Synthesis And Electrochemical Investigation Of Hexagonal Li_0.5TiO₂ And Spinel Type LiTi₂O₄ Anode Materials

As anode materials for lithium-ion batteries,Li_0.5TiO₂ and LiTi₂O₄ have very good cycle performance and high electrical conductivity.However,the synthesis processes of the two materials are complicated,and the electrochemical mechanism is not fully clear.In this thesis,Li_0.5TiO₂ and LiTi₂O₄ particles have been fabricated through magnesiothermic reduction and solid state reaction methods.Further,carbon coated materials have been synthesized.Their microstructure and composition have been characterized by XRD,SEM,XPS,ICP and TEM.Further,CV,discharge/charge cycling and electrochemical impedance spectroscopy have been employed to evaluate their electrochemical performance.?1?Hexagonal Li_0.5TiO₂ particles have been synthesized through magnesiothermic reduction of Li2TiO3 particles in a temperature range of 600?640 ?.The hexagonal lattice transfers to cubic with prolonged reduction time.?2?The initial charge/discharge capacities of the hexagonal Li_0.5TiO₂ are 140.0/324.0 mAh/g at 0.3 C.The carbon coating can enhance the electrochemical performance,the initial charge/discharge capacities of the carbon-coated hexagonal Li_0.5TiO₂/C can reach 176.6/539.9 mAh/g at 0.3 C.?3?The cubic,the hexagonal and the carbon-coated hexagonal Li_0.5TiO₂ undergo rapid capacity fading in the initial 10 cycles,and then the cyclic capacities are very stable.The hexagonal Li_0.5TiO₂ maintains its hexagonal structure after 100 discharge/charge cycles,indicating its high structural stability.?4?Spinel type LiTi₂O₄ particles have been synthesized through solid state reaction method using TiO/C,TiO2 and CH3COOLi ·2H2O as starting materials.Carbon-coated LiTi₂O₄/C has been further fabricated using pitch as carbon sources.?5?The electrochemical performance of LiTi₂O₄/C is better than LiTi₂O₄.The initial charge/discharge capacities of LiTi₂O₄ are 183.5/341.1 mAh/g at 0.2 C.Its reversible capacity is 176.2 mAh/g after 50 cycles.The initial charge/discharge capacities of LiTi₂O₄/C are 249.7/398.9 mAh/g at 0.2 C.In addition,the rate capability of LiTi₂O₄/C is higher than LiTi₂O₄.