Researchers team up to make better batteries

A team of researchers from Florida State University and Cornell University discovered that batteries made from inexpensive and safe components can provide three to four times more power than batteries built with today's state-of-the-art lithium-ion technology.

Researchers' work is published today in Nature Communications.

A. Nijamudheen, a post-doctoral researcher at the FAMU-FSU Engineering College, and Snehashis Choudhury, a doctoral student at Cornell University, as well as faculty members from both institutions, have undertaken an ambitious investigation into what hinders the current battery design and improvements. .

"If we look at the cost of batteries over time, it's not surprising to see that the vector is still headed up," said Choudhury. "The widespread adoption of technologies requiring batteries results in lower costs."

In hopes of reducing these costs, the researchers tackled some specific problems related to electrolytes, an essential component of building a battery that promotes the passage of ions from an electrode to the body. other.

The teams began to understand the chemical pathways through which electrolytes were degraded at the battery electrodes. Researchers have not only identified the mechanisms of electrolyte degradation, but they have also discovered multiple strategies to address this problem.

"We discovered that it was essential to control the ionic properties of the interphases formed at the negative electrode," said Nijamudheen.

Using quantum computation, Nijamudheen and his advisor, Jose Mendoza-Cortes, assistant professor of FAMU-FSU in Chemical Engineering, discovered that the problem stemmed from the way a component of electrolytes called diglyme undergoes polymerization. Polymerization is a process where molecules combine chemically to produce a molecule resembling a long chain called a polymer.

In the case of batteries, the electrolytes often separate and reform to create much larger molecules after prolonged contact with the negative and positive electrodes of a battery.

"While the degradation process itself is harmless, its byproducts prevent ions from accessing battery electrodes, which gradually reduces the amount of stored energy that can be recovered from the battery. a battery, "said Lynden Archer, a professor at Cornell University and Choudhury's advisor.

However, while certain types of polymers resulting from this process would prevent ions from reaching the electrodes, others have proven effective in extending battery life.

With their hand polymerization calculations, researchers began to study other types of electrolytes for which the polymerization process would not interfere with battery performance.

Generally, lithium batteries are made with organic carbonate electrolytes, but these electrolytes are highly flammable. An expensive thermal regulation infrastructure that provides cooling for overheated battery cells is therefore essential to reduce the risks of thermal runaway and battery fires.

The researchers instead tested a lithium nitrate electrolyte, a stable and non-flammable electrolyte.

With the help of this electrolyte, the researchers began conducting experiments on solid electrolyte interphase or SEI. The SEI is a protective layer formed on the negative electrode as a result of the decomposition of the electrolyte, usually during the first cycle of a battery.

"Once you have a good UTE, you have a good battery," said Mendoza-Cortes, also an assistant professor at the FAMU-FSU Engineering College. "The idea is to find an electrolyte and a solvent that can form a stable SEI and playing in your favor."

Researchers have developed a new type of SEI that spontaneously forms in a battery cell using sacrificial salt or molecular species introduced via electrolytes. They also introduced chain transfer agents – a chain of molecules – that interacted with diglyme to form a shield that protects the negatively charged electrode from degradation.

To evaluate the effectiveness of the design, the research team conducted a series of experiments on the battery's ability to be used and then recharged. They discovered that it could perform about 2,000 cycles, well beyond the usual 300 to 500 charge cycles associated with most lithium-ion batteries.

"Through this process, we could achieve unprecedented efficiency for this type of system," said Mendoza-Cortes. "In the end, we have improved the UTE, which would mean more energy that will last longer – there is a lot of potential there."