Fe content effects on electrochemical properties of Fe-substituted Li2MnO3 positive electrode material

Fe-substituted Li2MnO3 including a monoclinic layered rock-salt structure (C2/m), (Li1+x(FeyMn1-y)(1-x)O-2, 0 < x <1/3, 0.1 <= y <= 0.5) was prepared by coprecipitation-hydrothermal-calcination method. The sample was assigned as two-phase composite structure consisting of the cubic rock-salt (Fm (3) over barm) and nonoclinic ones at high Fe content above 30% (y >= 0.3), while the sample was assigned as a monoclinic phase (C2/m) at low Fe content less than 20%. In the monoclinic Li2MnO3-type structure, the Fe ion tends to substitute a Li (2b) site, which corresponds to a center position of Mn4+ hexagonal network in Mn-Li layer. The electrochemical properties including discharge characteristics under high current density (<3600 mA g(-1) at 30 degrees C) and low temperature (<-20 degrees C at 40 mAg(-1)) were severely affected by chemical composition (Fe content and Li/(fe + Mn) ratio), crystal structure (monoclinic phase content) and powder property (specific surface area). Under the optimized Fe content (0.2 < y < 0.4), the Li/sample cells showed high initial discharge capacity (240-300mAhg(-1)) and energy density (700-950mWhg(-1)) between 1.5 and 4.8V under moderate current density, 40mAg(-1) at 30 degrees C. Results suggest that Fe-substituted Li2MnO3 would be a non-excludable 3 V positive electrode material. (C) 2009 Elsevier B.V. All rights reserved.