The 18650 battery is the predecessor of the lithium-ion battery, so until now the lithium-ion battery industry basically only has a standard model of the 18650 battery, and the others are designed according to customer needs.

Lithium-ion batteries use liquid electrolytes, while polymer lithium-ion batteries are replaced by solid polymer electrolytes. This polymer can be solid or semi-solid (colloid). Therefore, the polymer lithium battery has various shapes and can be customized.
The 18650 battery and the like need a metal casing, but compared to polymer lithium batteries, the price is better.
Some people say that the 18650 battery will explode. In fact, the 18650 battery is equipped with a safety valve on the top. When the internal pressure of the battery is too high, the top safety valve will automatically pop up to reduce pressure. However, when the safety valve pops out, the lithium ions leaked from the 18650 battery will still catch fire due to contact with oxygen in the air.
Because the 18650 battery has a very good stability at work, it is widely used in various electronic fields: commonly used in high-end glare flashlights, portable power supplies, wireless data transmitters, electric thermal clothing, shoes, portable instruments, portable lighting equipment, portable Printers, industrial equipment, medical equipment, etc.