Extracting Lithium from the sea to meet the increasing demand for Lithium Ion Batteries

 So this post just hit r/all and I HAD to report on it. The potential for this technology is limitless and something we should be on the lookout for. Though the research was first published on March 30 and is fairly on the cutting edge of science, I'll try to limit the explanation with just High School Chemistry knowledge.

While we wait for Solid-State Batteries, we should be working on improving the Li-Ion batteries we've got now, and that's mostly going to involve better energy densities for Li-ion batteries, and better production processes.

It is no secret that Lithium mining is an extremely inefficient process that is not only unsafe for the environment, but also for the workers.  An alternative that's much more viable is long overdue. And that's where this new paper comes in.

Despite lithium being only available in extremely low concentrations in the sea, (about 0.1-0.2 ppm), given the size of the oceans, we can expect there to be about 180 billion tons of Lithium available in the sea. For context, one ten-thousandth of that can power the entire world for an entire year, if it was made in the form of a Tesla Batteries. That's a lot of Lithium available, almost five thousand times more than what's available on land, and with such low concentrations, there is no known side effect of extracting the lithium from sea water.

What is the challenge?

For one thing, the low concentrations of Lithium. It's a double-edged sword here. Extracting the lithium isn't expected to have any impact, but we'll be struggling to extract those few ions of lithium. If you remember chemical kinetics, you'll understand why. The rate of a reaction is directly proportional to the concentration of reactants. And at this rate, it's going to be extremely slow and energy-consuming.

For another, the extremely high concentrations of competing ions, like Potassium and Magnesium. If you're trying to isolate the positive lithium ions, then you're bound to attract other positive ions, like Hydrogen, Sodium, and Calcium. While Hydrogen will be liberated as a gas, you can't say the same about the other metallic ions, which remain as impurities if you're looking for lithium.

Ideas have been proposed with some form of Adsorption, with absorbents like FePO4, but they aren't particularly effective in filtering Lithium from Sodium. A notable improvement was using a TiO2 coating on the electrode to assist with the electrochmeisobtion. However, it's still extremely slow and has issues with regeneration. 

The bigger issue isn't with the monovalent ions like Sodium and Potassium. But rather with the multivalent ions like Magnesium or Calcium. To extract the lithium ions, you just need to be able to precipitate them and then collect them. When you introduce an anion to precipitate Lithium, the other cations, Sodium, and Calcium will also make slats. However, Sodium salts are typically more soluble than Calcium or Magnesium Salts, which makes it harder to the extraction of lithium.  

How was it achieved?

Well, you can drive the lithium ions towards the cathode with a simple electrochemical cell. But you'll be driving other cations as well. That's the big problem here.

In any electrochemical cell, you need a salt bridge separating the two half cells, which can allow the movement of ions, but not the liquid itself. If we can select a membrane that can allow only Lithium ions, that should solve the problem.

Enter Lithium-Lanthanum-Titanium-Oxide (LLTO). It's a material that's been previously used as a cathode coating for Lithium-Ion batteries.

This particular compound has a property that lets lithium ions easily deposit and diffuse.on it, by consuming relatively little energy. It has a perovskite-type crystal structure. Essentially, Titanium Oxide and Lanthanum form the core of the structure and support it, making it a stable structure. The lanthanum is arranged in alternate layers, which leaves a place for the little lithium ions to percolate. This ability for lithium ions to easily deposit and extract makes it a wonderful candidate for cathodes of Lithium-Ion batteries.

That also makes it a good candidate for a salt bridge for our use case, where we're trying to isolate the lithium ions. The lithium ions will be deposited on one end and diffused on the other end, and the layer effectively acts as a selectively permeable membrane.

Beyond that, the cell itself has three components. Seawater flows into a central feed chamber, where lithium ions are filtered into a second compartment through this LLTO. This compartment contains a buffer solution and a copper cathode with Platinum-Ruthenium Coating. The negative ions, like chloride ions, exit the feed chamber into a third chamber through a typical anion exchange membrane, into a NaCl solution, and a platinum-ruthenium anode. 

Okay, wait a minute. What's that Carbon Di-Oxide doing here? It's got no business here based on all that we've discussed. Well, you've got a buffer in the solution with a few phosphate ions in the cathode compartment. By pumping in some Carbon Di Oxide, you're setting off a chain reaction that leads to Hydrogen gas being liberated. Once Hydrogen gas is liberated, there's fewer cations in the compartment. And Le Chatelier's Principle tells us that the reaction will now go in forward direction,

So what are the results?

For round 1, deionized water was used for cathode stream and sea water was used for the initial feed solution. For round two onwards, the lithium enriched water from the previous round was used for the feed and cathode solutions. Each round went on for about 20 hours, with a voltage of about 3.25V across the electrodes.

As you can see, it's pretty effective in filtering out the other ions, while concentrating the lithium ions. After this, you can directly precipitate Lithium out as Li3PO4, with negligible impurities, meaning it can be directly used in Battery Production.

Byproducts? Side effects? What do we know?

For one thing, we've got Hydrogen gas and Chlorine gas as byproducts in the reaction. This can later be sold to recover the costs of electricity. 

The concentration of other salts after removing lithium is well less than 500 ppm. It could be treated as freshwater for all intents and purposes. You could integrate this system into a desalination plant for better economic viability. While you need better economic analysis to figure out how to scale this system up, the way things stand, it's looking pretty good. 

What about the impact on the environment? Pulling that much lithium out of the sea should lead to some form of impact down the line on the ecosystem. 0.2 parts per million isn't a lot, but then again, we don't really know how lithium is used by aquatic life. As this research paper mentions, naturally occurring lithium has been neglected due to it's low quantities, and lack of importance at an ecological level. While we have many studies that go into how excess Lithium can be toxic, in moderation it's associated with growth, among other functions. But we don't really know what the effects of deficiency of Lithium are. And as of today, this is the biggest challenge for this emerging technology.

However, since this research paper was just three months old at the time of publishing this post, clearly there's a lot of work left to do, and this needs a lot of further research. But what's there today? It's extremely promising.