Energy boost for pacemaker batteries

Technology News |
By Nick Flaherty

Researchers at MIT have boosted the energy of nonrechargeable primary battery cells by 50% with a new electrolyte material.

Replacing the battery in a pacemaker or other medical implant requires a surgical procedure, so any increase in the longevity of their batteries could have a significant impact on the patient’s quality of life, says researcher Betar Gallant, associate professor of mechanical engineering.

The increase in energy density at human body temperatures also means the primary batteries could be smaller and lighter for LED applications. Further development are looking at making the batteries operate efficiently at cooler temperatures, applications could also include sensors in tracking devices for shipments, for example to ensure that temperature and humidity requirements for food or drug shipments are properly maintained throughout the shipping process.

in a paper by MIT Kavanaugh Postdoctoral Fellow graduate student Alejandro Sevilla, Betar Gallant, and four others at MIT and Caltech.

That difference in capacity makes primary batteries “critical for applications where charging is not possible or is impractical,” says researcher Haining Gao.

The key is a liquid fluorinated compound that combines some of the functions of the cathode and the electrolyte in one compound, called a catholyte. This allows for saving much of the weight of typical primary batteries, says Gao.

While there are other materials besides this new compound that could theoretically function in a similar catholyte role in a high-capacity battery, says Gallant, those materials have lower inherent voltages that do not match those of the remainder of the material in a conventional CFx pacemaker battery.

“One of the key merits of our fluorinated liquids is that their voltage aligns very well with that of CFx,” she said.

The new cells also provide safety improvements over other kinds of proposed chemistries that would use toxic and corrosive catholyte materials, which their formula does not. Preliminary tests have demonstrated a stable shelf life over more than a year, an important characteristic for primary batteries, she says.

So far, the team has not yet experimentally achieved the full 50 percent improvement in energy density predicted by their analysis. They have demonstrated a 20 percent improvement, which in itself would be an important gain for some applications, says Gallant.

The design of the cell itself has not yet been fully optimized, but the researchers can project the cell performance based on the performance of the active material itself. “We can see the projected cell-level performance when it’s scaled up can reach around 50 percent higher than the CFx cell,” she says.

One big advantage of the new material, Gao says, is that it can easily be integrated into existing battery manufacturing processes, as a simple substitution of one material for another. Preliminary discussions with manufacturers confirm this potentially easy substitution, Gao says.

The basic starting material, used for other purposes, has already been scaled up for production, she says, and its price is comparable to that of the materials currently used in CFx batteries. The cost of batteries using the new material is likely to be comparable to the existing batteries as well, she says.

The team has already applied for a patent on the catholyte, and they expect that the medical applications are likely to be the first to be commercialized, perhaps with a full-scale prototype ready for testing in real devices within about a year.

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