Upload time:2020-12-30| Author:admin
With the rapid development of science and technology, the use range and role of lithium batteries have long been self-evident, but in our daily life, lithium battery accidents always emerge in endlessly, which always plague us. Analysis of common causes of lithium ion problems and solutions as follows:
Voltage is inconsistent, individual is low
1. Large self-discharge causes low voltage
The self-discharge of the cell is large, so that its voltage drops faster than others. The low voltage can be eliminated by checking the voltage after storage.
2. Uneven charge causes low voltage
When the battery is charged after testing, the battery cells are not evenly charged due to the inconsistent contact resistance or the charging current of the detection cabinet. The measured voltage difference is very small during short-term storage (12 hours), but the voltage difference is large during long-term storage. This low voltage has no quality problems and can be solved by charging. Stored for more than 24 hours to measure the voltage after being charged during production.
Internal resistance is too large
1. Differences in detection equipment caused
If the detection accuracy is not enough or the contact group cannot be eliminated, it will cause the display internal resistance to be too large. The AC bridge method principle should be used to test the internal resistance.
2. Storage time is too long
Lithium batteries are stored for too long, causing excessive capacity loss, internal passivation, and large internal resistance, which can be solved by charging and discharging activation.
3. Abnormal heating causes large internal resistance
The cell is being processed (spot welding, ultrasonic, etc.) to cause abnormal heating of the battery, causing the diaphragm to produce thermal closure, and the internal resistance is seriously increased.
Lithium battery expansion
1. Lithium battery swells when charging
When the lithium battery is charged, the lithium battery will naturally expand, but generally no more than 0.1mm, but overcharge will cause the electrolyte to decompose, the internal pressure will increase, and the lithium battery will expand.
2. Expansion during processing
Generally, abnormal processing (such as short circuit, overheating, etc.) causes the electrolyte to decompose due to excessive heating, and the lithium battery expands.
3. Expand while cycling
When the battery is cycled, the thickness will increase as the number of cycles increases, but it does not increase after more than 50 cycles. Generally, the normal increase is 0.3~0.6 mm. The aluminum shell is more serious. This phenomenon is caused by normal battery reactions. However, if the thickness of the shell is increased or the internal materials are reduced, the expansion phenomenon can be appropriately reduced.
The battery loses power after spot welding
The voltage of the aluminum shell cell after spot welding is lower than 3.7V, generally because the spot welding current roughly breaks down the internal diaphragm of the cell and short-circuits, causing the voltage to drop too fast.
Generally, it is caused by incorrect spot welding position. The correct spot welding position should be spot welding on the bottom or side with the mark "A" or "—". Spot welding is not allowed on the side and large side without marking. In addition, some spot-welded nickel strips have poor weldability, so they must be spot welded with a large current, so that the internal high-temperature resistant tape can not work, resulting in internal short-circuit of the battery.
The battery power loss after spot welding is also partly due to the large self-discharge of the battery itself.
Generally, there are the following situations when a battery explosion occurs:
1. Overcharge explosion
If the protection circuit is out of control or the detection cabinet is out of control, 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 protection circuit is out of control or the detection cabinet is out of control, so that the charging current is too large and the lithium ions are too late to be embedded, 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 and cause an explosion (rarely).
3. Explosion when ultrasonic welding plastic shell
When ultrasonic welding the plastic shell, the ultrasonic energy is transferred to the battery core due to the equipment. The ultrasonic energy is so large that the internal diaphragm of the battery melts, and the positive and negative electrodes are directly short-circuited, causing an explosion.
4. Explosion during spot welding
Excessive current during spot welding caused a serious internal short circuit to cause an explosion. In addition, during spot welding, the positive electrode connecting piece was directly connected to the negative electrode, causing the positive and negative electrodes to directly short-circuit and explode.
5. Over discharge explosion
Over-discharge or over-current discharge (above 3C) of the battery will easily dissolve and deposit the negative electrode copper foil on the separator, causing the positive and negative electrodes to directly short-circuit and cause an explosion (rarely occurs).
6. Explode when vibration falls
The internal pole piece of the battery is dislocated when the battery is violently vibrated or dropped, and it is directly short-circuited and exploded (rarely).
Low battery 3.6V platform
1. Inaccurate sampling of the detection cabinet or unstable detection cabinet causes the test platform to be low.
2. Low ambient temperature causes low platform (discharge platform is greatly affected by ambient temperature)
Caused by improper processing
(1) Move the positive electrode connecting piece of spot welding forcefully to cause poor contact of the positive electrode of the battery cell, which makes the internal resistance of the battery core large.
(2) The spot welding connection piece is not firmly welded, and the contact resistance is large, which makes the battery internal resistance large.
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