Al2O3 coated Li1.2Ni0.2Mn0.2Ru0.4O2 as cathode material for Li-ion batteries

Highlights: • A Li₂RuO₃-based Li-rich layered oxide Li_1.2Ni_0.2Mn_0.2Ru_0.4O₂ was prepared. • Al₂O₃ coating enhances the electrochemical performance of Li_1.2Ni_0.2Mn_0.2Ru_0.4O₂. • The phase transitions are identified utilizing in situ X-ray diffraction. Li₂MnO₃-based Li-rich cathode materials can offer high capacities for lithium-ion batteries but suffer from poor rate capability, low initial coulombic efficiency, and voltage fade upon extended cycling. Significant attention has been focused on the replacement of Li₂MnO₃ with other materials featuring Li₂MO₃ (M = Ru, Mo, etc.) components; however, the cycle performance of these materials is inferior. Herein, coating with Al₂O₃ is proposed to improve the electrochemical performance of the Li₂RuO₃-based Li-rich cathode material Li_1.2Ni_0.2Mn_0.2Ru_0.4O₂. Rietveld refinement data indicate Ru-Ru dimer formation in these samples. The Al₂O₃ coating can enhance the initial coulombic efficiency, cycling stability, rate performance, and mitigate the voltage decay. In situ X-ray diffraction (XRD) demonstrates that the compound remains a layered structure during the first cycle. The formation of Ru-Ru dimers is suggested to be responsible for the unusual lattice parameter changes during the initial charge.