aa alkaline battery.[Technology] Detailed explanation of the advantages and disadvantages of lithium iron phosphate power batteries

　　[Technology] Detailed explanation of the advantages and disadvantages of lithium iron phosphate power batteries

　　Lithium iron phosphate battery refers to a lithium-ion battery using lithium iron phosphate as the positive electrode material. The cathode materials of lithium-ion batteries mainly include lithium cobalt oxide, lithium manganate, lithium nickel oxide, ternary materials, lithium iron phosphate, etc. Among them, lithium cobalt oxide is the cathode material currently used in most lithium-ion batteries.

　　working principle

　　The full name of lithium iron phosphate battery is lithium iron phosphate lithium-ion battery. This name is too long, so it is simply called lithium iron phosphate battery. Because its performance is particularly suitable for power applications, the word "power" is added to the name, that is, lithium iron phosphate power battery. Some people also call it "lithium iron (LiFe) power battery."

　　significance

　　In the metal trading market, cobalt (Co) is the most expensive and has limited storage, nickel (Ni) and manganese (Mn) are relatively cheap, while iron (Fe) is the cheapest. The price of cathode materials is also in line with the price trends of these metals. Therefore, lithium-ion batteries made of LiFePO4 cathode material should be the cheapest. Another feature of it is that it does not pollute the environment.

　　The requirements for a rechargeable battery are: high capacity, high output voltage, good charge and discharge cycle performance, stable output voltage, capable of large current charge and discharge, electrochemical stability, and safety during use (not due to overcharge, overdischarge, or short circuit) etc. may cause combustion or explosion due to improper operation), wide operating temperature range, non-toxic or less toxic, and no pollution to the environment. Lithium iron phosphate batteries using LiFePO4 as the positive electrode are good in these performance requirements, especially in terms of large discharge rate discharge (5~10C discharge), stable discharge voltage, safety (no burning, no explosion), and lifespan (number of cycles). ), no pollution to the environment, it is the best, and it is currently the best high-current output power battery.

　　Structure and working principle

　　LiFePO4 serves as the positive electrode of the battery. It is connected to the positive electrode of the battery by aluminum foil. There is a polymer separator in the middle, which separates the positive electrode from the negative electrode. However, lithium ions Li can pass but electrons e- cannot pass. The right side is composed of carbon (graphite) The negative terminal of the battery is connected to the negative terminal 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 sealed by a metal casing.

　　When the LiFePO4 battery is charged, the lithium ions Li in the positive electrode migrate to the negative electrode through the polymer separator; during the discharge process, the lithium ions Li in the negative electrode migrate to the positive electrode through the separator. Lithium-ion batteries are named because lithium ions migrate back and forth during charging and discharging.

　　Main performance

　　The nominal voltage of LiFePO4 battery is 3.2V, the termination voltage is 3.6V, and the termination voltage is 2.0V. Due to the different quality and process of the positive and negative electrode materials and electrolyte materials used by various manufacturers, there will be some differences in their performance. For example, the same model (standard battery in the same package) has a large difference in battery capacity (10% to 20%).

　　What should be noted here is that lithium iron phosphate power batteries produced by different factories will have some differences in various performance parameters; in addition, some battery properties are not included, such as battery internal resistance, self-discharge rate, charge and discharge temperature, etc.

　　The capacity of lithium iron phosphate power batteries varies greatly and can be divided into three categories: small ones ranging from a few tenths to several milliamp hours, medium-sized ones tens of milliamp hours, and large ones hundreds of milliamp hours. There are also some differences in the same parameters of different types of batteries.

　　Over-discharge to zero voltage test

　　The lithium iron phosphate power battery using STL18650 (1100mAh) has been discharged to zero voltage test. Test conditions: Fully charge the 1100mAh STL18650 battery with a 0.5C charge rate, and then discharge it with a 1.0C discharge rate until the battery voltage is 0C. Then divide the batteries placed at 0V into two groups: one group is stored for 7 days, and the other group is stored for 30 days; after the storage expires, it is fully charged with a 0.5C charging rate, and then discharged with a 1.0C rate. Finally, compare the differences between the two zero-voltage storage periods.

　　The result of the test 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, the battery has no leakage, good performance, and the capacity is 98%; after 30 days of storage, the battery is subjected to 3 charge-discharge cycles. The capacity is restored to 100%.

　　This test shows that even if the battery is over-discharged (even to 0V) and stored for a certain period of time, the battery will not leak or be damaged. This is a feature that other types of lithium-ion batteries do not have.

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