The 18650 lithium-ion battery for electric vehicles is a standard battery type developed by Sony Group Corp in Japan, with 18 meaning 18mm in diameter, 65 indicating 65mm in length and 0 denoting a cylindrical battery. 18650 lithium-ion batteries have a nominal voltage of 3.6V or 3.7V per cell and a minimum end-of-discharge voltage of 2.5-2.75V. Common capacities range from 1200-3300mAh.
A significant number of EV manufacturers are now choosing 18650 lithium-ion batteries as their power source. The 18650 battery is the earliest, most mature and most stable lithium-ion battery and is widely used in electronic products. Over the years, Japanese manufacturers have accumulated extensive experience in the production process of 18650 batteries, resulting in a very high level of consistency and safety of the 18650 battery. Due to the small cell capacity of 18650 batteries, the number of cells required to drive an electric vehicle is high (7104 for the Model S), but their consistency is excellent, allowing for easy thermal management.
The charging and discharging efficiency and safety of lithium-ion batteries are directly linked to temperature, and the number of charge and discharge cycles is highly dependent on temperature. Lithium-ion batteries experience a rapid rise in temperature at 90°C-120°C due to their chemical instability, a phenomenon known as thermal runaway. For both of these reasons, most EV makers have set the temperature wall for their EV batteries at 50°C or less to ensure the economic and safe operation of the batteries. Although the 18650 Li-ion battery is not a new technology, it is still the best choice at this stage until there is a major breakthrough in battery technology.

Author Professor Wei-Keng Lin Education｜Ph.D., University of Maryland Occupation｜Professor, National Tsing Hua University  Specialty｜Electronic package heat dissipation, Heat pipe, Loop heat pipes(CPL，LHP，PHP), Energy-saving design, Solar heat storage and cooling, Heat flow system, Cooling of electronic components, Two-phase flow, Heat transfer elements of artificial satellite and high-altitude flying object