What is the yellow thing that appears in lithium batteries?
1. Graphite negative electrode of lithium battery pack is yellow.
This yellow is golden yellow, which is the characteristic color of LiC6 material. That is to say, when the CB value of lithium battery pack is designed reasonably, the negative electrode in the fully charged state Graphite is golden yellow; if the content of the conductive agent in the pole piece is too much, the golden yellow performance will not be obvious; if the CB design is too low, the golden yellow will appear white; here, the battery can be judged based on the golden yellow performance Whether the design is reasonable.
2. The diaphragm is yellow.
Generally, it is dark yellow, or khaki, which is a bit more vivid. It mostly occurs on the positive electrode side; the main reason is that the positive electrode voltage is too high and the oxidation is strong, which will oxidize the surface of the diaphragm. After the battery is cycled, the battery after overcharge, the diaphragm on the positive side is mostly yellow after disassembly; also, if the electrolyte contains overcharge additives, slightly increase the charging voltage, or the electrolyte moisture content exceeds the standard, The surface of the positive electrode separator will also appear dark yellow. This is mainly due to the yellowing of the separator after the additives are deposited on the surface of the separator. When the battery failure analysis, whether the separator has turned yellow is also an important basis to indicate whether the battery has experienced overcharge or high voltage. Of the loop.
3. The electrolyte is yellow.
Generally, if the electrolyte is stored for a long time, the color will gradually turn yellow, from inconspicuous light yellow to yellow to reddish brown; the main reason is that the additives in the electrolyte are decomposed Caused by; currently 99% of the electrolyte contains VC, which is very unstable. It must be added with a stabilizer. The storage time is too long. If it is exposed to water, high temperature, or acid, it will cause the stabilizer to fail. VC It decomposes and turns yellow; in addition, some additives and lithium salts will also decompose during storage and cause the color of the electrolyte to change.
4. Yellow short-circuit point
The yellow short-circuit point is generally on the diaphragm, and the diameter is generally about 0.5mm. There are two procedures to find the short-circuit point: short-circuit test process, generally called short-circuit tester In the battery, there will always be yellow and black short-circuit points, most of which are caused by dust and burrs; aging and low-voltage batteries will also find short-circuit points. There can be one more reason for the short-circuit. Metal impurities cause short-circuits, making the diaphragm appear Yellow short circuit point.
5. Adhesive paper is yellow
Yellow adhesive paper is generally high-temperature glue. Most of the base material is polyimide, and most of the glue system is silica gel; this is not absolute.
6. The lug glue is yellow
Currently, the color of the lug glue used in batches is black, white and yellow. They are all mass-produced products, and each manufacturer has different processes, and the habit of the three colors of the lugs is also different. It depends on the choice of the technicians.
7. NMP turns yellow
Sometimes, NMP turns yellow. According to the manufacturer's explanation, it is caused by the excessively high content of free ammonia in NMP. Not much attention has been paid to this issue; it seems that the yellow phenomenon of MP is relatively rare.
8. PVDF solution is yellow
This is not necessarily a bad thing, because according to the functional groups of PVDF, it will show different colors, from light yellow to reddish brown; but if the PVDF is not changed, the color If there is a change, this must be paid attention to.
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