The battery is developed by SolidEnergy Systems, a spinout of MIT founded in 2012. Qichao Hu, founder and former MIT postdoc, explained how it works in a news post on the MIT website.
Conventional rechargeable lithium batteries are used in a wide range of consumer products, ranging from phones to electric cars. They are based on lithium ion technology. While more durable and longer-lasting than alkaline batteries, their performance could be better. Hu and his team set out to build a lithium-based battery that could replace lithium ion tech.
The result is an “anode-free” lithium metal design. Lithium ion batteries have a graphite anode. SolidEnergy replaced this with a very thin sheet of lithium-metal foil. The idea is simple: lithium metal can hold many more ions than graphite so it should be able to power the battery for much longer.
The first prototype was demonstrated in October 2015. It was so successful that SolidEnergy was awarded $12 million in investments to keep developing its product. Now, it’s back with a near-final version that’s ready to go into consumer products.
SolidEnergy’s batteries have two times the energy density of a lithium-ion battery. That allows device manufacturers to create a battery half the size of current models but with the same capacity. Alternatively, a battery of the same physical size as a commercially available lithium ion one today would have double the capacity.
“With two-times the energy density, we can make a battery half the size, but that still lasts the same amount of time, as a lithium ion battery. Or we can make a battery the same size as a lithium ion battery, but now it will last twice as long,” said Hu.
Unlike other emerging battery technologies, the lithium-metal cells are highly scalable. They are also safe and long-lasting, suitable for almost immediate use in all the product families lithium ion is used for. Perhaps even more significantly, SolidEnergy can build its batteries using existing lithium ion manufacturing equipment, leading to a high return on investment for current battery brands that decide to switch to lithium-metal production.
It’s taken Hu a long time to get the technology to where it is today. Lithium metal batteries have been viewed as “kind of the holy grail” for batteries for decades but all previous efforts to create rechargeable ones have failed. Lithium metal reacts poorly with the battery’s electrolyte, creating resistance that reduces performance, generates heat and can lead to short circuits. Attempts to make the batteries safer have further reduced the battery’s performance, requiring it to be heated up before it starts working.
Hu faced similar challenges. He replaced the graphite anode with the lithium-metal sheet while working as a postdoc in the group of MIT professor and battery researcher Donald Sadoway. While this greatly reduced the size of the battery, it also introduced a major problem. Hu found the cells didn’t work until they were heated to 80 degrees Celsius, far too high for consumer electronics.
By persevering, Hu developed a solid and liquid hybrid electrolyte solution that reduced the need for heat. Additional innovations included a liquid electrolyte that isn’t flammable, preventing the battery from bursting into flame, and chemical modifications to stop the battery’s internals from reacting with the lithium metal. “Combining the solid coating and new high-efficiency ionic liquid materials was the basis for SolidEnergy on the technology side,” Hu said.
A few years later, SolidEnergy is ready to start production of lithium metal batteries. Hu is confident they are as safe and long-lasting as lithium ion ones while boasting double the energy density. The first smartphones for smartphones and wearables will be available early next year, followed by units for electric cars in 2018. Cells for drones will arrive first of all, however, demonstrating the benefits of lithium-metal technology from November 2016.
