Unveiling the impact of electrode curvature on N/P ratio variations in cylindrical lithium-ion batteries

Abstract

Cylindrical lithium-ion batteries offer several advantages over their flat-body counterparts, including a more robust structure. However, their inherent electrode curvature restricts both electrochemical performance and stability. This study investigates the impact of electrode curvature on cell behavior by simulating the curvature of cathode/anode layers at specific radial positions within the cylindrical cell to fabricate single-sheet cells with specific curvatures. Our analysis of the custom-fabricated and commercial 21700 cells reveals that electrode curvature varies with radial position, which leads to local variations in the negative-to-positive electrode capacity ratio (N/P ratio). These variations result in local electrochemical performance variations, causing capacity inconsistencies and increasing the risk of lithium-metal deposition. Moreover, using high-nickel cathode materials exacerbates this sensitivity to curvature, making it a crucial design consideration. Unlike flat-sheet batteries, cylindrical batteries require a tailored design approach that optimizes the N/P ratio while accounting for electrode curvature. Our findings provide crucial guidance for enhancing the design and performance of cylindrical batteries by mitigating curvature-related risks, thereby improving their safety and longevity.