For the first time, an attempt has been made for the possible augmentation and exploration of iodine substitution into LiFe0.4Mn0.6PO4 (LFMP) material is assessed as a cathode material for lithium ion batteries. Iodine substituted LiFe0.4Mn0.6(PO4)1−xIx (LFMPI, x = 0, 0.01, 0.015, and 0.02) have been synthesized by a solid-state reaction without any external carbon source. X-ray diffraction shows that the LFMP and LFMPI cathode materials have formed the same single crystalline phase; the values of lattice parameters and unit cell volume have been insignificantly changed by I− anion substitution. Uniformly distributed grains of the LFMPI samples with grain sizes in the range of 250 nm to 0.9 μm have been obtained by scanning electron microscopy. X-ray photoelectron spectroscopy for the LFMPI with x = 0.02 have clearly observed at 619.5 and 630.7 eV for I 3d5/2 and I 3d3/2, respectively. The electrochemical properties of the pure LFMP cathode material have been compared with those of I− anion substituted LFMPI samples. LFMPI with x = 0.015 has delivered the highest discharge capacity of 141.5 mAh g−1 at 0.1C, and LFMPI with x = 0.01 has 102.1 mAh g−1 at high rate of 3C. Iodine substituted LFMPI have demonstrated improved electrochemical properties with excellent reversible cycling.