Kyle Proffitt
Most of the world’s rechargeable batteries still depend on lithium as the key energy-carrying molecule, but as electrification increases, our mining efforts are not likely to keep up with demand. In addition to diversifying into sodium-ion and other battery chemistries, we need economical routes to a larger lithium supply. One such opportunity involves pulling lithium directly from salty liquid sources, and a team from the University of Chicago has just reported a fundamental understanding governing methods and materials that make this possible even when the lithium is outnumbered by sodium 1000 to 1. The work appeared July in Nature Communications (DOI: 10.1038/s41467-026-72755-4).
“We are putting the ions into a crystalline material … like how people are storing lithium charge in a battery material, it’s the same principle here,” explained final corresponding author Chong Liu. “We always can get to the level of 104 of lithium selectivity compared to all the other ions,” she added.
Battery Power Online spoke with Liu to learn how her group’s research will help us directly acquire lithium from saltwater.
How We Get Lithium
Currently, the world’s supply of lithium originates from just a few regions, and almost all of it transits China for refining and integration into battery materials. The bulk, about half, starts in Australia, where it’s mined from the ground as part of the mineral spodumene. Chile produces about one quarter of the world’s lithium, but there it is found in saltwater brines, particularly the Atacama salt flats. The largest known inland deposits are more brines in Argentina and Bolivia (the South American regions are collectively often referred to as the lithium triangle). These latter deposits are also the most concentrated known lithium samples, containing at up to 5,000 mg/L. In these locations, the process for extracting lithium can take 12-18 months and involves pumping brine to the surface to form large lakes, which are left to naturally evaporate and leave behind the salts.
The US also has large brine deposits, most notably the Smackover formation, which extends under portions of Arkansas, Louisiana, Texas, Alabama, Mississippi, and Florida. This geologic formation is estimated to contain a similar total quantity of lithium to that in the Atacama salt flats—enough to easily exceed worldwide demand today. The government is quite interested in pursuing these domestic supplies and is actively funding associated research.
Finally, the ocean contains an estimated 200 billion metric tons of lithium (roughly 50 times as much as all of the land-based lithium combined), but at a much lower concentration of about 0.18 mg/L (180 parts per billion).
Fishing for Lithium
Unlike the South American lithium triangle, lithium concentrations in the Smackover are closer to 500 mg/L and better suited to direct lithium extraction (DLE) techniques that pull lithium from a solution based on some material property. “Can we just fish out the lithium specifically?” Liu asked, describing this approach.
Of DLE methods, adsorption, which uses aluminum-based adsorbents that selectively bind lithium, is the only commercialized method. Adsorption requires a threshold lithium concentration and a heat source to operate most efficiently, and the lithium is eluted with water, requiring some concentration afterward.
Liu and her team are taking a different approach.
“We are developing these electrochemical intercalation-based reactions for lithium extraction, and they are extremely selective,” Liu said. The idea is to use current to drive lithium ions into the interlayer spacing of a crystalline material just like many electrodes for lithium-ion batteries.
In earlier publications, Liu’s group identified layered cobalt oxide as a promising material amenable to this technique. In effect, the layered oxide acts like a sponge that preferentially soaks up available lithium. However, depending on the brine source, lithium can be a minor species. “We have to deal with the competition of lithium to many other ions that exist in such brines, like sodium, magnesium, potassium, calcium … but all these other ions will be orders of magnitude higher in concentration,” Liu explained.
Thus, a major challenge is not only how to isolate lithium but how to do so when similar ions are present in vast excess. Sodium ions in particular are challenging to avoid, because they have the same (+1) charge and a similar, though slightly, larger size, meaning they can occupy the exact same lattice sites as lithium ions. Lithium and sodium ions can trade in and out of these positions through an ion exchange process.
Although cobalt oxide was previously shown to have greater specificity for lithium intercalation, there’s complexity regarding the intrinsic forces: the rate of ion exchange, how layered oxide particle size influences behavior, the proper current to apply. With more of this knowledge, “it is a fundamental question about how high of a selectivity of lithium we can get through either chemistry or material design,” Liu said.
Equilibrium Matters
The layered cobalt oxide Liu’s group used for intercalation can accept sodium, lithium, or a mix of both, in different amounts depending on how many vacancies—empty lattice spaces—remain. When both ions are present, the material settles toward a happy medium, a two-phase equilibrium—some regions of 48% sodium (one phase), and others of 94% lithium (second phase). Although the layered oxide can be pushed into other arrangements, the structure will naturally relax toward a mixture of just those two species through ion exchange and rearrangement. It’s very similar to an ice-water mixture, with liquid and solid both at 0 °C. Briefly heating will locally increase the temperature of liquid water, but the mixture will equilibrate, melting some ice, and return to a rebalanced mixture of liquid water and (less) solid ice, each at 0 °C. In the same way, an equilibrated composition for cobalt oxide can exist in ratios of Na0.48CoO2:Li0.94CoO2 anywhere from 100:0 to 0:100.
The vacancy level is a key parameter then, because as vacancies decrease along the equilibrium line, more lithium can be accepted, to the extreme where 6% vacancies correlate with 100% Li0.94CoO2—no sodium in the structure. Essentially the smaller lithium ions can access much more space relative to sodium, which is why the equilibrium is 48% sodium and 94% lithium in the first place. The researchers influence vacancies by driving ions into the lattice using voltage.
“We need lithium 0.94 as our final product; that ensures it’s all lithium,” she said. “What we are doing for this paper is to figure out in what way we can get to the lithium 0.94 as reversibly and as high purity as possible … because we could be stuck in some sort of metastable state where it’s not in equilibrium but trapped with a lot of sodium in there.”
Ion Exchange Vs. Intercalation
To maximize lithium, the effects of competing rates must be considered. Ions are driven to intercalate into the layered oxide material using current, but sodium ions in the lattice can naturally exchange with lithium ions in solution, and vice versa. Because the material has an innate preference for an equilibrium of Na0.48CoO2 and Li0.94CoO2, it will actually swap in minority lithium ions (despite being outnumbered 1000:1 here) as vacancies decrease, provided that the rates of intercalation and ion exchange are balanced appropriately. For this to happen, to get the most lithium into these materials, “the intercalation has to be slower than the ion exchange,” Liu explained. “Then the ion exchange can always take over to replace the sodium with lithium.”
Alternatively, “if we do intercalation too fast, then it will push the composition out of the lithium-rich region to the sodium-rich region,” Liu said, a state that instead relaxes toward an equilibrium “with a lot of sodium stuck in the structure.” Fortuitously, she explained, “naturally the selectivity will go up to a point where we almost fully intercalate this material; it will be able to overcome four orders of magnitude differences in concentration and just allow pure lithium in the structure.” In fact, the selectivity (defined as the preference to grab lithium ions relative to sodium ions) was 9.7 x 104, nearly five orders of magnitude. “The key of this paper,” she summarized, is “how we pull lithium into the structure, how fast we do that, and how that speed compares to the interactions with sodium in ion exchange … that competition really matters.”
Particle size is another parameter the group studied, revealing that smaller layered cobalt oxide particles are optimal because they enable faster ion exchange rates and thereby promote greater lithium selectivity.
Lithium Ion Release
Another important advance from the publication is the demonstration of repeated intercalation and recovery processes. After maximizing Li+ occupancy, the voltage can be reduced to pull lithium ions back out of the structure. Unlike the case for loading, which required the intercalation rate to exceed the ion exchange rate, the applied current is not critical for lithium release, so the loading and release processes are considered asymmetric. In practice, they recovered 99% pure lithium ions after repeated load/release steps.
Ultimately, the fundamental understanding from this study will allow researchers to choose how they apply current to drive intercalation. Liu provided a hypothetical example of a different material prepared using a different active material mass loading or alternate particle size. “Even though I don’t know … the morphology and the density of the electrode, as long as I put the material in to measure the ion exchange rate, then I know how much current I should apply for the lithium extraction process,” she explained.
Future Directions
Commercializing this technology is being pursued. Getting away from the critical mineral cobalt is desirable, and Liu confirms that they are studying manganese-rich layered oxides because they also show Li+ selectivity. She also confirmed that they are exploring the Materials Project database “to find the optimized material where we can consider getting rid of some of those expensive elements.”
Liu expects commercialization to involve some kind of flow system instead of the stationary vessels used in their experiments, but many intermediate optimizations are needed. “It cannot be only an effort of material science or chemistry; it has to be a group of people, a team effort from the very fundamental materials, chemistry, to engineering, to how we design the process, all that,” Liu said.
With sufficient optimization, perhaps one day we can even fish lithium from the ocean. Though not tested directly in this study, prior work from Liu’s group demonstrated that even this is possible in principle.