Detailed explanation of aging of lithium iron phosphate battery

1. Placing the lithium iron phosphate battery at high temperature or normal temperature for a period of time can ensure that the electrolyte can sufficiently infiltrate the pole pieces, which is beneficial to the stability of the performance of the lithium iron phosphate battery; 2. After the lithium iron phosphate battery undergoes a pre-formation process The graphite negative electrode inside the lithium iron phosphate battery will form a certain amount of SEI film, but this film has a compact structure and small pores. The aging of the lithium iron phosphate battery at high temperatures will help the SEI structure to reorganize and form a loose porous film. . 3. After the formation, the voltage of the lithium iron phosphate battery is in an unstable stage. After the active material in the positive and negative materials is aged, it can promote the acceleration of some side-uses, such as gas production, electrolyte analysis, etc., so that the lithium iron phosphate The electrochemical performance of lithium batteries quickly stabilized. 4. Eliminate unqualified lithium iron phosphate batteries with serious self-discharge, which is convenient for screening lithium iron phosphate batteries with high consistency. Among them, the aging process to screen internal micro-short circuit cells is an important purpose. The open circuit voltage of the lithium iron phosphate battery will drop during storage, but the amplitude will not be very large. If the open circuit voltage drops too fast or the amplitude is too large, it is an abnormal phenomenon. The self-discharge of lithium iron phosphate batteries can be divided into physical self-discharge and chemical self-discharge according to different reaction types. Considering the influence of self-discharge on the lithium iron phosphate battery, self-discharge can be divided into two types: self-discharge in which loss of capacity can be reversibly compensated and self-discharge in which permanent capacity loss is lost. Generally speaking, the energy loss caused by physical self-discharge is recoverable, while the energy loss caused by chemical self-discharge is basically irreversible. The self-discharge of the lithium iron phosphate battery comes from two aspects: 1. The self-discharge caused by the chemical system itself; this part is mainly caused by the side reaction inside the lithium iron phosphate battery, including the changes in the surface film of the positive and negative materials in detail; The potential change caused by the thermodynamic instability of the electrode; the dissolution and precipitation of foreign metal impurities; 2. The micro-short circuit inside the lithium iron phosphate battery caused by the separator between the positive and negative electrodes leads to the self-discharge of the lithium iron phosphate battery. When the lithium iron phosphate battery is aging, the change of the K value (voltage drop) is the formation and stabilization process of the SEI film on the surface of the electrode material. If the voltage drop is too large, it means that there is a micro short circuit inside, which can be judged as the lithium iron phosphate battery. unqualified products. The K value is a physical quantity used to describe the self-discharge rate of the battery. Its calculation method is the open circuit voltage difference of two detections divided by the time interval between two voltage detections △t, the formula is: Ku003d(OCV2-OCV1)/△t . Particles or trace metal residues on the pole piece, tiny defects on the diaphragm, and dust introduced during the assembly process of the cell, etc., will cause the internal micro short circuit of the cell. Regarding the micro-short circuit cell, the screening cannot be completed only by the capacity and primary voltage, so K value detection must be introduced: by accurately calculating the voltage drop rate to determine whether the cell has a micro-short circuit. There are two basic principles for the internal short circuit of a lithium iron phosphate battery caused by metal foreign bodies, as shown in Figure 2. Larger metal particles pierce the diaphragm straightly, causing a short circuit between the positive and negative electrodes, which is a physical short circuit. In addition, when metal foreign matter is mixed into the positive electrode, the potential of the positive electrode rises after charging. The metal foreign matter dissolves at high potential and diffuses through the electrolyte. Then the metal dissolved at the low potential of the negative electrode precipitates and accumulates on the surface of the negative electrode, and finally pierces the separator to form Short circuit, which is a chemical dissolution short circuit. Fe, Cu, Zn, Al, Sn, SUS, etc. are the most common metal foreign bodies on the site of lithium iron phosphate battery plants. 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: Is the life of lithium batteries really longer than that of lead-acid batteries?