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How to Measure Self-Discharge Current in EV Battery Cells

Self-Discharge Analyzer
Self-Discharge Analysis Software
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Measuring self-discharge current with a potentiostatic analyzer

Discerning whether newly formed lithium-ion (Li-ion) battery cells in electric vehicles (EVs) exhibit acceptable self-discharge behavior requires a potentiostatic measurement method. A low-noise, very stable DC source is set to match the cell's open-circuit voltage (OCV). The DC source connects to the cell through a micro-ammeter and the current flowing between the DC source and the cell is measured. When the cell self-discharges, the DC source takes over, furnishing current to maintain the cell at a constant voltage and state of charge.

As the DC source comes to equilibrium with the cell, the self-discharge current transitions from internally sourced to furnished externally from the DC source. Self-discharge current is measured using the micro-ammeter. The potentiostatic measurement method requires a self-discharge analyzer capable of quickly matching the voltage to within +/- 5 µV of the cell’s OCV before being applied. This process minimizes the introduction of any new charge or discharge changes, limiting measurement settling time to a minimum. The voltage applied to the cell must also be stable to minimize ongoing current noise on the self-discharge current measurement.

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Self-discharge measurement system

Self-discharge measurement system

Measuring the self-discharge behavior of li-ion cell designs requires the use of a potentiostatic analyzer to hold the cell’s voltage constant and stable. As a potentiostatic solution, the Keysight self-discharge measurement system offers fast battery cell characterization. It applies extremely stable voltage to the cell to minimize ongoing current noise on the self-discharge current measurement.
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