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 °C and 1200 °C. Their phase relation and electrical and electrochemical properties were investigated. Li2Mn1−xRuxO3 synthesized at 800 °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−xRuxO3 synthesized at 1200 °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 °C showed the lowest resistivity of 5.7 × 102 Ω 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.