Equivalent Circuit Model for Electrochemical Impedance Spectroscopy of Commercial 18650 Lithium-Ion Cell Under Over-Discharge and Overcharge Conditions

Abstract

This study endeavors to assess the impedance responses exhibited by 18650 Graphite||LiCoO₂ (C₆||LCO) cells under conditions of over-discharge and overcharge. The impedance measurements are conducted at a potential of 4.20 V, followed by subjecting the cells to over-discharge and overcharge scenarios. It is observed that the impedance magnitude experiences augmentation in both instances. Upon reaching a potential of 2.70 V, the electrochemical attributes of the cells revert to their normal state post over-discharge. However, the impedance characteristics persist even upon exceeding a potential of 4.70 V. These observations imply that overcharge induces enduring alterations in impedance behavior, while over-discharge is a reversible phenomenon. To delve deeper into the underlying mechanisms, an equivalent circuit process model is constructed. This model elucidates that over-discharge of Li-ion batteries is reversible, indicating the potential for restoration of original impedance behavior upon recharge. Conversely, overcharge precipitates permanent alterations in impedance behavior, engendering irreversible changes in battery characteristics. In summation, this study underscores the criticality of meticulously managing the charging and discharging processes of Li-ion batteries to avert irreversible impairment to impedance behavior, thereby safeguarding battery performance and longevity.