18650 Cylindrical Cell VS Pouch Cell 

18650 cylindrical cell and pouch cell (polymer batteries) are two common forms of lithium batteries, and they have differences in structure, performance, and application scenarios. Here's a detailed comparison of the main differences:

1. Structure and packaging form

18650 Cylindrical cell:

It is a rigid cylinder: a metal shell (usually steel or aluminum) encased, and the inside consists of a positive electrode, a negative electrode, a diaphragm, an electrolyte, and a safety valve. The 18650 reflects a single size: 18 mm in diameter, 65 mm in height ("0" for cylindrical), and the model is fixed for a modular design. The battery has an explosion-proof design: it is equipped with a safety valve on the top to release internal pressure in the event of overpressure, reducing the risk of explosion.

Pouch cell

Flexible packaging: The aluminum-plastic composite film (outer layer is nylon/PP, middle layer of aluminum foil, inner layer of heat sealing) is used as the shell, and the internal battery cell is laminated or wound structure.

Flexible shape: It can be customized as ultra-thin, square or special-shaped to adapt to the space needs of different equipment.

2. Energy density

18650 Cylindrical cell:

The volumetric energy density is low (about 250-300 Wh/L) due to the voids in the cylindrical structure (about 60-70% utilization rate when grouped). The capacity of the monomer is usually 1200-3500mAh (such as ternary lithium battery cells).

Pouch cell:

The energy density is higher (300-400Wh/L), due to the lack of metal shell and high space utilization rate (group utilization rate can reach more than 90%), the single capacity can easily achieve tens of Ah (such as large-capacity battery cells for electric vehicles).

3. Safety and thermal management

18650 Cylindrical cell：

The metal casing is puncture resistant, but a "jet" flame (safety valve directed pressure relief) can occur in the event of thermal runaway. Complex heat dissipation design is required when grouping (e.g., Tesla's liquid cooling pipeline gap arrangement).

Pouch cell:

Aluminium plastic film may melt at high temperatures, but when it is thermally uncontrolled, it usually bloated and the flame spreads more slowly.

The heat dissipation area is large, but it needs to rely on thermal management at the module level (such as thermal conductive adhesive and cooling plate).

4. Cost & Manufacturing

18650 Cylindrical cell：

Automated production is mature, and the cost of monomer manufacturing is low, but the cost of assemblies is high (welding, structural parts, etc.).

Suitable for standardized products, such as notebooks, power tools.

Pouch cell:

The cost of raw materials is low, because the aluminum-plastic film is cheaper than the metal shell, but the packaging process is complex and the production yield is high. It is more suitable for customized scenarios: for example, the customized battery pack design of car companies.

5. Comparison of advantages and disadvantages

Pick 18650 cylindrical batteries: Scenarios that require high reliability, standardization, and space insensitivity (e.g., power tools).

Pouch cell: Scenarios that pursue lightweight, high energy density, and flexible design (e.g., electric vehicles, flexible electronics).

With the advancement of technology, there is no clear dividing line between the two, some large cylindrical batteries have increased energy density, and bag batteries have also optimized the efficiency of pouch grouping through structural innovation. In the future, we look forward to seeing more technological innovations that can combine the best of both.

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