Sodium-ion batteries: the next step towards cheaper electric cars

Cheaper electric cars will depend on cheaper batteries. Right now, LFP batteries look like the strongest value option, but in the near term there may be an even more affordable alternative: sodium-ion batteries.

Sodium-ion batteries stand out immediately because they do not require lithium, unlike LFP (lithium iron phosphate). Even though LFP packs cost less than the more common NMC (nickel, manganese and cobalt), they are still lithium-ion batteries - and that is where the issue begins.

Although there is enough lithium on Earth, we are heading towards a situation where demand outstrips supply - meaning many more mines will be needed. That would push prices up, and it does not help that a small number of countries control this raw material, with China in the lead.

Sodium-ion batteries could be one way to tackle lithium-related constraints as the car industry moves towards full electrification. The question is: are they truly viable?

Advantages and disadvantages of sodium-ion batteries

In practice, sodium-ion batteries are similar to lithium-ion batteries - both elements sit in the same group of alkali metals - so they share comparable properties. Their operating principle is identical: there is a cathode and an anode, and sodium ions (rather than lithium ions) move between them to generate electricity.

They are not brand new technology either; sodium-ion batteries have existed since the 1980s. However, they only regained momentum in this century, precisely because lithium brings challenges of its own and batteries remain expensive.

So, what advantages do sodium-ion batteries offer compared with lithium-ion? Here are the key ones:

• Abundance - sodium (also found in salt) is the sixth most abundant material on the planet;
• Cost - abundance supports a lower price than lithium, and other materials used in the battery can also be cheaper (for example, copper can be replaced with aluminium);
• Environment - a sodium-ion battery does not require rare metals and is easier to recycle;
• Safety - they can be fully discharged, unlike lithium-ion batteries, and shipping is far safer, removing the risk of fire;
• Temperature range - unlike lithium-ion batteries, sodium-ion batteries perform very well in cold conditions, retaining 90% of output at -20 ºC;
• Charging - up to 80% of total capacity in under 20 minutes.

If sodium-ion batteries bring so many benefits, why are they not already in widespread use? As expected, there are drawbacks - significant enough that they have not been seriously adopted until now:

• Energy density - the big “Achilles’ heel”: lower than lithium-ion batteries, including LFP, which means more battery is required to achieve the same capacity;
• Mass - sodium is heavier than lithium, and when combined with lower energy density it can worsen the already high weight of electric vehicles;
• Service life - fewer charge/discharge cycles than lithium-ion batteries, especially LFP.

Development of sodium-ion batteries has accelerated in recent years, and these disadvantages are expected to be reduced. China’s giant CATL, for instance, has already presented a sodium-ion battery with energy density and service life that are competitive with LFP.

In the table below, you can see how sodium-ion batteries compare with lithium-ion batteries (LFP and NMC):

On cost (€/kWh), NMC batteries are the most expensive. LFP packs are on average 20% cheaper, while sodium-ion batteries are between 10–20% more affordable than LFP.

With production scaled up, they could become cheaper still. CATL estimates prices of 40 dollars per kWh for its second-generation sodium-ion batteries.

Will sodium-ion batteries replace lithium-ion batteries?

Despite the most recent promising progress - particularly around energy density and charge-cycle performance - it is very unlikely that sodium-ion batteries will completely replace lithium-ion batteries. Lithium-ion technology is advancing too.

Even so, sodium-ion batteries have clear room to establish themselves, especially in the lower segments where price is the deciding factor.

When will we see sodium-ion batteries in electric cars?

We probably will not have to wait long. In China, a test prototype of the Sehol E10X city car (a brand created through the joint venture between JAC Motors and the Volkswagen Group) was shown recently with sodium-ion batteries from HiNa Battery.

The pack has 25 kWh of capacity - with an energy density of 120 Wh/kg - and enables the E10X to travel 252 km between charges. That is an excellent figure, if we set aside the fact it is based on the Chinese cycle, which is far less demanding than the WLTP cycle.

It is unclear whether it will reach production, but China’s BYD has already promised a version of the small Seagull fitted with a sodium-ion battery. When it arrives, it is set to use a 30 kWh pack and offer a range of 305 km (again, on the Chinese cycle).