With the rapid development of technology, the scope and role of lithium batteries are self-evident. However, lithium battery accidents are still frequent in our daily lives, constantly troubling us. In view of this, we have compiled an analysis of the causes and solutions for common lithium-ion battery problems, hoping to provide you with convenience.
1. Inconsistent voltage, some voltages are too low.
1. High self-discharge results in low voltage.
The cell has a large self-discharge, causing its voltage to drop faster than others. The low voltage can be eliminated by checking the voltage after storage.
2. Uneven charge causes low voltage.
After battery testing, uneven charging of the cells can occur due to inconsistent contact resistance or charging current in the testing cabinet. The voltage difference is minimal during short-term storage (12 hours), but significant during long-term storage. This low voltage does not indicate a quality issue and can be resolved by recharging. Voltage was measured after charging and storage exceeding 24 hours during production.
II. High internal resistance
1. Differences in testing equipment cause
If the detection accuracy is insufficient or the contact current group cannot be eliminated, the displayed internal resistance will be too high. An instrument for testing internal resistance based on the AC bridge method should be used.
2. Excessive storage time
If lithium batteries are stored for too long, they will suffer from excessive capacity loss, internal passivation, and increased internal resistance. This can be resolved by reactivating them through charge and discharge.
3. Abnormal heating causes high internal resistance
During the processing of the battery cell (spot welding, ultrasonic treatment, etc.), the battery is abnormally heated, causing the separator to thermally close, resulting in a significant increase in internal resistance.
III. Lithium Battery Expansion
1. Lithium batteries expand during charging.
When a lithium battery is charging, it will naturally expand, but generally not exceeding 0.1mm. However, overcharging will cause the electrolyte to decompose, increase the internal pressure, and cause the lithium battery to expand.
2. Expansion during processing
Generally, this is caused by abnormal processing (such as short circuit, overheating, etc.), resulting in excessive internal heating, electrolyte decomposition, and lithium battery expansion.
3. Expansion during circulation
During battery cycling, the thickness increases with the number of cycles, but this increase generally stops after 50 cycles. The normal increase is typically 0.3-0.6 mm, with aluminum casings showing more pronounced thickness. This phenomenon is a normal result of battery reactions. However, increasing the casing thickness or reducing the amount of internal material can mitigate the expansion.
IV. Battery power loss after spot welding
If the voltage of an aluminum-cased battery cell drops below 3.7V after spot welding, it is generally because excessive welding current causes the internal diaphragm of the cell to break down and short-circuit, resulting in a rapid voltage drop.
This is usually caused by incorrect spot welding position. The correct spot welding position should be on the bottom or on the side marked "A" or "-". Spot welding should not be done on unmarked sides or the main surface. In some cases, the nickel strip has poor solderability, so a very high current must be used for spot welding, which makes the internal high-temperature resistant tape ineffective, causing an internal short circuit in the battery cell.
Some instances of battery power loss after spot welding are also due to the battery's own high self-discharge.
V. Battery Explosion
Battery explosions can generally be caused by the following situations:
1. Overcharge explosion
If the protection circuit or the detection cabinet malfunctions, causing the charging voltage to exceed 5V, the electrolyte will decompose, a violent reaction will occur inside the battery, the internal pressure of the battery will rise rapidly, and the battery will explode.
2. Overcurrent explosion
If the protection circuit or the detection cabinet malfunctions, the charging current may be too large, causing lithium ions to not have time to intercalate and instead form lithium metal on the electrode surface. This lithium metal can penetrate the separator, causing a direct short circuit between the positive and negative electrodes and resulting in an explosion (which is rare).
3. Explosion during ultrasonic welding of plastic casing
When ultrasonically welding a plastic casing, due to equipment malfunctions, the ultrasonic energy is transferred to the battery cell. The high ultrasonic energy causes the internal separator of the battery to melt, resulting in a direct short circuit between the positive and negative electrodes and causing an explosion.
4. Explosion during spot welding
Excessive current during spot welding can cause a severe internal short circuit, leading to an explosion. Additionally, during spot welding, the positive electrode connector is directly connected to the negative electrode, causing a direct short circuit between the positive and negative electrodes, which can also lead to an explosion.
5. Over-explosion explosion
Over-discharge or overcurrent discharge (above 3C) of a battery can easily cause the copper foil on the negative electrode to dissolve and deposit on the separator, resulting in a direct short circuit between the positive and negative electrodes and an explosion (which rarely occurs).
6. Explosion upon vibration and drop
When a battery cell is subjected to severe vibration or a drop, the internal electrode plates may become misaligned, causing a direct and serious short circuit and resulting in an explosion (this is rare).
VI. Low 3.6V battery platform
1. Inaccurate sampling or instability of the testing cabinet causes the test platform to be low.
2. Low ambient temperature causes a low discharge platform (the discharge platform is greatly affected by ambient temperature).
VII. Improper processing
(1) Moving the spot-welded positive electrode connector with force causes poor contact of the positive electrode of the battery cell, resulting in high internal resistance of the battery cell.
(2) The spot-welded connecting piece is not firmly welded, resulting in high contact resistance and high internal resistance of the battery.
