CR2032 button cell batteries

　　Lithium-ion battery manufacturing process analysis

　　The manufacturing of lithium-ion batteries is mainly divided into three stages of technology. The first is the production and manufacturing of pole pieces, the second is the packaging production of battery cells, and the third is the activation and sorting of batteries. Each stage corresponds to several important processes. The first stage accounts for the majority of battery production costs, the second stage determines the packaging form of the battery, and the third stage determines the battery grouping method and stability of use.

　　Today we will talk about the problem of corrosion and leakage in soft pack battery packaging. For soft pack batteries, the main process that plays a role in battery sealing is the packaging process. The quality of packaging directly determines the quality of battery performance. Simply put, it is not very clear whether the packaging is good or bad. It also needs to be analyzed in detail from the type of leakage. Generally speaking, the causes of corrosion and leakage of aluminum-plastic films can be divided into three categories: (1) Chemical corrosion. For lithium-ion batteries, because moisture will react with the electrolyte to produce HF, hydrofluoric acid is a particularly corrosive agent. The acid will cause serious damage to the aluminum plastic film, current collector, and cathode materials. The reaction is as follows:

　　After the aluminum-plastic film is corroded and damaged, the battery will become ineffective. (2) Electrochemical corrosion Corrosion and leakage of soft-pack batteries caused by electrochemical reactions are relatively difficult to detect. Generally, corrosion and leakage of soft-pack batteries will only be discovered as the use time becomes longer and the corrosion and leakage of the battery gradually become serious. Since this failure mode has a long incubation time, it can easily cause a customer trust crisis once it occurs. There are generally two conditions for electrochemical corrosion to occur: ① Ion short circuit. An ion short-circuit channel is formed between the aluminum layer of the aluminum-plastic film and the anode. ②Electronic short circuit. The aluminum layer of the aluminum-plastic film forms an electronic short-circuit channel with the anode. In this way, the aluminum layer of the aluminum-plastic film that encapsulates the battery core forms a short-circuit loop with the anode. The anode is the negative electrode of the battery core and is at a low potential. Once it comes into contact with aluminum, it will cause an electrochemical reaction through the electrolyte with high conductivity. As a result, the aluminum layer is continuously consumed. These two necessary conditions for battery corrosion during short circuit are indispensable. The place where ion channels are easy to form is when the PP layer at the edge sealing part is damaged during heat sealing, or the PP layer is damaged during folding, thus forming an ion channel between the aluminum layer and the negative electrode. The place where an electronic short-circuit channel is easily formed is that the tab packaging position is damaged, and the negative electrode tab is in contact with the aluminum layer to form an electronic channel. If the negative electrode extends too much, it will easily come into direct contact with the aluminum layer during heat sealing, causing an electronic short circuit. In addition to the electron channel inside the battery core, the unintentional contact of the negative electrode tab with the aluminum layer from the outside is also one of the reasons for the corrosion and leakage of the soft package, and this happens faster. When both ion channels and electron channels are formed, the aluminum layer of the aluminum-plastic film is gradually embedded with lithium ions to form a lithium-aluminum alloy. After the aluminum layer is corroded, water can penetrate into the battery without restraint, causing more intense damage and causing soft-pack batteries. Appearance leakage fails. (3) Physical reasons: Packaging failure caused by battery abuse, accidental bumps, and gas bulging in the battery itself can also cause battery leakage. Battery abuse, including battery overcharging, over-discharging, and high-temperature use, may cause the battery to produce gas, increase bulging, and cause packaging failure. Whether the battery is cycled at normal temperature, cycled at high temperature, or left at high temperature, it will produce varying degrees of bulging and gas production. According to current research results, the essence of the cell bloating is the decomposition of the electrolyte. There are two situations in which the electrolyte decomposes. One is that the electrolyte contains impurities, such as moisture and metal impurities, which cause the electrolyte to decompose and produce gas. The other is that the electrochemical window of the electrolyte is too low, causing decomposition during the charging process. The electrolyte contains After obtaining electrons, solvents such as EC and DEC will produce free radicals. The direct consequence of the free radical reaction is the production of low-boiling hydrocarbons, esters, ethers and CO2. If there is too much moisture inside the battery, it will also cause more gas to be produced, causing the battery to bulge and cause the weak points of the packaging to rupture.

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