Understanding Lithium Deposition in Lithium-Ion Batteries: The Link between Impedance Results and Electrochemical Behavior

Metallic lithium deposition (LD) is the key limiting factor for fast-charging of lithium-ion batteries, as it affects both safety and durability. The reliable detection of LD requires simple and rapid diagnostics, which has led to a widespread adaption of impedance-based LD detection methods in the literature. Most of these studies are largely phenomenological, offering limited insight into the underlying physicochemical mechanisms reflected in the impedance response. In contrast, this study takes an experimental approach by placing the cell under conditions where lithium deposition occurs as the main reaction. Thereby, a targeted analysis of its impact on impedance is enabled by slowly and homogeneously overcharging a graphite anode, which is combined with an oversized cathode in a three-electrode configuration. The setup allows to create controlled conditions from intercalation via the onset of LD to exclusively LD. The electrodes are analyzed using operando and ex-operando impedance measurements. Additionally, a distribution of relaxation times analysis is performed to gain deeper insight into the electrochemical processes under different LD conditions. This work thus bridges the gap between phenomenological detection methods and the fundamental understanding of LD, offering potential for an improved detection and prevention of LD and ultimately fast-charging of lithium-ion batteries.