In capacity measurements the battery is discharged until a specified voltage cut-off limit is reached. The battery voltage profile is recorded as a function of the discharge time. The discharged capacity (ampere hours, Ah) is calculated as the product of the applied current and time. Discharged energy (watt hours, Wh) is received by multiplying the capacity with the voltage.
The battery’s voltage profile and the achievable capacity depend on the used current value and temperature. Capacity measurements should be performed at all conditions relevant for the specific application to determine the battery performance.
Impedance measurements are divided in two different methods, DC Internal Resistance (DC-IR) and AC Internal Resistance (AC-IR).
In DC-IR measurement a specified discharge or charge current pulse is applied to the battery and simultaneously its voltage profile is recorded as a function of time. The internal resistance (milliohms, mΩ) of the battery is calculated based on measured delta voltage and applied current.
AC-IR is performed with specific impedance meter using 1kHz frequency.
Internal resistive behavior of the battery is measured to determine the power capability. The internal impedance affects the battery’s energy efficiency and also heat generation.
Electrochemical Impedance Spectroscopy
In Electrochemical Impedance Spectroscopy (EIS) the impedance is measured with wide range of frequencies to analyze battery’s dynamic behavior. Electrochemical impedance spectroscopy gives more detailed information on the different resistive components in comparison to 1 kHz and DC-IR measurements.
Extreme temperature tests
In extreme temperature tests the battery is charged and discharged in a wide temperature range to determine its behavior in conditions relevant for the specific application.
Cycle life tests
In cycle life tests the battery is repeatedly charged and discharged with specified voltages, currents, rest periods and temperatures to determine the battery lifetime in conditions relevant for the specific application.
In characterization the discharge and charge profiles are measured in conditions relevant for the specific application in order to gain data for the development of the battery algorithms such as battery monitoring, State Of Charge (SOC) and State Of Health (SOH).