Cause Analysis And Solution Of Common Problems Of Lithium Battery

（1）、 The voltage is inconsistent and a few are low

1. low voltage due to large self discharge

The self discharge of the cell is large, which makes the voltage drop faster than others. The low voltage can be eliminated by storing the post detection voltage.

2. low voltage caused by uneven charging

When the battery is charged after detection, the charge of the battery cell is uneven due to inconsistent contact resistance or charging current of the detection cabinet. The measured 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 problem and can be solved by charging. The voltage shall be measured after being stored for more than 24 hours after being charged during production.

（2）、Large internal resistance

1. caused by difference of testing equipment

If the detection accuracy is not enough or the contact group cannot be eliminated, the displayed internal resistance will be too large. The principle of AC bridge method shall be used to test the internal resistance instrument.

2. long storage time

Lithium batteries are stored too long, resulting in excessive capacity loss, internal passivation and large internal resistance, which can be solved by charging, discharging and activation.

3. large internal resistance caused by abnormal heating

During the processing (spot welding, ultrasonic wave, etc.) of the electric cell, the battery is abnormally heated, resulting in thermal closure of the diaphragm and serious increase in internal resistance.

（3）、Lithium battery expansion

1. lithium battery expands during charging

When the lithium battery is charged, the lithium battery will naturally expand, but generally not more than 0.1mm. However, overcharging will cause electrolyte decomposition, internal pressure increase and lithium battery expansion.

2. expansion during processing

Generally, abnormal processing (such as short circuit, overheating, etc.) causes excessive internal heating, electrolyte decomposition, and lithium battery expansion.

3. expansion during circulation

During cycling, the thickness of the battery will increase with the number of cycles, but it will not increase after more than 50 cycles. Generally, the normal increase is 0.3~0.6 mm. The aluminum shell is relatively serious. This phenomenon is caused by normal battery reaction. However, if the shell thickness is increased or the internal materials are reduced, the expansion phenomenon can be appropriately reduced.

（4）、The battery loses power after spot welding

The voltage of aluminum shell core after spot welding is lower than 3.7V, which is generally due to the short circuit caused by the breakdown of the internal diaphragm of the core due to the excessive spot welding current, resulting in the rapid voltage drop.

Generally, it is caused by incorrect spot welding position. The correct spot welding position should be spot welded at the bottom or on the side marked with "a" or "-". Spot welding is not allowed on the side and large side without identification. In addition, the weldability of some spot welded nickel strips 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 internal short circuit of the cell.

The battery power loss after spot welding is partly due to the large self discharge of the battery itself.

（5）、Battery explosion

Battery explosion generally occurs under the following conditions:

1. overcharge explosion

Out of control of the protection circuit or detection cabinet causes the charging voltage to be greater than 5V, causing electrolyte decomposition, violent reaction inside the battery, rapid rise of internal pressure of the battery, and battery explosion.

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 to cause lithium ions to be embedded, but lithium metal is formed on the surface of the electrode sheet, penetrating the diaphragm, and the positive and negative electrodes are directly short circuited to cause explosion (rarely).

3. explosion during ultrasonic welding of plastic shell

When ultrasonic welding the plastic shell, due to equipment reasons, the ultrasonic energy is transferred to the battery cell. The ultrasonic energy will cause the internal diaphragm of the battery to melt, and the positive and negative electrodes will be directly short circuited, resulting in explosion.

4. explosion during spot welding

During spot welding, the current is too large, causing serious internal short circuit and explosion. In addition, during spot welding, the positive connecting strip is directly connected with the negative electrode, so that the positive and negative electrodes are directly short circuited and explode.

5. over discharge explosion

Over discharge or over-current discharge (above 3C) of the battery is easy to dissolve and deposit the negative copper foil on the diaphragm, resulting in direct short circuit of the positive and negative electrodes and explosion (rarely occurring).

6. explosion in case of vibration drop

The internal pole pieces of the cell are misaligned when the cell is violently vibrated or dropped, resulting in direct and serious short circuit and explosion (rarely occurring).

（6）、Battery 3.6V platform low

1. the test platform is low due to inaccurate sampling of the test cabinet or instability of the test cabinet.

2. low ambient temperature causes low platform (discharge platform is greatly affected by ambient temperature)

（7）、Caused by improper processing

(1) Forcibly move the spot welded positive electrode connecting piece, resulting in poor contact of the positive electrode of the cell and large internal resistance of the cell.

(2) The spot welding connecting piece is not welded firmly, and the contact resistance is large, resulting in large internal resistance of the battery