Fe-based Nanomaterials As Anode For Lithium Ion Batteries

With the rapid development of social economy and improvement of people's living standard,people's demand for portable electronic products keeps growing,meanwhile the rapid development of electric vehicles has also greatly aroused the needs on lithium ion battery(LIB)with high energy density,high cycle rate,long cycle life,good safety and low cost.However,the commercial graphite anode material shows a low theoretical specific capacity of 372 mAh/g,which is far below the demand for emerging applications of LIB.Therefore,the development of a new type of anode material with higher energy density and better durability is an urgent research topic for LIBs.In exploring the possible alternatives to the graphite anodes in LIBs,the iron-based metal oxygen/sulfur compounds have a high theoretical capacity,low cost and high natural abundance,which have attracted much attentio.However,their practical application has been hindered due to the inherent low electron conductivity and the large volume expansion problem during the cyclic process leading to rapid capacity decay,poor cycle stability and low cycle life.In this thesis,iron-nickel bimetallic oxides and sulfides were obtained by chemical vaporization using metal organic framework as precursors,and their electrochemical properties were investigated as anode materials for lithium ion batteries.The main work is divided into the following two sessions:(1)NiFe2O4 NSs@CNR has been synthesised by heat treatment of the synthesized MOF without the adding of carbon material.This specific composite material combines the advantage of hollow structure and conductive carbon frame,and exhibit a better electrochemical performance.The specific capacity is still maintained at 1355 mAh/g after 100 cycles at 0.1 C.In addition,when the andoe is cycled at the higher rate of 1 C,the specifc capacity is 1045.6 mAh/g after 400 cycles.(2)By simple surface modification of the synthesized MOF material,that is,coating the thiourea and/or glucose,and then followed a simple annealing process,two similar bimetallic nickel sulfide and carbon composite nanomaterials,FeNi-S NPs/CNR and C@FeNi-S NDs/CNR were obtained.By the comparison of electrochemical cycle performance,C@FeNi-S NDs/CNR composites were found to be a promising anode material of LIBs with the advantages of the long cycle life and high stability.Specifically,the specific capacities ofC@FeNi-S NDs/CNR and FeNi-S NPs/CNR can reach 484.7 mAh/g and 212.1 mAh/g,respectively at 4 C.After 1000 cycles at 6 C,the specific capacities of the two anode materials still maintained at 361.0 mAh/g and 206.4 mAh/g,respectively.In addition,the C@FeNi-S NDs/CNR could even keep 93.4 mAh/g at 8 C after 2000 cycles.