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A Comparison of Flexible Cells, Square Cells, Columnar Cells 2017-09-06

Power batteries are typically composed of battery packs and protective circuit boards. The battery pack consists of a plurality of battery modules, which contain a plurality of cell units, i.e., a battery pack - a battery module-cell.

Cells are produced by the battery material, become the cells production process;

Batteries to the battery pack, and integrated protection board, called the pack process.

Cylindrical winding, square stacking and square winding are three important configurations of power cell batteries.

Cylindrical winding corresponds to "columnar battery".

Square stacking corresponds to "flexible battery".

Square winding corresponds to "square battery".

1. Cylindrical winding

Cylindrical winding is a very classic battery configuration, which has been applied in the nickel-metal hydride, 3C lithium-ion battery for a long time, the industry has accumulated a lot of experience in production design. The advantages of cylindrical winding are high production efficiency, good consistency and so on. Disadvantages are low space utilization caused by the cylindrical shape, the temperature distribution problems caused by radial thermal conductivity .

As the cylindrical battery radial thermal conductivity is poor, the number of coil winding can not be too much (18650 battery winding cycle is generally about 20 laps), so the monomer capacity is small, when used in electric vehicles, it needs a lot monomer to make up f the battery module and battery pack. Thus, the connection loss and the management complexity are greatly increased.

The shape of the cylindrical winding battery looks simple, but the internal design is complex. battery with good design involve electrochemical, thermal, electrical, mechanical and other areas of complex problems, setting high demand for he battery designers.

E.g: An aging failure form of a cylindrical battery during usage happened because of warped pole piece. The original reason of the warping might be the volume change of electrode layers in the cycle is inconsistent. The following picture showing us electrode shape of three 18650 battery’s cycle situation in the case of the storage, low rate cycle, high rate cycle, you can clearly see the warping phenomenon under the high magnification.



In order to solve this problem, we can add a pin at the center of the winding, inhibit the cell deformation

However,adding the pin will increase the cost, weight, etc. (electric car battery number is used in hundreds of thousands ), so that’s not the best choice.


2.Square stacked

Differ from the winding type which is a single piece of positive and negative, the laminated battery is made of multi-layer pole stack.

The advantages of square stacking are:

1) thin thickness (limited by the stamping strength of aluminum plastic film, generally not more than 1 cm), so heat dissipation is good;

2) pole pieces, each pole piece has a flange and pole ear welded together, current density on the the plate evenly distributed ;

3) thin, easy to form modules and battery pack, space utilization efficiency;

4) with the package of aluminum plastic film, light weight, close tightly to the cells after vacuuming , beneficial to reduce the invalid weight and volume.

However, the shortcomings of this configuration are:

1) The long-term reliability of aluminum-plastic film packaging is hard to guarantee

2) the battery body is soft, the contact between the pole pieces of the impedance may be larger, needing to be resolved in the module level or battery level;

3) compared to winding batteries, production efficiency is low.

3  The square winding type

The square winding type has the advantages of high space utilization and high production efficiency, which combines the making method of the appearance features of the square stack (but often the larger thickness) and the cylindrical winding type plate

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