| With the rapid development of the Internet,the demand for electric energy is increasing.Among all energy storage and conversion devices,lithium-ion batteries with high energy density,environmental friendly and no memory effect compared to traditional lead-acid batteries,have been widely used.In recent ten years,new anode materials have been developed to improve the reversible capacity and cycle performance of lithium-ion batteries.In the study of transition metal oxides,sulphides and phosphates,it is found that the effective way to improve the properties of materials is to maintain the structural stability of the materials,which requires structural design and optimization.In order to relieve the structure collapse of electrode material caused by volume change during charge and discharge,in this thesis,the structure design of metal sulfides,metal phosphates and metal oxides was carried out,and their properties were improved by nano-structure,compounding with carbon materials or hollow/porous structure to avoid excessive volume change in the process of charge/discharge cycles.The main results of the thesis are summarized as follows:1.To alleviate large volume change and improve poor electrochemical reaction kinetics of metal sulfides anode for lithium-ion batteries,an unique 3D Co3S4/Sb2S3/C nanocage architecture was synthesized through a partial vulcanization of precursors,calcination and in situ cation exchange process.The synergistic effect between components endows Co3S4/Sb2S3/C electrode with high structural stability and electrochemical activity,leading to excellent electrochemical performance.When used as anode material,Co3S4/Sb2S3/C retains a specific capacity of 1121.5 mAh g-1 at a current density of 0.1 A g-1 after 90 cycles.Besides,it exhibited a superior rate capacity of 1643 mA h g-1,1336.9 mA h g-1,940.8 mA h g-1,868.2 mA h g-1,724.1mA h g-1,562.4 mA h g-1 at current densites of 0.1 A g-1,0.2 A g-1,0.5 A g-1,1 A g-1 and 2 A g-1,correspondingly.The three-dimensional nanocage structure can provide abundant open pores and large surface area,improve the contaction between the electrode and electrolyte,shorten the transmission path of electron and ion,and buffer the volume change during cycle process,so as to improve the electrochemical performance of the material effectively.2.By using a metal-organic framework(FeNi-MOF)as template and carbon source,FeP/Ni2P@C nanospheres with a diameter of about 100nm were synthesized by calcination and further phosphating process.The FeP/Ni2P/C nanospheres were obtained by assembling the uniform FeP/Ni2P nanoparticals together through carbon.The electrochemical performace of FeP/Ni2P/C with different sizes were explored.When the electrode material is in smaller size,the(de)alloying process of the material caused smaller effect on the overall structure,thus showing a better cycle performance.The typical product showed a reversible specific capacity of 422 mA h g-1 at 0.5 A g-1 after 100 cycles.Even at 1 A g-1,the reversible specific capacity could reach 364 mA h g-1,exhibiting excellent rate performance.3.The hollow and porous TiO2 spheres with thin shells and an external diameter of about 500 nm were facilely synthesized by a novel one-pot template-free mixed solvent thermal method.We find the TiO2 nanospheres were assembled by many tiny nanoparticles and their shells have the average thickness of 50 nm.The experiment results indicates that the prepared TiO2 spheres after calcining at 500? showed better electrochemistry performance due to the increase of specific surface area and crystallinity.When used as anodes for LIBs,TiO2 spheres exhibited a better reversible capacity of 216 mA h g-1 at a current density of 0.1 A g-1 after 50 cycles and a superior rate capacity of 325,272,249,225,200 and 174 mA h g-1 at different current densities of 0.1,0.3,0.5,0.7,0.9 and 1 A g-1 respectively.This simple,facile and cost-effective strategy could be used in the mass production of hollow and porous TiO2 as well as other functional materials. |
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