Published on April 6th, 2018 | by Nicolas Zart0
Self-Healing Lithium-Metal Anodes for Higher Energy Density Batteries
April 6th, 2018 by Nicolas Zart
As part of the ever-evolving improvement of battery technology, there’s a lot of anode research going on around the world. One idea is to replace commonly used graphite with lithium metal for the anode, and that may have just gotten a notable boost thanks to some research out of New York State’s Rensselaer Polytechnic Institute.
Self-Healing Lithium-Metal Anodes = Better Lifespan for Better Energy Density
The race to much better energy density has not let off for well over a decade, and it seems to be growing stronger. Battery density has gotten better and its price has come down, but there’s plenty of room to improve. Those breakthroughs were mostly made by using different chemistries, but sometimes it’s just about improving known chemistries, including some known chemistries that offer high energy density (highly desirable in electric vehicles since it means more driving range for the same weight, or the same driving range at a lower weight).
One of the biggest challenges with certain battery chemistries is deterioration and loss of energy storage capacity due to dendrite buildup — this has left researchers unable to squeeze enough lifespan out of the batteries for commercial competitiveness. One potential new solution is to use heat to allow the lithium-metal battery to self-heal — that is, to eliminate dangerous dendrite buildup in its anodes. Dendrite buildup on lithium-metal electrodes reduces efficiency and eventually leads to the battery “wearing out,” to use a non-technical term. As a battery charges and discharges, dendrites form. The quicker the dendrite buildup occurs, the quicker the battery’s energy storage capacity falls below consumer acceptability. Think of it like plaque on your teeth — the longer you leave it there, the more likely it is to create cavities and shorten the “useful lifespan” of your teeth.
According to a piece on Green Car Congress, the new heating solution results in lithium dendrites merging and fusing into a uniform (smooth) surface. This also eliminates risks of electrical shorting in the battery cells and packs. Here’s more:
Despite their extremely high energy density, lithium (Li) metal electrodes are not currently deployable in commercial rechargeable batteries because electrochemical plating and stripping invariably leads to growth of dendrites that reduce coulombic efficiency and eventually short the battery. Numerous approaches have been proposed to eliminate dendrite formation.
Now, a team from Rensselaer Polytechnic Institute (RPI) is taking essentially the opposite approach. The researchers ramped up the current density (charge-discharge rate) of the battery, thereby triggering extensive self-heating of the resulting dendrites, resulting in the surface diffusion of lithium—in other words, spreading the dendrites into an even layer. A paper on their work is published in the journal Science.
One of the original researchers, Lu Li, explains it thusly: “It is generally accepted that the dendrite problem is exacerbated at high current densities. Here, we report a regime for dendrite evolution in which the reverse is true. In our experiments, we found that when the plating and stripping current density is raised above ~9 milliamperes per square centimeter, there is substantial self-heating of the dendrites, which triggers extensive surface migration of Li. This surface diffusion heals the dendrites and smoothens the Li metal surface. We show that repeated doses of high-current-density healing treatment enables the safe cycling of Li-sulfur batteries with high coulombic efficiency.”
Technically, by using the battery’s internal resistive heating, also known as Joule heating, which is the result of the metallic material resistance to current flow, you can smoothen out the dendrites — as demonstrated in a proof-of-concept using a lithium-sulfur battery.
Battery breakthroughs are something we’ve become used to over the years. The frenetic pace of development shames the petroleum industry and the billions of dollars given to it each and every year for an ever-elusive fuel source.
Lithium batteries have taken on the main electric mobility load over the past decade, and its exotic chemistries keep on hinting at ever more performance and lifespan. Self-healing lithium-metal anodes seem like another positive step forward.