In my previous post, I explained why measuring the self-discharge on Li-Ion cells is vitally important to both R&D and manufacturing. The downside of measuring self-discharge however, when using the traditional method of measuring the cell’s open circuit voltage (OCV) loss is the amount of time required, typically weeks.
I also shared that Keysight has introduced two new solutions, the BT2191A Self-Discharge Measurement System and the BT 2152A Self-Discharge Analyzer. These solutions utilize a new and different approach for measuring self-discharge of cells. Instead of relying on OCV loss over time (an indirect indicator of self-discharge) they instead directly measure the cell’s self-discharge current. We refer to this as the potentiostatic method for measuring self-discharge, as the test voltage is held constant for the duration of the testing. To review the details of all of this, click on the following title of my previous post “The Value of Measuring Self-Discharge on Li-Ion cells” to learn more!
The potentiostatic method for directly measuring the self-discharge current of cells takes typically hours or less to settle on the result, as illustrated in Figure 1. And as shared in the previous post, it takes even less time to discern cells having excess self-discharge from good ones.
Figure 1: Measurement of a Li-Ion cell’s self-discharge current using the BT2191A
There are challenges to using the potentiostatic method as well, to get meaningful results quickly. The most prominent challenge is the need for maintaining an extremely stable test voltage for the duration of the testing. The Keysight solutions address this in innovative ways. Another major challenge is having and maintaining the cell under test in a similarly stable state, which can be achieved by taking the appropriate steps and measures to do. Briefly this includes:
- Providing adequate rest time after subjecting the cell to any charging or discharging.
- Take appropriate steps to maintain the cell at an adequately constant temperature.
- Avoid temperature differences that can lead to transient thermo-electric voltage effects.
- Take advantage of having the cell at a state of charge (SoC) that leads to the most favorable result.
We have just released a new application note that goes into much greater details about measuring the self-discharge on Li-Ion cells, including:
- How the open circuit voltage method works.
- How the potentiostatic method works.
- Fundamentals on the technology incorporated into the Keysight solutions.
- Details on having and maintaining the cell in a stable state for applying the potentiostatic method.
So if Li-Ion cell and battery performance test are important to your work, you should find this new application note informative and helpful. To learn more about Li-Ion cell self-discharge, measurement approaches, and test solutions you can access this new application note by clicking on its title here: “Evaluate Self-Discharge of Lithium Ion Cells in a Fraction of the Time Traditionally Required”.
You should find it very informative!