Design Limitations of Thick Electrodes and High-Specific-Capacity Materials for High Energy Density in Cylindrical Lithium-Ion Batteries

Abstract

Among the various form factors of lithium-ion batteries, cylindrical cells are recognized for their standardized geometry, high manufacturability, and superior safety. Their compatibility with high-speed production processes also contributes to their excellent cost competitiveness. These cells adopt a jellyroll-type winding structure, where the electrode curvature progressively increases toward the core. To achieve higher energy densities, common strategies include increasing electrode thickness and employing high-specific-capacity active materials, such as nickel-rich cathodes and silicon–graphite composite anodes. While widely implemented in industry, the application of these approaches to cylindrical cells aiming for energy densities beyond 800 Wh·L⁻¹ requires a more comprehensive understanding of how curvature influences electrochemical performance. In this study, the design limitations of thick electrodes and high-specific-capacity materials— specifically nickel-rich cathodes and silicon-based anodes—were investigated for the development of high-energy-density cylindrical lithium-ion batteries. To replicate the jellyroll structure of cylindrical cells, a custom experimental tool was developed and fabricated using 3D printing. Various levels of curvature (0.33, 0.20, 0.10, and 0.05 mm⁻¹), corresponding to the jellyroll geometry of a 46XX cylindrical cell, were applied to single-stack pouch cells for evaluation. Specifically, the effect of the curvature (0.33 mm⁻¹) on electrodes with areal capacities of 3, 4, 5, and 6 mAh·cm⁻² was examined using an NCM811–Graphite system. To evaluate the mechanical properties of the electrodes under curvature, a three-point bending simulation based on tensile strength data and bending strength measurements was conducted. The results demonstrated that anode flexural stiffness decreased significantly with increasing thickness, and that thick anodes were vulnerable to curvature-induced mechanical stress. In addition, local variations in the N/P ratio caused by curvature led to lithium plating when using nickel-rich cathodes, due to their inherently low initial coulombic efficiency, thereby posing potential safety risks. The curvature applied to silicon-based anodes amplified their intrinsic volumetric expansion, leading to accelerated degradation. To address these issues, it is essential to improve the mechanical properties of the electrode by optimizing parameters such as binder type and molecular weight, active material morphology and particle size, composite density, and manufacturing processes. Furthermore, increasing the N/P ratio provides an effective buffer to mitigate the risk of lithium deposition. These results identify key limitations that must be addressed for the practical application of thick electrodes and high-capacity materials in cylindrical batteries and provide valuable design insights for the development of high-energy-density cylindrical lithium-ion batteries.