Page 16 - EngineerIT December 2022

ELECTRONICS

materials of the battery cell and cannot be Did you know that researchers at the CSIR made ground-breaking discoveries in the
observed directly, so Fincher developed evolution of lithium batteries way back in 1974, but due to lack of support and forward
a way of making thin cells using a thinking by government and industry at the time, the fortunes of lithium batteries
transparent electrolyte, allowing the passed South Africa by. The period of 1974 to 1994 is described by Michael Thackeray,
whole process to be directly seen and a major contributor to the development of the lithium battery, as “Twenty Golden
recorded. “You can see what happens Years of Battery Research and Development at the CSIR.
when you put a compression on the There appears to have been a general unawareness in the country to foresee the
system, and you can see whether or not impending impact of lithium battery technology that was to follow the consumer
the dendrites behave in a way that’s electronics boom in the 1990s. Thackeray, sensing a bright future for lithium battery
commensurate with a corrosion process technology and receiving an offer to continue his materials-related lithium battery
or a fracture process,” he says. research at Argonne National Laboratory, left CSIR for the United States in January
The team demonstrated that they 1994. The battery group that remained at CSIR continued to operate for another year
could directly manipulate the growth of before closing its operations. Read more in the August edition of EngineerIT. Read the
dendrites simply by applying and releasing full article here
pressure, causing the dendrites to zig and
zag in perfect alignment with the direction
of the force.
Applying mechanical stresses to the
solid electrolyte doesn’t eliminate the
formation of dendrites, but it does control
the direction of their growth. This means
they can be directed to remain parallel to
the two electrodes and prevented from
ever crossing to the other side, and thus
rendered harmless.
In their tests, the researchers used
pressure induced by bending the material,
which was formed into a beam with a
weight at one end. But they say that in
practice, there could be many different
ways of producing the needed stress. For
example, the electrolyte could be made In fact, a different kind of stress, called stack pressure, is often applied to battery cells,
with two layers of material that have by essentially squishing the material in the direction perpendicular to the battery’s plates
different amounts of thermal expansion, — somewhat like compressing a sandwich by putting a weight on top of it. It was thought
so that there is an inherent bending of the that this might help prevent the layers from separating. But the experiments have now
material, as is done in some thermostats. demonstrated that pressure in that direction actually exacerbates dendrite formation.
Another approach would be to “dope” “We showed that this type of stack pressure actually accelerates dendrite-induced failure,”
the material with atoms that would Fincher says.
become embedded in it, distorting it and What is needed instead is pressure along the plane of the plates, as if the sandwich
leaving it in a permanently stressed state. were being squeezed from the sides. “What we have shown in this work is that when
This is the same method used to produce you apply a compressive force you can force the dendrites to travel in the direction of
the super-hard glass used in the screens the compression,” Fincher says, and if that direction is along the plane of the plates, the
of smart phones and tablets, Chiang dendrites “will never get to the other side.”
explains. And the amount of pressure That could finally make it practical to produce batteries using solid electrolyte and
needed is not extreme: The experiments metallic lithium electrodes. Not only would these pack more energy into a given volume
showed that pressures of 150 to 200 and weight, but they would eliminate the need for liquid electrolytes, which are flammable
megapascals were sufficient to stop the materials.
dendrites from crossing the electrolyte. Having demonstrated the basic principles involved, the team’s next step will be to try
The required pressure is to apply these to the creation of a functional prototype battery, Chiang says, and then
“commensurate with stresses that to figure out exactly what manufacturing processes would be needed to produce such
are commonly induced in commercial batteries in quantity. Though they have filed for a patent, the researchers don’t plan to
film growth processes and many other commercialise the system themselves, he says, as there are already companies working on
manufacturing processes,” so should the development of solid-state batteries. “I would say this is an understanding of failure
not be difficult to implement in practice, modes in solid-state batteries that we believe the industry needs to be aware of, and try to
Fincher adds. use in designing better products,” he says. n

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