She paints for power

PRECISION MANUFACTURING: Christine Ho with the printer dispenser tool she uses to fabricate microbatteries. RACHEL SHAFERPRECISION MANUFACTURING: Christine Ho with the printer dispenser tool she uses to fabricate microbatteries. (Photo by Rachel Shafer.)There are lead-acid batteries for your car and nickel-cadmium ones for your Sony Walkman. Lithium-ion batteries juice your laptop, iPhone and high-definition, DVR-enabled, hidden camera wristwatch.

What will power our next-generation gizmos? The microdevices, nanodevices and picodevices of the future? Our prediction: the Christine Ho battery.

As an MSE graduate student, Ho (B.S.’05, M.S.’07, Ph.D.’10 MSE) developed a novel process of simultaneously fabricating and placing a tiny battery onto a one-square-centimeter RFID tag. The technology promises to not only power the smallest of smart devices but also accelerate a variety of energy applications, from better home energy monitoring systems to large-scale energy storage solutions for wind and solar farms.

Before she could dream big, though, Ho faced a teeny-weeny problem. “The big challenge at the micro level lies not in the battery chemistry or material,” Ho explains, “but in fabrication and integration with the device.”

Because microdevices range from the size of a sugar cube to microscopic, swapping a battery in and out as you would for a remote control is next to impossible. So microbatteries, which are as thick as two human hairs (and getting smaller), must be powerful, long-lived and built in.

Advancing the graduate work of previous students, Ho tackled the built-in component by means of a dispenser printer, a fabrication tool often used in the electronics industry. She and fellow students “painted” layers of zinc electrode, gel electrolyte and manganese dioxide electrode, one on top of the other, in a precise spot on the RFID tag. Within an hour, the material “sandwich” was ready for use as a built-in, thin-film zinc polymer battery.

To get the precision needed for creating batteries within small confines, Ho’s printer dispenses ink-like battery material via a syringe connected to a compressed air line and an electronic controller that tightly manipulates lateral and vertical movement. In comparison with other microbattery fabrication processes, the technique is fast, scalable and wastes little material. In other words, it suits manufacturing.

Most important, the technique works. During initial testing, Ho reports, the batteries it produced demonstrated promising energy storage results, in both slow and fast discharge rates, and consistent performance over 100 cycles. Next, she will test the batteries at 500 to 1,000 cycles, the lifecycle range for consumer devices and car batteries.

TINY BUT POWERFUL: A cross section of one of Ho’s microbatteries. Her initial testing suggests that the fabrication technique she developed will create batteries capable of not only storing energy to capacity but also performing consistently over many cycles. COURTESY CHRISTINE HOTINY BUT POWERFUL: A cross section of one of Ho’s microbatteries. Her initial testing suggests that the fabrication technique she developed will create batteries capable of not only storing energy to capacity but also performing consistently over many cycles. (Photo by Christine Ho.)Ron Hofmann (B.S.’64 ME), an independent energy consultant who advises Ho, calls the fabrication technique “an important, enabling technology . . . a major breakthrough.” He adds, “I predict that in five years her technique will be commonplace.”

Ho wants to commercialize it. For the past year, she’s been working with Ikhlaq Sidhu, director of the College of Engineering’s Center for Entrepreneurship and Technology, and Bev Alexander, director of the Haas Energy Institute’s Cleantech to Market program to clarify intellectual property and licensing questions, firm up business plans and win funding.

She’s come a long way from the day in 2001 when she arrived on campus as an MSE freshman, following her father into the discipline but with little sense of how she might shape her own career path.

Two years later, Ho answered a help wanted ad for a joint undergraduate research position in the labs of James Evans, professor of materials science and engineering, and Paul Wright, professor of mechanical engineering and CITRIS director. The job was affiliated with a multidisciplinary project building wireless sensing systems, specifically home energy monitoring systems, funded by the California Energy Commission. Evans and his research team were charged with determining power supply and storage solutions for the small wireless sensors or RFID tags that would be sprinkled throughout a room.

Soon, Ho was working under graduate student Dan Steingart (M.S.’02, Ph.D.’06 MSE), now assistant professor of chemical engineering at City College of New York. Steingart ignited not only her interest in microbattery design, Ho recalls, but also in its fabrication using various printing technologies. As she ran the difficult, exacting experiments Steingart gave her, they discussed world energy problems.

Before long, Ho discovered a personal calling in power and energy management. She rose to become the project’s lead researcher after Steingart graduated, and in August she earned her own Ph.D. “Most students don’t have the stamina and patience to see a single project like this all the way through,” Steingart says. “But she took this thing and owned it.”

“I can’t seem to let it go,” Ho says, laughing.

She is convinced her microtechnology will scale up for larger applications. Her batteries could power thin, flexible displays such as smart labels, newspaper e-readers and digital readouts on refrigerators, she says. Industrial-size printer dispensers could also churn out sheets and sheets of battery material for storing wind and solar energy for use in the grid.

Ho dreams of even more sophisticated applications, like a solar-powered home with her battery material installed in the walls that could, literally, trap that energy in-house instead of sending it back to the grid. “It’s a crazy concept,” she says, “but we calculated that you’d need less than 10 percent of the wall space to power a 2,600-square-foot home.”

Crazy, perhaps, but with Ho’s dedication and imagination, such a house seems entirely within the realm of possibility.