When it comes to battery energy storage solutions for our sustainable future I
sometimes feel like we're witnessing a phenomenon a bit like the gold rush of the mid 19th century.
Pretty much every week I read at least one news story about the latest breakthrough
in battery chemistry the researchers claim will revolutionize the EV market or the national grid.
But just like many of the 300,000 or so folks that rushed to California in 1848 following James
Marshall's discovery of gold at Sutter's Mill, a lot of these modern day pioneers are likely
to find that the apparently transformational material process that they've unearthed turns
out to be a pale imitation of the real thing. Lithium-ion batteries are of course the current
standout success story in the field and there's no doubt they've utterly changed our modern world.
But as we move ever more rapidly away from fossil fuels, vehicle manufacturers and energy providers
are constantly clamouring for new technologies with higher storage capacities and lower demands
on critical minerals. At the same time sectors like aviation are desperately looking for
lighter weight batteries that might just make flights longer than a thousand miles viable
in the future. One technology that's been kicking around on the "might one day be possible" list is
lithium sulphur batteries. But it's yet another example of a technology where any description
usually has to start with the phrase "in theory". So, in theory lithium sulphur batteries can store
as much as five times the energy of existing lithium ion batteries. As with so many other
technologies it sounds fantastic until researchers actually tried to build one.
In the case of lithium sulphur batteries they discovered that both electrodes were so unstable
that the result was an impractically short cycle life and an inherently slow power performance.
Scientists have been trying to fix these problems for at least a decade but they've never managed to
overcome the fundamental problem of achieving high capacity simultaneously with extended cycle life.
Until now. Possibly! To paraphrase the words of the great modern day philosopher Mary Poppins,
it appears that in this case it could be a spoonful of sugar that makes the medicine go down
Hello and welcome to Just Have a Think. So the scientists have got a tantalisingly promising
material in the form of sulphur but an agonisingly frustrating set of barriers to overcome.
That annoyingly slow power performance for example is largely due to very poor ion diffusion
across the thickness of the sulphur cathode. Lithium Sulphur batteries work in a fairly
standard way with energy being stored when positively charged lithium ions
are absorbed by an electrode, in this case made of sulphur particles. One of the results of that
absorption is the formation of lithium-containing sulphur compounds known as polysulfides. As the
battery discharges the polysulfides remove sulphur and gradually degrade the cathode.
And as they move across the electrolyte they form a sort of mossy growth that insulates the anode
and degrades performance. It's a phenomenon the science bods refer to as 'polysulfide shuttle'.
To make matters worse as the electrode gets charged it swells up to almost twice its
original size and then shrinks back down again at discharge. That expansion and contraction causes
distortion and cracking which also reduces the operational longevity of the system.
So while most lithium-ion batteries have a rated lifetime of somewhere between
500 and 1500 charge cycles, lithium sulphur batteries have previously only managed about 50.
Which is more or less useless. Pioneering research in 2010 and 2012 by nanotechnology expert Linda
Nazar and her team addressed the challenge of low conductivity in the sulphur cathode
and introduced polysulfide absorbance and mediators to the cathodes composition which
went some way towards fixing the polysulfide shuttle problem. More recently other researchers
developed what they called an expansion tolerant architecture to get over that distortion problem,
but even so the holy grail of high capacity plus long cycle life has largely remained unachievable
until this latest breakthrough from a group of scientists at Monash University in Australia.
The team had already managed to bump up the number of charge cycles by four times from
50 to about 200 by creating a springy matrix of carbon and sulphur compounds
that was better able to expand and contract without distortion or cracking.
But that still didn't really cut the mustard compared to existing lithium-ion batteries.
The real game changer was outlined in a research paper published in nature communications in
September 2021. It was actually inspired by the findings contained in a dusty old geochemistry
paper from the late 1980s which described how sugar can help soils retain sulphur compounds.
Hardly the sort of thing you're likely to read when you're in the field of battery chemistry,
but that's exactly what PhD student Yingyi Huang did. She took the paper to her professor Mainak
Majumber and they agreed that adding sugar to a lithium sulphur battery might just be worth a try.
To be more specific, the team were looking to gain an understanding of the interaction
between saccheride based binders and the lithium polysulfides or LIPs that were generated between
the anode and cathode as the batteries charged and discharged. What they found was that the LIPs very
happily interacted with glucose as a result of their lithium atoms binding with oxygen atoms in
the glucose molecule, and that different binding energies could be produced depending on the exact
type of lithium polysulfide in question. Those binding energies were much higher than the levels
previously achieved by an existing non-glucose binder called polyvinyl iodine fluoride or pvdf.
All very interesting I hear you ask, but what competitive advantage did these interacts bring?
Well according to the researchers, incorporating a glucose based additive into the springy cathode
matrix stabilizes the sulphur and prevents it from dispersing and coating the lithium electrode.
It also improves the web-like structure of the cathode opening up the matrix so there's
more space for lithium ions to interact with the sulphur. Their results show that 42% of
polysulfides eventually absorbed in the presence of glucose compared with only 16 percent with
previous methods. The consequence of the Monash team's improvements was an increase in the
battery's operational durability up to a thousand charge cycles. Much closer to existing lithium-ion
technology. And according to the team because these batteries don't need any rare elements like
cobalt and nickel they're much cheaper to produce than their lithium ion equivalents. The team are
confident that they can consistently produce a 1,000 charge cycle battery with a capacity of
500 watt hours per kilogram and in conjunction with an energy research company called Enserv
Australia they plan to reach full production levels for EV batteries within five years. They're
not the only team pursuing the huge potential of lithium sulphur battery technology though. In fact
just one week after the publication of the Monash paper an advanced materials company called Lyton,
based in Silicon Valley in California, launched their LytCell EV lithium sulphur battery platform.
Lyten have apparently just come out of stealth mode following several years working with the US
government to develop their technology into what they refer to as "various defence related
applications". They say what they've achieved is a graphene based lithium sulphur architecture
called Lyten Sulphur caging that performs the same function of arresting that pesky polysulfide
shuttle problem that we looked at earlier. They don't provide any specific detail on exactly how
their technology works but according to their promotional blurb Lyten 3d graphene is a novel
three-dimensional graphene material platform that can be engineered and tuned at the molecular level
to specific battery application requirements. Lyten claim their battery has the potential to
reach a gravimetric energy density of no less than 900 watt hours per kilogram which would
not only outperform the Monash team but also far exceed existing lithium-ion batteries, and
even the current crop of solid state batteries that are just starting to come to market.
Under Department of Defense test protocols a LytCell prototype design has apparently
demonstrated an operational durability of more than 1400 cycles with a charge time of less than
20 minutes, which would 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 lithium sulphur doesn't contain oxygen from metallic
oxides which is what drives the thermal runaway events that have plagued some electric vehicles
in the past. Production and market availability for the LytCell battery is expected by 2025.
Now you go folks out there know that I'm not a cynical man and I try to take an open-minded view
of these new technological advancements in the hope that they'll genuinely contribute towards
a more sustainable energy future. These two competing technologies are certainly
potentially very exciting but as is so often the case there's likely to be a lot more work required
before we see a fully formed commercial version of either of them. There's a world of difference
between a few battery cells being tested in carefully controlled laboratory conditions
versus mass-produced batteries getting churned out in harsh factory conditions with all the
challenges that that entails. And I imagine that's a caveat that some of you might want
to expand on a little further. So if you do, or if you've got actual experience of working with these
technologies or in facilities that produce EV batteries, then why not jump down to the comment
section below and leave your thoughts there. That's it for this week though. As always a big
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