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Sustainable Energy

Better Lithium Batteries to Get a Test Flight

The batteries should last twice as long as comparably sized rivals.

Scientists have known for decades that lithium-metal batteries offer a powerful combination of energy density and compactness. Unfortunately these batteries also present challenges: they are difficult to recharge and they have an unfortunate tendency to burst into flame.

Massachusetts-based startup SolidEnergy Systems, spun out of the MIT lab of Donald Sadoway in 2012, claims to have solved these problems with a novel anode structure and hybrid electrolyte. Qichao Hu, SolidEnergy’s founder, first showed a prototype last fall that is half the size of an iPhone 6 battery and offers more battery life per charge. The company says it will sell batteries for smartphones by early next year, and for electric vehicles in 2018. First, though, it’s going after a more specialized market: drones.

Specifically, Hu points to the high-altitude drones and balloons being developed to provide Wi-Fi in remote areas. “They need to be powered by batteries, but the current lithium-ion battery lifetime is very short and the batteries are heavy.” SolidEnergy’s new battery, he says, provides “the same capacity at half the volume and half the weight.”

Last fall SolidEnergy showed a prototype that's half the size of an iPhone 6 battery but offers more battery life per charge.

Selling batteries for drone makers could be a clever means of entry for a new battery company, many of which have had trouble competing with established battery providers like Panasonic, which has a multi-billion-dollar contract to supply electric-car maker Tesla with batteries. But while SolidEnergy’s technology is novel, it is still unproven at the scale necessary to grab a portion of the growing drone market, to say nothing of cell phones and electric vehicles.

Lithium-ion batteries, which are found in the preponderance of today’s cell phones and electric vehicles, use a variety of lithium-oxide compounds for the cathode, and a non-lithium material (usually graphite) for the anode. Lithium-metal batteries, on the other hand, use a metallic-lithium anode. It’s long been known that lithium-metal batteries offer higher energy densities, but their volatility makes them problematic.

SolidEnergy’s product is a lithium-metal battery that has a thin, high-energy anode made of lithium-metal foil, rather than the more common graphite. SolidEnergy’s key innovation, however, is in the electrolyte. To reduce the anode’s tendency to become “mossy,” or covered in bumps that tend to cause short circuits, Hu developed a hybrid electrolyte that consists of a thin, solid coating on the anode, which protects the lithium metal from reacting with the volatile electrolyte, and a liquid electrolyte in the cathode, which helps the battery function at lower temperatures.

The efficacy of the technology is hard to judge at this point because Hu has not published his work in a scientific journal. And SolidEnergy now faces the challenge that has derailed many promising battery startups: bringing the technology to market.

Hu launched SolidEnergy just as the battery startup A123 was filing for bankruptcy. “We had no facilities, no funding, no labs to build batteries,” Hu recalls. A visit to A123’s Waltham, Massachusetts, lab resulted in an unusual arrangement: the new company would use A123’s manufacturing line. “They had a nice facility to build batteries and they basically taught me how to build them,” Hu says. When A123 was acquired by the Chinese conglomerate Wanxiang Group in 2013, Hu signed an agreement to continue using the facility. That agreement expires this fall, and SolidEnergy is moving into more spacious quarters in Woburn. 

Using A123’s facility, says Hu, forced SolidEnergy to develop a prototype device that could be built using conventional lithium-ion manufacturing tools. “If we had built our own labs we would have been focused on materials, and we would basically have to develop an entire manufacturing process around it,” says Hu. “That’s the biggest issue with battery companies: they start with very interesting materials, and then invent a process around them that is not scalable. For us it was the opposite: we had to design a material that we could plug into a large-scale manufacturing line.”

Still, some question Hu’s ambitious schedule. “To go from a working prototype in October 2015 to consumer batteries in early 2017 and EVs in 2018 is an incredibly aggressive timetable,” says Jim McDowall, director of business development at battery maker Saft, in an e-mail.

A new report from Lux Research finds that a new energy storage technology costs about $1 billion over six years to bring to market. SolidEnergy has raised $18 million in two funding rounds to date.

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Last fall SolidEnergy showed a prototype that's half the size of an iPhone 6 battery but offers more battery life per charge.

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