Spinel oxy-fluoride compositions LiMn2-2yLiyMyO4-eta F eta (M=Fe, Co, and Zn) have been synthesized by a selective, low-temperature (450 degrees C) fluorination with NH4HF2 of the corresponding LiMn2-2yLiyMyO4 spinel oxides that were synthesized at 800 degrees C. With a given cation-substituted composition, the lattice parameter and reversible capacity increase with increasing fluorine content due to a lowering of the Mn oxidation state, confirming the bulk substitution of F- for O2- in the lattice. The fluorine incorporation with the low melting NH4HF2 also provides an added advantage of increased tap density due to a closer particle-particle contact. A correlation of the cyclability of the various compositions to Mn valence reveals that the Mn valence needs to be >3.6+ to impart good capacity retention at 25 and 55 degrees C.