Controlled Synthesis Of Hierarchical Porous Titanium Oxide Materials For Lithium Ion Batteries

Lithium ion batteries?LIBs?have attracted much attention,because of its good energy density,long cycle life and environmental friendly.As the main components in LIBs,electrode materials play key roles in the electrochemical properties.Compared with the traditional graphite electrode,titanium dioxide has been considered as a promising negative electrode material,owing to its high safety and good structural stability.In this dissertation,titanium dioxide is selected as the target negative material.In order to improve the electrical conductivity and lithium ion diffusion rate of titanium dioxide,we design the hierarchically porous and micro/nano structure and multiphase complex structure,and investigate the effects of morphology,size,conductive carbon,catalysis,crystal form and grain boundaries on the lithium storage performance and the structure evolution of the electrode material after cycling.The main contents and results are summarized as follows:?1?Preparation and lithium storage mechanism of ultra-thin nanosheet assembled yolk-structured brookite TiO₂ material.The mechanisms and influence factors of self-assembly process of brookite TiO₂ were analyzed.Then,ultra-thin nanosheet assembled yolk-structured copper/brookite TiO₂ composite material were also synthesized.The copper is used as a catalyst to reduce the potential barrier and improve the electron conductivity and the ultra-thin nanoplatelets provide short lithium ion transport path,thus the lithium storage capacity of the brookite TiO₂composite is improved.?2?Preparation and lithium storage mechanism of nanorod/chain-structured hierarchically porous anatase TiO₂ microspheres.The nano-chains are composed of interconnectednanocrystals.Electrochemicaltestsshowthatthe nanochains-structured TiO₂ has a better lithium storage performance than that of the nanorods-structured TiO₂.Specifically,after long-term cycling,a new phase LiTiO₂is found in the electrode materials,which is generated from the evolution of anatase phase.?3?Preparation and lithium storage mechanism of hierarchical porous core-shell structured amorphous/anatase TiO₂ hybrid.Benefiting from the porous core-shell structure,large specific surface area,chemical binding between Ti and carbon and the grain boundary of amorphous/anatase,the TiO₂ material exhibits excellent rate performance and good cycling stability.After long-time cycling at high current density,a newly emerged cubic LiTiO₂ phase exists in the form of nanodots attaching on the electrode surface separately.?4?Preparation and lithium storage mechanism of nanotube constructed hierarchical porous TiO₂-B/anatase/C material.The as prepared material is constructed by interconnected nanotubes.The excellent electrochemical performance of the porous TiO₂-B/anatase/C material is mainly due to the synergistic effect of large specific surface area,in-situ exsitence of carbon and hierarchically porous structure.?5?Preparation and lithium storage mechanism based on TiO₂ anode and spinel LiNi_0.5Mn_1.5O₄?LNMO?nanoparticles/nanorods cathode.Firstly,the LNMO nanoparticles/nanorods are synthesized and the lithium performance are invertigated.Then,the full cell has been fabricated based on the TiO₂ anode and LNMO cathode,demonstrating a good electrochemical performance.