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Being cheaper, more energy dense and longer lasting than lithium-ion technology, lithium-sulfur
batteries may be the holy grail of power storage. Besides fueling electric vehicles (EVs) adoption,
they could turbocharge the integration of renewables into our energy grid. However,
a technical fault has been holding back their economic feasibility…until now. An accidental,
yet major discovery may have finally unlocked their full potential. Could this lithium sulfur
discovery make it the future of battery storage? I’m Matt Ferrell … welcome to Undecided. Energy storage is the key to the future of
renewables. It’s why I’m so fascinated by different battery technologies and talk
about them so much. The king of the hill right now is lithium ion, which we’ve all used
and know well. We’ve got them in our pockets in smartphones, on our wrists with smart watches,
and now in our cars. However, there’s another kid in town that’s
been getting some attention: lithium-sulfur batteries. Over the last few years, they’ve
been touted as a strong candidate for marking a new energy storage era, but they haven’t
made it to the market yet. Now, a group of chemical engineers from Drexel University
have found a way to enable their real-world application. I’ll get to that in a minute,
but first let’s look at why a lithium-sulfur battery could be a revolutionary upgrade of
lithium-ion technology. The cathode of lithium-ion batteries is mostly
made of critical minerals such as nickel and cobalt. Yet, our hunger for EVs is driving
up the demand for these two raw materials. According to a recent study, Europe may face
nickel and cobalt shortages as early as 2030. The report also predicts that the EU will
need 100% more nickel and 330% more cobalt to become climate neutral by 2050. While our
planet stock may be enough to meet these targets, cobalt and nickel sourcing is not keeping
up with the demand. And that’s partly because of a slow progress in developing new mines.
For example, in the US it takes up to 10 years to secure a mine permit. On top of that, we’re
lacking processing facilities to turn the minerals into battery-friendly components.
Coupled with an insane demand, the slow-moving supply chain leads to shortages of battery
ingredients and therefore skyrocketing prices. Besides these problems, there are sustainability
issues behind their production. 70% of global cobalt comes from the Democratic Republic
of Congo (DCR), which has had some serious issues with forced and child labor. As for
nickel processing, we currently rely on wasteful and carbon-intensive methods. In particular,
Indonesian nickel is the least environmentally friendly, and there are concerns that they
are dumping mining tailings into the sea, polluting the waters as well. In contrast, being the 10th most abundant
element on Earth, sulfur is much easier to find than cobalt and nickel. Plus, it’s
obtained as a by-product of various industrial processes such as petroleum refining. In other
words, it’s a cheaper and greener feedstock. That’s why introducing sulfur in the cathode
formulation would relieve the pressure on the EV supply chain and could reduce cars’
cost. Perhaps one of the chief benefits would be that a byproduct could be turned into a
useful product. Aside from saving on raw materials, using
lithium-sulfur batteries could achieve up to 8x greater energy density than lithium-ion
designs. What does that mean in practice? For instance, if you were to swap your EV
lithium-ion battery with a lithium-sulfur one, you could drive your car roughly 8x longer
without needing a recharging station. Or keep your existing range with a much smaller, lighter,
and cheaper battery pack. However, lithium sulfur batteries are not
flawless. Their major problem is the so-called polysulfides shuttle. Basically, when the
battery is discharging, an oily carbonate-based electrolyte carries lithium ions from the
anode to the cathode. Here, the lithium ions react with the sulfur to form lithium sulfide.
Well ... it's a bit more complicated than that, but the key point is that the reaction
with the carbonate electrolyte creates an irreversible product. The trouble is that
some of these compounds get lost into the electrolyte solution and during the charging
stage are shuttled from the cathode towards the anode. Once they get there, polysulfides
may convert into a solid form and cover the electrode with an insulating layer. Besides
blocking the transport of lithium ions during the next discharging cycle, the irreversible
buildup of this barrier bites into the cathode. You may see why these mechanisms reduce both
the battery capacity and charging/discharging efficiency. Crazy as it sounds, a study found
that the aggressive reaction between polysulfides and the carbonate electrolyte solution may
shut down lithium sulfur batteries after the first cycle. In the best case scenario, you
can recharge these devices no more than 100 times. And that’s nothing when you think
that commercial lithium-ion batteries can last 2,000 cycles or more. That’s where
Drexel researchers’ fortuitous light bulb moment comes in. It’s not the first time scientists have
found something by chance. Think of viagra for instance. It was being tested as a heart
medication when a certain … um … let’s call it “side effect” caught their attention.
Well, this lithium-sulfur discovery isn’t x-rated, but could lead to a new path for
commercializing lithium sulfur batteries. With the aim of preventing polysulfides formation,
the Drexel team tried to isolate sulfur from the carbonate solution by locking it inside
the micropores of a carbon nanofiber matrix. As described in their paper published last
February, they attempted that by using a vapor deposition technique. Yet, something didn’t
quite work as expected. Instead of being trapped within the carbon framework, sulfur particles
were just lying on top of its surface. And that’s when something even more unexpected
happened. Despite sulfur particles and carbonate solution coming into contact, researchers
couldn’t see any polysulfides. Puzzled by their experiment outcome, they repeated the
test over 100 times. I reached out to Dr. Vibha Kalra, the paper’s lead author, to
find out more on their lucky discovery. “The first time we got this data, we thought
it was an artifact. And that's one of the reasons we ran almost a hundred cells. But
of course, in addition to the repeatability aspect, we did a lot of other electrochemical
tests to make sure that we were truly seeing a direct conversion from sulfur to lithium
sulfide without polysulfides. It took us months to convince ourselves that this is truly a
redox of sulfur going to lithium sulfide. And that's what's giving us this very high
energy storage.” After further investigation, scientists figured
out that, when changing from gas to solid, such as during vapor deposition coatings,
sulfur turned into one of its most elusive forms: The so-called monoclinic gamma-phase
sulfur. This doesn’t react with the carbonate-based electrolyte, which explains why polysulfides
were nowhere to be seen. What nobody can still explain is how they created that phase, as
it’s very rare and supposed to be unstable below 95 °C (203 °F). Despite the mystery,
after a year of testing Dr. Kalra and her co-workers proved their sulfur cathode stabilization
over 4,000 charge-discharge cycles, which is about 2x the duration of a lithium-ion
battery. To add to that, their initial battery capacity is about 3x that boasted by the lithium-ion
competition. Although this is not the first time scientists
designed high-performance lithium-sulfur batteries, the Drexel group’s magic trick is bringing
the device closer to mass production. Why’s that? Their unique solution eliminates the
polysulfide creation completely. While other researchers have tried to minimize the effects
by replacing the benchmark carbonate electrolyte with an ether-based solution, which doesn't
react in the same way. While this does address some of the polysulfide issues, it doesn't
stop the formation and also introduces a safety concern. These alternative electrolytes contain
compounds with boiling points as low as 42 °C (ca. 108 °F). As the battery warms up
during its operation, this will likely evaporate and the pressure buildup could then cause
battery damage. It’s a big engineering issue. Aside from greater safety, Dr. Kalra brought
up another crucial advantage in using carbonate electrolyte. “Carbonate electrolyte has been the electrolyte
of choice for the lithium industry for the last 30 years. The industry has developed
a lot of knowhow on these carbonate electrolytes. And that includes a wide range of additives
that perform a wide range of functions, such as flame retardancy, solid electrolyte interface
(SEI) formation and so on.” Which makes sense. It’s much easier to scale
something up when using well-established industrial practices, right? As a bonus of their fortunate sulfur-based
cathode stabilization, researchers said they could try their luck using sodium instead
of lithium for making the anode. And that would be a big improvement. To begin with,
sodium is around 1,400x more abundant than lithium in the earth’s crust. Extracting
and purifying lithium is more tricky and expensive than sodium as well. Just like cobalt and
nickel, conventional batteries’ keystone has been experiencing supply crunches and
rising prices. Since the beginning of 2022, the price of lithium doubled. In China, which
is by far the world’s largest EV battery manufacturer, lithium carbonate, the most
common battery-grade lithium form on the market, saw a 7-fold price increase over the last
year. You probably see why using sodium would make the battery way more affordable. Lithium sourcing poses sustainability risks.
Last January, green activists forced the Serbian government to scrap the Rio Tinto license
for developing what would have been Europe’s biggest lithium mine by output. Protesters
argued that the lithium mine would have polluted local water and land. Besides contaminating
it, lithium extraction consumes a lot of water. To be more specific, around 500,000 gallons
per ton of lithium. There are new techniques that are helping with that, which I’ve talked
about in previous videos. I’ll include links to those in the description. Anyway, the sodium incorporation is not on
top of Drexel’s agenda as the team will first have to resolve the scientific and technological
challenges associated with the current setup. “So, scientifically we wanna understand
the chemistry more and we want to more clearly answer the questions of how we are stabilizing
the gamma sulfur at room temperature when it's known to not stabilize under 95 °C (203
°F). We also want to understand how this particular crystal structure is enabling a
complete change of redox phenomena in the lithium sulfur batteries. Technologically,
we have run over a hundred cells to ensure the repeatability and reproducibility of our
data at the lab level. So, the technological steps would be to scale up the production
of this gamma sulfur and build prototype level batteries.” This sounds like a lot of work. So, how long
will it take? “We've been talking to a lot of industry
folks to get an understanding of the steps beyond where we are right now. And our understanding
for such a technology would be more in the range of five to six years.” I don’t know about you but this is much
sooner than I expected. Also, assuming this technology eventually pans out, it won't just
improve EV range. Dr Karla highlighted some possible use cases. “So I feel this could fit into many applications.
For example, something like drones, right? Where the weight is an issue and at the same
time we do need longer run times. Aerospace industry is another direction. So, there's
a lot of different applications.” But Dr Karla’s research group is not the
only one advancing lithium sulfur battery technology. Interestingly, there’s a company
who’s managed to accomplish a version of the carbon nanofiber matrix approach … somewhat
similar to what Drexel’s team was working on originally. Lyten claims to have caged
sulfur into 3D graphene structures, which mitigates the polysulfide shuttle effect.
Additionally, their architecture features a coating on top of their lithium anode to
inhibit the growth of dendrites, which is the other major cause for the failure of lithium
sulfur batteries. As heralded by the California-based firm in a press release, their LytCell™
prototype battery can run for over 1,400 cycles under the Department of Defense test protocols.
While their battery lifespan is not as long and robust as that measured by Drexel in the
lab with their discovery, Lyten seems to be one step ahead along the way to the market.
With a throughput of a quarter of a million cells per year, Lyten’s pilot plant is supposed
to go online at some point in 2022. Drexel's unexpected yet radical achievement
may be finally pulling the sought-after lithium sulfur battery within commercial reach. With
lower cost, higher power density and greater durability, this technology would change the
way we think about energy storage for good. Having said that, scientists will still need
to prove their optimized device outside of the lab. So, our cars, smartphones and drones
will have to wait a little longer before being supercharged to the next level. I’m pretty
excited by what this could mean for the future of our EVs and renewable energy. If you’d like to learn more about the science
behind lithium ion batteries and chemical reactions, I'd strongly recommend checking
out Brilliant. They have fantastic interactive courses, like the Electricity and Magnetism
course, that have helped me to get a better understanding of how current works. But if
you really want to get your head wrapped around some of what we covered with lithium sulfur
batteries and the chemistry behind it, The Chemical Reaction course has your back with
topics like ions and charge, as well as how chemical reactions are dominated by the movement
of electrons within and between substances. I had a good time going through both of these
and really enjoy being able to learn at my own pace. All of the concepts are taught through
fun and interactive challenges to help you understand the "why" of something ... not
just the "how." It helps to develop your intuition, which is my absolute favorite part about Brilliant.
Over the years I’ve found that’s how I learn best. Go to https://brilliant.org/Undecided
to sign up for free. And also, the first 200 people will get 20% off their annual premium
membership. Thanks to Brilliant and to all of you for supporting the channel. So have you come to a decision on this? Do
you think lithium-sulfur batteries will become one of the go to energy storage technologies?
Jump into the comments and let me know. If you liked this video, be sure to check out
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Jamie Higgs and Foxman150. And thanks to all of you for watching. I’ll see you in the
next one.
