investigated low cost, renewable sources for the silicon needed for his batteries, looking to rice husks and the 500,000 kilograms per year of discarded crab shells, which also offer a natural template for nanochannel arrays. In 2008, Cui founded a company called Amprius to commercialize his silicon anode technology, and he currently has technologies in production that are based on his first- and second-generation approaches.
Although Cui has focused his efforts on silicon thus far, he is already looking beyond silicon to other battery materials, including lithium metal anodes—the so-called “holy grail” of anode design, sulfur cathodes, and black phosphorus cathodes, and he has developed nanomaterials for other applications, including a transparent air filter that can trap more than 10 times its own weigh in particulate matter.
MRS TV sits down with the 2015 MRS Fall Meeting Chairs, Larry Nagahara and Louisa Torsi to discuss the technical symposia this year and some of the new trends they’re seeing at the meeting.
Over a very quick lunch and after a rigorous first morning of the Fall meeting, I am reminded how heavy the intellectual atmosphere becomes at such events. Immediately, feelings of motivation and inspiration from listening to this morning's technical sessions have taken root and will continue to persist for the remainder of the week. What is your favorite part of participating in MRS Meetings?
(Reflections on the lunchtime lecture by Arumugam Manthiram)
To move forward to a world that is completely run by renewable sources we face many challenges. The first obvious hurdle is to create electricity in the first place by a method that is as cheap as by using the more traditional fuels of coal, gas, and oil. The less obvious, but perhaps more immediately applicable challenge is to create an inexpensive way to store large amounts of energy.
In developing a storage method the challenge of providing power when the renewable source is not operating, such as when the sun is not shining or when the wind is not blowing, is overcome. The less obvious benefit and need is the ability to produce power producing facilities that only need to meet the average daily amount of power consumed, instead of the peak.
This means energy storage is of great value even now before the dropping price of renewable energy sources lead to their general adoption. By coupling energy storage with current plants, over-sized equipment or peaking plants will not have to be purchased and maintained for the few hours during the day, and in some cases the few hours per year ( like during peak air conditioning season) when they are needed. Additionally, plants can run more efficiently at a constant rate at cruise speed, rather than being run up to 100% to meet peaks.
As Dr. Manthiram stated, “Energy will be one of the greatest challenges facing humanity”. Indeed, energy is what drives humanity forward and has been a great motivator of advancement. By working to make the current imperfect systems better, by adding storage, we can make our energy usage cleaner while working to arrive at the time where we are completely powered by renewable sources.
Ali Khademhosseini, Harvard-MIT Division of Health Sciences and Technology
Nano-and Microfabricated Hydrogels for Regenerative Engineering
Written by Ashley A. White
Biological systems and patient need are two primary inspirations for Ali Khademhosseini’s portfolio of research, which he outlined in his talk Sunday evening. Although an engineer by training, Khademhosseini works at Harvard Medical School, where he engages in what he calls “patient-inspired” engineering, allowing patient and clinician needs to guide his research. The applications of his work are manifold, including cardiovascular diseases, musculoskeletal trauma, or ulcers to name a few. He looks to nature for guidance, mimicking biological structures and systems and examining relationships between tissue architecture and function. His talk focused on a few key examples of his work.
The first example Khademhosseini described was developing better surgical adhesives for wound closure. Today’s commercially available adhesives force a tradeoff between good mechanical properties and biocompatibility. Khademhosseini has managed to achieve both aspects with protein-based hydrogels. Synthesis of the hydrogels begins with recombinant proteins, made from those found naturally in our bodies that give our tissues elasticity. Next, the proteins are modified with methacrylate groups and finally crosslinked. The resulting rubbery gel has tunable and impressive mechanical properties (e.g., extensibility up to 400% before rupture), it demonstrates better adhesion strength than commercially available materials, and it has performed well, mechanically and biologically, in large animal models. Next, Khademhosseini plans to move to clinical application.
Another issue Khademhosseini’s research has addressed is improving minimally invasive surgeries. In his talk, he highlighted the example of treating aneurysms. Today, small metallic coils can be packed into an aneurysm to induce coagulation. However, the coils remain in the body permanently and are extremely expensive at $3000 a piece. Khademhosseini described a better solution through a shear-thinning, nanoclay-based composite that is biocompatible, cost effective, and can be delivered through a catheter. The nanocomposite is composed of nanoparticles that have an asymmetric charge distribution, allowing them to interact with various polymers, forming reversible bonds. The nanocomposites’ mechanical properties can be varied by adjusting the ratio of nanoparticle to polymer. The materials are injectable, designed to flow when pressure is applied but maintain their shape once in place, and they are hemostatic, inducing blood coagulation. In vivo tests in rodent and porcine models have shown that the material successfully blocks blood flow in a similar amount of time to commercially available materials, and then degrades over time, allowing natural tissue to replace it.
Khademhosseini also reviewed some other areas of his work, including electrically active biomaterials that incorporate carbon nanotubes, mimicking the conductive aspects of natural tissues and enabling bioactuators and soft robotics. In addition, he detailed his progress in three-dimensional (3D) printing by integrating advances in materials science and microfluidic systems.
In addition to discussing his research, Khademhosseini stressed the impact that mentorship and collaboration have had on his career, citing colleagues like Robert Langer (Massachusetts Institute of Technology) and Kristi Anseth (University of Colorado in Boulder). He dedicated the talk to his students.
In the upcoming days, Science Writers and Guest Bloggers will post news and comments from the 2015 Materials Research Society Fall Meeting. These will include reports on Chad Mirkin’s Plenary presentation on “Programmable Materials and the Nature of the DNA Bond,” and the award presentations, including the talk by Richard H. Friend who is this year’s Von Hippel Award recipient. Highlights from the technical sessions will be reported here as well as personal impressions from this year’s Guest Bloggers.