Design And Formation Of Some Metal Oxides-based Anode Materials And Lithium Storage Performance

With the development of portable elecotronics and electric vehicles,people are more and more thirsty for the power energy.Lithium ion batteries(LIBs),as one of the popular energy storage system,can not meet the people's demand on high performance,especially on long life ability,owing to its current limited performance.Metal oxides are one of promise alternative anode materials for LIBs because they usually possess about double higher theoretical capacities than the traditional anode graphite(372mAh g-1).But,the metal oxides have a low electronical conductivity and a large volume variation which can lead to the pulvation and disintegration of electrode materials during the lithiation/de-lithiation process.Therefore,people are attempting to solve those problem for obtaining the high performance which can meet the people's demand in the future.In this dissertation,we try to conquer the problem of metal oxides about the low rate and inferior cycling performance based on the microstructures and chemical components.The simple,eco-friendly and facile methods were applied to synthesize different metal oxides and their composites with diversified structures.Moreover,the corresponding formation mechanisms are presented,and the disscussions are given about the lithium storage performance based on the designed structure and components.Firstly,the red-headed calliandra-like and dandelion-flower-like precursors were prepared by solvothermal reaction.Then,the corresponding flower-like mesoporous Co3O4 were obtained by heating the precursors in air.By studying the effects of experimental conditions,such as the proportion of solvent,the amount of urea,and reaction time on the microstructure and morphologies,some conclusions are given as follows.The high and low concentration of ethylene glycol can lead to the formation of sheet-like and needle-like sub-structures,respectively.YWhile,the high and low concentration of urea can lead to the formation of needle-like and sheet-like su-structures,respectively.The formation mechanism of red-headed calliandra-like precursor is splitting process,while,that of the dandelion-flower-like precursor is multistep splitting-in situ dissolution-recrystallization growth process.The obtained Co3O4products exhibit superior capacity,rate performance and cycling performance compared to commercial Co3O4 due to their unique hierarchical and mesoporous structure.Uniform core-shell hollow Mn3o4/CuO@TiO2 submicroboxes were designed and formed by a facile and multi-step method.By systemtic characterization,we find core-shell intermediate was synthesized by a part self-sacrificing and in situ growth reaction with the truncated octahedral Cu2O template.Then,after the etching process with ammonia aqueous,the hollow precursor was obtained.At last,the target product was prepared by in situ hydrolysis and coating,and subsequent heat treatment.When tested as LIBs anode,we compared the target product Mn3O4/CuO@TiO2 with hollow Mn3O4/CuO.The Mn3O4/CuO@TiO2exhibits better electrochemical performance than the hollow Mn3O4/CuO due to the unique core-shell hollow structure and component.Typically,the Mn3O4/CuO@TiO2still delivers 583 mAh g-1 after 150 cycles at 0.2A g-1 which is the 97.1%and 92.8%of the second discharge and theoretical capacities,respectively.Even at 1.6A g-1(about 2.5 C),it still possesses about 40%of the theoretical capacity.Additionally,the TiO2 coatings strengthen the stability of hybrid's hollow structure.After 150 cycles,the Mn3O4/CuO@TiO2 submicroboxes still remain the initial structure,while the structure of hollow Mn3O4/CUO is collapsed.The yolk-shell precursor was obtained by a facile interfacial reaction at 30?.Subsequently,the yolk-shell CuO@CuFe2O4 heterogeneous hybrid was prepared by calcining the precursor in air.A reasonable formation mechanism was proposed based on the characterizations.When evaluating the lithium storage performance,the heterogeneous hybrid exhibits superior electrochemical performane compared to CuO.In details,at the current densities of 0.1,0.2,0.4,0.8 and 1.6 A g-1,the yolk-shell CuO@CuFe2O4 delivers the average discharge capacities of 618,529,462,391 and 334 mAh g-1,respectively.However,the CuO only possesses 199,152,121,98 and 76 mAh g-1 at the same current densities,respectively.Importantly,the hybrid still shows 505 mAh g-1 after 200cycles at 0.5 A g-1,while the CuO delivers only 36 mAh g-1.The enhanced lithium storage performance of the yolk-shell CuO@CuFe2O4 heterogeneous hybrid benefits from the unique and stable yolk-shell structure.Three different hierarchical hybrids with quasi-hexagonal Cu1.5Mn1.5O4 nanoplates decorated on hollow CuO were synthesized by Kirkendall effect.According to the characterization,we find different heating rates can impact the combination forms of Cu1.5Mn1.5O4 nanoplates and CuO.The quasi-hexagonal Cu1.5Mn1.5O4 nanoplates were assembled into branch-like shell decorated on the CuO surface under the low heating rate.However,the high heating rate led to a compact Cu1.5Mn1.5O4 shell outside of the CuO core.The CuO@Cu1.5Mn1.5O4 hybrid with branch-like shell shows the best cycling and rate performance.Typically,it can exhibit 451 mAh g-1 after 200cycles at 500 mA g-1,while the other CuO @Cu1.5Mn1.5O4 hybrids with more compact shell show 309 and 175mAh g-1.The superior lithium storage perfonnance results from the special hierarchical structure.The branch-like shell provides more contact and reaction sites and shorts the trasportatin length of lithium ion.The composite of crystal MnSn(OH)6 nanoparticles and nitrogen doped reduced graphene oxide was formed by solvothermal reaction in which the ammonia aqueous acted as the nitrogen source and precipitant.The target composite of amorphous hollow MnSnO3 nanoparticles and nitrogen doped reduced graphene oxide was synthesized by a appropriate heat treatment.The target composite possesses a excellent lithium storage performance which is not only better than both the pure amorphous hollow MnSnO3 nanoparticles and nitrogen doped reduced graphene oxide,but also superior to many other tin-based oxides and their composites.The target composite shows reversible capacities of 811,714,605,504 and 408 mAh g-1 at 0.1,0.2,0.4,0.8 and 1.6A g-1,respectively.It is noted that the nanocomposite shows no capacity fading when the current density turns back to 0.1 A g-1 and exhibits the reversible capacity of 744 mAh g-1 after the following 65 cycles.Importantly,it still shows the reversible capacity of 610 mAh g-1 after 1000 cycles at 0.4 A g-1.We attribute the excellent lithium storage performance to the synergic effect between the amorphous hollow MnSnO3 nanoparticles and nitrogen doped reduced graphene oxide.