Cylindrical Lithium Batteries — Overview

Abstract

Cylindrical lithium batteries can be categorized by active material into LiFePO4 (lithium iron phosphate), LiCoO2 (cobalt oxide), LiMn2O4 (manganese oxide) and ternary lithium batteries (NMC). By casing type they can be steel-can or polymer-encapsulated cells. Each material system has its own advantages.

1. What is a cylindrical lithium battery?

Cylindrical lithium batteries are categorized by active material—LiFePO4, LiCoO2, LiMn2O4 or ternary NMC. By casing they are steel-can or polymer cases. Different chemistries offer different strengths.

Currently, cylindrical cells are mostly steel-can LiFePO4. Compared to other types, cylindrical cells are easy to manufacture, offer larger capacity, higher output voltage, good cycle life, stable output voltage and electrochemical performance, wide operating temperature range, and are environmentally friendly. Cylindrical cells are widely used in solar lamps, lawn lights, backup power, power tools and various toys.

Typical cylindrical cell components include: can, top/bottom caps, cathode, anode, separator, electrolyte, PTC element, gasket, safety valve, etc. Generally, the can serves as the negative terminal and the cap as the positive; the can is nickel-plated steel.

2. Common cylindrical cell sizes

Cylindrical cells are commonly named with five digits: the first two digits indicate diameter, the third/fourth indicate height, and the final digit indicates a round cell. Common sizes include 10440, 14500, 16340, 18650, 21700, 26650.

(Cell naming rule)

10440

The 10440 cell measures 10 mm diameter and 44 mm height, similar in size to AA cells. Capacity is usually a few hundred mAh and it is used in mini electronics such as flashlights and mini speakers.

14500

The 14500 cell is 14 mm diameter and 50 mm height, typically 3.7V or 3.2V with nominal capacity around 1600 mAh. It is commonly used in consumer electronics such as wireless audio, toys and digital cameras.

16340

The 16340 cell (16 mm × 34 mm) is common in high-output flashlights, headlamps and laser lights, offering compact size with reasonable capacity.

18650

The 18650 cell (18 mm × 65 mm) is notable for high energy density—often reaching around 170 Wh/kg—making it a cost-effective, mature cell used widely in devices and battery packs.

21700

The 21700 cell (21 mm × 70 mm) increases volume and packaging efficiency, improving single-cell and system energy density versus 18650, and is widely used in electronics, EVs, power tools and street lighting.

26650

The 26650 cell (26 mm × 65 mm) typically has nominal voltage around 3.2V and capacities around 3200 mAh. With strong capacity and consistency, it is emerging as an alternative to 18650 in some power applications.

32650

The 32650 cell (32 mm × 65 mm) offers high continuous discharge capability suitable for power tools, UPS and wind-power applications.

3. Manufacturing and processing

During battery assembly, cylindrical cells undergo multiple welding steps. Automated welding can easily cause double-sheet (double-feed) issues. The Atonm double-sheet detection system can accurately detect single vs double metal sheet feeding and protect tab and electrode welding.