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