Synthesis, phase relation and electrical and electrochemical properties of ruthenium-substituted Li2MnO3 as a novel cathode material

Layered oxides, ruthenium-substituted Li2MnO3, were synthesized at 800 degrees C and 1200 degrees C. Their phase relation and electrical and electrochemical properties were investigated. Li2Mn1-xRuxO3 synthesized at 800 degrees C clearly separated into two phases, manganese-rich and ruthenium-rich phases, except for the narrow composition range of 0 <= x <= 0.05, while Li2Mn1-xAuxO3 synthesized at 1200 degrees C formed two solid solutions in the whole composition range across a structural transition between x=0.6 and 0.8. The electrical resistivity of Li2Mn1-xRuxO3 decreased with increasing ruthenium content. Li2Mn0.2RU0.8O3 (x = 0.8) synthesized at 1200 degrees C showed the lowest resistivity of 5.7 x 10(2) Omega cm at room temperature. The discharge capacity and cycling performance were improved by the ruthenium substitution. Li2Mn0.4Ru0.6O3 (x = 0.6) exhibited a discharge capacity of 192 mAh g(-1) in the initial cycle and 169 mAh g(-1) in the tenth cycle with high and almost constant charge-discharge efficiencies of 99% from the second to tenth cycle at a current rate of 1/10C. The ruthenium substitution to Li2MnO3 is quite effective to improve electrical conductivity and charge-discharge performance. (C) 2010 Elsevier B.V. All rights reserved.