Lithium iron phosphate battery structure, working principle and performance analysis

Lithium iron phosphate battery refers to a lithium battery that uses lithium iron phosphate as the positive electrode material. The cathode materials of lithium batteries mainly include lithium cobalt oxide, lithium manganate, lithium nickelate, ternary materials, and lithium iron phosphate. Among them, lithium cobalt oxide is currently the cathode material used in most lithium batteries. Significance In the metal trading market, cobalt (Co) is the most expensive and has a small amount of storage, nickel (Ni) and manganese (Mn) are cheaper, and iron (Fe) has more storage. The price of the cathode material is also consistent with the price of these metals. Therefore, the lithium battery made of LiFePO4 cathode material should be very cheap. Another feature of it is that it has no pollution to the environment. As a rechargeable battery, the requirements are: high capacity, high output voltage, good charge and discharge cycle performance, stable output voltage, high current charge and discharge, electrochemical stability, safety in use (not due to overcharge, overdischarge and short circuit Burning or explosion caused by improper operation), wide operating temperature range, non-toxic or less toxic, and non-polluting to the environment. Lithium iron phosphate batteries using LiFePO4 as the positive electrode are good in these performance requirements, especially in high discharge rate discharge (5～10C discharge), discharge voltage is stable, safety (non-burning, non-explosive), and life (cycle times) ). It is the best in terms of no pollution to the environment, and is currently the best high-current output power lithium-ion battery. Structure and working principle LiFePO4 is used as the positive electrode of the battery, which is connected with the positive electrode of the battery by aluminum foil. In the middle is a polymer separator, which separates the positive electrode and the negative electrode. However, lithium ion Li can pass through but electron e- cannot pass. The negative electrode of the battery composed of graphite) is connected to the negative electrode of the battery by copper foil. Between the upper and lower ends of the battery is the electrolyte of the battery, and the battery is hermetically sealed by a metal casing. When the LiFePO4 battery is charged, the lithium ion Li in the positive electrode migrates to the negative electrode through the polymer separator; during the discharge process, the lithium ion Li in the negative electrode migrates to the positive electrode through the separator. Lithium batteries are named after lithium ions move back and forth during charging and discharging. Critical performance The nominal voltage of LiFePO4 battery is 3.2V, the final charging voltage is 3.6V, and the final discharge voltage is 2.0V. Due to the different quality and technology of the positive and negative materials and electrolyte materials used by various manufacturers, there will be some differences in their performance. For example, the battery capacity of the same model (standard battery in the same package) is quite different (10%-20%). What I want to explain here is that lithium iron phosphate power lithium-ion batteries processed by different factories will have some differences in various performance parameters; in addition, some battery properties are not listed, such as battery internal resistance, self-discharge rate, charge and discharge temperature Wait. The capacity of lithium iron phosphate power lithium-ion batteries is quite different, which can be divided into three categories: small-scale a few to a few milliamperes, medium-scale tens of milliamp-hours, and large-scale hundreds of milliamp-hours. Similar parameters of different types of batteries also have some differences. Over-discharge to zero voltage test: STL18650 (1100mAh) lithium iron phosphate power lithium-ion battery is used for over-discharge to zero voltage test. Experimental conditions: The 1100mAh STL18650 battery was overflowed with a 0.5C charge rate, and then discharged with a 1.0C discharge rate until the battery voltage was 0C. The batteries placed at 0V are divided into two groups: one group is stored for 7 days, the other group is stored for 30 days; after the storage expires, the battery is charged at 0.5C, and then discharged at 1.0C. Finally, compare the difference between the two zero-voltage storage periods. The result of the experiment is that after 7 days of zero voltage storage, the battery has no leakage, good performance, and the capacity is 100%; after 30 days of storage, there is no leakage and good performance, and the capacity is 98%; the battery after 30 days of storage is subjected to 3 charge-discharge cycles. The capacity has returned to 100%. 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: What is the future of lithium battery equipment?