Where are we at with Li metal?
part 1 of 2
Making lithium metal at scale and putting it into cells is the key to unlocking lots of the next generation battery technologies. Today Román Healy is back with part 1 of 2 focused on making lithium metal.
Lithium, an element that played a key role in medicine during the 19th and 20th centuries, was first used to treat gout and later became important in psychiatric care. It was even included in early formulations of 7Up, where it was marketed as a health-boosting beverage. Today, lithium has taken the throne in another field: the battery industry. It is a critical component in enabling rechargeable batteries, which are found everywhere in our lives.
Back in the 1980s, Molicel released the first Li-metal battery but safety issues, which I will touch on later, forced the company to reclaim them. After that, Sony released the first rechargeable Li-ion cell containing a carbon-based anode instead of lithium metal. Since then, most Li-based rechargeable batteries have used carbon-based anodes (typically graphite). With the interest of reaching higher energy densities and the rise of all solid-state batteries, lithium metal is seen as one of the routes to next-generation batteries.
Graphite anodes are considered safer because lithium ions intercalate between their layered structure rather than depositing as metallic lithium. This suppresses the formation of dendrites: needle-like structures that can penetrate the separator and cause internal short circuits. However, this enhanced safety comes with notable trade-offs:a limited theoretical gravimetric capacity of about 372 mAh/g, reduced volumetric energy density and lower cell voltages.
Lithium metal anodes rely on lithium plating and stripping, processes that are more prone to dendrite formation. If these issues can be effectively mitigated, they offer high theoretical gravimetric capacity of 3,860 mAh/g.
Next-generation batteries (i.e solid-state and liquid Li-metal, Li-sulfur, Li-air) are key to enabling higher gravimetric and volumetric energy densities, which would expand batteries’ capabilities beyond portable electronics and EVs.
How do we go from natural resources to Li metal?
An entire article could be devoted to the lithium supply chain, however; the purpose of this discussion is to focus on lithium metal. This section will briefly run through all the steps and pinpoint the most important.
Lithium does not occur in nature in its metallic form. Hard-rock resources include minerals such as spodumene, lepidolite, and petalite, with spodumene being the most widely used due to its abundance. Brines, which might be more familiar to the general public as they are found in tins, are water bodies such as underground aquifers where lithium is present in solution as dissolved lithium salts.
The hard rock route requires freeing the lithium salt from the crystal lattice. The first step involves mining. Taking spodumene as an example, it is found in pegmatite deposits, which are highly abundant in Australia, making up over 70% of the world’s spodumene supply. Once mined, the ores are crushed and ground to make separation of spodumene and other mineral rocks easier. Then, a heating step is required to convert the naturally found α-phase to β-phase. Such a step is critical, as the β-phase is less dense, and has a more open crystal lattice making lithium more accessible.
Lithium leaching is typically performed with sulfuric acid (H2SO4) which has a strong affinity to lithium and high conversion efficiency. The result of this step is a lithium sulfate (Li2SO4) rich solution that also contains impurities. After the purification step, lithium carbonate (Li2CO3) can be precipitated and recovered. Lithium hydroxide (LiOH) can also be obtained, but not directly through precipitation. Some companies like Tesla have opted for an acid-free route that involves using NaCl followed by high-energy milling. By using NaCl as a cationic source, lithium can be easily displaced and LiCl is obtained and then converted to LiOH. This process, however, is used to obtain precursors for cathode synthesis rather than for Li-metal synthesis.
The brine route generally involves less steps but requires longer times. To start, the lithium-containing brine has to be pumped from underground reserves, which also carries other dissolved salts. These brines are then left to evaporate over long periods of time in ponds/lakes. This concentrates the brine, and non-lithium salts precipitate. Once the brine has reached a desired concentration, a chemical treatment is carried out to remove additional impurities. Lastly, like the mineral route, once the solution is purified, lithium is recovered through precipitation of lithium carbonate.
It must be noted that processing techniques like direct lithium extraction are gaining momentum as they aim to bypass the evaporation step by selectively trapping lithium ions from the brine.
Alternative routes, like lithium clay, have been gaining popularity in the US as hard-rock or brines are not widely available and countries look for mineral sovereignty. The steps followed are very similar to the hard-rock route, with the exception that no phase transition is needed, so leaching can be done directly after mining. Although finer particles make lithium extraction easier due to shorter diffusion paths, larger surface areas increase leaching solution consumption and make separation of solid-liquid more challenging.
Once lithium carbonate or lithium hydroxide are obtained, they are converted into anhydrous lithium chloride (LiCl) and mixed with potassium chloride (KCl) to lower the melting point of the salt mixture. This molten LiCl–KCl system is then used as the electrolyte for molten-salt electrolysis. At the positive electrode, chloride ions are oxidized to form chlorine gas, while at the negative electrode, liquid lithium metal is produced. Due to its low density, the molten lithium floats to the surface, allowing for easier collection. Companies that carry out this electrolysis step typically also manage the metal-forming operations, as they have necessary equipment to prevent air or moisture exposure, which would affect the final product due to the high reactivity of lithium. In this final stage, lithium metal is cast into ingots, and in some cases rolled into sheets or foils.
After this complex and multi-step processing route, lithium metal is shipped to companies aiming to integrate it into next-generation battery technologies. In the next part, I will discuss the industrial requirements and performance challenges, as well as highlight companies that are making significant progress toward enabling lithium metal batteries at scale.
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