Recent experimental work [1] revealed a novel aging mechanism in large-format lithium-ion batteries termed Electrolyte Motion Induced Salt Inhomogeneity (EMSI). This mechanism arises from the coupling of cyclic electrolyte flow—driven by electrode swelling during charge/discharge—with through-plane lithium salt (LiPF₆) concentration gradients. The resulting in-plane concentration inhomogeneity (on cm-scale) causes premature capacity fade, resistance growth, and localized lithium plating, particularly in cells with high pore filling ratios operating under fast-charging conditions. While this phenomenon is demonstrated in [1] through post-mortem chemical analysis and explored its mechanism via 2D simulations assuming in-plane symmetry, critical questions remain regarding the 3D nature of electrolyte redistribution, the influence of partial pore saturation, and the multi-scale temporal dynamics governing EMSI development. This work presents a comprehensive 3D computational framework for modeling EMSI in lithium-ion cells, leveraging Abaqus’s [2] fully coupled electrochemical-thermal-mechanical-hydraulic (ETHM) analysis capabilities. The framework extends the Newman pseudo-2D (P2D) electrochemical model [3] to 3D and incorporates lithiation-induced swelling with full poromechanical coupling—accounting for electrode deformation, pore pressure evolution via Darcy flow, pore structure changes in response to mechanical loading, and partial saturation effects through relative permeability and capillary pressure relationships. We explore and reveal insights into several fundamental aspects of EMSI, including asymmetric flow patterns and concentration gradients inaccessible to 2D symmetry assumptions, the role of cell breathing in driving electrolyte redistribution under constrained conditions, the interplay between characteristic time and length scales governing Li⁺ diffusion/migration versus pore pressure diffusion, lithium plating onset distribution and its coupling with local salt depletion, and how partial saturation influences EMSI development through incomplete electrolyte backflow.