Open Circuit Voltage (OCV) is the voltage of a battery cell (or pack) when it is not under any load or being charged. OCV is determined by the chemical state (the equilibrium of the electrochemical reactions) in the cell, and it varies with state of charge (SOC): For instance, a lithium-ion cell might have an OCV of about 4.2 V when 100% charged, dropping gradually to around 3.7–3.8 V at 50%, and then to maybe 3.0 V or lower when near 0%. Monitoring OCV (especially after resting a cell) can provide an estimate of its SOC, which is why many battery management systems use OCV vs SOC lookup tables for fuel gauging when the device is at rest.
NOVONIX uses OCV measurements in characterizing new cell chemistries. For example, when testing a new electrode chemistry, they will often measure the OCV curve by discharging very slowly and recording the stabilized voltage. NOVONIX uses the OCV curve to analyze phase transitions or reactions that occur at specific voltages. They also looks at OCV drift: as cells age, their OCV curve can subtly shift (due to changes in chemistry, like loss of lithium inventory or changes in electrode properties). By analyzing these shifts, they get insight into what’s happening internally. Overall, OCV is a fundamental characteristic of battery behavior that NOVONIX measures to understand and improve cell performance.
