What tests are required from battery cells to modules?

During the process from cells to modules, a number of key tests are indeed conducted to ensure the performance, safety and reliability of the battery. The following is a detailed explanation of the battery OCV test, module insulation test and module EOL test:

1. Cell OCV test

Definition: OCV (Open Circuit Voltage) test is a test of the open circuit voltage, AC internal resistance and case voltage of a single battery.

Purpose: It helps to detect the performance parameters of the battery and calculate the initial SOC (State of Charge) of the battery. The charge and discharge status, capacity and aging degree of the battery can be evaluated by measuring the OCV of the battery.

Testing method: Mainly by connecting probes to the voltage tester and internal resistance tester, and touching them to the positive and negative electrodes of the battery to measure the battery characteristics. The current OCV test is mainly semi-automatic detection. Workers manually place the battery in the test device. The probes of the test device contact the positive and negative terminal ears of the battery to perform the OCV test, and then manually unload and sort.

Accuracy requirements: OCV testing requires an OCV accuracy of 0.1mv and a case voltage accuracy of 1mv.

2. Module insulation test

Definition: Module insulation testing is an important quality control method in the battery module production process. It mainly tests the insulation resistance and insulation strength of the battery module to verify whether the insulation performance of the battery module meets the design requirements and related standard.

Purpose:

Verify insulation performance: Module insulation testing can accurately detect whether there is poor insulation in the battery module, thereby promptly discovering and dealing with potential safety hazards.

Ensure product quality: Through module insulation testing, it can be ensured that the battery module has reached the expected insulation performance requirements before leaving the factory, thereby improving the overall quality of the product.

Ensure user safety: As a core component of electric vehicles and energy storage systems, battery modules have a direct impact on the insulation performance of users’ safety. Module insulation testing can ensure that battery modules will not cause electrical failures or fires due to insulation problems during use.

Testing method: In the square case battery module automated production line, module insulation testing is usually completed through professional insulation testing equipment. These devices can accurately measure the insulation resistance and insulation strength of battery modules and record the test data for subsequent analysis. During the testing process, if it is found that the insulation performance of the battery module does not meet the requirements, it will need to be repaired or scrapped.

3. Module EOL test

Definition: EOL (End of Line) testing is a series of automated and semi-automated testing processes that conduct comprehensive performance and safety testing of assembled battery modules.

Test content:

Scan code identification: By scanning the QR code or barcode on the battery module, the test equipment can automatically obtain relevant information about the module, such as model, batch number, production date, etc.

Recipe calling: Based on the information recognized by scanning the QR code, the test equipment will automatically call the preset test recipe (test program), which contains all test items and test standards for this model of module.

Voltage collection: The test equipment will automatically collect the total voltage of the battery module and the voltage of the individual cells to evaluate the consistency and health of the voltage.

Temperature monitoring: Through the built-in temperature sensor or external temperature probe, the test equipment can monitor the temperature inside the battery module in real time to determine the thermal management performance of the module.

Internal resistance test: Use a dedicated internal resistance tester to calculate the internal resistance of the battery module by measuring the voltage and current changes of the battery module under specific conditions to evaluate its electrical performance.

Insulation withstand voltage test: Use a high-voltage tester to conduct insulation resistance and withstand voltage tests on the battery module to ensure that the insulation performance between the module and the shell and the module's ability to withstand high voltages meet safety standards.

Other performance tests: Depending on the requirements of the test formula, it may also include other performance test items such as capacity test, charge and discharge performance test, OCV and SOC determination records (self-discharge inspection).

Data recording and analysis: During the test process, all test data will be recorded in real time and saved in the test equipment. After the test is completed, the test equipment will process and analyze the collected data and compare it with the preset standard values to determine whether the battery module is qualified.

Result determination: Based on the results of data analysis, the testing equipment will automatically determine whether the battery module passes the EOL test. Qualified products will automatically flow into the next station for subsequent processing, while unqualified products will be automatically discharged or marked for subsequent processing.

Test report: The test equipment will also generate a detailed test report, including test time, test items, test data, judgment results and other information for subsequent quality traceability and analysis.

To sum up, the process from battery cells to modules will go through a number of key tests such as battery cell OCV test, module insulation test and module EOL test. Together, these tests ensure the high quality, safety and reliability of battery modules.