Synthesis of lithium manganese oxide powder by microwave-enhanced water-assisted solid-state reaction

Abstract

Conventional solid-state reactions for synthesizing metal oxides at high temperatures often result in high energy consumption and significant carbon emissions, posing potential environmental burdens. In response to the growing demand for low-carbon-emitting processing, this study employs a water-assisted solid-state reaction (WASSR) method combined with microwave irradiation to synthesize LiMnO₂ under relatively low-temperature conditions. This lithium-rich oxide can be used as a cathode material for lithium batteries. This synthesis route represents a sustainable approach in inorganic chemistry. According to the thermodynamic assessment, the Gibbs free energy difference for the synthesis of LiMnO₂ using LiOH as the lithium source is lower than that using Li₂CO₃ as the reactant. The WASSR approach may effectively facilitate the LiOH-based endothermic reaction, thereby promoting the formation of LiMnO₂ under relatively mild conditions. A comparative analysis indicates that the WASSR method reduces carbon emissions by two orders of magnitude compared to a conventional method. The nanostructure of the synthesized powder was characterized using X-ray diffraction to determine phase composition and purity. The crystallite size was estimated using the Scherrer equation. The local structure on the surface of nano-powders was studied by Raman spectroscopy, and the surface morphology was characterized by scanning electron microscopy. The sample obtained using deionized water at a Li/Mn molar ratio of 0.27 % yielded LiMnO₂ with the highest purity of 78 % and a crystallite diameter of 41 nm. The WASSR microwave-assisted technique not only enables low-temperature synthesis and crystallinity control of oxide materials but also offers substantial carbon reduction potential, making it suitable for the development of sustainable materials such as lithium battery cathodes.