How a design tweak could help pacemaker batteries last longer

How a design tweak could help pacemaker batteries last longer

Rechargeable Lithium-ion cells are a hot topic in the battery industry. They power everything, from phones to EVs. But with their growth in popularity since they were commercially released in the 1990s, another type of battery has taken a backseat in research: non-rechargeable batteries. This is a problem considering the many devices that depend on them, such as pacemakers. Researchers from MIT hope to address this gap by refocusing their efforts on older battery systems and trying improve their energy capacities by using a new type electrolyte.

” We knew we needed higher energy density batteries in order to allow for longer life for devices such as pacemakers,” said Haining Gao, a MIT postdoctoral fellow. “But there have only been a few innovations over the past 40 years. So we started there .”

These non-rechargeable options are also known as primary batteries. They have a higher energy capacity than the rechargeable ones. This makes them good candidates for products such as medical implants that can’t be recharged easily. However, they will eventually run out of juice, just like all primary batteries.

Here’s the way they work.

Most primary batteries contain electrolytes ,, which you may be familiar with from sports drinks such as Gatorade. They’re exactly the same thing. Electrolytes are just substances that split into ions when dissolved in a solution, which in the case of our bodies, conduct electrical charges that make our muscles move, among other things.

[Related: An AI called Dragonfly is helping design faster-charging batteries]

In batteries, electrolytes are used to conduct the movement of charged ions (like lithium ions in a li-ion battery, or potassium hydroxide in a non-rechargeable battery) between the positive and negative ends, called the cathode and anode, respectively. Electrons gather at the anode, where they repel each other and want to move to an area with fewer electrons, leading them to travel along a circuit to the positive cathode. When an object such as a lightbulb, is placed along the circuit, the electrons are forced through it to move on to the anode. Without the electrolyte, all of this is impossible. Primary batteries don’t last forever.

On the right, a traditional primary battery, and on the left, the new catholyte battery depicted in yellow
Researchers estimate this catholyte battery could have up to a 50 percent greater energy density than regular primary batteries. MIT researchers

In the case of pacemaker batteries, they only last about five to 10 years, says Gao. Gao and her team tried to extend their life span by choosing a different liquid electrolyte. It’s actually a combination electrolyte/cathode that they call a catholyte. Gao says that most traditional batteries use a solid-cathode material. Gao says that this material and the electrolyte are both dead weight and have been replaced with the combined cathode-electrolyte solution to improve the battery’s efficiency.

” Now we have more of a battery’s mass being used for energy conversion,” said Betar Gallant (MIT associate professor of mechanical engineering).

The researchers’ initial analyses estimated that the battery’s energy density could increase by 50 percent, but so far, their research has only resulted in a 20 percent increase. Still, Gao says this is mostly due to limitations of their lab setup, and 50 percent is still the goal. Gao says, “We believe it’s still possible.”

It could be beneficial to extend the life of high energy primary batteries in many situations where rechargeable batteries are not an option. This is not only for pacemakers. Gao says, “We are also considering applying this to unmanned vehicle, defense applications and tracking for cargo and space exploration.”

While rechargeable batteries are preferred for their sustainability, Gao suggests that primary batteries could have a longer life span to make them more sustainable. This means that pacemakers will need fewer batteries as they live longer, which will reduce battery waste and the number of required battery replacement surgeries.

The researchers hope to have a prototype with more advanced technology within one to two years. They don’t expect that the price of these batteries will be much higher than they are now. They hope that their work will highlight the need to revive interest in the still-stable field of primary battery research.

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