While trying to create a rechargeable battery that is able to power electric vehicles (EVs) for hundred of miles on only one charge, researchers have attempted to replace the graphite anodes currently used in EV batteries with lithium metal anodes.
However, while lithium metal extends an EV’s driving extent by 30 to 35 percent, it also shortens the battery’s life because of lithium dendrites, which are small treelike defects that appear on the lithium anode over the course of many charges and discharge cycles. What is worse is that dendrites short-circuit the cells in the battery if they make contact with the cathode.
Stopping Dendrites Expand
For years and years, scientists believed that hard, solid electrolytes, including those made from ceramics, would function best to prevent dendrites from getting to the cell. But the issue with that approach, many discovered, is that it did not stop dendrites from taking shape or ‘nucleating’ in the first place.
Now, experts at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with Carnegie Mellon University, have published a paper in the journal Nature Materials, titled ‘Universal chemomechanical design rules for solid-ion conductors to prevent dendrite formation in lithium metal batteries,’ a new type of soft, solid electrolytes. These electrolytes, made from both ceramics and polymers, can stop dendrites in the early nucleation phase before they can spread and make the battery fail.
Solid-state energy storage technologies, including solid-state lithium metal batteries, which use a solid electrode and a solid electrolyte, are able to provide high energy density merged with safety, but the technology has to bypass various materials and processing challenges.
“Our dendrite-suppressing technology has exciting implications for the battery industry,” said co-author Brett Helms, a staff scientist in Berkeley Lab’s Molecular Foundry. “With it, battery manufacturers can produce safer lithium metal batteries with both high energy density and a long cycle life.”
According to Helms, the new lithium metal batteries manufactured with the electrolyte could also be used to power electric aircraft.
Material Realization of a Rechargeable Battery
To prove the dendrite-suppressing functions of the new soft polymers of intrinsic microporosity, or PIMs composite electrolyte, the team of researchers used X-rays at Berkeley Lab’s Advanced Light Source to generate 3D images of the interface between lithium metal and the electrolyte.
The study and other data confirmed predictions from a new physical model for electrodeposition of lithium metal, which considers both chemical and mechanical features of the solid electrolytes.
“In 2017, when the conventional wisdom was that you need a hard electrolyte, we proposed that a new dendrite suppression mechanism is possible with a soft solid electrolyte,” said co-author Venkat Viswanathan, an associate professor of mechanical engineering and faculty member at Scott Institute for Energy Innovation at Carnegie Mellon University who led the theoretical studies. “It is amazing to find a material realization of this approach with PIM composites.”
A recipient under the Advanced Research Projects Agency-Energy’s (ARPA-E) IONICS program, 24M Technologies, has added these materials into larger format batteries for EVs and eVTOL (electric vertical takeoff and landing) aircraft.
“While there are unique power requirements for EVs and eVTOLs, the PIM composite solid electrolyte technology appears to be versatile and enabling at high power,” explained Helms.