Back in 2021 I made a video looking at a very
promising battery technology that apparently had several competitive advantages over the
market dominant lithium ion. The new upstart used a lithium sulfur chemistry. According to
the Encyclopaedia of analytical science sulfur is the 10th most abundant material on earth,
available in the ocean, in the atmosphere, in the Earth's crust, and in practically all
plant and animal life. Enthusiastic proponents of lithium sulfur technology suggest it could,
in theory, store as much as five times more energy than existing Lithium-ion batteries.
It's quite a claim isn't it? And one that's right now probably provoking an understandably
sceptical reaction in you good folks who've been patiently watching video after video from dozens
of YouTubers like me over the past few years all telling you about the next game changing battery
technology that's going to disrupt the market! And sure enough, as I discovered when I made that
first video, early versions of the chemistry did have significant shortcomings. We'll have a look
at what they were in a moment but essentially they resulted in a battery that was pretty
unstable, with an impractically short cycle life, and an inherently slow power performance.
Scientists in various research facilities around the world have been working on the problem
since the early 2000s and by the time we took a look at progress 18 months ago or so there
were a couple of promising approaches in the offing. Since then even more new scientific
research papers have been published outlining yet more alternative approaches that also claim to
improve performance of lithium sulfur chemistry. So what's going on then? Like who's actually
got the best technology here and is there a genuine possibility that one of this lot
might actually successfully bolt one of their batteries to anything useful in the near
future, like an electric vehicle for example? Hello and welcome to Just Have a Think. We'll
try to establish whether this lithium sulfur idea has got any realistic chance of disrupting the
energy storage market a bit later in the video, but first of all let's take a quick look at how
it works and what caused those initial problems. The basic principle of energy storage using
electrodes and a liquid electrolyte is one that will no doubt be familiar to you. In a typical
lithium-ion battery cell, lithium atoms are stored in the crystalline structure of the anode
in a process the scientists call intercalation. When a load is attached to the cell the lithium
ions travel across the electrolyte and electrons travel out through a circuit. Then they hook
up again on the cathode side, which in the case of an NMC battery contains minerals like
nickel, manganese and cobalt, hence the name. Lithium-sulfur chemistry has some very
specific differences to that setup. For a start its cathode doesn't contain any nickel,
manganese or cobalt. I'm sure you've heard all sorts of terrible things about those critical
minerals in the news over the past few years, so taking them out of battery chemistries wherever
possible is probably not a bad thing to aspire to. Inside a lithium-sulfur battery cell the lithium
reacts with the solid sulfur to create what are known as polysulfides which are soluble in the
electrolyte and are therefore free to float across the separator and over to the anode
on the other side. Sulfur itself is actually an electrical insulator so in order for this
chemistry to work at all the sulfur has to sit on some kind of electrically conductive material.
If you just stuck a solid lump of sulfur into the cell then at best you might get some small
interactions at the surface but that's about it. What you need is for the sulfur to be highly
distributed on some kind of conductive scaffold, and developers have been playing with all sorts of
ideas for this in recent years including the use of things like carbon nanofibers or exfoliated
graphite, which is also a nanomaterial, or even a very exotic substance called Bucky
Balls or Buckminster Fullerene to give it its proper name. Fully explaining what they are
would take another entire video which would probably melt my brain but suffice to say
they're made up of 60 carbon atoms fused together into a sphere and they're only found in
laboratories or outer space! A sulfur cathode has a potential theoretical specific capacity of
something like 1670 milliamp hours per gram... That compares very favourably to an NMC cathode
which comes in at only about 150 milliamp hours per gram, so it's not hard to see the attraction,
both for the boffins in the science department and the bean counters in the finance department. But
that whopping number turned out to be a bit of a double-edged sword for our dear friends in the
research labs because it makes balancing the two electrodes much more of a challenge. Graphite is
usually the go-to material for the anode side of a modern battery and its specific capacity is about
380 milliamp hours per gram. That's close enough to work quite nicely with an NMC cathode, but it
doesn't work quite so well with the much higher capacity of sulfur. You really need something on
the anode side that's a closer match. That's led researchers towards materials like lithium metal,
which comes with its own challenges like dendrite formation, which we've touched on in previous
videos on the channel. If the dendrites grow large enough they can short-circuit the cell which
is not something you want under any circumstances. That's actually one of the challenges that have
hampered progress in the solid state industry, but it's apparently being worked on
and we're told it's not insurmountable. But the development challenges kept coming like
an unwanted gift that just keeps giving. The next couple of issues happen at the anode side of
the cell. If it's not controlled properly the soluble lithium sulfide coming off the cathode
can do one of two very unhelpful things when it arrives over here. It can either break down in a
redox reaction and flow back to the cathode where it recombines again and starts floating back and
forth in a perpetual motion known as polysulfide shuttle. That results in a phenomenon the science
bods called infinite charge, where it charges up once and then won't charge anymore because those
polysulfides just keep bouncing between the two electrodes. So that's quite irritating. The second
thing that can happen at the anode is a reaction with whatever the anode is made of. That can
cause a very unwelcome mossy-like growth known as surface electrolyte interphase or SEI. That's not
ideal either because if too much of that builds up then your anode starts to act like an electrical
insulator. Back at Monash University one of the boffins went off on a slightly random scientific
research tangent which I won't bore you with here but which you can find out about by jumping back
to my original video. That tangential discovery allowed the team to come up with a glucose based
binder that helped prevent the SEI build up on the anode. It turned out the lithium atoms in the
polysulfide very happily combined with the oxygen atoms in the glucose molecule, so by integrating
the glucose based additive into the cathode matrix the Monash team were able to stabilize the
sulfur and minimize the anode coating problem. It also improved the web-like structure of the
cathode which opened up the matrix to provide more surface area for lithium to interact with
the sulfur. Their results showed that 42 percent of polysulfides eventually are absorbed in the
presence of glucose compared with only 16% with previous methods, and that meant an energy density
of 500 watt hours per kilogram and an increase in the battery's operational durability up to a
thousand charge cycles. All of which brings us nicely to the Silicon Valley start-up called Lyten
Inc. who are probably the closest to actually getting a lithium sulfur battery to market. Now
there wasn't a great deal of information available when we first took a look at these guys back in
2021 but more little snippets have filtered out in various articles and interviews in the interim
period between then and now so it's probably worth returning to their technology here to see if it
still stacks up. Lyten claim their battery has the potential to reach a gravimetric energy density
of no less than 900 watt hours per kilogram. That not only outperforms the Monash team but also
far exceeds existing Lithium-ion batteries and even the current crop of solid-state batteries
that are just starting to come to market. In visual terms a single Lyten battery has the
equivalent energy density of three typical 2170 lithium-ion batteries and it's significantly
lighter too which is something we'll come back to in a moment. Lyten's USP is the development
of a highly engineered mesoporic type of carbon for their cathode based on their patented 3D
graphene technology. That allows them to create a kind of hierarchy of pore structures that
facilitate something called polysulfide caging which alleviates the problems of SEI coating and
polysulfide shuttling that we just looked at. Now I'm not smart enough to take you through
the minutiae of the chemical reactions here but my layman's understanding of it is that
it's a combination of mechanical and chemical caging structures or interactions that allow the
polysulfides to do their energy release work but then keep them where they are so they don't
interact with the rest of the bulk electrolyte or the anode. Lyten reckons that this allows
them to tightly control the redeposition of the polysulfides in order to release as much of that
potential 1670 milliamp hours per gram of energy as possible from the sulfur. Under Department of
Defense test protocols a Lyten cell apparently demonstrated an operational durability of more
than 1400 cycles with a charge time of less than 20 minutes. That would you put it right up there
with the longest lasting EV batteries available today. And as a very important additional benefit,
Lyten's batteries will be safer in vehicles than conventional lithium-ion batteries because, as
I mentioned earlier lithium sulfur contains no nickel, manganese or cobalt, nor the oxides
that go with them, which are what drive the thermal runaway events that have plagued some
electrical vehicles in the past. Testing show that the battery could be overcharged at
twice the rate of charge for the cell for over four hours and its internal temperature
increased by only about 10 degrees Celsius. Lyten also claim that the interdispersed graphene
and sulfur cathode architecture allows the battery to continue performing well in test temperatures
as low as minus 30 degrees Celsius. And according to their CEO, Dan Cook, they'll be able to do all
that for significantly less than 80 dollars per kilowatt hour. If that's true then it would make
the lithium sulfur battery extremely competitive compared to existing lithium-ion costs. The very
light cell weight that I touched on a moment ago has obvious advantages for electric vehicles but
perhaps more importantly for objects that have to fight against gravity like drones for example
or even electrically powered planes like this one from Israeli company Eviation, which by
the way has more than two billion dollars of pre-orders already. With a lighter battery on
board the flight distances of these planes will be significantly enhanced. So when will we see
these batteries actually hit the market then? Well Lyten are up and running already actually.
On November 4th 2022 they announced their first 3D graphene fabrication facility located at their
headquarters in San Jose, California and they plan to reach volume production of lithium sulfur cells
within a couple of years. Lyten certainly look like they could be in prime position to corner the
market if they can get a wiggle on and get volume production up and running in the time scales
they're projecting. But there are plenty of others trying to find that Holy Grail of performance
versus cost and longevity. At least three new research papers have been published just in the
last year or so, each with their own take on how to most efficiently and effectively eliminate
some of the issues we've discussed today. So I guess Lyten will need to keep a careful
eye on the competition in the coming years. That's it for this week. A huge thank you
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