Scientists have uncovered a root cause of the growth of needle-like structures—known as dendrites and whiskers—that plague lithium batteries, sometimes causing a short circuit, failure, or even a fire.
The team, led by Chongmin Wang at the Department of Energy’s Pacific Northwest National Laboratory, has shown that the presence of certain compounds in the electrolyte—the liquid material that makes a battery’s critical chemistry possible—prompts the growth of dendrites and whiskers. The team hopes the discovery will lead to new ways to prevent their growth by manipulating the battery’s ingredients. The results were published online Oct. 14 in Nature Nanotechnology.
Dendrites are tiny, rigid tree-like structures that can grow inside a lithium battery; their needle-like projections are called whiskers. Both cause tremendous harm; notably, they can pierce a structure known as the separator inside a battery, much like a weed can poke through a concrete patio or a paved road. They also increase unwanted reactions between the electrolyte and the lithium, speeding up battery failure. Dendrites and whiskers are holding back the widespread use of lithium metal batteries, which have higher energy density than their commonly used lithium-ion counterparts.
The PNNL team found that the origin of whiskers in a lithium metal battery lies in a structure known as the “SEI” or solid-electrolyte interphase, a film where the solid lithium surface of the anode meets the liquid electrolyte. Further, the scientists pinpointed a culprit in the growth process: ethylene carbonate, an indispensable solvent added to electrolyte to enhance battery performance.
It turns out that ethylene carbonate leaves the battery vulnerable to damage.