Introduction to charging techniques and methods of lithium iron phosphate batteries

Charging method of lithium iron phosphate battery pack (1) Constant voltage charging method: During the charging process, the output voltage of the charging power supply remains constant. With the change of the state of charge of the lithium iron phosphate battery pack, the charging current is automatically adjusted. If the specified voltage is constant, it can not only ensure the full charge of the power lithium battery, but also minimize gassing and water loss. This charging method only considers the change in the single state of the battery voltage, and cannot effectively reflect the overall charging status of the battery. Its initial charging current is too large, which often causes damage to the power lithium battery. In view of this shortcoming, constant voltage charging is rarely used. (2) Constant current charging method: During the entire charging process, the charging current is kept constant by adjusting the output voltage. Keep the charging current constant, the charging rate is relatively low. The constant current charging control method is simple, but because the acceptable current capacity of the lithium-ion battery pack gradually decreases with the progress of the charging process, in the later stage of the charging, the power receiving capacity of the power lithium battery decreases, and the charging current utilization rate is greatly reduced. The advantages of this method are simple, convenient, and easy to implement, and the charging power is easy to calculate. (3) Constant current and constant voltage charging method: This charging method is a simple combination of the above two. The constant current charging method is used in the first stage to prevent excessive charging current at the beginning of constant voltage charging. The second stage adopts the constant voltage charging method to prevent the phenomenon of overcharging during constant current charging. Lithium iron phosphate battery packs are the same as any other sealed rechargeable batteries. The charging must be controlled, and excessive charging is not allowed, otherwise the battery will be easily damaged. Lithium iron phosphate batteries generally adopt a charging method of constant current first and then voltage limiting. (4) Chopping wave charging method: Use the chopping method to charge. In this method, the current of the constant current source is unchanged, and the switch tube is controlled to turn on for a period of time and then turn off for a period of time, cyclically. The advantage of this method is that when the battery is charged through an external circuit, The presence of ions inside the battery requires a certain response time. If it is continuously charged, its capacity potential may be reduced. After charging for a period of time, adding a turn-off time can allow the ions appearing at the two poles of the battery to have a diffusion process, giving the battery a time for digestion, which will greatly increase the utilization rate of the battery and improve the charging. effect. Tips for charging lithium iron phosphate batteries 1. Before solving the problem, we must first understand the structure and working principle of lithium iron phosphate batteries. LiFePO4 is used as the positive electrode of the battery. It is connected to the positive electrode of the battery by aluminum foil. The polymer separator is in the middle. The positive electrode is separated from the negative electrode, but lithium ions can pass but electrons cannot pass. On the right is the battery negative electrode composed of carbon (graphite), which is connected to the battery negative electrode 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 a lithium iron phosphate battery is charged, the lithium ions in the positive electrode migrate to the negative electrode through the polymer separator; during the discharge process, the lithium ions in the negative electrode migrate to the positive electrode through the separator. Lithium-ion batteries are named after lithium ions move back and forth during charging and discharging. 2. When the battery is charged, lithium ions migrate from the surface of the lithium iron phosphate crystal to the surface of the crystal. Under the use of electric field force, they enter the electrolyte, pass through the diaphragm, and then migrate to the surface of the graphite crystal through the electrolyte, and then are embedded in the graphite crystal. Grid. At the same time, electrons flow to the aluminum foil collector of the positive electrode through the conductor, flow to the copper foil collector of the negative electrode through the tab, battery pole, external circuit, negative pole, and negative lug, and then flow to the graphite negative electrode through the conductor. The charge on the negative electrode is balanced. After the lithium ions are deintercalated from the lithium iron phosphate, the lithium iron phosphate is converted into iron phosphate. 3. When the battery is discharged, lithium ions are extracted from the graphite crystal, enter the electrolyte, pass through the diaphragm, and then migrate to the surface of the lithium iron phosphate crystal through the electrolyte, and then re-embed into the lithium iron phosphate crystal lattice through the surface. . At the same time, the battery flows to the copper foil collector of the negative electrode through the conductor, flows to the aluminum foil collector of the battery positive electrode through the tab, battery negative pole, external circuit, positive pole, and positive tab, and then flows to the iron phosphate through the conductor. Lithium positive electrode balances the charge of the positive electrode. Matters needing attention: once again remind the lithium iron phosphate battery to pay attention to waterproof and dustproof when in use, so there should be no water in the storage place, which will affect the performance and service life of the battery. 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 article: Why is the lithium-ion battery pack of electric vehicles bulging?