Why choose 18650 batteries for new energy electric vehicles?
As for the technical route of using the 18650 battery cell as the battery of new-energy electric vehicles, people may turn to tesla first. During the development of electric vehicle batteries, tesla tested many kinds of batteries, but then focused on the High security 18650 battery. So what are the advantages and disadvantages of the 18650 battery?
In fact, 18650 refers to the appearance specification of the battery, which is a standard battery model set by Japanese SONY in order to save costs. 18 means 18mm in diameter, 65 means 65mm in length, and 0 means cylindrical battery. 18650 battery originally refers to nickel-metal hydride battery and lithium ion battery, but now it mostly refers to lithium ion battery because nickel-metal hydride battery is less used. The nominal voltage of 18650 lithium ion battery is generally 3.6v or 3.7v. Small discharge termination voltage is generally 2.5 ~ 2.75V. Common capacity is 1200 ~ 3300mAh.
Long life 18650 battery is an early, mature and stable lithium ion battery, which is widely used in electronic products. In contrast, stacked lithium-ion batteries are far from mature. Common ones are square batteries and soft-pack batteries, and even the size, size and position of the pole ear are not uniform. The production process of battery manufacturers cannot meet the requirements. If the consistency of the battery is not up to the requirement, the management of battery groups formed by a large number of battery strings and parallel connections will not allow each battery to perform better, and the 18650 battery cell can solve this problem.
In summary, the High temperature resistance 18650 battery has a small capacity and a large number of required monomers (Model S has 7,104), but the consistency is good. The capacity of the cascade battery can be made larger (20 Ah to 60 Ah), the number of monomers can be reduced, but the consistency is poor. By contrast, it is difficult to invest a lot of money and manpower to improve the production process of cascade batteries with battery suppliers at present. Therefore, when developing Roadster and Model S, Tesla's only option is to purchase batteries from the market and develop battery systems by itself. Developing a battery system that manages more than 6,000 cells with good consistency should be less technically difficult than developing a battery system that manages more than 200 cells with poor consistency. Even if the number of individual cells increases, it will be easier to manage them if they are reliable.