The Three Major Li-ion Battery Form Factors: Cylindrical, Prismatic, and Pouch

September 06, 2024 by Romesh Gupta

As the demand for lithium-ion (Li-ion) batteries continues to surge, understanding the nuances of the various battery form factors—cylindrical, prismatic, and pouch—is crucial. Each form factor offers distinct advantages and challenges, influencing their application across diverse industries. In this blog, we’ll explore these three major battery formats, their thermal management, and their compatibility with different lithium chemistries, including those that minimize the use of controversial rare metals like cobalt.

Cylindrical Cells: The Tried and True

Overview Cylindrical cells, one of the earliest forms of lithium-ion batteries, consist of rolled sheets of anodes, cathodes, and separators housed in a cylindrical can. This classic design is prevalent in many applications, from consumer electronics to electric vehicles (EVs).

Advantages

Mechanical Stability: The cylindrical shape distributes internal pressure evenly, enhancing the cell's ability to tolerate high internal pressure.

• Manufacturing Efficiency: Automated manufacturing processes are well-suited to cylindrical cells, making them cost-effective and reliable.

Thermal Management: Cylindrical cells' circular cross-section facilitates easier coolant circulation, simplifying thermal management.        

Challenges

• Packing Density: The round shape results in less efficient space utilization within battery packs.

Thermal Distribution: Heat generation is concentrated, potentially posing challenges in high-capacity applications.

Chemistry Compatibility Cylindrical cells often use Nickel Manganese Cobalt (NMC) chemistries with controlled cobalt content or Nickel Cobalt Aluminum (NCA) chemistries, which have lower cobalt content compared to traditional NMC formulations. Advances in chemistry, such as NMC 811, further reduce cobalt use.

Prismatic Cells: The Space Maximizer

Overview Prismatic cells feature large, flat sheets of electrodes and separators housed in a rectangular or cubic metallic or hard-plastic container.

 This design is favored for its efficient use of space.        

Advantages

• Space Utilization: The box-like shape allows for optimal packing of cells, making it ideal for high-capacity applications like EVs and energy storage systems (ESS).
• Thermal Management: While challenging, improved designs can manage heat distribution effectively.

Challenges

Mechanical Stress: Corners and edges can experience stress, potentially causing damage or non-uniform electrolyte distribution.

• Manufacturing Cost: Prismatic cells can be more expensive to produce compared to cylindrical cells.

Chemistry Compatibility

Prismatic cells are suitable for various chemistries, including Lithium Iron Phosphate (LiFePO4), which contains no cobalt. Additionally, prismatic cells can incorporate reduced-cobalt NMC variants, making them versatile for different applications.        

Pouch Cells: The Flexible Contender

Overview Pouch cells use a flexible foil as the cell container, offering a minimalist approach that reduces weight and allows for more adaptable designs.

Advantages

Flexibility: Pouch cells can be easily shaped to fit the available space in a product.

Weight Reduction: The absence of a rigid enclosure decreases the overall weight of the battery.        

Challenges

• Swelling: Pouch cells can swell by up to 8-10% after extensive cycles, requiring careful design considerations to accommodate this expansion.
• Support Structure: Due to their soft construction, pouch cells need proper support to prevent damage.

Chemistry Compatibility Pouch cells are often used with high-energy-density chemistries, including LiFePO4, which eliminates cobalt. Newer formulations of NMC with reduced cobalt content are also used, balancing flexibility with lower cobalt use.

Conclusion: Choosing the Right Form Factor and Chemistry

The choice between cylindrical, prismatic, and pouch cells depends on various factors including space utilization, thermal management, and chemical composition. Each form factor offers unique benefits and challenges, making it crucial to match the form factor with the intended application and desired chemistry.

As the industry continues to innovate, understanding these form factors and chemistries will be key to developing efficient, safe, and environmentally-friendly battery solutions.