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
The 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.
The 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.
Printable batteries
The other innovation that Imprint Energy has developed is that it’s printing out its batteries using standard screen printing technology. Most batteries are made by coating the materials onto foils, which are then assembled into cells.
In Imprint Energy’s Alameda lab, CEO MacKenzie shows me one of two battery printing machines on site and a variety of screens that look sort of like t-shirt silk screening screens. The battery materials are printed like ink onto the screens in whatever shapes the client 
requires. Customers will pay a premium for batteries created to the custom shapes of their devices.
The company can churn out 100 cells a day on the machines in its lab. That’s tiny in the world of the battery giants in Asia, but it’s large enough to get samples out to potential customers. Down the road — potentially two to three years — the company will scale up manufacturing to a large commercial scale, but it won’t likely be building its own factories. More likely, it will work closely with manufacturing partners or license its technology.
An eye on wearables
While it’s still early days for Imprint Energy, the team’s end goal is the wearable electronics market, both for consumers (like Nike’s FuelBand and the FitBit line) as well as the health sector (such as implanted monitors). The wearables industry could reap the most benefits from the novel and thin shapes of the batteries, as well as the safe and less toxic materials.
Co-founder Kincaid is a wearables buff. He shows me his own Nike FuelBand on his wrist during the interview, and he says he’s eagerly awaiting the arrival of his Misfit Shine. For the wearables industry, Imprint Energy’s zinc poly batteries could enable an entirely new type of device that’s more hidden, more streamlined, or more functional. Given that wearable electronics is an emerging sector, and one that could become a lot more mainstream over the next few years, disruptive design could ultimately completely change the wearable industry.
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