A potential cathode material for lithium ion batteries has been developed using a boron polyanion substituted lithium iron manganese phosphate, LiFe0.4Mn0.6(PO4)1−x(BO3)x (x=0 to 0.03). Without any external carbon source, the material has been synthesized by solid-state reaction using ball-mill and was subsequently characterized by X-ray diffraction, scanning electron microscopy, electron energy loss spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and galvanostatic charge–discharge measurement. The LiFe0.4Mn0.6(PO4)1−x(BO3)x samples show a single-phase crystalline nature with X-ray diffraction analysis, and enhanced discharge capacity at various C-rates as compared to that of pure LiFe0.4Mn0.6PO4. Among several LiFe0.4Mn0.6(PO4)1−x(BO3)x samples, LiFe0.4Mn0.6(PO4)0.995(BO3)0.005 demonstrated the best cycleability, exhibiting an initial discharge capacity of 159.4mAhg−1 at 0.1C and 113mAhg−1 at 3C. LiFe0.4Mn0.6(PO4)1−x(BO3)x demonstrates enhanced electrochemical properties with excellent reversible cycling via boron polyanion substitution.