The full name of LiFePO4 battery is LiFePO4lithium ion battery. Because its performance is particularly suitable for powerapplications, the word "power" is added to the name, that is, LiFePO4power battery. Some people call it "lithium-iron power battery", andyou all know the charging skills of LiFePO4? Here are some charging tips for LiFePO4batteries.
1. Beforesolving the problem, we first need to understand the structure and workingprinciple of LiFePO4 battery. LiFePO4 is used as the positive electrode of thebattery. The aluminum foil is connected to the positive electrode of thebattery. The polymer separator is in the middle. It separates the positiveelectrode from the negative electrode. Ions can pass but electrons cannot pass.On the right is the battery negative electrode composed of carbon (graphite),and the copper foil is connected to the battery negative electrode. Thebattery's electrolyte is between the upper and lower ends of the battery, andthe battery is hermetically sealed by a metal case. During charging of theLiFePO4 battery, lithium ions in the positive electrode migrate to the negativeelectrode through the polymer separator; during discharge, lithium ions in thenegative electrode migrate to the positive electrode through the separator.Lithium-ion batteries are named because lithium ions migrate back and forthduring charge and discharge.
2. Whenthe battery is charged, lithium ions migrate from the surface of the LiFePO4crystal to the crystal surface. Under the action of the electric field force,it enters the electrolyte, passes through the separator, and then migrates tothe surface of the graphite crystal through the electrolyte, and then embedsthe graphite crystal. Grid. At the same time, electrons flow through theconductor to the aluminum foil collector of the positive electrode, and then tothe copper foil current collector of the negative electrode through the tab,battery pole, external circuit, negative pole, and negative electrode, and thenflow through the conductor to the graphite negative electrode. The negativecharge is in equilibrium. After lithium ions are deintercalated from LiFePO4,LiFePO4 is converted into iron phosphate.
3. Whenthe battery is discharged, lithium ions are de-intercalated from the graphitecrystal, enter the electrolyte, pass through the separator, and then migrate tothe surface of the LiFePO4 crystal through the electrolyte, and thenre-embedded into the crystal lattice of LiFePO4. . At the same time, thebattery flows through the conductor to the copper foil collector of thenegative electrode, flows to the aluminum foil current collector of the batterythrough the tab, the battery negative pole, the external circuit, the positivepole, and the positive pole, and then flows to the iron phosphate through theconductor. Lithium positive electrode to balance the charge of the positiveelectrode.
Note: Once again remind the LiFePO4 battery topay attention to waterproof and dustproof when used, so there must be no waterin the storage place, which will affect the battery performance and servicelife.
Correct charging method of LiFePO4 battery pack
It is recommended to use the CCCV chargingmethod for charging the LiFePO4 battery pack, that is, constant current firstand then constant voltage. Constant current is recommended to be 0.3C. Constantvoltage recommendation 3.65. That is, 0.3C current charging during constantcurrent. When the battery voltage reaches 3.65V, use 3.65V constant voltagecharging. Stop charging when the charging current is lower than 0.1C (or0.05C), that is, the battery has been charged. full. When you charge with aconstant voltage power supply, you should also look at the charging current. Itis recommended not to charge with too high voltage. After adjusting thevoltage, ensure that the charging current is below 0.5C, which is good for thebattery.
Generally, the upper limit voltage of LiFePO4battery is 3.7 ~ 4V, and the lower limit voltage of discharge is 2 ~ 2.5V.Considering the five aspects of discharge capacity, median discharge voltage,charging time, percentage of constant current capacity, and safety, constantcurrent and constant voltage are used. For the charging solution of LiFePO4battery pack, it is reasonable to set the charging limit voltage at 3.55 ～ 3.70V, the recommended value is 3.60 ～ 3.65V, and the lower limit discharge voltage is 2.2V ~ 2.5V.
The charger of the LiFePO4 battery pack isdifferent from ordinary lithium batteries. The maximum termination chargevoltage of a lithium battery is 4.2 volts; the LiFePO4 battery pack is 3.65volts. When the LiFePO4 battery pack is charged, it is a balanced cableconnected to the charging board. Generally, the battery is directly charged inseries from both ends, and the charger voltage is greater than the battery packvoltage. The cable detects the voltage of each single cell, which is equivalentto connecting a voltage regulator tube in parallel, and the charging voltage ofthe single cell does not exceed the regulated value, while the other batterycells continue to charge by bypassing the voltage regulator tube.
Because the power of each cell is almost full atthis time, it is only balancing each cell, so the charging current is small,and each cell is fully balanced. The charger can only protect the terminalvoltage of the entire battery pack. The balanced charging board ensures thateach cell is overcharged and that each cell is fully charged. It cannot stopcharging the entire lithium battery pack because one cell is full.
Charging method of LiFePO4 battery pack
(1) Constant voltage charging method: During thecharging process, the output voltage of the charging power source remainsconstant. With the change of the state of charge of the LiFePO4 battery pack,the charging current is automatically adjusted. If the specified constantvoltage value is appropriate, it can not only ensure the full charging of thepower battery, but also minimize outgassing and water loss. This chargingmethod only considers the change of the single state of the battery voltage andcannot effectively reflect the overall charging status of the battery. Itsinitial charging current is too large, which often causes damage to the powerbattery. In view of this disadvantage, constant voltage charging is rarelyused.
(2) Constant current charging method: During theentire charging process, the charging current is kept constant by adjusting theoutput voltage. Keeping the charging current constant, its charging rate isrelatively low. The constant current charging control method is simple, butbecause the acceptable current capacity of the lithium battery pack graduallydecreases with the progress of the charging process, in the later stage ofcharging, the power receiving capacity of the power battery decreases, and theutilization rate of the charging current is greatly reduced. The advantages ofthis method are simple operation, convenience, easy implementation, and easycalculation of the charge capacity.
(3) Constant current and constant voltagecharging method: This charging method is a simple combination of the above two.The first stage uses a constant current charging method to avoid excessivecharging current at the beginning of constant voltage charging. The secondstage uses a constant voltage charging method to avoid overcharging caused byconstant current charging. Like any other sealed rechargeable battery, the LiFePO4battery pack must be controlled to prevent overcharging, otherwise it willeasily damage the battery. LiFePO4 battery generally adopts the charging methodof constant current first and voltage limiting.
(4) Chopper charging method: Charging is usedfor charging. In this method, the current of the constant current source doesnot change, and the switch tube controls it to turn on for a period of time andthen turn off for a period of time. This method has the advantage that when thebattery is charged through an external circuit, The ion generation inside thebattery requires a certain response time. If it is continuously charged, it mayreduce its potential for capacity. And after charging for a period of time,adding a turn-off time can allow the ions generated by the battery poles tohave a diffusion process, so that the battery has a "digestion" time,which will greatly increase the battery utilization and improve Chargingeffect.