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Degradation phenomena are not distributed uniformly in a large-format cell. To better understand the inhomogeneous degradation in large-format cells, a two-dimensional model was developed for a LiMn2O4 (LMO)/Carbon cell. The model includes both the non-uniform porous electrode properties and the electrode mismatch. The simulation results show that when the anode edge is extended over the cathode edge, the LMO particles near the edge suffer larger potential difference, larger charge/discharge depth, and higher insertion-induced stress. Therefore, the predicted loss of LMO is more pronounced near the edge as has been seen experimentally. The influence of different design adjustable parameters (such as: the anode extension length, the capacity ratio, the porosity, and the electrode thickness) and electrolyte properties (such as: the diffusion coefficient and the ionic conductivity) on the cathode performance. Among them, the over-potential behavior of the cathode is most sensitive to the extent of the electrode mismatch. Larger anode extensions will increase the possibility of the LMO degradation at the cathode edge. This suggests that a longer extension of the anode is not better for improvement of cell life. An optimal design of the anode extension length should be carried out.