Ally Winning, European Editor, PSD
Researchers around the world are looking at different battery chemistries, trying to find a battery that can improve on the lithium-ion ones that we use today. A better battery would offer faster charging, higher capacity, a longer lifespan and be safer. Probably the new battery chemistry that offers the greatest short term potential is lithium-metal. These batteries have an anode that is made of lithium itself, whereas the anode in a Li-ion battery is made from graphite, which acts as a host for the lithium ions. Instead of only a portion of the anode being useful, the whole of a lithium-metal anode is usable, giving a theoretical storage capacity that is half again as much as a Li-ion battery of a similar size. Lithium-metal batteries have been researched for several decades, and there’s one remaining problem that needs to be overcome before their use can be more widespread. As meal accumulates on the battery’s electrodes, thin, metallic structures called dendrites grow. The dendrites can degrade battery performance and lead to failures which, in some cases, can even ignite fires. If dendrites could be stopped from forming, then the full potential of lihium-metal batteries could be reached.
A new study by Stanford researchers has looked at the problem of dendrites from a theoretical perspective. A paper from the study has recently been published in the Journal of The Electrochemical Society. It describes how the researchers developed a mathematical model that brings together the physics and chemistry involved in dendrite formation. The new model offers the insight that swapping in new electrolytes – the medium through which lithium ions travel between the two electrodes inside a battery – with certain properties could slow or even stop dendrite growth.
The cause of dendrite formation has been difficult to find, Laboratory work is labor intensive, and results have proven hard to interpret. The researchers developed a mathematical representation of the batteries’ internal electric fields and transport of lithium ions through the electrolyte material, alongside other relevant mechanisms.
With the results of the study in hand, other researchers can focus on physically plausible material and architecture combinations. “Our hope is that other researchers can use this guidance from our study to design devices that have the right properties and reduce the range of trial-and-error, experimental variations they have to do in the lab,” Hamdi Tchelepi, a professor of energy resources engineering at Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth). said.
The new strategies for electrolyte design indicated by the study include pursuing materials that are anisotropic, meaning they exhibit different properties in different directions - like wood, which is stronger in the direction of the grain. In the case of anisotropic electrolytes, these materials could fine tune the complex interplay between ion transport and interfacial chemistry, thwarting buildup that proceeds dendrite formation. The researchers say that some liquid crystals and gels display these desired characteristics, the researchers suggest.
The study also suggests the usefulness of battery separators – membranes that prevent electrodes at opposite ends of the battery from touching and short-circuiting. New kinds of separators could be designed that feature pores which cause lithium ions to pass back and forth through the electrolyte in an anisotropic manner.
“An enormous amount of research goes into materials design and experimental verification of complex battery systems, and in general, mathematical frameworks have been largely missing in this effort,” said co-author Daniel Tartakovsky, a professor of energy resources engineering at Stanford.
This work was funded by the Air Force Office of Scientific Research, Hyundai Motor Group, and by a gift from TotalEnergies.