Supratim Das’s quest for the perfect battery began in the dark. Growing up in Kolkata, India, Das saw that a ready supply of electric power was a luxury his family didn’t have. “I wanted to do something about it,” Das says. Now a fourth-year PhD candidate in MIT chemical engineering who's months away from defending his thesis, he’s been investigating what causes the batteries that power the world’s mobile phones and electric cars to deteriorate over time.
Lithium-ion batteries, so-named for the movement of lithium ions that make them work, power most rechargeable devices today. The element lithium has properties that allow lithium-ion batteries to be both portable and powerful; the 2019 Nobel Prize in Chemistry was awarded to scientists who helped develop them in the late 1970s. But despite their widespread use, lithium-ion batteries, essentially a black box during operation, harbor mysteries that prevent scientists from unlocking their full potential. Das is determined to demystify them, by first understanding their flaws.
In principle, rechargeable batteries shouldn’t expire. In practice, however, they can only be recharged a finite number of times before they lose their ability to hold a charge. An ordinary battery eventually stops working when the terminals of the battery — called electrodes — are permanently altered by the ions passing from one terminal of the battery to the other. In a rechargeable battery, the electrodes recover when an external charger sends those ions back where they came from.
Lithium ion batteries work the same way. Typically, one electrode is made of graphite, and the other of lithium compounds with transition metals such as iron, cobalt, or nickel. At the lithium electrode, lithium atoms part ways with their electrons, swim through the battery fluid (electrolyte), and wait at the other electrode. Meanwhile, the electrons take the long way around. They flow out the battery, through a device that needs the power, and into the second electrode, where they rejoin the lithium ions. When a mobile phone is plugged in to be charged, the ions and electrons retrace their steps, and the battery can be used again.
When a battery is charged, however, not all the lithium ions make it back. Every charging cycle leaves ions straggling at the graphite electrode, and the battery loses capacity over time. Das found this perplexing, because it meant that draining a phone’s battery didn’t harm it, but recharging it did. He addressed this conundrum in a couple of open-access academic publications in 2019.
There was also another problem. When a battery is “fast-charged” — a feature that comes with many of the latest electronics — lithium ions start layering (plating) over the carbon electrode, instead of transporting (intercalating) into the material. Prolonged lithium plating can cause uncontrolled growth of fractal-like dendrites. This can cause short-circuiting, even fires.
In his doctoral research, Das and collaborators have been able to understand the microscopic changes that degrade a battery’s electrodes over its lifetime, and develop multiscale physics-based models to predict them in a robust manner at the macro-scale. Such multiscale models can aid battery manufacturers to substantially reduce battery health diagnostics costs before it is incorporated into a device, and make batteries safer for consumers. In his latest project, he’s using that knowledge to investigate the best way of charging a lithium-ion battery without damaging it. Das hopes his contributions help scientists achieve further breakthroughs in battery science and make batteries safer, especially when the latest technology is often closely guarded by private companies. “What our group is trying to do is improve the quality of open access academic literature,” Das says. “So that when other people are trying to start their research in batteries, they don’t have to start at the theory from five to 10 years ago.”
Das is well-placed to walk between the worlds of academia and industry.
As an undergraduate in Indian Institute of Technology (IIT) Delhi, Das learned that chemical engineers could use equations and experiments to invent technology like drugs and semi-conductors. “Just the fact that here I was in college, learning something that gave me the power to potentially impact the lives of N number of people in a positive manner, was utterly fascinating to me,” Das says. He also interned at a consumer goods company, where he realized that academia would allow him more freedom to pursue ambitious ideas.
In his sophomore year, Das wrote to a professor at the Hong Kong University of Science and Technology, seeking an opportunity to do research. He flew out that summer, and spent weeks learning about high-power lithium-ion batteries. “It was an eye-opening experience,” Das recalls. He returned to his coursework, but the idea of working on batteries had taken hold. “I never thought that something I can do with my own hands can potentially make impact at the scale that battery technology does,” Das says. He continued working on research projects and made key contributions in the field of multiphase chemical reaction engineering during his undergraduate degree, and eventually wound up applying to the graduate program at MIT.
In his second year of graduate work, Das spent a semester as a technical consultant for Shell in Houston, Texas and Emirates Global Aluminum in Dubai. There, he learned lessons that would prove invaluable in his graduate work. “It taught me problem formulation,” Das says. “Identifying what is relevant for stakeholders; what to work on so as to best use the team's skill sets; how to distribute your time.”
After Das’s experience in the field, he discovered that as a scientist he could share valuable knowledge about battery research and the future of the technology with energy economists. He also realized that policymakers considered their own criteria when investing in technology for the future. Das believed that such a perspective would help him inform policy decisions as a scientist, so he decided that after completing his PhD, he would pursue an MBA focusing on energy economics and policy at MIT’s Sloan School of Management. “It will allow me to contribute more to society if I’m able to act as a bridge between someone who understands the hardcore, microscopic physics of a battery, and someone who understands the economic and policy implications of introducing that battery into a vehicle or a grid,” Das says.
Das believes that the program, which begins next fall, will allow him to work with other energy experts who bring their own knowledge and skills to the table. He understands the power of collaboration well: at college, Das was elected president of a dorm of 450-plus residents and worked with students and administration to introduce new facilities and events on campus. After arriving in Cambridge, Massachusetts, Das helped other students manage Ashdown House, represented chemical engineering students on the Graduate Student Advisory Board, and served in the leadership team for the MIT Energy Club, spearheading the organization of MIT EnergyHack 2019. He also launched a community service initiative within the Department of Chemical Engineering; once a week, students mentor school children and volunteer at nonprofits in Cambridge. He was able to attract funding for his initiative and was awarded by the department for successfully mobilizing 80-plus students in the community within the span of a year. “I’m constantly surprised at what we can achieve when we work with other people,” Das says.
After all, other people have helped Das make it this far. “I owe a lot of success to a number of sacrifices my mom made for me, including giving up her own career,” he says. At MIT, he feels fortunate to have met mentors like his advisor, Martin Bazant, and Practice School directors Robert Fisher and Brian Stutts, and the many colleagues who have offered answers to his questions. “Here, I’ve discovered what it means to synergize with really smart people who are really passionate — and really nice at the same time,” Das says. “Grateful is the one word I’d use.”