Assembly And Lithium Ion Storage Properties Of 3D Nanostructures Of Transition Metal Oxides

The research work reported in this thesis mainly focus on solving the key scientific problems of the traditional transition metal oxide anodic nanoparticles,such as poor cyclic stability and low packing density,and micro-particles,including low capacity,poor rate capability and poor stability.Therefore,Three dimensional?3D?nanostructured transition metal oxides secondary microspheres,including binary nickel cobalt oxide mesoporous microspheres anode materials and composition gradient manganese-rich ternary nickel cobalt manganese porous microsphere cathode material,are designed and successfully assembled via a scalable solvo/hydro-thermal method to achieve high energy density,meanwhile,the rate capability,the cyclic life and the safety of transition metal oxides secondary microspheres are further improved by precisely controlling the morphology,the size,the pore structure and the composition distribution of the 3D nanostructures by reasonable adjustment of the assembly process.The specific research works are as follows:?1?With the aid of urea served as precipitant and self-template,well-organized agave-stricta-like NiCo?OH?2CO3 arrow microspheres precursor are successfully assembled through optimized hydrothermal reaction process.After suffering a optimized pyrolysis process in air,the dispersed multi-phase hybrid crystal structure,mesoporous structure with the favorable specific surface area are introduced during the decomposition of NiCo?OH?2CO3 microspheres.Due to the synergistic effects of abovementioned characteristics,the multi-phase nickel cobalt oxide with a total composition of Ni1.5Co1.5O4 shows comparable high rate performance,but much better cyclic performance,than that of the pure phase Ni1.5Co1.5O4.?2?Low-valent pure phase NiCoO₂ hierarchical microspheres built by mesoporous arrow array are also prepared by pyrolyzing the NiCo?OH?2CO3 microspheres under nitrogen gas.Compared to the multi-phase Ni1.5Co1.5O4 obtained by annealing in air,the first cycle irreversible capacity loss of the mesoporous NiCoO₂ hierarchical microsphere decrease about 200 mAh g-1,while both materials exhibit good cyclic stability and rate capability.?3?As for cathode materials,composition gradient nickel-cobalt-manganese carbonate microspheres with a manganese-rich core and ternary shell are successfully built by a scalable solvothermal method,making use of the differencies of the solubility among different carbonate precipitates within the weakly acidic conditions.The preparation mechanism and the effect of L-ascorbic acid on the morphology,composition distribution,crystal structures and the electrochemical properties of of carbonate precursors,intermediate oxides and the final composition gradient lithium nickel-cobalt-manganese oxide with a total composition of LiNi0.2Co0.3Mn0.5O₂ are deeply discussed.The obtained experimental results prove that L-ascorbic acid is helpful for obtaining LiNi0.2Co0.3Mn0.5O₂ mesoporous microspheres with better monodisperse,smaller and more uniform particle size,more dense structure and small gradient difference.Heartening,the final obtained layered ternary oxide cathode materials deliver superior rate capability,excellent cyclic stability and thermal stability,as well as high tap density,which are benefited from the nature of Mn-rich,composition gradient and mesoporous structure 3D nanostructure.