Lithium Batteries Micro-short Circuit Aanalysis

- Jan 06, 2019-

What does lithium batteries micro-short circuit means?


It means that: lithium batteries have micro-short-circuit phenomenon between the internal cell and the cell or within a single cell. This short circuit will not directly burn out the battery, but reduce the performance of the battery in a short period of time (weeks or months), resulting in a single cell or the whole battery pack completely unusable.

 

Micro-short circuit is the main cause of self-discharge of lithium-ion batteries. 

It is mainly manifested in the following aspects: 

1). The voltage of a single cell in lithium-ion batteries decreases rapidly when discharging, and rises rapidly when charging.

2). The direct manifestation is that the batteries may be completely voltage-free or unable to charge and discharge. 


The reasons are list as follows:

 

1. Dust and other impurities:

 

In the process of making the cell, when laminating or rolling, dust or other sharp impurities adhere to the cell diaphragm and pierce the diaphragm because the air environment is not up to the standard, which causes the micro-short circuit of the cell.

 

2. Cell sperator dislocation:

It has been found that a brand of lithium battery voltage problems, and can not charge and discharge, the reason is that Best Things can not be sister, finally, there is no way, can only dismantle the cell, in the process of the cell dismantling, found the ultimate problem is that the edge of the diaphragm shrinks, leading to direct contact between positive and negative electrodes in the cell, cell damage (such as: the separation between positive and negative materials). Membrane was originally 150 PX 2 and now reduced to 125 PX 2. After that, the positive and negative electrodes inside the cell contacted directly and the cell burned out. This is due to the errors in production design.

 

3. Poor quality sperator:

 

The quality of the cell diaphragm is not up to the standard, and the battery pack is often charged and discharged with high current. The diaphragm can not withstand the huge lithium ion flow in a short period of time, which leads to local or large area damage, and directly leads to severe heating, scalding and damage of the cell.

 

Cause of material problem: 1). Impurity of cathode material, 2)  long time in the air, 3) not thorough drying caused.

 

4. Welding:

 

Usual spot welding and other welding methods will lead to micro-welding or welding bubbles, micro-welding will lead to easy to fall off and so on. Now the most scientific and effective method for battery group welding is to use ultrasonic welding technology, which will not cause micro-short-circuit problems due to positive and negative electrode welding.