We investigate the effect of surface area of the lithium manganese spinel (LMO) cathode on the high‐temperature storage performance of lithium‐ion pouch cells. Using ~200 mAh design capacity, pouch cells were fabricated and their storage performance at high temperature was investigated according to changes in the LMO surface area. Cell performance and electrode analysis revealed that LMO with a large surface area exhibited a poor storage with a large decrease in capacitance and a more severe increase in resistance. This was mostly attributed to the change in surface morphology of anodes in each cell, indicative of the fast growth of a solid electrolyte interface film caused by high dissolution of Mn²⁺ ions in the high‐surface‐area LMO.​