- See also: EV Charging Options | EV Range Variables | Battery Cell Balancing
There are (currently) two different types of chemistry used in the manufacture of batteries that store electrical energy to power the motors in electric vehicles. Lithium Nickel Manganese Cobalt (NMC) batteries have been the most common type of Lithium battery in local EVs, but now Lithium Ferrous Phosphate (LFP) batteries are finding their way into an increasing number of new EVs.
And that has led to plenty of discussion about ‘which battery is best’….
What is a battery?
Batteries store electrical energy. This energy is created by a chemical reaction.
Lithium EV batteries store 400 volts of energy in most vehicles, though some store 800 volts.
We are all familiar with smaller batteries that have two electrical terminals – a positive terminal (also known as the cathode) and a negative terminal (also known as the anode). EV batteries are no different in this regard – they have a positive and a negative terminal.
Inside a battery are materials that create a chemical reaction, which causes electrons to flow between the anode and the cathode.
If those electrons can be channelled via an electronic device, on their way from the anode to the cathode, that electronic device comes to life – be it a light or a motor, etc.
Many portable electronic devices – radios, torches, phones, cameras, etc, are equipped with a battery, providing the electrical energy that causes the device to operate when the electrons move from the battery through the wires connecting the anode to the cathode.
A Lithium battery is able to be recharged when the electrons that have gathered on the cathode are pushed back to the anode, through an electrolyte that is between the anode and cathode.
Electric Vehicles are equipped with a very large battery, usually located under the floor of the car. This battery stores electrical energy to power the vehicle’s electric motor. (Electronic accessories are powered by a separate 12V battery.)
Depending on the particular vehicle, the battery will be an LFP battery or an NMC battery. Both are now widely deployed in popular EVs.
An individual Lithium battery cell, which is where the chemical reaction takes place, produces around 3-4 volts. To produce the 400 volts required to power an electric vehicle, at least 100 cells (usually several hundred, or even thousands of cells) are joined together in a package that we know as a single battery pack.
LFP and NMC – what is the difference?
Both types of battery operate when Lithium ions move between the anode and the cathode.
In an LFP battery (Lithium Ferrous Phosphate) the cathode is made from Lithium iron phosphate, while the cathode is made from carbon or graphite.
In an NMC battery (Nickel Manganese Cobalt) the cathode is made from Lithium, nickel, manganese and cobalt, and the anode is made from carbon or graphite.
Each battery chemistry has pros and cons, generally based on cost and performance, both short term and long term.
Over the past few years, LFP batteries (also known as LiFePo4 batteries) have become popular in the camping and caravan world, powering camping lights and fridges. LFP batteries are excellent for storing electrical energy very safely, and are only 1/3rd of the weight of the old Lead Acid batteries they are replacing in caravans and Campervans. A 12 volt lead-acid battery (like we used to start the motor in our old combustion vehicles) weighs in at around 33kg, while the equivalent Lithium battery weighs in at around 12kg, while providing twice the energy storage capacity.
As rechargeable Lithium battery technology has developed, NMC batteries have become popular for use in portable electronic devices, since they are very ‘energy dense’, packing more energy storage into a package that is the same size and weight as a lower capacity LPF battery. LFP batteries have been more commonly deployed in stationary storage situations – eg caravans and residential installations.
The storage capacity of all batteries deteriorates over time, especially with continual discharging and recharging. Each time a battery is discharged and then recharged is referred to as a ‘cycle’.
- LFP batteries are claimed to suffer only minor performance degradation over 4000 to 5000 cycles.
- NMC battery performance doesn’t begin to deteriorate until beyond 2500 cycles.
- LFP batteries are less energy dense that NMC batteries…
- NMC batteries have greater energy storage capacity, for their size and weight, than similar sized LFP batteries.
- LFP batteries are cheaper to manufacture than NMC batteries.
There are also some ethical issues involved in the discussion regarding the production of batteries – in particular the sourcing of manganese and cobalt for NMC batteries. (Plenty of info available on the net!)
Which battery is best for an EV?
Both batteries are fine in an EV.
Manufacturers favour NMC batteries in long range models, because they pack more energy storage into the same size battery. An LFP battery can supply 100-150 Wh/kg, while an NMC battery can supply 150-200 Wh/kg.
LFP batteries are cheaper that NMC batteries, so they will often be the preferred option in lower cost EVs.
How about the long term battery lifespan?
If one ‘cycle’ is a full recharge, and an LFP battery has a lifespan of 5000 cycles then, at one recharge cycle a week, you can expect a lifespan of around 96 years. (In theory at least.)
For an NMC battery, with a lifespan of 2500 cycles, at one full recharge cycle each week, your battery lifespan will be reduced to only 48 years.
What about maximum charge capacity?
The long term storage capacity of both LFP and NMC batteries will degrade over time, and this degradation will increase if the batteries are stored (without use) at 100% SoC (State of Charge).
The overall lifespan of NMC batteries, before they begin to degrade, is said to be improved if the battery is regularly charged to only 80% SoC.
LFP batteries are not so affected in day-to-day use and can be charged regularly to 100% SoC, if being discharged regularly by driving the car.
Neither LFP nor NMC batteries like being stored at a full state of charge for extended periods of time. Even an LFP battery, which is happy being charged to 100% for daily use, shouldn’t be left sitting for weeks at a 100% SoC. If you are going away and leaving the car in the garage for a month or two, an LFP battery will prefer sitting at 70% SoC, rather than 100%. Ditto for an NMC battery.
The Bottom Line
Both battery chemistries are just fine for use in an EV.
Your LFP battery can be regularly charged to 100% for daily use, but it doesn’t matter too much if it is only charged to 80%.
For daily use, the experts suggest that your NMC battery will have an improved lifespan if regularly charged to only 80% – but it isn’t an issue if you charge it to 100% when needed for a longer trip, as long as you don’t leave it sitting at 100% SoC for weeks at a time. Charge tonight, drive tomorrow.
Both LFP and NMC batteries benefit from being charged to 100% at least every couple of months, to initiate cell balancing. This is a function built into the internal battery electronics – the Battery Management System (BMS) – that ensures the hundreds of individual 4 volt cells that make up the 400 volt Lithium battery are all equally charged. (The overall performance of a battery is affected by the performance of the weakest cell.)
It is early days, but despite all the fear and gloom, it is expected that most Lithium batteries may well outlast the life of the car.
- See also: EV Charging Options | EV Range Variables | Battery Cell Balancing
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