Phases in the solid-state solution series Li 2 Cr x Mn 2 - x O 4 were prepared as single-phase compounds over the range 0 < x < 2. The unit cell volume decreases smoothly with increasing chromium content as Cr 3 + , with a smaller ionic radius, is substituted for Mn 3 + . The X-ray powder diffraction patterns of phases in the range 1.5 x < 2 are similar to that of LiCrO 2 , while the diffraction patterns of Li 2 Cr x Mn 2 - x O 4 phases over the range 0 < x 1.25 resemble that of λ-Li 2 Mn 2 O 4 . Selected phases of Li 2 Cr x Mn 2 - x O 4 were formed into cathodes and evaluated in lithium-ion cells with petroleum coke-based anodes.