This video is brought to you by Brilliant. 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 one of these videos over here. And thanks
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of you for watching. I’ll see you in the next one.