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A new battery that could revolutionize wearables

A young battery startup called Imprint Energy has designed a new type of battery that uses zinc and can be screen printed. It’s innovation could enable entirely new types of wearable electronics.
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Picture a Nike FuelBand that’s just a small ring on your index finger, or a cell phone that’s as slim and pliable as a credit card. Those types of thin, tiny or just down right unusual shapes could be created if there were batteries that were both slim, flexible and also powerful enough to run the gadgets. It’s the batteries, it turns out, that are the main barrier to modern electronics design.

But in a small, brightly-lit lab in an office park behind the Oakland Airport in Alameda, Calif., a young startup called Imprint Energy, is using research created at the University of California, Berkeley to develop just such a battery that could free gadget makers from the constraints of the standard lithium ion battery. Well, that’s the plan anyways.

Using zinc, instead of lithium, and screen printing technology, Imprint Energy is already churning out low volumes of its ultra-thin, energy-dense, flexible, and low cost rechargeable batteries for pilot customers.
The battery barrier

Nike FuelBand batteryThe problem is, it’s hard to make standard lithium ion batteries thin and flexible, explained Imprint Energy CEO Devin MacKenzie to me in an interview in the startup’s lab last week. There’s a “lot of packaging,” required to seal off the highly reactive lithium in the battery from the environment, said MacKenzie. If you’ve ever seen YouTube videos of lithium batteries that catch on fire in the air or water, you know why those barriers are needed.

But this architecture also makes lithium ion batteries rigid and potentially bulky. Even the slimmest laptops like the Macbook Air, or tablets like the iPad, faced design limitations created by the size and weight of the batteries. The Nike FuelBand uses a curved (called conformal in battery terms) lithium polymer battery, but if you look closely at the shape of the band (photo left), the battery is the only part of the bracelet that isn’t pliable.
Upsides of zinc

Imprint Energy’s battery tackles the problem of rigidity and bulkiness by simply throwing out the lithium. The company, which now has a staff of 8, was founded in 2010 by U.C. Berkeley PHD students Christine Ho and Brooks Kincaid, and more they recently raised seed funding from Dow Chemical and CIA fund In-Q-Tel.

6877161476_54aa965721_zThe company uses zinc for the anode part of the battery, and combines that with a solid polymer electrolyte and a cathode made of a metal oxide. A battery is made up of an anode on one side and a cathode on the other, with an electrolyte in between — zinc ions (in Imprint’s case) travel from the anode to the cathode through the electrolyte, creating a chemical reaction that allows electrons to be harvested along the way.

MacKenzie tells me that while zinc has been used for years in batteries, it’s been difficult to make zinc batteries rechargeable. That’s because when zinc is combined with a liquid electrolyte it creates something called dendrites, which are tiny fibers that grow and get in the way of the charging reaction. Imprint Energy solved this hurdle by using an electrolyte made of a solid polymer combined with the zinc.

Using zinc means Imprint’s batteries can have far less “packaging” because zinc isn’t highly reactive with the environment. In other words, the batteries can be made much more thinly. They can also be made as tiny as a few hundred microns thick (the width of a couple human hairs). Batteries that small could power tiny digital smart labels, like freshness detector stickers on food.

Zinc also makes Imprint’s batteries more safe and less toxic than lithium-based batteries. The team at Imprint can work on the zinc batteries in the open air. And the zinc batteries are a safer option for creating devices that sit on — or even in — the body. Imagine a lithium battery powering a heart device inside a person’s chest cavity, and the battery leaks lithium into the person’s body. Yikes.
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