The Rise of 21700 Lithium Batteries
Emergence of 21700 Lithium Batteries
The widely used 18650 batteries have a long history of development, and although relatively mature compared to other types of battery technologies, they still face issues such as high heat generation, complex grouping, and inability to achieve fast charging. In this context, the 21700 cylindrical lithium-ion battery came into being. In January 2017, Tesla and Panasonic jointly developed the new 21700 battery, emphasizing that it is currently the most energy-dense and cost-effective battery that can be mass-produced.
The 21700 battery is a cylindrical battery type, with “21” referring to the outer diameter of the cylindrical battery being 21mm, and “70” indicating the length of the cylindrical battery being 70mm. The 21700 was developed to meet the requirements of electric vehicles for longer driving ranges and to improve the effective utilization of vehicle battery space. Compared to the commonly used 18650 cylindrical lithium-ion batteries, the 21700 has a capacity that can be over 35% higher, using the same materials.
Four Major Advantages of 21700 Lithium Batteries
1. A 35% Increase in Battery Cell Capacity
Taking Tesla’s production of 21700 batteries as an example, switching from the 18650 model to the 21700 model can increase the capacity of individual battery cells to 3-4.8Ah, a significant increase of 35%.
2. Approximately 20% Increase in Battery System Energy Density
According to data released by Tesla, the energy density of the 18650 battery system used in the early stages was about 250Wh/kg, while the energy density of the 21700 battery system produced later was around 300Wh/kg, representing nearly a 20% increase in volumetric energy density compared to the original 18650.
3. Estimated Cost Reduction of About 9%
Analysis of battery price information released by Tesla indicates that the selling price of the 21700 battery power lithium battery system is $170/Wh, while the selling price of the 18650 battery system is $185/Wh. After using 21700 batteries in the Model 3, the cost of the battery system alone can be reduced by approximately 9%.
4.Estimated Weight Reduction of About 10%
The overall volume of the 21700 is greater than that of the 18650, and with the increase in individual capacity, the energy density of each cell is higher. Therefore, the number of battery cells required for the same energy can be reduced by about one-third. This, coupled with a reduction in the number of metal structural components and electrical components in the battery pack, further reduces the weight of the battery. After Samsung SDI switched to a new set of 21700 batteries, they found a 10% reduction in weight compared to the current batteries.
The high reliability and stability of the 18650 battery type are maintained, and the performance of the 21700 battery is significantly improved in all aspects compared to the 18650. Furthermore, compared to other battery types, the 21700 is similar to the more mature 18650 battery in terms of battery raw material selection, manufacturing processes, and technological procedures. Therefore, most of the production lines for 18650 and 21700 batteries are compatible, and some companies opt for a prudent approach by adjusting production lines to be compatible with both 21700 and 18650.
The pursuit of high specific energy in power batteries has become an irreversible trend, and many battery companies are beginning to focus on the layout of 21700 batteries. Some companies import production lines from abroad but assemble them themselves, allowing them to invest less and achieve the transition from 18650 to 21700.