Correct Charging Method of Lifepo4 Battery

The full name of  lifepo4 battery is lithium iron phosphate lithium-ion 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 power battery", and do you all know the charging techniques of lithium iron phosphate? PROnewenergy will introduce to you the charging techniques of lithium iron phosphate batteries.

1. Before solving the problem, first we need to understand the structure and working principle of lithium iron phosphate battery. 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, but lithium Ions can pass through but electrons cannot. On the right is the negative electrode of the battery composed of carbon (graphite), which 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 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 because lithium ions migrate back and forth during charging and discharging.

2. When the battery is charging, lithium ions migrate from the surface of the lifepo4 crystal to the surface of the crystal. Under the action of the electric field force, they enter the electrolyte, pass through the separator, 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 tab, 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 deintercalated from the graphite crystal, enter the electrolyte, pass through the separator, and then migrate to the surface of the lithium iron phosphate crystal through the electrolyte, and then are re-embedded into the lattice of the lithium iron phosphate 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 positive electrode of the battery 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.

Note: Once again, we remind you that lithium iron phosphate batteries should be waterproof and dustproof when using them, so there should be no water in the storage place. This will affect the performance and service life of the battery.

Lithium iron phosphate battery

Correct charging method of lifepo4 battery pack

It is recommended to use CCCV charging method for charging lithium iron phosphate battery pack, that is, constant current first and then constant voltage. The constant current recommendation is 0.3C. The constant voltage recommendation is 3.65. That is, 0.3C current charging during the constant current process. When the battery voltage reaches 3.65V, use 3.65V constant voltage charging. When the charging current is lower than 0.1C (or 0.05C), stop charging, that is, the battery has been full. When you charge with a constant voltage power supply, you also need to check the charging current. It is recommended not to charge at too high a voltage. After adjusting the voltage, make sure the charging current is below 0.5C, which is good for the battery.

Generally, the charging upper limit voltage of lithium iron phosphate battery is 3.7~4V, and the discharge lower limit voltage is 2~2.5V. Taking into account the five aspects of discharge capacity, discharge median voltage, charging time, constant current capacity percentage, and safety, constant current and constant voltage are adopted. According to the charging plan, for lithium iron phosphate battery packs, it is more reasonable to set the charging limit voltage at 3.55~3.70V, the recommended value is 3.60~3.65V, and the lower discharge limit voltage is 2.2V~2.5V.

The charger of lithium iron phosphate battery pack is different from that of ordinary lithium battery. The maximum charge termination voltage of lithium batteries is 4.2 volts; the lithium iron phosphate battery pack is 3.65 volts. When charging the lithium iron phosphate battery pack, the cables connected to the balanced charging board are usually directly connected in series from both ends for overall charging. The charger voltage is greater than the battery pack voltage. The cable is used to detect the voltage of each single cell, which is equivalent to connecting two voltage regulator tubes in parallel. The charging voltage of a single battery will not exceed the voltage regulator value, while other single cells continue to be charged and charged through the voltage regulator tube in bypass.

Because the power of each cell is nearly full at this time, it is just balancing each cell, so the charging current is small, and each cell is fully charged to replenish the balance. The charger can only protect the terminal voltage of the entire battery pack. The balanced charging board ensures that each cell is overcharged and each cell is fully charged. Charging of the entire lithium battery pack cannot be stopped just because one cell is full.

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. As the state of charge of the lithium iron phosphate battery pack changes, the charging current is automatically adjusted. If the specified voltage constant value is appropriate, it can not only ensure the full charging of the power battery, but also minimize gas evolution and water loss. This charging method only considers changes in a single state of 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 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. Keeping the charging current constant, the charging rate is relatively low. The constant current charging control method is simple, but because the acceptable current capability of the lithium battery pack gradually decreases as the charging process proceeds, in the later stages of charging, the power battery's ability to receive electricity decreases, and the charging current utilization rate is greatly reduced. The advantages of this method are simple operation, convenience, easy implementation, and easy calculation of charging capacity.

(3) Constant current and constant voltage charging method: This charging method is a simple combination of the above two. The first stage adopts the constant current charging method to avoid excessive charging current at the beginning of constant voltage charging. The second stage uses a constant voltage charging method to avoid overcharging caused by constant current charging. Lithium iron phosphate battery packs are the same as any other sealed rechargeable batteries. Charging must be controlled and overcharging is not allowed, otherwise the battery will be easily damaged. Lithium iron phosphate batteries generally use a charging method of constant current first and then voltage limiting.

(4) Chopping charging method: charging using chopping method. Under this method, the current of the constant current source remains unchanged, and the switch tube is controlled so that it is turned on for a period of time and then turned off for a period of time, and the cycle repeats. The advantage of this method is that when the battery is charged through an external circuit, The ion generation inside the battery requires a certain response time, and if it is continuously charged, it may reduce its capacity potential. After charging for a period of time, adding a shutdown time can allow the ions generated at the two poles of the battery to diffuse, giving the battery a "digestion" time, which will greatly increase the battery's utilization rate and improve Charging effect.