What are the structure and working principle of lithium iron phosphate battery

The full name of the lithium iron phosphate battery is the lithium iron phosphate battery, this name is too long, referred to as the lithium iron phosphate battery. Because its performance is particularly suitable for power use, the word power is added to the name, that is, lithium iron phosphate power lithium-ion battery. Some people call it lithium iron (LiFe) power lithium-ion battery. Significance: In the metal trading market, cobalt (Co) is the most expensive, and storage capacity is not much, nickel (Ni) and manganese (Mn) are cheaper, and iron (Fe) is the cheapest. 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 the cheapest. Another feature of it is that it does not pollute 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 pollution-free environment, and is currently the best lithium-ion battery with high current output power. Structure and working principle: The internal structure of LiFePO4 battery is shown in Figure 1. On the left is LiFePO4 with olivine structure as the positive electrode of the battery. It is connected to the positive electrode of the battery by aluminum foil. In the middle is a polymer separator, which separates the positive electrode from the negative electrode, but the lithium ion Li+ can pass but the electron e- cannot pass. The negative electrode of the battery composed of carbon (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. Important 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%). The key performance of lithium iron phosphate power lithium-ion battery is listed in Table 1. In order to compare with other rechargeable batteries, the performance of other types of rechargeable batteries is also listed in the table. What I want to explain here is that there are some differences in various performance parameters of lithium iron phosphate power lithium-ion batteries processed by different factories; 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. Here we analyze the parameters of a currently widely used small standard cylindrical packaged lithium iron phosphate power lithium-ion battery. Its external dimensions: diameter 18mm, height 650mm (model 18650), its parameter performance is shown in Table 2. 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. Then divide the 0V batteries into two groups: one group is stored for 7 days, and 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, good performance, and the capacity is 98%; the battery after 30 days of storage is subjected to 3 charge and discharge cycles. The capacity has returned to 100%. This experiment shows that even if the battery is over-discharged (even to 0V) and stored for a period of time, the battery will not leak or be damaged. This is a feature that other types of lithium batteries do not have. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.