Why is 18650 battery called 18650?

There are several specifications of cylindrical lithium batteries. Among them, 18650 is the most commonly used, and the volume power is also more commonly used, so why is it called 18650?

18650 actually refers to the shape of the battery. It is a standard battery model set by SONY in order to save costs. Among them, 18 means 18mm in diameter and 65 means The length is 65mm, and 0 represents a cylindrical battery. 18650 batteries originally referred to nickel-metal hydride batteries and lithium-ion batteries. As nickel-metal hydride batteries are now less used, they now refer to lithium ion batteries. The nominal voltage of a single cell of 18650 lithium ion battery is generally 3.6V or 3.7V; the minimum discharge termination voltage is generally 2.5~2.75V. The common capacity is 1200～3300mAh.

18650 battery is the earliest, most mature and most stable lithium ion battery, which is widely used in electronic products. Over the years, Japanese manufacturers have accumulated a lot of experience in the production process of 18650 batteries, so that the consistency and safety of the 18650 batteries produced have reached a very high level.

In contrast, stacked lithium-ion batteries are far from mature. The common ones are square batteries, soft-pack batteries, and even the size, size, and location of the tabs are not uniform. Battery manufacturers have The production process of the battery can not meet the conditions, most of which are controlled by humans, and the consistency of the battery does not reach the level of the 18650 battery. If the consistency of the battery fails to meet the requirements, the management of the battery pack formed by a large number of battery strings and parallel will not allow the performance of each battery to better play, and 18650 batteries can solve this problem.

In summary, the cell capacity of the 18650 battery is small, and the number of cells required will be a lot (ModelS has 7104), but the consistency is very good; the capacity of the stacked battery can be made larger (20 Ah to 60Ah), the number of monomers can be reduced, but the consistency is poor.

With regard to energy density, it is necessary to distinguish between the energy density of a single cell and the energy density of a battery pack. In terms of the energy density of the single battery, the 18650 battery is higher than the laminated lithium-ion battery. The energy density of the 33 Ah lithium-ion battery used by Nissan LEAF is 157 Wh/kg, the energy density of the laminated battery used by GMVolt is about 150 Wh/kg; and the energy density of the 18650 battery used by Roadster is about 211 Wh/kg. However, the 18650 battery management system is more complicated, and the additional weight will make the energy density of the battery pack much lower than the energy density of a single cell. The weight of the Roadster battery pack is 450 kg and the energy density is 118 Wh/kg, while the weight of the LEAF battery pack is 225 kg and the energy density is 107 Wh/kg. At the battery pack level, the energy densities of the two are already on par.

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