The traditional 18650 battery, with a mature supply chain and low cost, is an ideal lithium-ion battery that has found wide applications in the consumer electronics field. However, due to their smaller capacity, when used in the electric vehicle sector, it often requires assembling tens of thousands of individual cells into battery packs, which significantly increases the complexity of battery pack management. Therefore, under the leadership of Tesla, a storm of replacing 18650 batteries with 21700 batteries has been initiated. Here, I will provide a comprehensive introduction.
Both the 18650 cell and the 21700 cell are named based on their dimensions. The 18650 cell has a length of 65 millimeters and a diameter of 18 millimeters, while the 21700 cell is 70 millimeters long and 21 millimeters wide. These two cell types have a significant size difference, with one being noticeably larger than the other. This size difference allows the 21700 cell to have a larger capacity and, as a result, higher power compared to the 18650 cell.
· Similarities between 18650 and 21700 Cells:
- They are both lithium-ion batteries and have high discharge rates.
- Both 18650 and 21700 cells have the same voltage, which is 3.7V.
- Both types of cells have a relatively long lifespan.
- Working Principle of Cells: When charging a battery, lithium ions are generated on the positive electrode of the battery. These generated lithium ions move through the electrolyte to the negative electrode. The negative electrode, typically made of layered graphite, contains many micro-pores. The lithium ions that reach the negative electrode become embedded in these micro-pores. The more lithium ions are embedded, the higher the charge capacity of the battery.
· Differences Between 18650 and 21700 Batteries:
(1) Size
As mentioned earlier, the 18650 battery is 65 millimeters long and has an 18-millimeter diameter, while the 21700 battery is 70 millimeters long and 21 millimeters wide.
(2) Capacity
18650 batteries typically have capacities ranging from 1200mAh to 3600mAh, while 21700 batteries generally offer capacities between 3000mAh and 5000mAh.
(3) Weight
The weight of an 18650 battery is approximately 48 grams, while a 21700 battery weighs around 60 grams. (Weight may vary slightly depending on specifications.)
(4) Price
Due to the updated features and capabilities of 21700 batteries, they tend to be more expensive compared to 18650 batteries.
(5) Application Areas
18650 batteries are commonly used in devices with lower power requirements, such as handheld electronic devices, laptop battery packs, and electronic cigarettes. In contrast, 21700 batteries, with their higher energy density and better performance, are typically employed in high-end electronic devices, including electric vehicles, power tools, and high-performance portable lighting, among others.
· Working Principle of Cells
When a battery is charged, lithium ions are generated on the positive electrode of the battery. These generated lithium ions then move through the electrolyte towards the negative electrode. The negative electrode, which is typically composed of layered graphite, contains numerous micro-pores. The lithium ions that reach the negative electrode become embedded within the micro-pores of the carbon layers. The more lithium ions are embedded, the higher the charging capacity of the battery.
· Application Areas of 18650 and 21700 Batteries:
18650 batteries are commonly used in devices with lower power requirements, such as handheld electronic devices, laptop batteries, and electronic cigarettes, among other portable devices.
21700 batteries, due to their higher energy density and better performance characteristics, are typically employed in high-end electronic devices. These applications include electric vehicles, power tools, medical diagnostic instruments, medical UPS systems, electric wheelchairs, and more.
Electronic devices like emergency power lights, portable media players, and Bluetooth speakers often use 18650 batteries as their power source. However, electric bicycles and electric cars may utilize both 21700 and 18650 cells for their power needs.
· Can a 18650 charger be used to charge a 21700 battery?
Yes, chargers designed for 18650 cells can be used to charge 21700 cells. Chargers are not dependent on the cell’s capacity, so they will charge 21700 cells in the same way they charge 18650 cells. In comparison to 18650 cells, 21700 cells can support the same or even higher charging currents.
· Can 21700 batteries be used as a replacement for 18650 batteries?
Yes, 21700 batteries can be used as a replacement for 18650 batteries as long as there are no size constraints, as the dimensions of 21700 cells are different from those of 18650 cells.
· Advantages of 21700 Batteries:
Due to the higher energy density of individual cells, only one-third of the cells are required, which reduces the complexity of system management. This, in turn, decreases the use of metals and electronic components, significantly reducing the weight of lithium batteries. Overall energy density will be improved to a certain extent.
With the larger capacity of individual cells, the number of cells required in a battery pack will be greatly reduced when using 21700 cells.
21700 batteries offer a higher energy density compared to the well-known 18650 batteries, and the cost can actually decrease when used in large quantities. In summary, 21700 batteries maintain the high reliability and stable performance of 18650 batteries while providing significant improvements in battery performance across various aspects.
· Disadvantages of 18650 and 21700 Batteries:
In comparison to 18650 batteries, 21700 batteries have a larger capacity but also require longer charging times. The larger size of 21700 cells can shorten their cycle life, reduce battery safety, and adaptability. Safety concerns primarily revolve around the potential for excessive heat generation due to their higher capacity. The manufacturing cost of 21700 batteries is also relatively high.
18650 batteries are more prone to overcharging and over-discharging, like other lithium-ion batteries, and their capacity tends to decrease over time.
In applications such as electric vehicles and some high-power fields, 18650 batteries may not provide sufficient capacity. A single 18650 cell typically has a maximum capacity of 3.5Ah, and for higher energy density and cost-efficiency, it may not be feasible. This results in the need for a larger number of cells in battery modules, increasing the cost and complexity of battery management. 21700 cells, on the other hand, are slightly larger in size and offer higher capacity, making them suitable for applications with high capacity requirements.
· Application Areas of 18650 and 21700 Batteries:
18650 batteries are commonly used in devices with lower power requirements, such as handheld electronic devices, laptop batteries, and electronic cigarettes, among other portable devices.
21700 batteries, due to their higher energy density and better performance characteristics, are typically employed in high-end electronic devices. These applications include electric vehicles, power tools, medical diagnostic instruments, medical UPS systems, electric wheelchairs, and more.
Electronic devices like emergency power lights, portable media players, and Bluetooth speakers often use 18650 batteries as their power source. However, electric bicycles and electric cars may utilize both 21700 and 18650 cells for their power needs.
· How to choose between 18650 and 21700 battery cells?
The main advantage of 21700 batteries over 18650 batteries is their increased capacity, which leads to longer runtime. 18650 batteries typically offer a capacity ranging from 1.5Ah (1500mAh) to 3.0Ah (3000mAh). High-end 18650 batteries (3.0Ah) face production challenges, which is why many manufacturers opt for 2.5Ah (2500mAh) batteries. In contrast, 21700 batteries, commonly used in power tools, start with a capacity of 3.0Ah (3000mAh) and can go as high as 4.0Ah (4000mAh). This means you can find compact (1P) battery packs labeled with 3Ah or 4Ah, while larger (3P) battery packs can reach 12Ah.
Here’s a capacity comparison for typical power tool batteries:
18650:
Compact 1P battery: 2.0Ah–3.0Ah (36 Wh–54 Wh) Standard 2P battery: 4.0Ah–6.0Ah (72Wh to 108Wh) High-capacity 3P battery: 9.0Ah (162Wh) 21700:
Compact 1P battery: 3.0Ah–4.0Ah (54 Wh–72 Wh) Standard 2P battery: 6.0Ah–8.0Ah (108Wh–144Wh) High-capacity 3P battery: 9Ah–12Ah (162 Wh–216 Wh) When choosing between 18650 and 21700 lithium-ion batteries for power tools, the decision depends on your specific application. 18650 batteries are more portable due to their size and weight, while 21700 batteries offer more significant capacity and longer runtime but come with larger dimensions and weight. In practical applications, both can meet the requirements of power tools. Your choice should be based on the specific needs of your tools and applications.
·Typical applications of 21700 battery cells
A typical application for 21700 cells is in the Tesla Model 3, which utilizes Panasonic 21700 5000mAh batteries.
