The differential capacity and coulombic efficiency of blended Li/LiMn2O4-Li[Ni1/3Mn1/3Co1/3]O-2 half cells were examined using high-precision constant-current chronopoteniometry. The experiments showed that the addition of even modest amounts of Li[Ni1/3Mn1/3Co1/3]O-2 to the relatively low energy density LiMn2O4 electrodes produced a significant improvement in capacity retention. Li[Ni1/3Mn1/3Co1/3]O-2 was also found to help suppress Mn dissolution from LiMn2O4, and a correlation between Mn dissolution, capacity retention and coulombic efficiency was found. The retained Mn ions reduce the increase of x in Li1+xMn2-xO4 at the particle surfaces. If x in Li1+xMn2-xO4 increases, a more Li rich, lower capacity material results, so by suppressing the increase of x, better capacity retention results. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.056210jes] All rights reserved.