The 4 V rechargeable capacity of the spinel LiMn2O4 was stabilized by substituting less than 1 mole percent (m/o) Mn3+ with Cr3+. The optimum composition was determined as LiCr0.012Mn1.988O4, which had a discharge capacity exceeding 110 mAh/g even after 100 cycles, although improved stabilities were attained for all Cr-modified compositions studied (0.1 to 7.0 m/o Cr3+ substitution). The effects of varying electrolyte salt, temperature, and current density were also investigated. Capacity losses in 4 V LiMn2O4-based spinel systems were attributed to Mn dissolution into the electrolyte causing structural degradation of the cathode and an increase in cell polarization from deposited Mn interfering with Li+ transport through the anodic solid-electrolyte interphase. Substitution of even a small amount of Mn3+ by trivalent Cr3+ minimized this dissolution and resulted in enhanced cathodic electrochemical stability.