Despite billions of dollars in investment and the launch of several high-profile startups, the energy sector still faces a fundamental and seemingly insoluble challenge: it’s very hard to store lots of power in a way that’s compact, long-lasting, and low-cost. A growing number of researchers are hoping to solve that with what are known as three-dimensional batteries, which can take several forms but tend to have porous, sponge-like structures, as opposed to the traditional “2-D” form: thin layers of metal in a liquid electrolyte solution inside a box (see “A Stretchable, Bendable and More Powerful Smart Watch Battery” and “Batteries: Cheapest Form of Grid Power?”).
Over the last several months, a startup called Prieto Battery, spun out of Colorado State University in Fort Collins, has succeeded in producing what founder Amy Prieto calls “the first true 3-D battery that can be charged and discharged, and that will hold a charge”—in other words, that fills the basic requirements of a conventional battery. 3-D batteries could be cheaper to make, faster to charge, safer, smaller, and less environmentally toxic than conventional batteries. What’s more, because they can be made lightweight, flexible, and in an almost limitless variety of shapes, they could offer energy storage applications previously unimaginable.
Prieto’s 3-D solid-state battery represents two radical departures from today’s batteries: what they’re made of and how they’re made. In the Prieto lab, just below the Rocky Mountain foothills, a series of eight shallow water-filled bins sit in a recessed table. Next to the line is a rack with rolls of copper foam of varying densities. The foam is the raw material for the batteries, onto which the anode—made of copper antimonide (copper blended with antimony)—is electroplated. The foam is so porous it’s mostly air, but a small fragment could contain an enormous surface area. Increasing the surface area reduces the distance that the ions have to travel, thus increasing both power and energy density.
Once the foam is coated with the anode, it’s layered with a polymer electrolyte that provides a physical barrier across which ions (but not electrons) can move. Finally, the cathode is applied in the form of a dark, inky slurry. The final product is a foam battery a couple of inches across and the thickness of a sheet of paper. Sealed in a plastic pouch, the Prieto batteries can charge quickly, store up to twice as much energy per unit of volume as conventional batteries, and lack lithium-ion batteries’ unfortunate propensity to overheat.
The idea of porous materials being used for battery components is not new: many conventional lead-acid batteries, for example, use lead foam in the anode. The notion of an entire battery made with a porous internal architecture arose from the work of Debra Rolison, a research chemist at the Naval Research Laboratory who heads the lab’s Advanced Electrochemical Materials Section. Rolison began researching new catalyst materials for fuel cells in the early 1990s, and in 1998 she proposed a battery composed of carbon aerogels—porous materials into which a cathode material can be inserted to create a 3-D battery. When she first presented the idea, she says, “99 percent of the people thought I was wacked out of my brain.” But a number of researchers are now pursuing the concept—some with novel materials such as portabella mushrooms and cellulose from wood pulp.
3-D battery technology like Prieto’s, says Max Hamedi, a Harvard researcher who is working on elastic foam batteries made from wood pulp, “has the potential to surpass any battery that you can build in 2-D systems. This work is just exploding right now.”
Prieto has from the start sought simplicity, using common materials in a low-cost manufacturing process that can easily be scaled up. The company’s first product is not a full battery but a drop-in replacement copper foam anode that will replace graphite anodes in conventional batteries. In September Prieto announced a partnership with Intel that enables the startup to draw on the expertise of the chip maker’s Technology Manufacturing Group. Prieto’s first replacement anodes could be on the market by late 2016, says its founder, and a complete battery could follow by 2018.
There are, of course, other companies driving innovation in solid-state batteries. Sakti3 is working on solid-state lithium-ion batteries that are one-half to one-third the size of conventional systems, with the same energy storage capacity (see “A Breakthrough Battery Gets a Big Backer”). Seeo, a California-based startup focused on solid-state batteries with lithium-metal anodes, was recently acquired by Bosch, one of the auto industry’s major suppliers (see “A Prototype Battery Could Double the Range of Electric Cars”). Neither of these companies uses a 3-D foam architecture.
“We see the potential for Prieto’s technology to contribute to innovations in wearables, where solid-state batteries with high energy density could enable compelling new usages,” says Mark Pontarelli, the general manager of Intel’s internal business incubator. “The copper foam could be used to create batteries that precisely fill empty spaces in a design, providing more battery life without growing the size of the product.”
As Pontarelli indicates, the first applications are likely to be small—in wearable systems and consumer electronics, for instance—but there is no evident reason why foam batteries could not work in electric vehicles and, one day, grid-scale storage systems.
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