Optimizing Chemical Composition and Preparation Conditions for Fe -Substituted Li2MnO3 Positive Electrode Material

Optimized Fe-substituted Li 2 MnO 3 [Li 1+x (Fe y M n1-y ) 1-x O 2 , 0 < x < 1/3, 0.3 < y < 0.7], a positive electrode material, exhibited high initial charge and discharge capacity (200-320 and 150-215 mAh/g, respectively) during charge-discharge tests between 2.5 and 4.5 or 4.8 V at 60°C. All samples were obtained from a mixed-alkaline hydrothermal reaction using the Fe-Mn coprecipitate, KOH, LiOH·H 2 O, and KClO 3 . The hydrothermally obtained samples showed an initial discharge capacity (150-200 mAh/g) when the Fe content, y, was less than 0.6. Both the initial charge and discharge capacities were governed by their Li contents. The electrochemical characteristics were improved by postheating treatment (500-750°C) with LiOH H 2 O. The initial discharge capacity for the samples with y = 0.5 reached 215 mAh/g and capacity fading with cycles was less than in the hydrothermally obtained sample. The initial discharge capacity, energy density, and cycle efficiency were improved by maximizing their respective specific surface areas through minimization of their primary particle size. The electrochemical performance of Fe-substituted Li 2 MnO 3 means that it is an attractive candidate as an inexpensive 3-V-class positive electrode material that is suitable for large-scale lithium-ion batteries. We note, however, that the capacity fade observed on extended cycling must be suppressed if this material is to become commercially viable (or practical).