Methods for Measuring the Mechanical Safety Vent Pressure of Lithium ion Battery Cells

The Lithium ion battery is the preferred source of power for many wireless and portable consumer products. A typical battery pack with lithium ion cells features a variety of active and passive safety devices and protection circuitry to prevent or mitigate potential cell failures. One of the passive safety components in a lithium ion cell is the cell-can's mechanical safety vent, which is intended to release the internal pressure of the cell when a specified pressure is reached, but prismatic cells swell and cylindrical cells bulge during pressurization. It is therefore, desirable to test the cell's venting mechanism in a controlled manner in order to ensure that both the cell's can and the performance of the safety vent is not compromised and that the results are not skewed by the test method. A suitable test setup should not inhibit the natural expansion of the cell's can during the test. This paper discusses the various venting mechanisms employed by prismatic and cylindrical lithium ion cells and test methods to characterize the mechanical safety vent's opening pressure for both cylindrical and prismatic cells