Non-stoichiometric spinel compounds Li1.02MxMn1.95O4−yFy (M = Co, Y, and Ga) were prepared for the first time by the rheological phase reaction method. The Li1.02MxMn1.95O4−yFy samples were characterized by X-ray diffraction, while the particle size and shape of the Li1.02MxMn1.95O4−yFy were observed by scanning and transmission electron microscopy. The as-prepared samples were used as cathode materials in lithium-ion batteries, their electrochemical properties were tested, and the results showed that the non-stoichiometric spinels Li1.02MxMn1.95O4−yFy had better cycling performance than pure LiMn2O4. In addition, among the different non-stoichiometric spinel samples, the Li1.02Mn1.95Co0.02Y0.01Ga0.01O3.97F0.03 sample not only had higher charge/discharge capacity, but also showed the best cycling performance, as the loss of its capacity was only 7% after 100 cycles. The possible reasons for the outstanding electrical properties of Li1.02Mn1.95Co0.02Y0.01Ga0.01O3.97F0.03 are also discussed.