Analysis of 18650 and 21700 batteries in the lithium battery market.
In recent years, the rapid development of new energy vehicles has driven the prosperity of the lithium battery market. Lithium ion batteries play an important role in new energy vehicles due to their high energy density, large capacity, low self discharge rate, and environmental characteristics. As the core component of new energy vehicles, the status of power batteries is self-evident, and lithium-ion batteries stand out in the field of power batteries due to their excellent performance. At present, the widely used cylindrical lithium-ion batteries in the market mainly include 18650 batteries and 21700 batteries.
18650 battery performance
1.1 Technological maturity and security
The 18650 battery, a lithium-ion battery based on the standards of Sony Corporation in Japan, has been shining in the field of electronic products since its launch. The "18" in its name represents diameter, "65" represents length, and "0" indicates that it is a cylindrical design. The 18650 battery technology is mature and highly consistent. In the field of new energy vehicles, Tesla's electric vehicle battery technology route has chosen the 18650 battery. This decision is not accidental, but based on the multiple advantages of 18650 batteries.
Firstly, the 18650 battery technology is mature and highly consistent. Before the rise of new energy vehicles, they were widely used in various electronic products, accumulating rich experience and production technology. These technologies have been effectively transformed in the field of automotive batteries, enabling 18650 batteries to reach a considerable level of safety, durability, and performance.
Secondly, the safety performance of 18650 batteries is also quite outstanding. In the battery management system, a large number of 18650 batteries can be used in parallel without worrying about the consistency of the battery pack. The performance of each battery can be fully utilized, ensuring the stability and safety of the entire battery system. The 8650 lithium battery has excellent safety performance, not only does it not explode or burn, but it is also non-toxic and pollution-free, and has passed RoHS trademark certification.
In addition, the 18650 battery is packaged in a steel shell, which can minimize safety accidents and improve overall safety in extreme situations such as car collisions.
1.2 Size and Energy Density
The 18650 battery has a small size and controllable energy. Compared to using large-sized battery cells, even if a unit in the battery pack malfunctions, its impact can be effectively reduced. In addition, the capacity range of 18650 lithium batteries is between 1200mAh and 3600mah, which is much higher than the 800mAh of general batteries. After being combined into a battery pack, the capacity can exceed 5000mAh, which is one and a half to two times the capacity of nickel hydrogen batteries of the same weight, and the self discharge rate is extremely low. Its energy density can currently reach a level of 250Wh/kg, fully meeting Tesla's high range requirements.
Characteristics and advantages of 21700 battery
2.1 Technological Innovation
However, despite the mature and superior performance of 18650 battery technology, it still faces problems such as high heat generation, complex grouping, and inability to achieve fast charging. Against this backdrop, the 21700 cylindrical ternary battery was born and gradually gained attention.
On January 4, 2017, Tesla announced that the new 21700 battery jointly developed with Panasonic had begun mass production, emphasizing that it is currently the battery with the highest energy density and lowest cost among mass-produced batteries. The 21700 battery, a new model of cylindrical battery, adapts to the demand for longer range of electric vehicles with its unique specifications, while improving the effective utilization of battery space.
2.2 Performance Enhancement
Compared to the common 18650 cylindrical lithium battery, the 21700 battery can increase its capacity by more than 35% under the same material conditions. The new 21700 battery has four significant advantages:
The battery cell capacity has significantly increased. Taking Tesla's 21700 battery as an example, after switching to this model, the battery cell capacity can reach 3-4.8Ah, an increase of 35% compared to before.
The energy density of the battery system has significantly increased. Tesla's data shows that the energy density of its early 18650 battery system was about 250Wh/kg, while the energy density of its later produced 21700 battery system increased to about 300Wh/kg, an increase of nearly 20%.
The system cost is expected to decrease by about 9%. According to Tesla's disclosed battery price information, the power lithium battery system of the 21700 battery is priced at $170/Wh, which is more economical than the $185/Wh of the 18650 battery system. After adopting 21700 batteries on Model 3, the cost of the battery system alone can be reduced by about 9%.
The system weight is expected to decrease by about 10%. Although the overall volume of the 21700 battery is larger than that of the 18650 battery, the increase in its individual capacity results in a higher energy density per cell. Therefore, under the same energy demand, the number of required battery cells can be reduced by about one-third. This not only reduces the complexity of system management, but also reduces the number of metal structural components and electrical accessories required for the battery pack, thereby reducing the weight of the battery. Samsung SDI found that the system weight has decreased by 10% compared to existing batteries after switching to the new 21700 battery.
On the basis of maintaining the high reliability and stable performance of 18650 batteries, 21700 batteries have achieved significant improvements in various aspects of performance. At the same time, it maintains a high degree of similarity with 18650 batteries in terms of raw material selection, manufacturing process, and technical flow, which makes most of the production lines of 18650 and 21700 compatible. Many companies choose to make improvements on their production lines to achieve production modes compatible with 21700 and 18650. Although some companies choose to import production lines from abroad, they all adopt independent research and development in the assembly process, thus achieving the transformation from 18650 to 21700 at a lower cost.
