Inconsistent voltage, individual low
1. Large self-discharge causes low voltage
The self-discharge of the battery cell makes its voltage drop faster than others. The low voltage can be eliminated by checking the voltage after storage.
2. Uneven charging causes low voltage
After the battery is detected, the charging of the battery is uneven due to the inconsistent contact resistance or the charging current of the test cabinet. The voltage difference is very small when stored for a short time (12 hours), but the voltage difference is large when stored for a long time. This low voltage has no quality problems and can be solved by charging. After charging in production, store it for more than 24 hours to measure the voltage.
The internal resistance is too large
1. Caused by differences in detection equipment
If the detection accuracy is insufficient or the contact group cannot be eliminated, the internal resistance of the display will be too large, and the internal resistance instrument should be tested using the principle of the AC bridge method.
2. Long storage time
Lithium battery storage is too long, resulting in excessive capacity loss, internal passivation, internal resistance becomes large, can be solved by charging and discharging activation.
3. Abnormal heating causes large internal resistance
During the processing of the battery core (spot welding, ultrasonic wave, etc.), the battery is abnormally heated, and the separator is thermally closed, and the internal resistance is severely increased.
Lithium battery expansion
1. Lithium battery expands when charging
When the lithium battery is charged, the lithium battery will naturally swell, but it generally does not exceed 0.1mm, but overcharge will cause the electrolyte to decompose, the internal pressure will increase, and the lithium battery will swell.
2. Expansion during processing
Generally, abnormal processing (such as short circuit, overheat, etc.) causes the internally heated electrolyte to decompose and the lithium battery expands.
3. Swell when cycling
When the battery is cycled, the thickness will increase with the number of cycles, but it will not increase after more than 50 weeks. The normal increase is generally 0.3~0.6 mm, and the aluminum shell is more serious. This phenomenon is caused by normal battery reaction. However, if the thickness of the shell is increased or the internal materials are reduced, the expansion phenomenon can be appropriately reduced.
The battery has a power failure after spot welding
After spot welding, the voltage of the aluminum shell battery is lower than 3.7V, generally because the spot welding current is too large, the internal diaphragm of the battery is broken down and short-circuited, causing the voltage to fall too fast.
Generally, it is caused by the incorrect spot welding position. The correct spot welding position should be spot welded at the bottom or marked “A” or “—” side. Unmarked sides and large faces cannot be spot welded. In addition, some of the spot welding nickel strips have poor weldability, so a large current spot welding must be used, so that the internal high temperature resistant tape cannot work, causing internal short circuits in the battery core.
After spot welding, the battery is powered down partly due to the large self-discharge of the battery itself.
There are several cases of battery explosion:
1. Overcharge explosion
The control circuit is out of control or the detection cabinet is out of control, so that the charging voltage is greater than 5V, causing the electrolyte to decompose, a violent reaction occurs inside the battery, the internal pressure of the battery rises rapidly, and the battery explodes.
2. Overcurrent explosion
The control circuit is out of control or the detection cabinet is out of control, so that the charging current is too large, causing lithium ions to be too late to insert, and lithium metal is formed on the surface of the pole piece, penetrates the diaphragm, and the positive and negative electrodes are directly short-circuited to cause an explosion (rarely occur).
3. Explosion when ultrasonic welding plastic shell
When ultrasonic welding the plastic shell, the ultrasonic energy is transferred to the battery core due to equipment reasons. The ultrasonic energy is very large, which melts the internal separator of the battery, and the positive and negative electrodes are directly short-circuited, causing an explosion.
4. Explosion during spot welding
Excessive current during spot welding causes an internal serious short circuit to explode. In addition, the positive electrode connection piece is directly connected to the negative electrode during spot welding, so that the positive and negative electrodes are directly short-circuited and explode.
Over-discharge or over-current discharge (above 3C) of the battery can easily dissolve the negative electrode copper foil and deposit it on the separator, causing a direct short circuit between the positive and negative electrodes and causing an explosion (rarely occurring).
6. Explode when vibration drops
The internal pole pieces of the battery are misaligned when the battery is violently vibrated or dropped, which is directly severely short-circuited and explodes (rarely).
Low battery 3.6V platform
1. Inaccurate sampling of the test cabinet or unstable test cabinet results in a low test platform.
2. Low ambient temperature causes low platform (discharge platform is greatly affected by ambient temperature)
(1) Forcibly moving the positive electrode connection spot of the spot welding leads to poor contact of the positive electrode of the battery cell and makes the internal resistance of the battery cell large.
(2) The spot welding connection piece is not welded firmly, and the contact resistance is large, so that the internal resistance of the battery is large.
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Contact: Geely Zhang
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