The Synthesis And Electrochemical Properties Research Of Lithium-Manganese Based Cathode Materials For Li-ion Batteries

As the medium for the energy conversion of new energy resources and electronic devices,secondary batteries have attracted more and more attention.Among the various batteries,Li-ion batteries are highly expected owning to the low cost,small volume,environment-friendliness and excellent electrochemical performance.However,the energy density of commercial Li-ion batteries cannot meet the increasing applied demands.Therefore,the developing of a new electrode material with high energy density has been urgent.Lithium-Manganese based compounds,such as LiMnPO₄,have been considered as the candidate power sources for their abundant resources,environmental friendliness,high voltage plateau and energy density.In this work,the controlling syntheses of spinel LiMn₂O₄,layered LiMnO₂ and olive LiMnPO₄ were investigated.Furthermore,the relationship between different morphologies or crystals structure with their electrochemical performance was also investigated.The three contents of this work are listed as follows:1.Large-scale controlled synthesis and property research of porous onion-liked LiMn₂O₄.A novel onion-liked LiMn₂O₄ electrode material was synthesized by solid-state method on a large scale and the morphology evolution mechanism was investigated systematically associating with the ion equilibrium in solution and dominant growth of crystallographic direction.In addition,the conventional sphere and cubic LiMn₂O₄ were synthesized via the same template method by adjusting pH of the precursor solution vitally.The electrochemical measurements show that the novel onion-shaped LiMn₂O₄ possesses the excellent energy density of 530 Wh g^-1?vs.Li/Li+?,which is attributed to the multi-layered structure and porosity.2.The impact of Li contents on the structure transformation of layered LiMnO₂.Three kinds of layered LiMnO₂?lacked,enough and riched?was synthesized by solid-state method,and the influence of Li/Mn ratio on the structure transformation was discussed.The Li_0.75MnO₂ presents excellent cyclic stability,owning to the appearance of Mn₃O₄.In detail,the crystal structure of Mn₃O₄ is similar to that of LiMn₂O₄,thus stabilized the structure while phase transformation.In addition,Al-ion doped LiMnO₂ was fabricated to improve the stability of material and the electrochemical performances were measured.3.The synthesis and electrochemical properties of olive LiMnPO₄.The LiMnPO₄/C was synthesized by combining the solvothermal method and solid-state method,with the sucrose as the carbon source.The result indicates that the conductivity of carbon coated LiMnPO₄ was promoted vitally.Coincided with the results of thermogravimetric analysis,the LiMnPO₄ with 50wt% sucrose displays superior conductivity and rate capacity.Moreover,nickel powder was conducted as the 3D conductive framework,and the electrochemical properities of composite materials were studied.