Lithium vs Sodium

Almost everyone arriving at this comparison is asking about batteries, so the answer first. If the cell has to be carried — a phone, a laptop, a car — lithium, and nothing else is close on energy per kilogram. If the cell sits on the ground next to a substation and never moves, sodium is a serious contender and getting more so.

Underneath the battery question there is a genuinely interesting chemical one, because lithium is not a well-behaved member of its own group and sodium is the textbook standard against which its oddity is measured.

Why lithium wins on energy density

Three properties compound. Lithium's standard electrode potential is the most negative of any element in aqueous solution, at −3.04 volts against sodium's −2.71, so a lithium cell can be built at a higher voltage. Lithium's atomic mass is under seven, less than a third of sodium's. And the lithium ion is small enough to slot into host lattices that will not accept a sodium ion at all.

Voltage times capacity divided by mass is the whole of gravimetric energy density, and lithium wins all three terms. Commercial nickel-rich lithium cells reach the high two hundreds of watt-hours per kilogram; lithium iron phosphate sits lower, in the range that has nevertheless taken over most standard-range electric cars. Sodium-ion cells shipping today land around 120 to 160, with second-generation designs aiming higher.

That gap is not going to close by clever engineering. It is set by the atomic masses.

What sodium-ion actually buys

The case for sodium is not performance, and vendors who pitch it as a lithium replacement are overselling. The case is cost, supply and a handful of genuine behavioural advantages.

• Both current collectors can be aluminum. Lithium alloys with aluminum at the anode, so lithium cells need copper foil on that side. Sodium does not, so a sodium cell can use the cheaper, lighter metal throughout — a real saving that has nothing to do with the price of the active material.
• The cathode need contain no nickel or cobalt. Layered sodium oxides, polyanionic phosphates and Prussian blue analogues all work, and the elements they use are cheap.
• Cells can be shipped at zero volts. A fully discharged sodium-ion cell is not damaged by being at zero state of charge, which simplifies transport and storage in a way lithium cells cannot match.
• Cold performance is better. Sodium-ion cells retain more of their capacity below freezing, which matters for stationary storage in continental climates.

The anode is different too: hard carbon rather than graphite, because sodium ions do not intercalate into graphite the way lithium ions do. That is a manufacturing difference rather than a disadvantage, and it has the side effect of decoupling sodium cells from the graphite supply chain entirely.

Sodium's other route into storage is not sodium-ion at all. High-temperature sodium-sulfur cells, which run with both electrodes molten at around 300 °C, have been deployed at grid scale for decades, and sodium-nickel-chloride cells occupy a similar niche. Neither has any lithium analogue.

The price of lithium is the whole business case

Sodium is the sixth most abundant element in the crust and about one per cent of seawater by mass. Lithium is a trace element by comparison, concentrated economically in only two kinds of deposit: the brines beneath the salt flats of Chile, Argentina and Bolivia, and hard-rock spodumene, mostly Australian. Refining is concentrated further still.

That asymmetry drove an extraordinary price swing. Lithium carbonate went from a few thousand dollars a tonne at the start of the decade to well over ten times that at the end of 2022, then fell most of the way back. The spike is what funded sodium-ion development; the collapse is why the technology's commercial rollout has been slower than the 2022 announcements implied. Sodium's own raw material cost is close to irrelevant to the price of a finished cell, which is the structural point: sodium chemistry is insulated from exactly the volatility that makes lithium uncomfortable.

Lithium is the odd one out in its own group

Lithium's ion is so small and its charge density so high that it behaves less like the alkali metal below it and more like magnesium, one group across and one period down — the classic diagonal relationship. The differences from sodium are systematic rather than incidental:

• Of the whole group, only lithium will take nitrogen straight out of the air at ordinary temperature and turn it into a nitride. Sodium does nothing of the kind.
• Heat lithium carbonate or lithium hydroxide and both give up their carbon dioxide or water to leave the oxide behind; the sodium counterparts hold together to far higher temperatures.
• Lithium's fluoride, carbonate and phosphate are all poorly soluble in water, while the corresponding sodium salts dissolve freely — a reversal of the usual expectation that alkali metal salts are soluble.
• Burned in excess oxygen, lithium gives the simple oxide, sodium gives the peroxide and potassium the superoxide. Only the smallest cation is content with a plain oxide ion.

That last trend has a practical tail: the superoxide of potassium releases oxygen on contact with carbon dioxide and water vapour, which is why it appears in emergency breathing apparatus, and why the trend down the group is more than a curiosity.

The two elements meet in a kidney

Lithium carbonate has been a psychiatric medicine since John Cade's 1949 report from Australia, and it remains one of the most effective long-term treatments for bipolar disorder despite the mechanism still being argued over.

Its connection to sodium is direct and clinically important. The kidney's proximal tubule handles the lithium ion much as it handles the sodium ion, so when sodium intake falls or sodium is being lost, lithium reabsorption rises with it and blood lithium concentration climbs. With a therapeutic window as narrow as lithium's, that interaction between two chemically similar ions is a monitored risk rather than a footnote.

Outside the cell

Before batteries, lithium's largest markets were elsewhere and they have not gone away. Lithium stearate greases tolerate heat and water better than the sodium and calcium soaps they displaced. Glass-ceramics built on lithium aluminosilicate barely change size at all when heated, which is what suits them to cooktops and telescope mirror blanks. Lithium oxide added to a glass or enamel melt lowers its viscosity. And in fusion research, lithium-6 is the breeding material for tritium, which gives one isotope of a light metal a role no other element can fill.

Sodium's non-battery life was covered thoroughly by the chemical industry long before anyone thought of storing electricity in it, and it is still overwhelmingly a chemistry of compounds rather than of the metal.

Which cell for which duty

• Anything that moves and has a range figure — lithium.
• Grid storage, backed by a cheap and diversified supply chain — sodium-ion, and the case strengthens whenever lithium prices rise.
• A battery that will be stored discharged or shipped internationally in quantity — sodium-ion.
• Cold-climate stationary storage — sodium-ion.
• High-temperature grid storage with decades of field history — sodium-sulfur.
• A grease, a low-expansion ceramic, or a tritium blanket — lithium, none of which has anything to do with batteries.