What is the lithium-ion battery over?

　　Author ：Iflowpower – Portable Power Station Supplier

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

The average person thinks below 4.24V, may not be too high. 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, the discharge capacity will be higher than the normal lithium ion battery. Please see the medium over charge and experience data experiment is the battery: GY383450. Nominal capacity: 550mAh.

Nominal charging limit voltage 4.20V charging system: The voltage is lower than charging limited pressure, after the voltage reaches the charging limit voltage, the maintenance voltage is unchanged, the current gradually decreases to 20 mA Charging termination. This is a conventional CC / CV charging mode.

Discharge system: 1C (550mA), discharge termination voltage 2.75V system is fully referred to national standard implementation. We can try to change the charging limit voltage, deliberately The experimental product is overcharged.

List the experimental forms as follows: Cycle recharge limit voltage V charging capacity MAH discharge capacity MAH and rated capacity ratio% of the first 4.204565 This is the rated capacity second 4.204818% third time 4.

20V569564100 % The fourth time 4.35V633627112% is for comparison, indicating that the rated capacity of the battery has little variation after being overcharged. From it can get a conclusion, overcharge can increase the capacity of the battery.

But this trend Not the same, when I continued to overcharge this lithium ion battery with 4.35V charging limit. The conclusion is not as optimistic.

After the 50th, the battery capacity is 480mAh. It is already 85% of the rated capacity. And when I conducted a normal circulation of this model in the past, my capacity was still more than 88% of the rated capacity at 150 cycles.

It can be seen that overcharged battery life. In addition to mentioned Yes, the over-charged battery has been slightly drum, the original thickness is 3.84mm, and the thickness is 4.

25mm after 50 cycles. Since the voltage above 4.35V is not reached by the lithium-ion battery associated with the protection line All major users often encounter this phenomenon.

Many unqualified egg recharges (often available above nickel-hydrogen and lithium-ion gear can be selected) is a culprit. Su So higher than 4.35V What is the look? I am doing the safety experiment.

It is to remove the protection line of the battery, and then charge the lithium-ion battery core with a voltage of 5.0V. The result is 3 ~ 4 hours In the future, the battery is severely drum, and some unqualified cells exploded.

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.