Synthesis And Electrochemical Performances Of Composite Materials Of Co₃O₄ And TiO₂ As Anodes For Lithium Ion Battery

As a commercial anode material for lithium ion betteries,graphite carbon materials have not satisfied the increasing energy demand due to its various disadvantages such as low energy density,inferior rate capability and the safety issues,which caused by the generation of the lithium dendrite during the repeated charge and discharge processes.Intercalation t ransition metal oxide of TiO₂ has been widely researched for its intrinsic characteristics,such as it s high lithium insertion potential?1.5 V?,environmental benignity and long life span.However,the low electric conducivity and specific capacity have significantly restricted its electrochemical performances.Conversion t ransition metal oxide of Co₃O₄ has attracted numerous research interests due to its tremendous features such as high energy density,corrosion resistance and chemical stability.Unfortunately,Co₃O₄ suffers from drastic volume expansion during reduction process,resulting in a serious structure pulverization,rapid capacity decay and poor cycling performance.Graphene,which possesses extraordinary mechanical strength and ultralarge specific surface area,has been considered to be an ideal functional material to improve electrical conductivity and alleviate volumetric expansion of the electrode materials.For these cases,we have synthesized superior anode materials through morphology optimization and hybrid compound.This thesis mainly includes three aspects:?1?Three-dimensional mesoporous TiO₂/graphene?TiO₂/G?microspheres have been successfully synthesized through a simple hydrothermal method with tetrabutyl orthotitanate and graphene oxide as raw materials.The TiO₂/G microspheres possess a large specific surface area?258 m2 g-1?,pore size?7.8 nm?and pore volume?0.86 cm3 g-1?.This unique structure endows TiO₂/G microspheres with great electrochemical performances.It delivers a high reversible capacity of 185 m Ah g^-1 after 100 cycles at 0.2 C and displays an improved rate capability at different rates of 0.1-10 C,which are superior to the commercial graphite and soft carbon.Even at the 1 C rate,TiO₂/G can also display excellent cyclic performance.?2?One-dimensional Co₃O₄/graphene?Co₃O₄/G?microrods hybrids were synthesized by a facile hydrothermal reaction with CoCl₂·6H₂O and graphene oxide as raw materials,and the electrochemical performances has been researched.It exhibits high initial discharge and charge capacity of 1591 and 957 m Ah g^-1 at 0.1 C,the corresponding coulombic efficiency is 60 %.Also it retains a reversible capacity of more than 560 m Ah g^-1 after 70 cycles.In addition,Co₃O₄/G microrods can deliver a better rate capability.?3?One-dimensional mesoporous Co₃O₄@TiO₂ core-shell nanofibers were synthesized through a hydrothermal reaction combined with hydrolysis,Co?NO₃?₂·6H₂O and tetrabutyl orthotitanate as the raw materials.This electorde displays excellent cyclic performance and rate capability.The initial discharge and charge capacities are 1034 and 711 m Ah g^-1,and maintain a discharge capacity of 639 m Ah g^-1 after 100 cycles at 0.2 C.