Impact of Size and Position of Lithium Metal Reference Electrodes on the Measurement of Lithium-Plating Overpotential

Lithium (Li) plating is a major cause of degradation that reduces the capacity of Li-ion batteries. The driving force for the Li plating is dependent on surface overpotential at the graphite-electrolyte interface in the negative electrode (NE). However, there is no experimental method for directly measuring the surface overpotential. Therefore, this overpotential has been estimated by introducing a reference electrode (RE) and measuring the potential difference between the NE current collector and the RE, assuming that the potential difference is the same as Li-plating overpotential. However, this estimation could include significant errors that depend on charging rate, size, and the location of the RE. In this work, we built a pseudo three-dimensional physics-based electrochemical model to understand the trends in the accuracy of prediction of Li-plating overpotential using REs of different sizes placed at different locations. The simulation results indicated that a 50- μ m diameter RE could predict the Li-plating overpotential with an error of about 15 mV even at a high charging rate of 3C in the pouch cell. In addition, the RE located inside the cell was expected to have higher accuracy, and its potential provides a conservative estimate for the onset of Li plating of the pouch cell.