Samuel R. Schraer ’16 never thought that he would find his feet wet in research so early and so deeply at Cornell. But Professor Tobias Hanrath, Chemical and Biomolecular Engineering, saw Schraer’s burning curiosity and took him in. Now, together with his team in the Hanrath Energy Lab, Schraer is doing research on scalable nanowire production for batteries.
Indeed, the world’s energy consumption is increasing just as energy sources and applications are diversifying. To accommodate these trends, the ability to store energy as it moves throughout different systems becomes more important.
The battery is a major part of that bottleneck, and here Schraer is pulling knowledge from the frontiers and bringing it closer to application. He is developing ways to scale up the production process of silicon and germanium nanowires. These semiconducting structures have proved to be superior battery anodes, the negative ends of batteries responsible for “pushing” electrons out of batteries into external electric circuits. Nanowires are limited, however, by manufacturing cost constraints.
“The trick for us,” Schraer explains, “is that if we want real batteries to be produced on an industrial level, batteries using this [nanowire] battery technology, the process through which we produce nanowires has to be something that’s scalable and cost effective.”
Current batteries, while reliable, have limited capacity and are increasingly insufficient to meet growing needs. “With batteries right now, when you cycle a battery (a charge and a discharge constitutes one cycle), you are internally moving lithium ions between a carbon-based (usually graphite) anode and a lithium source cathode. When the battery is used, the flow of lithium ions between the anode and the cathode creates an electrical current, which means useful power,” Schraer explains. He also elucidates the fact that batteries can operate only if the anode material can withstand the repeated entrance and exit of lithium ions, which today’s common graphite anodes can easily achieve.
The issue is battery capacity. “The problem with the current materials is that they store relatively less lithium, which means the batteries don’t last as long as they could with different anode materials,” Schraer remarks. Schraer compares this shortcoming with the untapped advantages of other materials. “Something like silicon or germanium has been known for some time to theoretically be able to store a lot more lithium than current battery technology can. Silicon, for example, has a theoretical charge capacity of about 4200 mAh/gram,” says Schraer, an exceedingly higher number compared to graphite’s mere 372 mAh/gram. Graphite is very commonly used in current batteries.
In exchange, however, both silicon and germanium usually have very low lifespan. “The problem is that if you take bulk silicon and cycle it in a battery, the stresses of cycling and the stresses of being filled with lithium and having lithium being removed over and over literally breaks the [anode] structure,” says Schraer.
This is where nanowires offer a possible breakthrough. Schraer continues, “If you use some sort of nanowire structure in cycling a battery . . . they just dilate volumetrically and maintain the same shape instead of breaking.” Therefore, if battery anodes were built with silicon-based or germanium-based nanowires, then it would be possible to enjoy both long battery lifetimes and significantly improved capacity.
Schraer and his team hope to replicate this promising property on an industrial level. This challenge is key for the battery industry; past techniques traditionally produced very small quantities of nanowires. Benjamin Richards, a graduate student and Schraer’s close mentor, explains that “nanowire technology was developed by the microelectronics industry using thin film deposition approaches. This produced micrograms of homogeneous nanowires; however, kilograms of nanowire material are required to make a single battery for an electric vehicle.”
Schraer is developing ways to scale up the production process of silicon and germanium nanowires.
Prompted by this looming challenge, the team is making great strides. “We are scaling the process up, and we are making bigger and bigger prototypes of ways to build these nanowires at a more time- and resource-effective manner.” He lets on that companies and organizations have shown keen interest in the research. Some key details of his team’s projects cannot be revealed, but Schraer made it clear that the possibilities stemming from this research go beyond batteries and are simply overwhelming. “The technology that makes scalable nanowires and scalable semiconducting materials [is] very appealing, because you can use them for batteries, solar cells, sensors, circuits, in computers—you use them in a whole host of different areas of technology. There’s countless other ways that this can be applied.”
The Undergraduate’s Research Experience
Asked about the research environment at Cornell, Schraer happily articulates that he “loves it; it is a very great environment.” He initially had doubts about his ability to make a meaningful contribution, but quickly cast them aside. “It’s a really supportive environment, and it’s really exciting to be learning as I go.” Schraer’s interactions with Richards and with Professor Hanrath reflect his claims. “Ben is always willing to teach what I need to know. It’s very fluid; Ben trusts me to work on my own, but he’s also happy to help me with new experiments. So I get to work with someone very experienced in the field like Ben on a frequent basis. I also meet with Professor Hanrath, and he is always really supportive, always with great advice for me as a researcher, but also for my life as an undergraduate planning for the future. He advises me on how to present my work better at meetings, write better scientifically, and advises on graduate school.”
Schraer knows that he would not have been here without the support of the people he met along the way. His high school physics teacher had encouraged him to pursue science in light of his potential. Professor Hanrath and his team have also played great roles, looking past his inexperience as a freshman and helping shape his intellectual rigor. In return, Schraer wants to give back. He views his position as co-president of the Cornell University Research Board as “an opportunity to give other people that kind of encouragement as well.” He does this by organizing Fall Forums and Spring Forums, at which hundreds of undergraduates present their own research projects to the general Cornell community, showcasing the vast range of research opportunities on campus. “Everyone is always so scared of not being able to meaningfully contribute [to research], and I like being able to tell them that finding research is a doable thing; it is attainable. I did it, I came in very inexperienced, and I like helping people find the same kind of passion that I do.” In this way, Schraer’s intellectual passion runs full cycle.