The reason why lithium battery separators undergo weak point testing is that,

The reason is that the separator is the physical and electrical barrier separating the positive and negative inside the battery, and its insulation integrity directly determines the reliability of the battery.

A tiny 'electrical weakness' can become a thermal runaway, fire, or even...

1、 What is the 'weak point' of lithium battery separator?

Electrical Weak Point refers to the weak point area in the diaphragm where the local insulation performance is significantly lower than the overall level,

Common types include:

Micro pores (caused by foreign objects piercing or uneven stretching during the production process)

Metal/carbon impurity particles (introduced by raw material pollution or equipment wear)

Uneven thickness or thin areas (caused by fluctuations in coating or stretching processes)

Gel point or unmelted polymer aggregate

These weak points are invisible to the naked eye and difficult to detect through conventional optical inspection, but they will first break down under high voltage, forming electronic pathways.

2、 Why is electrical weakness so dangerous?

When a lithium battery is working, there is a potential difference of 3.0-4.2 V (or even higher) between the positive and negative electrodes.

The diaphragm acts as an insulator to prevent electrons from directly passing through, allowing lithium ions to migrate.

But if there is an electrical weakness:

1. Local electric field concentration → decrease in breakdown voltage;

2. Electronic penetration through the diaphragm → positive and negative micro short circuits occur;

3. Joule heating is generated at the short-circuit point → the temperature rises sharply (up to several hundred degrees Celsius);

4. Trigger SEI film, electrolyte combustion, positive oxygen release → chain reaction leading to thermal runaway;

5. May cause smoking, fire, etc.