Residual moisture test of lithium battery pole piece

The residual moisture test of lithium battery electrodes and its impact on performance. Lithium batteries have become the standard power source for portable mobile devices. In recent years, they have developed rapidly in electric vehicles and energy storage devices. The requirements of battery safety, energy density, power density, cycle life and reliability have also been continuously improved, and the function of lithium batteries is affected by many factors, including not only the battery planning, raw materials, process level, equipment accuracy and other aspects, but also the environment Factors such as temperature, cleanliness and water. Even a small amount of impurities will adversely affect the cycle stability and safety of lithium batteries. Therefore, it is necessary for us to pay attention to the processing process and strictly control the quality. At the same time, the control of moisture is very critical. Commercial lithium batteries are processed in a large, boring room with strict environmental water control. Before the battery is packaged, all components are boring. This article collects and shares with you the basic knowledge of battery testing and water control. 1. The substrate mechanism of water damage to battery functions. Lithium batteries assume that water is too high and will react with the electrolyte. First, the water reacts with the lithium in the electrolyte to form HF: H2O+LiPF6→POF3+LiF+2HF Hydrofluoric acid is a very corrosive acid, which can corrode the metal parts inside the battery and cause the battery to eventually leak . In addition, if HF destroys the SEI film, it will continue to react with the main components of SEI: ROCO2Li+HF→ROCO2H+LiFLi2CO3+2HF→H2CO3+2LiF. After all, LiF accumulates in the battery, resulting in irreversible lithium ions in the negative electrode of the battery. The chemical reaction consumes active lithium ions and reduces the energy of the battery. When the water content is satisfied, more gas will appear, and the pressure inside the battery will increase, which will cause stress and deformation of the battery, battery swelling, leakage and other dangers. 2. Check the residual moisture in the pole piece. The residual water in the electrode membrane of the battery is generally hundreds of parts per million. The water content is relatively low and cannot be measured by a simple method. The Karl Fischer coulometric method is generally used to detect trace water. , Its principle is electrochemical method. The Cartesian reagent instrument reaches equilibrium, and the water sample is injected into the electrolytic cell. The water iodine and sulfur dioxide are oxidized and recovered. In the presence of pyridine and methanol, pyridine hydroiodic acid and methyl pyridine are generated. The iodine is electrolyzed at the anode, and then the continuous oxidation reaction is resumed. Until the water is exhausted, according to the rules of Faraday electrolysis, the contact between electrolytic iodine and electrolysis power consumption is proportional to the following reaction: H2O+I2+SO2+3C5H5N->2C5H5N, HI+C5H5N, SO3 in the electrolysis process, the electrode reacts As follows: Anode: 2I--2e→I2 Cathode: I2+2e→2I-2h++2e-H2 Writing From this reaction, we can see that 1 mol of iodine oxidizes 1 mol of sulfur dioxide, which requires 1 mol of water. Therefore, the amount of electricity to electrolyze iodine is equal to the amount of electricity to electrolyze water. The electricity required for electrolysis of 1 mole of iodine is 2×96493 coulombs, and the electricity required for electrolysis of 1 millimole of water is 96493 millicoulos. Calculate the moisture content of the sample according to formula (1): where: W sample moisture content, g; Q electrolysis power, mC; 18 water molecular weight. The overall structure of the Fischer-Cullen trace moisture detection instrument is shown in Figure 1. The first one contains a Fischer electrolytic cell and a sample heating device. The sample bottle is sealed with a sample, and then the temperature of the sample bottle must be heated to evaporate the sample, and then Using monotonous natural gas water vapor to the electrolysis cell will participate in the reaction, and then determine the electrolysis process, moisture content and titration of the electricity. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete it. Previous article: Is it necessary to charge a new mobile phone for 8 hours?