The University of Michigan Chemical Sciences and Engineering team, led by Professor Nicholas Kotov, has developed a “new bio-inspired battery membrane” with recycled Kevlar fibers that could quintuple battery life electric vehicles and have a lifespan of 1,000 cycles.
The research center in Ann Arbor, Michigan, is one of the best in the world, and Kotov, whose research focuses on the development of biomimetic nanocomposites, nanoparticle self-assembly and chiral nanostructures, worked to change the narrative on lithium-sulfur cells. “There are a number of reports claiming several hundred cycles for lithium-sulfur batteries, but this comes at the expense of other parameters: capacity, charge rate, resilience and safety,” Kotov said in a statement. University press. “The challenge these days is to manufacture a battery that increases the cycle rate from the previous 10 cycles to hundreds of cycles and meets multiple other requirements, including cost.”
Lithium-sulfur batteries can afford five times the capacity of standard lithium-ion cells, which are used in electric vehicles. However, as Prof. Kotov mentioned in his quote, the lifespan is greatly reduced due to chemical reactions between molecules. The most common reason for the shortened life cycles of lithium-sulfur batteries is dendrites, which are appendages designed to receive communications from other cells. These can pierce the cell membrane, reducing the life and therefore the life cycle of a battery cell.
Another problem is that polysulfides, or small molecules of lithium and sulfur, can form and flow to the lithium. They bind and cause blockages, reducing the efficiency of the membrane. “The membrane is needed to allow lithium ions to flow from lithium to sulfur and back, and to block lithium and sulfur particles, called lithium polysulfides.”
However, Kevlar, the same material used in body armor, can prevent dendrites from penetrating the membrane by using dense aramid fibers present in the material. The cells developed by Kotov and his team use recycled Kevlar fibers. Kevlar “may enable lithium-sulfur batteries to overcome their Achilles’ heel in lifespan”, caused by the two previously mentioned reactions between molecules.
An example of the Kevlar system is shown in the images below, as the typical Celgard membrane on the left allows lithium polysulfides to flow through. The Kevlar membrane (right) prevented the polysulphides from passing through.
“Achieving record levels for multiple parameters for multiple material properties is what is needed now for car batteries,” Kotov said. Kotov added that the lithium-sulfur battery design is “almost perfect” due to its capacity and efficiency reaching theoretical limits. It can also perform more resiliently than lithium-ion cells in hot and cold climates, both of which affect range and efficiency. However, fast charging could reduce the number of lifespans, Kotov added.
Lithium-sulfur batteries could be a good alternative because sulfur is more readily available and plentiful than cobalt, which is controversial due to its mining practices. However, automakers like Tesla are reducing cobalt in their batteries in the running for other metals, like nickel, instead. Sulfur’s short lifespan and instability, as it changes size by 78% during charging, has reduced the possibility of automakers using it in the past, The Independent reported.
The research was funded by the National Science Foundation and the Department of Defense.
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