[[TitleIndustry]]

Lithium ion common problem analysis and solution

Date:May 13, 2019

With the rapid development of technology, the scope and role of lithium batteries have long been self-evident, but in our daily life, the problem of lithium battery accidents is always endless, which is always plaguing us. In view of this, Xiaobian specially sorted out lithium. I think the reasons for the common problems of ions and the solutions are expected to be convenient for everyone.


First, the voltage is inconsistent, the individual is low


1. High self-discharge causes low voltage


The self-discharge of the battery core makes the voltage drop faster than others, and the low voltage can be eliminated by detecting the voltage after storage.


2. Uneven current causes low voltage


When the battery is tested, the charge of the battery is uneven 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.


Second, the internal resistance is too large


1. Detecting device differences


If the detection accuracy is not enough or the contact electric power group cannot be eliminated, the internal resistance of the display will be too large. The internal resistance instrument test should be tested by the principle of AC bridge method.


2. Long storage time


Lithium batteries are stored too long, resulting in excessive capacity loss, internal passivation, and increased internal resistance, which can be solved by charge and discharge activation.


3. Abnormal heat caused by internal resistance


The battery is processed (spot welding, ultrasonic, etc.) to abnormally heat the battery, causing the diaphragm to thermally close and the internal resistance is seriously increased.


Third, lithium battery expansion


1. Lithium battery expands while charging


When the lithium battery is being charged, the lithium battery naturally expands, but generally does not exceed 0.1 mm, but overcharging causes the electrolyte to decompose, the internal pressure increases, and the lithium battery expands.


2. Swell during processing


Generally, processing abnormalities (such as short circuit, overheating, etc.) occur, causing internal heat to be excessively decomposed by the electrolyte, and the lithium battery is expanded.


3. Swell during circulation


When the battery is circulating, the thickness will increase with the number of cycles, but it will 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 is caused by normal battery reaction. However, if the thickness of the casing is increased or the internal material is reduced, the expansion phenomenon can be appropriately reduced.


Fourth, 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 not correct. The correct spot welding position should be spot welded at the bottom or with the mark "A" or "-" side. The unmarked side and large face cannot be spot welded. In addition, some spot welding 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 circuit of the battery core.


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


Five, battery explosion


There are several situations in which 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, the internal reaction of the battery reacts violently, the internal pressure of the battery rises rapidly, and the battery explodes.


2. Overcurrent explosion


If the protection circuit is out of control or the control cabinet is out of control, the charging current is too large, so that the 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 electrodes are directly short-circuited to cause an explosion (rarely occurring).


3. Ultrasonic welding of plastic casing when exploding


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.


4. Explosion during spot welding


When the spot welding is too large, the internal short circuit will cause an 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.


5. Over-explosion


Over-discharge or over-current discharge of the battery (above 3C) tends to cause the negative copper foil to be dissolved and deposited on the separator, so that the positive and negative electrodes are directly short-circuited to cause an explosion (rarely occurring).


6. Explosion when the vibration falls


The inner pole piece of the battery core caused by the vibrating or falling of the battery core is dislocated, and the battery is directly short-circuited and explodes (rarely occurs).


Sixth, the battery 3.6V platform is low


1. Inaccurate sampling of the test cabinet or instability of the test cabinet results in a low test platform.


2. Low ambient temperature causes the platform to be low (discharge platform is greatly affected by ambient temperature)


7. Improper processing


(1) Forcefully move the spot welding positive electrode connecting piece to cause poor contact of the positive electrode of the battery core, so that the internal resistance of the battery core is large.


(2) The spot welding tab is not welded firmly, and the contact resistance is large, so that the internal resistance of the battery is large.


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