Impacts of negative to positive capacities ratios on the performance of next-generation lithium-ion batteries

The capacity ratio between the negative and positive electrodes (N/P ratio) is a simple but important factor in designing high-performance and safe lithium-ion batteries. However, existing research on N/P ratios focuses mainly on the experimental phenomena of various N/P ratios. Detailed theoretical analysis and physical explanations are yet to be investigated. Here, by combining physics-based modeling and experiments, quantitative understandings of the effects of different N/P ratios for batteries with the silicon-graphite composite anode and the LiNi_0.8Co_0.1Mn_0.1O₂ cathode (Si-Gr/NMC811) are investigated. The results reveal that higher N/P ratios enabled better cycling performance, while the choice of the ratio is a multi-facet optimization problem. Both the equilibrium open-circuit potential and the dynamic overpotentials of various electrochemical polarization are found to affect the electrode utilization at different N/P ratios. Due to the opposite trends of electrode utilization with respect to the N/P ratio, batteries need to be optimized with the help of mathematical simulations to identify the best design, rather than using a simple N/P ratio of 1, to meet specific needs.