What causes the performance of lithium batteries to decline

Generally speaking, the electrolyte is stable, but lithium batteries are quite special. A passivation film is formed on the anode, called the solid electrolyte interface (SEI). This layer separates the anode from the cathode, but allows ions to pass through much like a separator. Essentially, the SEI layer must be formed to make the battery work. The film stabilizes the system and allows the lithium battery to have a longer service life, but this will result in a decrease in capacity. Electrolyte oxidation also occurs on the cathode, permanently reducing the capacity. In order to guard against the membrane becoming too strict, the additives are mixed with the electrolyte consumed during the formation of the SEI layer. It is difficult to track their existence during the evaluation. This makes proprietary additives a trade secret, including their ingredients and usage levels. Regarding additives, he is vinylene carbonate (VC). This chemical substance can improve the cycle life of lithium ions, especially at higher temperatures, and the internal resistance is very low depending on the use and age of use. VC also maintains a stable SEI film on the anode, without the adverse side effects of electrolyte oxidation on the cathode. It is said that academia and research lag behind battery manufacturers in terms of knowledge and choice of additives, so this is a big secret. For most commercial lithium batteries, the SEI layer will be analyzed at a battery temperature of 75-90°C (167-194°F). The battery type and state of charge (SoC) will affect the breakdown at high temperatures. Without proper cooling, self-heating behavior may occur, leading to thermal runaway. Laboratory detection on the 18650 battery stated that this thermal event may take two days to complete. The flammability of lithium ion electrolytes is also a problem, and experiments have been conducted to process non-flammable or reduced flammable electrolytes through additives or development of non-organic ionic liquids. Research has also been conducted on operating lithium ions at low temperatures. Drying or slowly transforming the liquid electrolyte into a solid form is another aging event that reduces the performance of lithium ions. When the electrolyte flows away, the battery is scrapped. The fluidity of the electrolyte is another health indicator related to all battery chemistry. Disclaimer: Some pictures and content of articles published on this site are from the Internet, please contact to delete if there is any infringement. Previous: Analysis of the balance of power lithium battery packs