State of Health Determination of Batteries by Analyzing the Rate of Increase of Their Temperature

Lithium-ion batteries are the main technology on which the global green energy initiative has been based in recent years. As a source of energy, they have a high energy density and long life. Their use is relatively safe and production costs are relatively low. They are currently used in various types of electric vehicles, space applications, and much of the consumer portable electronics. Battery Prognostics and health management depends on State of health (SOH) monitoring. SOH is the main parameter for the safety and reliable work of the batteries. In most cases, it is determined by measuring the impedance of the battery. This is related to some limitations arising from the method of measurement, which is contact and requires the connection of multiple measuring wires to the batteries. In this article, we present a model to determine the SOH of the battery which uses the rate of increase of battery temperature during the discharge cycle. The study is carried out by a project team consisting of scientists from Plovdiv University and Technical University - Sofia within a project funded by the Bulgarian Research Fund. The proposed model is based on an in-depth analysis of the physical laws describing the processes of raising the battery temperature during its operation. Attention is paid to the relationship between these processes and battery degradation. For the purposes of the study, we have used the NASA Battery Data Set. Based on these data, the relationship between the rate of increase of the battery temperature during its discharge and the number of discharge cycles is derived, which is associated with changes in its capacity and degradation. To determine the rate of increase of the battery temperature over time, the first derivatives of the temperature function at the same discharge current but after a different number of discharge cycles are calculated. To illustrate the process in detail, these dependencies are presented graphically. Since the rate of increase of the battery temperature depends on the magnitude of the discharge current and the ambient temperature, the dependences for two operating modes are derived: discharge current with magnitude 2A and 4A at an ambient temperature of 24 degrees Celsius. The proposed model for determining the SOH of the battery using the relationship between the rate of change of its surface temperature and the number of discharges in the process of its operation is an accurate tool that can help to ensure the safety, quality, and reliability of the battery.