One Simple Trick Prolongs Battery Charge

One of the biggest problems with smart devices is battery life. The capacity of the battery always seems to have run out just when you need it most. This is especially true for laptops. Personally, I often find that my own laptop runs out of charge after a full day at an exhibition, which is a major inconvenience, as that’s the time I want to jot down notes from meetings and catch up with emails. I thought it was only the capacity of the battery itself that was too small, but according to a recent discovery, it may be that the way that the laptop battery was manufactured contained a simple flaw that allowed it to self-discharge. The solution could be as simple as replacing the tape that holds the electrodes together.

That was the discovery that researchers from Dalhousie University in Nova Scotia made, almost by accident. That chance discovery could help extend battery life by replacing the tape that causes the self-discharge.

"In commercial battery cells there is tape, similar to Scotch tape, that holds the electrodes together and chemical decomposition of this tape creates a molecule that leads to the self-discharge," says Michael Metzger, an assistant professor and the Herzberg-Dahn chair and in the Department of Physics and Atmospheric Science at Dalhousie University. He continued, "in our laboratory we do many highly complex experiments to improve batteries, but this time we discovered a very simple thing, and no one would have thought that this has such a huge impact on how the lithium-ion cells degrade."

Dr. Metzger and his colleagues wanted to understand why Li-ion battery cells self-discharge. As part of their research, they opened several cells after exposing them to different temperatures. They discovered that the electrolyte solution in the cell was bright red, something they had never seen before. They then began exploring the cause, placing cells with common electrolyte solution into ovens at four different temperatures. One at 25^oC remained clear, while the sample at 55^oC was light brown and the highest one at 70^oC was red. They then did a chemical analysis and looked at the chemical composition of the electrolyte. They found that the polyethylene terephthalate, or PET, in the tape decomposes and creates the molecule that leads to the self-discharge. The molecule is called a redox shuttle because it can travel to the positive side of the electrode, then to the negative side and then back to the positive side. That shuttling between the electrodes creates the self-discharge, just like lithium is supposed to do. However, the shuttle molecule is doing it all the time in the background, even when the battery is not supposed to release energy.

"We never expected to find anything like that, because no one looks at these inactive components, such as tapes and plastic foils in the battery cell. It really needs to be considered if you want to limit side reactions in the battery cell," Metzeger says of the tape made from PET, a strong, lightweight plastic used widely in packaging.

The researchers outlined their findings in two new papers in the Journal of The Electrochemical Society.

The information could lead to a fix that might involve replacing the PET tape with a more stable material that won't degrade.

Dalhousie University