Introduction to the reason of battery self-discharge

There are two reasons for excessive self-discharge: physical micro-short circuit and chemical reaction. 1. There are many cases of physical micro-short circuit caused by physical micro-short circuit, which can be divided into the following categories: a. Dust and burrs. Many manufacturers of self-discharged batteries will find black spots on the diaphragm when they are disassembled. The middle position is mostly dust. Breakdown, the edge position is mostly burrs, which is easier to distinguish; b. Why do the positive electrode metal impurities fall into this category? In fact, the positive electrode metal impurities also penetrate the separator after the charging reaction. The formation of black spots on the diaphragm also causes physical micro-short circuits; for example, many positive iron-lithium materials will face the problem of excessive self-discharge, which is caused by excessive iron impurities. c. Metal impurities in the negative electrode due to the formation of the galvanic cell, the metal impurities in the negative electrode will be freed and deposited at the diaphragm to cause the diaphragm to conduct and form a physical micro-short circuit. Some low-end negative electrode materials in China often encounter this situation; d. The metal impurities of auxiliary materials such as adhesive tape 2, chemical reaction a, moisture group, a friend gave a document explanation: moisture causes electrolyte analysis, releases a large number of electrons, and the electrons are embedded in the positive electrode oxidation structure, thereby causing The positive electrode potential drops, resulting in low voltage; in addition, moisture is a catalyst in the entire battery, which will generate strong Lewis acid, which will continuously corrode the SEI film and consume the lithium source and cause the battery to low voltage. b. Electrolyte solvents. Some electrolyte solvents will cause the battery voltage to drop too fast. I tried a solvent before. After adding it, the ion conductivity has a clear effect, but the self-discharge rate is 3 times faster than the normal solvent; Possible mechanism: These solvents are not resistant to oxidation, and a slow chemical reaction occurs during storage, which consumes capacity and causes the voltage to drop. c. The SEI film is not formed well. During the storage process, the warehouse has a certain temperature, which causes the SEI film to fall off and re-react, resulting in battery flatulence and low pressure. d. Poorly packaged tabs are over-sealed, which may cause corrosion of tabs and consume the low voltage of the lithium source; over-sealing of other locations, the electrolyte may corrode the aluminum foil through the CPP layer, resulting in perforation of the aluminum-plastic film, and moisture entering and causing low-pressure flatulence. In many cases, flatulence and low pressure appear together, and this time it is often more serious; the most common low pressure is caused by dust and burrs. Everyone will say that this aspect of control is controlled, but it is more troublesome to operate: For example: the optimization of the formula, especially those that pursue high performance, uses a material with a larger BET, and adds a lot of conductive agents. A lot of research is needed to control the balance between performance and powder removal; workshop The management of many manufacturers pays more attention to the control of dust, but the actual implementation level is not enough. Let me answer some of the questions mentioned by the friends in the last post: 1. The moisture is analyzed in the formation stage, why it will cause low pressure. Actual moisture will be analyzed in the formation stage, but its products, such as those formed by the reaction with lithium salt POF3, PF5, etc., in the subsequent charging and discharging process, will gather and react to form water again, that is to say, a part of the water introduced before the formation is a kind of catalyst, which is constantly reacting in the battery. We have also done it. After a test, after the liquid injection, the self-discharge rate was found to be much faster when it was intentionally leaked for 45 minutes. 2. How metal ions cause a short circuit Whether it is a negative electrode or a positive electrode, it may cause a short circuit, because it is the same mechanism. If the positive electrode contains, the charge will be deposited on the negative electrode or the separator; the negative electrode is also the same, if it is metal ions , It is ionized after liquid injection, and it will also be deposited on the negative electrode or the separator during charging. Sometimes we will find copper in the negative electrode, that is, the copper of the negative electrode is ionized and deposited on the surface of the negative electrode. 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 article: What is battery CB certification? What materials do I need to prepare for battery application for CB certification?