Modeling the Positive Electrode Side Reaction for a High Voltage Lithium-Ion Battery

Side reactions in battery electrodes lead to a decrease in battery performance and lifespan. In this work, the side reaction in the positive electrode is examined both computationally and experimentally. Computationally, a transport model was created using the finite element method to track the lithium concentration, potential, and current in each part of the battery. The transport model employs concentrated solution theory and Butler-Volmer kinetics. The side reaction was accounted for with an extra current in the positive electrode. Different functions based on physical conditions were fitted to this current and correlated to our experimental results to determine an expression for the side reaction rate. Experimentally, a lithium-ion half-cell, coin-cell was charged to 4.6 V at 45°C. The coin cell was held at this potential and temperature for 60 hours. The resulting current at this potentiostatic hold correlates to the relaxation of concentration gradients and the side reaction current. Additionally, the concentration of carbon-conductive additive in the positive electrode, the temperature, and the potential were varied to determine how each factor affects the side reaction rate. By performing both a computational and experimental study, we are able to incorporate an expression for the side reaction into our model with physical significance.