The simplest solution to common faults of lithium batteries
Now more and more electric vehicles and cars are using lithium batteries, but they will encounter more or less problems in the process of using lithium batteries, so today keheng lithium battery summarizes the reasons for the abnormality of lithium batteries, including lithium batteries Capacity, lithium battery internal resistance, lithium battery voltage, ultra-thick size, open circuit, etc. are summarized and shared with you.
The common faults and causes of lithium batteries are as follows:
The voltage is inconsistent, and the individual is low
1. Large self-discharge causes low voltage
Solution: The self-discharge of the battery cell is large, so that its voltage decreases faster than others. The low voltage can be eliminated by checking the voltage after storage.
2. Uneven charge causes low voltage
Solution: When the battery is charged after testing, the battery is charged unevenly due to the inconsistent contact resistance or the charging current of the testing cabinet. The voltage difference is small in short-term storage (12 hours), but the voltage difference is large in long-term storage. This low voltage has no quality problem and can be solved by charging. After charging during production, store it for more than 24 hours to measure the voltage.
The internal resistance is too large
1. Detecting equipment differences
Solution: If the detection accuracy is not enough or the contact electric group cannot be eliminated, it will cause the display internal resistance to be too large, and the AC bridge method should be used to test the internal resistance instrument for detection.
2. storage time too long
Solution: Lithium batteries are stored for too long, resulting in excessive capacity loss, internal passivation, and increased internal resistance, which can be solved by charging and discharging activation.
3. Abnormal heat causes large internal resistance
Solution: The battery is abnormally heated during processing (spot welding, ultrasonic wave, etc.), causing the diaphragm to thermally close, and the internal resistance is seriously increased.
Lithium battery expansion
1. Lithium battery expands when charging
When the lithium battery is charged, the lithium battery will naturally expand, but generally it does not exceed 0.1mm, but overcharging 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 internal 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 with the number of cycles, but it will not increase after more than 50 cycles. Generally, the normal increase is 0.3~0.6mm, and 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 material is reduced, the expansion phenomenon can be appropriately reduced.
4. The battery has power down after spot welding
The voltage of the aluminum shell cell is lower than 3.7V after spot welding, generally because the spot welding current is too large, and the internal diaphragm of the cell is broken down and short-circuited, causing the voltage to drop too fast.
It is generally caused by the incorrect spot welding position. The correct spot welding position should be spot welding at the bottom or on the side marked with "A" or "-". The side and large faces without marking cannot be spot welded. In addition, the weldability of spot welding nickel tape is too poor, so a large current must be used for spot welding, so that the internal high temperature resistant tape can not work, resulting in a short circuit inside the cell.
The power failure of the battery after spot welding is also partly due to the large self-discharge of the battery itself.
There are generally the following situations for a battery explosion:
1. overcharge explosion
The protection 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 protection 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 embedded too late, and lithium metal is formed on the surface of the pole piece, penetrating the diaphragm, and the positive and negative electrodes are directly short-circuited to cause an explosion (rarely).
3. Explosion while ultrasonically welding plastic enclosures
When ultrasonic welding plastic shells, due to equipment reasons, the ultrasonic energy is transferred to the battery core. The ultrasonic energy is very large and the internal diaphragm of the battery is melted, and the positive and negative electrodes are directly short-circuited, resulting in an explosion.
4. Explosion during spot welding
Excessive current during spot welding will cause serious internal short circuit and explosion. In addition, during spot welding, the positive connection piece is directly connected to the negative electrode, so that the positive and negative electrodes are directly short-circuited and then exploded.
5. over discharge explosion
Over-discharge or over-current discharge (above 3C) of the battery can easily dissolve and deposit the negative electrode copper foil on the separator, causing the positive and negative electrodes to be directly short-circuited and explode (rarely).
6. Explosion when dropped by vibration
The internal pole pieces of the cell are dislocated when the cell vibrates or falls, causing a direct and severe short-circuit and explosion (rarely).
The battery 3.6V platform is low
1. Inaccurate sampling of the detection cabinet or instability of the detection cabinet causes the test platform to be low.
2. The ambient temperature is too low, causing the platform to be low (the discharge platform is greatly affected by the ambient temperature)
Caused by improper processing
(1) Forcefully moving the spot-welded positive connection piece causes poor contact of the positive electrode of the cell, which increases the internal resistance of the cell.
(2) The spot welding connection piece is not welded firmly, and the contact resistance is large, which makes the internal resistance of the battery large.