A group of Harvard researchers announced last week that they have designed a stable lithium-metal solid-state battery that can be charged and discharged at least 10,000 times “at a high current density.”
Lithium-metal solid-state battery cells are widely seen as an important piece of the future for electric cars within the next decade—not just because they can pack more energy into a smaller space, with less weight, but because they eliminate most of the risks of explosion or fire.
Harvard lithium-metal battery – controlled dendrites
Despite those advantages, a potentially shorter lifetime and performance that can degrade over time are among the things that keep the tech from being widely used in EVs today.
Those early failure issues are largely related to dendrites that grow from the surface of the cathode during charging, pushing into the electrolyte and causing shorts within the cell. QuantumScape, one of the companies considered at the lead in solid-state tech that might be used in EVs as soon as the middle of the decade, reportedly spent a decade and more than $300 million on finding the right solid separator to keep lithium dendrites from getting through.
But the materials science researchers claim to have found a solution for that issue that allows dendrites—in a controlled way. The new method effectively “sandwiches” different materials, each with varied stabilities, between the cathode and anode, thus preventing the penetration of lithium dendrites “not by stopping them altogether but rather by controlling and containing them.”
Harvard lithium-metal battery – BLT approach
The researchers liken the lithium-metal battery to a BLT sandwich, in which the lithium metal anode is at the outside, with the lettuce—the coating of graphite—just inside that. A layer of tomatoes—the first electrolyte—is inside that, with the bacon at the core as the second electrolyte.
“Our strategy of incorporating instability in order to stabilize the battery feels counterintuitive but just like an anchor can guide and control a screw going into a wall, so too can our multilayer design guide and control the growth of dendrites,” said Luhan Ye,a graduate student and co-author of the paper on the method, published in Nature. “The difference is that our anchor quickly becomes too tight for the dendrite to drill through, so the dendrite growth is stopped.”
So far the battery is just a “proof-of-concept design”—meaning that it’s far from prototypes, production methods, scaling up, and all the practical aspects that can make a battery that’s a good idea in theory not work so well in practice. But professor Xin Li notes that the flexibility and versatility of the design “makes it potentially compatible with mass production procedures in the battery industry.”
General Motors prototype lithium-metal battery cell
Any solid-state tech for EVs remains a few years from scaling up. Mercedes-Benz is already offering solid-state cells from France’s Bolloré Group in some of its electric buses, although these are a niche product with unusual operating parameters. A number of automakers, including BMW and Honda, see solid-state cells arriving later in the decade. And Toyota, despite being timid on EV plans, is reportedly soon testing solid-state cells in EVs.
And with the BLT idea, whoever commercializes or trademarks the design already has some clever starting points for branding.