Meaning
Open circuit benchmarks represent the potential difference of a cell when zero external current is flowing and the internal chemical gradients are fully relaxed. Establishment of equilibrium potential occurs once the rates of lithium intercalation and deintercalation reach a steady state balance. This value serves as the fundamental point from which all state of charge and capacity estimations are calculated in control software.
State Stability
Thermodynamic forces determine the resting voltage based on the concentration of lithium in the negative and positive active materials. When tracking equilibrium potential users must account for the hysteresis between the charge and discharge paths of specific materials like lithium iron phosphate. This measurement remains the most reliable way to calibrate the aging models used in high density packs.
Reference Standard
Voltage readings under load deviate from the resting state due to internal resistance and mass transfer limits. Determining the equilibrium potential requires an extended rest period to ensure that internal ion clouds have evenly distributed across the electrode plates. It provides the baseline for assessing the real impedance of the storage device.
Chemical Limit
Maximum and minimum voltage limits guard against overcharging and over discharging the electrodes beyond safe levels. Consistent equilibrium potential monitoring helps identify loss of lithium inventory or degradation of the cathode structure over thousands of cycles.
