A potential 4 V cathode material for lithium batteries was investigated. The crystal chemistry of the olivine-type of Li(Mny2+Fe1-y2+)PO4 (discharged state) and its delithiated form (Mny3+Fe1-y3+)PO4 (charged state) were comparatively studied using X-ray diffraction,Mossbauer spectroscopy, and ab initio calculations. A strong oxidizer, nitronium tetrafluoroborate, NO2BF4, was used for chemical delithiation of Li(Mny2+Fe1-y2+)PO4 to obtain (Mny3+Fe1-y3+)PO4. The strong electron/lattice interaction induced by the trivalent manganese (3d(4)) in (Mny3+Fe1-y3+)PO4 (charged state) is highlighted as the intrinsic obstacle to generating the full theoretical capacity (ca. 170 mAh/g) of the Mn-rich phase (y > 0.8), followed by an efficient cathode performance of the optimized Li(Mn0.6Fe0.4)PO4.