While developing electrochromic window technology, researchers at the Department of Energy's National Renewable Energy Laboratory (NREL) unexpectedly discovered a revolutionary thin-film lithium battery technology—one that holds promise for many applications. But it's not really surprising. According to NREL Senior Scientist Edwin Tracy, electrochromic technologies that dynamically control transmitted light in highperformance windows are really nothing more than thin-film batteries that change color.
Through their electrochromic windows expertise, Tracy and his NREL research colleagues, See-Hee Lee and Ping Liu, saw a way to make solid-state, thin-film lithium batteries in a reverse configuration, a long sought-after goal in the field.
"Thin-film batteries can degrade very fast," Tracy said. "That's because the reactive lithium metal anode is necessarily constructed on the top and thus more prone to environmental exposure. If there were a way to bury it beneath the cathode and electrolyte in a reverse configuration, it would be a much more durable device."
With no program funding to support their idea, they came into the lab on a Saturday and constructed the battery, burying the anode. The following week, they tested it, and then broke the good news to their group leader, NREL Senior Scientist Roland Pitts, who liked it despite its lack of application in high-end "smart" windows.
But without an industrial partner—and being somewhat far afield from their day-to-day electrochromics work—the new battery structure was shelved for five years. The patent on the technology was issued in 2004. Soon thereafter, the buried-anode lithium-ion battery attracted the interest of Battelle Ventures, which eventually brought in entrepreneur M. Scott Faris, who launched Planar Energy Devices in 2007 as an NREL spinoff to commercialize the technology.
From NREL's patented design, Planar developed the PowerPlane UX, a coin-sized battery that has a high-charge capacity and minimizes corrosion. And because the solid-state lithium batteries are made from inorganic materials, they don't suffer from potential thermal runaway and fires.
The NREL technology allows for a breakthrough in manufacturing as well.
"With the NREL technology, we can deposit all of the thin films at ambient temperatures, enabling the use of polymers and flexible substrates, as well as new types of high-capacity cathode materials," Pitts said. "Now we can make high-capacity, solid-state batteries on a true roll-to-roll manufacturing line, making it a very low cost approach."
The PowerPlane UX battery might be small, but when it comes to commercializing it, Planar is thinking big—aiming at markets for power tools, renewable-energy storage, and electric and hybrid vehicle batteries, which analysts predict will grow by billions of dollars in the next five years. In recognition of its commercial viability, the microbattery received three awards in 2009: an R&D 100 Award, an FLC Excellence in Technology Transfer award, and the World Technology Network's energy award.
Planar expects to have large-scale buried-anode batteries on the market in two years, said Andrea Wesser, Planar product manager. When it does hit the market, this new technology will change the way many electronic devices are used and designed.
