CATL's Sodium-Ion Battery, Explained
Better than Lithium?
The video is below.
This video has consistently been one of the most popular on the channel, and its popularity has lasted over the months.
Sodium Ion batteries are an interesting technology. I don’t see them as being disruptive to lithium ion, because the fundamental chemistries mean that they can never match up in certain critical features. Yet they are attracting a lot of attention because of their cost and their more environmental friendly measure. But is that enough to give them an advantage in the market? I don’t know.
Contemporary Amperex Technology or CATL recently unveiled their first generation sodium ion batteries for commercial use. I have been hearing a lot about this technology and thought that it would be worth talking about.
Scientists started off developing sodium ion batteries right alongside lithium ion batteries. Over time, lithium rose to dominance and sodium fell by the wayside. But now things have changed, and sodium ion batteries have started to see renewed interest.
In this video, we will briefly review sodium ion batteries, their state of development, and what their commercialization means for the renewable energy market at large.
What Are Sodium Ion Batteries?
Sodium ion batteries share a similar structure with lithium-ion batteries. They have a cathode, an anode, a porous separator between the two, and an electrolyte. When the battery is being used, ions migrate back and forth between the cathode and anode.
The primary difference between the two battery types is that their components are made of different compounds. That is actually part of the appeal. It is likely that commercial sodium ion batteries can share the same engineering and production methods as lithium ion batteries.
The single biggest advantage that sodium ion batteries have over lithium ion batteries has to do with the availability of certain raw materials, and linked to that - cost.
Almost all of the world's lithium comes from four countries: Australia, Chile, China, and Argentina. And this element is not particularly easy nor environmentally friendly to extract. Furthermore, there are other critical elements like cobalt which present particularly large environmental and humanitarian concerns.
The global supply of sodium by contrast is essentially unlimited. There are over 1,000 times more sodium than lithium in the earth's crust. This translates to a raw ingredient cost of $150 per ton as compared to lithium's $5,000 - a 30x decrease.
History: Ford in the 1960s
Researchers have been trying to commercialize sodium ion batteries side by side with lithium ion batteries. Development kicked off in the early 20th century, when it was discovered that molten salts were capable of conducting high amounts of sodium ions.
In 1968, scientists at the Ford Company developed a sodium-sulfur battery for use in electric vehicles. It was essentially made of a tube of metallic sodium dipped into another tube of liquid sulfur.
Ford felt that a 350 pound sodium-sulfur battery could provide 200-300 miles of range for a 1,350 pound car running at 40 miles an hour. The minimum charge time was said to be half an hour.
The biggest challenge was that it only worked at very high temperatures: 570 to 660 degrees Fahrenheit or 300 to 350 degrees Celsius. As you might expect, this caused safety and longevity issues - especially in cars. For instance, at those temperatures, the aluminum-based container tubes would react with the battery chemicals and rupture.
Ford never was able to commercialize the technology for a working electric vehicle. And it makes a lot of sense why molten salt batteries as they are called have yet to see wide use in mobile electronics. But they do have several real-world applications. The most common is to provide power for guidance systems in missiles.
But they are also ideal for extreme environments. I just finished a video about using them on the surface of Venus!
Ford eventually sold this technology to a Japanese company called NGK. Today, they are sold as stationary battery solutions for peak energy use and grid stabilization.
History: Lithium Ion Dominance
The Oil Crises of the 1970s revitalized interest in this technology. In 1985, South African researchers created a new version of the molten salt battery using nickel chloride and sodium tetrachloroaluminate.
The ZEBRA battery as it was called held a lot of promise. But in 1989 Sony successfully commercialized the lithium-ion battery and its advantages quickly won over the industry. From then on, research largely focused there.
Today, lithium ion battery technologies largely dominate the industry. They are the first choice for use in electric vehicles, stationary batteries, and mobile gadgets.
But in the 2000s, concerns began emerging with regards to the supply of raw materials. Like as I mentioned earlier, natural sources of lithium are limited and that cannot be the case if we want to be truly serious about a carbon-free economy.
Secondly, a less heralded reason has to do with intellectual property rights. So many patents have been filed around lithium ion technologies that new companies have to be extremely careful not to run afoul of the lawyers. Sodium ion battery technologies in contrast offer far larger green fields.
Thus starting in the 2010s, people started taking a second look at sodium ion batteries - which would again use sodium, but at room temperatures. The number of publications relating to sodium ion batteries began to quickly rise - and in recent years have even surpassed that of lithium ion batteries.
Mixes
Batteries, especially prototypes, wildly differ from one another. But for the most part, scientists have started to hone in on a few high-potential sodium ion battery chemistries.
Most studies have converged on making the anodes from a substance called "hard carbon". It can also be colloquially described as charcoal.
The electrolyte makes sure that the sodium ions can travel from the anode to the cathode. These have to be of low viscosity, high conductivity, and be electrochemically stable. Researchers have generally chosen sodium salts dissolved in solvents of organic carbonate. Though there is plenty of research advocating for other options too. I won’t cover them here.
The cathode is where much of the latest research has been focused on, same as with the lithium ion battery. Makes sense since the cathode is the single most expensive component in the whole thing - and is key to its overall viability. Many candidate materials have emerged as potential contenders.
The most common and closely studied class of cathode material are sodium layered oxides. These are pretty wild. They have a crystalline structure made up of sheets of metal oxides with sodium ions sandwiched in between.
They are distinguished with a P2, O3, and P3 notation that refers to their geometries.
The reason why they show so much promise is because their crystalline structures have a lot in common with that of lithium cobalt oxide, the first legit cathode material in lithium-ion batteries.
There has been a whole lot of research in cathode materials for sodium ion batteries. Other researched candidates include sulfides, phosphates, fluorophosphates, carbonophosphates, vanadium-based polyanionic compounds, and so on. CATL, for their part, has opted to make their cathodes out of something else.
Previous Examples
There has a been a whole lot of experimentation in the past years. The science has moved fast, and the first few sodium ion battery products have started to inch towards the market.
The first really, actually commercial-ready sodium-ion battery looks to be a 18650 cell created by the French research agency CNRS CEA in 2015.
18650 is a standard format size and refers to the battery's dimensions. 18 millimeters wide, 65 millimeters tall, and the 0 means that it is a cylindrical format. The reported energy density is about 90 watt hours per kilogram.
Two years later in 2017, the agency spun off the research into a startup called Tiamat Energy. The company's long term objective is to develop low-voltage systems for hybrid vehicles, and help ensure French technological sovereignty.
In June 2020, researchers at Washington State University and Pacific Northwest National Laboratory announced a more advanced sodium ion battery. Its creators speculate that the battery might be able to achieve a practical specific energy of ~160 watt hours per kilogram.
This is comparable to current lithium iron phosphate batteries. That being said, we should temper our expectations here. Sodium has lower ionization potential or ionization energy than lithium. This means that sodium ion batteries will have lower energy densities and operating voltages than their lithium counterparts. And it is not clear whether they can ever catch up to top line lithium ion batteries in this regard.
There are also a number of other technology startups trying to commercialize sodium ion batteries. Some examples include UK-based Faradion Limited, Sweden-based Altris AB, China-based HiNa Battery, and US-based Natron Energy.
Now that we have very, very briefly gone over the current state of the research in sodium ion batteries, we can review the CATL announcement and get some perspective here.
CATL's Battery
In their announcement, CATL gave a few details about how their sodium ion battery works.
The anode is made out of hard carbon, as is commonly the case.
They noted that their hard carbon anode features a "unique porous structure", which lengthens its cycle lifetime and allows for more sodium ion movement.
For the cathode however, they are using something interesting. They mention that they are using a substance called Prussian white.
Prussian white is an analogue of a pigment called Prussian Blue. First synthesized over 300 years ago, the dye makes a beautiful blue shade and has been noted for removing heavy toxic metals from the body. It is very cheap, easily made and nontoxic.
But some time in the early 2010s, researchers also noticed its suitability for use in sodium ion battery cathodes. They have good discharge rates, and can sustain their capacity over many charge cycles. Some tests have shown 95% retention even after 10,000 cycles.
One big drawback of Prussian Blue cathodes - and there will always be drawbacks - is that they lose a lot of their capacity in the presence of moisture.
Other companies have been exploring Prussian blue cathodes. Notable companies include the aforementioned Altris AB and Natron Energy.
CATL said that their first generation sodium ion battery can achieve energy densities of up to 160 watt hours per kilogram. This is comparable to the Washington State battery unveiled last June which as I mentioned, is in turn competitive with current lithium iron phosphate batteries. The second generation hopes to be over 200 watt hours per kilogram.
Furthermore, like as I mentioned, the engineering and manufacturing processes are similar between sodium and lithium ion batteries. So CATL can really take advantage of this by tightly integrating their sodium ion offering into their existing lithium ion infrastructure and product ecosystem.
It is worth keeping in mind though that since the two preparatory processes will have so much overlap, sodium ion battery costs will not be drastically lower than lithium ion batteries. Most of the savings will come from cheaper raw material costs.
It is like how gasoline prices don't rise and fall in step with oil prices. One paper estimates that the end users will see 10-30% price savings using sodium-ion, with all things being equal.
They called out battery system integration capabilities where they can mix and match sodium and lithium ion batteries into one single system. Lithium ion batteries, which right now have higher energy densities, are automatically used by the system when sodium ion falls short. So that is kind of interesting.
Conclusion
We talk a lot about new and exciting battery chemistries. But the reality is that a lot of these concepts do not see commercialization, and far fewer get widely adopted.
For instance, lead acid batteries have been around for 150 years. Their energy densities are not comparable with lithium ion and their materials are quite toxic.
Yet because lead acid batteries are cheap and reliable they are still very widely used. In 2020, global lead acid battery sales totaled nearly $50 billion. Inertia really means a whole lot.
So not everything will be a lithium ion battery-level of success. And it looks like sodium ion batteries will never be able to replace lithium in certain use cases like mobile phones and other electronic gadgets.
But they have potential in short-range electric vehicles and especially in stationary power systems. Places where space is less of a big deal, making their lower energy density not so much of a confounding factor.
For instance, energy storage for solar and wind renewables. Those areas, which operate at scale, can also really appreciate the cost savings.
There are already some small startups in the space. But CATL is no ordinary enterprise. They are the biggest battery company in the world and it appears that they will pour a lot of resources into this endeavor, leveraging their size, manufacturing skill, and R&D savvy to make this work. Let us see if they will succeed and help sodium ion live up to its full potential.