Meaning
Measurement of the rate of open circuit voltage drop over a specific period defines an analytical technique used to assess cell self-discharge. In quality control, K value metrology identifies cells with internal micro-short circuits before they are assembled into modules. This testing method is inapplicable to cells that have not reached chemical equilibrium after the initial formation and aging steps.
Voltage Assessment
Voltage measurements are recorded at precise time intervals under tightly controlled temperature conditions to calculate the self-discharge rate in millivolts per day. High-resolution digital voltmeters are employed in K value metrology to detect minute voltage shifts that indicate a defective cell. For example, a standard lithium-ion cell might exhibit a normal decay of less than 0.1 millivolts per day, whereas a cell with an internal short circuit will show a significantly higher rate of decline.
This measurement is typically performed over a period of several days to ensure statistical confidence. The resulting value is then compared against established threshold limits to determine whether the cell is accepted or rejected.
Process Integration
Cell manufacturers implement this testing step during the late stages of production after the initial aging period has completed.
Rejection Threshold
Cells with a high K value are rejected to avoid assembly risks.
