Vibha Kalra, PhD
America’s growing demand for electric vehicles (EVs) has shed light on the
significant challenge of sustainably sourcing the battery technology
necessary for the broad shift to renewable electric and away from fossil
fuels. In hopes of making batteries that not only perform better than those
currently used in EVs, but also are made from readily available materials, a
group of Drexel University chemical engineers have found a way to introduce
sulfur into lithium-ion batteries — with astounding results.
With global sales of EVs more than doubling in 2021, prices of battery
materials like lithium, nickel, manganese and cobalt surged and supply
chains for these raw materials, most of which are sourced from other
countries, became bottlenecked due to the pandemic. This also focused
attention on the primary providers of the raw materials: countries like
Congo and China; and raised questions about the human and environmental
impact of extracting them from the earth.
Even before supply and demand threw battery materials sourcing into chaos,
the industry had been chasing a potential solution: sulfur. The element’s
natural abundance and chemical structure allow batteries to store more
energy and could be an environmental and commercial windfall. A recent
breakthrough by researchers in Drexel Engineering, published in
Communications Chemistry, provides a way to sidestep the obstacles that have subdued lithium- sulfur
(Li-S) batteries in the past, finally pulling the sought-after technology
within commercial reach.
Their discovery is a new way of producing and stabilizing a rare form of
sulfur that functions in carbonate electrolyte — the energy-transport liquid
used in commercial Li-ion batteries. This development would not only make
Li-S batteries commercially viable, but they would have three times the
capacity of Li-ion batteries and last more than 4,000 recharges — the
equivalent of 10 years of use, which is also a substantial improvement.
“Sulfur has been highly desirable for use in batteries for a number of years
because it is earth-abundant and can be collected in a way that is safe and
environmentally friendly. And as we have now demonstrated, it also has the
potential to improve the performance of batteries in electric vehicles and
mobile devices in a commercially viable way,” said
Vibha Kalra, PhD
, George B. Francis Chair professor in the College’s Department of Chemical
and Biological Engineering and one of the lead researchers on the project.
“At first, it was hard to believe that this is what we were detecting,” said
Rahul Pai, a doctoral student in the chemical and biological engineering and
coauthor of the research. “In the last century there have only been a
handful of studies that produced monoclinic gamma sulfur and it has only
been stable for 20-30 minutes at most. But we had created it in a cathode
that was undergoing thousands of charge-discharge cycles without diminished
performance.”
After more than a year of testing, the sulfur cathode remains stable and, as
the team reported, its performance has not degraded in 4,000
charge-discharge cycles, which is equivalent to 10 years of regular use.
And, as predicted, the battery’s capacity is more than three-fold that of a
Li-ion battery.
“While we are still working to understand the exact mechanism behind the
creation of this stable monoclinic sulfur at room temperature, this remains
an exciting discovery and one that could open a number of doors for
developing more sustainable and affordable battery technology,” Kalra said.
Replacing the cathode in Li-ion batteries with a sulfur one would alleviate
the need for sourcing cobalt, nickel and manganese. Supplies of these raw
materials are limited and not easily extracted without causing health and
environmental hazards. Sulfur, on the other hand is found everywhere in the
world and exists in vast quantities in the United States because it is a
waste product of petroleum production.
Kalra suggests that having a stable sulfur cathode that functions in
carbonate electrolyte, will also allow researchers to move forward in
examining replacements for the lithium anode — which could include more
earth-abundant options, like sodium.
“Getting away from a dependence on lithium and other materials that are
expensive and difficult to extract from the earth is a vital step for the
development of batteries and expanding our ability to use renewable energy
sources,” Kalra said. “Developing a viable Li-S battery opens a number of
pathways to replacing these materials.”
In addition to Kalra and Pai,
Maureen Tang, PhD
, an associate professor, and Arvinder Singh, PhD, who was a postdoctoral
researcher, all in Drexel Engineering’s Department of Chemical and
Biological Engineering, are contributing to this research. It is supported
by the Drexel Ventures Innovation Fund and the National Science Foundation.
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