If you're one of those folks who've been kind enough to listen to my ramblings every Sunday
for the last four years or so you'll know that I'm no expert when it comes to complex scientific
matters. I'm sadly not one of those people who can instantly tell you the atomic number of
every element in the periodic table or even which family each of those elements sits within.
But I do remember my chemistry teacher lobbing small chunks of soft metal into beakers of water
back in the 80s, when safety gear was only vaguely optional, and being highly entertained by the
vigorous reactions that ensued. And if I remember rightly those metals were things like lithium,
sodium and potassium, and they were all part of the same group of highly reactive elements
known as the alkali metals. Today of course we all know that lithium has gone on to be the
absolute rock star of modern day energy storage, leaving its close relations in relative obscurity.
But lithium is by no means an inexhaustible resource on our planet. There are only really four
countries in the world that have large reserves - Argentina, Chile, Australia and China. And China
is importing most of the lithium it uses anyway so that it can hoard its own supply ready for when
the rest of the world runs out... because, you know, why wouldn't you? And the world may well run
out if we don't get our recycling and repurposing systems sorted out properly in the coming years.
An average electric vehicle has about 10 kilograms of lithium in its battery packs. According to PV
magazine if EV sales continue to rise as expected there'll be three billion of them on the roads by
2040 and we'll have got through pretty much all of the existing 26 million tons of lithium available
today. And it's pretty difficult to extract too, requiring large amounts of carbon heavy energy
and causing lots of undesirable environmental impacts. Plus most lithium ion batteries require
other rare elements like cobalt, which is mostly sourced from the Democratic Republic of Congo,
with all the environmental and human rights issues that you've no doubt heard about as well.
By contrast, lithium's less sexy sibling, sodium, is abundantly available all over
the place. There's more than a thousand times more sodium in the earth's crust than there is lithium.
It's a constituent part of sodium chloride, which is of course salt. It's actually mostly made from
soda ash, but in any case as the sixth most abundant element on the planet
it's pretty easy to get hold of compared to lithium. So it makes you wonder why it wasn't
sodium rather than lithium that became the darling of electrochemical engineers around the world,
and why our modern lifestyles aren't all powered by sodium ion batteries instead of lithium ion.
Well that's a very good question! I'm glad you asked! And it looks like the world's biggest
battery maker, CATL of China, agrees with you because they've just revealed a sodium ion
battery that challenges existing lithium-ion technology for energy density and longevity
and which could genuinely revolutionize the future of energy storage
Hello and welcome to Just Have a Think. So why didn't CATL and all the other battery firms
just use sodium in the first place I hear you ask. Well like most things I delve into in the
scientific world it turns out it wasn't quite as straightforward as our scientific friends may have
hoped for. The basics of the two battery types are very similar. There are two electrodes and two
charge collectors, one negative and one positive, which sit on either side of an electrolytic
solution with a separator membrane in the middle to block the flow of electrons inside the battery.
As the system charges, the lithium or sodium atoms release electrons which flow out from the cathode
and through the electrical circuit to the anode on the other side where they're physically captured
within the anode structure. Meanwhile the lithium or sodium ions travel across the electrolyte to
reach the same destination. When the system is connected to a device, the stored electrons move
back out of the battery, producing an electrical current that powers the device,
before returning to their original position in the cathode. And the ions move back across the
electrolyte to join them. The main drawback of using sodium instead of lithium was energy density
and weight. Sodium ion batteries were achieving something like 150 watt hours per kilogram
compared to well over 200 watt hours per kilogram for lithium-ion batteries. That's a competitive
disadvantage that our market-driven economies simply would not tolerate at the time. Sodium is
three times heavier too, so even though the sodium component accounted for only about five percent
of the overall battery weight it still made them heavier than their lithium-based cousins. Sodium
ions are also physically larger than lithium ions which meant they couldn't move freely between the
layers in a graphite anode in the way that lithium ions could, so the insertion and extraction of
sodium ions into and out of the electrodes put higher demands on whichever material was used.
But, as the largest battery producer in the world, CATL have always been at the forefront of research
and development. With more than 5,000 people in a dedicated R&D team and state-of-the-art
computer simulation technology, they're constantly searching for more sustainable ways of producing
these essential products, mindful of the finite nature of the resources available.
They're already making lithium-ion phosphate batteries for all Tesla cars sold in China for
example. Those batteries also have a lower energy density than standard lithium-ion batteries but
importantly they don't contain any cobalt. And Tesla has announced that it'll be switching over
to lithium-ion phosphate batteries for all of its standard production vehicles worldwide, so
it's not difficult to imagine that CATL are taking incremental steps towards replacing lithium-based
batteries altogether. Back in July 2021 they launched the first generation of their sodium
ion battery technology with an energy density of 160 watt hours per kilogram and a zero to eighty
percent charge time of just 15 minutes. The major point of difference with this newer technology
was in the materials used for the electrodes. The cathode material is something called Prussian
White which, according to the science bods, is a 'fully reduced and sodiated form of Prussian Blue
with a high working capacity, high theoretical capacity, and low toxicity, which circumvents
the need for a reactive sodium loaded anode in cell assembly'. Now if you know precisely what
all that means then you're a smarter human than me! And if you're not sure what all that means but
you'd like to find out then I'll leave a link in the description section below to a page where you
can access that explanatory paper. Suffice to say, Prussian White is a very cheap, easily produced,
non-toxic material with good discharge rates and an ability to maintain a capacity as high as
95 percent after 10,000 cycles, which makes it a very attractive option for a battery cathode. Over
on the anode side, which in lithium ion batteries is generally made of graphite, CATL has developed
a hard carbon material with a uniquely porous structure that they say enables the abundant
storage and fast movement of those larger sodium ions giving it an overall performance and cycle
life equivalent to graphite. And because sodium ions don't tend to form an alloy with aluminium,
CATL have been able to use an aluminium foil as the current collector on the anode side instead of
the more commonly used copper. Not only does that make each battery about eight percent cheaper,
it also makes them ten percent lighter. Plus the properties of sodium salt makes it
possible to use a less concentrated electrolyte solution, which saves even more money. CATL say
they can manufacture their new sodium batteries using exactly the same machinery and processes
that they use for their lithium ion production, so no expensive new setup required either. And
just as a cherry on top of the happy little CATL cake, it turns out that sodium ion batteries have
much better thermal stability than lithium ion too so there's an improvement in safety ratings.
So I think it's fair to say that our friends at CATL were really quite pleased with themselves.
on a second generation sodium ion battery which they claim will surpass 200 watt-hours per
kilogram, which is even better than lithium-ion phosphate technology and getting up towards
the level of performance currently achieved by standard nickel based lithium cobalt batteries.
Full production is scheduled to come online as early as 2023
with CATL looking to supply not only Tesla and other automakers,
but also low-cost stationary energy storage facilities for electricity grids around the
world, helping to smooth the path for the rapid implementation of renewable energy.
As with all these apparently revolutionary new announcements in the world of battery storage
systems, it's important not to get too carried away with the slick marketing presentations
and instead focus solely on the real world performance and commerciality of the product.
There have been loads of grand promises made by various industry newcomers in the past
all claiming to be the next big market disruptor, but very few of those designs
have ever really come to fruition. Having said that of course, CATL are a pretty serious
outfit who do tend to do exactly what they say they'll do, so if I was a betting man I'd say we
may well be seeing electric vehicles powered by sodium ion batteries within the next few years.
You may disagree with me on that one of course. If you do,
or if you think sodium ion batteries are the best thing since sliced bread, then jump down to the
comments section below and leave your thoughts there. That's it for this week though. As always,
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