Sodium-ion batteries: the affordable future of electric cars

For electric cars to become more affordable, cheaper batteries will also be required. LFP batteries currently appear to be the strongest option, but another, even more affordable alternative could soon emerge: sodium-ion batteries.

Unlike LFP (lithium iron phosphate) batteries, sodium-ion batteries do not require lithium. Although LFP batteries cost less than the more widespread NMC (nickel, manganese and cobalt) units, they are still lithium-ion batteries. That is where the issue lies.

While there is enough lithium on Earth, demand is heading towards exceeding supply, meaning that many more mines will be needed. This will push prices upwards, and control of this raw material is concentrated in a small number of countries, led by China.

Sodium-ion batteries could provide an answer to the challenges associated with lithium on the road towards the full electrification of the car. But are they genuinely viable?

Advantages and disadvantages

Sodium-ion batteries are broadly similar to lithium-ion batteries: both elements belong to the alkali metal group and share comparable properties. Their operating principle is exactly the same, with a cathode and an anode between which sodium ions, rather than lithium ions, move to generate electricity.

Nor are they entirely new. Sodium-ion batteries have existed since the 1980s, but they have only attracted renewed interest this century, precisely because of the challenges posed by lithium and the high cost of batteries.

What advantages do sodium-ion batteries offer over lithium-ion batteries? Here they are:

• Abundance - sodium, which is also found in salt, is the sixth most abundant material on Earth;
• Cost - its abundance makes it cheaper than lithium, while the other materials used to make the batteries are also less expensive; for instance, copper can be replaced with aluminium;
• Environment - sodium-ion batteries do not require rare metals and are easier to recycle;
• Safety - unlike lithium-ion batteries, they can be fully discharged, making them much safer to transport and eliminating the risk of fire;
• Temperature range - unlike lithium-ion batteries, sodium-ion batteries work very well in cold conditions, retaining 90% of their performance at -20 °C;
• Charging - they can reach 80% of total capacity in under 20 minutes.

If sodium-ion batteries offer so many benefits, why are they not already in widespread use? As expected, they have some drawbacks, substantial enough to have prevented their adoption until now:

• Energy density - this is their main “Achilles’ heel”, as it is lower than that of lithium-ion batteries, including LFP units, requiring more batteries to achieve the same capacity;
• Mass - sodium is heavier than lithium and, combined with lower energy density, this could worsen the already excessive weight of electric vehicles;
• Service life - they offer fewer charging and discharging cycles than lithium-ion batteries, particularly LFP batteries.

Development of sodium-ion batteries has gathered momentum in recent years, and these disadvantages are expected to be reduced. Chinese giant CATL, for example, has already unveiled a sodium-ion battery with energy density and service life that are competitive with LFP batteries.

The table below shows how sodium-ion batteries compare with lithium-ion batteries, including LFP and NMC types:

When it comes to cost (€/kWh), NMC batteries are the most expensive. LFP batteries are, on average, 20% cheaper, while sodium-ion batteries cost between 10–20% less than LFP batteries.

However, as production scales up, they could become even cheaper. CATL estimates a price 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 advances in energy density and charging-cycle life, it is highly unlikely that sodium-ion batteries will completely replace lithium-ion batteries. The latter are continuing to evolve as well.

Nevertheless, sodium-ion batteries have room to establish themselves in the market, particularly in the lower segments, where price is a crucial factor.

When will sodium-ion batteries appear in electric cars?

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

The battery has a capacity of 25 kWh, with an energy density of 120 Wh/kg, and enables the E10X to travel 252 km between charges. That is an excellent figure, provided the fact that it uses the Chinese cycle, which is far less demanding than the WLTP cycle, is overlooked.

It is not known whether it will reach production, but fellow Chinese manufacturer BYD has already promised a version of the small Seagull fitted with a sodium-ion battery. When it arrives, it will have a 30 kWh battery and a range of 305 km, again measured on the Chinese cycle.