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 Li2MnO3 has significant theoretical capacity as a cathode material for Li-ion batteries. Pristine Li2MnO3 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 LiMnO2 in Li2MnO3. The Rietveld refinement analysis shows that, after a reduction reaction with stearic acid at 340 °C for 8 h, pristine Li2MnO3 changes into a Li2MnO3–LiMnO2 (0.71/0.29) composite, and the monoclinic Li2MnO3 changes from Li2.04Mn0.96O3 in the pristine Li2MnO3 (P–Li2MnO3) to Li2.1Mn0.9O2.79 in the reduced Li2MnO3 (R-Li2MnO3), indicating the production of a large amount of oxygen vacancies in the R-Li2MnO3. 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-Li2MnO3 shows much better electrochemical properties than P-Li2MnO3. For example, when charged–discharged galvanostatically at 20 mA·g–1 in a voltage window of 2.0–4.8 V, R-Li2MnO3 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-Li2MnO3 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 Li2MnO3 as a cathode material for Li-ion batteries.