At first Amy Prieto didn't know what she was looking at. The video on the laptop screen showed a pair of hands attaching a battery to an LED, which immediately lit up. This was in March of this year, and Prieto, a chemistry professor at Colorado State University and CEO and cofounder of Prieto Battery, was sitting in an Italian restaurant in northern Colorado. Derek Johnson, the company's other cofounder, sat beside her.

"He asked if we could meet somewhere on his way home, which was highly unusual," says Prieto, whose modest, soft-spoken demeanor seems unlikely for someone who runs her own company. She'd worked with Johnson for eight years, starting when he became her first post-doctoral fellow at CSU and then later the director of engineering and technology development at Prieto Battery, a nine-person company. Johnson runs the day-to-day research at the lab, overseeing the R&D of the company's next-generation battery that Prieto had first proposed in 2005. Typically, he'd email updates or call as they happened. Tonight was different. He wouldn't say why, but Johnson wanted to meet.

For all the suspense, this was hardly a secretive huddle in a darkened dive bar. They met at a place close to CSU and Prieto's house. Johnson drank iced tea, Prieto a ginger ale. Prieto's daughter—dad was out of town—ate ice cream. But Prieto had questions. She asked if the video was yet another test. Or maybe it showed a partial version of their battery powering an LED? She was baffled. And then it suddenly clicked for her. This wasn't a test. This was real.

Prieto is at the forefront of one of the most important but least-talked-about technological frontiers. With their fast charging times and high energy density, lithium-ion batteries have revolutionized the way we live. They power our phones, tablets, laptops, and a growing number of electric and hybrid vehicles. They are seldom seen, but we are surrounded by them. And yet even as lithium-ion became the battery chemistry of choice in the '90s, scientists and researchers were already searching for the next big thing in battery technology. Now, with rechargeable devices and electric cars proliferating, the push to find a superior replacement has only increased. But to understand why this is such a challenge, it first helps to know how a lithium-ion battery works.

Lithium-ion, or Li-ion, batteries rely on a delicate balance of power among four core components. The anode and cathode, called electrodes, push lithium ions toward one another across a small sea of conductive liquid electrolytes, releasing the electrons that power a connected device. The electrons flow in one direction when the battery is charging, and the other when it's discharging. Between the two electrodes is a separator, a perforated film soaked in the liquid electrolyte that only lets the ions through while keeping the anode and cathode from touching. If they do make contact, the entire system could short, heating up until the combustible electrolyte bursts into flames.

It's that bursting-into-flames part that has received a lot of attention in the past few years, with a rash of electric-vehicle fires and the occasional laptop blaze grabbing headlines. But the truth is that lithium-ion batteries rarely combust, and gas-powered cars are much more likely to end up as a crispy heap on the side of the road. Although battery fires are a legitimate concern, the impetus to innovate beyond Li-ion is based primarily on energy and the quest to pack more of it into smaller, cheaper spaces.

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As recently as February the post-lithium-ion future of batteries could be summed up in two words: lithium–air. Often described as a battery that breathes, lithium–air batteries use the flow of air to release a huge amount of electrons, or energy, from the anode. This design cuts down on the weight and cost of the overall cell, which translates into vast improvements in energy density. Electric cars, for example, could go from a 100-mile range per charge to as much as 500 miles. And lithium–air seemed to be right around the corner. IBM's high-profile Battery 500 Project hoped to have commercial applications locked down before 2020.

But this past March the head of IBM's project backed away from lithium–air, citing high costs. By June the other major player in lithium–air was out too. The biggest problem was the purity of the O 2 being pulled into the cells, says Jeff Chamberlain, deputy director of development and demonstration at the Joint Center for Energy Storage Research. Any water, CO 2 , or nitrogen could kill the battery and possibly even set it ablaze. The additional cost and complexity of building a suitable filtration system would dull lithium–air's edge over lithium-ion batteries, which continue to see slow but steady power improvements. "It's still better than today's lithium-ion, but at best equivalent with tomorrow's lithium-ion," Chamberlain says.

The rise and fall of lithium–air is indicative of the larger world of battery research: There's no shortage of scientific solutions that seem capable of dethroning lithium- ion, but the road to commercialization is complicated. Despite filing its own alternative battery patent last year, electric carmaker Tesla Motors is developing what it calls a Gigafactory, a $5 billion facility that will allow the company to build 500,000 Li-ion batteries a year. This might be the technology we're stuck with for decades to come—long after its energy capacity has been maxed out.

Maybe the most promising thing about Prieto's battery is that it's still, in fact, a lithium-ion battery. But Prieto's design takes that precarious sandwich of two-dimensional layers—anode, separator, and cathode, with liquid electrolytes acting like an oozing condiment—and mashes it into a thicket of intertwined materials. The anodes and cathodes aren't separate components but, rather, two different coatings slathered on to the same Brillo-like copper mesh. Laying them on top of one another increases their total surface area and shortens the distance that electrons have to travel. Prieto calls this a three-dimensional solid-state lithium-ion battery because its energy flows along all of those coated filaments, instead of swimming in a liquid in one direction or the other.

Matt Nager

If Prieto Battery's 3D design makes it to mainstream production, griping about the limitations of lithium-ion will be all but obsolete. We'll be too busy fast-charging our devices and running them for longer stretches to notice that the underlying ebb and flow of ions hasn't really changed. But to see her battery succeed, Prieto is in the same race against the clock as every other startup.

It took four years for Prieto to form a company and five more to develop a prototype. Meanwhile the major battery makers have been marching inexorably forward, tweaking existing models to eke out more energy density. "With someone like Panasonic, every year their battery is a few percent better than the year before," says Paul Braun, a professor of materials science and engineering at the University of Illinois at Urbana- Champaign. "Compound that over 30 years and that's significant. With small companies and universities, the only way we're going to make an impact is if we provide two times or more better performance."

Braun is hoping to do just that, having spun off his research in porous, or nanostructured, anodes and cathodes into a company called Xerion. Though built differently from Prieto's, his battery also relies on the increased surface area and pathways for electrons and ions that come with using electrodes that aren't solid blocks. Braun believes that his lattice- like anodes and cathodes will provide double or triple the capacity and power of traditional lithium-ion batteries within 5 to 10 years—a common, and fairly ambiguous, time frame in this business.

One of the more successful battery startups, Amprius, is already selling its own nanostructured electrodes to phone makers, providing a 20 percent boost in capacity to existing smartphones. But Amprius is currently at the conservative end of the battery race, using comparatively modest improvements to compete with established players.

Prieto Battery has a two-pronged approach to commercialization. Later this year the startup hopes to begin selling a more traditional drop-in anode that is safer, has three times the energy density, and can be swapped into standard Li-ion cells. Then there's the company's moon shot: the 3D battery whose fivefold increase in total power and nonflammable design could completely reinvent lithium-ion batteries.

For a Moon Shot to work, the rockets need to fire. Or, in the case of Prieto Battery, the LED has to light up. The video that Johnson had Prieto watch at the Italian restaurant that night showed something like liftoff. The video was of the company's 3D battery prototype, and it was incontrovertible proof that they had cracked the final problem.

Complications with that polymer electrolyte—the conductive material between the anode and cathode layers—had essentially brought the battery's development to a halt. And all of a sudden the science was done. "That was really, really cool," Prieto says. "Once we made that breakthrough in the polymer electrolyte, I started realizing that this would actually work."

But it's early for Prieto and Johnson to declare victory. The challenges that remain are of the daunting, startup variety. The biggest? Convincing larger companies to actually build Prieto's 3D batteries. Prieto has a head start, though. Her plan from the outset was to not only design a battery but to develop low-cost, highly modular manufacturing techniques to make it. The company has already created a small pilot production line in its lab space at CSU. The goal was to show companies how to tiptoe into production, as opposed to investing in a $40 million plant.

Incredibly, this production line isn't a miniature clean room or outfitted with vapor traps to suck away hazardous fumes. Prieto's approach largely avoids the toxic chemicals found in standard Li-ion batteries—something she says is "a moral choice." It's an environmental decision that also has potential economic benefits, cutting the expense associated with disposing of or recycling such materials.

Prieto can't share the names of the strategic partners that are showing interest, but she sees her battery's ultrastable chemistry as a perfect initial match for the military's unmanned submersibles, which can't use standard lithium-ion packs because of the fire hazard. And the company plans to get its 3D solid-state cells into a limited number of consumer applications by 2016.

These are the best-case scenarios, of course, and assume breakthroughs that have nothing to do with science. "You can imagine why this was challenging to pitch to investors in the beginning," Prieto says. "On the one hand they want transformational approaches. But it is very hard to quantify, in terms of time and resources, how long it will take to make a major discovery." Now there's no more guessing. "I'm really excited," Prieto says. "The major discoveries are done."

Which leaves her next-generation batteries where so many promising technologies ultimately lie: at the mercy of the people with the money.

How a 3D Battery Works

Matt Nager

Because of its nontraditional, mesh-like design, Prieto Battery's 3D battery has much more surface area than a typical lithium-ion battery. That means it can potentially hold up to five times more energy and can charge in a fraction of the time. Each battery starts out with a copper-foam substrate that gets layered with the main battery components (1). First, the anode, which is made of the copper antimonide, is electroplated on to the substrate (2). The second layer, called the polymer electrolyte, keeps the anode and cathode layers from touching, which can cause shorts and fires (3). The polymer electrolyte also safely allows ions to travel between the anode and cathode. By using a solid-state electrolyte as opposed to the standard yet highly flammable liquid electrolyte, the 3D battery is largely fireproof. The final cathode layer is applied in the form of a slurry (4) that covers everything and gives the battery structure when it sets (5). The battery's unique design also allows it to be shaped for odd spaces before the final cathode layer is applied.

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