1.1 18650 Are Best for Early Stages of Electric Vehicles
18650 batteries with its characteristics of highly mature technology, a high degree of automation, guaranteed battery and lower costs (2Ah/USD/Cell) is the best choice to power electric vehicles in the early stages to make cost down.
2170 and 18650 Size
However, 18650 Cell is very limited by its size volume, which is generally between 2.0-2.6AH/cell for mass production. At present, while there is a huge demand for more energy density for lithium battery, the current 18650 cell can’t increase much on capacity.
Related: Cylindrical 18650/21700 Batteries More Suitable For Electric Vehicles?
1.2 Upgrade the Model
There are mainly 2 Ways to increase the power density of the lithium battery :
#1: improving/changing the mechanism of the lithium battery material, which needs new material development and progress is slow.
#2: Changing its physical size or production process.
At present, without a huge breakthrough in battery materials, starting from the product design model, ie: increase in the battery “diameter and length” to achieve a higher capacity will be our final choice. The 18650 has completed its historical mission, the future of “XL” lithium battery model is now coming.
2. 21700 Battery Performance and Cost
2.1. battery energy density can be increased by more than 20%
21700 battery power density is better than 18650 batteries. According to the current disclosure of Tesla, under the existing conditions, the energy density of 21700 battery systems is approximately 20% higher than the 250WH to the original 18650-300 Wh battery system. At the same time, according to the Panasonic lithium battery power test in monomer batteries, the bulk density of its 21,700 battery is significantly higher than that of the 18650 cell monomer.
Below is table for comparison of 21700 vs 18650
Table 1: 21700 batteries and 18650 comparison
2.2. battery system cost down by about 9%
21700 costs decreased by about 9%. According to Tesla, the battery information disclosed in the price, the 21,700 lithium battery system is expected to sell for $ 170 ., Compared to the price of 18650 for $ 185, the price decline may be about 8.1%. 18650 system costs about 171 US dollars, MH, the transition to 21700, the cost of the system can be about 9% of the decline, to 155 US dollars Zhn.
Samsung says that after switching to a new 21700 battery, the system can reduce the component and weight by 10% compared to the current battery. Thus, further reduction in the weight of the battery, the energy density of the entire machine will be partially updated.
2.3. But Why 21700, not Other Types?
In comparison with other types of lithium ion battery cells,21700 is of course not the best Performance ever battery cell, but it is the best choice for energy density and energy cost.The physical dimensions of the cylindrical cores increase not only the energy density but also the productivity coefficient of cyclic life. It is assumed that the capacity of 10% per liter, the life cycle will be reduced by a factor of about 20%, charge-discharge to reduce $, and the core will have about 20% temperature increase. If you continue to increase the Size, you will increase the risk of damage to safety.
Discussion: Advantages and Disadvantages of 21700 Battery
In the economic aspect, the cylindrical core rises to the mature process of 18650, and the cost is carried out in a prerequisite to guarantee a good product price and consistency. If the size is too large, security and manufacturability will shrink, leading to a larger cylinder of 26500, 32650, and therefore not large-scale to occupy the main cause of the market.