Designfax weekly eMagazine

Subscribe Today!

Archives

View Archives

Partners

Manufacturing Center
Product Spotlight

Modern Applications News
Metalworking Ideas For
Today's Job Shops

Tooling and Production
Strategies for large
metalworking plants

Assembly tape could cause phone and laptop battery drain

Edited by Mike Foley, Designfax

In a fascinating discovery, researchers at Dalhousie University in Canada have concluded that some adhesive tape used to assemble commercial lithium-ion batteries can contribute to charge loss while devices sit idle. The researchers have identified an alternative to the tape that almost entirely prevents the power losses.

The discovery came after the team determined previously that a tape made of polyethylene terephthalate (PET) and commonly used in lithium-ion batteries is not chemically stable during battery operation, leading devices like computers and phones to lose their charge even if not being used -- a phenomenon called self-discharge.

The Dalhousie University researchers opened 10 randomly chosen, discarded cell phone batteries from major battery manufacturers and found all of the cells used PET tape. [Photo courtesy of the researchers]

 

 

 

 

The finding prompted the scientists to look into other options from commercially available tape materials, leading them to discover that using chemically stable polypropylene (PP) tape instead of PET can decrease self-discharge by up to 70% and increase battery life up to 10%.

PhD student Anu Adamson and Michael Metzger, an assistant professor and the Herzberg-Dahn chair and in the Department of Physics and Atmospheric Science, led the research initiative described in a new paper published in Nature Materials.

When asked about how the tape is used in the devices, Adamson told Designfax exclusively via email, "Most commercial cells are assembled by stacking or rolling (the positive and negative) electrodes, and tape is used to secure the stack/jellyroll of electrodes -- i.e., the tape is used for mechanical support during assembly. After the stack/jellyroll has been assembled and inserted into the cell casing, it serves no function. The exact amount of tape used depends on the cell's size, type, and manufacturer. However, thinner tapes are preferred to avoid adding unnecessary weight to the cell."

How does the tape end up affecting a device's ability to hold a charge?

Adamson explained, "Let's assume you have a cell phone at 100% charge; you leave it for a couple of hours (assume no background apps are running) and find the battery at 90%. This is called self-discharge and is the property of the battery the PET tape affects the most.

"PET is a common polymer typically used to produce plastic bottles, and this polymer is composed of a monomer called dimethyl terephthalate (DMT). DMT can transport electrons inside the battery instead of the outer circuit -- i.e., through your device -- meaning the energy stored in the battery is essentially going to waste. We found that when PET tape is used in a lithium-ion battery cell, it will dissolve into DMT monomers, resulting in self-discharge."

To probe how often PET tape is used in lithium-ion cells, the researchers opened 10 randomly chosen, discarded cell phone batteries from major battery manufacturers and extracted the tapes. They found all of the cells used PET tape. They also opened four cylindrical 18650 cells. Two contained PET tape, and two used PP tape.

"Therefore, it is highly likely that PET tape is used in many electronic devices," said Adamson.

It's such an interesting finding overall that we wondered how the discovery came about. Adamson explained, "In August 2022, my colleague Sebastian Büchele had recently discovered dimethyl terephthalate (DMT) as the redox shuttle molecule inducing self-discharge in lithium-ion batteries. However, we did not know where this molecule originated from. We thought of and tried out a few hypotheses, which all failed.

"While working on these hypotheses, I found a paper on PET recycling in dimethyl carbonate (DMC), demonstrating that DMT can be obtained from PET depolymerization. Therefore, I realized there must be some PET in the 402035-sized pouch cells used in our lab. I opened one of the commercial dry pouch cells we use in our lab and performed Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) measurements on all plastic parts found in the cell (separator, tapes, cell casing). After this, I compared the obtained spectra to a PET reference spectrum.

"The ATR-FTIR spectrum from the tape matched perfectly with PET, and when the PET tape was kept in a mixture of the proposed reagents (DMC, methanol, and lithium methoxide), it dissolved into DMT monomers. Thus, I deduced that the DMT redox shuttle molecule must originate from PET tape."

Adamson said changing the type of tape from PET to PP would not require any changes to the process manufacturing of battery cells, but the result would put a stop to tape-induced self-discharge. "It would be a matter of swapping the roll of tape on the manufacturing line," said Adamson. "Polypropylene also has suitable physical properties -- it is often used in separators, and some of the commercial cells we investigated already used polypropylene tape. The price point of polypropylene is similar to PET, and not a lot of tape is used in cells. Therefore, there would be no significant increase in cost for battery manufacturers," Adamson said.

Where does this research go from here?

Adamson said, "Multiple electronics manufacturers have contacted us about the issue and about implementing our solution. Replacing PET jellyroll tape with PP tape is simple and does not increase costs for electronics manufacturers, but it reduces self-discharge, making it reasonable to make the change."

Source: Dalhousie University

Published October 2023

Rate this article