How to Detect High Self-Discharge Lithium-Ion Cells

+ Battery Self-Discharge Analyzer

Identify Cells With Excessive Self-Discharge

High self-discharge detection begins by directly measuring the self-discharge current of rested lithium-ion cells under stable electrical and thermal conditions. In the potentiostatic method, a low-noise direct current source is first adjusted to closely match the cell’s open-circuit voltage (OCV). The source is then connected to the cell through a low-current measurement path and maintains the cell at essentially constant voltage and state of charge (SOC). As internal self-discharge continues, the external source supplies the current needed to replace the charge being lost within the cell. After the source and cell approach equilibrium, this externally supplied current represents the cell’s self-discharge current. For high self-discharge detection, the current-versus-time behavior of individual cells can be compared across a cell population rather than waiting for each cell to reach its final equilibrium value. Cells with abnormally high leakage can begin separating from the normal population early in the measurement, making direct self-discharge current measurement suitable for battery cell screening. Direct current measurement provides a different observable: the rate at which charge is being lost.

Reliable lithium-ion cell self-discharge screening also requires control of factors that can create transient or fluctuating currents unrelated to the cell’s final self-discharge level. Cells should be sufficiently rested after charging or discharging because charge redistribution inside the cell continues as charge reaches equilibrium throughout its internal structure. If a cell has not fully rested, additional current may initially flow into or out of the cell and then decay exponentially, potentially affecting interpretation of early measurement data. Temperature is another measurement variable because lithium-ion cell voltage can change by many tens of microvolts per degree Celsius. State of charge also influences the test because lithium-ion self-discharge decreases considerably at low SOC and becomes more difficult to measure. During battery cell screening, engineers should therefore monitor current, cell voltage, and temperature continuously and evaluate abnormal current behavior in the context of these parameters. Programmable series resistance can also be used to balance measurement settling time against sensitivity to external influences such as temperature changes. When multiple cells are measured under comparable conditions, their current-versus-time traces provide a population-level view of self-discharge behavior.

High Self-Discharge Cell Detection Solution

Perform high self-discharge detection by measuring multiple lithium-ion cells under controlled potentiostatic conditions and comparing their current-versus-time behavior to identify cells that separate from the normal population. The Keysight Self-Discharge Analyzer is designed for direct self-discharge current measurement and can measure up to 32 cells simultaneously, supporting parallel battery cell screening. The Self-Discharge Analysis Software provides an interactive graphical interface for configuring and analyzing measurements across multiple lithium-ion cells. In the documented sixteen-cell test, three cells with excessive self-discharge separated visibly from the main population within minutes. This multi-trace analysis enables high self-discharge detection before every cell necessarily reaches its final equilibrium current, while retained voltage and temperature measurements provide context for interpreting transient or environmentally induced variations during lithium-ion battery testing.

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