How to improve the fast charge and discharge performance of lithium batteries?

The process of fast charging of lithium batteries is the process of fast relocation of Li+ into the negative electrode of the positive electrode. The particle size of the positive electrode material can affect the response time and ion dispersion path in the electrochemical process of the battery. According to research, as the crystal grain size of the material decreases, the dispersion coefficient of lithium ions increases. However, as the size of the material particles decreases, the pulping will show severe particle agglomeration and uneven composition during processing. Together, the nanoparticles will reduce the compaction density of the pole pieces and touch the area of u200bu200bthe electrolyte during the charging and discharging process. Increase the secondary response and affect the function of the battery. A more reliable method is to coat and modify the positive electrode material. For example, the conductivity of LFP itself is not very good. After the surface is coated with carbon material or other materials, the conductivity can be improved, which is conducive to the rapid charging of the battery. Features. 02 Fast charging of negative electrode materials lithium batteries means that lithium ions are quickly released and swim to the negative electrode. At this time, the negative electrode materials are required to have the ability to quickly insert lithium. The negative electrode materials used for fast charging of lithium batteries include carbon materials, lithium titanate and other new materials. Regarding carbon materials, because the lithium-intercalation potential is similar to the potential of lithium separation, in the case of conventional charging, lithium ions are generally preferentially inserted into graphite, but under fast charging or low temperature conditions, lithium ions may be separated on the surface to form branches. Crystal lithium. Dendrite lithium pierces the SEI, causing Li+ secondary loss and reducing battery capacity. When the lithium metal reaches a certain amount, it will grow from the negative electrode to the separator, posing a risk of short-circuiting the battery. Regarding LTO, it is a zero-strain oxygen-containing negative electrode material, and SEI will not occur during battery operation, and its combination with lithium ions can be stronger, and it can meet the requirements of fast charge and fast discharge. At the same time, it is precisely because the SEI cannot be formed, the negative electrode material will directly touch the electrolyte, which promotes the occurrence of side effects. The problem of gas production in LTO batteries has been delayed and can only be alleviated by surface modification. As mentioned earlier in the 03 electrode solution, due to the inconsistency between the lithium ion migration speed and the electron transmission rate during the fast charging process, the battery will have a greater polarization. So in order to minimize the negative reaction caused by battery polarization, the following three requirements will be the direction of electrolyte development: 1. High dissociation degree electrolyte salt; 2. Solvent recombination-lower viscosity; 3. Interface control-membrane impedance Lower. 04 The relationship between processing technology and fast charging The requirements and influence of fast charging have been analyzed from three key materials such as positive and negative electrode materials and electrode liquid. The following is a process plan that has a relatively large impact. The battery manufacturing process parameters directly affect the migration resistance of lithium ions in various parts of the battery before and after the battery is activated. Therefore, the battery manufacturing process parameters have an important impact on the function of the lithium battery. (1) Slurry Regarding the properties of the slurry, on the one hand, it is necessary to maintain the uniform dispersion of the conductive agent. Because the conductive agent is evenly distributed among the active material particles, a relatively uniform conductive network can be formed between the active materials and between the active material and the current collector. It has the purpose of collecting micro currents, reducing the touch resistance, and improving the movement rate of electrons. . The other is to prevent the excessive dispersion of the conductive agent. In the process of charging and discharging, the crystal structure of the positive and negative materials will change, which may constitute the peeling off of the conductive agent, which will increase the internal resistance of the battery and affect its function. (2) In theory, the area density of the pole pieces cannot have both a rate-type battery and a high-capacity battery. When the surface density of the positive and negative pole pieces is low, the dispersion speed of lithium ions can be increased, and the resistance of ion and electron transfer can be reduced. The lower the areal density, the thinner the pole piece, and the smaller the change in the structure of the pole piece due to the continuous insertion and extraction of lithium ions during charging and discharging. However, if the areal density is too low, the energy density of the battery will decrease and the cost will increase. Therefore, it is necessary to consider the areal density in a generalized manner. The picture below shows a 6C charge and 1C discharge of a lithium cobalt oxide battery. For example, you can see: (3) Before the consistency of the pole piece coating, a friend asked, will the inconsistent surface density of the pole piece affect the battery? By the way, regarding the fast charging function, the most important thing is the consistency of the negative pole piece. If the surface density of the negative electrode is inconsistent, after rolling, the internal porosity of the active material will be quite different. The difference in porosity will cause the difference in internal current distribution, which affects the composition and function of the SEI during the battery formation stage, and ultimately affects the fast charging function of the battery. (4) Pole piece compaction density Why do pole pieces need to be compacted? One is to improve the specific energy of the battery, and the other is to improve the battery function. The electrode material is different, the best compaction density is also different. To improve the compaction density, the smaller the porosity of the electrode pole piece, the tighter the connection between the particles, and the smaller the thickness of the pole piece under the same areal density, thus reducing the migration path of lithium ions. When the compaction density is too large, the electrolyte infiltration is not good enough, which may damage the data structure and conductive agent dispersion, and winding problems will occur later. The same is the lithium cobalt oxide battery 6C charge 1C discharge, the impact of compaction density on the specific discharge capacity is as follows: 05 Formation aging and other carbon anode batteries, formation-aging is the key process of lithium batteries, this process will affect SEI the quality of. The uneven thickness of SEI or unstable structure will affect the battery's fast charging ability and cycle life. In addition to the above several important factors, the production of battery cells and the charging and discharging system will have a greater impact on the function of lithium batteries. Following the extension of the time of use, the battery charging rate should be moderately reduced, otherwise it will increase the polarization. Disclaimer: The articles published on this website are all from the Internet. If there is any infringement, please contact to delete it. 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: What is the difference between lithium battery 18650 and 26650?