Effect of Curvature of the Electrodes on the Electrochemical Behavior of Li-Ion Batteries

Abstract

Unlike the flat electrodes assumed in many physics-based battery models, cylindrical and prismatic cells in electric vehicles exhibit curvature. For example, the electrodes of 18650/21700 cylindrical cells have curvatures around = 0.5−1 (2mm-radius) near their axis, while maximum curvatures of electrodes of prismatic cells can reach =7−1 (0.143mm-radius) at the vertex of their wound jellyroll. This study analyzes the impact of electrode curvature on electrochemical behavior using a pseudo-two-dimensional (P2D) battery model. Simulation results show that curvature has a minimal effect on charge/discharge profiles and direct current internal resistance, even for highly curved electrodes. Importantly, the curvature found in typical cylindrical cells ( = 0.5−1) does not significantly alter the lithium plating behavior relative to flat electrodes, justifying the flat electrode assumptions. However, substantial differences in lithium plating behavior are expected for the vertex of the wound jellyroll. At 0°C, this difference reaches as high as 36 mV indicating more significant risk of lithium plating for concave anode electrodes. Considering the repeated alternation of concave and convex anode configurations in the jellyroll manufacturing process, careful attention is required when designing jellyrolls. These findings also suggest that adopting jellystacks instead of jellyrolls for prismatic cells, could better mitigate curvature induced lithium plating.