Taking Batteries Outside the Box

by Gordy Slack

(Above: Christine Ho and Brooks Kincaid, co-founders of Imprint Energy, a battery startup incubated at CITRIS.)

Another story on this project recently appeared on the UCOP site.

Efforts to create an inexpensive sticker that can monitor temperature will likely employ battery technology developed by Christine Ho and incubated at CITRIS’s Marvell Lab. The device could be stuck on the side of a package of perishable food or pharmaceuticals to record the product’s temperature over time so consumers can be assured they are buying a safe product.

This useful flexible device is being developed by ThinFilm Electronics, based in Oslo Norway, which will fuse its own printed memory components to printed temperature sensors, to printed transistors, and finally to printed batteries made by Imprint Energy, the UC Berkeley company started by Ho.

The ultra-thin, printable batteries are safe, long-lasting, flexible, disposable, and easy to manufacture: a combination the energy storage industry has long sought, says Ho. The batteries are also solid-state, she says, and can be compressed, ripped, or cut up into pieces of any size or shape and still hold a charge.

Dr. Christine Ho as a graduate student with the printer dispenser tool she used to fabricate microbatteries. RACHEL SHAFER PHOTO.

Ho is a material scientist with both a B.A. and Ph.D. from UC Berkeley. As a graduate student she sought energy-storage solutions for microsensors and various tiny wireless devices. Under the tutelage of professors Paul Wright and James Evans, she experimented with printable batteries made from a variety of materials but was “especially drawn to one of the oldest battery chemistries around,” she says. Zinc.

The problem with traditional zinc batteries, and the reason the element has been neglected by forward-thinking researchers, is that they have seemed inextricably linked to aqueous acids or corrosive alkaline electrolytes made of potassium hydroxide.  It has been an industry assumption that zinc batteries, because of these dangerous components, could be made neither disposable nor rechargeable, both key qualities in a 21st-century battery for portable electronic devices.

In a breakthrough that served as the thesis for her dissertation and that is the core of Imprint Energy’s intellectual property, Ho proved that assumption wrong by developing a benign material that works as an electrolyte in zinc batteries and makes them both disposable and rechargeable.  She patented the material, which she calls a “high-conductivity polymer electrolyte,” or HCPE, before her graduation in 2010. Her degree newly in hand, Ho teamed up with Haas Business School graduate, Brooks Kincaid, to form Imprint Energy.

Ho’s initial impetus was to create a rechargeable power storage option for tiny wireless sensors, but Imprint’s business model now focuses on the gigantic portable consumer electronics market that can exploit the design advantages of the new batteries.

“Our sweet spot is in the consumer market. It is large and growing,” says Kincaid, pointing to products like the Nike Fuelband, a flexible wristband sensor device that tracks athletic activity. The safety and high capacity of Imprint’s batteries, the ability to print them in different shapes and sizes, their disposability, and their affordability, all make them a good alternative to the lithium-based rechargeables that are now the industry standard.

“There is a lot of buzz around making things flexible, conformable to your body, or to a curved shape,” says Ho. “A lot of displays coming out are curved, and electronics are on flexible substrates. But until now, batteries have always been rectilinear, hard, boxes that have saddled design to a certain form factor. We have lifted that barrier, which has interested a lot of potential customers and partners in this technology.”

Imprint’s zinc batteries, trademarked Zink Poly, are much easier to make than their lithium counterparts, says Ho. They do not require the same super-controlled, clean-room conditions to make because their materials are not flammable or corrosive. For the same reason, Imprint’s zinc batteries do not require a lot of inflexible packaging to protect users and devices from dangerous ingredients.

“Some lithium-ion batteries also need to be in rigid housing because pressing or flexing of the pack can result in serious performance degradation,” says Ho.

Imprint Energy also has a versatile and scalable manufacturing process that—like the zinc batteries it produces—is a novel application of a traditional technology, screen printing.  It is the same screen process used to print on T-shirts and paper, and it is easy to use existing printing equipment with little-to-no modification to print the batteries.

“There are tons of these printers everywhere, so we do not have to invest millions of dollars in manufacturing equipment,” Ho says. “And with screen printing, we can make lots of batteries in one run. Once we optimize the materials for printing and get the process down, we will be able to scale volumes to thousands, millions, and even higher.”

The CITRIS research environment
was key to the development of the core innovation, the new electrolyte, HCPE, and also to the way the idea was ushered into a real-world business prospect. Ho participated in poster sessions and meet-and-greets at CITRIS that introduced her to industry representatives and gave her a much better sense of how her innovations might be applied, she says.

Imprint won five national and international business-plan competitions to secure early funding.  Additional launch money came from a National Science Foundation Small Business Innovation Research grant and a UC Discovery grant.   Ho and Kincaid remained in the nurturing CITRIS environment for the first year after Imprint’s 2010 incorporation. They bought a corporate membership to the Marvell Nanofabrication Lab, which they used to develop their first prototypes. With those first batteries as potent evidence for the validity of their plan, Ho and Kincaid were able to get a seed grant from a large chemical company, which funded Imprint’s move to Alameda in March.

“We couldn’t have done this without our relationships and access at the Nanolab,” says Kincaid. “It would have been too expensive and risky to get started all on our own.”

The shift to their own facility in Alameda has been exciting, says Ho, and for now their aim is to remain, like their batteries, as flexible as possible. “Portable electronic devices are our focus, and we are developing devices with several prospective partners in that space, but we can imagine eventually working in all different energy storage sectors,” says Ho.

The first fully-functional prototype for the new temperature monitoring stickers is expected later this year.