What is the reason why lithium batteries can't be overcharge?

　　Author ：Iflowpower – Portable Power Station Supplier

Strictly speaking, the voltage of the lithium-ion battery is charged above the boundary B (4.20V) is overcharged. But the overchargy also has a degree of size.

The average person thinks below 4.24V, may not be too full. Or "can The micro-charge.

The battery specification of the lithium-ion battery manufacturer also also indicates that the charging limit voltage is 4.20V +/- 0.04V.

Between the boundary A and the boundary B (higher than 4.24V, less than 4.35) V) This area can be called medium to charge.

Lithium-ion batteries in this voltage range, which will be higher than normal lithium ion batteries. Please see the middle and charge experience data experiment is the battery: GY383450 Nominal capacity: 550mAh. Nominal charging limit voltage 4.

20V charging system: The voltage is lower than the charging limit pressure, the voltage reaches the charging limit voltage, the maintenance voltage is constant, the current gradually decreases to 20 mA After the charging is terminated. This is a conventional CC / CV charging mode. Discharge system: 1C (550mA), discharge termination voltage 2.

75V We can try to change the charging limit lithium-ion battery voltage, deliberately overcharge this experiment. The experimental form is as follows: Cycle recharge limiting voltage V charge capacity MAH discharge capacity MAH and rated capacity ratio% first 4.20V570565 This is the rated capacity second time 4.

20 V610608108% third 4.204% 4.35V633627112% The third time is to make comparisons.

After the transition is performed, the rated capacity of the battery varies. It can be conclusively, and you can increase the battery capacity. But this trend is not the same, when I take this The block battery has been using the 4.

35V charging restriction voltage. After the conclusion is not so optimistic. After the 50th, the battery capacity is 480mAh.

It is already 85% of the rated capacity. And I have to this model in the past When the battery performs a normal cycle, its capacity is still more than 88% of the rated capacity at 150 cycles. It can be seen that the overcharged life of the battery is shortened.

In addition, the over-charge battery has been slightly Drums, the original thickness is 3.84 mm, and the thickness is 4.25mm after 50 cycles.

Since the voltage above 4.35V is not reached by the lithium-ion battery of the protection line. All major users often encounter Mid time to charge this phenomenon.

Many unqualified egg recharges (often available above nickel-hydrogen and lithium-ion gear) is the pre-charge culprit. So what is more than 4.35V? I When making a safety experiment, the protection line of the battery is removed, and then charging the lithium ion battery core with a voltage of 5.

0V. The result is that after 3 ~ 4 hours, the battery is severely drum, and part Unqualified battery cell explosion. Under electron microscopy, lithium electrical intelligence is extremely layered, and the positive electrode is some of the stacked corners, and the shape varies depending on the anode material.

The tight evolution of over-discharge is caused by a negative plate layer collapse. When charging, the number and convenience of lithium ions in the negative electrode plate is limited. Capacity drops, new internal resistance, shortened life is not recovered.

More terrible! The battery has reached the full state. The insertion reaction of the negative electrode is made into a deposition of the lithium metal on the surface of the negative electrode, and the amount of heat generated by the solvent caused by overcharge is much higher than that of the heat of the lithium ion and the solvent reaction in the reversible state): The increase in battery temperature, metal lithium and solvent, the reaction of lithium carbon and solvent occur, the battery is in fire, exploding. With the analysis of the electrolyte, the tanguger and lithium metal can also react.

After the charge, the top on the plate is a needle-shaped lithium metal crystallization, and the diaphragm will occur. Mask, exacerbated self-discharge; heavy crystal short circuit current caused battery temperature rapidly, electrolyte analysis gasification. This situation, whether the temperature is too high to make the material burns exploded.

Or the shell is first striking, so that the air invested in and lithium metals, all of which were bombed in combustion explosion.