The selection of Lithium-ion cells for EV battery packs is an important factor in guaranteeing both performance and safety. Three of the most popular chemistries available on the market are LFP (Lithium Iron Phosphate), NMC (Lithium Nickel Manganese Cobalt Oxide) and NCA (Lithium Nickel Cobalt Aluminium Oxide).
A Lithium-ion battery pack consists of various Lithium-ion cells connected in series and parallel to achieve the required voltage and ampere-hour respectively.
Lithium-ion Batteries in EV (Electric Vehicles):
Three most popular Lithium-ion cell chemistries in the market are LFP (Lithium Iron Phosphate), NMC (Lithium Nickel Manganese Cobalt Oxide) and NCA (Lithium Nickel Cobalt Aluminium Oxide).
LFP cell chemistry is safer, cheaper and has higher cycle life compared to NMC and NCA cell chemistries. But the downside of LFP is that its high stability makes it heavier (low gravimetric energy density in Wh/Kg) and bulkier (low volumetric energy density in Wh/L) compared to NMC and NCA cell chemistries. Hence, it is a common understanding that if LFP cells fit in a given dimension to achieve the required voltage and ampere-hour, it is highly preferred for its high value proposition. Hence, LFP is very popular in low range EVs. LFP cells using graphite anode max out at close to 180Wh/Kg and 400Wh/L.
LFP cells can easily perform beyond 60°C but they tend to have a hard time charging below 0°C.
If LFP cells do not fit in a given dimension of a battery pack to achieve the required voltage and ampere-hour, NMC cells are preferred. Its gravimetric energy density and volumetric energy density are balanced, meaning it is better than LFP but tends to be lower than NCA. NMC experiences thermal runaway at an earlier temperature than LFP.
NMC is preferred in high range vehicles. There are various compositions of NMC such as 111, 442, 532, 622 and 811. These days 532 and above variants are available for use in EVs. The higher the nickel content (if the first digit of the variant number is higher), the gravimetric energy density and volumetric energy density increases but it reduces the stability of the cell and leads to lower safety, lower cycle life, lower rate of charge and discharge. NMC cells are not recommended to operate above 60°C but can charge up to some extent below 0°C.
If NMC cells do not fit in a given dimension of a battery pack to achieve the required voltage and ampere-hour, NCA cells are preferred. Its gravimetric energy density and volumetric energy density is higher compared to LFP and NMC. Tesla popularised NCA cells by use in all its previous EV models. But in recent days, Tesla EVs has shifted to LFP cells in lower range vehicle in some markets (hotter countries). NCA cells using silicon graphite anode achieve more than 250Wh/Kg and 700Wh/L. NCA experiences the earliest thermal runaway compared to LFP and NMC. Moreover, the heat released in terms of Joules per gram is also higher than LFP and NMC. NCA cells are to be handled with good thermal management in a battery pack.
Lithium-ion Batteries in ESS (Energy Storage System):
LFP cell chemistry is the most preferred choice since there is no space or weight restriction in most ESS applications. These applications charge and discharge the battery slowly compared to EVs and do not experience frequent pulse current which can reduce cycle life, as is the case in EVs where peak pulse charge current is experienced during regenerative braking and peak pulse discharge current is experienced during acceleration.
LFP cells are highly suitable for the high life required in BESS (Battery Energy Storage System) and hence LFP cells have the maximum market share in the BESS market segment.
Author
Founder, R&D expert
Bollini Energy
