The Difference Between Cylindrical Lithium-ion Battery And Square Lithium-ion Battery
May 13, 2022
The Difference Between Cylindrical Lithium-ion Battery And Square Lithium-ion Battery
Ternary lithium-ion batteries have three packaging forms: cylindrical lithium-ion batteries, square lithium-ion batteries and soft-pack lithium-ion batteries. Cylindrical batteries and square batteries are mostly made of steel or aluminum, and soft pack batteries are made of aluminum-plastic film. What is the difference between cylindrical ternary lithium batteries and square ternary lithium batteries?
1. Energy density ratio
The energy density ratio refers to the capacity per unit weight of the battery. According to the current domestic mainstream 18650 (1.75AH), the energy density ratio of cylindrical monomer can reach 215WH/Kg, and the energy density ratio of square monomer can reach 205WH/Kg based on 50AH. The system grouping rate of 18650 is about 60%, and the square is about 70%. (The system grouping rate can be imagined to put hams in the box, and the gap between the square hams is smaller, so the system grouping rate is higher.)
In this way, the energy density ratio of the 18650 battery pack system is about 129WH/Kg, and the energy density ratio of the square battery pack system is about 143WH/Kg. In the future, when the energy density ratio of 18650 and square monomers reaches the same, square lithium battery packs with higher grouping rate will have more obvious advantages.
2. Magnification
Charge/discharge rate = charge/discharge current/rated capacity, the higher the rate, the faster the charging speed supported by the battery. The mainstream horizontal energy-type battery 18650 manufactured in China is around 1C, and the square can reach around 1.5-2C (thermal management needs to be handled), which is still some distance from the 3C that is the policy target. However, it is entirely possible that the square manufacturing process will become more and more perfect to achieve the established target 3C.
3. Cycle life
After 2000 cycles of 1C charge and 1C discharge, the remaining capacity of the best square cells can still reach 80%, while the capacity of the best 18650 cells is only 70%. It can be seen that the cycle life of the square battery is better than that of the 18650 battery.
4. Consistency
The consistency of battery cells is the biggest headache for battery cell companies. For our users, the more the number of battery cells, the more difficult it is to control the consistency. Assuming that the defective rate of a cell is one in 100,000, the round cell battery pack is composed of 7,000 18650 cells, and the square cell battery pack is composed of 250 cells. A battery pack without defective products is considered qualified. Then the pass rate of the round cell battery pack is 0.99999^7000=93.2%, and the pass rate of the square cell battery pack is 0.99999^245=99.7%. Of course, the theoretical knowledge of battery consistency is much more complicated than this. Here, Paike just cites an example to show that using a square-cell battery pack with a larger single capacity and a smaller number is more conducive to controlling the consistency.
5. Manufacturing cost
The manufacturing cost includes material cost, equipment cost, artificial hydroelectric field cost and invisible auxiliary material cost. At present, the comprehensive cost of 18650 of mainstream enterprises can be controlled at about 0.5 yuan/WH, and the comprehensive cost of square shape is about 0.8 yuan/WH.
Before the rise of the new energy vehicle industry, 18650 cells have been widely used in various fields such as electronic products and industrial equipment. However, the single capacity of the 18650 cell is relatively low, which is not enough to meet the requirements of electric vehicles, so Tesla has developed the 21700 model. At present, the high degree of automation of equipment is the place where cylindrical enterprises can save labor costs the most, but the production and sales chain of cylinders is very mature, and there is almost no room for compression.
There is still a lot of room for improvement in size and electrode thickness for square cells. In terms of size, they are getting bigger and bigger. From the initial 20AH to the current 50AH batch products appear on the market. The larger the capacity, the lower the WH cost, so it is entirely possible that the cost will be the same when the large-capacity square is mass-produced.
