Comprehensive study of the influence of aging on the hysteresis behavior of a lithium iron phosphate cathode-based lithium ion battery - An experimental investigation of the hysteresis

In this work a detailed investigation of the hysteresis behavior of the open circuit voltage (OCV) in a lithium iron phosphate (LiFePO4) cathode-based lithium-ion cell is presented. For the first time the hysteresis behavior of the OCV in a LiFePO4 cell is investigated in detail, taking the aging state of the cells into account as a fundamental factor. Tests were carried out in a time window of more than two years on cells in different aging states. The dependency of the major and minor loops of the OCV on temperature, current rate, short-term history and aging are shown and deeply discussed. The results show that the characteristics of the hysteresis of the OCV change completely during battery lifetime, not only concerning the major OCV boundaries but also regarding the single minor loops obtained through partial charge/discharge processes. The paper discusses the results considering different approaches presented in the literature published by date, and addresses the necessity of understanding the physic-chemical behavior of the cell in order to correctly determine the battery state in the application.