Battery vibration test – an important part of battery quality assurance

The main components affected by vibration and shock on the inside of a li-ion battery include:

Electrode
Repeated shock and vibration can cause tiny cracks in the electrode material, primarily the anode. This creates “dead spots” where there is no electrical contact and “hot spots” where resistance increases, reducing battery performance and life.

Separator
The polyolefin separator film between the electrodes can fatigue and tear due to continuous stress, bringing the electrodes into contact and causing internal short circuits. Separator membranes are also more prone to clogging, inhibiting ion flow.

Electrolyte
Vibration can cause the liquid electrolyte to slosh inside the battery, wearing down the sealing points and encapsulating materials. Battery electrolyte leakage increases over time, reducing the electrolyte levels needed to maintain chemical reactions.

Internal connection
Mechanical stress can loosen solders and connectors between electrodes and tabs, increasing electrical resistance and heat buildup during charging and discharging, resulting in reduced capacity and increased risk of overheating.

Reasons for battery vibration test

Battery vibration test is to evaluate the ability of power battery around safety indicators. Among them, the safety indicators of the vibration test include: sufficient insulation, no sharp change, no combustion, no explosion, no leakage, no cracking, etc.

These indicators are closely related to the consistency of the battery cell. It can be said that the vibration test also indirectly assesses the performance consistency of the battery cell. Battery vibration test is also the minimum requirement for market access of power batteries.

For example, during and after the vibration test of the battery pack, at least there will be no fire or explosion due to thermal runaway, and sharp changes in voltage are not allowed. There should be no cracking of the shell structure or leakage of chemical liquid, and the insulation structure should be intact.

The propagation of vibration energy often has a certain destructive effect on the insulation structure of the power battery. As a product structure designer, it is necessary to consider whether the insulation structure can withstand various vibrations in the road conditions of electric vehicles, so as to ensure that the safety indicators will not be reduced.

Therefore, battery cells, modules, battery packs, and electrical connections need to be designed with sufficient electrical clearances and creepage distances. It is necessary to ensure the mechanical stability of the battery system insulation material structure in the vibration environment. Even if there is a certain change in the lithium ion battery structure after long-term use, it can still ensure that the insulation will not fail.

The steps of the battery vibration test

Pretreatment requirements for samples before vibration

Before battery vibration testing, battery pack or system samples need to go through a preconditioning cycle. In order to ensure that the performance of the sample is in an active or stable state during the battery vibration test.

It is proposed here that the sample that fails the pretreatment (such as the battery capacity does not meet the requirements) cannot be subjected to the vibration test and will be returned to the battery manufacturer as an unqualified sample.

Judgment of passing preprocessing:

● The discharge capacity change of the sample for two consecutive times is not higher than 3% of the rated capacity, and the pretreatment is successful.

● The five consecutive charge-discharge cycles of the sample are all normal, and the pretreatment is successful.

Frequency response check

The battery pack fixing plate (housing support foot) is the first introduction point of the vibration stress transmission path of the battery sample. The fixed position and number of fixed points of the battery vibration test sample coupled with the vibrating table must meet the loading conditions.

The test sample and the fixed position and number of fixed points of the fixture coupling installation must comply with the loading conditions. Therefore, before doing the battery vibration test of the power battery, do a frequency response check first.

Preparation of test monitoring equipment

During the battery vibration test process, the power battery has a certain state of charge SOC. It cannot be ruled out that the voltage (including the battery cells) will be abnormal, that is, a sharp voltage change occurs during the vibration test.

Therefore, it is necessary to monitor the voltage of the power battery in real time. In addition, during the test, thermal runaway including battery cells cannot be ruled out. Similarly, it is also necessary to monitor the temperature of the power battery in real time.

Monitoring devices such as voltage and temperature should be prepared before the vibration test. If there is a sharp change in the voltage specified by the manufacturer, the battery vibration test should be stopped, which also means the failure of the battery vibration test.

Summary

Whether electric vehicles can completely replace traditional fuel vehicles depends on breakthroughs in power battery technology. The safety of power batteries is the primary issue. The vibration environment runs through the entire use of electric vehicles, and the vibration of complex road conditions will have an adverse effect on the safety of the power battery.

After mastering the correct battery vibration test, it is possible to verify whether the safety of the power battery product meets the specified requirements, and to clarify whether the product structure design has reached the basic mechanical strength.