Oxygen Vacancies and Stacking Faults Introduced by Low-Temperature Reduction Improve the Electrochemical Properties of Li₂MnO₃ Nanobelts as Lithium-Ion Battery Cathodes

Among the Li-rich layered oxides Li 2 MnO 3 has significant theoretical capacity as a cathode material for Li-ion batteries. Pristine Li 2 MnO 3 generally has to be electrochemically activated in the first charge–discharge cycle which causes very low Coulombic efficiency and thus deteriorates its electrochemical properties. In this work, we show that low-temperature reduction can produce a large amount of structural defects such as oxygen vacancies, stacking faults, and orthorhombic LiMnO 2 in Li 2 MnO 3 . The Rietveld refinement analysis shows that, after a reduction reaction with stearic acid at 340 °C for 8 h, pristine Li 2 MnO 3 changes into a Li 2 MnO 3 –LiMnO 2 (0.71/0.29) composite, and the monoclinic Li 2 MnO 3 changes from Li 2.04 Mn 0.96 O 3 in the pristine Li 2 MnO 3 (P–Li 2 MnO 3 ) to Li 2.1 Mn 0.9 O 2.79 in the reduced Li 2 MnO 3 (R-Li 2 MnO 3 ), indicating the production of a large amount of oxygen vacancies in the R-Li 2 MnO 3 . High-resolution transmission electron microscope images show that a high density of stacking faults is also introduced by the low-temperature reduction. When measured as a cathode material for Li-ion batteries, R-Li 2 MnO 3 shows much better electrochemical properties than P-Li 2 MnO 3 . For example, when charged–discharged galvanostatically at 20 mA·g –1 in a voltage window of 2.0–4.8 V, R-Li 2 MnO 3 has Coulombic efficiency of 77.1% in the first charge–discharge cycle, with discharge capacities of 213.8 and 200.5 mA·h·g –1 in the 20th and 30th cycles, respectively. In contrast, under the same charge–discharge conditions, P-Li 2 MnO 3 has Coulombic efficiency of 33.6% in the first charge–discharge cycle, with small discharge capacities of 80.5 and 69.8 mA·h·g –1 in the 20th and 30th cycles, respectively. These materials characterizations, and electrochemical measurements show that low-temperature reduction is one of the effective ways to enhance the performances of Li 2 MnO 3 as a cathode material for Li-ion batteries.