It is well known that ternary lithium-ion batteries come in three packaging forms: cylindrical, square and flexible. Cylindrical batteries and square batteries are mostly made of steel or aluminum shells, while soft battery is made of aluminum plastic film.
Due to the current quality of aluminum plastic film and soft pack battery technology are very immature, we will not talk about.
Today we are going to talk about the difference between cylindrical and square ternary lithium-ion batteries.
Energy density ratio
The energy density ratio refers to the capacity of a battery per unit weight. The energy density ratio of cylindrical monomer can reach 215Wh /Kg according to the current domestic mainstream 18650 (1.75Ah), and the energy density ratio of square monomer can reach 205Wh /Kg according to 50Ah. The system group rate of 18650 is about 60%, and the square is about 70%. (The system grouping rate can be thought of as having ham in a box; the gap between the square hams is smaller, so the system grouping rate is higher.)
In this way, the energy density ratio of 18650 battery pack system is about 129Wh /Kg, and the energy density ratio of square battery pack system is about 143Wh /Kg. In the future, when the energy density ratio of 18650 and square cells reaches the same level, the square lithium-ion battery pack with higher group rate will have more obvious advantages.
Times willfulness
Charge-discharge ratio = charge-discharge current/rated capacity. The higher the ratio, the faster the battery can charge. Domestic manufacturing mainstream level energy type cell 18650 at about 1C, square up to about 1.5-2C (need to deal with thermal management), there is still some distance from the policy goal of 3C. But it's possible that the cube manufacturing process will get better and better and achieve the 3C goal.
Cycle life
When 1C is charged and 1C is discharged for 2000 cycles, the remaining capacity of the best square cell can still reach 80%, while that of the best 18650 cell is only 70%. Thus, the cycle life of the square battery is better than that of the 18650 battery.
consistency
The consistency of the cell is the most headache for the cell company. For our users, the more cells, the more difficult it is to control the consistency.
Assuming that the defect rate of one cell is 1/100,000, the round cell battery pack is composed of 7,000 18,650 cells, and the square cell battery pack is composed of 250 cells, one battery pack without defect is considered qualified. Then the pass rate of the circular battery pack is 0.99999^7000=93.2%,
The qualified 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 that, and here the paperback is just an example of how using a smaller number of square cell packs with a larger number of cells is better for controlling consistency.
The manufacturing cost
The manufacturing cost includes material cost, equipment cost, artificial water and electricity site cost and invisible auxiliary material cost. Now the comprehensive cost of 18650 in mainstream companies can be controlled at about 0.5 yuan/Wh, and the comprehensive cost of square is about 0.8 yuan/Wh.
Before the rise of the new energy vehicle industry, 18650 cell has been widely used in various fields such as electronic products and industrial equipment. However, the 18650 cell has a relatively low capacity, which is not enough to meet the requirements of electric vehicles, so Tesla has developed the 21700 model. At present, the high degree of equipment automation is the place where the cylinder company can save the most labor costs, but the production and marketing chain of the cylinder has been very mature, and the compressed space is almost gone.
The size and electrode thickness of the square cell still have a lot of room for improvement. In terms of size, it is getting bigger and bigger, from the initial 20Ah to the present 50Ah batch products appear on the market. The larger the capacity, the lower the cost of the WH, so we think it is possible to achieve the same cost as the cylinder when it comes to mass production.
