Mechanical engineer Siva Nadimpalli is targeting a key roadblock in the development of high-capacity, affordable and long-lived batteries with a multi-year Faculty Early Career Development (CAREER) Program grant from the National Science Foundation (NSF).
Nadimpalli, who specializes in fracture mechanics, has developed new methods for examining the breakdown of the materials and interfaces in batteries that connect the active particles responsible for energy storage. The durability of these interfaces is critical for sustaining electrochemical reactions. When they degrade, the active particles become electrically isolated, diminishing both the battery's charging capacity and its overall life.
"Batteries need to be lightweight, low-cost and durable to meet future energy storage demands," says Nadimpalli, an assistant professor in NJIT's Department of Mechanical and Industrial Engineering. "If we can solve these problems, we will see new generations of battery-powered machines such as electric cars become commercially viable options."
"Also, there are many applications in the aerospace and biomedical device sectors that will benefit with improved, powerful and lightweight batteries," he adds. Nadimpalli compares battery electrodes to another composite, concrete, in which a polymer links active particles as the cement mix connects rocks.
"Material scientists are trying to come up with new 'cement types' to solve the problem of electrode degradation and they try them one by one," he says. "But I think it will be helpful to develop methods that allow us to understand at the fundamental molecular or atomic level what's happening at these interfaces that's causing them to break down."
NSF CAREER awards, described by the agency as among its "most prestigious," are highly selective grants that support early-career researchers with "the potential to serve as academic role models in research and education and to lead advances in the mission of their department or organization."
For his part, Nadimpalli has developed novel techniques, incorporating optical methods, among others, to see how materials operate in situ, inside a working battery, rather than investigating them after they have degraded.
He has also come up with so-called 'multi-physics' mathematical models that allow him to predict how mechanical forces can impact chemical reactions in battery materials, and to assess their corresponding electrical performance on, say, the current supplied by batteries at any voltage.
While newer materials such as silicon in lithium-ion batteries can, for example, store 10 times as much energy as compared to graphite in current batteries, silicon has mechanical problems, limiting durability, Nadimpalli notes. His experimental methods will allow him to study the fracture behavior of materials and their interfaces found in almost all existing and many emerging rechargeable battery chemistries.
"The mechanics of this interface failure is the least understood problem in battery performance, in part because the interfaces in batteries are complex and their properties change continuously," he says. "We're trying to establish fracture criteria that will be useful in validating many varieties of batteries in order to develop new electrode material designs for emerging battery technologies."
Nadimpalli is working with both graduate and undergraduate students in his lab. As part of his award, he is tasked with creating a lab module for students that demonstrates the process of stress generation - the cause of mechanical damage - during electrochemical cycling. That module will be modified and adapted into outreach programs, while also enabling elementary teacher trainees from the Newark school system to participate in the research.
In a separate project in his lab, Nadimpalli and his students are studying another avenue of battery failure, the chemical "side reactions" that occur between materials in batteries that also diminish capacity.
They posit that while nanoscale surface coatings such as oxides have the potential to make high-energy-density and high-power-density battery technologies a reality, their poorly understood breakdown during electrochemical charging and discharging cycling remains a major roadblock. To better understand this degradation, they are proposing novel experimental methods that include the measurement of stresses in silicon oxide nanofilms deposited on electrodes and the simultaneous measurement of their electrochemical behavior.
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