Recently, Professor Li Li's research team from the School of Metallurgy at NEU achieved a significant breakthrough in cathode materials for sodium-ion batteries. Their research paper titled "An ammonia-induced universal synthesis approach for manganese-based layered oxides" was published in the top-tier international academic journal Nature Communications. This study proposes a universal synthesis strategy for manganese-based layered oxides induced by ammonia gas, improving upon traditional solid-state reactions. By simply introducing dicyandiamide as an additional component, a straightforward and versatile synthesis method has been developed, significantly enhancing the overall performance of manganese-rich layered transition metal oxides. Professor Li Li serves as the sole corresponding author, with NEU as the primary affiliated institution
In this study, the team employed in situ variable-temperature X-ray diffraction (XRD), in situ XRD, X-ray absorption fine structure spectroscopy, and thermogravimetric analysis to systematically investigate the mechanism by which ammonia released from dicyandiamide decomposition regulates material structure and properties. The findings reveal that during sintering, ammonia released from dicyandiamide occupies oxygen vacancies, thereby lowering crystallization temperature and alleviating internal stresses during material growth, which facilitates the formation of high-quality crystal structures. Density functional theory calculations confirm that oxygen vacancies effectively suppress Jahn-Teller distortion in Mn³⁺ octahedra via electron delocalization. During desodiation, the band gap narrows and the density of states near the Fermi level increases significantly. Neutron diffraction data visualizes the sodium ion migration pathways shortened by oxygen vacancy optimization, as analyzed using the maximum entropy method.
Electrochemical tests demonstrate that these structural advantages lead to a 6.7-fold enhancement in rate performance and significantly enhance cycling stability when applied as a cathode in sodium-ion batteries. This strategy is equally applicable to other manganese-based layered transition metal oxides, validating the method's universality and providing new insights for the targeted design and synthesis of high-performance sodium-ion battery electrode materials. The NEU Analytical Testing Center has provided crucial support for the structural characterization of the working materials, particularly in the field of fine microstructure electron microscopy analysis.
