In this paper, a reduced-order, Multi-Scale, Multi-Dimensional (MSMD) model is developed to achieve accurate and fast simulation of the 2D distribution of thermal and electrochemical properties across the surface of a large-format Li-ion battery cell. Since the proposed model aims at supporting long-term simulation, virtual design and optimization studies, minimization of the computational complexity is achieved through analytical Model Order Reduction (MOR) based on a Galerkin projection method. The model is then verified against experimental data and a high-fidelity numerical model at various input current conditions. Results show that the computational complexity of the MSMD model is significantly reduced without sacrificing the accuracy in characterizing the distribution of the electrochemical and thermal properties. Finally, the impact of the applied current and thermal boundary conditions on the distribution of transverse current density is also evaluated. Temperature and temperature gradients are some of the key factors that influence the performance and degradation of Li-ion batteries. Despite in Hybrid Electric Vehicles (HEVs) or Electric Vehicles (EVs) the average pack temperature is regulated by the thermal management systems, thermal gradients may still occur within the pack or across individual cells.1-3 For instance, when cooling plates are in contact with only one side of the cells, the heat generated inside each cell will be dissipated to the cooling plates along a preferential direction. Therefore, thermal gradients in the order of ±5• C are common, and particularly in high-power packs for HEVs or high-performance EVs. 4,5 Thermal gradients on the cell surface are particularly critical in large-format batteries because hot spots may induce localized changes in the physical and chemical properties of the electrodes and electrolyte solution, which in turn can increase the local transverse current density and ultimately cause non-uniform degradation of the electrodes.6,7 Multiscale characterization methods have in fact evidenced that the non-uniform utilization of electrode surface leads to highly uneven degradation. 8,9 Furthermore, cell-to-cell variations in large battery packs (due to packaging constraints) may lead to non-uniform heat transfer in packs and induce further thermal gradients among the various cells. 10,11 This motivates the development of procedures and tools that allow for characterization and prediction of thermal gradients in large-format Lithium ion batteries, and understanding their impact on the performance and durability.Multi-Scale, Multi-Dimensional (MSMD) modeling approaches have been proposed to simulate the distribution of surface temperature and Lithium concentration in large format, prismatic cells. As a first approximation, the rate of heat generation within the cell can be approximated as uniform across the surface.12-16 More recently, this simplification has been abandoned in favor of more rigorous approaches that accurately compute the local heat generation rate ...