With an energy density 2-3 times higher than its competitors, lithium-metal batteries (LMBs) have long been seen as the “ultimate solution” for high-energy batteries.
But tapping this theoretic potential to create electric vehicles, drones, automated aircraft, renewable energy storage and other uses has proven problematic. Safety concerns and comparatively short battery lifespans have kept high-energy LMBs from the market.
Researchers from the UChicago Pritzker School of Molecular Engineering (UChicago PME) and SES AI Corp have shown a new path, demonstrating how optimizing the rates at which the batteries charge and discharge can create longer-lasting, powerful LMBs. In a recent paper in ACS Energy Letters, the team adjusted these rates to create a battery that retained more than 80% capacity after 1,000 cycles, a major increase in performance.
“This exciting new research sheds light on the significant impact of charge/discharge rates on interactions at the component level, uncovering vital degradation mechanisms,” said UChicago PME Prof. Shirley Meng, who was recently named a Liew Family Professor in Molecular Engineering. “The enhanced cycling durability we demonstrated offers a promising direction for the utilization of lithium-metal batteries.”
Charge and discharge
The first few times a battery charges and discharges, a thin film called a solid-electrolyte interphase (SEI) is deposited on the battery’s negatively charged anode. Far from a nuisance, this build-up is actually key to the battery’s performance, forming a protective layer that keeps the battery working better for longer.
Lithium-metal batteries, however, form an unstable SEI. As the battery runs, the lithium ions will continue to plate on the protective film. If the lithium is deposited under the SEI, it forms the protective layer and the battery operates smoothly. But if it develops on top of the SEI, the battery corrodes faster. With an LMB’s unstable film, it can be impossible to tell which is happening.
“In the ideal case, lithium should be deposited under the SEI, which is the solid-electrolyte interface. And then the interface acts as a protective layer, but sometimes it can plate it above this interface, which is not good,” said co-first author Wurigumula Bao, a UChicago PME project scientist at Meng’s Laboratory for Energy Storage and Conversion. “But from the morphological examination on the top of this electrode, we cannot tell this difference.”
A misplaced plating layer can shorten the battery’s lifespan dramatically.
“Although lithium-metal batteries have a very obvious advantage, which is energy density, the problem is that the cycling life is much shorter,” said co-first author Yunya Zhang of SES AI Corp, which is a founding member of the UChicago Energy Transition Network. “With common cycling conditions, the cycling life of a lithium-metal battery is probably three to five times shorter than that of a lithium-ion battery.”
The research team found that a lithium-metal battery that charges slowly but discharges quickly broke past many of these hurdles.