A cell is like an AA battery you will find at home. It is a casing with a positive and negative terminal and inside are three active elements – the anode, cathode and inert liquid electrolyte.

Multiple cells make a battery. When you read about a battery here, it is pack of cells that are wired together.

Later, when we cover battery life and replacement you will see that often a degraded battery has dead cells. These cells can be replaced far more cheaply than an entire battery. This isn’t always possible as oxygen getting into a pack with a more volatile chemistry like NMC can lead to fires. Some car makers get around this by an intermediate between cell and battery – the module.

In short:

  • A cell is where the electrochemical reaction takes place releasing power
  • A module is a pack of cells
  • A battery is a pack of cells or modules

Let’s now take a look at chemistries.

Chemistries and Safety

NMC and LFP seem to have won the race to be the best chemistries to use in EVs today. What does this mean?

There are three active parts of a battery – the anode that stores positive ions, the cathode that stores negative ions and the electrolyte that they travel between. When a battery is turned on the lithium ions flow between the anode and cathode, creating a current.

When you introduce a current to the battery from the outside, the lithium flows from the cathode to the anode. This is how charging works. The higher the current the quicker this will happen, though too high and a chemical reaction will occur where lithium metal spikes (‘dendrites’) reach out from the cathode to the cathode and cause a short. The short causes a fire – that’s why EV makers limit how much you can charge a car with their chargers.

Anodes have changed little over the years. They are almost always graphite. There are chemicals added as different manufacturers’ ‘secret sauce’ (Tesla may differ from BMW for eg) but these don’t significantly alter energy density. Chemists are spending their time looking for the perfect cathode.

NMC

NMC is the gold standard automotive drive battery chemistry of today. Cars using it currently have energy densities of typically 220Wh/kg.

Better energy density is achieved by using different chemistries on the cathode. NMC is the gold standard for automotive batteries as nickel is one of the best storage metals for lithium. The problem is nickel is a reactive metal so manganese is used to make it less so, and the cobalt is a fire retardant.

Where it comes to performance, NMC batteries can be charged and discharged more quickly. If you want an EV that gives you whiplash as it does 0-60 in three seconds, an NMC battery is ideal. There are drawbacks however.

Cobalt is found in greatest concentrations in countries like the Democratic Republic of Congo, where its mining has caused great environmental destruction and harm to human health. The environmental and human cost has made manufacturers queasy about making a supposedly environmentally sustainable form of transport using it. This is why chemists are trying to ‘squeeze out’ cobalt from EV batteries, and they have been successful to some extent, getting it down to as little as 10% of the cathodes without knock on safety issues.

Nickel is becoming very expensive due to global demand for it in cathodes. This, and the cobalt issue, is why you will generally find NMC batteries in premium end cars. LFP however, is going into EVs at the middle and lower end of the market.

LFP

Lithium ion phosphate cathode batteries are increasingly going into middle and lower end cars thanks to the battery density, that differs from cell density. Currently, EV makers are getting 150Wh/kg, but this is set to increase to as much as 170Wh/kg in 2023.

LFP (also known as LiFePO) batteries are significantly less energy dense than NMC. However, they have more stable chemistry and are less prone to fire than NMC. This means for smaller batteries by volume with fewer safety systems required to be in the cars. Thanks to these factors, more cells can be fit into less space.

Thanks to their stability you can charge LFP batteries to 100%. NMC by comparison can only be routinely charged to 80%, and slow charged the rest of the way. With a battery pack getting you 300 miles, you will need a rest break at least within that distance for your body’s sake! Within the time it takes for a pee and a coffee, you can get another 100% charge in that time. That could mean in a race between a NMC car and an LiFePO car you will be stopping to charge for less time and your overall journey could be comparable in time overall!

You won’t get the hair raising performance of a car with an NMC battery. LFPs won’t release the sort of energy to let a car hit 60 in sub-3 seconds, though you will get there in a lot less time than an equivalent ICE! Nor will we see such vehicles capable of taking 150kW of charge on an ultra-rapid charger.

A final thing to note is that since iron is one of the commonest elements on the planet, we won’t be seeing the price spike anything like that of nickel ores. LFP cells are far cheaper to make and the batteries they sit in are cheaper too. With these factors, LFP is very competitive despite its lower headline energy density and the cars’ performance.

Luxury vs Standard Range Batteries

Today you will find that luxury car models will use NMC and smaller EVs will have LiFePO. For many years the NMC chemistry was the winner when it came to EV drive batteries. Despite its chemical instability, it gave far and away better energy density than LFP. NMC battery demand also sent the cost of environmentally damaging cobalt and nickel ores rocketing, making EVs a lot more expensive to make.

Up to around 2020, NMC batteries had an energy density of around 200 watt-hours (Wh) per kilogram while LiFePO could manage around 130Wh/kg. A 500kg NMC battery would give around 100kWh and a 500kg LiFePO battery, around 65kWh. Both of these are now greater due to advances in technology.

Where it came to a luxury car like a Tesla Model S 100D such weight was fine in a comfortable saloon, and would give a range of around 300 miles per charge in those days. For a mid-sized car like a Model 3, it wouldn’t handle well with a half tonne LFP battery, so Tesla stuck to NMC with a lower range thanks to the lower weight of the battery.

LiFePO is cheaper and a lot less prone to runaway ‘dentrification’ that leads to battery fires than NMC, so it was never out of the race. In 2021 Chinese battery makers BYD launched the Blade battery which fit more cells into a battery casing than its competitors. This gets around 150Wh/kg – or 75kWh/500kg. Smaller cars could have significantly greater range as other efficiencies through the drive system were added.

LFP has taken off, with many global car brands incorporating BYD Blades into their machines. BYD’s immediate rivals CATL have just launched a LiFePO battery with even greater density that we will see in a number of car brands in 2023.

CATL have dispensed with the module and battery casing and now put cells direct into the chassis. This means a lot less packaging and an even lower power to volume as well as higher battery power density. By 2023 this will be happening in a lot of smaller EVs too as the race for ever greater energy density takes another step forward.

Choosing a Battery Makeup

Choosing a car and thereby battery is a question of performance, range and comfort. Where it comes to comfort, people will choose a car according to their income and the way they like to be perceived. You may see someone has traded in their Audi or BMW for a Tesla recently as they have similar levels of comfort.

Tesla offer two broad lines – the standard range and long range. The standard range cars being made today have LFP while the long range, NMC. You may be the sort who feels the need to have shiny things to show off your wealth, and a car with an NMC is definitely that thanks to the increased cost of the metals in the cells!

You may however lead a lifestyle where you need to do long runs on a regular basis. For the same reason you’d choose a large BMW or Jaguar for those longer runs, you may choose a big car with a big, dense battery so you don’t have to stop so often.

For most people covering 7,000 miles a year, a car with a LFP battery is perfectly fine. If you can charge it in 20 minutes to 80% on a 50kW charger then you don’t have to stop too long every time you do!

Used Cars

Where it comes to used cars you will run into different chemistries. The older (5 years +) EVs won’t have great range and not all will be able to be charged very quickly thanks to the nature of the battery chemistry and the manufacturers’ charging systems. Ask about the battery health and real world range of the car now. An older Leaf will still do 100 miles, which for most driving is still ample!

Lifespan of a Battery and Replacement

Most EVs will get 125,000 miles before they fall to 80% of their listed range. Considering most ICE vehicles will get 150,000 miles before falling apart that’s not terrible. A range of factors can contribute to shorter life:

  • How often it has been fast-charged (the fewer the batter)
  • How many miles it has done in a given year (charge/discharge cycles)
  • With NMC, how often it has been charged to 100%

Where it comes to ICEs, you’d not be in a hurry to buy a car from an 19 year old lad or a taxi driver. The 18 year old will have likely had it driving at high speeds while the taxi driver will have put big mileage into it.

While kids who like race cars in supermarket car parks haven’t quite caught onto EVs yet, taxi drivers have thanks to the cost per mile. They will have put a lot of fast charges into it, so there will be a high number of charge/discharge cycles that ultimately reduce the life of the battery.

High mileage drivers may not care too much about long-term battery health so a regular 100% charge may have been done out of necessity. This will be shown in the car’s battery health. Avoid high mileage, lower age cars if possible!

Replacement

Some manufacturers are very careful to only let licensed and certified technicians look at their cars. Tesla is one of those. While that does mean extra cost (the same as with ICE dealerships) it does pay to pay someone who knows what they are doing.

If a battery does start to fail there are three things the dealership can do:

  • Replace the whole battery
  • They can replace a module
  • Switch off dead cells/modules and switch on redundant cells/modules using software.

As you can imagine the third option is going to be cheaper than the first. Where it comes to a warranty repair, the dealership may try to do the cheaper options too, and it is worth asking them what exactly they are doing so you know for any future failures.

Charge Time

No matter what charger used, your car’s charging unit will limit the amount of charge it will receive. If it won’t take more than 22kW then even if you hook it up to a 150kW charger, it will still take 22kW. As we have indicated above, this is down to safety – too much power put into a battery will cause a battery fire.

It is all very well having a full battery that does 400 miles per charge but all too often that won’t be enough. Particularly with NMC, you should keep your battery between 20% and 80% charged most of the time. EV drivers like that 20% bottom as a cushion thanks to the problem of broken chargers too – as with your bank overdraft, it’s nice to have in case of emergency!

Most EV drivers will want to slow charge their cars at home. It is far cheaper than a paid for site and you can slow charge the battery to 100%. Fast and rapid chargers tend to go onto trickle charge when they hit 80% and given the shortage of chargers on the road, that could mean someone asking you to unplug at that stage anyway.

When it comes to miles per hour charged, there are there are four categories:

  • Slow charging is 3.5kW to7.5kW, and will add up to 15 or 30 miles per hour respectively
  • Fast charging is 22kW, and can give up to 90 miles per hour plugged in
  • Rapid is 43-50kW and will give up to 90 miles in half an hour
  • Ultra-rapid chargers are 150kW and up, and will give typically 200 miles in 30 minutes.

Online giant, Amazon has installed the UK’s first 350kW chargers for its electric HGV fleet. These are the first five such chargers in the UK and will add over 800 miles of charge in an hour! Again, plug your old Leaf into one of those and you’ll still get 22kW…

Generally speaking the faster the charge you want, the more you will pay per kWh. While on a home slow charge you will pay less than 28p/kWh, on an ultra-rapid charger this could be 90p/kWh in future. For those who like the lower costs of driving an EV that can be prohibitive.

Mothballing Your Car

Perhaps you have got COVID-19 or have had to look after your sick mother as her full time carer? There will be times when you leave your car for a long time.

Generally speaking you should unplug the 12V battery, and then leave it mothballed with 80% charge on the drive battery and then you should be fine. If it is an emergency, then the old EV driver habit of leaving 20% battery charge in as a minimum should be fine.

If possible you should charge it every couple of months. That means in an ideal world, plugging it in in the garage and topping it up to 80%.

This does differ between car makers. As ever, read the manual for detailed information.

A Word on Fires

A final myth to bust: EVs are far less prone to fires than ICE cars. Research from the US National Transportation Safety Board showed that in 2020, 25.1 EVs had fires reported for every 100,000 sold.

By comparison 1,529.9 ICE cars for every hundred thousand vehicles sold caught fire. Hybrids were a different league again, with 3,474.5 cars per 100,000 sold.

In short, just under one EV caught fire for every 60 ICE cars. One EV caught fire for every 138.4 hybrids.

EVs are far safer than ICE. Can’t say much more than that!