CR2032 button cell.Technical knowledge about the use and maintenance of lithium batteries

　　How should we maintain the lithium battery of our favorite machine correctly? This problem has been bothering many loyal mobile phone users, including me. After consulting some information, I recently had the opportunity to consult with a PhD student majoring in electrochemistry and the deputy director of a well-known domestic battery research institute. Now I will write down some relevant knowledge and experiences I have recently acquired for the benefit of all readers.

　　The positive electrode material of lithium-ion batteries usually consists of active compounds of lithium, and the negative electrode is carbon with a special molecular structure. The main component of the common cathode material is LiCoO2. When charging, the potential applied to the two poles of the battery forces the compound of the cathode to release lithium ions and embed them in the carbon in which the molecules of the cathode are arranged in a lamellar structure. During discharge, lithium ions are precipitated from the carbon in the lamellar structure and recombine with the compound of the positive electrode. The movement of lithium ions creates an electric current.

　　Although the principle of chemical reaction is very simple, in actual industrial production, there are many more practical issues that need to be considered: the material of the positive electrode needs additives to maintain the activity of multiple charges and discharges, and the material of the negative electrode needs to be designed at the molecular structure level to Accommodate more lithium ions; the electrolyte filled between the positive and negative electrodes, in addition to maintaining stability, also needs to have good conductivity and reduce the internal resistance of the battery.

　　Although lithium-ion batteries rarely have the memory effect of nickel-cadmium batteries, the principle of the memory effect is crystallization, and this reaction almost never occurs in lithium batteries. However, the capacity of lithium-ion batteries will still decrease after repeated charging and discharging. The reasons are complex and diverse. Mainly due to changes in the positive and negative electrode materials themselves. From a molecular level, the hole structure that accommodates lithium ions on the positive and negative electrodes will gradually collapse and become blocked. From a chemical point of view, it is the active passivation of the positive and negative electrode materials, causing side reactions to generate stable lithium ions. Other compounds. Physically, the positive electrode material gradually peels off, which ultimately reduces the number of lithium ions in the battery that can move freely during charging and discharging.

　　Overcharging and over-discharging will cause permanent damage to the positive and negative electrodes of lithium-ion batteries. From a molecular level, it can be intuitively understood that over-discharging will cause the negative electrode carbon to excessively release lithium ions and cause its lamellar structure to collapse. Overcharging will force too many lithium ions into the negative carbon structure, making it impossible for some of the lithium ions to be released. This is why lithium-ion batteries are usually equipped with charge and discharge control circuits.

　　Unsuitable temperatures will trigger other chemical reactions inside the lithium-ion battery to produce compounds that we do not want to see. Therefore, many lithium-ion batteries are equipped with protective temperature-control separators or electrolyte additives between the positive and negative electrodes. When the battery heats up to a certain level, the pores of the composite membrane close or the electrolyte denatures, and the internal resistance of the battery increases until the circuit is broken, and the battery no longer heats up, ensuring that the battery charging temperature is normal.

　　Can deep charging and discharging increase the actual capacity of lithium-ion batteries? Experts told me unequivocally that this makes no sense. They even said that the so-called "activation" of the first three full charges and discharges, based on the knowledge of their two doctors, could not figure out why this is necessary. However, why do many people change the capacity marked in the Battery Information after deep charge and discharge? What follows? will be mentioned.

　　Lithium-ion batteries generally have management chips and charge control chips. There are a series of registers in the management chip, which store values such as capacity, temperature, ID, charging status, and number of discharges. These values will gradually change during use. I personally think that the main function of the instruction in the instruction manual, "It should be fully charged and discharged once a month or so after use, is to correct the improper values in these registers so that the battery's charge control and nominal capacity match the actual situation of the battery."

　　The charging control chip mainly controls the charging process of the battery. The charging process of lithium-ion batteries is divided into two stages, the constant current fast charge stage (when the battery indicator light is yellow) and the constant voltage current decreasing stage (the battery indicator light flashes green). In the constant current fast charge stage, the battery voltage gradually increases reaches the standard voltage of the battery, and then switches to the constant voltage stage under the control chip. The voltage no longer rises to ensure that it will not be overcharged. The current gradually weakens to 0 as the battery power increases, and charging is finally completed.

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