For the past three decades, lithium has been the element at the heart of every rechargeable battery that matters, from the one in your phone to the packs stacked beneath the floor of a Tesla. Now, a different element, one row down on the periodic table and roughly a thousand times more abundant in the Earth’s crust, is about to take a share of that work. CATL, the world’s largest battery manufacturer, has begun mass production of sodium-ion battery cells for electric vehicles, with the first passenger cars rolling off production lines by mid-2026.
The cells, branded Naxtra, achieve an energy density of 175 watt-hours per kilogram. That is lower than the best lithium-ion cells on the market, but it is high enough to power a car for around 600 kilometres on a single charge under Chinese test-cycle conditions, roughly 370 miles. More striking is how they perform in the cold. CATL says the Naxtra cells retain more than 90 per cent of their capacity at minus 40 degrees Celsius and can charge at temperatures as low as minus 30 without degradation. Lithium iron phosphate cells, the current workhorse of affordable EVs, lose significant capacity well before those temperatures are reached.
The engineering case for sodium is straightforward. Sodium is the sixth most common element on Earth. It can be extracted from seawater, rock salt, or the brine waste from desalination plants. Lithium, by contrast, is concentrated in a handful of countries, primarily Australia, Chile, and China, and its price has been volatile. A sodium-ion cell uses no cobalt, no nickel, and no copper current collectors. Instead, it uses aluminium foil for both the cathode and anode current collectors, which is cheaper, lighter, and more widely available.
The trade-off has always been energy density. Sodium ions are larger and heavier than lithium ions, which means they store less energy per unit of weight. CATL’s achievement is to push sodium-ion density to a level competitive with lithium iron phosphate (LFP), currently the dominant chemistry in Chinese and increasingly in European EVs. At 175 Wh/kg, Naxtra is not far off the 180-200 Wh/kg range typical of production LFP packs.
CATL’s chief scientist, Wu Kai, said the company had systematically addressed over 100 engineering challenges to reach this point. Four barriers in particular had to fall: extreme water control during manufacturing, gas generation within the hard carbon anode, adhesion of the electrolyte to aluminium foil, and the development of self-forming anode systems. Each of those problems sounds niche, but each was serious enough to have stalled previous attempts at commercial-scale production.
Engineering Deep Dive: Sodium-Ion Batteries
The basic architecture of a sodium-ion cell mirrors that of a lithium-ion cell. There is a cathode (positive electrode), an anode (negative electrode), a liquid electrolyte that carries ions between them, and a separator that prevents short circuits. During discharge, sodium ions travel from the anode through the electrolyte to the cathode, while electrons flow through the external circuit, doing useful work. During charging, the process reverses.
CATL’s Naxtra uses a layered oxide composite cathode, a crystal structure where sodium ions sit between sheets of metal oxide. The metals in the cathode are typically iron and manganese, both cheap and abundant. The anode uses hard carbon, a disordered form of carbon produced by heating biomass or polymers at high temperatures. Unlike the graphite anodes used in lithium-ion cells, hard carbon has a turbostratic structure, meaning its carbon layers are randomly oriented rather than neatly stacked. This randomness creates voids and interlayer spaces large enough to accommodate sodium ions, which are about 30 per cent wider than lithium ions.
The water control problem is specific to sodium-ion chemistry. Sodium compounds are far more hygroscopic (water-absorbing) than their lithium equivalents. Even tiny amounts of moisture in the manufacturing environment can degrade the cathode material and generate gas inside sealed cells. CATL’s solution involved developing new drying protocols and controlled-atmosphere production lines that maintain moisture levels below parts-per-million thresholds throughout the entire manufacturing chain.
Gas generation in hard carbon anodes occurs during the first charge cycle, when the solid electrolyte interphase (SEI) forms on the anode surface. This layer is essential. It allows sodium ions to pass while blocking electron flow, preventing further decomposition of the electrolyte. But if the SEI forms unevenly or too thickly, gas bubbles can create pockets that reduce capacity and cause swelling. CATL engineered both the electrolyte formulation and the initial charging protocol to produce a thin, uniform SEI.
Students studying A-level Chemistry will recognise the electrochemical principles at work: redox reactions driving ion transfer, the role of electrolytes as ionic conductors, and the relationship between electrode potential and energy storage. The concept of crystal structure, taught in A-level Chemistry and Materials modules, is directly relevant to understanding why layered oxides and hard carbons work as electrode materials.
Perhaps the most intriguing engineering detail is the safety system. CATL’s proprietary electrolyte forms a passive insulation layer when the cell is damaged, and incorporates what the company calls “interface dendrite blocking technology.” Dendrites are needle-like metal growths that can form on an anode during fast charging, potentially piercing the separator and causing a short circuit. CATL’s approach creates a chemical barrier that blocks dendrite propagation, acting as a firewall against thermal runaway.
The cold-weather performance connects to the activation energy of ion transport. At low temperatures, the electrolyte becomes more viscous and ion mobility drops. Sodium ions, despite being larger, maintain better transport properties in CATL’s electrolyte formulation at extreme cold, partly because the electrolyte was specifically engineered for low-temperature performance. The result is nearly three times the discharge power of equivalent LFP cells at minus 30 degrees, a meaningful advantage for EV owners in Scandinavian, Canadian, or Scottish winters.
CATL is targeting full GWh-scale production by the end of 2026, with the first sodium-ion passenger vehicles expected from Chinese automaker Changan. Whether sodium-ion cells will complement or compete with LFP in the longer term depends on how quickly the energy density gap narrows. CATL has indicated it aims to match LFP performance within three years. If that target holds, the economics of cheap, abundant sodium could reshape not just the EV market but also grid-scale energy storage, where cost per kilowatt-hour matters more than weight.
- CATL has begun mass production of Naxtra sodium-ion battery cells for electric vehicles
- Energy density of 175 Wh/kg approaches lithium iron phosphate performance
- Cells retain over 90% capacity at minus 40°C, significantly outperforming LFP in cold weather
- Uses no cobalt, nickel, or lithium, with aluminium foil instead of copper collectors
- First sodium-ion passenger vehicles expected from Changan by mid-2026
