Analysis of capacity loss of lithium iron phosphate power lithium-ion battery pack

Lithium Iron Phosphate Power Lithium-ion Battery Capacity Loss Analysis Fund Project: National 63 Program Fund (2003AA501350), Fundamental Research Funds for Central Universities (CDXS11151156). Hu Yinquan (1978-), male, doctor. The problem of excessively rapid battery capacity decay is conducive to the effective use of battery packs, slows down the speed of battery pack capacity decay, and prolongs the cycle life of the battery pack. 1 Battery charge and discharge mechanism and self-discharge analysis 1.1 Battery charge and discharge mechanism Lithium iron phosphate cathode material has a regular olivine structure, and a lot of research on the structure and characteristics of lithium iron phosphate batteries has been carried out. Lithium iron phosphate battery refers to a lithium battery using lithium iron phosphate as the positive electrode material. During charging and discharging, the polymer film separates the positive and negative electrodes, preventing electrons from passing through, and allowing lithium ions to pass through. According to formula (1) and formula (2), the charge and discharge reaction between LFePODFeP04 is carried out. During the charging process, lithium ions escape from UFeP0 and 4 and migrate to the negative electrode through the diaphragm, and the positive electrode forms FeP0 and 4 phases. During the discharge process, lithium ions escape from the negative electrode, migrate to the positive electrode through the separator, and insert FeP04 to form UFeP04. Since the coordination relationship of ferro-oxygen does not change much during charging and discharging, although there is a phase change in the process of removing lithium, there is no volume effect that affects the electrochemical performance of lithium. Battery self-discharge analysis Battery self-discharge refers to the natural loss of battery capacity when the battery is not in use. Under normal circumstances, the degree of self-discharge of the battery is mainly affected by factors such as cathode material, battery manufacturing process, electrolyte performance, temperature and time. Self-discharge will cause the battery to lose some capacity. The self-discharge of the battery is greatly affected by temperature and state of charge. If the negative electrode is fully charged and the positive electrode self-discharges, the internal capacity balance of the battery will be destroyed, resulting in permanent capacity loss. During long-term or frequent self-discharge, lithium may be deposited on the carbon, exacerbating the capacity imbalance between the two electrodes. In practice, battery self-discharge also includes the power consumed by the battery management system. 2. It is the on-board discharge of the battery pack. A single battery test module tests the voltage and temperature of each battery. The touch screen module detects the total voltage and current of the battery pack, and controls the charging process of the battery pack. The number of batteries in each battery pack of low-voltage electric vehicles is 16, connected in series. totalvoltage is a touch screen module, used to detect the total voltage and total current of the battery pack, and display the total voltage, total current, cell voltage, temperature and other important information on the touch screen module in real time. The touch screen module communicates with the charger, balance module, and motor controller through the CAN bus at the same time, and monitors the charging and discharging process of the power battery pack, which is the core of the management system. The charging process of the lithium iron phosphate power lithium ion battery is as follows: Initially, the charger for charging the lithium iron phosphate power lithium ion battery, the single battery voltage and temperature test of the single battery test module, the test results can be communicated with the touch screen of the processor, and the touch screen series of micro-processing The charger monitors and controls the charging process. The battery is charged in series according to the voltage of a single battery. When the series of charging ends, the touch screen module detects that the state of charge of a certain battery or multiple batteries is low, and to start the balance module, the touch screen sends a signal to start the balance module of the corresponding battery. When the balance charging module completes the balance charging of each battery, the balance charging module stops working, and the touch screen microprocessor displays that the battery pack is fully charged. Through the charging experiment of lithium iron phosphate power lithium-ion battery, it is verified that the balance charging module can well balance the charging of each single battery in the battery pack. Through the balance charging device of the battery pack, each battery in the battery pack can be fully charged. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Suggestions for the development of solid-state lithium battery and hydrogen fuel power battery industry