Open-circuit voltage measurement of Lithium-Iron-Phosphate batteries

This paper evaluates some techniques for the reduction of the measuring time required to obtain an accurate and exhaustive characterisation of the Open-Circuit Voltage (OCV) of a Lithium-Iron-Phosphate (LiFePO₄) battery. The OCV is a very important parameter of a battery equivalent electrical model, typically used in the model-based design of a battery management system. OCV characterisation is quite a time consuming task, as OCV relaxation lasts for several minutes or hours after the battery current is interrupted. This task is especially challenging in a LiFePO₄ battery, as the latter shows pronounced hysteresis, which dramatically increases the number of OCV points to be measured. In order to reduce the measuring time, we investigate the OCV independence from the current rate at which the state-of-charge is adjusted and the possibility to predict the fully relaxed OCV value by modelling the relaxation phenomenon.