Manufacturing electric vehicle (EV) battery packs starts with the individual cells, which serve as the primary energy storage units for powering the vehicle’s electric motor.
The configuration and design of these cells can significantly impact key performance metrics of an EV, including energy density, operational efficiency, and thermal management. This article explores the different EV battery cell pack designs, analyzing their advantages, limitations, and influence on overall vehicle performance.
EV battery cell pack designs are built around three primary cell types: cylindrical, prismatic, and pouch. Each design offers unique advantages, with no definitive “best” option among the three.
Cylindrical cells
The cylindrical cell comprises a negative electrode (anode) layer, a plastic separator, and a positive electrode (cathode) layer, manufactured as long sheets, rolled up, and placed inside a metal casing. The assembly is then filled with a liquid electrolyte to facilitate ion movement.
Figure 1. Cylindrical battery cells. (Image: ETAuto)
Cylindrical battery cell packs are the most common and can be found in many common devices, including TV remotes and electric bikes. These cells are the most cost-effective to manufacture due to their simple design and mature technology. Their durable metal casing offers strong mechanical protection against vibrations and physical impacts. Additionally, cylindrical cells have efficient thermal management, helping to prevent overheating during high power draw.
However, these cells can present challenges in achieving optimal cell matching and balancing, as slight variations in cell characteristics may affect overall performance. Additionally, when integrated into an EV pack, the cylindrical shape of the cells creates gaps between them, which reduces the overall energy density of the pack and limits the vehicle’s range. While some of this space can be used for cooling in EVs, it still results in inefficient use of volume, reducing the overall packing efficiency.
Despite these drawbacks, cylindrical cells remain reliable for many EV manufacturers, especially for smaller vehicles and high-performance EVs. When comparing lifespan, cylindrical cells typically have a shorter lifespan than prismatic cells but outlast pouch cells.
Prismatic cells
Prismatic cells are characterized by their rectangular or square shape. Internally, the anode, cathode, and separator sheets are pressed together and placed into a rectangular casing of metal (aluminum or steel) or hard plastic. The casing protects the internal components, manages internal pressure, and aids in thermal management by efficiently dissipating heat.
Figure 2. A look inside a prismatic battery cell. (Image: Quantum Scape)
Prismatic cells are designed to optimize space efficiency by eliminating gaps in cylindrical cells, enabling a denser arrangement within the battery pack. However, they come in a limited range of standard sizes, which often requires automakers to design custom battery cases to accommodate each specific cell. This can lead to an increase in EV production costs.
Prismatic cells are often chosen for cars and larger EVs, such as trucks and buses, due to their high energy density and space efficiency.
The rectangular shape of prismatic cells allows for a more compact and uniform arrangement within battery packs, maximizing available space. This makes them ideal for vehicles that require larger batteries to support longer ranges or higher power outputs. While they can be more expensive to manufacture, their ability to scale for larger applications makes them a favorable choice in the automotive industry.
However, prismatic cells are more prone to short circuits and performance inconsistencies due to their stacked layers of positive and negative electrodes. Additionally, their larger size can present challenges for effective thermal management.
Pouch cells
Pouch cells consist of several layers stacked together, including a cathode, anode, and a separator that keeps the electrodes apart while allowing ions to pass through. These layers are then sealed in a flexible, foil-based pouch made from a combination of materials like aluminum and plastic. The pouch casing is lightweight and flexible, unlike the rigid enclosures of cylindrical or prismatic cells.
Figure 3. Pouch battery cells. (Image: Medium)
Pouch cells are unique because they lack a hard casing around the cells, allowing for higher cell-level energy density and lower manufacturing costs. Due to their inexpensive materials and simpler design than prismatic cells, pouch cells allow for rapid manufacturing, making them a cost-effective and efficient option for high-volume production.
However, these cells are notorious for their fragility and environmental sensitivity. Pouch cell batteries naturally expand slightly during typical operation, which can become even more pronounced under high current draw and near the end of their state of charge. Due to their sensitivity, even a deep puncture of the outer casing can trigger a thermal runaway.
Compared to other battery cell types, pouch cells are significantly less reliable and pose more significant safety risks during operation. When in use, these cells require careful handling.
The ideal design
The design and configuration of EV battery cells each bring distinct advantages and challenges. Cylindrical cells offer durability, cost-effectiveness, and efficient thermal management but sacrifice some packing efficiency.
Prismatic cells maximize space utilization and are well-suited for larger vehicles but have higher manufacturing costs and potential thermal management issues. Pouch cells stand out for their lightweight and flexible design but face significant reliability and safety concerns.
Ultimately, the choice of battery cell type depends on the specific requirements of the EV, including its size, range, and performance goals. As battery technologies continue to evolve, manufacturers may find innovative ways to mitigate the limitations of each design, driving advancements in EV efficiency, safety, and sustainability.
References
- Electric Vehicle Battery Cells Explained, Laserax
- EV Battery Cell Formats for Lithium Metal, Quantum Scape
- Prismatic vs. Pouch Cells: Key Differences and Benefits, Goldenmate
Filed Under: Batteries, FAQs