What are the characteristics of three different packaging methods for lithium batteries?

Some people have made statistics on the 17 successful electric cars. The results show that the eight models are square-wound, the seven models are square-layered, and the two models are cylindrically wound. The differences in the choice of battery configurations for electric vehicles also reflect the advantages and disadvantages of these configurations.

Cylindrical winding, square stacking and square winding are three important configurations of power batteries. Here, the cylindrical winding type corresponds to the "column battery" in the stem of the problem, the square package is the "soft bag" in the stem of the problem, and the square winding type corresponds to the "square" in the stem. Some people have made statistics on the 17 successful electric cars. The results show that the eight models are square-wound, the seven models are square-layered, and the two models are cylindrically wound. The differences in the choice of battery configurations for electric vehicles also reflect the advantages and disadvantages of these configurations.

Cylindrical winding

The cylindrical winding type is a very classical battery configuration. It has been used for a long time in nickel-hydrogen and 3C lithium ion c. The industry has also accumulated a lot of production design experience. The advantages of cylindrical winding type include high production efficiency, good consistency, etc. The disadvantages include low space utilization caused by cylindrical shape and temperature distribution caused by poor radial heat conduction. Due to the poor thermal conductivity of the cylindrical battery, the number of windings of the battery should not be too large (the number of windings of the 18650 battery is generally about 20 circles), so the monomer capacity is small, and it needs a large amount when used in an electric vehicle. The battery modules and battery packs are individually assembled, and the connection loss and management complexity are greatly increased.

The shape of a cylindrically wound battery looks simple, but the internal design is not simple. Good battery design is a complex problem involving many fields such as electrochemistry, heat, electricity, machinery, etc., and puts high demands on battery designers. I want to give two small examples.

Example 1: The following figure shows the internal dimensions (unit: mm) of a certain 18650 battery. The lengths of the positive and negative poles are increased by nearly 1.5 meters, but the width of the ear used for drainage is only 4 mm. Battery designers need to carefully select the parameters of the ear (position, number, etc.) and electrode coating in order to reduce the uneven current distribution on the plate and reduce the uneven temperature distribution inside the battery.

To solve this problem, a simple method is to add a pin at the center of the winding to suppress the deformation of the core.

2. Square cascading

Unlike the wound type, which is formed by winding a single positive and negative electrode sheet, the laminated battery is formed by laminating a plurality of electrode sheets. The advantages of square stacking include: 1) thin thickness (limited by the stamping strength of aluminum plastic film, generally no more than 1cm), so the heat dissipation performance is very good; 2) many pole pieces, each piece has a flange and The tabs are welded together, and the current density distribution on the plate is uniform; 3) the sheet type is easy to form the module and the battery pack, and the space utilization efficiency is high; 4) the aluminum plastic film package is light in weight, and is vacuumed and electrically The tight fit of the core helps to reduce the ineffective weight and volume.

However, the shortcomings of this configuration include:

1) The long-term reliability of the aluminum-plastic film package is difficult to guarantee, as shown in the following figure:

2) The battery body is soft, and the contact resistance between the pole pieces may be large, which needs to be solved at the module level or the battery level;

3) Compared with the wound battery, the production efficiency is low.

3. Square winding

The square winding type combines the square-layered appearance features (but tends to be thicker) and the cylindrically wound plate manufacturing method, which has the advantages of high space utilization and high production efficiency. However, the design of this type of battery is also the most complicated. There are many design variables to consider, and it is also necessary to consider the cooperation between the housing and the battery core. In summary, in order to compare the advantages and disadvantages of various configurations, we need to analyze the advantages and disadvantages of battery design from many angles such as heat, mechanical and reliability, and not only the traditional electrochemical characteristics. This is a new challenge and new opportunity for the battery industry after the development of electric vehicles.

The page contains the contents of the machine translation.