Synthesis And Electrochemical Investigation Of Porous Spherical Ti-based Oxides

The spinel type Li4Ti5O12 and anatase type TiO2 have extremely long cyclic life and high safety as anode materials for lithium ion batteries.However,their low electrical conductivity severely limits their application.In this thesis,porous spherical Ti-based oxides as composite anode materials have been synthesized through aesorol-pyrolysis route combined with solid-state calcinations,in which the carbonaceous materials configure three-dimensional electrical conductivity network.The microstructure and electrochemical properties of the porous spherical Ti-based oxides have been investigated,and the conclusions are as follows:(1)Self-assembly mechanism of the mesoporous Li4TisO12/C hollow spheres has been investigated,which indicates that LiNO3 and aerosol temperature are very important factors controlling formation of the hollow spheres.The mesoporous Li4Ti5O12/C hollow spheres have excellent cyclic capacity and stability,as well as rate capability.The initial reversible capacity is 164.3 mAh/g at current density of 0.5 C,and the capacity fading rate per cycle is only 0.012%.At current density of 30 C,the reversible capacity reaches over 60%of the theoretical capacity.Li4Ti5Oi2/TiO2/C composites with different contents of TiO2 and Li4Ti5O12 have been prepared.Compared with the Li4Ti5O12/C composites,the cyclic capacity,stability and rate capability of the Li4TisO12/TiO2/C composites are better.At the current density of 100 mAh/g,the initial charge-discharge capacities of the Li4Ti5Oi2/TiO2/C composite with Li4Ti5O12 molar content of 34%are 235.3/305.7 mAh/g,the reversible capacity reaches 193.2 mAh/g after 100 cycles.The initial charge-discharge capacities of the Li4TisO12/TiO2/C composite with Li4Ti5O12 molar sample of 67%are 204.6/286.6 mAh/g,and the reversible capacity maintains 166.9 mAh/g after 100 cycles.These electrochemical properties are better than those of the Li4TisO12/C composite,indicating that TiO2 can improve the electrochemical properties of the composites.(3)At 0.2 C current density,the first-cycle charge-discharge capacities of porous Li4Ti5O12/Graphene/C spherical composites are 171.2/185.6 mAh/g,and the reversible capacity maintains 167.7 mAh/g after 100 cycles.The first-cycle charge-discharge capacities of Li4Ti5O12/CNT/C spherical composites are 165.7/173.6mAh/g,and the reversible capacity maintains 164.4 mAh/g after 100 cycles.Both composite anode materials display excellent cyclic stability.