To improve the cycle performance of spinel LiMn2O4 as the positive electrode of 4V lithium secondary batteries, the spinel oxysulfide Li1.02Mg0.1Mn1.9O3.99S0.01 is synthesized by a sol–gel method using adipic acid as a chelating agent. The structural and electrochemical properties of the synthesized material are examined. Highly crystallized Li1.02Mg0.1Mn1.9O3.99S0.01 is synthesized at 750°C in an oxygen atmosphere. Both cation and anion doping of spinel lithium manganese oxides are very effective for improving the cycle performance of lithium batteries.