Estimation of Battery State of Health Using the Two-Pulse Method for LiFePO4 Batteries

Nowadays, it has been necessary to investigate battery storage systems as a part of the massification of renewable energies, with a particular emphasis on batteries, which are the most crucial components in these systems. In this study, the two-pulse method is applied to LiFePO4 battery cells to test the effectiveness of this method in this chemistry, based on previous validations in lead-acid cells. As a result, approximate values for the state of health (SOH) and state of charge (SOC) of the battery are obtained, with an estimated average standard error of the mean (SEM) less than 10%. An innovative aspect of the method is the inclusion of Lithium-based chemistry to verify the method and the comparison of the SOH obtained with the strain and temperature of a cell. These measurements can help to complement the information on the state of health of the battery cells. The method's applicability to lithium-ion cells has been confirmed, although it requires suitable equipment for its correct application. Not all equipment can deliver uniform and controlled current pulses. Finally, it is necessary to consider some restrictions as a minimum current of at least 15% of the battery capacity value is required. The initial characterization may take some time, although parameter values can be found in the literature for certain technologies like lead-acid. The parameter values vary depending on the chemistry.