Structure Design And Electrochemical Performance Of Carbon Nanotubes Reinforced ZnO Alloy Anode

Lithium-ion batteries(LIBs)have become a research hotspot and be widely used in various fields due to its outstanding performance,such as the high energy density and voltage platform,low self discharge rate,no memory effect as well as the environment friendly etc.However,the energy density of existing commercial electrode materials has been unable to meet the needs of people,especially the negative graphite material,which has already close to its theoretical capacity in the practical applications.Therefore,it is imperative to find high-capacity materials instead of graphite negative.Among the numerous candidate materials,ZnO has many advantages of low price,easy preparation and pollution-free,which is considered to be a promising anode material for the new generation LIBs.Despite these advantages,the huge volume change during the lithiation-delithiation process of ZnO may produce severe stress,Which will lead to crack of material's surface,even pulverization and exfliation,and ultimately causing a rapid decrease of cycle performance.In addition,the electronic conductivity of ZnO is also poor,which could reduce the charge-discharge property in high current.In order to solve these problems,we put ZnO anode materials for our object,staring from controlling its morphology and structure,compounding with MWCNTs.We use self-assembly metheod and calcination to prepare different morphological structures of ZnO/MWCNTs composites to reduce the volume effect,enhance the stability and conductivity of the electrode,so as to improve the cycle stability and rate performance of ZnO.(1)Firstly,zinc ions and organic are designed to obtain ZnO on the functionalized carboxylwalled MWCNTs by self-assembly.The specific method is to form a metal organic framework ZIF-8 in the functionalized-MWCNTs suspension by self-assembly metheod,and the obtained composites were then calcined to prepare the designed product.Effects of heat treatment temperature on the structure and composition of the final materials were investigated,and the optimum calcination temperature was ultimately determined to be 450 oC.Comparing with the pure ZnO prepared by calcination with ZIF-8,the series of MWCNTs could effectively avoid the agglomeration of ZnO nanoparticles and increase the structural stability and electronic conductivity of the electrode materials.The designed composites manifest enhanced cycle performance with high reversible capacity of 372mAh/g after 80 cycles at a current density of 200 mA/g.(2)The rate performance and cycle stability of the S-MCZO are unsatisfactory.For these problem,we have designed a insertion structure of ZnO/MWCNTs nanocomposite by adjusting the size and structure of ZnO nanoparticles as well as change its combination with MWCNTs.We investigated the effects of organic ligands and calcination temperatures on the composition,morphology and structure of the final materials.The as-synthesized porous L-MCZO was proved to be inserted and intertwined with MWCNTs,and each ZnO polyhedron is composed of small building blocks with sizes of about 10 nm.When tested as anode material for(LIBs),the L-MCZO reveals a high reversible capacity of 419.8 mAh/g after 100 cycles at a current density of 200 mA/g,and even at the high current density of 1000 mA/g,it can still remain a specific capacity of 326.8 mAh/g.Both the rate performance and cycle stability of ZnO/MWCNTs nanocomposite have been greatly improved.