A novel <i>in situ</i> detection method for lithium plating thickness in pouch cell

Lithium plating on the surface of anode electrodes poses significant hazards to cell performance. Lithium deposition not only leads to thickness growth and cell swelling but also promotes the formation of lithium dendrites, which can penetrate the cell's separator. However, thickness changes serve as an accurate indicator for detecting lithium plating in cells. This study aims to precisely monitor the state of lithium plating by tracking thickness changes. An experimental in situ swelling monitor with a resolution of 0.1 μm is developed to detect cell swelling without requiring the disassembly of the cell during normal operation. A lithium cobalt oxide pouch cell is then tested under various ambient temperatures and charging rates using this setup. The precise conditions for lithium plating, including specific temperature, state of charge, voltage, and capacity, are identified. Furthermore, a multi-physics coupled equation system for lithium dendrite formation is proposed to align with the experimental conditions. The results demonstrate that higher currents accelerate lithium plating due to increased polarization, with a dendrite window under charge rate 1C and state of charge (SOC) = 16%. Additionally, lithium dendrites are more likely to form during high-rate charging at low temperatures, with approximately 5% of lithium ions contributing to dendrite formation, with a dendrite window under temperature 0 °C and SOC = 27%. In a summary, thickness detection is a valid method to unveiling the dendrite state inside the battery.