Charge And Discharge Of 18650 Lithium Battery

According to industry standards, for lithium batteries, the nominal capacity is generally the smallest capacity. This capacity is a batch of batteries. At 25 ° C, it is first filled with cc / cv0.5c and left for a period of time ( It is usually 12 hours). Discharge at a constant current of 0.2c to 3.0v (there is also a standard of 2.75V, but the impact is not great, and 3v to 2.75v will soon fall without much capacity). The value of the discharged capacity is due to the fact that a batch of batteries must have individual The difference is the capacity value of the battery with the lowest capacity. That is to say, the actual capacity of any battery in this batch should be greater than or equal to the nominal capacity.

1, 18650 lithium battery charging process

Some chargers are implemented using cheap solutions, which are not good enough in control accuracy, which can easily cause abnormal battery charging and even damage the battery. When choosing a charger, try to choose a big brand 18650 lithium-ion battery charger. Quality and after-sales are guaranteed to extend the battery life. The brand-guaranteed 18650 lithium-ion battery charger has four protections: short-circuit protection, over-current protection, over-voltage protection, and reverse battery protection. Overcharge protection: When the charger overcharges the lithium-ion battery, in order to prevent the internal pressure from rising due to temperature rise, the charging state needs to be terminated.

For this reason, the protection device needs to monitor the battery voltage. When it reaches the battery overcharge voltage, it will activate the overcharge protection function and stop charging. Over-discharge protection: In order to prevent the over-discharge state of the lithium-ion battery, when the voltage of the lithium-ion battery is lower than its over-discharge voltage detection point, the over-discharge protection is activated, the discharge is suspended, and the battery is maintained in a low quiescent current standby mode. Over-current and short-circuit protection: When the discharge current of the lithium-ion battery is too large or a short-circuit condition occurs, the protection device will activate the over-current protection function.

Lithium battery charging control is divided into two stages. The first stage is constant current charging. When the battery voltage is lower than 4.2V, the charger will charge at a constant current. The second stage is the constant voltage charging stage. When the battery voltage reaches 4.2V, due to the characteristics of the lithium battery, if the voltage is higher, it will be damaged. The charger will fix the voltage at 4.2V, and the charging current will gradually decrease. When it is reduced to a certain value (usually when the current is set at 1/10), the charging circuit is cut off, the charging completion indicator lights up, and charging is completed.

 Excessive charge and discharge of lithium-ion batteries can cause permanent damage to the positive and negative electrodes. Over-discharge causes the anode carbon sheet layer structure to collapse, and the collapse will prevent lithium ions from being inserted during the charging process; overcharging will cause too much lithium ions to be embedded in the anode carbon structure, causing some of them to no longer be released.

2, 18650 lithium battery charging principle

The working principle of a lithium-ion battery is its charging and discharging principle. When the battery is charged, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move to the negative electrode through the electrolyte. The carbon of the negative electrode has a layered structure, and it has many micropores. The lithium ions that reach the negative electrode are embedded in the micropores of the carbon layer. The more lithium ions are embedded, the higher the charging capacity.

The same reason, when the battery is discharged (that is, the process of using the battery), the lithium ions embedded in the carbon layer of the negative electrode come out and move back to the positive electrode. The more lithium ions returned to the positive electrode, the higher the discharge capacity. What we usually mean by battery capacity is the discharge capacity.

It is not difficult to see that during the charge and discharge process of lithium-ion batteries, lithium ions are in a moving state from positive electrode → negative electrode → positive electrode. If we compare the lithium ion battery to a rocking chair, the two ends of the rocking chair are the poles of the battery, and lithium ion is like an excellent sportsman, running back and forth on both ends of the rocking chair. So, the experts gave the lithium-ion battery a cute name, rocker-type battery.