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

A potential 4 V cathode material for lithium batteries was investigated. The crystal chemistry of the olivine-type of Li ( Mn y 2 + Fe 1 − y 2 + ) PO 4 (discharged state) and its delithiated form ( Mn y 3 + Fe 1 − y 3 + ) PO 4 (charged state) were comparatively studied using X-ray diffraction, Mössbauer spectroscopy, and ab initio calculations. A strong oxidizer, nitronium tetrafluoroborate, NO 2 BF 4 , was used for chemical delithiation of Li ( Mn y 2 + Fe 1 − y 2 + ) PO 4 to obtain ( Mn y 3 + Fe 1 − y 3 + ) PO 4 . The strong electron/lattice interaction induced by the trivalent manganese ( 3 d 4 ) in ( Mn y 3 + Fe 1 − y 3 + ) PO 4 (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 ( Mn 0.6 Fe 0.4 ) PO 4 . © 2001 The Electrochemical Society. All rights reserved.