What is cylindrical cell ?

A cylindrical cell is a type of rechargeable (or sometimes primary) battery where the core components are rolled up ("jelly roll") and housed inside a rigid, cylindrical metal can (typically steel or aluminum). They are one of the most common and mature battery form factors.

Here's a breakdown of their key characteristics and features:

Shape

As the name suggests, they have a cylindrical shape, similar to a standard AA or AAA battery, but often much larger.

Structural composition

A typical cylindrical cell consists of a housing, a cap, a positive electrode, a negative electrode, a separator, an electrolyte, a ptc element, a gasket, a safety valve, etc. Generally, the battery casing is the negative terminal of the battery, and the cap is the positive terminal. The battery casing is made of nickel-plated steel plate.

• • Jelly Roll: The core consists of thin sheets of anode material, cathode material, and separator rolled together into a spiral ("jelly roll"). This maximizes surface area within the cylinder.

  • Metal Can: The jelly roll is inserted into a durable metal cylinder. This provides excellent mechanical stability and protection.

  • Electrolyte: Liquid electrolyte fills the space within the can and between the electrode layers.

  • Terminals: Positive (+) and negative (-) terminals are located at each end of the cylinder. The positive terminal usually has a raised cap with a safety vent mechanism, while the negative terminal is the flat base (or vice versa depending on design).

  • Safety Vent: A critical feature designed to rupture and release pressure if internal gas builds up due to overheating or malfunction, preventing explosion.

Common models

Cylindrical lithium-ion cells are usually represented by five digits. Starting from the left, the first two digits indicate the diameter of the battery, the third and fourth digits indicate the height of the battery, and the fifth digit indicates the roundness. Common cylindrical cell models include:

• 18650: The most famous type. ~18mm diameter, ~65mm height. Used extensively in laptops, power tools, and early Tesla vehicles.

• 21700: ~21mm diameter, ~70mm height. Increasingly popular, offering higher capacity/power than 18650. Used in newer Tesla models, e-bikes, power tools.

• 26650: ~26mm diameter, ~65mm height. Often used in higher-power applications like larger flashlights or solar storage.

• 4680: ~46mm diameter, ~80mm height. Tesla's newer, larger format designed for higher energy density, power, and simplified manufacturing.

• Others: Many other sizes exist (14500, 10440, 32650, etc.).

Advantages

• Mature & Proven: Decades of manufacturing refinement lead to high reliability and consistent quality.
• Robust & Durable: The rigid metal casing provides excellent mechanical strength, crush resistance, and protection.
• Excellent Thermal Management: The cylindrical shape and metal can efficiently transfer heat generated during operation to the outside environment or a cooling system. This is crucial for performance and safety.
• Manufacturing Efficiency: Highly automated, high-volume production lines exist, keeping costs relatively low.
• Standardization: Standard sizes allow for easier integration into different battery packs and compatibility across manufacturers.
• Safety: The strong casing contains internal failures well, and the pressure vent provides a critical safety release.

Disadvantages

• Packaging Inefficiency: When packed into a rectangular battery module/pack, the inherent round shape creates empty spaces ("voids") between cells, reducing the overall volumetric energy density of the pack compared to prismatic or pouch cells.
• Complex Pack Assembly: Building large battery packs requires many individual cells (thousands in an EV), along with complex wiring, busbars, and battery management system (BMS) connections.
• Weight: The metal casing adds weight compared to pouch cells.
• Thermal Gradient: In very large cylindrical cells (like 4680), managing heat uniformly across the larger jelly roll can be a challenge.

Common Applications

• Electric Vehicles (EVs): Tesla (historically 18650/21700, now 4680), Lucid, Rivian, and others.
• Electric Bikes/Scooters
• Power Tools (Drills, Saws, etc.)
• Laptop Computers
• Flashlights
• Portable Electronics
• Consumer Electronics (Vapes, etc.)
• Stationary Energy Storage Systems (ESS)

In essence

A cylindrical cell is a robust, standardized, and reliable battery design where the electrodes are rolled into a spiral and housed in a strong metal tube. Its excellent thermal performance, durability, and mature manufacturing make it a dominant choice, especially for applications demanding high power and reliability, despite some packaging inefficiencies. Tesla's heavy reliance on them for EVs has significantly boosted their prominence in recent years.