Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with Carnegie Mellon University, have reported in the journal Nature Materials a new class of soft, solid electrolytes made from both polymers and ceramics that suppress dendrites in that early nucleation stage, before they can propagate and cause the battery to fail.

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 diverse materials and processing challenges.

Our dendrite-suppressing technology has exciting implications for the battery industry. With it, battery manufacturers can produce safer lithium metal batteries with both high energy density and a long cycle life.

—co-author Brett Helms, a staff scientist in Berkeley Lab’s Molecular Foundry

Helms added that lithium metal batteries manufactured with the new electrolyte could also be used to power electric aircraft.

Key to the design of these new soft, solid-electrolytes was the use of soft polymers of intrinsic microporosity (PIMs), the pores of which were filled with nanosized ceramic particles. Because the electrolyte remains a flexible, soft, solid material, battery manufacturers will be able to manufacture rolls of lithium foils with the electrolyte as a laminate between the anode and the battery separator.

These lithium-electrode sub-assemblies, or LESAs, are attractive drop-in replacements for the conventional graphite anode, allowing battery manufacturers to use their existing assembly lines, Helms said.

To demonstrate the dendrite-suppressing features of the new PIM composite electrolyte, the Helms team used X-rays at Berkeley Lab’s Advanced Light Source to create 3D images of the interface between lithium metal and the electrolyte, and to visualize lithium plating and stripping for up to 16 hours at high current.

The Helms team used X-rays at Berkeley Lab’s Advanced Light Source to create 3D images of the interface between lithium metal and the electrolyte. (Credit: Brett Helms/Berkeley Lab)

Continuously smooth growth of lithium was observed when the new PIM composite electrolyte was present, while in its absence the interface showed telltale signs of the early stages of dendritic growth.

These and other data confirmed predictions from a new physical model for electrodeposition of lithium metal, which takes into account both chemical and mechanical characteristics 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. It is amazing to find a material realization of this approach with PIM composites.

—co-author Venkat

Viswanathan is an associate professor of mechanical engineering and faculty fellow at Scott Institute for Energy Innovation at Carnegie Mellon University and led the theoretical studies for the work.

An awardee under the Advanced Research Projects Agency-Energy’s (ARPA-E) IONICS program, 24M Technologies, has integrated these materials into larger format batteries for both EVs and electric vertical takeoff and landing aircraft, or eVTOL.

This work was supported by the Advanced Research Projects Agency–Energy (ARPA-E) and the DOE Office of Science. Additional funding was provided by the DOE Office of Workforce Development for Teachers and Scientists, which enabled undergraduate students to participate in the research through the Science Undergraduate Laboratory Internships program.

Resources

• Fu, C., Venturi, V., Kim, J. et al. (2020) “Universal chemomechanical design rules for solid-ion conductors to prevent dendrite formation in lithium metal batteries.” Nat. Mater. 19, 758–766 doi: 10.1038/s41563-020-0655-2