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Important components of lithium-ion battery pack soft pack module

The basic components include: module control board (commonly known as BMS slave board), battery monomer, conductive connectors, plastic frame, cold board, cooling pipeline, pressing plates at both ends, and a set of fasteners that combine these components together.

Analysis of design points

1. Structural design requirements

Structural reliability: seismic resistance, dynamic fatigue resistance;

Controllable process: no over soldering or false soldering, ensuring that the battery core is 100% undamaged;

Low cost: The automation cost of PACK production line is low, including production equipment and production losses;

Easy to disassemble: The battery pack is easy to maintain and repair, with low cost, and the battery cells can be used in multiple stages with good usability;

Necessary heat transfer isolation can be achieved to prevent the rapid spread of heat runaway, and this step can also be considered in the pack design.

Problem: The individual energy density of soft pack cells has higher room for improvement compared to cylindrical and square cells, but it requires higher module design requirements and is difficult to control safety. These are all issues that need to be addressed in structural design.

2. Thermal design requirements

The physical structure of a soft pack battery cell determines that it is not easy to explode. Generally, only when the pressure that the shell can withstand is high enough, it is possible to explode. However, as the internal pressure of a soft pack battery cell increases, pressure and liquid leakage will begin from the edge of the aluminum plastic film. At the same time, the soft pack battery cell is also one of several battery cell structures, with the best heat dissipation.

The current mainstream cooling methods have shifted to liquid cooling and phase change material cooling. Phase change material cooling can be used in conjunction with liquid cooling, or alone in less harsh environmental conditions. In addition, there is another process that is still widely used in China, which is adhesive pouring. Here is filled with thermal conductive adhesive with a thermal conductivity much greater than that of air. The heat emitted by telecommunications is transferred to the module shell by thermal conductive adhesive, and further dissipated into the environment. This way, it is unlikely that the battery cells will be replaced separately again, but it also to some extent prevents the spread of heat runaway.

Of course, it is not easy to mature the liquid cooling technology for lithium-ion battery packs and soft pack cells. It is necessary to consider the fixation, sealing, insulation, and other aspects of the liquid cooling plate.

3. Electrical design requirements

Electrical design includes two parts: low voltage and high voltage.

Low voltage design generally considers several aspects of functionality. Collect battery voltage and temperature information to the module slave control board or the so-called module controller installed on the module through the signal acquisition harness; The module controller is generally designed with balancing function (active balancing, passive balancing, or both); A small number of relay on-off control functions can be designed on the slave control board or on the module controller; Connect the module controller and the main control board through CAN communication to transmit module information.

High voltage design is important for the series and parallel connection between cells, as well as for the external connection and conductivity between modules. Generally, only the series connection is considered between modules. These high-voltage connections need to meet two requirements: firstly, the distribution of conductive parts and contact resistance between the cells should be uniform, otherwise the detection of individual voltage will be interfered with; Secondly, the resistance should be small enough to prevent waste of electrical energy in the transmission path.

4. Safety design requirements

Safety design can be divided into three backward requirements: good design to ensure that accidents do not occur; If not, if an accident occurs, it is best to give early warning and give people time to reflect; If a malfunction has already occurred, the design goal becomes to prevent the accident from spreading too quickly.

The first goal is to achieve a reasonable layout, a good cooling system, and a reliable structural design;

For secondary targets, sensors should be more widely distributed to every possible fault point, comprehensively detecting voltage and temperature, and preferably monitoring the internal resistance of each cell;

The lowest goal can be achieved by setting fuses between battery cells and modules, and setting firewalls between modules to design strength redundancy in response to potential structural collapse after disasters occur. This is the direction of high-performance soft package modules.

5. Lightweight design requirements

The most important purpose of lightweight design is to pursue range, eliminate all unnecessary burdens, and embark on the journey with ease. If lightweight can be combined with cost reduction, then everyone will be even more pleased.

There are many ways to reduce weight, such as increasing the energy density of battery cells;

In detail design, while ensuring strength, pursue the lightness of structural components (such as selecting thinner materials and digging larger holes in the board);

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