Surface Coating To Improve The Performance Of Li Mn₂O₄ With Hydrothermal Process And Its Effects For Li⁺ Diffusion

Spinel lithium manganese oxide(Li Mn2O4) is one of the most promising cathode materials for Power type and energy storage type lithium-ion batteries, because of its effectiveness, high potential, non-toxicity, as well as fast charge and discharge reactions.However, the rapid capacity fading at elevated-temperature limits its commercialization.The uniform and homogeneous nickel oxides coating layer is formed on surface of spinel Li Mn2O4 to improve the high operating temperature performance via a novel dynamic hydrothermal process. The effects of structure and morphology on the properties of Li Mn2O4 are investigated in details. The mechanism in improvement is also further investigated by the Density Functional Theory(DFT).we coated the nickel oxides layers on the surface of Li Mn2O4 particles, via a novel alcohol-solvent dynamic hydrothermal process. Various instruments are used to investigate the structure and morphology.The results reveal that there is no structural change of coated Li Mn2O4, and the thickness increases with the Ni/Mn molar ratio. The thickness of the coating layer will affect the spread of the lithium ion. However, too thick a coating layer will limit the diffusion of lithium ions and make the optimization effect lower. The average valence increase of Mn within the spinel structure can strengthen the stability of the spinel structure, which is beneficial to suppress Jahn-Teller distortion. The existence of coating layer provides a safer surface for the Li Mn2O4 particles, and works as a acidic isolated protective layer with suppressing the dissolution of Mn ions and reducing the solid-electrolyte interface. The coated Li Mn2O4 exhibits excellent cycling performance at high operating temperature(55℃), compared to that of pristine sample.The pristine and coated Li Mn2O4 crystal model are studied with Vienna Ab-initioSimulation Package(VASP). Based on the stable crystal structure of Li Mn2O4 after optimization, we find that the Mn-O bond becomes shorter and more stable, and there are all Mn4+ at the(001) surface of coated Li Mn2O4 crystal model. The simulated results match with the experiment results, and further explains the improved performance of coated Li Mn2O4 cathodes in Li-ion batteries.