January 30, 2019

Seven problems and solutions about lithium battery

1, the voltage is inconsistent, the individual is low

  • The self-discharge leads to a low voltage, and the cell self-discharge is large, so that its voltage is lowered faster than others, and the voltage can be eliminated by storing the post-detection voltage.
  • The uneven voltage causes the voltage to be low. When the battery is tested, the battery is not charged due to the contact resistance or the inconsistent current of the test cabinet. In the short-term storage (12 hours), the voltage difference is small, but the voltage difference is large when stored for a long time. This low voltage has no quality problem and can be solved by charging. Store the voltage for 24 hours after charging in production.

2, the internal resistance is too large

  • If the detection accuracy is not enough or the contact electric power cannot be eliminated, the internal resistance of the display will be too large. The internal resistance instrument should be tested by the principle of AC bridge method.
  • The storage time is too long, the lithium battery is stored too long, resulting in excessive capacity loss, internal passivation, and internal resistance becomes large, which can be solved by charging and discharging activation.
  • The abnormal heat is caused by the internal resistance, and the battery is processed abnormally (spot welding, ultrasonic wave, etc.) to cause the battery to be abnormally heated, so that the diaphragm is thermally closed and the internal resistance is seriously increased.

3, lithium battery expansion

  • Lithium battery expands when charging, lithium battery will naturally expand when charging, but generally does not exceed 0.1mm, but overcharge will cause electrolyte decomposition, internal pressure increases, lithium battery expands.
  • The expansion during processing is generally caused by abnormal processing (such as short circuit, overheating, etc.), causing internal heat to be excessively decomposed by the electrolyte and the lithium battery to expand.
  • When the cycle is expanded, the thickness of the battery increases with the number of cycles, but it does not increase after more than 50 weeks. Generally, the normal increase is 0.3~0.6 mm, and the aluminum shell is more serious. This phenomenon belongs to the normal battery. The reaction is caused. However, if the thickness of the casing is increased or the internal material is reduced, the expansion phenomenon can be appropriately reduced.

4, the battery has a power failure after spot welding

  • The voltage of the aluminum shell after spot welding is lower than 3.7V. Generally, the spot welding current is too short to cause the internal diaphragm of the battery to break down, causing the voltage to drop too fast. Generally, the spot welding position is incorrect. The correct spot welding position should be spot welded at the bottom or marked with “A” or “—”. The unmarked side and large surface cannot be spot welded. In addition, some of the spot-welded nickel strips have poor solderability, so large current spot welding must be used, so that the internal high-temperature resistant tape does not work, causing internal short-circuiting of the cells. The battery power loss after spot welding is also partly due to the large self-discharge of the battery itself.

5, battery explosion
There are several situations in which a battery explosion occurs:

  • Overcharge explosion, protection line out of control or control cabinet out of control so that the charging voltage is greater than 5V, causing the electrolyte to decompose, the battery reacts violently inside, the battery internal pressure rises rapidly, and the battery explodes.
  • Over-current explosion, protection line out of control or out of control of the detection cabinet makes the charging current too large, so that lithium ions are not embedded, and lithium metal is formed on the surface of the pole piece, penetrating the diaphragm, and the positive and negative poles are directly short-circuited to cause an explosion (rarely occurring).
  • When the plastic shell is ultrasonically welded, when the plastic shell is ultrasonically welded, the ultrasonic energy is transferred to the battery core due to the equipment. The ultrasonic energy is so great that the internal diaphragm of the battery is melted, and the positive and negative electrodes are directly short-circuited to cause an explosion.
  • Explosion during spot welding, excessive current during spot welding causes internal severe short-circuit to cause explosion. In addition, the positive connection piece is directly connected to the negative electrode during spot welding, so that the positive and negative electrodes are directly short-circuited and then exploded.
  • Over-explosion, battery over-discharge or over-current discharge (above 3C) easily dissolves the negative copper foil onto the diaphragm, causing the positive and negative electrodes to be directly short-circuited to produce an explosion (rarely occurring).
  • Explosion when the vibration is dropped, the internal pole piece of the battery core is dislocated when the battery is violently vibrated or dropped, and the battery is directly short-circuited and exploded (rarely occurs).

6, the battery 3.6V platform is low

  • Inaccurate sampling of the test cabinet or instability of the test cabinet results in a low test platform.
  • Low ambient temperature causes the platform to be low (discharge platform is greatly affected by ambient temperature)

7, Improper processing

  • Forcefully moving the spot welding positive electrode connection piece causes poor contact of the positive electrode of the battery core, so that the internal resistance of the battery core is large.
  • The spot welding tab is not welded firmly, and the contact resistance is large, so that the internal resistance of the battery is large.