Mathematical fitting for the variation in capacity of lithium iron phosphate batteries corresponding to cycles

Abstract

The capacity of lithium iron phosphate (LiFePO 4 ) batteries decreases as the usage cycles increase. In order to investigate the relationship between the number of charge/discharge cycles and the battery capacity, two batteries were cyclically charged and discharged using an automatic testing system, while simultaneously collecting the capacity data. The tested batteries were composed of different materials and had a capacity of 15 Ah. Each battery was cyclically charged and discharged 800 times. The batteries are analyzed and compared with each other to create fitted curves. The developed mathematical fitting,

The correlation between the capacity fade of LiFePO4 batteries and cycle life

“…In EMAC 2013 [9], the relationship between voltage variation and SoC was investigated and a mathematical model was developed, particularly for batteries in different conditions; in EMAC 2015 [10], the relationship between capacity fade and cycle number was investigated and a mathematical model was developed as well; However, the model cannot estimate the capacity variation of a LiFePO 4 battery at around the first 180 cycles because the capacity varies obviously due to the activation of the electrochemical reaction inside a LiFePO 4 battery. Therefore, a new model is proposed to fully describe the capacity variation of a LiFePO 4 battery in this paper, particularly for the beginning period (around the first 180 cycles of the cycle life) of a LiFePO 4 battery.…”

“…This study was conducted in order to observe the variation in capacity as the number of cycles increases, and then to develop a new model derived from the electrical circuit model and Butler-Volmer kinetics to analyse the battery status. The modified Thevenin circuit model is composed of an open-circuit voltage (OCV) source, a series resistor (R series ) and two resistor-capacitor (RC) circuits as shown in Figure 1 [10,11]. RC circuits are used to investigate both charge and discharge behaviours of the battery.…”