Lithium

Feather-light and silver-white, lithium is the least dense of all solid elements — so buoyant that it floats on water even as it reacts violently with it. Though it sits at the top of the alkali metals column, its behavior is often tamer than sodium or potassium; a chunk of lithium dropped in water fizzes energetically rather than bursting into flame. That single valence electron makes lithium extraordinarily eager to give up a charge, which is exactly why engineers prize it for rechargeable batteries. From the smartphones in pockets to the grid-scale storage systems smoothing out solar and wind power, lithium's electrochemical talent has quietly become the backbone of the modern energy economy. At just 0.534 grams per cubic centimeter, it is also the lightest of all metals by density.

Rechargeable lithium-ion batteries dominate consumer electronics and electric vehicles, exploiting lithium's high electrochemical potential and the ability of lithium ions to shuttle rapidly between electrodes. A typical electric-vehicle battery pack contains tens of kilograms of lithium compounds. Beyond energy storage, lithium carbonate and lithium citrate are first-line mood-stabilizing drugs for bipolar disorder, an application discovered serendipitously in the 1940s. In metallurgy, small additions of lithium improve the strength-to-weight ratio of aluminum alloys used in aircraft frames. Lithium hydroxide is the preferred absorbent for carbon dioxide in spacecraft and submarine life-support systems because it captures CO2 more efficiently per unit mass than alternatives. Lithium stearate thickens greases for high-temperature applications ranging from jet engines to industrial machinery. Molten lithium fluoride serves as a solvent in proposed molten-salt nuclear reactors. Globally, lithium demand is projected to multiply several times over as electrification of transport accelerates.

Johan August Arfwedson, a young Swedish chemist working in Jöns Jacob Berzelius's Stockholm laboratory, identified an unknown alkaline component in the mineral petalite in 1817. The substance behaved like the known alkali metals sodium and potassium but produced a characteristic crimson flame and had a lighter atomic weight than either. Berzelius named it 'lithion' from the Greek lithos, meaning stone, to distinguish its mineral origin from sodium and potassium, which were first found in plant ashes. Arfwedson failed to isolate the pure metal, as did Humphry Davy using electrolysis. It was William Thomas Brande in 1821 who first produced tiny quantities of metallic lithium by electrolysis of lithium oxide. Large-scale production remained impractical until the mid-twentieth century, when electrolysis of fused lithium chloride became the standard industrial method. The discovery of its mood-stabilizing effect by John Cade in 1949, and the Cold War demand for lithium-6 in hydrogen bomb programs, each dramatically expanded its importance.

Lithium is dispersed broadly but thinly through Earth's crust, averaging about 20 parts per million by mass — roughly as abundant as cobalt or nickel but never concentrated into rich, easily mined veins of pure metal. It occurs mainly in pegmatite minerals such as spodumene, lepidolite, and petalite, which form when silica-rich magmas cool slowly and incompatible elements accumulate in residual fluids. The other major source is ancient lake brines: in the high Andean plateau of South America — the so-called Lithium Triangle spanning Chile, Argentina, and Bolivia — evaporation of shallow saline lakes has concentrated lithium in subsurface brines over millions of years. The Atacama Desert's Salar de Atacama hosts the world's largest and most economical lithium brine deposits. Seawater contains roughly 0.17 parts per million of lithium, an enormous total reservoir but too dilute for economical extraction with current technology.

Lithium carbonate, Li2CO3, is arguably the most commercially important lithium compound, used both in battery-grade processing and as a psychiatric medication for bipolar disorder. Lithium hydroxide monohydrate, LiOH·H2O, is preferred for synthesizing high-nickel cathode materials in next-generation batteries because it avoids carbonate impurities. Lithium chloride, LiCl, is the feedstock for electrolytic production of the metal and also serves as a dehumidifier in industrial air-conditioning systems. Lithium hydride, LiH, stores hydrogen compactly and reacts with water to release hydrogen gas rapidly, making it useful in emergency inflation systems. Lithium aluminum hydride, LiAlH4, is an indispensable reducing agent in organic synthesis, capable of converting esters, amides, and carboxylic acids to alcohols or amines under mild conditions. Lithium niobate, LiNbO3, is a ferroelectric crystal used in electro-optic modulators and surface acoustic wave filters for telecommunications.

• Lithium is so light that a block of it the size of a brick would weigh only about 540 grams — less than a pound and a half — and it would float on water before reacting with it.
• The universe's lithium was mostly made in the first few minutes after the Big Bang alongside hydrogen and helium, making it one of only three elements produced by Big Bang nucleosynthesis.
• In the 1940s, Australian psychiatrist John Cade discovered lithium's mood-stabilizing properties almost by accident while testing urate compounds on guinea pigs; his simple observation transformed the treatment of bipolar disorder.
• Lithium-6, one of the element's two stable isotopes, was produced in enormous quantities during the Cold War because it reacts with neutrons to generate tritium, a key fuel for thermonuclear weapons.
• A single kilogram of lithium can store roughly the same electrical energy as 40 kilograms of lead-acid battery material, which is why the shift to lithium-ion chemistry transformed portable electronics.