Structural Regulation Of Transitional Metal Oxide Nanocomposites For Their Li Storage Performances

Under the background of the increasingly serious environmental pollution and energy crisis,the exploration of new energy source is imminent.Since 1990,the lithium-ion battery has developed rapidly.However,there still are urgent problems to be solved in the practical application.Transition metal oxide has always been a hot spot of research because of its high theoretical capacity.However,the transition metal oxide usually causes a sharp volume expansion in the process of charging and discharging which leads to the larger initial irreversible capacity loss.The main research work is divided into the following parts:（1）First of all,the SnO₂ nanoparticles were grown on the surface of three-dimensional graphene by hydrothermal method and coated with nitrogen-doped carbon.Then the three-dimensional structure of3DG@Sn O₂@N-C with good conductivity was obtained followed by freeze-drying and heat treatment.The cycle performance and rate performance of the electrode were improved due to the combination of the three-dimensional conductive structure of graphene,the higher theoretical specific capacity of tin oxide and the structural stability of the carbon cladding.Simultaneously,in this paper,the influence of mass ratios of graphene and SnO₂ on the rate performance and cycling performance of electrode materials was optimized and analysized.The reversible specific capacity of 1349.5 mAh g^-1 was still maintained after 100 cycles under the current density of 100 mA g^-1.At the same time,the high discharge specific capacity of 726 mAh g^-1 after charging and discharging at high current densitiy was still obtained when current densitiy comes back to 200 mA g^-1.（2）Cubicα-Fe₂O₃ was coated with TiO₂ layer by hydrothermal method,and thenα-Fe₂O₃@TiO₂ of hollow structure was obtained by hydrochloric acid immersion etching.α-Fe₂O₃ having a higher theoretical capacity and TiO₂ having good cycling stability are combined together.The hollowα-Fe₂O₃@TiO₂alleviates the expansion ofα-Fe₂O₃ during charging and discharging to a certain extent.The reversible specific capacity can return to 767.8 mAh g^-1 when back to 100 mA g^-1 after charge and discharge at higher current density.The FT-1 h still has good circulation performance after the test of the rate performance under high current density and it still has good circulating performance after 100 cycles under the current density of 100 mA g^-1,the reversible specific capacity maintained at 893.7 mAh g^-1,and the cycle retention is up to 98.47%.However,The pureα-Fe₂O₃ and the pure TiO₂ have low reversible specific capacity.（3）The cubicα-Fe₂O₃ was treated by hydrothermal etching,and then a porous cube was obtained after being etched along the body-centered direction.Carbon was coated by a simple way of stirring to obtain the Fe₃O₄@N-C,thus the conductivity of electrode materials was improved to some extent.A composite material with good structural stability was obtained by regulating the acid concentrations,and the cycle stability of the electrode was improved.The discharge specific capacity was still up to 985.6 mAh g^-1 after200 cycles at a current density of 100 mA g^-1.