Making lithium-ion batteries safer and more powerful requires the right formula

A research team at Purdue University published a study on the relationship between the activity and inactive elements of lithium-ion batteries and how the micro and nanostructures of their respective components reflect the performance and safety of the battery.

The study was recently published on the cover of ACS Applied Materials & Interfaces magazine.

“Rechargeable batteries are everywhere,” said ParthaMukherjee, associate professor of mechanical engineering and research principal. “We may carry two or three portable electronic products with us at any time. But the interaction between the different elements of the battery itself is still unclear. My research hopes to bridge this gap.”

At Mukherjee's laboratory, the Energy and Transportation Science Laboratory (ETSL), researchers study various forms of energy transportation and storage, including batteries and fuel cells. They use computer modeling to propose new configurations involving constituent elements and then test different phenomena in the lab.

“It’s like baking a cake,” Dr. AashutoshMistry, a candidate for mechanical engineering said. “How much dough should you use? How many cherries should you put in so that it tastes good? In the same way, let's look at the basic proportions or recipes of these battery electrodes. Anything you change microscopically will ultimately affect overall performance. "

"For example, let's look at electric cars," Mukherjee said. “People are interested in three things. Performance: How fast can I drive? Life: How long can I drive before charging? Finally: security issues. We have seen these batteries fail in public in an amazing way, on smart phones and the explosion in electric cars. So, these three aspects: performance, life and safety are very important. This can be a tricky balance and make everything right."

Sometimes their labs are working hard to reproduce intentional failures. In a typical electric car, the battery is not a huge unit, but thousands of separate batteries are connected together. If it fails, what happens to other people nearby? For one test, a sample module of 24 units (about one brick size) was deliberately overcharged. One cell explodes, setting all the cells on fire in a chain reaction.

“The temperature and pressure inside a battery is very high, it melts the metal casing and causes a fire,” Dr. said. Candidate Daniel Robles, because he was holding a plastic bag scorched body. “In an electric car, there are thousands of such batteries, which are all under your seat! That's why it's important to understand the basics of these phenomena, so we can prevent it from happening.”

Rechargeable batteries typically comprise a positive electrode and a negative electrode, composed of "active material" to store lithium. Between the two electrodes is a membrane and there is a liquid electrolyte throughout the process to transport lithium ions. Finally, the combination of electrochemically inactive materials such as conductive additives and binders (referred to as "second phase") helps to shape the physical components in the composite porous electrode and enhance electrical conductivity. In a published study, Mukherjee and his team studied the relationship between active and secondary phases at the micro and nano scales - porosity, physical shape and their interactions. Changing any of these characteristics can result in significant changes in the overall performance of the battery.

“We are still in the early stages of understanding these complex interactions,” Mukherjee said. “But this is the key to our research. We connect micro and nano-scale development with battery performance, life and safety.”

With the popularity of rechargeable batteries, research has become more important. “From portable electronics to vehicles, even in large power grids, batteries are being used extensively. This is a very exciting time for energy storage research.”

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