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Sodium-Ion Battery: Better than Lithium-Ion?

Last updated Mar 30, 2022
We all know that lithium has become 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 four countries in the world with large reserves – Argentina, Chile, Australia, and China.

China is importing most of the lithium it uses anyway to hoard its own supply ready for when the rest of the world runs out.

Sodium Beats Lithium

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 kg of lithium in its battery pack. According to PV Magazine, if EV sales continue to rise as expected, there’ll be 3 billion of them on the roads by 2040, and we’ll have got through pretty much all of the existing 26 million tonnes of lithium available today.

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 mainly sourced from the Democratic Republic of Congo with all the environmental and human rights issues that you’ve no doubt heard about.

By contrast, lithium’s less sexy sibling, sodium, is abundantly available all over the place. There’s more than 1,000 times more sodium in the earth’s crust than lithium. It’s a constituent part of sodium chloride, of course, salt.

It’s actually mostly mined 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.

Why Weren’t Sodium-Ion Batteries Rather than Lithium-Ion in the First Place?

Since the sodium-ion battery is safer, cheaper and cleaner than lithium-ion, why it wasn’t sodium rather than lithium that became the darling of electrochemical engineers worldwide and why our modern lifestyles aren’t all powered by sodium-ion batteries instead of lithium-ion.

That’s a very good question. 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, which could genuinely revolutionize the future of energy storage.

So, why didn’t CATL and all the other battery firms just use sodium in the first place?

It wasn’t quite as straightforward as our scientific friends may have hoped for.

Basics of Sodium-Ion and Lithium-Ion Batteries

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 up, 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 anodes’ 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 its original position in the cathode.

The ions move back across the electrolyte to join them.

Disadvantages of Sodium-Ion Batteries

The main drawback of using sodium instead of lithium was energy density and weight. Sodium-ion batteries achieved something like 150 Wh/kg, compared to well over 200 Wh/kg for lithium-ion batteries. That’s a competitive disadvantage that our market-driven economies simply would not tolerate at the time.

Sodium ions are three times heavier, too. Even though the sodium component accounted for only about 5% of the overall battery weight, it still made them heavier than their lithium-based cousins.

They’re also physically larger than lithium-ions, which meant they couldn’t move freely between 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.

As the largest battery producer globally, CATL has 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.

For example, they’re already making lithium-iron-phosphate batteries for all the Tesla cars sold in China. Those batteries also have a lower energy density than standard lithium-ion batteries, but importantly, they don’t contain any cobalt.

Rivian and Tesla have announced that it’ll be switching over to lithium-iron-phosphate batteries for all of its standard production vehicles worldwide, so it’s not difficult to imagine that CATL is taking incremental steps towards replacing lithium-based batteries altogether.

Sodium-Ion Battery Progress

Back in July 2021, CATL launched the first generation of their sodium-ion battery technology, with an energy density of 160 Wh/kg and a 0 to 80% charge time of just 15 minutes. The primary point of difference with this newer technology was in the materials used for the electrodes. The cathode material is something called Prussian White.

According to 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.

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% 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 unique porous structure that enables the abundant storage and fast movement of those larger sodium ions giving it an overall performance and cycle life equivalent to graphite.

Because sodium ions don’t tend to form an alloy with aluminum, CATL has been able to use an aluminum foil as the current collector on the anode side instead of the more commonly used copper. Not only does that make each battery about 80% cheaper, it also makes them 10% lighter.

Plus, the properties of sodium salt make it possible to use a less concentrated electrolyte solution, which saves even more money.

CATL says they can manufacture their new sodium batteries using exactly the same machinery and processes for their lithium-ion production, so no expensive new set-up is required either. 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, so there’s an improvement in safety ratings too.

In January 2022, the company applied for a patent on a second-generation sodium-ion battery that they claim will surpass 200 Wh/kg, which is even better than lithium-iron-phosphate technology and getting up to the current performance levels of 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 slick marketing presentations and instead focus solely on the real-world performance and commerciality of the product.

There’ve been loads of grand promises made by various industry newcomers in the past, all claiming to be the next market disruptor. But very few of those designs have come to fruition. Having said that, CATL is a pretty serious outfit who do tend to do exactly what they say they’ll do. We may well be seeing electric vehicles powered by sodium-ion batteries within the next few years.

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