18650 vs. Pouch Cells: Which Is Better Suited for Electric Vehicles?

In January 2017, Tesla, the world-renowned electric vehicle (EV) brand, announced that its Gigafactory in Nevada had commenced mass production of lithium-ion battery cells. Co-designed by Tesla and Panasonic, the new cylindrical 21700 lithium-ion cell was slated for use in Tesla’s energy storage products and the new Model 3 sedan.

From the 18650 to the 21700, cylindrical lithium-ion cells seem to be gaining unprecedented momentum. However, while Tesla remains committed to cylindrical form factors like the 18650, two other major global EV brands—the Nissan Leaf and the Chevrolet Volt—have taken a different path. Records show that both the Nissan Leaf and Chevy Volt opt for laminated pouch cells for their traction batteries.

Why do these world-class EV brands choose such vastly different battery architectures? What are the respective pros and cons of 18650 cells and pouch cells in automotive applications?

The Core Difference: Electrolyte State

As the two dominant power battery form factors on the market today, 18650 cells and lithium polymer pouch cells are primarily distinguished by their casing materials.

• 18650 cells typically feature a steel enclosure (where “18” denotes an 18 mm diameter, “65” denotes a 65 mm length, and “0” indicates a cylindrical shape) and utilize a wound internal structure for the electrodes and separators.

• Lithium polymer pouch cells utilize an aluminum-plastic laminate film for packaging, with internal electrodes and separators arranged in a laminated (layer-by-layer stacked) structure.

Despite differences in exterior form and internal structure, the underlying chemistry remains virtually identical. Both configurations consist of a cathode, an anode, and electrolyte. The cathode typically uses materials like lithium cobalt oxide (LCO), lithium nickel manganese cobalt oxide (NMC/ternary materials), lithium iron phosphate (LFP), or lithium manganese oxide (LMO). The anode is generally made of graphite, while the electrolyte is a lithium hexafluorophosphate (LiPF6) solution.

The fundamental distinction lies in the state of one key internal component—the electrolyte. Lithium polymer pouch cells use a polymer electrolyte, which is typically a gel or a solid, whereas 18650 cells generally use a liquid electrolyte.

Trade-offs and Distinct Application Sectors

Both 18650 lithium-ion cells and lithium polymer pouch cells have unique advantages and disadvantages:

• 18650 Cells: Currently benefit from highly automated production lines, yielding excellent cell-to-cell consistency and safety standards. Furthermore, their compact size and light weight offer unique advantages for modularity and standardization during system development. Consequently, many industry experts view 18650 cells as the optimal choice for powering new energy EVs at this stage.

  • The Drawback: Their primary disadvantage is a relatively low single-cell capacity (typically around 2–4 Ah). This requires a massive number of cells in an EV battery pack, which significantly complicates the battery management system (BMS) tasked with maintaining cell consistency and managing thermal dissipation.

• Lithium Polymer Pouch Cells: These offer higher single-cell capacity and can be manufactured to be ultra-thin, highly customizable in surface area, and flexible in shape (enabling ultra-thin profiles down to 0.33 mm or 0.50 mm).

  • The Drawback: Their main downsides are poorer cell-to-cell consistency and low mechanical strength. Due to these characteristics, lithium polymer pouch cells are increasingly favored in consumer electronics like smartphones, laptops, and power banks. However, because gel (or solid) electrolytes exhibit lower conductivity and higher internal resistance, pure lithium polymer pouch cells are rarely used in electric vehicles today.

Pouch Cells Are Not Exclusively Lithium Polymer

Since lithium polymer pouch cells are rarely applied in EVs, what type of batteries do the laminated pouch cells in the Nissan Leaf actually use?

In reality, though “pouch cell” is often used interchangeably with “lithium polymer battery,” not all pouch cells are lithium polymer. Pouch cells can also utilize liquid electrolytes, and the Nissan Leaf’s batteries are precisely that: liquid-electrolyte pouch cells.

Whether utilizing polymer or liquid chemistry, pouch cells generally rely on aluminum-plastic laminate packaging. This laminate film is thin and structurally fragile. In extreme scenarios such as vehicle collisions, the film can easily rupture, potentially triggering safety incidents—a primary flaw of pouch cells in new energy vehicles.

To mitigate this safety risk, Nissan added an external aluminum shell around each four-cell module in the Leaf pack. Despite this reinforcement, electrolyte leakage has remained a critical issue for the Nissan Leaf, earning it a notorious reputation among owners as a “leak king” and drawing frequent criticism.