A chance discovery in a Canadian laboratory could help extend the lifespan of batteries in laptops, phones and electric cars.
According to scientists at Dalhousie University in Halifax, the common sticky tape on batteries may be the reason many devices lose some of their power while turned off or not in use, a phenomenon known as self-discharge.
“In our lab we do a lot of very complex experiments to improve batteries, but this time we discovered something very simple,” Michael Metzger, an assistant professor in Dalhousie University’s department of physics and atmospheric science, said in a news release. “In commercial battery cells there is a tape, like duct tape, that holds the electrodes together and there is a chemical breakdown of this tape, creating a molecule that leads to self-discharge.”
The solution is simple, too, Metzger says: Replace the polyethylene terephthalate, or PET, plastic tape commonly used inside batteries with something more durable and stable.
“It’s a commercially relevant discovery,” Metzger said. “It’s a small thing, but it can definitely help improve battery cells.”
Metzger and his team have been trying to understand why lithium-ion battery cells in idle devices tend to lose some of their power and self-discharge, something that has long frustrated consumers and manufacturers alike. .
“Every lithium-ion cell manufacturer in the world wants the self-discharge to be as small as possible,” Metzger told CTVNews.ca in a joint statement with graduate student Anu Adamson. “In every battery there is a small self-discharge rate that slowly depletes the battery. This is very inconvenient for users and a huge headache for the industry.”
The electrodes that power the batteries are separated by an electrolyte solution that is usually a form of lithium. After exposing several battery cells to different temperatures, the researchers were surprised to see that the electrolyte solution had turned bright red when it should normally be transparent, something they had never seen before. The discovery was made by Adamson and two other students.
Chemical analysis of the red electrolyte solution revealed that at higher temperatures, a new molecule had been created inside the battery through the breakdown of common PET adhesive tape, which is often used to bond components inside batteries. batteries. Strong and lightweight, PET is also often used for plastic packaging, beverage bottles, clothing fibers, and more.
The researchers realized that the red molecule, dimethyl terephthalate, acted as a redox shuttle, meaning it can shuttle electrons between the positive and negative electrodes of a battery, creating self-discharge and depleting power even when the battery is not in use. Ideally, the transport of electrons within a battery should only occur when a device is turned on.
“It’s a very simple thing: it’s in every plastic bottle, and no one would have thought that this has such a big impact on how lithium-ion cells degrade,” Metzger said in the news release. “It’s something we never expected because nobody looks at these inactive components, these tapes and plastic sheets in the battery cell, but it really has to be considered if you want to limit side reactions in the battery cell.”
The findings are described in a pair of studies published January 20 and 23 in the peer-reviewed Journal of The Electrochemical Society. The researchers are now testing PET tape substitutes.
“Since the PET on the tape is the culprit that creates the redox shuttle, we need to replace it with a polymer that is more stable and won’t break down in the harsh chemistry of a lithium-ion battery,” Metzger and Adamson told CTVNews. California. “So far, the results look very promising and we plan to publish a new research paper on improved polymers for lithium-ion battery ribbons soon.”
According to the researchers, their work has attracted the interest of “some of the world’s largest computer hardware companies and electric vehicle manufacturers,” who are eager to reduce self-discharge and improve battery performance.
“We visited some of these companies and they are planning to implement more stable polymers in their battery cells,” Metzger said.
In the statement, Metzger noted: “One of the engineers said, ‘I heard you found something wrong with the PET tape.’ So, I explained what is causing this self-discharge and asked, ‘What are you using in your cells? ‘ He said, ‘PET tape’.”
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