Advancing battery powers electric flight and long-range electric cars

In search of a rechargeable battery that can power electric vehicles (EVs) for hundreds of miles on a single charge, scientists have strived to replace the graphite anodes currently used in EV batteries with lithium metal anodes.

But while lithium metal extends the driving range of an EV by 30-50%, it also shortens the life of the battery due to lithium dendrites, small streak-like defects that form on the anode of lithium over the course of many charge and discharge cycles. What’s worse, dendrites short-circuit the battery cells if they come in contact with the cathode.

For decades, researchers assumed that solid, hard electrolytes, like ceramic ones, would work best to prevent dendrites from making their way through the cell. But the problem with that approach, many found, is that it didn’t stop dendrites from forming or “nucleating” in the first place, like small cracks in a car’s windshield that eventually spread.

Now, researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with Carnegie Mellon University, have reported in the journal. Natural materials A new class of soft and solid electrolytes, made of polymers and ceramics, that suppress dendrites at that early stage of nucleation, before they can spread and cause the battery to fail.

The technology is an example of Berkeley Lab’s multidisciplinary collaborations at its user facilities to develop new ideas for assembling, characterizing, and developing materials and devices for solid-state batteries.

Solid-state energy storage technologies, such as solid-state lithium metal batteries, which use a solid electrode and a solid electrolyte, can provide high energy density combined with excellent safety, but the technology must overcome various materials and processing challenges.

“Our dendrite suppression technology has interesting implications for the battery industry,” said co-author Brett Helms, staff scientist at the Berkeley Lab Molecular Foundry. “With it, battery manufacturers can produce lithium metal batteries. safer with high energy density and long life. “

Helms added that lithium metal batteries made from the new electrolyte could also be used to power electric planes.

A gentle approach to dendrite suppression

The key to designing these new soft and solid electrolytes was the use of intrinsically microporous soft polymers, or PIMs, whose pores were filled with nano-sized ceramic particles. Because the electrolyte remains a flexible, soft, and solid material, battery manufacturers will be able to manufacture lithium foil coils with the electrolyte as the laminate between the anode and the battery separator. These lithium electrode subsets, or LESAs, are attractive replacements for the conventional graphite anode, allowing battery manufacturers to use their existing assembly lines, Helms said.

To demonstrate the dendrite suppression characteristics of the new PIM composite electrolyte, the Helms team used X-rays at the Berkeley Lab advanced light source to create three-dimensional images of the interface between the lithium metal and the electrolyte, and to visualize the coating and lithium removal. for up to 16 hours at high current. Continuous and smooth growth of lithium was observed when the new PIM compound electrolyte was present, while in its absence the interface showed telltale signs of the early stages of dendritic growth.

These and other data confirmed the predictions of a new physical model for electrodeposition of metallic lithium, which takes into account the chemical and mechanical characteristics of solid electrolytes.

“In 2017, when the conventional wisdom was that you need a hard electrolyte, we proposed that a new dendrite suppression mechanism be possible with a soft solid electrolyte,” said co-author Venkat Viswanathan, associate professor of mechanical engineering and faculty member at Scott Institute for Energy Innovation at Carnegie Mellon University, who led theoretical studies for the job. “It is surprising to find a materialization of this approach with PIM compounds.”

An award winner under the IONICS program of the Advanced Energy Research Projects Agency (ARPA-E), 24M Technologies, has integrated these materials into larger format batteries for both EV and EVV (Electric Vertical Takeoff and Landing) aircraft.

“While there are unique power requirements for EVs and eVTOLs, PIM Composite Solid Electrolyte technology appears to be versatile and enables high power,” Helms said.