Mechanical stress modeling in jellyroll-wound lithium-ion cells is critical for understanding structural integrity, performance degradation, and safety risks. Cylindrical coordinate finite element analysis (FEA) provides an effective framework for analyzing stress distribution, particularly in the complex geometry of spiral-wound electrodes. The anisotropic nature of layered components, including current collectors, active materials, and separators, necessitates a detailed approach to capture radial, circumferential, and axial stress gradients.

The jellyroll structure consists of multiple concentric layers wound under tension, creating inherent residual stresses. During cycling, lithiation-induced expansion in anode materials such as graphite or silicon generates additional mechanical loads. These stresses are non-uniform due to edge effects, where the termination of electrode layers introduces localized discontinuities. FEA in cylindrical coordinates (r, θ, z) allows explicit representation of radial compression, hoop stresses, and axial constraints imposed by cell casing.

Radial stress distribution is dominated by contact pressure between adjacent windings. Active material expansion during charging increases radial compression, particularly near the core where curvature is highest. Studies indicate radial stresses can exceed 10 MPa in high-energy-density cells, leading to separator deformation and increased risk of internal short circuits. The stress gradient from core to outer layers follows a logarithmic decay due to decreasing curvature and cumulative compliance of wound layers.

Circumferential (hoop) stresses arise from winding tension and differential expansion between anode and cathode. During cycling, anode expansion exceeds cathode contraction, creating tensile hoop stresses in the cathode and compressive stresses in the anode. Edge effects amplify these stresses near electrode terminations, where stress concentrations can reach 1.5 times the bulk values. FEA reveals that incomplete electrode coverage or misalignment during winding exacerbates these edge effects, potentially causing delamination or active material cracking.

Axial stresses are influenced by constraint conditions at the cell's top and bottom surfaces. Constrained swelling leads to through-thickness compressive stresses, while unconstrained designs exhibit stress relaxation through buckling or layer separation. In cylindrical cells, the central mandrel provides axial stiffness, creating a non-linear stress distribution along the z-axis. Thermal gradients during operation further modulate axial stresses, with temperature differentials of 10°C generating measurable stress variations.

Material anisotropy plays a significant role in stress distribution. Copper and aluminum current collectors exhibit orthotropic elastic properties, with higher in-plane stiffness compared to through-thickness direction. This anisotropy causes stress redistribution, particularly at layer interfaces. The separator, typically a porous polymer membrane, acts as a stress buffer but undergoes plastic deformation under sustained loads, altering long-term stress patterns.

Tension gradients from the winding process create residual stresses that persist throughout cell life. Modern winding equipment applies controlled tension profiles, but residual hoop stresses ranging from 5 to 20 MPa remain in as-manufactured cells. These pre-stresses interact with operational loads, affecting fatigue behavior. FEA simulations incorporating winding history show improved prediction accuracy for deformation modes.

Cyclic loading leads to stress evolution through several mechanisms. Plastic deformation of metallic components causes stress relaxation, while viscoelastic behavior in polymer separators introduces time-dependent effects. Repeated lithiation cycles generate progressive particle cracking in active materials, gradually modifying the global stress field. Simulations coupling electrochemical cycling with mechanical models demonstrate increasing stress heterogeneity with cycle count.

Thermal effects introduce additional complexity. Differential thermal expansion between materials creates temperature-dependent stress components. A 1°C temperature rise typically generates 0.1 to 0.3 MPa thermal stress in standard cell designs. During fast charging, localized heating near current collectors produces thermal stress concentrations that can exceed electrochemical expansion stresses.

Failure modes correlate strongly with stress patterns. High radial compression near the core promotes separator pore closure, increasing ionic resistance. Excessive hoop stresses at edges initiate electrode cracking, while axial stresses contribute to jellyroll buckling in unconstrained designs. FEA-based failure prediction maps show good agreement with experimental post-mortem analysis of aged cells.

Validation of FEA models requires multi-scale experimental data. Digital image correlation measurements on sectioned cells provide displacement fields for comparison with simulations. X-ray computed tomography reveals internal deformation patterns, while in-situ strain gauges offer localized stress measurements. Advanced inverse modeling techniques reconcile discrepancies between simulated and measured stress distributions.

Practical implications of stress analysis include improved cell design and manufacturing. Optimized winding tension profiles can mitigate edge stress concentrations, while graded electrode designs help distribute mechanical loads. Material selection based on stress compatibility reduces degradation rates, particularly for high-capacity anodes. Thermal management systems can be tailored to minimize thermo-mechanical stresses during operation.

Future developments in modeling will incorporate more sophisticated material laws, including fracture mechanics for active materials and viscoplastic models for polymer components. Coupled electro-chemo-mechanical simulations will enable full-cycle stress prediction, accounting for interdependencies between lithium concentration, temperature, and mechanical strain. These advances will support the development of next-generation cells with enhanced mechanical reliability.

The comprehensive understanding of stress distribution in jellyroll cells enables systematic improvements in battery performance and safety. Cylindrical coordinate FEA provides the necessary framework to analyze these complex multi-physics interactions, guiding both fundamental research and industrial cell design. Continued refinement of modeling approaches will be essential as battery technologies evolve toward higher energy densities and more demanding applications.