How to Measure Lithium-Ion Cell Self-Discharge Current

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Measure Cell Self-Discharge Current Directly

Lithium-ion cell self-discharge current measurement with the potentiostatic method requires a low-noise, highly stable direct current source, a microammeter capable of resolving very small currents, and controlled cell conditions. The measurement begins with a rested cell whose open-circuit voltage (OCV) has stabilized after charging or discharging. The direct current source is adjusted to match that OCV as closely as possible before it is connected to the cell. Once connected, the source holds the cell at essentially constant voltage and state of charge (SOC), while the microammeter measures the current flowing between the source and the cell. As the cell continues its internal self-discharge process, the external source progressively supplies the charge that would otherwise be lost from the cell. After the source and cell reach equilibrium, the externally supplied current corresponds to the cell’s self-discharge current, providing a direct measurement of charge loss over time. This potentiostatic self-discharge measurement differs from the delta-OCV method, which infers self-discharge from a small voltage decrease over an extended interval. Because lithium-ion cell voltage changes only slightly across much of its SOC range, delta-OCV testing can require days to weeks of monitoring. Direct self-discharge current measurement instead resolves the current associated with the loss of charge and can reach a usable result in hours or less, depending on cell condition and the measurement objective.

Cell preparation and environmental control determine how quickly the measured current settles to the true self-discharge level. After charging or discharging, charge redistribution within the cell can continue for an extended period; a cell that has not reached equilibrium can initially source or absorb additional current that decays with time and is superimposed on the desired self-discharge current. Temperature must also remain stable because a lithium-ion cell’s voltage has a temperature coefficient that can produce changes of many tens of microvolts per degree Celsius. State of charge also affects the measurement: self-discharge decreases considerably at low SOC, making the current more difficult to resolve, while the temperature coefficient of voltage generally increases. During acquisition, engineers should continuously log cell current, voltage, and temperature so that current settling can be evaluated alongside environmental and electrical conditions. The resulting current-versus-time traces show the approach toward equilibrium; when a trace levels off, the external source is furnishing the cell’s self-discharge current. In the documented 18650-cell example, a 2.4 Ah cell settled near 7 µA after two hours, while cells with excessive self-discharge separated from the main population within minutes. For multi-cell lithium-ion battery self-discharge testing, comparing aligned current traces also helps engineers distinguish normal population behavior from unusually high self-discharge while retaining voltage and temperature records for measurement context.

Lithium-Ion Self-Discharge Current Measurement Solution

Perform the test by matching a stable direct current source to the cell’s open-circuit voltage and measuring the current supplied to hold the cell at constant voltage and state of charge. The Keysight self-discharge measurement solution combines the self-discharge analyzer with the self-discharge analysis software for potentiostatic lithium-ion cell self-discharge current measurement. The analyzer matches the applied measurement voltage of the cell’s open-circuit voltage (OCV) before application and maintains applied-voltage stability, reducing disturbances that can extend settling time or appear as current noise. The software provides a graphical interface for configuring measurements and analyzing logged current, voltage, and temperature over time. Together, these capabilities support direct potentiostatic self-discharge measurement while giving engineers the electrical and thermal data needed to interpret settling and identify stable current levels.

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