According to the actual high-voltage risk faced by a single battery in module assembly, the insulation resistance or leakage current of the coated battery is measured at a specific voltage to select qualified batteries, so that they can meet the insulation requirements of the module after shipment.

Before the insulation test, ensure that the battery entering the insulation test is qualified in basic electrical performance, and the battery has been preliminarily screened for voltage and internal resistance by the battery cell sorting machine, and exclude batteries with abnormal voltage (such as overcharge/undervoltage) or mismatched internal resistance, to avoid interference with the insulation test results due to voltage/internal resistance problems (such as high-voltage breakdown risk or leakage current misjudgment),

Principle: Apply DC or AC voltage to the insulating film on the surface of the battery to be tested. After a certain period of polarization, the resistance corresponding to the leakage current flowing through the dielectric (composite dielectric of the insulating film and the air layer) is called the insulation resistance.

The equivalent circuit diagram is as follows:

• i1 is the capacitive current: the DC voltage acts on the insulator, and the moment of pressure application is relative to charging the capacitor, this part of the current decays quickly
• i2 is the absorption current: the absorption current of the inhomogeneous medium is composed of slow polarization and interlayer polarization
• i3 is the leakage current: there are very few weakly bound or free electrons in the dielectric, and after a certain period of time, this current gradually stabilizes. The insulation resistance mentioned here refers to the pure resistance that causes I3

How To Screen Batteries By Leakage Current? 

When there are metal particles or the insulating film is damaged, the insulation will be broken down. At this time, the leakage current will increase rapidly and the corresponding resistance will decrease rapidly. Therefore, the selection of the test voltage needs to consider the corresponding breakdown voltage of various types of damaged products, so that the resistance or leakage current of normal products and bad products will be significantly different, so that the battery cells with damaged insulating film appearance can be selected through this test.

In addition, the equivalent DC voltage used for insulation testing is 1.414 times the AC voltage, so that the DC and AC voltage peaks are equal. The battery is compressed by the setting mechanism to ensure that the insulating film is in close contact with the end where the voltage is applied, reduce the measurement error, and fully consider the insulation condition of the battery when it is stressed in the module.

For Example

The defective insulating film of the bad battery leads to insufficient withstand voltage, which will cause breakdown at a certain voltage. When the breakdown occurs, the leakage current will increase rapidly. As shown in the figure below, as the test voltage increases within a certain range, the leakage current gradually increases, and there is a certain linear relationship. The normal product voltage and leakage current show a good linear relationship; the leakage current of the battery with a damaged insulating film will surge at a certain voltage and break down.

Battery insulation testing is crucial for early identification of risks such as failure and safety of lithium-ion batteries, and is a very important process in manufacturing.

Acey New Energy is a high-tech enterprise. Our R&D team specializes in researching and manufacturing high-end equipment for lithium-ion batteries. Our business covers semi-automatic & fully automatic assembly machines for cylindrical, prismatic, and pouch battery packs; battery cell charge discharge tester and battery pack test system; lab-scale fabrication machines for coin cells, cylindrical cells, and pouch cells; battery environmental safety testing equipment; battery materials; and supercapacitor production equipment, etc.