Sodium-ion batteries and cheaper electric cars

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

The first big difference is that sodium-ion batteries do not need lithium, unlike LFP (lithium iron phosphate). Even though LFP packs are cheaper than the more widespread NMC (nickel, manganese and cobalt) cells, they are still lithium-ion batteries - and that is where the issue lies.

Although there is plenty of lithium on Earth, we are moving towards a situation where demand outstrips supply, which means many more mines will be required. That would push prices up, and it does not help that control of this raw material sits with a small number of countries, led by China.

Sodium-ion batteries could be a way to answer lithium-related challenges as the automotive world moves towards full electrification. The question is whether they are genuinely viable.

Advantages and disadvantages

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

They are not completely new technology either: sodium-ion batteries have existed since the 1980s. However, interest has ramped up this century, precisely because lithium brings challenges and battery costs remain high.

So what advantages do sodium-ion batteries have over lithium-ion packs? 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 battery materials can also be cheaper (for example, copper can be replaced with aluminium);
• Environment - sodium-ion batteries do not require rare metals and are easier to recycle;
• Safety - they can be fully discharged, unlike lithium-ion batteries, making transport far safer and removing the risk of fire;
• Temperature range - unlike lithium-ion batteries, sodium-ion cells perform very well in the cold, retaining 90% performance at -20 ºC;
• Charging - up to 80% of total capacity in under 20 minutes.

If the benefits are so compelling, why are they not already in widespread use? Predictably, there are drawbacks - significant enough to have limited adoption so far:

• Energy density - the major "Achilles' heel": lower than lithium-ion batteries, including LFP, which means more cells are needed to deliver the same capacity;
• Mass - sodium is heavier than lithium, and combined with lower energy density this can worsen the already high weight of electric vehicles;
• Service life - fewer charge/discharge cycles than lithium-ion batteries, especially compared with LFP.

Development has gathered pace in recent years, and it is expected that these weaknesses will be reduced. China’s CATL, for example, has already unveiled a sodium-ion battery with energy density and service life that are competitive against LFP.

In the comparison table referenced below, you can see how sodium-ion batteries stack up against lithium-ion batteries (LFP and NMC).

On costs (€/kWh), NMC batteries are the most expensive. LFP batteries are, on average, 20% cheaper, and sodium-ion batteries are 10-20% more affordable than LFP.

With production scaling 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 - in both energy density and charging cycles - it is very unlikely that sodium-ion batteries will completely replace lithium-ion batteries. Lithium-ion technology is also continuing to evolve.

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

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

It likely will not take long. In China, a test prototype of the Sehol E10X city car (a brand born from the joint venture between JAC Motors and the Volkswagen Group) was shown recently, fitted with sodium-ion batteries from HiNa Battery.

The pack is 25 kWh in capacity - with an energy density of 120 Wh/kg - and enables the E10X to travel 252 km between charges. That is an excellent figure, as long as we do not forget it is measured on the Chinese cycle, which is far less demanding than the WLTP cycle.

It is not yet clear whether it will reach production, but another Chinese company, BYD, has already promised a version of the small Seagull equipped with a sodium-ion battery. When it arrives, it will have a 30 kWh battery and a range of 305 km (again, on the Chinese cycle).