If you have even a passing acquaintance with
this channel, you’ll know that I’m constantly banging on about the next ‘exciting battery
breakthrough’. They’re coming at us thick and fast these days, aren’t they?
According to this recent article, having started at virtually zero in 2017,
global battery energy storage capacity has grown so exponentially that by 2025 it's
projected to surpass the mighty pumped hydro as the largest energy storage medium in the world.
Now, of course, just like all the other so-called ‘green’ technologies, batteries are not a silver
bullet that’ll solve the climate emergency. I’m often accused of believing that technology alone
can drag humanity out of its current existential predicament, which always makes me wonder
whether those critics have watched any of the dozens and dozens of videos I’ve made explaining
quite specifically why technology alone CANNOT drag humanity out of its current existential
predicament. There are myriad other problems and challenges that we’ll need to overcome in the
coming decades. But batteries ARE definitely a thing. And they‘re a thing that’s not going away.
The tricky challenge with so many new developments popping out of labs all over the world right
now, is to work out which ones are legitimate contenders and which ones are no more than
delusional hopium on the part of their inventors. Fortunately, a group of proper grown-ups
with impressive credentials and doctorates, and all that lovely stuff, recently
conducted a study of what they see as the most likely challengers
to the lithium-ion overlord. So, I thought I’d spend a bit of
time having a look at their findings. Hello and welcome to Just Have a Think, The study in question comes from the
world-renowned Fraunhofer Institute for Systems and Innovation Research in Germany. It’s called ‘Alternative Battery
Technologies – Roadmap 2030+” and it’s been developed as part
of a project called BEMA 2, funded by the German Federal Ministry
of Education and Research, or BMBF. I won’t attempt to read out what the
acronym BEMA stands for in German because I have a pathological aversion
to making a complete tit of myself, but I’ve written it out on screen
here so you can see what I mean. Anyhow… the clever boffins at Fraunhofer
highlighted four distinct technology families for their study, and then drilled down into
each category to look at the different flavours available within them. Obviously the grand-daddy
of the metal-ion category is lithium-ion. We’ve looked at it and its close relative
sodium-ion on several occasions, including the recent video about Natron in the USA, which
you can jump back to by clicking up there. Both those technologies are already on the market,
so if we consider them in terms of the industry standard Technology Readiness Level ladder,
they both sit right up there on the top rung. But there are a couple of other options in this
family that the Fraunhofer team say are worth considering. First up is Magnesium-ion.
Magnesium is a highly abundant material, and its chemical composition gives it
a relatively high theoretical energy capacity. The challenge that developers are
currently grappling with is finding the optimum combination for the cathode and anode materials.
The exciting bit, if you’re a battery chemist, is that magnesium-ion cells are intrinsically
safe, partly because they don’t tend to promote the growth of the dreaded dendrites
that can afflict lithium-ion batteries. And partly because magnesium itself has a
high auto-ignition temperature of four-hundred and seventy-three degrees Celsius compared to
lithium’s one-hundred and seventy-nine Celsius. That means ultra-fast charging times
are a very real possibility. Magnesium is also less reactive to air than lithium
because of its self-passivating behaviour. Even more encouraging is the fact that
metal oxide configurations are achieving good operating voltages between two-point-four and
three-point-nine volts, and they look like they’ve got the potential to reach energy densities
of around six-hundred and fifty Watt-hours per kilogram, which is almost three times higher
than the best current lithium-ion technology. The less exciting bit, if you’re a battery
salesman, is that Magnesium-ion batteries are still at the fundamental research stage,
which means they only reach rung number three on our Technology Readiness Level ladder
Zinc is another interesting option in the metal-ion family. Zinc is an already
well-established raw material in global supply chains with an availability
about ten times higher than lithium. There’s also a very good recycling
industry in place for Zinc, which ticks an important sustainability box. And Zinc is pretty stable in water too,
which means battery chemists can use benign aqueous electrolytes instead of the slightly
nasty organic solutions used in lithium-ion. The trouble is, they only currently achieve a
potential difference of between one and two volts, which is significantly lower than lithium-ion.
Energy density is lower as well. Even the long-term projection is for a gravimetric density
somewhere between fifty and a hundred-and-twenty Watt-hours per kilogram, so we’re probably not
looking at the future of electric mobility here. Having said that, water-based
electrolytes are non-flammable, so a zinc-ion battery will be a very safe battery, and there may be some applications where
that gives it the edge, for example in utility-scale stationary energy storage or as
a direct replacement for lead acid batteries. Just like magnesium though, Zinc-ion is only
at the very early stages of its development. There are a lot of challenges to overcome, including hydrogen generation at the anode
which can cause loss of zinc-ions, and unwanted side-reactions as the zinc-ions intercalate,
or nestle, into the anode materials. For all those reasons, Zinc joins magnesium on
rung number three of our TRL ladder. A more recent development has been in
Aluminium-ion batteries. Aluminium is a metal we’re all very familiar with.
It’s highly abundant and already one of the most recycled materials on the planet.
What’s attracting the battery chemists though is the potential of aluminium-ion to be used as a
link between lithium-ion batteries and so-called hybrid-ion-capacitors. That’s because they can
achieve a power density of nine thousand Watts per kilogram, which is way higher than
lithium-ion, with a potential C-rate, which means how many times a cell can
be charged or discharged in one hour, of a hundred and eighty. That equates to three
full charges every minute, which is much more like a capacitor than a battery. They also keep
going for more than twenty-thousand charge cycles. The boffins reckon they can potentially double
those figures in the short to medium term too, so there’s a lot to like here as an
extremely useful complimentary technology to work alongside lithium-ion for fast
power delivery tasks in electric vehicles, or for stabilization of smart grids and micro
grids. Challenges include the highly corrosive nature of the ionic electrolyte fluid and less
corrosive but still problematic materials in the current collectors and cell casings.
They are expected to be very cheap though when they come to market – maybe twenty
percent less expensive than lithium-ion. Nevertheless, we’re still a few years away from a
commercial product so TRL ladder rung three it is. Metal-sulphur batteries work in a very
different way to metal-ion batteries. Sulphur can react with lithium, sodium, magnesium
and some other metals to form metal-sulphides. This is another one we’ve looked at in
a couple of previous videos which I’ve linked in the description section below.
Lithium-Sulphur batteries operate at room temperature with discharge voltages between
two and two-point four volts and very decent energy densities between three and
four hundred watt-hours per kilogram, at least at cell level anyway.
You do need more individual cells at that lower voltage though, to reach the same
system level voltage as a lithium-ion battery, so it’s not yet clear whether that cell energy
density will scale up. The study points out that lithium sulphur cells might require higher
external pressure and have a cycling stability that’s not as good as lithium-ion. So, the
development goal here is to design large format cells that have both high energy density and
can last more than a few hundred charge cycles. They won’t be fast charges though. The
chemical nature of the interaction between lithium and sulphur means you’re looking at
one full charge per hour or maybe even less, so again, we won’t be seeing these things
in electric vehicles. Lithium sulphur cells also currently use a flammable electrolyte,
and you still have the propensity of lithium to build up into dendrites at the electrode
face. So, there’s still a lot of work ahead, part of which will also be in finding the
optimum carbon scaffold structures to minimise the polysulphide shuttle effect that we looked
at in our previous video on sulphur batteries, where polysulphides get into a bit of a doom
loop of continuous movement from anode to cathode and back again, effectively making
the cell useless after the first charge. There are already pretty good
working solutions for that though, so it is by far an insurmountable goal. All
in all, lithium-sulphur is looking reasonably promising for stationary storage applications, and
in fact the technology using liquid electrolytes sits somewhere between rung five and rung
seven on our ladder. Solid electrolytes are also being developed, although they’re a couple
of rungs behind in terms of technology readiness. Just as we saw earlier with metal-ion batteries,
sodium represents an interesting alternative to lithium in metal-sulphur chemistry and most of
the operational parameters are very similar. Sodium-sulphur probably won’t pack the same
punch as lithium-sulphur but you do win that important advantage of resource availability,
so in some applications that may be the check box that seals the deal. But again, there
are plenty of challenges to overcome. Sodium has an even greater tendency than lithium to
lay down dendrites and its higher reactivity combined with a flammable organic electrolyte
is far from ideal from a safety perspective. Ceramic solid electrolytes would mostly get
around that problem, and exotic materials like hollow carbon tubes and graphene will
help with some performance issues, but those materials are by no means cheap or commonplace.
So, the study puts sodium-sulphur on rung four. The third category on the Fraunhofer
list is Metal-air batteries, which, as the name suggests, comprise a metal
electrode, some sort of electrolyte and what’s known as a ‘gas diffusion electrode’
or GDE on the opposite side of the cell. That set up allows oxygen to be drawn from the
surrounding atmosphere or in some cases from an oxygen tank. You get electrical energy from a
chemical reaction between the metal and oxygen, so the capacity of the cell is largely
dependent on the type of metal used. Yet again, Lithium is a promising candidate
in this sector because it offers a very high theoretical energy density and decent
voltage. On paper you could be getting as high as three-thousand-five-hundred Watt-hours
per kilogram at three volts, but in real world prototyping, the higher the energy density, the
lower the number of cycles achieved. Best results so far have been five hundred watt-hours per
kilogram but with only ten useful charge cycles. You also still get the dendrite problem, so
these things are a long way off, and although substantial improvements have been made during the
past decades, the study suggests this chemistry still needs some more basic research work, so
it’s currently at the bottom of our TRL ladder. Zinc-air batteries, on the other hand, have
been commercially available for several years. The trouble is, the zinc oxide produced by the
oxygen reduction reaction can’t be recovered, so it massively inhibits the capacity
to recharge the battery by effectively absorbing the anode during discharge.
There are ways around even that limitation though, for example by mechanically replacing the zinc
anode or by replacing the electrolyte within a flow system. That research work has apparently
been going on for several years, but despite many announcements and a few prototype systems,
no-one has yet managed to produce a commercially available rechargeable Zinc-air battery, so for
the purposes of the energy transition, zinc-air also languishes towards the bottom of the ladder.
Last but by no means least, comes the good old Redox Flow Battery, which we’ve looked at several
times here on the Just Have a Think channel. These things have two tanks of electrolyte
solution on either side of a cell stack. As the two solutions are pumped in, the
cell stack converts electrical energy into chemical energy and vice versa.
Vanadium is the most common and most mature technology in this sector, and Vanadium
redox flow batteries, or V-RFBs are currently already commercially available, so they
sit right at the top of the TRL ladder. Redox flow batteries really aren’t trying
to perform the same role as the rest of the technologies featured in this report. They are
by their very nature relatively heavy and bulky bits of kit, so they are firmly aimed at the
stationary energy storage market. They don’t have the same high energy density as lithium-ion
batteries, but they are very well suited to longer duration discharge between five and ten hours,
and they offer an extremely long operational lifetime because you’re not getting any electrode
deformation on each charge and discharge cycle. They’re also easily scalable. If you want a
bigger system, you simply increase the size of the electrolyte tanks, or add more tanks.
Now, you might be asking “what about Solid State batteries, Dave”. That’s a fair question.
And it’s a big question. So big in fact that the Fraunhofer institute is currently producing
an entirely separate study dedicated solely to analysing the various solid-state options that
are in development around the world right now. And, of course, when I get my hands on that
report, I will bring you those findings as well, so stay tuned, make sure you’re subscribed
to the channel on YouTube and make sure you’ve hit the notification
bell too so you don’t miss it. That’s it for this week though. I’ve been away for my editing desk for the
last few days, while I’ve been busy hosting discussion panels at the Everything
Electric LIVE show up in Harrogate, so there’s no video next week, but
I’ll be back on Sunday the 9th June with more news and views from the world
of climate change and sustainable energy. A massive thank you, as always, to the
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