• EV Batteries
• Battery Basics
• Cell Chemistry & Parts
• Cell formats
• Battery Pack & Configuration
• Battery Management System
• Thermal Management
• Cell Balancing
• Charging
• Degradation
• Buffer
• Manufacturers
• Warranty

Cell formats

Several types of cell formats exist for battery cells used in electric vehicles.

Cylindrical Housing

A cylindrical cell consists of sheet-like anodes, separators, and cathodes that are sandwiched, rolled up, and packed into a cylinder-shaped can. This form factor has been used by battery manufacturers for years, with sizes like AAA and AA commonly used in electronics.

Advantages

1. Mechanical Stability: The round shape distributes internal pressure from side reactions almost evenly over the cell circumference, allowing the cell to tolerate higher internal pressure without deformation.
2. High Production Throughput: The cylindrical form factor allows for a high throughput of cells from production lines.

Tesla is one of the few EV manufacturers that use cylindrical cells. BMW will start using them in the next generation.

Common Sizes

Prismatic Housing

Li-ion cells with prismatic housing consist of large sheets of anodes, cathodes, and separators sandwiched, rolled up, and pressed to fit into a hard-plastic or metallic housing in cubic form. The electrodes can also be assembled by layer stacking rather than jelly rolling.

Advantages

• Space Optimization: The box-like shape optimizes the available space when combining prismatic cells into packs.

Disadvantages

• Stress on Components: Parts of a prismatic cell’s electrode and separator sheets close to the container corners can experience more stress, potentially damaging the electrode coating and leading to non-uniform electrolyte distribution.

Pouch Housing

Pouch cells do not have a rigid enclosure like prismatic and cylindrical cells and use a sealed flexible foil as the cell container.

Advantages

• High Packaging Efficiency: Achieves a 90 to 95 percent packaging efficiency, the highest among battery packs.
• Flexible Size: The flexible foil allows for various sizes and shapes.
• Weight Reduction: Eliminating the metal enclosure reduces weight.

Disadvantages

• Swelling: Designers must allocate enough space for cell swelling, which can be as much as 8% to 10% after 500 cycles.

Blade

Blade batteries are a type of lithium-ion battery that use a unique “blade” design for their cells. Unlike traditional cylindrical or prismatic cells, blade batteries are thin and flat, resembling the shape of a blade or wafer.

Advantages

• Compact and Efficient: The blade design allows for a more compact and efficient battery pack.
• Better Heat Dissipation: The flat shape provides more surface area for cooling.
• Safety: Use of a ceramic separator between the anode and cathode layers provides better protection against internal short circuits and thermal runaway.

Blade batteries are primarily produced by the Chinese battery manufacturer BYD.