How do sodium-ion batteries work, and can they replace lithium?

Why sodium-ion batteries matter

Most rechargeable batteries in phones, laptops and electric cars today use lithium. Sodium-ion batteries are an alternative that uses sodium, the element found in table salt. Sodium is widely available, so the hope is that these batteries can be cheaper to make and less exposed to supply shortages. A 2021 briefing from the Faraday Institution, the UK's battery research institute, makes this case, noting that sodium is far more common than lithium.

The trade-off is weight. Sodium ions are larger than lithium ions, and the hard carbon anodes most sodium-ion cells use hold less charge than the graphite used in lithium-ion cells, so sodium-ion cells end up heavier for the energy they store. That matters most in cars and anything else that has to carry its own battery. It matters less for a battery that sits in one place, which is why the Faraday Institution sees fixed storage, where cost matters more than weight or volume, as a natural fit. In its November 2023 announcement, Northvolt said its first sodium-ion cell was designed primarily for energy storage.

This article separates three things: what has been shown by independent tests, what companies have reported about their own products, and what is still speculation.

How it works

Sodium-ion batteries work on the same general principle as lithium-ion batteries, but use sodium ions in place of lithium ions. In both, ions shuttle between two electrodes. According to the Faraday Institution, the ions are stored in the negative electrode when the battery is charged and in the positive electrode when it is discharged. Because sodium ions are larger than lithium ions and behave differently, the electrode materials have to be different.

The negative electrode, or anode, is where the design differs most. Lithium-ion cells typically use graphite. Hard carbon has become the most popular anode choice for sodium-ion cells, although the Faraday Institution notes that how sodium is stored in hard carbon is still debated. CATL's 2021 announcement describes a hard carbon anode with a porous structure, paired with a Prussian white cathode. Northvolt's 2023 cell used the same pairing: a hard carbon anode and a Prussian White-based cathode, with no graphite.

What has been demonstrated

The sources checked for this article contain no independent test results for any named sodium-ion product. The figures below come from the manufacturers themselves and are not backed by third-party testing. The Faraday Institution briefing is a review of the field, not a test of these products. Companies say they have built sodium-ion cells and, in one case, a product they describe as mass produced. These are company statements, not independent demonstrations. They do not show how the cells perform across a full range of conditions over many years.

What is reported

The figures below are company claims. None of them has been checked against independent test data in the sources reviewed here.

CATL, 2021

In a press release dated 29 July 2021, CATL said its first-generation sodium-ion cell reaches up to 160 Wh/kg at cell level. It said the cell can charge to 80% in 15 minutes at room temperature, keep more than 90% of its capacity at -20°C, and reach a system integration efficiency above 80%. The company also said its next-generation target is energy density above 200 Wh/kg. That is a target, not a result.

Northvolt, 2023

Northvolt announced on 21 November 2023 that a sodium-ion cell, developed with research partner Altris, had been validated at over 160 Wh/kg at Northvolt Labs in Västerås, Sweden. The company said the cell was free from lithium, nickel, cobalt and graphite, and that it was designed primarily for energy storage. This is a validation result reported by the company itself. The release gives no independent test conditions.

These were Northvolt's plans as of November 2023. On 12 March 2025, Northvolt filed for bankruptcy in Sweden. The sources reviewed here do not show what has happened to its sodium-ion work since then.

CATL Naxtra, 2025

On 21 April 2025, CATL unveiled Naxtra, which it describes as the world's first mass-produced sodium-ion battery. The same page also calls it "mass-producible", so the release itself is not consistent on whether it was already in mass production. The company says the passenger-vehicle version reaches 175 Wh/kg, offers over 10,000 cycles and a 500 km range, and retains 90% of usable power at -40°C. The announcement gives no test conditions or independent verification for these figures. A company describing its own product as mass produced is a claim to check, not a fact the sources confirm.

What is speculative

Several things people hope for are not established by any source checked here.

• Cost parity with lithium-ion. No source reviewed for this draft shows that sodium-ion cells currently cost less than cheap lithium-ion cells. The Faraday Institution's 2021 briefing estimated that the bill of materials could be 20 to 30% lower than for lithium iron phosphate cells once production reaches a similar scale. That is a projection, not a measured result.
• Large-scale home storage. Northvolt's stated aim in 2023 was energy storage, but whether sodium-ion packs become cheap and safe enough for homes is not shown by these sources.
• The 200 Wh/kg next-generation goal. This is a target CATL set in 2021. Nothing reviewed here shows it has been reached.

Limits and open problems

• Energy density. The best reported figures, 160 to 175 Wh/kg, are company claims. The Faraday Institution explains that hard carbon anodes hold less charge than graphite and lose more of it on the first cycle, which makes cells heavier. This is why sodium-ion cells suit fixed storage, where weight matters less, better than long-range cars.
• Company claims without independent data. Cycle life, cold-weather power and mass production all come from manufacturer announcements. Test methods and conditions are not published in the sources reviewed.
• Hard carbon and supply chains. These cells depend on hard carbon anodes. In 2021 the Faraday Institution described the sodium-ion supply chain as immature, with cells made in relatively small batches. The sources reviewed here do not show how that has changed since.

What to watch next

• Independent test results for commercial sodium-ion cells, including cycle life and cold-weather performance, published with their conditions.
• Third-party cost data that compares sodium-ion and lithium-ion cells at the same scale.
• Whether companies reach the 200 Wh/kg target that CATL set for its next generation.
• The supply of hard carbon anode material as production grows.
• Whether the Naxtra product, and any sodium-ion storage projects, are reported by independent observers as performing as claimed.