Three yellow problems in lithium batteries

The substance can show color because it absorbs a certain amount of visible light, and the unabsorbed part reflects back and shows a specific color. In lithium-ion batteries, the three primary colors of red, yellow and blue are everywhere. Today’s post mainly describes the yellow problems encountered in the production and finished products of lithium-ion batteries: 1. The graphite anode is yellow. This yellow is golden yellow. The characteristic color presented by LiC6, that is to say, when the CB value of the lithium ion battery is designed reasonably, the negative electrode graphite in the fully charged state is golden yellow; if the content of the conductive agent of the pole piece is too much, the golden yellow performance will not be Clearly; if the CB design is too low, the golden yellow will appear white; here, you can judge whether the battery design is reasonable based on the performance of the golden yellow. 2. The yellow diaphragm is generally dark yellow, or khaki, which is a bit more vivid, mostly on the positive electrode side; mainly because the positive electrode voltage is too high and the oxidation is strong, which oxidizes the surface of the diaphragm; the battery after cycling After the battery is overcharged, the diaphragm on the positive side of the positive electrode is mostly yellow after disassembly; also, if the electrolyte contains overcharge additives, the charging voltage is slightly increased, or the moisture content of the electrolyte exceeds the standard, the surface of the positive electrode diaphragm will also appear Dark yellow, this is mainly caused by additives deposited on the surface of the diaphragm after analysis to cause the diaphragm to turn yellow; when the battery fails to decompose, whether the diaphragm turns yellow is also an important basis to indicate whether the battery has experienced overcharge or high voltage cycles. 3. The electrolyte is yellow. Generally, if the electrolyte is stored for too long, the color will gradually turn yellow, from inconspicuous light yellow to yellow to reddish brown; it is mainly caused by the analysis of the additives in the electrolyte; currently 99% The electrolyte contains the VC component, which is very unstable. It is necessary to add a stabilizer. The storage time is too long. When exposed to water, high temperature, or acid, the stabilizer will become invalid, and the VC will turn yellow after analysis; , There are some additives and lithium salts that will also undergo analysis 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 processes to find the short-circuit point: short-circuit detection process, the battery called by the general short-circuit detector will always be Find the yellow and black short-circuit points, most of which are caused by dust and burrs; aging 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 points. 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. The color of the lug glue currently used in batches is black, white and yellow. They are all mass-produced products, and each manufacturer has a different process, and the habit of the three colors of the lugs is also different, depending 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 high content of free ammonia in NMP. There is not much attention to this problem; it is rare that NMP appears yellow. 8. PVDF solution showing yellow color is not necessarily a bad thing, because depending on the functional functional groups of PVDF, it will show different colors, from light yellow to reddish brown; but if your PVDF is not changed, the color changes, This should be paid attention to. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: Copper foil of lithium battery material