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Electric Vehicle Battery Cells Explained

authorIcon By Stéphane Melançon on May 06, 2022 topicIcon Batteries

Title photo: EV Battery Design courtesy of Tech Space

EV batteries are one of the most important components of electric vehicles, and they are the most expensive. By replacing internal combustion engines, they can drastically reduce pollution all over the world, as transportation currently represents 27% of the world’s greenhouse gas emissions.

EV batteries are composed of cells, and there are many types of cells. In this article, we will break them down in categories and go over the most important types. We will also discuss possible future cell types and how they can change the automotive industry.

  1. The 3 Cell Formats Used in Electric Car Batteries
  2. The Most Common Cell Chemistries Used in EVs
  3. Energy Cells vs. Power Cells: What is the Difference?
  4. Supercapacitors and Ultracapacitors to Boost Power
  5. Future EV Battery Cell Types

The 3 Cell Formats Used in Electric Car Batteries

There are three basic types of battery cells used in electric vehicles: cylindrical cells, prismatic cells, and pouch cells. There are also coin cells, which are used in research and development for testing purposes, but never actually used in electric vehicles.

The number of cells in an EV varies widely based on the cell format. On average, EVs with cylindrical cells have between 5,000 and 9,000 cells. This is in stark contrast with pouch cells, which only have a few hundred cells, and an even lower number in prismatic cells. 

Cylindrical Cells

A cylindrical cellCylindrical cells are the least expensive format to manufacture because they are already self-contained in a casing that offers good mechanical resistance. The technology is not only cost-efficient, but it is also mature, making it a format easy to manufacture.

Because of their shape, cylindrical cells have limitations in terms of power. For this reason, EVs with smaller batteries such as hybrid vehicles use pouch or prismatic cells to deliver more power during accelerations.

Cylindrical cells need to be manufactured in a smaller format than other types of cells to make sure they dissipate heat well, helping prolong the battery life. That’s why the most common cylindrical cell formats are the 18650 and 21700. Larger formats such as the 4680 are viable because their new internal design allows more efficient heat transfer to the thermal adhesives used in structural batteries.

Prismatic Cells

A prismatic cellPrismatic cells can be 20 to 100 times larger than cylindrical cells. They can typically deliver more power and store more energy for the same volume because less material is used for the casing. The casing’s shape and thickness also allow better heat management than cylindrical cells.

Prismatic cells are popular among Chinese manufacturers because their preferred cell chemistry (the lithium iron phosphate battery) currently mostly exists in the prismatic format. Lately, prismatic cells have been gaining in popularity elsewhere in the world. While cylindrical cells used to be the most popular format, prismatic cells might take over a large share of the market in the upcoming years.

Pouch Cells

A pouch cellPouch cells are made to deliver more power than other cell types. They are also very efficient when it comes to space usage. Their soft plastic casing, however, means they have the lowest mechanical resistance of all cell types. For this reason, an additional structure needs to be added during pouch cell assembly to protect them from mechanical damage.

The Most Common Cell Chemistries Used in EVs

A cell’s chemistry is a mix of materials in the battery that makes possible electron sharing between two electrodes (the anode and the cathode) to obtain the desired electric potential. Electrons go from one electrode to the other, and vice versa. 

There are many chemistries, and each one uses different materials that come at different costs. The cell’s chemistry has a huge impact on the cost of the battery. Since the battery is the most expensive part in an electric vehicle, it’s an important consideration when it comes to minimizing production costs.

Here are the most common cell chemistries used in electric vehicles:

  • Lithium Ion (Li-Ion): Lithium-ion cells are the most popular cell types because of their cost efficiency. They offer the best trade-off between energy storage capacity and cost efficiency. There are many types of li-ion cells. The Tesla Model 3, for example, used NCA cells (lithium nickel cobalt aluminium oxide) until 2021. In China, certain Tesla Model 3 cars are now using LFP cells (lithium iron phosphate).
  • Nickel Manganese Cobalt (NMC): Nickel Manganese Cobalt cells offer a great balance between power and energy. They were the favorite chemistry for two generations of Chevy Volts.
  • Nickel Metal Hydride (Ni-MH): The Nickel Metal Hydride chemistry was used in the very first hybrid cars such as the Prius because it was the most affordable technology at the time. Nowadays, they have mostly been outclassed by lithium batteries but are still used in some hybrid electric vehicles such as the 2020 Toyota Highlander.
  • Lithium Sulphur (Li-S): Lithium Sulphur cells have a high-energy storage capacity, making them attractive for EV buses. However, they need to be heated up before they can be operated, making their use more complex and less attractive.
  • Lead-Acid: Lead-acid batteries have been used in the most popular EVs for decades: golf carts! Although their performance is low compared to other cell types, it’s enough to meet the needs of low-performance EVs like golf carts. Lead-acid batteries are low maintenance and easy to replace. Unlike other types of batteries, mechanics do not need to contact battery manufacturers for maintenance and replacement. But now, as li-ion batteries are becoming cheaper and easier to access, the popularity of lead-acid batteries is dropping, as some golf carts are starting to use lithium-ion batteries instead. 

Energy Cells vs. Power Cells: What is the Difference?

An image showing electric power compared to electric energy using a water hose as an analogy

Image courtesy of : FreeingEnergy

 

Batteries can be optimized to store more energy (energy cells) or deliver more power (power cells). Generally, it makes more sense to use energy cells in larger batteries and power cells in smaller ones. As the battery gets larger, the total power is split between a higher number of cells, and each cell needs to deliver less power. 

Hybrid cars, for example, have a smaller battery and often require power cells. Power cells allow keeping the battery small while meeting power needs. 

Power cells are not limited to smaller batteries. They are also used in high-performance electric vehicles such as Formula E. In fact, they are well adapted to any vehicle with a low autonomy and a high-power demand. 

Supercapacitors and Ultracapacitors to Boost Power

Supercapacitors and ultracapacitors are similar to batteries in that they are energy storage systems, but they’re not quite the same thing. While batteries use chemical reactions to store energy, ultracapacitors store an electrostatic charge.

Ultracapacitors have a high power throughput and are used in conjunction with batteries to boost power. They can deliver a lot of power in a short time, and they can do it hundreds of thousands of times without significant degradation. 

Ultracapacitors have a very low energy density, so they do not contribute to the battery’s range. But when they are mixed in a lithium-ion battery pack, they manage power and energy demands in a very good manner. Ultracapacitors are there for high power surges. Batteries are there for high autonomy.

Due to the importance of ultracapacitors for batteries, Tesla bought Maxwell Technologies in 2019, a huge company manufacturing ultracapacitors, to complement their research being done on batteries. 

Watch the following video to get a wider perspective on supercapacitors.

 

Future EV Battery Cell Types

New types of battery cells are currently being developed for electric vehicles, taking EVs to new levels in terms of power, range, production costs, and so on. 

One of the most promising technologies is the solid-state battery. The technology is similar to lithium-ion batteries, but it features solid electrolyte instead of liquid. Solid-state batteries will provide faster charges, more power, and lower production costs. They are expected to be ready for the market around 2030.

Liquid air battery technology, another development that uses air to store energy, is very promising as well but is far from being ready due to its short life cycle. Mohammad Asadi, Assistant Professor of Chemical Engineering, explains the implications of this technology for electric vehicles:

Imagine you have an electrical vehicle today that can run just 300 miles on a single charge. If you replace that battery with our technology, the lithium-air battery technology, you can drive up to 1,500 to 2,000 miles–increasing your driving range five to six times with the same weight and the same volume

Breakthrough in Lithium-air Batteries Could Help Put More Electric Vehicles On The Road

Conclusion

The electrification of the automotive industry is forcing manufacturers to evolve quickly and adopt new technologies they may not fully understand yet. Cells need to be assembled into battery modules and/or packs. The high degree of precision that they demand means many traditional technologies may no longer be viable.


If you want to discuss your EV battery project, contact our experts today. They can help you understand the implications of your project and see how laser technology can help.

 

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Stéphane Melançon's picture

Stéphane Melançon

Technical expert and consultant in batteries and electrical propulsion systems, Stéphane holds a Physics degree with specializations in Photonics, Optics, Electronics, Robotics, and Acoustics. Invested in the EV transformation, he has designed industrial battery packs for electrical bikes. In his free time, he runs a YouTube channel on everything electrical.