Comparing NMC and LFP batteries in EVs

Why do some electric vehicles use NMC batteries while others use LFP batteries?

Nearly all electric vehicles (EVs) on the roads use lithium-ion batteries. What makes these batteries different from one another is the chemistry of the positive cathode electrode.

There are two main types of cathode materials: NMC, which consists of nickel, manganese and cobalt oxides; and LFP, from iron and phosphate blends. NMC and LFP batteries make up more than 90 per cent of the lithium-ion battery packs used in EVs today.

LFP batteries are cheaper to make. Lithium and iron are commonly available in the market and thus accessible to battery manufacturers. To a large degree, this is why many mass-market EVs use this type of battery chemistry.

Charging discipline is not as critical for an LFP battery pack compared with an NMC one. An LFP battery has stable chemistry and can be charged only every couple of days. Charging it up to 100 per cent does not degrade the LFP battery as much as with NMCs.

Also, LFP-powered EVs are preferably used at a lower state of charge.

Constantly charging and using them at a level that is nearing the maximum state of charge will result in a phenomenon called lithium inventory loss. This is when there is a permanent reduction of lithium ion in the electrolyte, reducing the accessible battery capacity.

LFP batteries have a narrow operating voltage range. Manufacturers recommend charging them up to 100 per cent once a month. Doing this resets the battery management system and accurately reflects the range. This, however, is an additional step in the ownership experience and will not significantly impact the life cycle of the battery.

NMC batteries are pricier to make than LFPs because of the raw materials used. But they are also more energy-dense. With a higher nominal voltage of 3.7 volts compared with 3.2 volts for LFPs, NMC batteries have a performance advantage. This is demonstrated in how the technology is used in Formula E, the electric racing series.

Regularly charging NMCs to 100 per cent, or maintaining them at full charge, causes greater chemical degradation. You also do not want to run the battery charge down too low. This is because stress occurs at the cellular level of NMC batteries. The lattice structure undergoes severe volume changes as the state of charge drops.

When the charge level gets really low, these changes become so severe that cracks can form in the lattice. Ideally, you want to charge the battery more frequently rather than wait until the charge level gets too low.

As battery chemistry improves, LFP batteries are expected to be even more widely used. Their stability and lower risk of thermal runaway make them a preferred long-term solution for manufacturers. However, the range, chemical stability and flexibility of using NMCs over long distances for multiple cycles cannot be overlooked.