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The full name of Lithium Iron Phosphate is Lithium Iron Phosphate Lithium Ion Battery. Because of its performance is particularly suitable for power applications, it is added to the name of the word "power", that is, lithium iron phosphate power battery. Some people also call it "lithium iron power battery", and lithium iron phosphate charging skills you all understand? The following will introduce you to the lithium iron phosphate battery charging skills.
1, before solving the problem, first we need to understand the structure and working principle of lithium iron phosphate battery LiFePO4 as the positive electrode of the battery, connected by aluminum foil and the positive electrode of the battery, the middle is the polymer diaphragm, which separates the positive electrode from the negative electrode, but lithium ions can pass through but not electrons, the right side is composed of carbon (graphite) battery negative electrode, connected by copper foil and the negative electrode of the battery. Between the top and bottom of the battery is the battery's electrolyte, and the battery is hermetically sealed by a metal casing. Lithium iron phosphate batteries are charged with lithium ions in the positive electrode migrating towards the negative electrode through the polymer diaphragm; during discharge, lithium ions in the negative electrode migrate towards the positive electrode through the diaphragm. Lithium-ion batteries are named for the lithium ions that migrate back and forth during charging and discharging.
2, when the battery is charged, lithium ions migrate from the face of the lithium iron phosphate crystal to the surface of the crystal, under the action of electric field forces, into the electrolyte, through the diaphragm, and then migrate through the electrolyte to the surface of the graphite crystal, and then embedded in the graphite lattice. At the same time, electrons flow through the conductive body to the aluminium foil collector of the positive electrode, through the pole lug, cell pole post, external circuit, negative pole post, negative pole lug to the copper foil collector of the negative electrode, and then through the conductive body to the negative graphite electrode, so that the charge of the negative electrode reaches equilibrium. After lithium ions are de-embedded from lithium iron phosphate, lithium iron phosphate is converted into iron phosphate.
3, when the battery is discharged, lithium ions are deembedded from the graphite crystal, enter the electrolyte, cross the diaphragm, then migrate through the electrolyte to the surface of the lithium iron phosphate crystal, and then re-embedded into the lattice of lithium iron phosphate via the surface. At the same time, the battery flows through the conductive body to the copper foil collector of the negative electrode, through the pole lug, the negative electrode column of the battery, the external circuit, the positive electrode column, the positive electrode lug to the aluminum foil collector of the positive electrode of the battery, and then through the conductive body to the positive electrode of lithium iron phosphate, so that the charge of the positive electrode reaches equilibrium.
Note: Once again, lithium iron phosphate batteries in use to pay attention to water and dust, so the storage place can not have water, which will affect the performance and service life of the battery.
Correct charging method for LiFePO4 battery packs
Lithium iron phosphate battery pack charging is recommended to use the CCCV charging method, that is, constant current first and then constant voltage. Constant current recommended 0.3C. Constant voltage recommended 3.65. that is, constant current process 0.3C current charging, when the battery voltage reaches 3.65V, using 3.65V voltage 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 balanced voltage power supply, also depends on the charging current, it is recommended not to charge with too high a voltage, adjust the voltage to ensure that the charging current is below 0.5C, which is good for the battery.
General lithium iron phosphate battery charging upper voltage 3.7 ~ 4V, discharge lower voltage 2 ~ 2.5V, taking into account the discharge capacity, discharge median voltage, charging time, constant current capacity percentage, safety of these five aspects, the use of constant current and constant voltage charging scheme, for lithium iron phosphate battery pack, charging limit voltage set at 3.55 ~ 3.70V more reasonable, the recommended value of 3.60 ~ 3.65 V, the lower limit of discharge voltage 2.2V ~ 2.5V.
The charger of LiFePO4 battery pack is different from ordinary lithium batteries. The maximum termination charge voltage for lithium batteries is 4.2 volts; lithium iron phosphate battery pack is 3.65 volts. Lithium iron phosphate battery pack charging, is a balanced charging board connected to the row of wires, generally from both ends of the direct series overall charging, charger voltage is greater than the battery pack voltage. The row of wires to detect the voltage of each single cell, equivalent to a voltage regulator in parallel, the single cell charging voltage will not exceed the voltage regulator value, while other single cells continue to charge through the voltage regulator bypass charging.
Because the power of each single cell is close to full at this point, it is only balancing each single cell, so the charging current is small, supplementing the balance of each cell full. Charger can only protect the entire battery pack end voltage, balance charging board is to ensure that each single cell individual overcharge and each single cell are full, can not be caused by a full cell and stop the entire lithium battery pack charging.
Lithium iron phosphate battery pack charging method
(1) constant voltage charging method: in the charging process, the output voltage of the charging power supply remains constant. With the lithium iron phosphate battery pack charge state changes, automatically adjust the charging current, if the specified voltage constant value is appropriate, it can ensure that the power battery is fully charged, but also to minimize gas and water loss. This charging method only takes into account the changes in the single state of the battery voltage and does not effectively reflect the overall charging condition of the battery. Its starting charging current is too high and often causes damage to the power cell. In view of this drawback, constant voltage charging is rarely used.
(2) Constant-current charging method: Throughout the charging process, the charging current is kept constant by adjusting the output voltage. Keeping the charging current constant, the charging rates are relatively low. The constant current charging control method is simple, but because the acceptable current capacity of the lithium battery pack is gradually reduced as the charging process proceeds, by the late stage of charging, the power battery's ability to be charged decreases and the charging current utilisation rate is greatly reduced. The advantage of this method is simple operation, convenient, easy to implement, 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 first stage uses the constant current charging method, avoiding the excessive charging current at the beginning of constant voltage charging. The second stage uses the constant voltage charging method, avoiding the phenomenon of overcharging caused by constant current charging. Lithium iron phosphate battery pack and any other sealed rechargeable battery, to control the charging, not indiscriminate charging, otherwise it is easy to damage the battery. Lithium iron phosphate batteries generally use constant current followed by voltage limiting charging method.
(4) Chopper charging method: the use of chopper method of charging. Under this method, the constant current source current remains unchanged, while the switching tube is controlled so that it turns on for a period of time and then turns off for a period of time, and the cycle repeats itself. The advantage of this method is that: when charging the battery 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. By adding a shut-off time after a period of charging, the ions produced at both poles of the battery are allowed to diffuse, giving the battery time to "digest", which will greatly increase the utilisation of the battery and improve the charging effect.