Akku4Future - measurement methods to gather data for computing state indication

Lithium ion batteries require a strict operation window in terms of the terminal voltage, load current and cell temperature. Battery management systems (BMS) have to ensure safe operation of lithium ion batteries. The functionality of such BMS features the estimation of the state of the cell and provides some information (mostly the state of charge) to the user. The state indication is of high importance as the knowledge about the health of the battery enables the BMS to act if the battery health gets worse, or even can slow down the battery aging process by acting preventively. The paper describes measurement strategies to create data for the quantification of the state of charge (SOC) and state of health (SOH) of a lithium ion battery. A measurement setup was established to enable automated cycling of the test cells to age rapidly. During cycling the cell capacity is monitored for being representative for the aging of the cell. The measurements are used to determine a n equivalent electrical circuit. The derived parameters can be used to estimate the actual state of the cell. The understanding of the cell is basis for designing a sufficient and accurate state indication system.