Crystal Chemistry of the Olivine-Type Li(Mn[sub y]Fe[sub 1−y])PO[sub 4] and (Mn[sub y]Fe[sub 1−y])PO[sub 4] as Possible 4 V Cathode Materials for Lithium Batteries

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Abstract
A potential 4 V cathode material for lithium batteries was investigated. The crystal chemistry of the olivine-type of Li(Mny2+Fe1−y2+)PO4Li(Mny2+Fe1−y2+)PO4 (discharged state) and its delithiated form (Mny3+Fe1−y3+)PO4(Mny3+Fe1−y3+)PO4 (charged state) were comparatively studied using X-ray diffraction, Mössbauer spectroscopy, and ab initio calculations. A strong oxidizer, nitronium tetrafluoroborate, NO2BF4,NO2BF4, was used for chemical delithiation of Li(Mny2+Fe1−y2+)PO4Li(Mny2+Fe1−y2+)PO4 to obtain (Mny3+Fe1−y3+)PO4.(Mny3+Fe1−y3+)PO4. The strong electron/lattice interaction induced by the trivalent manganese (3d4)(3d4) in (Mny3+Fe1−y3+)PO4(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),(y>0.8), followed by an efficient cathode performance of the optimized Li(Mn0.6Fe0.4)PO4.Li(Mn0.6Fe0.4)PO4. © 2001 The Electrochemical Society. All rights reserved.