[Abstract] the physical size of a cylindrical battery increases not only its energy density but also its cycle life and power magnification, researchers say. According to the calculation, the capacity of the battery increases by 10%, the cycle life of the battery will decrease by about 20%, the charge discharge rate will be reduced by 30~40%, and the battery will have a temperature rise of about 20%.
In early 2017 the investor conference, Tesla announced a new 21700 joint R & D and Matsushita Electric core mass, Tesla said this battery will be produced in Gigafactory super battery factory, and stressed that this is the product of the highest energy density and the lowest cylindrical electric core currently available in mass production. Subsequently, domestic enterprises have poured into 21700 of the army:
In June 28th, lithium could announce that its 21700 battery finished in Hubei, Kimcheon, and was officially launched in 2019;
July 3rd, the wisdom of energy officially announced its 21700 battery production plan, smart energy will build 6 new 21700 product lines;
In July 20th, Suzhou force produced an annual output of 4GWh 21700 power battery project officially announced production.
For battery material performance, by increasing the volume to increase the energy density of enterprises become the object of focus; however, the increase in the physical size of cylindrical cell will also reduce the cycle life and rate and safety; while for the production of batteries to 18650 enterprises, the production line of general production cost change is lower, but blindly increase battery size is not a permanent solution.
21700 what's so magical about it?
The most intuitive difference between the 21700 and the 18650 batteries is that the size becomes larger.
Because of the limitation of battery material performance, increasing the energy density by increasing the volume becomes the focus of the enterprise. China clearly proposed in 2020, power battery monomer energy density exceeded 300Wh/kg, power battery system energy density reached 260Wh/kg; in 2025, the power battery system energy density to reach 350Wh/kg. The energy density requirements for the continuous improvement of power lithium batteries will continue to contribute to the change in the Li ion battery model.
Tesla disclosed earlier this year, in the existing conditions, the production of its 21700 battery system energy density of about 300Wh/kg, compared to its original 18650 battery system 250Wh/kg increased by about 20%. The capacity of single cell battery promotion means that the number of the equivalent energy required for batteries is reduced by about 1/3, so reduce the system management difficulty, simplified metal structure parts number, although a single electric core weight and cost increase, but the battery system PACK the weight and the cost has been reduced.
Is the battery really bigger, the better?
The large scale battery is the result of the balance of physical and economic results.
Some researchers say the physical size of a cylindrical battery increases not only its energy density but also its cycle life and magnification. According to the calculation, the capacity of the battery increases by 10%, the cycle life of the battery will decrease by about 20%, the charge discharge rate will be reduced by 30~40%, and the battery will have a temperature rise of about 20%. If continue to increase the size of the big, will face the risk of sacrificing security, which is why 26500, 32650 cylindrical batteries and other large-scale power market failed to dominate the cause of the market.
In July 12th, the State Administration of quality supervision, inspection and quarantine, the National Standardization Management Committee approved the electric vehicle power battery standards 3, including "GB/T 34013-2017 electric vehicle battery product size", will be implemented on February 1, 2018.
At the present stage, the production line of domestic battery enterprises is mainly based on 18650 cylinders. The production line transformation mainly involves slitting, winding, assembling and forming of the middle and back sections, and the cost of adjusting the die for the semi-automatic line is low. Battery manufacturers from the original mainstream 18650 to 21700, more convenient, will not invest too much equipment, technical innovation costs and new equipment investment, the next 21700 batteries will be likely to usher in an increase.
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