Fe content effects on electrochemical properties of Fe-substituted Li(2)MnO(3) positive electrode material

Fe-substituted Li(2)MnO(3) including a monoclinic layered rock-salt structure (C2/m), (Li(1+x)(Fe(y)Mn(1-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 ([MathML equation]) and monoclinic 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 Li(2)MnO(3)-type structure, the Fe ion tends to substitute a Li (2b) site, which corresponds to a center position of Mn(4+) hexagonal network in Mn-Li layer. The electrochemical properties including discharge characteristics under high current density ( < 3600 mA g(-1) at 30 'C) and low temperature ( < -20 'C at 40 mA g(-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 (240-300 mAh g(-1)) and energy density (700-950 mWh g(-1)) between 1.5 and 4.8 V under moderate current density, 40 mA g(-1) at 30 'C. Results suggest that Fe-substituted Li(2)MnO(3) would be a non-excludable 3 V positive electrode material.