Investigation of Lithium-ion batteries by Electrochemical Impedance Spectroscopy

Kurzfassung

Energy storage with secondary batteries is considered a core technology and a prerequisite for the emergence of a sustainable mobile society. Demand for modern batteries with high energy density is increasing continuously due to the rapid advances in the broad application of advanced portable electronic devices, electric vehicles (EVs), smart grids and many others. In In order to run batteries in a secure and lifetime optimized way, it is essential to determine the state of charge (SOC) and the state of health (SOH) accurately. A useful useful tool for the characterization of batteries and battery components is the electrochemical impedance spectroscopy (EIS). In order to run lithium ion batteries in a secure and lifetime optimized way, it is essential to understand the formation of the Solid Electrolyte Interface (SEI) at different temperatures and cell degradation behavior due to load cycling and calendar aging. Thereby, cell degradation is associated with an increasing cell resistance. For automotive applications battery cells will usually be replaced when the cell capacity drops under 80% or the internal ohmic resistance is doubled in comparison to the new state. A very useful and non-destructive method to detect increasing cell resistances during cell operation is electrochemical impedance spectroscopy (EIS). One main reason for increasing ohmic resistances during load cycling is attributed to a growing solid electrolyte interface (SEI) located at the phase boundary between graphite anode and electrolyte.