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As early as the investor meeting in early 2017, the new 21700 cells jointly developed began mass production. Tesla said that this battery will be produced in the factory and emphasized that this is the highest energy density of cylindrical cells currently available for mass production And the lowest cost product. Subsequently, domestic enterprises have poured into the army of 21700 Battery:
Due to the limitation of battery material performance, increasing the energy density by increasing the volume has become an important consideration for enterprises; however, the increase in the physical size of cylindrical batteries will also reduce cycle life, rate and safety; It is said that the general production change cost of the production line is lower, but blindly increasing the battery size is not a long-term solution.
The most intuitive difference between 21700 and 18650 batteries is that they have become larger.
Due to the limitation of battery material performance, increasing the energy density by increasing the volume has become an important consideration for enterprises. China clearly proposes that the energy density of power battery cells will exceed 300Wh / kg in 2020, and the energy density of power battery systems will reach 260Wh / kg; in 2025, the energy density of power battery systems will reach 350Wh / kg. The continuously increasing energy density requirements of power lithium batteries are bound to continue to promote the change of power lithium battery models.
According to the information disclosed by Tesla earlier this year, under the current conditions, the energy density of its 21700 battery system is about 300Wh / kg, which is about 20% higher than the 250Wh / kg of its original 18650 battery system. The increase in the capacity of a battery cell means that the number of cells required for the same energy is reduced by about 1/3, which has reduced the difficulty of system management and simplified the number of accessories such as metal structures. Although the weight and cost of a single cell have increased However, the weight and cost of the battery system PACK have been reduced.
"Large" batteries are the result of a comprehensive balance of physical and economical performance.
Some researchers claim that increasing the physical size of cylindrical batteries will not only increase energy density, but will also reduce cycle life and rate performance. It is estimated that for every 10% increase in capacity, the battery cycle life will be reduced by about 20%; the charge and discharge rate will be reduced by 30 ~ 40%; and the battery will have a temperature rise of about 20%. If you continue to increase the size, you will face the risk of sacrificing safety, which is why 26500, 32650 cylindrical batteries, etc. have failed to occupy the mainstream market of power batteries on a large scale.
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