(1) Cell test sorting: Due to the randomness of cell manufacturing conditions, the performance parameters of the batteries produced are not the same. In order to effectively combine cells with the same or similar performance, they should be classified according to their performance parameters. Cell test is to classify cells by testing their output current, voltage, power, etc., to improve the utilization rate of the battery, and to produce qualified battery modules. The equipment for sorting cells is called a cell sorter, and automatic cell sorting equipment is used in automated production. In addition to sorting the performance parameters of the cells, the appearance of the cells should also be sorted, focusing on the color difference and grid line size.
(2) Laser scribing: It is to use a laser scribing machine to cut the whole cell into the cell with the required specification and size of the module according to the needs. For example, when making some low-power modules, the entire battery piece must be cut into quarters, six quarters, and nine quarters. Before the cell is cut, it is necessary to design the cutting circuit in advance, compile the cutting program, and use the leftover material as much as possible to improve the utilization rate of the cell.
(3) Cell single welding (front welding): Welding the interconnection bar to the main grid line on the front (negative) of the cell. The welding is required to be straight and firm, and the interconnection bar should not fall off by gently lifting the interconnection bar in the direction of about 45° by hand. Excessive welding temperature and long time will cause low tear strength or battery breakage. A constant temperature electric soldering iron is generally used for manual welding, and an automatic welding machine is used for mass production. The length of the ribbon is about twice the length of the side of the cell. The extra ribbon is connected to the back electrode of the back cell during the back welding.
(4) Cell series welding (back welding): Back welding is to connect a specified number of battery pieces in series to form a battery string, then use a bus bar to weld several battery strings in series or parallel, and finally combine the battery module and lead out the positive and negative leads. The positioning of the cells during manual welding mainly depends on the die plate. There are 9 to 12 grooves on the mold plate for placing battery slices. The size of the groove corresponds to the size of the battery. The position of the groove has been designed. Different specifications of modules use different templates. The operator uses an electric soldering iron and solder wire to weld the front electrode (negative electrode) of the “front battery” to the back electrode (positive electrode) of the “rear battery”. The use of mold plates ensures the uniformity of the spacing between the cells. At the same time, the cells of each string are required to be evenly spaced and have the same color.
(5) Mid-term testing: The string-welded cells are tested on a module tester to see if the test results meet the design requirements. Through the mid-test, the virtual soldering of the cells and the ceramic cracks of the cell itself can be found. After passing the test, the next process can be carried out. Standard test conditions: AM1.5, module temperature 25℃, irradiance 1000W/m2. The test results have the following parameters: open circuit voltage, short circuit current, working voltage, working current, maximum power, etc.
(6) Laminated laying: The back side is connected in series and passed the inspection of the module string, and the glass and the cut EVA, TPT backplane are laid in a certain level, ready to be laminated. The glass should be cleaned in advance, and EVA and TPT should be cut in advance according to the required size (generally 10mm larger than the glass size). When laying, ensure the relative position of the battery string and glass and other materials, and adjust the distance between the battery string and the distance between the battery string and the edge of the glass to lay a good foundation for lamination. (Laying level: from bottom to top: glass, EVA, battery, EVA, TPT backplane.)
(7) Module lamination: Put the laid battery module into the laminator, draw out the air in the module by vacuuming, and then heat to melt the EVA and pressurize the melted EVA to fill the gap between the glass, the battery sheet and the TPT back sheet film. At the same time, the air bubbles in the middle are discharged, the battery, glass and back plate are tightly bonded together, and finally the modules are cooled and solidified to take out the modules. The lamination process is a key step in module production, and the lamination temperature and lamination time should be determined according to the properties of EVA. During lamination, the EVA is expanded and cured due to pressure to form burrs, so after lamination, a sharp knife should be used to cut it off. It is required that the single chip in the laminated module has no chipping, no cracks, no obvious displacement, and no continuous bubble or delamination channel can be formed between the edge of the module and any part of the circuit.
Read more: Later manual production line process of battery module