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How to charge the lithium iron phosphate battery correctly?

2020-10-13


The full name of the LiFePO4 is the lithium iron phosphate battery. Since its performance is particularly suitable for power applications, the word "power" is added to the name, i.e. lithium iron phosphate battery. Some people call it a "lithium iron power battery", and iron phosphate lithium charging skills you all understand? Here's a look at the charging techniques for lithium iron phosphate batteries.

1, Before solving the problem, first of all, we need to understand the structure and working principle of lithium iron phosphate battery LiFePO4 as the positive pole of the battery, by aluminum foil and battery positive connection, the middle is the polymer diaphragm, it separates the positive and negative poles, but lithium ions can pass and electrons can not pass, the right side is composed of carbon (graphite) battery negative pole, by copper foil and the negative pole of the battery connection. Between the upper and lower ends of the battery is the electrolyte of the battery, which is enclosed in a metal enclosure. When charging a lithium-iron phosphate battery, the lithium ions in the positive pole migrate through the polymer diaphragm to the negative pole, and during discharge, the lithium ions in the negative pole migrate through the diaphragm to the positive. Lithium-ion batteries are named after lithium-ions that migrate back and forth during charge and discharge.

2. When the battery is charged, the lithium ion migrates from the surface of the lithium iron phosphate crystal to the crystal surface, under the effect of electric field force, into the electrolyte, through the diaphragm, and then through the electrolyte to the surface of the graphite crystal, and then embedded in the graphite lattic. At the same time, electrons flow through the conductive body to the positive aluminum foil assembly electrode, through the polar ear, battery pole column, external circuit, negative pole column, negative ear flow to the negative pole of the copper foil collection fluid, and then through the conductive body flow to the graphite negative pole, so that the negative pole charge up to balance. After lithium ion is de-embedded from lithium iron phosphate, lithium iron phosphate is converted into iron phosphate.

3, When the battery discharge, lithium ions from the graphite crystal out of the inlay, into the electrolyte, through the diaphragm, and then by electrolyte migration to the surface of the lithium iron phosphate crystal, and then re-surface embedded in the lattib of lithium phosphate. At the same time, the battery through the conductive body to the negative pole of the copper foil collection electrode, through the polar ear, battery negative column, external circuit, positive pole column, positive ear flow to the battery positive aluminum foil collection fluid, and then through the conductive body flow to the lithium iron phosphate positive pole, so that the positive charge up to balance.

Note: Again remind lithium iron phosphate battery in use should pay attention to waterproof and dustproof, so the storage place can not have water, which will affect the performance and service life of the battery.

The correct charging method for lithium iron phosphate battery pack.

Charging of lithium iron phosphate battery packs is recommended using the CCCV charging method, i.e. constant flow and constant pressure. Constant flow recommends 0.3C. Constant voltage is recommended 3.65. i.e. 0.3C current charge during constant current, when the battery voltage reaches 3.65V, charge at 3.65V constant voltage, stop charging when the charging current is below 0.1C (or 0.05C), i.e. the battery is fully charged. When you charge with a counterweight power supply, also look at the charging current, it is recommended not to charge with too high voltage, adjust the voltage, to ensure that the charging current is below 0.5C, so good for the battery.

General lithium phosphate battery charging upper voltage 3.7 to 4V, discharge lower voltage 2 to 2.5V, comprehensive consideration of discharge capacity, discharge medium voltage, charging time, constant flow capacity percentage, safety of these 5 aspects, the use of constant current constant voltage charging scheme For lithium iron phosphate battery pack, the charging limit voltage is set at 3.55 to 3.70V, the recommended value is 3.60 to 3.65V, and the discharge lower voltage is 2.2V to 2.5V.

The charger of the lithium phosphate battery pack is different from the ordinary lithium battery. The maximum termination charge voltage for lithium batteries is 4.2 volts, while the lithium phosphate battery pack is 3.65 volts. Iron phosphate lithium battery pack charging, is balanced charging plate line, generally from both ends directly series overall charging, charger voltage is greater than battery pack voltage. The line detects the voltage of each unit core, which is equivalent to a regulator in a side-by-side, and the single charge voltage does not exceed the regulatory value, while the other unit batteries continue to charge through the regulator bypass charging.

Because at this point the power of each unit is close to full, just balancing each monolith, so the charging current is small, supplementing the balance of each core full. Charger can only be to protect the entire battery pack end voltage, balanced charging plate is to ensure that each unit overcharged and each unit is full, can not be because there is a charge cell full and cause the entire lithium battery pack to stop charging.

The charging method of lithium iron phosphate battery pack.

(1)   Constant voltage charging method: During charging, the output voltage of the charging power supply remains constant. With the change of the charge state of the lithium iron phosphate battery pack, the charging current is automatically adjusted, and if the specified constant voltage value is appropriate, it can not only guarantee the full charging of the power battery, but also minimize the degassing and water loss. This charging method only considers the change of the single state of battery voltage and does not effectively reflect the overall charging condition of the battery. Its starting charging current is too large, often causing damage to the power battery. Due to this disadvantage, constant voltage charging is rarely used.

(2)   Constant current charging method: The charging current is kept constant by adjusting the output voltage throughout the charging process. Keep the charging current unchanged, its charging rate is relatively low. Constant current charging control method is simple, but because the acceptable current capacity of lithium battery pack is gradually decreased with the process of charging, to the later stage of charging, the power battery power capacity is reduced, the charging current utilization rate is greatly reduced. The advantage of this method is that the operation is simple, convenient, easy to implement, charging power is easy to calculate.

(3)   Constant current constant voltage charging method: This charging method is a simple combination of the above two. The first stage adopts the constant current charging method, which avoids the charging current at the beginning of constant voltage charging. The second stage adopts the constant voltage charging method, which avoids the phenomenon of overcharging when the constant current is charged. Lithium iron phosphate battery pack, like any other sealed rechargeable battery, should be controlled for charging and should not be overcharged, otherwise it is easy to damage the battery. Lithium iron phosphate batteries generally use the charging method of the first constant current and then the pressure limit.

(4)   Chopper charging method: The chopper method is used to charge. Under this method, the current of the constant current source does not change, and the switch tube is controlled so that it is turned on for a period of time and then shut down for a period of time, cycle back and forth, the advantage of this method is that when charging the battery through an external circuit, the ion generation inside the battery needs a certain response time, if it is continuously charged, it may reduce the potential of its capacity. And after charging for a period of time, add a shutdown time, you can let the battery polar ions have a diffusion process, so that the battery has a "digestion" time, which will make the battery utilization greatly increased, improve the charging effect.


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