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. Li₂Mn _1-xRu_xO₃ 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 Li₂Mn _1-xRu_xO₃ 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 Li₂Mn _1-xRu_xO₃ decreased with increasing ruthenium content. Li₂Mn_0.2Ru_0.8O₃ (x = 0.8) synthesized at 1200 °C showed the lowest resistivity of 5.7 × 10 ² Ω cm at room temperature. The discharge capacity and cycling performance were improved by the ruthenium substitution. Li₂Mn _0.4Ru_0.6O₃ (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.